Anatomical evaluations of the adipose tissue surrounding the flexor hallucis longus tendon: A study using gross anatomy and magnetic resonance imaging

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Grossly, we observed the flexor hallucis longus tendon and surrounding tissues in nine cadavers. Using MRI, we quantitatively evaluated each tissue from the horizontal plane in 40 healthy ankles. Macroscopic autopsy revealed the presence of adipose tissue behind the ankle joint between the flexor hallucis longus and fibula, and horizontal cross-sections showed an oval-shaped adipose tissue surrounding the tendon. The cross-sectional area on MRI was 14.4 mm 2 (11.7–16.7) for the flexor hallucis longus tendon and 120.5 mm 2 (100.3–149.4) for the adipose tissue. Additionally, the volume of the adipose tissue was 963.3 mm 3 (896.2–1,115.6). We demonstrated that the presence of adipose tissue surrounding the flexor hallucis longus tendon may be involved in the function and pathological conditions of the tendon. Health sciences/Anatomy Health sciences/Anatomy/Musculoskeletal system/Muscle Health sciences/Anatomy/Musculoskeletal system/Tendons flexor hallucis longus tendon talocrural joint adipose tissue Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Introduction Adipose tissues, which are present around tendons, plays a role in reducing friction and compressive stress [ 1 , 2 ]. In addition, adipose tissues contain nerve endings that serve the nociceptive function of tendons [ 1 , 3 , 4 ]. Moreover, because adipose tissues surrounding tendons also moves with tendon and joint movement [ 5 ], decreased movement of adipose tissue may cause tendinopathy and postoperative pain [ 6 , 7 ]. Therefore, adipose tissue is one of the important tissues for understanding the pathogenesis of tendinopathy [ 8 ], and it is necessary to determine adipose tissue distribution for treatment in the field of rehabilitation and orthopedics. The flexor hallucis longus (FHL) originates at the distal two-thirds of the posterior fibula and interosseous membrane of the lower leg, transitions into a tendon at the distal tibia, passes through the fibro-osseous tunnel, changes direction with the sustentacular tail, and courses towards the base of the great toe phalanx [ 9 , 10 ]. Tendon disorders of the FHL muscle reportedly occur in the fibro-osseous tunnel between the great toe sesamoid [ 11 ], at the junction of the tendon of the flexor digitorum longus [ 12 ] and the base of the great toe phalanx [ 13 ]. Particularly, disorders occur more frequently between the fibro-osseous tunnel and great toe sesamoid because of the poorer blood flow to the FHL tendon than that in other regions, considerable changes in the course of the tendon, and the application of excessive stress [ 11 ]. Although the affected area is more distal to the talocrural joint, some patients experience pain around the talocrural joint after an ankle injury [ 14 , 15 ]. Furthermore, previous studies using magnetic resonance imaging (MRI) reported that some cases of pain around the FHL tendon after ankle trauma showed scarring of the surrounding tissue [ 16 ]. Although adipose tissue may also be present around the FHL tendon, its detailed anatomical structure remains unclear. Combined examination using gross anatomy and MRI has been performed for anatomical observations of adipose tissue [ 17 – 19 ]. This study aimed to investigate the presence of adipose tissue surrounding the FHL tendon through gross dissection and MRI. Materials and methods 1. Gross anatomical examination Subjects for systematic dissection included nine cadavers and nine feet (average age: 86.8 ± 3.2 years; 4 men, 5 women; 5 left feet, 4 right feet). To determine the structure of the FHL tendons and surrounding tissues, patients with a history of trauma, including fractures around the ankle and soft tissue injuries, were excluded. An autopsy was carefully performed while inspecting each tissue to identify the FHL tendon and surrounding structures behind the ankle. The same procedure was performed by the same examiner for all cadavers. First, the skin and subcutaneous adipose tissue were removed from the posterior ankle joint. The Achilles tendon and Kager’s fat pad were distally exposed to observe their positional relationship with the deep FHL tendon and structures. To observe the positional relationship between the FHL tendon and surrounding tissues, we identified and removed the long and short peroneus, tibialis posterior, tibial nerve, and tibial posterior artery. Subsequently, the trochlea of the talus was used as an indicator to traverse the FHL tendon and surrounding tissues, which were also observed in the horizontal plane. Morphometry was performed using a digital caliper (SCALE-BK -150 – MM, Waves, JAPAN) to measure the long and short axes of the FHL tendon and surrounding tissues at the level of the talar trochlea. Each measurement was performed three times, and the average value was used in all analyses. 2. MRI study A total of 40 feet from 20 healthy adults (12 men and 8 women; mean age, 22.3 ± 1.0 years) were examined. Patients with a history of fracture around the FHL tendon, those with tendon disorders of the ankle joint, and those with significant limitation of range of motion or pain in the ankle joint were excluded. The study design was approved by the ethics committee of XXXX (XXX – 2021–033), and all procedures were performed in accordance with the Declaration of Helsinki (last modified in 2013) and the Japanese guideline entitled, “Ethical Guidelines for Medical and Health Research Involving Human Subjects.” All participants provided written informed consent. A. Morphometry of the FHL tendon and surrounding adipose tissues Using a 3.0-T MRI scanner (MAGNETOM Skyra; Siemens Healthineers, Japan), the patients were laid in a supine position with their knees extended and their legs parallel to the long axis of the gantry; the ankles were fixed in the plantar–dorsiflexed neutral position. T1-weighted spin echo images were captured using body coils with a matrix of 512 × 512, field-of-view of 350 mm, TR/TE of 700/8.8 ms, flip angle of 120°, and with no gap at 3-mm intervals from the distal lower leg to the calcaneus, focusing on the height where the FHL and soleus muscles meet. FHL tendons and surrounding adipose tissue were identified from the horizontal plane. After observing the positional relationship of each tissue, they were traced with reference to a slice of the trochlea of the talus, and their cross-sectional area (CSA) and volume were measured. The volume was calculated by adding all measured CSAs and multiplying them by the slice thickness (3 mm) [ 20 ]. Observations and measurements were quantitatively evaluated using Horos ver. 4.0 (Horos Project, USA). B. Relationship between morphometrics and physical characteristics of patients We investigated the influence of the physical characteristics of the patients on the morphometrics of the surrounding adipose tissue of the FHL tendon. Patients’ characteristics, including body height, body weight, body mass index, lower leg length, and foot length, were measured, and the relationship between sex, left–right comparisons, and basic characteristics in each of the surrounding adipose tissue were assessed. C. Examining the positional relationship between the FHL tendon and surrounding adipose tissue The positional relationship between the FHL tendon and surrounding adipose tissues was investigated. Based on the slice level of the trochlea of the talus, a straight line passing through the center of the talus and center of the Achilles tendon was defined as the y-axis, and the line perpendicular to the y-axis passing through the maximum bulge of the lateral malleolus was defined as the x-axis, with an intersection point at the origin (0, 0) (Fig. 1 ). Positive values were defined as lateral or posterior, whereas negative values were defined as medial or anterior. Thereafter, we measured the coordinate centers of the FHL tendon and surrounding reference adipose tissue, the Achilles tendon, peroneal tendon, and tibialis posterior tendon to confirm their positional relationships. The coordinate center was measured using ImageJ image analysis software (National Institutes of Health, USA). Statistical analysis The relationship between height, weight, lower leg length, and foot length in each value of the surrounding adipose tissue was examined using Spearman’s correlation coefficient, and the Mann–Whitney U test was used for sex- and left–right side-based comparisons. SPSS Statistics 20.0 (IBM, USA) was used for all analyses, with significance set at < 5%. Results 1. Gross anatomical examination In the posterior ankle joint, adipose tissue was observed between the FHL tendon, fibula, and lower lateral malleolus in all nine feet (Fig. 2 a). Transverse observation of the FHL tendon and adipose tissue from a horizontal plane using the trochlea of the talus as a reference point revealed oval-shaped adipose tissue surrounding the tendon; the deep (anterior) layer was in contact with the posterior articular capsule and ligament of the talocrural joint (Fig. 2 b), and this tissue could be clearly distinguished from Kager’s fat pad, which is a single layer of adipose tissue located in the superficial layer (posterior) of the FHL tendon (Fig. 3 ). Horizontal cross-section morphometry of the FHL tendon and surrounding adipose tissue revealed mean dimensions of 6.3 ± 0.8 mm and 3.2 ± 0.5 mm in the major and minor axes, respectively, for the FHL tendon and 22.1 ± 1.3 mm and 7.6 ± 2.2 mm in the major and minor axes, respectively, for adipose tissue (Fig. 4 ). 2. MRI study A. Observation and morphometry of the FHL tendon and surrounding adipose tissue On axial MRI images (horizontal plane), the FHL tendon at the level of the talocrural joint in all 40 feet was surrounded by oval-shaped adipose tissues, while the ligament and posterior articular capsule of the talocrural joint were in the deep layer (Fig. 5 ). When the CSAs of the FHL tendon and adipose tissue were measured using the trochlea of the talus as an index, the median CSA of the FHL tendon was 14.4 mm 2 (11.7–16.7 mm 2 ) and that of the adipose tissue was 120.5 mm 2 (100.3–149.4 mm 2 ) (Fig. 6 ). Furthermore, the median volume of adipose tissue was 963.3 mm 3 (896.2–1,115.6 mm 3 ). B. Relationship between morphometrics of adipose tissue surrounding the FHL tendon and physical characteristics of the patients Data on the physical characteristics of all patients are presented in Table 1 . Table 1 Patients’ physical characteristics Men n = 12 (24 feet) Women n = 8 (16 feet) Total n = 20 (40 feet) Age (y) 23.0 (21.0–23.0) 23.0 (22.5–23.0) 23.0 (21.0–23.0) Body height (cm) 175.5 (169.9–179.9) 161.8 (158.7–164.7) 168.3 (164.2–175.6) Body weight (kg) 71.7 (63.3–76.0) 58.4 (54.3–60.0) 63.3 (58.4–73.6) BMI (kg/m 2 ) 22.2 (21.5–24.2) 21.6 (21.1–23.2) 22.2 (21.2–23.5) Leg length (cm) 37.7 (36.3–40.0) 34.5 (34.0–36.1) 36.4 (35.2–38.0) Foot Length (cm) 25.8 (24.8–26.5) 22.8 (22.2–23.5) 24.2 (23.0–26.0) Y, years; cm, centimeter; Kg, kilogram; BMI, body mass index The CSA of the adipose tissue demonstrated positive correlation with body height (r = 0.60), body weight (r = 0.62), body mass index (r = 0.50), lower leg length (r = 0.40), and foot length (r = 0.57) of the patients. Additionally, the adipose tissue volume demonstrated positive correlation with body height (r = 0.66), body weight (r = 0.63), body mass index (r = 0.40), lower leg length (r = 0.48), and foot length (r = 0.63) (Table 2 ). Table 2. Relationship between the cross-sectional area and volume of adipose tissue and patients’ physical characteristics a: Relationship between the cross-sectional area of adipose tissue and physical characteristics Adipose tissue CSA r value p value Body height (cm) 0.60 <.05 Body weight (kg) 0.62 <.05 BMI (kg/m 2 ) 0.50 <.05 Leg length (cm) 0.40 <.05 Foot Length (cm) 0.57 <.05 b: Relationship between the volume of adipose tissue and physical characteristics Adipose tissue Volume r value p value Body height (cm) 0.66 <.05 Body weight (kg) 0.63 <.05 BMI (kg/m 2 ) 0.40 <.05 Leg length (cm) 0.48 <.05 Foot Length (cm) 0.63 <.05 CSA, cross-sectional area; cm, centimeter; Kg, kilogram; BMI, body mass index The CSA and volume of the adipose tissue were significantly greater in men than those in women (p 0.05) (Fig. 8 ). C. Positional relationship between the FHL tendon and surrounding adipose tissues The coordinate centers (x, y) of the FHL tendon, adipose tissue, Achilles tendon, peroneal tendon, and tibialis posterior tendon are presented in Table 3 . Additionally, the adipose tissue surrounding the FHL tendon was at the level of the peroneal tendon (Fig. 9 ). Table 3 Mean value of the center of coordinates in each tissue (mm) FHL-T Adipose tissue A-T P-T TP-T x value −6.8 ± 1.9 3.5 ± 1.3 0.2 ± 0.7 25.5 ± 2.3 −23.2 ± 2.4 y value 7.9 ± 3.0 9.7 ± 2.4 32.1 ± 3.5 9.0 ± 2.3 −9.0 ± 2.7 Each value (x, y) represents the distance (mm) from the origin (0,0). FHL-T, flexor hallucis longus tendon; A-T, Achilles tendon; P-T, peroneal tendon; TP-T, tibialis posterior tendon Discussion This study aimed to evaluate the presence of adipose tissue surrounding the FHL tendon through anatomical observations and MRI findings. The clarification of these structures aims to enhance our understanding of diseases, guiding treatment selection for post-traumatic posteromedial ankle pain, such as ankle sprains and fractures, encountered in clinical practice. In gross posterior view of the ankle, adipose tissue was present in the gap between the FHL tendon and fibula, while horizontal section of the talocrural joint revealed oval-shaped adipose tissue surrounding the FHL tendon. Although the FHL part of Kager’s fat pad is in the superficial layer [ 5 ] of the FHL tendon, the boundary of each tissue was clearly demarcated from the ligament, suggesting that the adipose tissue surrounding the FHL tendon is different from Kager’s fat pad. Morphometric analysis indicated that the volume of the adipose tissue surrounding the FHL tendon was 963.3 mm 3 (median: 896.2–1,115.6 mm 3 ). Malagelada et al. [ 21 ] reported that the volume of Kager’s fat pad to be 10.6 mL (10,600 mm 3 ) using the Archimedean principles from cadaver dissection. The measurement of tissue volume using MRI in this study has also been validated in previous studies [ 22 , 23 ], and the volume of the adipose tissue surrounding the FHL tendon measured in this study was approximately 1/10 the size of Kager’s fat pad. Additionally, when the relationship between the adipose tissue CSA and volume and physical characteristics of patients was examined, a positive correlation was observed between each physical characteristic, which was significantly greater in men than in women. Patel et al. [ 24 ] examined the relationship between the FHL tendon and physical characteristics of patients using B-mode ultrasound and reported a positive correlation between the tendon form and foot length. Rosso et al. [ 25 ] examined the sex-based differences in the Achilles tendon length and its relationship with lower leg length and body height using MRI and reported that the Achilles tendon length was significantly longer in men than in women, demonstrating a positive correlation with lower leg length and body height. Furthermore, a report investigating the relationship between the form of the intrinsic foot muscles, including their CSA and thickness, and physical characteristics using ultrasound imaging showed a positive correlation between the form of the intrinsic foot muscles and body height, body weight, foot length, and arch height [ 26 ]. Thus, it can be said that the size of organs and tissues constituting the body, such as muscles, tendons, and adipose tissues, is proportional to the body size. Similarly, the CSA and volume of adipose tissue is positively correlated with the physical characteristics, suggesting that the morphology of adipose tissue may be influenced by body size. The adipose tissue around the tendon of the lower limbs is represented by Kager’s fat pad [ 5 , 21 , 27 ] around the Achilles tendon and infrapatellar fat pad [ 28 , 29 ] around the patellar tendon. Adipose tissue not only serves as a buffer to avoid direct collision between the tendon/ligament and bone [ 21 , 30 ] but also has proprioceptive and nociceptive functions for the tendon [ 1 , 3 ] because of the presence of nerve endings and neuro-related proteins. Adipose tissue surrounding the FHL tendons may also be involved in the function and diseases of FHL tendons. However, the results of this study are insufficient to clarify the involvement of adipose tissue in diseases of the FHL tendon. Therefore, further evaluation is needed on this topic. Conclusions we evaluated the presence of surrounding adipose tissue in the FHL tendon through gross dissection and MRI examination. Adipose tissue, which is different from Kager’s fat pad around the adjacent Achilles tendon, was observed around the FHL tendon. Abbreviations FHL, flexor hallucis longus; MRI, magnetic resonance imaging; CSA, cross-sectional area. Declarations Acknowledgements The authors thank Editage (www. editage.com) for English language editing. In addition, the authors acknowledge and thank the anonymous individuals who generously donated their bodies in order for this study to be performed. Data availability statement The data that support the findings of this study will be available from the corresponding author upon reason- able request. Conflict of interest The authors declare that they have no conflict of interest. Funding statement The authors did not receive support from any organization for the submitted work. Permission to reproduce material from other sources clinical trial registration This study was conducted after obtaining prior approval from the Ritsumeikan University Ethics Review Committee (BKC - LSMH - 2021 - 033). Author Contributions The conception and design of the study were done by T. K. and Y. S. The acquisition of data was taken care of by T. K., T. K., H. S., K. I. Analysis and/or interpretation of data was carried out by T. K., T. K., H. S., K. I., M. F., and N. H. The drafting of the article was done by T. K., Y. S. and K. S. Revising the article critically for important intellectual content was taken care of by K. S. All authors have contributed significantly to the study, approved the article, and agreed with the submission. References Benjamin, M. et al. Adipose tissue at entheses: the rheumatological implications of its distribution. A potential site of pain and stress dissipation?. 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Cite Share Download PDF Status: Published Journal Publication published 23 Jul, 2024 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 13 Jun, 2024 Reviews received at journal 11 Jun, 2024 Reviews received at journal 31 May, 2024 Reviewers agreed at journal 22 May, 2024 Reviewers agreed at journal 22 May, 2024 Reviewers invited by journal 21 May, 2024 Editor assigned by journal 21 May, 2024 Editor invited by journal 15 May, 2024 Submission checks completed at journal 11 May, 2024 First submitted to journal 09 May, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4392485","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":304030504,"identity":"c3b18c47-5871-44b3-9fe5-3c9c4cbacecf","order_by":0,"name":"Tatsuhito Kawada","email":"","orcid":"","institution":"Ritsumeikan University","correspondingAuthor":false,"prefix":"","firstName":"Tatsuhito","middleName":"","lastName":"Kawada","suffix":""},{"id":304030505,"identity":"8c311b66-96fe-42d3-9cd7-952098e20671","order_by":1,"name":"Yasushi Shinohara","email":"data:image/png;base64,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","orcid":"","institution":"Ritsumeikan University","correspondingAuthor":true,"prefix":"","firstName":"Yasushi","middleName":"","lastName":"Shinohara","suffix":""},{"id":304030506,"identity":"66873855-c633-4ba9-822b-dbfcd46c77ab","order_by":2,"name":"Toshiyuki Kurihara","email":"","orcid":"","institution":"Ritsumeikan University","correspondingAuthor":false,"prefix":"","firstName":"Toshiyuki","middleName":"","lastName":"Kurihara","suffix":""},{"id":304030507,"identity":"ff21f3ef-3bc9-47af-8e41-9c86212a89ef","order_by":3,"name":"Hayato Satake","email":"","orcid":"","institution":"Ritsumeikan University","correspondingAuthor":false,"prefix":"","firstName":"Hayato","middleName":"","lastName":"Satake","suffix":""},{"id":304030508,"identity":"16cf932d-a8ea-4b27-a2b5-e38a50ee951b","order_by":4,"name":"Kana Itokawa","email":"","orcid":"","institution":"Ritsumeikan University","correspondingAuthor":false,"prefix":"","firstName":"Kana","middleName":"","lastName":"Itokawa","suffix":""},{"id":304030509,"identity":"15def0e6-7e1d-44d1-a415-74a254cd3784","order_by":5,"name":"Masaki Fukuyoshi","email":"","orcid":"","institution":"Nagoya Sports Medicine \u0026 Orthopedic Clinic","correspondingAuthor":false,"prefix":"","firstName":"Masaki","middleName":"","lastName":"Fukuyoshi","suffix":""},{"id":304030510,"identity":"4be50984-dfb4-4112-ac52-486f7dff8e5a","order_by":6,"name":"Norio Hayashi","email":"","orcid":"","institution":"Musculoskeletal Functional Anatomy Research Institute","correspondingAuthor":false,"prefix":"","firstName":"Norio","middleName":"","lastName":"Hayashi","suffix":""},{"id":304030512,"identity":"3f0cfe00-0f82-43fc-982d-026fe674718f","order_by":7,"name":"Katsumasa Sugimoto","email":"","orcid":"","institution":"Nagoya Sports Medicine \u0026 Orthopedic Clinic","correspondingAuthor":false,"prefix":"","firstName":"Katsumasa","middleName":"","lastName":"Sugimoto","suffix":""}],"badges":[],"createdAt":"2024-05-09 04:33:36","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4392485/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4392485/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-024-67831-y","type":"published","date":"2024-07-23T16:15:42+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":57036052,"identity":"a656712f-8fe9-4a88-9e18-8397651bb8d6","added_by":"auto","created_at":"2024-05-23 18:36:31","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":20181,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eCoordinate axis settings\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eX-axis: Straight line to the Y-axis through the maximum bulge of the lateral malleolus.\u003c/p\u003e\n\u003cp\u003eY-axis: Straight line through the center of the talus and center of the Achilles tendon.\u003c/p\u003e\n\u003cp\u003eRed circle: each center point; yellow circle: origin\u003c/p\u003e\n\u003cp\u003eFHL-T, flexor hallucis longus tendon; A-T, Achilles tendon; P-T, peroneal tendon; TP-T, tibialis posterior tendon; T, talus, MM, medial malleolus; LM, lateral malleolus; Pos, posterior;\u003c/p\u003e\n\u003cp\u003eAnt, anterior; Lat, lateral, Med: medial.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392485/v1/3ab826fdf1cbeeadc7db2a47.jpg"},{"id":57036058,"identity":"f0a51e75-9f1a-41d3-9a0c-eca38519282b","added_by":"auto","created_at":"2024-05-23 18:36:32","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":50847,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eAdipose tissue surrounding the flexor hallucis longus tendon\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea:\u003c/strong\u003e Adipose tissue surrounding the flexor hallucis longus tendon of the left ankle joint (posterior view).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eb: \u003c/strong\u003eAdipose tissue surrounding the flexor hallucis longus tendon at the level of the talocrural joint (horizontal).\u003c/p\u003e\n\u003cp\u003eDotted line: contour of adipose tissue\u003c/p\u003e\n\u003cp\u003eFHL-T, flexor hallucis longus tendon; T, talus; C, calcaneus; MM, medial malleolus; LM, lateral malleolus; Pos, posterior; Ant, anterior; Lat, lateral; Med, medial\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392485/v1/e6385abfaf97dcc1bd821eec.jpg"},{"id":57036056,"identity":"19a1f92c-b21b-4236-bf22-845d31c040fa","added_by":"auto","created_at":"2024-05-23 18:36:31","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":44708,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eBorder between adipose tissue surrounding the flexor hallucis longus tendon and superficial Kager’s fat pad\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eBlack dotted line: boundary with Kager’s fat pad\u003c/p\u003e\n\u003cp\u003eFHL-T, flexor hallucis longus tendon; KFP, Kager’s fat pad; Lat, lateral; Med, medial\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392485/v1/87a6f0fa35d6eeff4d97a802.jpg"},{"id":57036059,"identity":"bb07d57a-52a9-4ecc-8af2-b9281fbbf12d","added_by":"auto","created_at":"2024-05-23 18:36:32","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":47192,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eMethods for measuring the major and minor axis of the flexor hallucis longus tendon and surrounding adipose tissue\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe maximum width of each tissue was defined as the major axis, and the maximum length was defined as the minor axis.\u003c/p\u003e\n\u003cp\u003eWhite double arrows: major axis; black double arrows: minor axis\u003c/p\u003e\n\u003cp\u003eFHL-T, flexor hallucis longus tendon; LM, lateral malleolus\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392485/v1/93522375b5938c4ce78fac0c.jpg"},{"id":57036061,"identity":"70e9525e-f3e8-44cd-b0d7-b698c2bc4d8d","added_by":"auto","created_at":"2024-05-23 18:36:32","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":29761,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eMagnetic resonance image of adipose tissue surrounding the flexor hallucis longus tendon\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea:\u003c/strong\u003e At the level of the trochlea of the talus\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eb:\u003c/strong\u003e One slice proximal to the trochlea of the talus\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ec:\u003c/strong\u003e One slice distal to the trochlea of the talus\u003c/p\u003e\n\u003cp\u003eDotted line: contour of adipose tissue\u003c/p\u003e\n\u003cp\u003eFHL, flexor hallucis longus; FHL-T, flexor hallucis longus tendon; T, talus; MM, medial malleolus; LM, lateral malleolus; Pos, posterior; Ant, anterior; Lat, lateral; Med, medial\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392485/v1/bd733ac83ac5bb74a13227c5.jpg"},{"id":57036054,"identity":"496cda52-19ea-4593-8383-4c54b50e6d9d","added_by":"auto","created_at":"2024-05-23 18:36:31","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":14714,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eMethod of measuring the cross-sectional area of adipose tissue around the flexor hallucis longus tendon\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe cross-sectional area of adipose tissue was defined as the difference between the cross-sectional area of the flexor hallucis longus muscle and that of adipose tissue.\u003c/p\u003e\n\u003cp\u003eBlack dotted line: adipose tissue trace section\u003c/p\u003e\n\u003cp\u003eWhite line: flexor hallucis longus trace section\u003c/p\u003e\n\u003cp\u003eFHL, flexor hallucis longus; FHL-T, flexor hallucis longus tendon\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392485/v1/fe84f1a8e2055fff91f67ee5.jpg"},{"id":57036057,"identity":"3a3b3db5-72d0-479a-b4fd-137c9b117d78","added_by":"auto","created_at":"2024-05-23 18:36:32","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":17973,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eCross-sectional area and volume of adipose tissue by gender\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea:\u003c/strong\u003e Adipose tissue cross-sectional area by gender\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eb:\u003c/strong\u003e Adipose tissue volume by gender\u003c/p\u003e\n\u003cp\u003eCSA, cross-sectional area\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392485/v1/fcd48d98f34a38d5a6ad5110.jpg"},{"id":57036060,"identity":"f1a36c26-fef8-42c0-8f50-8382b14d5f58","added_by":"auto","created_at":"2024-05-23 18:36:32","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":17173,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eLeft–right comparison of cross-sectional area and volume of adipose tissue\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea:\u003c/strong\u003e Left–right adipose tissuecross-sectional area\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eb:\u003c/strong\u003e Left–right adipose tissue volume\u003c/p\u003e\n\u003cp\u003eCSA, cross-sectional area\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392485/v1/a6bc4b986b56e32429879022.jpg"},{"id":57036055,"identity":"05739fd0-1737-47c6-89b1-a6b3612f3fad","added_by":"auto","created_at":"2024-05-23 18:36:31","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":19521,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eCoordinate center of each tissue\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eWhite circle: origin\u003c/p\u003e\n\u003cp\u003eBlack circle: coordinate center of each tissue\u003c/p\u003e\n\u003cp\u003eFHL-T, flexor hallucis longus tendon; A-T, Achilles tendon; P-T, peroneal tendon，TP-T, tibialis posterior tendon\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392485/v1/413061fe988d729aae125e00.jpg"},{"id":61597964,"identity":"bcc56928-2941-4158-bb7f-1909d579e298","added_by":"auto","created_at":"2024-08-01 17:33:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1165837,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4392485/v1/d0115101-6e8a-4420-bb32-90c99a885f12.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Anatomical evaluations of the adipose tissue surrounding the flexor hallucis longus tendon: A study using gross anatomy and magnetic resonance imaging","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAdipose tissues, which are present around tendons, plays a role in reducing friction and compressive stress [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In addition, adipose tissues contain nerve endings that serve the nociceptive function of tendons [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Moreover, because adipose tissues surrounding tendons also moves with tendon and joint movement [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], decreased movement of adipose tissue may cause tendinopathy and postoperative pain [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Therefore, adipose tissue is one of the important tissues for understanding the pathogenesis of tendinopathy [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], and it is necessary to determine adipose tissue distribution for treatment in the field of rehabilitation and orthopedics.\u003c/p\u003e \u003cp\u003eThe flexor hallucis longus (FHL) originates at the distal two-thirds of the posterior fibula and interosseous membrane of the lower leg, transitions into a tendon at the distal tibia, passes through the fibro-osseous tunnel, changes direction with the sustentacular tail, and courses towards the base of the great toe phalanx [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Tendon disorders of the FHL muscle reportedly occur in the fibro-osseous tunnel between the great toe sesamoid [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], at the junction of the tendon of the flexor digitorum longus [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] and the base of the great toe phalanx [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Particularly, disorders occur more frequently between the fibro-osseous tunnel and great toe sesamoid because of the poorer blood flow to the FHL tendon than that in other regions, considerable changes in the course of the tendon, and the application of excessive stress [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Although the affected area is more distal to the talocrural joint, some patients experience pain around the talocrural joint after an ankle injury [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Furthermore, previous studies using magnetic resonance imaging (MRI) reported that some cases of pain around the FHL tendon after ankle trauma showed scarring of the surrounding tissue [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Although adipose tissue may also be present around the FHL tendon, its detailed anatomical structure remains unclear. Combined examination using gross anatomy and MRI has been performed for anatomical observations of adipose tissue [\u003cspan additionalcitationids=\"CR18\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThis study aimed to investigate the presence of adipose tissue surrounding the FHL tendon through gross dissection and MRI.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e1. Gross anatomical examination\u003c/h2\u003e \u003cp\u003eSubjects for systematic dissection included nine cadavers and nine feet (average age: 86.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2 years; 4 men, 5 women; 5 left feet, 4 right feet). To determine the structure of the FHL tendons and surrounding tissues, patients with a history of trauma, including fractures around the ankle and soft tissue injuries, were excluded.\u003c/p\u003e \u003cp\u003eAn autopsy was carefully performed while inspecting each tissue to identify the FHL tendon and surrounding structures behind the ankle. The same procedure was performed by the same examiner for all cadavers.\u003c/p\u003e \u003cp\u003eFirst, the skin and subcutaneous adipose tissue were removed from the posterior ankle joint. The Achilles tendon and Kager\u0026rsquo;s fat pad were distally exposed to observe their positional relationship with the deep FHL tendon and structures. To observe the positional relationship between the FHL tendon and surrounding tissues, we identified and removed the long and short peroneus, tibialis posterior, tibial nerve, and tibial posterior artery. Subsequently, the trochlea of the talus was used as an indicator to traverse the FHL tendon and surrounding tissues, which were also observed in the horizontal plane. Morphometry was performed using a digital caliper (SCALE-BK -150 \u0026ndash; MM, Waves, JAPAN) to measure the long and short axes of the FHL tendon and surrounding tissues at the level of the talar trochlea. Each measurement was performed three times, and the average value was used in all analyses.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2. MRI study\u003c/h2\u003e \u003cp\u003eA total of 40 feet from 20 healthy adults (12 men and 8 women; mean age, 22.3\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0 years) were examined. Patients with a history of fracture around the FHL tendon, those with tendon disorders of the ankle joint, and those with significant limitation of range of motion or pain in the ankle joint were excluded. The study design was approved by the ethics committee of XXXX (XXX \u0026ndash; 2021\u0026ndash;033), and all procedures were performed in accordance with the Declaration of Helsinki (last modified in 2013) and the Japanese guideline entitled, \u0026ldquo;Ethical Guidelines for Medical and Health Research Involving Human Subjects.\u0026rdquo; All participants provided written informed consent.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eA. Morphometry of the FHL tendon and surrounding adipose tissues\u003c/h2\u003e \u003cp\u003eUsing a 3.0-T MRI scanner (MAGNETOM Skyra; Siemens Healthineers, Japan), the patients were laid in a supine position with their knees extended and their legs parallel to the long axis of the gantry; the ankles were fixed in the plantar\u0026ndash;dorsiflexed neutral position. T1-weighted spin echo images were captured using body coils with a matrix of 512 \u0026times; 512, field-of-view of 350 mm, TR/TE of 700/8.8 ms, flip angle of 120\u0026deg;, and with no gap at 3-mm intervals from the distal lower leg to the calcaneus, focusing on the height where the FHL and soleus muscles meet. FHL tendons and surrounding adipose tissue were identified from the horizontal plane. After observing the positional relationship of each tissue, they were traced with reference to a slice of the trochlea of the talus, and their cross-sectional area (CSA) and volume were measured. The volume was calculated by adding all measured CSAs and multiplying them by the slice thickness (3 mm) [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Observations and measurements were quantitatively evaluated using Horos ver. 4.0 (Horos Project, USA).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eB. Relationship between morphometrics and physical characteristics of patients\u003c/h2\u003e \u003cp\u003eWe investigated the influence of the physical characteristics of the patients on the morphometrics of the surrounding adipose tissue of the FHL tendon. Patients\u0026rsquo; characteristics, including body height, body weight, body mass index, lower leg length, and foot length, were measured, and the relationship between sex, left\u0026ndash;right comparisons, and basic characteristics in each of the surrounding adipose tissue were assessed.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eC. Examining the positional relationship between the FHL tendon and surrounding adipose tissue\u003c/h2\u003e \u003cp\u003eThe positional relationship between the FHL tendon and surrounding adipose tissues was investigated. Based on the slice level of the trochlea of the talus, a straight line passing through the center of the talus and center of the Achilles tendon was defined as the y-axis, and the line perpendicular to the y-axis passing through the maximum bulge of the lateral malleolus was defined as the x-axis, with an intersection point at the origin (0, 0) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Positive values were defined as lateral or posterior, whereas negative values were defined as medial or anterior.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThereafter, we measured the coordinate centers of the FHL tendon and surrounding reference adipose tissue, the Achilles tendon, peroneal tendon, and tibialis posterior tendon to confirm their positional relationships. The coordinate center was measured using ImageJ image analysis software (National Institutes of Health, USA).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eThe relationship between height, weight, lower leg length, and foot length in each value of the surrounding adipose tissue was examined using Spearman\u0026rsquo;s correlation coefficient, and the Mann\u0026ndash;Whitney U test was used for sex- and left\u0026ndash;right side-based comparisons. SPSS Statistics 20.0 (IBM, USA) was used for all analyses, with significance set at \u0026lt;\u0026thinsp;5%.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e1. Gross anatomical examination\u003c/h2\u003e\n \u003cp\u003eIn the posterior ankle joint, adipose tissue was observed between the FHL tendon, fibula, and lower lateral malleolus in all nine feet (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea). Transverse observation of the FHL tendon and adipose tissue from a horizontal plane using the trochlea of the talus as a reference point revealed oval-shaped adipose tissue surrounding the tendon; the deep (anterior) layer was in contact with the posterior articular capsule and ligament of the talocrural joint (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb), and this tissue could be clearly distinguished from Kager\u0026rsquo;s fat pad, which is a single layer of adipose tissue located in the superficial layer (posterior) of the FHL tendon (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eHorizontal cross-section morphometry of the FHL tendon and surrounding adipose tissue revealed mean dimensions of 6.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8 mm and 3.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 mm in the major and minor axes, respectively, for the FHL tendon and 22.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3 mm and 7.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.2 mm in the major and minor axes, respectively, for adipose tissue (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e2. MRI study\u003c/strong\u003e\u003c/p\u003e\u003cspan\u003e\n \u003cp\u003e\u003cstrong\u003eA. Observation and morphometry of the FHL tendon and surrounding adipose tissue\u003c/strong\u003e\u003c/p\u003e\n \u003c/span\u003e\n \u003cp\u003eOn axial MRI images (horizontal plane), the FHL tendon at the level of the talocrural joint in all 40 feet was surrounded by oval-shaped adipose tissues, while the ligament and posterior articular capsule of the talocrural joint were in the deep layer (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). When the CSAs of the FHL tendon and adipose tissue were measured using the trochlea of the talus as an index, the median CSA of the FHL tendon was 14.4 mm\u003csup\u003e2\u003c/sup\u003e (11.7\u0026ndash;16.7 mm\u003csup\u003e2\u003c/sup\u003e) and that of the adipose tissue was 120.5 mm\u003csup\u003e2\u003c/sup\u003e (100.3\u0026ndash;149.4 mm\u003csup\u003e2\u003c/sup\u003e) (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). Furthermore, the median volume of adipose tissue was 963.3 mm\u003csup\u003e3\u003c/sup\u003e (896.2\u0026ndash;1,115.6 mm\u003csup\u003e3\u003c/sup\u003e).\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eB. Relationship between morphometrics of adipose tissue surrounding the FHL tendon and physical characteristics of the patients\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eData on the physical characteristics of all patients are presented in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003ePatients\u0026rsquo; physical characteristics\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMen\u003c/p\u003e\n \u003cp\u003en\u0026thinsp;=\u0026thinsp;12 (24 feet)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eWomen\u003c/p\u003e\n \u003cp\u003en\u0026thinsp;=\u0026thinsp;8 (16 feet)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003cp\u003en\u0026thinsp;=\u0026thinsp;20 (40 feet)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAge (y)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23.0\u003c/p\u003e\n \u003cp\u003e(21.0\u0026ndash;23.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23.0\u003c/p\u003e\n \u003cp\u003e(22.5\u0026ndash;23.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23.0\u003c/p\u003e\n \u003cp\u003e(21.0\u0026ndash;23.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eBody height (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e175.5\u003c/p\u003e\n \u003cp\u003e(169.9\u0026ndash;179.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e161.8\u003c/p\u003e\n \u003cp\u003e(158.7\u0026ndash;164.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e168.3\u003c/p\u003e\n \u003cp\u003e(164.2\u0026ndash;175.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eBody weight (kg)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e71.7\u003c/p\u003e\n \u003cp\u003e(63.3\u0026ndash;76.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e58.4\u003c/p\u003e\n \u003cp\u003e(54.3\u0026ndash;60.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e63.3\u003c/p\u003e\n \u003cp\u003e(58.4\u0026ndash;73.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eBMI (kg/m\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22.2\u003c/p\u003e\n \u003cp\u003e(21.5\u0026ndash;24.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21.6\u003c/p\u003e\n \u003cp\u003e(21.1\u0026ndash;23.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22.2\u003c/p\u003e\n \u003cp\u003e(21.2\u0026ndash;23.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eLeg length (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e37.7\u003c/p\u003e\n \u003cp\u003e(36.3\u0026ndash;40.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e34.5\u003c/p\u003e\n \u003cp\u003e(34.0\u0026ndash;36.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e36.4\u003c/p\u003e\n \u003cp\u003e(35.2\u0026ndash;38.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eFoot Length (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25.8\u003c/p\u003e\n \u003cp\u003e(24.8\u0026ndash;26.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22.8\u003c/p\u003e\n \u003cp\u003e(22.2\u0026ndash;23.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e24.2\u003c/p\u003e\n \u003cp\u003e(23.0\u0026ndash;26.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"4\"\u003eY, years; cm, centimeter; Kg, kilogram; BMI, body mass index\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eThe CSA of the adipose tissue demonstrated positive correlation with body height (r\u0026thinsp;=\u0026thinsp;0.60), body weight (r\u0026thinsp;=\u0026thinsp;0.62), body mass index (r\u0026thinsp;=\u0026thinsp;0.50), lower leg length (r\u0026thinsp;=\u0026thinsp;0.40), and foot length (r\u0026thinsp;=\u0026thinsp;0.57) of the patients. Additionally, the adipose tissue volume demonstrated positive correlation with body height (r\u0026thinsp;=\u0026thinsp;0.66), body weight (r\u0026thinsp;=\u0026thinsp;0.63), body mass index (r\u0026thinsp;=\u0026thinsp;0.40), lower leg length (r\u0026thinsp;=\u0026thinsp;0.48), and foot length (r\u0026thinsp;=\u0026thinsp;0.63) (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eTable 2. Relationship between the cross-sectional area and volume of adipose tissue and patients\u0026rsquo; physical characteristics\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003ea:\u003c/strong\u003e Relationship between the cross-sectional area of adipose tissue and physical characteristics\u003c/p\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eAdipose tissue CSA\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003er value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003ep value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eBody height (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e0.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026lt;.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eBody weight (kg)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e0.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026lt;.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eBMI (kg/m\u003csup\u003e2\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e0.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026lt;.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eLeg length (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e0.40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026lt;.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eFoot Length (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e0.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026lt;.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003cstrong\u003eb:\u003c/strong\u003e Relationship between the volume of adipose tissue and physical characteristics\u003c/p\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eAdipose tissue Volume\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003er value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003ep value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eBody height (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e0.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026lt;.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eBody weight (kg)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e0.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026lt;.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eBMI (kg/m\u003csup\u003e2\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e0.40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026lt;.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eLeg length (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e0.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026lt;.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eFoot Length (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e0.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026lt;.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\u003cp\u003eCSA, cross-sectional area; cm, centimeter; Kg, kilogram; BMI, body mass index\u003c/p\u003e\u003cp\u003eThe CSA and volume of the adipose tissue were significantly greater in men than those in women (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e). However, no significant difference was observed between the left and right feet (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05) (Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003eC. Positional relationship between the FHL tendon and surrounding adipose tissues\u003c/h2\u003e\n \u003cp\u003eThe coordinate centers (x, y) of the FHL tendon, adipose tissue, Achilles tendon, peroneal tendon, and tibialis posterior tendon are presented in Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. Additionally, the adipose tissue surrounding the FHL tendon was at the level of the peroneal tendon (Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e).\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eMean value of the center of coordinates in each tissue (mm)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFHL-T\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAdipose tissue\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eA-T\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eP-T\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTP-T\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003ex value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u0026minus;6.8\u0026thinsp;\u0026plusmn;\u0026thinsp;1.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u0026minus;23.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003ey value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.7\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e32.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u0026minus;9.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\"\u003eEach value (x, y) represents the distance (mm) from the origin (0,0).\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\"\u003eFHL-T, flexor hallucis longus tendon; A-T, Achilles tendon; P-T, peroneal tendon; TP-T, tibialis posterior tendon\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis study aimed to evaluate the presence of adipose tissue surrounding the FHL tendon through anatomical observations and MRI findings. The clarification of these structures aims to enhance our understanding of diseases, guiding treatment selection for post-traumatic posteromedial ankle pain, such as ankle sprains and fractures, encountered in clinical practice.\u003c/p\u003e \u003cp\u003eIn gross posterior view of the ankle, adipose tissue was present in the gap between the FHL tendon and fibula, while horizontal section of the talocrural joint revealed oval-shaped adipose tissue surrounding the FHL tendon. Although the FHL part of Kager\u0026rsquo;s fat pad is in the superficial layer [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] of the FHL tendon, the boundary of each tissue was clearly demarcated from the ligament, suggesting that the adipose tissue surrounding the FHL tendon is different from Kager\u0026rsquo;s fat pad.\u003c/p\u003e \u003cp\u003eMorphometric analysis indicated that the volume of the adipose tissue surrounding the FHL tendon was 963.3 mm\u003csup\u003e3\u003c/sup\u003e (median: 896.2\u0026ndash;1,115.6 mm\u003csup\u003e3\u003c/sup\u003e). Malagelada et al. [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] reported that the volume of Kager\u0026rsquo;s fat pad to be 10.6 mL (10,600 mm\u003csup\u003e3\u003c/sup\u003e) using the Archimedean principles from cadaver dissection. The measurement of tissue volume using MRI in this study has also been validated in previous studies [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], and the volume of the adipose tissue surrounding the FHL tendon measured in this study was approximately 1/10 the size of Kager\u0026rsquo;s fat pad. Additionally, when the relationship between the adipose tissue CSA and volume and physical characteristics of patients was examined, a positive correlation was observed between each physical characteristic, which was significantly greater in men than in women. Patel et al. [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] examined the relationship between the FHL tendon and physical characteristics of patients using B-mode ultrasound and reported a positive correlation between the tendon form and foot length. Rosso et al. [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] examined the sex-based differences in the Achilles tendon length and its relationship with lower leg length and body height using MRI and reported that the Achilles tendon length was significantly longer in men than in women, demonstrating a positive correlation with lower leg length and body height. Furthermore, a report investigating the relationship between the form of the intrinsic foot muscles, including their CSA and thickness, and physical characteristics using ultrasound imaging showed a positive correlation between the form of the intrinsic foot muscles and body height, body weight, foot length, and arch height [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Thus, it can be said that the size of organs and tissues constituting the body, such as muscles, tendons, and adipose tissues, is proportional to the body size. Similarly, the CSA and volume of adipose tissue is positively correlated with the physical characteristics, suggesting that the morphology of adipose tissue may be influenced by body size.\u003c/p\u003e \u003cp\u003eThe adipose tissue around the tendon of the lower limbs is represented by Kager\u0026rsquo;s fat pad [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] around the Achilles tendon and infrapatellar fat pad [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] around the patellar tendon. Adipose tissue not only serves as a buffer to avoid direct collision between the tendon/ligament and bone [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] but also has proprioceptive and nociceptive functions for the tendon [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] because of the presence of nerve endings and neuro-related proteins.\u003c/p\u003e \u003cp\u003eAdipose tissue surrounding the FHL tendons may also be involved in the function and diseases of FHL tendons. However, the results of this study are insufficient to clarify the involvement of adipose tissue in diseases of the FHL tendon. Therefore, further evaluation is needed on this topic.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003ewe evaluated the presence of surrounding adipose tissue in the FHL tendon through gross dissection and MRI examination. Adipose tissue, which is different from Kager\u0026rsquo;s fat pad around the adjacent Achilles tendon, was observed around the FHL tendon.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eFHL, flexor hallucis longus; MRI, magnetic resonance imaging;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCSA, cross-sectional area.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAcknowledgements\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors thank Editage (www. editage.com) for English language editing. In addition, the authors acknowledge and thank the anonymous individuals who generously donated their bodies in order for this study to be performed.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eData availability statement\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study will be available from the corresponding author upon reason- able request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eConflict of interest\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFunding statement\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors did not receive support from any organization for the submitted work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003ePermission to reproduce material from other sources clinical trial registration\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was conducted after obtaining prior approval from the Ritsumeikan University Ethics Review Committee (BKC - LSMH - 2021 - 033).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAuthor Contributions\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe conception and design of the study were done by T. K. and Y. S. The acquisition of data was taken care of by T. K., T. K., H. S., K. I. Analysis and/or interpretation of data was carried out by T. K., T. K., H. S., K. I., M. F., and N. H. The drafting of the article was done by T. K., Y. S. and K. S. Revising the article critically for important intellectual content was taken care of by K. S. All authors have contributed significantly to the study, approved the article, and agreed with the submission.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBenjamin, M. et al. Adipose tissue at entheses: the rheumatological implications of its distribution. A potential site of pain and stress dissipation?. Ann Rheum Dis, 63(12), 1549\u0026ndash;1555 (2004). https://doi.org/10.1136/ard.2003.019182\u003c/li\u003e\n\u003cli\u003eClavert, P., Dosch, J.C., Wolfram-Gabel, R., Kahn, J.L. New findings on intermetacarpal fat pads: anatomy and imaging. Surg Radiol Anat, 28(4), 351\u0026ndash;354 (2006). https://doi.org/10.1007/s00276-006-0106-z\u003c/li\u003e\n\u003cli\u003eShaw, H.M., Santer, R.M., Watson, A.H., Benjamin, M. Adipose tissue at entheses: the innervations and cell composition of the retromalleolar fat pad associated with the rat Achilles tendon. J Anat, 211(4), 436\u0026ndash;443 (2007). https://doi.org/10.1111/j.1469-7580.2007.00791.x\u003c/li\u003e\n\u003cli\u003eAbreu, M.R., Chung, C.B., Trudell, D., Resnick, D. Hoffa\u0026apos;s fat pad injuries and their relationship with anterior cruciate ligament tears: new observations based on MR imaging in patients and MR imaging and anatomic correlation in cadavers. Skelet Radiol, 37(4), 301\u0026ndash;306 (2008). https://doi.org/10.1007/s00256-007-0427-y\u003c/li\u003e\n\u003cli\u003eTheobald, P. et al. The functional anatomy of Kager\u0026rsquo;s fat pad in relation to retrocalcaneal problems and other hindfoot disorders. J Anat, 208(1), 91\u0026ndash;97 (2006). https://doi.org/10.1111/j.1469-7580.2006.00510.x\u003c/li\u003e\n\u003cli\u003eHe, L., Genin, J., Delzell, P. Ultrasound diagnosis and percutaneous treatment of Achilles tendon tethering: a case series. Skelet Radiol, 45(9), 1293\u0026ndash;1298 (2016). https://doi.org/10.1007/s00256-016-2416-5\u003c/li\u003e\n\u003cli\u003eHannon, J., Bardenett, S., Singleton, S., Garrison, J.C. Evaluation, treatment, and rehabilitation implications of the infrapatellar fat pad. Sports Health, 8(2), 167\u0026ndash;171 (2016). https://doi.org/10.1177/1941738115611413\u003c/li\u003e\n\u003cli\u003ePingel, J. et al. Inflammatory and metabolic alterations of Kager\u0026rsquo;s fat pad in chronic Achilles tendinopathy. PLOS ONE, 10(5), e0127811 (2015). https://doi.org/10.1371/journal.pone.0127811\u003c/li\u003e\n\u003cli\u003eMichelson, J., Dunn, L. Tenosynovitis of the flexor hallucis longus: a clinical study of the spectrum of presentation and treatment. Foot Ankle Int, 26(4), 291\u0026ndash;303 (2005). https://doi.org/10.1177/107110070502600405\u003c/li\u003e\n\u003cli\u003eTheodoropoulos, J.S., Wolin, P.M., Taylor, D.W. Arthroscopic release of flexor hallucis longus tendon using modified posteromedial and posterolateral portals in the supine position. Foot (Edinb), 19(4), 218\u0026ndash;221 (2009). https://doi.org/10.1016/j.foot.2009.02.002\u003c/li\u003e\n\u003cli\u003ePetersen, W., Pufe, T., Zantop, T., Paulsen, F. Blood supply of the flexor hallucis longus tendon with regard to dancer\u0026rsquo;s tendinitis: injection and immunohistochemical studies of cadaver tendons. Foot Ankle Int, 24(8), 591\u0026ndash;596 (2003). https://doi.org/10.1177/107110070302400804\u003c/li\u003e\n\u003cli\u003eWei, S.Y., Kneeland, J.B., Okereke, E. Complete atraumatic rupture of the flexor hallucis longus tendon: a case report and review of the literature. Foot Ankle Int, 19(7), 472\u0026ndash;474 (1998). https://doi.org/10.1177/107110079801900709\u003c/li\u003e\n\u003cli\u003eKrackow, K.A. Acute, traumatic rupture of a flexor hallucis longus tendon: a case report. Clin Orthop Relat Res. 150:261\u0026ndash;262 (1980). https://doi.org/10.1097/00003086-198007000-00044\u003c/li\u003e\n\u003cli\u003eLiu, S.H., Mirzayan, R. Posteromedial ankle impingement. Arthroscopy, 9(6), 709\u0026ndash;711 (1993). https://doi.org/10.1016/s0749-8063(05)80514-6\u003c/li\u003e\n\u003cli\u003eLui, T.H. Endoscopic adhesiolysis of the flexor hallucis longus muscle. Foot Ankle Spec, 7(6), 492\u0026ndash;494 (2014). https://doi.org/10.1177/1938640014546859\u003c/li\u003e\n\u003cli\u003eLo, L.D. et al. MR imaging findings of entrapment of the flexor hallucis longus tendon. AJR, 176(5), 1145\u0026ndash;1148 (2001). https://doi.org/10.2214/ajr.176.5.1761145\u003c/li\u003e\n\u003cli\u003eStaeubli, H.U., Bollmann, C., Kreutz, R., Becker, W., Rauschning, W. Quantification of intact quadriceps tendon, quadriceps tendon insertion, and suprapatellar fat pad: MR arthrography, anatomy, and cryosections in the sagittal plane. AJR Am J Roentgenol, 173(3), 691\u0026ndash;698 (1999). https://doi.org/10.2214/ajr.173.3.10470905\u003c/li\u003e\n\u003cli\u003eSkaf, A.Y. et al. Pericruciate fat pad of the knee: anatomy and pericruciate fat pad inflammation: cadaveric and clinical study emphasizing MR imaging. Skelet Radiol, 41(12), 1591\u0026ndash;1596 (2012). https://doi.org/10.1007/s00256-012-1447-9\u003c/li\u003e\n\u003cli\u003eTakumi, O. et al. Presence of adipose tissue along the posteromedial tibial border. J Exp Orthop, 8(1), 92 (2021). https://doi.org/10.1186/s40634-021-00408-0\u003c/li\u003e\n\u003cli\u003eKusagawa, Y. et al. Associations between the size of individual plantar intrinsic and extrinsic foot muscles and toe flexor strength. J Foot Ankle Res, 15(1), 22 (2022). https://doi.org/10.1186/s13047-022-00532-9\u003c/li\u003e\n\u003cli\u003eMalagelada, F. et al. Pressure changes in the Kager fat pad at the extremes of ankle motion suggest a potential role in Achilles tendinopathy.\u0026rdquo; Knee Surg Sports Traumatol Arthrosc, 28(1), 148\u0026ndash;154 (2020). https://doi.org/10.1007/s00167-019-05585-1\u003c/li\u003e\n\u003cli\u003eCulvenor, A.G., Cook, J.L., Warden, S.J., Crossley, K.M. Infrapatellar fat pad size, but not patellar alignment, is associated with patellar tendinopathy. Scandinavian Med Sci Sports, 21(6), 405\u0026ndash;411 (2011). https://doi.org/10.1111/j.1600-0838.2011.01334.x\u003c/li\u003e\n\u003cli\u003evan der Heijden, R.A. et al. Quantitative volume and dynamic contrast-enhanced MRI derived perfusion of the infrapatellar fat pad in patellofemoral pain. Quant Imaging Med Surg, 11(1), 133\u0026ndash;142 (2021). https://doi.org/10.21037/qims-20-441\u003c/li\u003e\n\u003cli\u003ePatel, N.N., Labib, S.A. The Achilles tendon in healthy subjects: an anthropometric and ultrasound mapping study. J Foot Ankle Surg, 57(2), 285\u0026ndash;288 (2018). https://doi.org/10.1053/j.jfas.2017.10.005\u003c/li\u003e\n\u003cli\u003eRosso, C. et al. Physiological Achilles tendon length and its relation to tibia length.\u0026rdquo; Clin J Sport Med, 22(6), 483\u0026ndash;487 (2012). https://doi.org/10.1097/JSM.0b013e3182639a3e\u003c/li\u003e\n\u003cli\u003eFranettovich Smith, M.M., Hides, J.A., Hodges, P.W., Collins, N.J. Intrinsic foot muscle size can be measured reliably in weight bearing using ultrasound imaging. Gait Posture, 68, 369\u0026ndash;374 (2019). https://doi.org/10.1016/j.gaitpost.2018.12.012\u003c/li\u003e\n\u003cli\u003eGoodman, L.R., Shanser, J.D. The pre-Achilles fat pad: an aid to early diagnosis of local or systemic disease. Skelet Radiol, 2, 81\u0026ndash;86 (1977). https://doi.org/10.1007/BF00360986\u003c/li\u003e\n\u003cli\u003eSaddik, D., McNally, E.G., Richardson, M. 2004. \u0026ldquo;MRI of Hoffa\u0026rsquo;s fat pad.\u0026rdquo; Skelet Radiol, 33(8), 433\u0026ndash;444. https://doi.org/10.1007/s00256-003-0724-z\u003c/li\u003e\n\u003cli\u003eGallagher, J., Tierney, P., Murray, P., O\u0026rsquo;Brien, M. The infrapatellar fat pad: anatomy and clinical correlations.\u0026rdquo; Knee Surg Sports Traumatol Arthrosc, 13(4), 268\u0026ndash;272 (2005). https://doi.org/10.1007/s00167-004-0592-7\u003c/li\u003e\n\u003cli\u003eKuhns, J.G. Changes in elastic adipose tissue. J Bone Joint Surg Am, 31(3), 541\u0026ndash;547 (1949).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"flexor hallucis longus tendon, talocrural joint, adipose tissue","lastPublishedDoi":"10.21203/rs.3.rs-4392485/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4392485/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study aimed to evaluate the presence of adipose tissue surrounding the flexor hallucis longus (FHL) tendon through gross dissection and magnetic resonance imaging (MRI). Grossly, we observed the flexor hallucis longus tendon and surrounding tissues in nine cadavers. Using MRI, we quantitatively evaluated each tissue from the horizontal plane in 40 healthy ankles. Macroscopic autopsy revealed the presence of adipose tissue behind the ankle joint between the flexor hallucis longus and fibula, and horizontal cross-sections showed an oval-shaped adipose tissue surrounding the tendon. The cross-sectional area on MRI was 14.4 mm\u003csup\u003e2\u003c/sup\u003e (11.7\u0026ndash;16.7) for the flexor hallucis longus tendon and 120.5 mm\u003csup\u003e2\u003c/sup\u003e (100.3\u0026ndash;149.4) for the adipose tissue. Additionally, the volume of the adipose tissue was 963.3 mm\u003csup\u003e3\u003c/sup\u003e (896.2\u0026ndash;1,115.6). We demonstrated that the presence of adipose tissue surrounding the flexor hallucis longus tendon may be involved in the function and pathological conditions of the tendon.\u003c/p\u003e","manuscriptTitle":"Anatomical evaluations of the adipose tissue surrounding the flexor hallucis longus tendon: A study using gross anatomy and magnetic resonance imaging","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-23 18:36:24","doi":"10.21203/rs.3.rs-4392485/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-06-14T03:41:13+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-11T13:23:15+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-05-31T10:04:36+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"193700839003342514630551064028945872393","date":"2024-05-22T06:21:01+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"304190179576293395925291814436277104529","date":"2024-05-22T06:10:39+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-05-21T13:19:39+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-05-21T13:09:54+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-05-15T16:00:20+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-05-11T04:02:37+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-05-09T04:17:45+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e3e7fb59-77d3-4ca2-9b7b-66505a7d49e7","owner":[],"postedDate":"May 23rd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":32097909,"name":"Health sciences/Anatomy"},{"id":32097910,"name":"Health sciences/Anatomy/Musculoskeletal system/Muscle"},{"id":32097911,"name":"Health sciences/Anatomy/Musculoskeletal system/Tendons"}],"tags":[],"updatedAt":"2024-08-01T17:08:30+00:00","versionOfRecord":{"articleIdentity":"rs-4392485","link":"https://doi.org/10.1038/s41598-024-67831-y","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2024-07-23 16:15:42","publishedOnDateReadable":"July 23rd, 2024"},"versionCreatedAt":"2024-05-23 18:36:24","video":"","vorDoi":"10.1038/s41598-024-67831-y","vorDoiUrl":"https://doi.org/10.1038/s41598-024-67831-y","workflowStages":[]},"version":"v1","identity":"rs-4392485","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4392485","identity":"rs-4392485","version":["v1"]},"buildId":"J0_U0BvcaRcwD8yVFaRlm","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}