Distal Femoral Interlocking Screw Length Can Be Estimated Using “Anatomic Zones” During Femoral Intramedullary Nailing

Distal Femoral Interlocking Screw Length Can Be Estimated Using “Anatomic Zones” During Femoral Intramedullary Nailing | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Distal Femoral Interlocking Screw Length Can Be Estimated Using “Anatomic Zones” During Femoral Intramedullary Nailing Douglas Zhang, Hayden Baker, Mary Kate Erdman, Anthony Christiano, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6112990/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Purpose: The aim of this study is to evaluate whether “anatomic zones” along the distal femur can be used to estimate distal interlocking screw length during femoral intramedullary nailing. Methods: A retrospective “anatomical control” cohort was used establish anatomic zones along the length of the distal femur and estimated screw length within each zone. Estimated screw lengths for each zone were based on mean cortex-to-cortex length at each zone as measured on computed tomography (CT). A prospective cohort was enrolled to evaluate agreement between these estimated screw lengths and depth-gauge measurements for each zone. Agreement was evaluated using mean differences between estimated screw lengths and depth-gauge measurements, an intraclass correlation coefficient (ICC), and Bland-Altman analysis. Results: The retrospective cohort of 56 patients was used to establish eight anatomic zones. Screw length estimates ranged between 42.1mm in the most proximal zone to 80.2mm in the most distal zone. The prospective cohort included 74 patients (126 screws), was 63.51% male (n=47), with mean age 44.2±24.7 years, mean height 173.2±12.7cm, and mean BMI 28.5±10kg/m 2 . The mean absolute value difference between zone-estimated screw lengths and depth-gauge measurements was 3.9mm±2.9mm, ranging 2.7mm-5.6mm depending on zone. The ICC was 0.94 (95%CI [0.91,0.96], p<0.01). Bland-Altman analysis revealed a bias of -0.86mm with limits of agreement at +8.6mm and -10.3mm. Conclusion: Anatomic zone-based screw length estimates derived from CT data show strong agreement with depth-gauge measurements and are a potential strategy to reduce operative time and errors in screw length selection. depth-gauge interlocking screws femoral shaft fractures intramedullary nailing radiation exposure operation time Figures Figure 1 Figure 2 Introduction The standard treatment for femoral shaft fractures is intramedullary nailing. The goal of intramedullary nailing is to create a static, locked construct to permit early weightbearing and mobilization [ 1 , 2 ]. Interlocking screws are crucial components of this construct securing femoral axial and rotational stability [ 1 , 3 ], but the insertion of these screws is technically demanding and can be associated with complications, namely injury to neurovascular structures [ 4 – 9 ]. The selection of the appropriate length screws is traditionally guided by depth-gauge measurement devices, and confirmation of appropriate screw length is often accomplished using fluoroscopy. However, the use of a depth-gauge can be time-consuming, and technical error can lead to inappropriate screw sizes, additional local soft-tissue injury, and increased radiation exposure [ 10 – 13 ]. Furthermore, depth-gauges have been shown to be imperfect measuring tools, with factors such as depth-gauge design, bony geometry, and surgeon experience contributing to variable accuracy [ 12 , 14 , 15 ]. Current research into strategies focused on improving the process of selecting appropriate-length screws during intramedullary nailing is scarce has centered on investigating appropriate locking screw sizes in the proximal femur [ 11 , 16 ]. Collinge et al. previously reported that lengths for locking screws in the proximal femur can be selected based on standardized, set distances from the lesser trochanter, potentially reducing the need for depth-gauge measurements [ 11 ]. However, it is unknown whether anatomic landmarks in the distal femur can be utilized to guide interlocking screw selection. A method to simplify or supplement the process of selecting appropriate length screws for distal locking may improve operating efficiency while also reducing radiation exposure and screw prominence. This study aims to determine if quickly identifiable anatomic “zones” can be used to predict interlocking screw lengths and to compare this anatomic zone-based technique to the standard method of depth-gauge measurement. Methods A two-phase study was conducted, involving a preliminary retrospective “anatomical control” cohort used to establish anatomic zones with predictable screw lengths, and a prospective “clinical validation” cohort. Subjects in both cohorts were skeletally mature patients at a single level 1 trauma center with femoral fractures being treated with intramedullary nailing. The “anatomical control” cohort consisted of patients with x-ray and fine-cut (< 3mm) computed tomography (CT) scan data available for review and measurement after their initial treatment for femoral fracture. Subjects in the prospective “validation cohort” were patients undergoing femoral intramedullary nailing who were enrolled in the study at the time of their surgery. This study received institutional IRB approval, and all study procedures were conducted in accordance with ethical guidelines set forth by the IRB (IRB19-1981). Determining Estimated Screw length for Each Zone The retrospective anatomical control cohort underwent standard radiographic assessment including x-ray and CT scans. “Anatomic zones,” were generated based on established reproducible radiographic landmarks visible on intra-operative lateral films and CT scans. Eight 10mm “anatomic zones” (Zones A, B, C, D, E, F, X, Z) were created using Zones A and C as anchor zones. Zone C centered on a line drawn perpendicular to the posterior metaphyseal flare where it meets the posterior cortex, while Zone A, the most distal zone, originates at the posterior aspect of Blumensaat’s line (Fig. 1 ). Two orthopedic surgery residents reviewed all fine-cut CT data to collect measurements for each zone. Zone-estimated femoral width was derived from the mean outer cortex-to-cortex length measured at the midpoint of each zone on CT. Using this measured cortical width, each zone was given a suggested screw length. The suggested screw lengths for each zone were determined using a “next size up” approach to align with commercially available screw sizes, where the measured zone-estimated femoral width was rounded-up to the nearest 2.5mm for screws 60mm. For all patients, basic patient characteristics such as age, sex, height, and BMI were documented. Clinical Evaluation A prospective cohort of patients undergoing fixation of a femoral shaft fracture with intramedullary nailing was enrolled to validate the zone-estimated screw lengths. Data on patient characteristics, including age, sex, height, and BMI were collected for all patients enrolled. Four fellowship-trained orthopedic trauma surgeons performed all surgeries. During intramedullary nail fixation of the femur, the positions of the interlocking screw holes in the nail were assessed by the treating surgeon. Intra-operatively the surgeons were asked to report the corresponding anatomic zones based on the established zones determined by the retrospective cohort. Following zone selection, surgeons then proceeded to complete interlocking screw insertion using standard drilling, depth-gauge measurements, and screw insertion. Depth-gauge measurements, and final implanted screw lengths were documented. The intra-operatively recorded anatomic zones and depth-gauge measurements were used to calculate the degree of agreement between zone-estimated screw lengths and depth-gauge measurements. Statistical Analysis Descriptive statistics, including calculation of means and standard deviations for all variables, were performed for both the retrospective and prospective cohorts. To detect differences between the characteristics of the retrospective and prospective cohorts, chi-squared and t-tests were performed to evaluate differences in proportions and means respectively. Linear mixed model multivariable regression was used to determine factors significantly associated with cortex-to-cortex width measured on CT for the retrospective cohort or final implanted screw length for the prospective cohort. Covariates analyzed included anatomic zone (with Zone A serving as the reference zone), age, sex, height, and BMI. In the prospective cohort, differences between depth-gauge measurements, CT measurement-based zone-estimated screw lengths, and final implanted screw lengths were calculated. Critical evaluation of the level of agreement between the two different measurement techniques involved calculation of the intraclass correlation coefficient (ICC) and Bland-Altmann analysis with upper and lower limits of agreement (LOA) set at ± 1.96 standard deviations. In general, higher ICC values indicate greater agreement, where ICC values of 0.90 are demonstrative of poor, moderate, good, and excellent agreement, respectively [ 17 ]. Lastly, the percent of perfect and ‘acceptable’ (within 2.5mm) agreement between the zone-suggested screw and the implanted screw was calculated. All statistical methods were conducted using R Statistical Software (v4.1.2; R Core Team 2021), and p-values < 0.05 were considered statistically significant. Results Overall, 130 patients were included in this study, with 56 patients in the retrospective cohort and 74 patients in the prospective cohort. The retrospective cohort was 78.6% male (n = 44), with mean age 33.9 ± 14.6 years, mean height 174.0 ± 12.2cm, and mean BMI 27.0 ± 6.0 kg/m 2 (Table 1 ). The CT measurement-based zone-estimated screw lengths ranged between 42.13 ± 4.60mm in the most proximal zone, Zone Z, to 80.17 ± 6.59mm in the most distal zone, Zone A (Table 2 ). Using the “next-size-up” approach, the suggested screw lengths corresponding to the zone-estimated screw lengths for each zone ranged from 42.50mm (Zone Z) to 85mm (Zone A). Table 1 Retrospective and Prospective Cohort Characteristics Retrospective Prospective p - values n = 56 n = 74 Male Sex (n, %) 44 (78.6%) 47 (63.5%) 0.06 Age (years, mean ± SD) 33.9 ± 14.6 44.2 ± 24.7 < 0.01 Height (cm, mean ± SD) 174.0 ± 12.2 173.2 ± 12.7 0.72 BMI (kg/m2, mean ± SD) 27.0 ± 6.0 28.5 ± 10.0 0.32 Table 2 Zone-Estimated Screw Length According to Computed Tomography Data and Zone-Suggested Screw Length* By Zone Zone Average Zone-Estimated Screw Length (mm, mean ± SD) n = 56 patients Zone-Suggested Screw Length* (mm) A 80.2 ± 6.6 85.0 B 72.1 ± 8.3 75.0 C 59.7 ± 6.6 60.0 D 52.9 ± 5.8 55.0 E 48.4 ± 5.2 50.0 F 45.7 ± 5.1 47.5 X 43.7 ± 5.0 45.0 Z 42.1 ± 4.6 42.5 * Suggested screw lengths were chosen using a "next-size-up rule," where screw sizes were available in 2.5mm increments for lengths 60mm The zone-estimated screw lengths derived from the retrospective cohorts had standard deviations small enough such that they were deemed acceptable for use in the prospective clinical validation cohort. The prospective cohort was 63.5% male (47/74), with mean age 44.2 ± 24.7 years, mean height 173.2 ± 12.7cm, and mean BMI 28.5 ± 10 kg/m 2 (Table 1 ). Compared to the retrospective cohort, the prospective cohort was significantly younger (p < 0.01). There were no significant differences with respect to sex, height, or BMI (Table 1 ). Linear mixed-model regression analyses revealed anatomic zone (βs = -38.0 in Zone Z to -8.1 in Zone B) and BMI (β = 0.41) to be significantly associated with cortex-to-cortex width measured on CT (ps < 0.01). In the prospective cohort, anatomic zone (βs = -38.5 in Zone Z to -9.4 in Zone B), height (β = 0.19), and BMI (β = 0.12) were found to be significantly associated with final implanted screw length (ps < 0.01). Age and sex were not found to be associated with cortex-to-cortex width in the retrospective cohort or final implanted screw length in the prospective cohort. Across all zones, the ICC between zone-estimated screw lengths and depth-gauge measurements was 0.94 (95%CI [0.91,0.96], p < 0.01), and Bland-Altmann Analysis revealed a bias of -0.86mm (LOAs of + 8.57mm/-10.29mm) (Fig. 2 ). When examining the mean absolute difference between zone-estimated screw length and depth-gauge measurement the difference was 3.88mm ± 2.96mm overall and ranged from 2.73mm (Zone F) − 5.58mm (Zone C) between different zones (Table 3 ). In all zones, the zone-estimated screw lengths exhibited greater differences from the final implanted screw lengths than depth-gauge measurements (Table 3 ). When assessing the percentage of zone-suggested screw lengths that agreed with final implanted screw lengths, perfect agreement occurred 33.33% of the time, while agreement within 2.5mm occurred in 48.4% of zone-suggested screw lengths. Table 3 Depth-gauge Measurement, Final Implanted Screw Length, and Various Absolute Value Mean Differences (Depth-gauge Measurement vs. Final Implanted Screw Length, Depth-gauge Measurement vs. Zone-Estimated Screw Length, and Zone-Estimated Screw Length vs. Final Implanted Screw Length) by Zone Zone (Total n = 126 Screws) Depth-gauge Measurement (mm, mean ± SD) Final Implanted Screw Length (mm, mean ± SD) Depth-gauge Measurement vs. Zone-Estimated Screw Length (mm, mean ± SD) Depth-gauge Measurement vs. Final Implanted Screw Length (mm, mean ± SD) Zone-Estimated Screw Length vs. Final Implanted Screw Length (mm, mean ± SD) A (n = 26) 81.6 ± 5.3 81.9 ± 5.3 4.4 ± 3.2 1.4 ± 1.7 4.2 ± 3.6 B (n = 16) 70.8 ± 4.5 72.5 ± 4.5 3.6 ± 2.8 2.0 ± 1.6 3.7 ± 2.4 C (n = 17) 64.3 ± 4.6 64.5 ± 4.2 5.6 ± 3.3 1.2 ± 1.6 5.4 ± 3.4 D (n = 19) 55.1 ± 5.6 55.9 ± 4.6 4.2 ± 4.2 1.6 ± 1.7 4.3 ± 3.4 E (n = 13) 49.6 ± 4.9 50.0 ± 4.5 3.9 ± 2.9 1.0 ± 1.3 3.6 ± 2.9 F (n = 16) 46.7 ± 3.7 47.7 ± 3.2 2.7 ± 2.5 1.4 ± 1.2 2.9 ± 2.3 X (n = 10) 43.1 ± 4.2 44.0 ± 4.6 2.9 ± 2.9 0.9 ± 1.2 3.0 ± 3.4 Z (n = 9) 38.3 ± 2.8 40.0 ± 2.8 3.9 ± 2.7 1.7 ± 1.3 2.5 ± 2.5 Discussion Locking of femoral intramedullary nails is known to be difficult in large part due to the technical demands of selecting and inserting appropriate length locking screws using the perfect circles technique [ 10 – 13 , 18 ]. The process of inserting these screws is not without risks, including increased radiation exposure, additional local soft tissue injury, and vascular injury [ 4 , 5 , 7 , 10 – 12 ]. Selection of correct screw lengths is typically guided by depth-gauge measurements; however, depth-gauges are known to have imperfect accuracy, with many patient and operator factors influencing their utility [ 12 , 14 , 15 ]. While research into ways to improve the process of selecting appropriate-length locking screws is limited, previous research suggests that the use of anatomic landmarks in the proximal femur to guide interlocking screw selection during intramedullary nailing is a potential method to decrease reliance on depth-gauge measurements [ 11 , 16 ]. The present study aimed to apply a similar strategy based on anatomic landmarks to the selection of locking screws lengths in the distal femur and to compare this strategy with the traditional method of screw length selection guided by depth-gauge measurements. Overall, this study revealed a small absolute mean difference between anatomic zone-estimated screw lengths and depth-gauge measurements, as well as a very high ICC and small Bland-Altman bias. The high ICC and low Bland-Altman bias demonstrate overall excellent agreement between depth-gauge measurements and screw lengths estimated using standardized anatomic zones derived from CT data. These results are similar to what has been previously reported in the literature by Collinge et al. regarding use of the lesser trochanter as an anatomic landmark to guide proximal femoral locking screw selection (Collinge 2015). While less commonly reported in the literature compared to vascular complications of proximal femur locking screw insertion, distal femur locking screw insertion has also been associated with risk to vascular structures, namely the distal femoral artery [ 4 , 5 , 7 ]. Other cited concerns regarding improper interlocking screw lengths include discomfort due to screw prominence and screw backout [ 19 – 22 ]. Our method of estimating distal femur locking screw length based on anatomic landmarks may serve as an additional safeguard against screw-length related complications in the distal femur by suggesting when a depth-gauge measurement may be inaccurate. Another notable finding was that anatomic zones were found to be independently associated with both cortex-to-cortex width measured on CT in the retrospective cohort and with final implanted screw length in the prospective cohort. Additionally, when compared to other factors analyzed, anatomic zone also had greater magnitudes of association with cortex-to-cortex width and final implanted screw length than various patient factors analyzed, including height, BMI, age, and sex. It is important to acknowledge that height and BMI were also found to be significant factors associated with final screw length. This is consistent with some current literature that have shown that higher BMI is associated with larger cross-sectional dimensions of the femur [ 23 , 24 ]. However, the magnitudes of the associations with height and BMI were relatively small in comparison. Still, this suggests that patient factors may influence distal femoral anatomy and impact the accuracy of using these distal femoral anatomic zones for estimating screw length, and implementing practical methods to account for patient height and BMI may increase the accuracy of this method. Limitations The limitations of the technique described should be considered. Despite the strong agreement between depth-gauge measurements and zone-based estimates demonstrated by the high ICC and low bias in our study, the wide Bland-Altman LOAs (-10.29mm, 8.57mm) suggest variable precision associated with this technique. Compared to the LOAs associated with using the lesser trochanter to guide proximal locking screw length selection reported by Collinge et al., the LOAs shown in this study are wider, which suggests less reliability [ 11 ]. Similarly, the percent of zone-suggested screw lengths that agree with final implanted screw lengths are also lower in this study compared to percentages reported by Collinge et al. There are a few potential reasons for these findings. First, the present study includes zones with drastically different anatomical sizes (metaphyseal flair versus the femoral shaft) which likely accounts for some of the inherent variability seen. Second, the “next-size-up” rule that was used to determine suggested screw lengths in this study is likely not accurate for all zones. For example, in Zone A, depth-gauge measurements, zone-estimated screw length, and final implanted screw lengths all suggest that 80mm may be closer to the best screw length for that zone than the 85mm length chosen using the “next-size-up” rule. Other contributing factors affecting precision may be related to how facile this method is to apply. For example, the anatomic landmarks used in this study (i.e. where the posterior metaphyseal flare meets the posterior cortex, the posterior aspect of Blumensaat’s line) are less straight forward to identify than simpler anatomic landmarks such as the lesser trochanter. In addition to the limitations of the technique described, it is also important to discuss the study limitations. First and foremost, extrapolation of our findings to other settings is limited by the small sample size and single center design. The small sample sizes of both the retrospective and prospective cohorts likely contributed to the variable agreement observed between zone-estimated screw lengths and depth-gauge measurements. Larger sample sizes better capturing a wider variety of patients are needed to clarify if the observed variability results from true variability between individual anatomy. Presently, large databases of CT data are being used to design standardized osteosynthesis plates that conform to the anatomy in a wide variety of patients [ 25 ]. Our findings demonstrate the utility in using CT data to establish standardized screw-length estimates based on anatomic location along the distal femur, and larger databases with more CT data have the potential to result in improved screw length estimates. Additionally, an important limitation of this study is that it did not involve using zone-estimated screw lengths to guide screw selection. This is crucial to consider as we found greater concordance between depth-gauge measurements and final implanted screw length; however, this is expected, as depth-gauge measurements were ultimately used to guide screw selection, while zone-based estimates were not. Conclusion The current standard method of guiding screw length selection with depth-gauges can be technically challenging and has variable accuracy. The use of standardized anatomic zones to estimate distal femoral interlocking screw lengths is a potential alternative or supplement to depth-gauge measurements. While this tool provides a generalized guideline of potential screw size, this study shows that there are limitations of the technique in terms of variability, possibly due to diversity in distal femoral anatomy among patients. Future studies with larger sample sizes should be aimed at evaluating the clinical implementation of this technique. Declarations No funding was received for conducting this study. Competing Interests Statements and DeclarationsDr. Mary Kate Erdman or an immediate family member serves as a board member, owner, officer, or committee member of American Academy of Orthopaedic Surgeons, Foundation of Orthopaedic Trauma, and Orthopaedic Trauma Association.Dr. Jason Strelzow is a consultant for Acumed LLC, OrthoXel, and Stryker.The remaining authors have no statements or declarations. Author Contribution D.Z. performed data collection for the prospective cohort, wrote the main manuscript text, and prepared all figures and tables.H.B. performed data collection for the retrospective cohort and prepared Figure 1.M.E., A.C., and J.S. performed data collection for the prospective cohort and provided crucial guidance for project design and execution. H.B. and J.S. provided the initial study concept and ideas.All authors helped with preparation and review of the manuscript. 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Statements and Declarations Dr. Mary Kate Erdman or an immediate family member serves as a board member, owner, officer, or committee member of American Academy of Orthopaedic Surgeons, Foundation of Orthopaedic Trauma, and Orthopaedic Trauma Association. Dr. Jason Strelzow is a consultant for Acumed LLC, OrthoXel, and Stryker. The remaining authors have no statements or declarations. Cite Share Download PDF Status: Posted Version 1 posted 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. We do this by developing innovative software and high quality services for the global research community. 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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-6112990","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":421721360,"identity":"8c7aa57f-f5ef-4aa5-bd1e-5d804f3596be","order_by":0,"name":"Douglas Zhang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABB0lEQVRIie3LPWrDMBiAYQmDvAjPzpA7CARqTVvnKhIGT06WgulQTKGgLiazO/UKhV5AYIgXt1kzBrwEmkFT6NRGTjNGhmwZ9MIHn34eAFyuS0yZWZsh/UEDwNHxAT4NEX4ksDqbePh/HyZBU9INfywmV/5n/X0n41ng191Gg9vxuzpNRm3Lrvmi9qJylt5MZXKPcMqiCqTURsgqY4QjhYjKGJ1KJWQIGMWgFsPkt8BkuWU0OhB/Z8jfEKFrIb2wXzp4IJh2GCgrGbWLHIh5Tchqy2D5lQiJsxxWJKGvFhI0zx9a74oJWWZU/+SxeHtpzM1DPJ5biAmFJxZi/d7naevicrlcrr49YkRldC2kEl4AAAAASUVORK5CYII=","orcid":"","institution":"University of Chicago Pritzker School of Medicine","correspondingAuthor":true,"prefix":"","firstName":"Douglas","middleName":"","lastName":"Zhang","suffix":""},{"id":421721361,"identity":"d4af4dde-f77d-4164-b628-d09ad8f9b4cd","order_by":1,"name":"Hayden Baker","email":"","orcid":"","institution":"Hospital for Special Surgery","correspondingAuthor":false,"prefix":"","firstName":"Hayden","middleName":"","lastName":"Baker","suffix":""},{"id":421721362,"identity":"b9a5125d-9089-4ae0-aafe-e04fbcda16c8","order_by":2,"name":"Mary Kate Erdman","email":"","orcid":"","institution":"University of Chicago Medical Center","correspondingAuthor":false,"prefix":"","firstName":"Mary","middleName":"Kate","lastName":"Erdman","suffix":""},{"id":421721363,"identity":"a684f0a2-b589-425c-8752-d2550d3d2a02","order_by":3,"name":"Anthony Christiano","email":"","orcid":"","institution":"University of Chicago Medical Center","correspondingAuthor":false,"prefix":"","firstName":"Anthony","middleName":"","lastName":"Christiano","suffix":""},{"id":421721364,"identity":"c3107544-022e-4f3c-a820-11687ce2625b","order_by":4,"name":"Jason Strelzow","email":"","orcid":"","institution":"Washington University Medical Center","correspondingAuthor":false,"prefix":"","firstName":"Jason","middleName":"","lastName":"Strelzow","suffix":""}],"badges":[],"createdAt":"2025-02-26 12:08:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6112990/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6112990/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":77701026,"identity":"3d4cc643-3d33-48d6-8a75-2179bfdc93ae","added_by":"auto","created_at":"2025-03-04 11:20:01","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":41756,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStandardized Anatomic Zones, Lateral View.\u003c/strong\u003eEight anatomic zones (Zones A, B, C, D, E, F, X, Z), spanning 10mm each. Zone C corresponds to a line drawn perpendicular to the posterior metaphyseal flair where it meets the posterior cortex, while Zone A begins at the level of the posterior aspect of Blumensaat's line.\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6112990/v1/ad54c6d943784f8eb2d3f2ef.jpg"},{"id":77701028,"identity":"fc8d00a9-fdbe-451b-9687-cee7b18fbdf1","added_by":"auto","created_at":"2025-03-04 11:20:01","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":26135,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eBland-Altmann Plot Illustrating the Degree of Agreement Between Zone-Estimated Screw Length and Depth-gauge Measurement.\u003c/strong\u003eEach screw (n=126) is represented by a datapoint. The mean difference (bias) between zone-estimated screw length and depth-gauge measurement was -0.86mm, while the upper and lower limits of agreement (corresponding to a 95% confidence interval for the measured bias) were +8.57mm, and - 10.29mm, respectively.\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6112990/v1/d18010a401a4000abcd82d0f.jpg"},{"id":78995361,"identity":"8faa478d-2c60-438c-b499-d212823ff08b","added_by":"auto","created_at":"2025-03-22 01:16:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":925584,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6112990/v1/678837a9-dbd8-44f1-94e9-884fb85b9c72.pdf"}],"financialInterests":"Competing interest reported. Statements and Declarations\n \nDr. Mary Kate Erdman or an immediate family member serves as a board member, owner, officer, or committee member of American Academy of Orthopaedic Surgeons, Foundation of Orthopaedic Trauma, and Orthopaedic Trauma Association.\n \nDr. Jason Strelzow is a consultant for Acumed LLC, OrthoXel, and Stryker.\n \nThe remaining authors have no statements or declarations.","formattedTitle":"Distal Femoral Interlocking Screw Length Can Be Estimated Using “Anatomic Zones” During Femoral Intramedullary Nailing","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe standard treatment for femoral shaft fractures is intramedullary nailing. The goal of intramedullary nailing is to create a static, locked construct to permit early weightbearing and mobilization [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Interlocking screws are crucial components of this construct securing femoral axial and rotational stability [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], but the insertion of these screws is technically demanding and can be associated with complications, namely injury to neurovascular structures [\u003cspan additionalcitationids=\"CR5 CR6 CR7 CR8\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The selection of the appropriate length screws is traditionally guided by depth-gauge measurement devices, and confirmation of appropriate screw length is often accomplished using fluoroscopy. However, the use of a depth-gauge can be time-consuming, and technical error can lead to inappropriate screw sizes, additional local soft-tissue injury, and increased radiation exposure [\u003cspan additionalcitationids=\"CR11 CR12\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Furthermore, depth-gauges have been shown to be imperfect measuring tools, with factors such as depth-gauge design, bony geometry, and surgeon experience contributing to variable accuracy [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eCurrent research into strategies focused on improving the process of selecting appropriate-length screws during intramedullary nailing is scarce has centered on investigating appropriate locking screw sizes in the proximal femur [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Collinge et al. previously reported that lengths for locking screws in the proximal femur can be selected based on standardized, set distances from the lesser trochanter, potentially reducing the need for depth-gauge measurements [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. However, it is unknown whether anatomic landmarks in the distal femur can be utilized to guide interlocking screw selection. A method to simplify or supplement the process of selecting appropriate length screws for distal locking may improve operating efficiency while also reducing radiation exposure and screw prominence.\u003c/p\u003e \u003cp\u003eThis study aims to determine if quickly identifiable anatomic \u0026ldquo;zones\u0026rdquo; can be used to predict interlocking screw lengths and to compare this anatomic zone-based technique to the standard method of depth-gauge measurement.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eA two-phase study was conducted, involving a preliminary retrospective \u0026ldquo;anatomical control\u0026rdquo; cohort used to establish anatomic zones with predictable screw lengths, and a prospective \u0026ldquo;clinical validation\u0026rdquo; cohort. Subjects in both cohorts were skeletally mature patients at a single level 1 trauma center with femoral fractures being treated with intramedullary nailing. The \u0026ldquo;anatomical control\u0026rdquo; cohort consisted of patients with x-ray and fine-cut (\u0026lt;\u0026thinsp;3mm) computed tomography (CT) scan data available for review and measurement after their initial treatment for femoral fracture. Subjects in the prospective \u0026ldquo;validation cohort\u0026rdquo; were patients undergoing femoral intramedullary nailing who were enrolled in the study at the time of their surgery. This study received institutional IRB approval, and all study procedures were conducted in accordance with ethical guidelines set forth by the IRB (IRB19-1981).\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003cdiv id=\"Sec4\" class=\"Section3\"\u003e \u003ch2\u003eDetermining Estimated Screw length for Each Zone\u003c/h2\u003e \u003cp\u003eThe retrospective anatomical control cohort underwent standard radiographic assessment including x-ray and CT scans. \u0026ldquo;Anatomic zones,\u0026rdquo; were generated based on established reproducible radiographic landmarks visible on intra-operative lateral films and CT scans. Eight 10mm \u0026ldquo;anatomic zones\u0026rdquo; (Zones A, B, C, D, E, F, X, Z) were created using Zones A and C as anchor zones. Zone C centered on a line drawn perpendicular to the posterior metaphyseal flare where it meets the posterior cortex, while Zone A, the most distal zone, originates at the posterior aspect of Blumensaat\u0026rsquo;s line (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTwo orthopedic surgery residents reviewed all fine-cut CT data to collect measurements for each zone. Zone-estimated femoral width was derived from the mean outer cortex-to-cortex length measured at the midpoint of each zone on CT. Using this measured cortical width, each zone was given a suggested screw length. The suggested screw lengths for each zone were determined using a \u0026ldquo;next size up\u0026rdquo; approach to align with commercially available screw sizes, where the measured zone-estimated femoral width was rounded-up to the nearest 2.5mm for screws\u0026thinsp;\u0026lt;\u0026thinsp;60mm and the nearest 5mm for screws\u0026thinsp;\u0026gt;\u0026thinsp;60mm. For all patients, basic patient characteristics such as age, sex, height, and BMI were documented.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e\n\u003ch3\u003eClinical Evaluation\u003c/h3\u003e\n\u003cp\u003eA prospective cohort of patients undergoing fixation of a femoral shaft fracture with intramedullary nailing was enrolled to validate the zone-estimated screw lengths. Data on patient characteristics, including age, sex, height, and BMI were collected for all patients enrolled. Four fellowship-trained orthopedic trauma surgeons performed all surgeries. During intramedullary nail fixation of the femur, the positions of the interlocking screw holes in the nail were assessed by the treating surgeon. Intra-operatively the surgeons were asked to report the corresponding anatomic zones based on the established zones determined by the retrospective cohort. Following zone selection, surgeons then proceeded to complete interlocking screw insertion using standard drilling, depth-gauge measurements, and screw insertion. Depth-gauge measurements, and final implanted screw lengths were documented. The intra-operatively recorded anatomic zones and depth-gauge measurements were used to calculate the degree of agreement between zone-estimated screw lengths and depth-gauge measurements.\u003c/p\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eStatistical Analysis\u003c/h2\u003e \u003cp\u003eDescriptive statistics, including calculation of means and standard deviations for all variables, were performed for both the retrospective and prospective cohorts. To detect differences between the characteristics of the retrospective and prospective cohorts, chi-squared and t-tests were performed to evaluate differences in proportions and means respectively.\u003c/p\u003e \u003cp\u003eLinear mixed model multivariable regression was used to determine factors significantly associated with cortex-to-cortex width measured on CT for the retrospective cohort or final implanted screw length for the prospective cohort. Covariates analyzed included anatomic zone (with Zone A serving as the reference zone), age, sex, height, and BMI.\u003c/p\u003e \u003cp\u003eIn the prospective cohort, differences between depth-gauge measurements, CT measurement-based zone-estimated screw lengths, and final implanted screw lengths were calculated. Critical evaluation of the level of agreement between the two different measurement techniques involved calculation of the intraclass correlation coefficient (ICC) and Bland-Altmann analysis with upper and lower limits of agreement (LOA) set at \u0026plusmn;\u0026thinsp;1.96 standard deviations. In general, higher ICC values indicate greater agreement, where ICC values of \u0026lt;\u0026thinsp;0.5, 0.5\u0026ndash;0.75, 0.75\u0026ndash;0.90, and \u0026gt;\u0026thinsp;0.90 are demonstrative of poor, moderate, good, and excellent agreement, respectively [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Lastly, the percent of perfect and \u0026lsquo;acceptable\u0026rsquo; (within 2.5mm) agreement between the zone-suggested screw and the implanted screw was calculated.\u003c/p\u003e \u003cp\u003eAll statistical methods were conducted using R Statistical Software (v4.1.2; R Core Team 2021), and p-values\u0026thinsp;\u0026lt;\u0026thinsp;0.05 were considered statistically significant.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eOverall, 130 patients were included in this study, with 56 patients in the retrospective cohort and 74 patients in the prospective cohort.\u003c/p\u003e \u003cp\u003eThe retrospective cohort was 78.6% male (n\u0026thinsp;=\u0026thinsp;44), with mean age 33.9\u0026thinsp;\u0026plusmn;\u0026thinsp;14.6 years, mean height 174.0\u0026thinsp;\u0026plusmn;\u0026thinsp;12.2cm, and mean BMI 27.0\u0026thinsp;\u0026plusmn;\u0026thinsp;6.0 kg/m\u003csup\u003e2\u003c/sup\u003e (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The CT measurement-based zone-estimated screw lengths ranged between 42.13\u0026thinsp;\u0026plusmn;\u0026thinsp;4.60mm in the most proximal zone, Zone Z, to 80.17\u0026thinsp;\u0026plusmn;\u0026thinsp;6.59mm in the most distal zone, Zone A (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Using the \u0026ldquo;next-size-up\u0026rdquo; approach, the suggested screw lengths corresponding to the zone-estimated screw lengths for each zone ranged from 42.50mm (Zone Z) to 85mm (Zone A).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eRetrospective and Prospective Cohort Characteristics\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRetrospective\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eProspective\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ep - values\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;56\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;74\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMale Sex (n, %)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e44 (78.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e47 (63.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.06\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eAge (years, mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e33.9\u0026thinsp;\u0026plusmn;\u0026thinsp;14.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e44.2\u0026thinsp;\u0026plusmn;\u0026thinsp;24.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eHeight (cm, mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e174.0\u0026thinsp;\u0026plusmn;\u0026thinsp;12.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e173.2\u0026thinsp;\u0026plusmn;\u0026thinsp;12.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBMI (kg/m2, mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e27.0\u0026thinsp;\u0026plusmn;\u0026thinsp;6.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e28.5\u0026thinsp;\u0026plusmn;\u0026thinsp;10.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.32\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eZone-Estimated Screw Length According to Computed Tomography Data and Zone-Suggested Screw Length* By Zone\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZone\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAverage Zone-Estimated Screw Length \u003c/p\u003e \u003cp\u003e(mm, mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;56 patients\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eZone-Suggested Screw Length* (mm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eA\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e80.2\u0026thinsp;\u0026plusmn;\u0026thinsp;6.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e85.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eB\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e72.1\u0026thinsp;\u0026plusmn;\u0026thinsp;8.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e75.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e59.7\u0026thinsp;\u0026plusmn;\u0026thinsp;6.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e60.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eD\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e52.9\u0026thinsp;\u0026plusmn;\u0026thinsp;5.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e55.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eE\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e48.4\u0026thinsp;\u0026plusmn;\u0026thinsp;5.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eF\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e45.7\u0026thinsp;\u0026plusmn;\u0026thinsp;5.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e47.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eX\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e43.7\u0026thinsp;\u0026plusmn;\u0026thinsp;5.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e45.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eZ\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e42.1\u0026thinsp;\u0026plusmn;\u0026thinsp;4.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e42.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003e* Suggested screw lengths were chosen using a \"next-size-up rule,\" where screw sizes were available in 2.5mm increments for lengths\u0026thinsp;\u0026lt;\u0026thinsp;60mm and in 5mm increments for lengths\u0026thinsp;\u0026gt;\u0026thinsp;60mm\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe zone-estimated screw lengths derived from the retrospective cohorts had standard deviations small enough such that they were deemed acceptable for use in the prospective clinical validation cohort.\u003c/p\u003e \u003cp\u003eThe prospective cohort was 63.5% male (47/74), with mean age 44.2 \u0026plusmn; 24.7 years, mean height 173.2 \u0026plusmn; 12.7cm, and mean BMI 28.5 \u0026plusmn; 10 kg/m\u003csup\u003e2\u003c/sup\u003e (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Compared to the retrospective cohort, the prospective cohort was significantly younger (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01). There were no significant differences with respect to sex, height, or BMI (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eLinear mixed-model regression analyses revealed anatomic zone (βs = -38.0 in Zone Z to -8.1 in Zone B) and BMI (β\u0026thinsp;=\u0026thinsp;0.41) to be significantly associated with cortex-to-cortex width measured on CT (ps\u0026thinsp;\u0026lt;\u0026thinsp;0.01). In the prospective cohort, anatomic zone (βs = -38.5 in Zone Z to -9.4 in Zone B), height (β\u0026thinsp;=\u0026thinsp;0.19), and BMI (β\u0026thinsp;=\u0026thinsp;0.12) were found to be significantly associated with final implanted screw length (ps\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Age and sex were not found to be associated with cortex-to-cortex width in the retrospective cohort or final implanted screw length in the prospective cohort.\u003c/p\u003e \u003cp\u003eAcross all zones, the ICC between zone-estimated screw lengths and depth-gauge measurements was 0.94 (95%CI [0.91,0.96], p\u0026thinsp;\u0026lt;\u0026thinsp;0.01), and Bland-Altmann Analysis revealed a bias of -0.86mm (LOAs of +\u0026thinsp;8.57mm/-10.29mm) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). When examining the mean absolute difference between zone-estimated screw length and depth-gauge measurement the difference was 3.88mm \u0026plusmn; 2.96mm overall and ranged from 2.73mm (Zone F) \u0026minus;\u0026thinsp;5.58mm (Zone C) between different zones (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). In all zones, the zone-estimated screw lengths exhibited greater differences from the final implanted screw lengths than depth-gauge measurements (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). When assessing the percentage of zone-suggested screw lengths that agreed with final implanted screw lengths, perfect agreement occurred 33.33% of the time, while agreement within 2.5mm occurred in 48.4% of zone-suggested screw lengths.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDepth-gauge Measurement, Final Implanted Screw Length, and Various Absolute Value Mean Differences (Depth-gauge Measurement vs. Final Implanted Screw Length, Depth-gauge Measurement vs. Zone-Estimated Screw Length, and Zone-Estimated Screw Length vs. Final Implanted Screw Length) by Zone\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZone\u003c/p\u003e \u003cp\u003e(Total n\u0026thinsp;=\u0026thinsp;126 Screws)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDepth-gauge Measurement\u003c/p\u003e \u003cp\u003e(mm, mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFinal Implanted Screw Length\u003c/p\u003e \u003cp\u003e(mm, mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDepth-gauge Measurement vs. Zone-Estimated Screw Length\u003c/p\u003e \u003cp\u003e(mm, mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDepth-gauge Measurement vs. Final Implanted Screw Length\u003c/p\u003e \u003cp\u003e(mm, mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eZone-Estimated Screw Length vs. Final Implanted Screw Length\u003c/p\u003e \u003cp\u003e(mm, mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eA (n\u0026thinsp;=\u0026thinsp;26)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e81.6\u0026thinsp;\u0026plusmn;\u0026thinsp;5.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e81.9\u0026thinsp;\u0026plusmn;\u0026thinsp;5.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4.2\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eB (n\u0026thinsp;=\u0026thinsp;16)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e70.8\u0026thinsp;\u0026plusmn;\u0026thinsp;4.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e72.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.7\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eC (n\u0026thinsp;=\u0026thinsp;17)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e64.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e64.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e5.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eD (n\u0026thinsp;=\u0026thinsp;19)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e55.1\u0026thinsp;\u0026plusmn;\u0026thinsp;5.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e55.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.2\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.6\u0026thinsp;\u0026plusmn;\u0026thinsp;1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eE (n\u0026thinsp;=\u0026thinsp;13)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e49.6\u0026thinsp;\u0026plusmn;\u0026thinsp;4.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50.0\u0026thinsp;\u0026plusmn;\u0026thinsp;4.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eF (n\u0026thinsp;=\u0026thinsp;16)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e46.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e47.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.7\u0026thinsp;\u0026plusmn;\u0026thinsp;2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eX (n\u0026thinsp;=\u0026thinsp;10)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e43.1\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e44.0\u0026thinsp;\u0026plusmn;\u0026thinsp;4.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.9\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.0\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eZ (n\u0026thinsp;=\u0026thinsp;9)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e38.3\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e40.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eLocking of femoral intramedullary nails is known to be difficult in large part due to the technical demands of selecting and inserting appropriate length locking screws using the perfect circles technique [\u003cspan additionalcitationids=\"CR11 CR12\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The process of inserting these screws is not without risks, including increased radiation exposure, additional local soft tissue injury, and vascular injury [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Selection of correct screw lengths is typically guided by depth-gauge measurements; however, depth-gauges are known to have imperfect accuracy, with many patient and operator factors influencing their utility [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. While research into ways to improve the process of selecting appropriate-length locking screws is limited, previous research suggests that the use of anatomic landmarks in the proximal femur to guide interlocking screw selection during intramedullary nailing is a potential method to decrease reliance on depth-gauge measurements [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. The present study aimed to apply a similar strategy based on anatomic landmarks to the selection of locking screws lengths in the distal femur and to compare this strategy with the traditional method of screw length selection guided by depth-gauge measurements. Overall, this study revealed a small absolute mean difference between anatomic zone-estimated screw lengths and depth-gauge measurements, as well as a very high ICC and small Bland-Altman bias.\u003c/p\u003e \u003cp\u003eThe high ICC and low Bland-Altman bias demonstrate overall excellent agreement between depth-gauge measurements and screw lengths estimated using standardized anatomic zones derived from CT data. These results are similar to what has been previously reported in the literature by Collinge et al. regarding use of the lesser trochanter as an anatomic landmark to guide proximal femoral locking screw selection (Collinge 2015). While less commonly reported in the literature compared to vascular complications of proximal femur locking screw insertion, distal femur locking screw insertion has also been associated with risk to vascular structures, namely the distal femoral artery [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Other cited concerns regarding improper interlocking screw lengths include discomfort due to screw prominence and screw backout [\u003cspan additionalcitationids=\"CR20 CR21\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Our method of estimating distal femur locking screw length based on anatomic landmarks may serve as an additional safeguard against screw-length related complications in the distal femur by suggesting when a depth-gauge measurement may be inaccurate.\u003c/p\u003e \u003cp\u003eAnother notable finding was that anatomic zones were found to be independently associated with both cortex-to-cortex width measured on CT in the retrospective cohort and with final implanted screw length in the prospective cohort. Additionally, when compared to other factors analyzed, anatomic zone also had greater magnitudes of association with cortex-to-cortex width and final implanted screw length than various patient factors analyzed, including height, BMI, age, and sex. It is important to acknowledge that height and BMI were also found to be significant factors associated with final screw length. This is consistent with some current literature that have shown that higher BMI is associated with larger cross-sectional dimensions of the femur [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. However, the magnitudes of the associations with height and BMI were relatively small in comparison. Still, this suggests that patient factors may influence distal femoral anatomy and impact the accuracy of using these distal femoral anatomic zones for estimating screw length, and implementing practical methods to account for patient height and BMI may increase the accuracy of this method.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eLimitations\u003c/h2\u003e \u003cp\u003eThe limitations of the technique described should be considered. Despite the strong agreement between depth-gauge measurements and zone-based estimates demonstrated by the high ICC and low bias in our study, the wide Bland-Altman LOAs (-10.29mm, 8.57mm) suggest variable precision associated with this technique. Compared to the LOAs associated with using the lesser trochanter to guide proximal locking screw length selection reported by Collinge et al., the LOAs shown in this study are wider, which suggests less reliability [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Similarly, the percent of zone-suggested screw lengths that agree with final implanted screw lengths are also lower in this study compared to percentages reported by Collinge et al. There are a few potential reasons for these findings. First, the present study includes zones with drastically different anatomical sizes (metaphyseal flair versus the femoral shaft) which likely accounts for some of the inherent variability seen. Second, the \u0026ldquo;next-size-up\u0026rdquo; rule that was used to determine suggested screw lengths in this study is likely not accurate for all zones. For example, in Zone A, depth-gauge measurements, zone-estimated screw length, and final implanted screw lengths all suggest that 80mm may be closer to the best screw length for that zone than the 85mm length chosen using the \u0026ldquo;next-size-up\u0026rdquo; rule. Other contributing factors affecting precision may be related to how facile this method is to apply. For example, the anatomic landmarks used in this study (i.e. where the posterior metaphyseal flare meets the posterior cortex, the posterior aspect of Blumensaat\u0026rsquo;s line) are less straight forward to identify than simpler anatomic landmarks such as the lesser trochanter.\u003c/p\u003e \u003cp\u003eIn addition to the limitations of the technique described, it is also important to discuss the study limitations. First and foremost, extrapolation of our findings to other settings is limited by the small sample size and single center design. The small sample sizes of both the retrospective and prospective cohorts likely contributed to the variable agreement observed between zone-estimated screw lengths and depth-gauge measurements. Larger sample sizes better capturing a wider variety of patients are needed to clarify if the observed variability results from true variability between individual anatomy. Presently, large databases of CT data are being used to design standardized osteosynthesis plates that conform to the anatomy in a wide variety of patients [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Our findings demonstrate the utility in using CT data to establish standardized screw-length estimates based on anatomic location along the distal femur, and larger databases with more CT data have the potential to result in improved screw length estimates. Additionally, an important limitation of this study is that it did not involve using zone-estimated screw lengths to guide screw selection. This is crucial to consider as we found greater concordance between depth-gauge measurements and final implanted screw length; however, this is expected, as depth-gauge measurements were ultimately used to guide screw selection, while zone-based estimates were not.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe current standard method of guiding screw length selection with depth-gauges can be technically challenging and has variable accuracy. The use of standardized anatomic zones to estimate distal femoral interlocking screw lengths is a potential alternative or supplement to depth-gauge measurements. While this tool provides a generalized guideline of potential screw size, this study shows that there are limitations of the technique in terms of variability, possibly due to diversity in distal femoral anatomy among patients. Future studies with larger sample sizes should be aimed at evaluating the clinical implementation of this technique.\u003c/p\u003e"},{"header":"Declarations","content":" \u003cp\u003eNo funding was received for conducting this study.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003cp\u003eStatements and DeclarationsDr. Mary Kate Erdman or an immediate family member serves as a board member, owner, officer, or committee member of American Academy of Orthopaedic Surgeons, Foundation of Orthopaedic Trauma, and Orthopaedic Trauma Association.Dr. Jason Strelzow is a consultant for Acumed LLC, OrthoXel, and Stryker.The remaining authors have no statements or declarations.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eD.Z. performed data collection for the prospective cohort, wrote the main manuscript text, and prepared all figures and tables.H.B. performed data collection for the retrospective cohort and prepared Figure 1.M.E., A.C., and J.S. performed data collection for the prospective cohort and provided crucial guidance for project design and execution. H.B. and J.S. provided the initial study concept and ideas.All authors helped with preparation and review of the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBrumback RJ, Uwagie-Ero S, Lakatos RP, et al (1988) Intramedullary nailing of femoral shaft fractures. Part II: Fracture-healing with static interlocking fixation. JBJS 70:1453\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRicci WM, Gallagher B, Haidukewych GJ (2009) Intramedullary Nailing of Femoral Shaft Fractures: Current Concepts. JAAOS - J Am Acad Orthop Surg 17:296\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHajek PD, Bicknell HRJ, Bronson WE, et al (1993) The use of one compared with two distal screws in the treatment of femoral shaft fractures with interlocking intramedullary nailing. A clinical and biomechanical analysis. 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Eur J Orthop Surg Traumatol 34:2909\u0026ndash;2913. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00590-024-04006-5\u003c/span\u003e\u003cspan address=\"10.1007/s00590-024-04006-5\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHaddad DK, Sain J, Pushilin S, Sagebien CA (2025) Screw migration of retrograde femur intramedullary nail with locking washer: A report of three cases. J Orthop Rep 4:100380. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jorep.2024.100380\u003c/span\u003e\u003cspan address=\"10.1016/j.jorep.2024.100380\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAgostini GM, Ross AH (2011) The Effect of Weight on the Femur: A Cross-Sectional Analysis. J Forensic Sci 56:339\u0026ndash;343. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/j.1556-4029.2010.01648.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1556-4029.2010.01648.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHarrington KI, Wescott DJ (2015) Size and Shape Differences in the Distal Femur and Proximal Tibia between Normal Weight and Obese American Whites. J Forensic Sci 60:S32\u0026ndash;S38. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/1556-4029.12579\u003c/span\u003e\u003cspan address=\"10.1111/1556-4029.12579\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePetersik A, Homeier A, Hoare SG, et al (2018) A numeric approach for anatomic plate design. Injury 49:S96\u0026ndash;S101. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/S0020-1383(18)30312-7\u003c/span\u003e\u003cspan address=\"10.1016/S0020-1383(18)30312-7\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"depth-gauge, interlocking screws, femoral shaft fractures, intramedullary nailing, radiation exposure, operation time","lastPublishedDoi":"10.21203/rs.3.rs-6112990/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6112990/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003ePurpose: \u003c/strong\u003eThe aim of this study is to evaluate whether “anatomic zones” along the distal femur can be used to estimate distal interlocking screw length during femoral intramedullary nailing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods:\u003c/strong\u003e A retrospective “anatomical control” cohort was used establish anatomic zones along the length of the distal femur and estimated screw length within each zone. Estimated screw lengths for each zone were based on mean cortex-to-cortex length at each zone as measured on computed tomography (CT). A prospective cohort was enrolled to evaluate agreement between these estimated screw lengths and depth-gauge measurements for each zone. Agreement was evaluated using mean differences between estimated screw lengths and depth-gauge measurements, an intraclass correlation coefficient (ICC), and Bland-Altman analysis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe retrospective cohort of 56 patients was used to establish eight anatomic zones. Screw length estimates ranged between 42.1mm in the most proximal zone to 80.2mm in the most distal zone.\u003c/p\u003e\n\u003cp\u003eThe prospective cohort included 74 patients (126 screws), was 63.51% male (n=47), with mean age 44.2±24.7 years, mean height 173.2±12.7cm, and mean BMI 28.5±10kg/m\u003csup\u003e2\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eThe mean absolute value difference between zone-estimated screw lengths and depth-gauge measurements was 3.9mm±2.9mm, ranging 2.7mm-5.6mm depending on zone. The ICC was 0.94 (95%CI [0.91,0.96], p\u0026lt;0.01). Bland-Altman analysis revealed a bias of -0.86mm with limits of agreement at +8.6mm and -10.3mm.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAnatomic zone-based screw length estimates derived from CT data show strong agreement with depth-gauge measurements and are a potential strategy to reduce operative time and errors in screw length selection.\u003c/p\u003e","manuscriptTitle":"Distal Femoral Interlocking Screw Length Can Be Estimated Using “Anatomic Zones” During Femoral Intramedullary Nailing","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-03-04 11:11:56","doi":"10.21203/rs.3.rs-6112990/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"1a6066d8-1239-40d1-8fe1-8e3fbb2fdabd","owner":[],"postedDate":"March 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-03-22T01:08:10+00:00","versionOfRecord":[],"versionCreatedAt":"2025-03-04 11:11:56","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6112990","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6112990","identity":"rs-6112990","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}