The significance of rudimentary ulnas and fibulas in the development of angular limb deformities in horses and some other comments.

The significance of rudimentary ulnas and fibulas in the development of angular limb deformities in horses and some other comments. | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL Equine Veterinary Education This is a preprint and has not been peer reviewed. Data may be preliminary. 30 October 2025 V1 Latest version Share on The significance of rudimentary ulnas and fibulas in the development of angular limb deformities in horses and some other comments. Authors : Joerg Auer 0000-0002-4062-9802 , Carlotta Valletti [email protected] , and Thomas Schmitz Authors Info & Affiliations https://doi.org/10.22541/au.176182574.42282825/v1 268 views 212 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Carpal valgus deformities remain a common challenge in foals, yet their aetiology is often multifactorial and rarely attributable to a single anatomical anomaly. Recent case reports by Müller et al. (2025) suggest that rudimentary ulnas may play a causative role in these deformities, but such claims warrant closer scrutiny. Since the early 1980s, when Auer reported partial ossification of rudimentary ulnas in about 20% of foals with a valgus deformity, these structures have been documented radiographically without consistent evidence of causation. Only in specific small breeds, such as Shetland Ponies and Miniature Horses, has the presence of complete ulnas or fibulas been clearly linked to severe developmental changes requiring early surgical correction. Outside such breed-specific forms of atavisms, the argument for causality is weak. A closer look at the three cases reported by Müller et al. illustrates this point. The first case reflected poor neonatal management, with abnormal (most likely incomplete at the time of birth) ossification of the cuboidal carpal bones far more relevant than any ulnar remnant. The second case showed an acceptable surgical response. The third case barely demonstrated a rudimentary ulna radiographically, making the supposed benefit of surgery questionable. In all three cases, the presence of an ossified ulna appears incidental rather than determinative. The real challenge remains proper diagnosis and timing of intervention. Radiographic assessment must be performed orthogonally to the carpal frontal plane, and clinicians should remain aware of methodological differences between bisecting line and parallel line measurements. In terms of treatment, transphyseal screw placement is effective at the distal metacarpus and metatarsus, but far less reliable at the distal radius, where prolonged growth increases the risks of overcorrection, and physeal injury. In light of the available evidence, the conclusions by Müller et al. overstate the role of rudimentary ulnas in carpal valgus deformities. Clinical Commentary The significance of rudimentary ulnas and fibulas in the development of angular limb deformities in horses and some other comments. J.A. Auer*, C. Valletti, T.R. Schmitz Equine Department, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland * Corresponding author: Jörg Auer [email protected] Keywords: foals, angular limb deformities, rudimentary ulna, atavism Summary Carpal valgus deformities remain a common challenge in foals, yet their aetiology is often multifactorial and rarely attributable to a single anatomical anomaly. Recent case reports by Müller et al. (2025) suggest that rudimentary ulnas may play a causative role in these deformities, but such claims warrant closer scrutiny. Since the early 1980s, when Auer reported partial ossification of rudimentary ulnas in about 20% of foals with a valgus deformity, these structures have been documented radiographically without consistent evidence of causation. In most breeds, they represent incidental findings rather than pathogenic agents. Only in specific small breeds, such as Shetland Ponies and Miniature Horses, has the presence of complete ulnas or fibulas been clearly linked to severe developmental changes requiring early surgical correction. Outside such breed-specific forms of atavisms, the argument for causality is weak. A closer look at the three cases reported by Müller et al. illustrates this point. The first case reflected inadequate neonatal management by the initial veterinarian, with abnormal (most likely incomplete at the time of birth) ossification of the cuboidal carpal bones, which were more likely to be relevant than any ulnar remnant. The second case showed an acceptable surgical response, yet retained ossification gaps that do not completely support the claim of primary causality. The third case barely demonstrated a rudimentary ulna radiographically, making the benefit of surgery questionable. In all three cases, the presence of an ossified ulna could have been incidental rather than determinative. The real challenge remains proper diagnosis and timing of intervention. Radiographic assessment must be performed orthogonally to the carpal frontal plane, and clinicians should remain aware of methodological differences between bisecting line and parallel line measurements. In terms of treatment, transphyseal screw placement is effective at the distal metacarpus and metatarsus, but far less reliable at the distal radius, where prolonged growth increases the risks of overcorrection, physeal injury, and screw failure. These technical and biological realities deserve more emphasis than speculative associations with rudimentary ulnas. In light of the available evidence, the conclusions by Müller et al. might overstate the role of rudimentary ulnas in carpal valgus deformities. They could be regarded, as in most foals, as evolutionary curiosities rather than pathological drivers. The key determinants of outcome remain accurate radiographic assessment, careful case selection, and timely intervention. Misattributing causality potentially risks misguiding treatment strategies and obscuring the real, multifactorial nature of angular limb deformities in foals. Preface When a paper is submitted it is reviewed by two to three reviewers and if they find the paper is publishable it goes forward to be published, if the editor is content with the referees’ conclusions (referees are generally selected based on their particular areas of expertise). When I (first author) accepted to write a Clinical Commentary to it, and read it all the way, I wasdisappointed in the content. It is my opinion that the reviewers of this case series ( Surgical management of carpus valgus deformity caused by persistent ulna in three large breed foals , by Müller et al., 2025), should not have accepted it because of several deficiencies. I talked to the publishers of EVE to stop it, but according to them this is not possible after the reviewers accepted it for publishing. I then talked to the two senior authors, both of whom I have great respect for. After discussing my objections to the paper with them, we came to the conclusion that I would go forward in writing my Clinical Commentary and delineate my objections. I do apologise to the authors of the above-mentioned paper about my critical statements, but it is my firm belief that in a Clinical Commentary misrepresented data should be identified and discussed. General Comments The presence of rudimentary ulnas in foals has been mentioned in the literature since the introduction of the hemicircular transection and periosteal elevation (HCPTE) technique (Auer and Martens, 1982). The methodology described that it was important to transect the “ligamentous” ulna at the lateral aspect of the distal radius, as it could hinder equal growth along the entire physis (Auer and Martens, 1982). Auer (1992) reported that approximately 20% of foals presenting with carpal valgus deformities and treated with HCPTE exhibited partial ossification of the rudimentary ulna. In these cases, the rudimentary ulna was partially removed with a rongeur (Auer 1992). Therefore, the foals described by Dubuc and Da Silveira (2019) and Müller et al. (2025) merely listed a different technique. Whether the ossified rudimentary ulna caused the development of the angular limb deformity has, to date, never been proven, except in Shetland Ponies and Miniature Horses (see later). Therefore, the title of the case series described by Müller et al. (2025) is inappropriate. Complete Fibula and Ulna in Shetland Ponies Speed (1958) first mentioned complete fibulas in three Shetland ponies born on open hill country. The foals ran with their mothers and were not carefully observed by their owner. They were first presented at 4 months of age because of lameness and an abnormal gait. Radiographs revealed persistent fibulas. Unfortunately, only one page of the publication could be acquired by the authors of the present “Clinical Commentary”. Nevertheless, it is the assumption of the authors that the ulna had similar changes because these growth defects are usually noted in fore- and hindlimbs simultaneously (Hermans, 1969, Shamis and Auer, 1985, Rafati et al., 2016). Shamis and Auer (1985) described a Shetland Pony, suffering from complete ulnas and fibulas and Tyson (2004) reported a similar case of a Miniature Horse. It was interesting to note (Shamis and Auer 1985) that the distal epiphysis of the ulna did not extend as far distally as in the normal foal, where it attaches to the distal radial physis as “ulnar styloid process”. In the Shetland Pony, the distal ulnar and radial physes were not fused and showed degenerative changes between the two bones (Shamis and Auer 1985). Additionally, a “stair-step” was noted along the antebrachial joint. The distal fibular epiphyses were loosely (ligamentous) attached to the distal tibial epiphyses, and the articular surfaces, including the wedge-shaped lateral trochlear ridge of the tali, showed marked degenerative changes (Shamis and Auer 1985). It was interesting to note that the mid-portion of the fibula had osseous attachments to the tibia, which was a clear indication of growth retardation of the lateral aspect of the tibia and fibula. Because of these severe developmental changes, Shetland foals should be evaluated within the first two weeks after birth, including radiographs, and potential corrective procedures implemented. Early surgical segmental resection (1 cm) of the distal ulna and tibia is recommended. Additionally, the distal tibial epiphysis should be placed in the correct position and attached to the distal tibial epiphysis by means of at least one, or better two, 3.5 mm cortex screws inserted using lag technique to reduce mobility between the two epiphyses. The aspect of the development of the appendicular skeleton of the horse was calculated in a theoretical deconstruction of the evolutionary mechanism by Bhattacharjee (2019). The author predicts that the next step will be the complete ossification between the remaining metacarpal and metatarsal bones. The presence of complete ulnas and fibulas is judged as an atavism (Hall, 2010), a regression, to horses of the Miocene period (several million years ago). At that time, the complete ulnas and fibulas had important functions in weight-bearing (Speed 1958). It has been reported that “normal” parents may have offspring with the anomaly, which suggests the presence of an autosomal, recessive component (Hermans, 1969). Rafati et al. ( 2016 ) described the causes for the development of this atavism: large deletions at the SHOX locus in the pseudoautosomal region, severe gene defects. Clinically, the problem is always described in the fore- and hindlimbs, except by Speed (1958). Case Selection The three cases described by Müller et al. (2025) showed ossification of the ulna in some form. They were all considered as causes for the development of angular deformities present. Case 1 was born with incomplete ossification of the cuboidal carpal and probably also of the tarsal bones. It is the only reasonable explanation of the degenerative changes noted radiographically at the time of presentation to the clinic at the age of 2.5-months. Because of the initial improper management of the new born foal, the immature cuboidal carpal bones, containing a wide rim of pliable precursor cartilage, ossified in an abnormal configuration, in a “wedge-shaped” form. As everybody knows, the front limbs of foals are attached to the body by 7 pairs of muscles. To gain more stability of the lanky, long legs (relative to their body), young foals brace their elbows at the chest wall, which rotates their limbs outward, therefore placing more weight on to the lateral aspects of fore limbs, and squeezing the pliable precursor cartilage excessibly. The foal should have been treated with splint bandages for two to four weeks, depending on the severity of the immaturity (Auer et al., 1982). The rudimentary ulna has, in this case, to be judged as an accidental finding. It was not the cause of the malformation of the carpi, including the angular limb deformity. Even before the resection of the rudimentary ulna was performed, it was clear that the surgery would be unsuccessful. An interesting side note is here in place: Incomplete ossification of the cuboidal carpal bones occurs simultaneously in the cuboidal tarsal bones (Auer et al., 1982). So, the foal must have suffered from collapse of the third and central tarsal bones, accompanied by a “hopping” hindlimb gait. The three-day-old foal (case 2) showed relatively well-developed rudimentary ulnas and wedge-shaped distal radial epiphyses. There was also a radiographic decrease in ossification at the lateral aspect of the distal radial physis, which could have represented precursor cartilage. This foal responded well to the surgery, but even the postoperative radiographs show a certain gap in ossification between the styloid process of the distal radius and the ulnar carpal bone. It has also been shown that surgical manipulations in the physeal regions induce hormonal growth hormone modulation, which may influence the growth rate like the one induced by HCTPE (von Rechenberg et al., 2010). Case 3 was a 4.5-week-old foal with slightly wedge-shaped distal radial physes. The rudimentary ulna is faintly visible; the partial resection of it had most likely only a minimal effect on the correction of the deformity. Radiographic evaluation of angular limb deformities Frequently, the degree of angular limb deformities is measured by drawing bisecting lines along the centre of the radius and the third metacarpal bone. At the point where the two lines cross each other, the angle can be measured, as shown in Müller et al. (2025). Frequently, the bisecting lines are not correctly drawn along the centre of the bones, especially in the radius. This may be partially caused by the angle of the radiographic view (Bramlage and Auer, 2006; Bischofberger and Auer, 2019). The correct radiograph should be taken orthogonally relative to the carpal frontal plane. This plane depends on the orientation of the front limb, which may have a slight outward rotation. Also, in many DP radiographic views, the third metacarpal bones are presented orthogonally, whereas the radius shows some obliquity, preventing the drawing of true bisecting line. On such radiographs it is impossible to determine the true deviation angle, using this technique. It is important to define the bisecting line by two points along the radius in the metaphysis and not by one point in the epiphysis and one in the metaphysis as shown in Fig 3 (Müller et al., 2025). If done correctly, it would have placed the crossing point of the bisecting lines in both carpi at the physis, thereby defining the deformity in the distal epiphyses and metaphyses of the radii. Dependent upon where the crossing point of the two bisecting lines is located over the carpal region, the deformity can be assessed as caused by asymmetric growth of the distal radius (proximal to the antebrachiocarpal joint) or by partial incomplete ossification of the carpal bones (distal to the antebrachiocarpal joint). There exists another technique to evaluate the deformity. A bisecting line is drawn along the third metacarpal bone up to the carpometacarpal joint. The next lines are drawn along the carpometacarpal-, the middle carpal-, the antebrachiocarpal joints, and the distal radial physis. Ideally, all these lines should be parallel to each other and perpendicular to the bisecting line along the third metacarpal bone. Any divergence of two adjacent parallel lines associates a deformity and its angle to that location (Fig. 1). This technique allows correct determination of a deformity to a location, even if the x-rax beam was not orthogonal relative to frontal carpal plane. If this technique of evaluation is applied to the radiographic views of the three cases in Müller et al. (2025), it can be stated that the imaginary line along the physes in cases 2 and 3 diverges slightly from the three lines along the joints. Transphyseal screw for correction of angular limb deformities Single transphyseal screw insertion for correction of angular limb deformities was first introduced by Hunt (2000) for application in the distal third of the metacarpal and metatarsal bones. The benefit of this technique in these locations is the local short-time growth activity (a few months). On the other side of the coin is the distal radius, where active growth is present, in intervals, over an almost 2-year period (Bramlage and Auer 2006). Generally good results have been reported in both locations (Kay and Hunt, 2009; Gary et al., 2017). Complications have been reported by Carlson et al. (2012). However, only two of 568 foals developed complications. They occurred at the distal radius. Al Ruggles of Rood and Riddle Equine Clinic (Ruggles, personal communication, 2025) states that “ We advise clients to wait until April or so of the yearling year to apply transphyseal screws in the distal radius. The belief is that it is best to have the foals in during the spring growth phase of the horse in the local area, where the correction of the deformity can be controlled, and to try to prevent overcorrection and/or physeal collapse after removal. When the implant is placed in younger foals, there is a risk of overcorrection. Additionally, there exists also the potential of failure to work, since the screw may have inadequate purchase to temporarily retard growth in the epiphysis. Further problems may arise with physitis, which is most commonly encountered at the distal medial radius in yearlings with screws placed laterally.” Fig. 2 represents a 2-week-old foal with severe bilateral valgus deformities. Note the marked physeal ectasia at the medial aspect of the physis in both fore limbs (Fig. 2b, arrows). This foal was managed with by HCTPE laterally and screw and plate application medially. The one-year follow-up radiographs show good correction of the deformity with a minor deformity still persisting. It is very likely that if this foal were managed by insertion of transphyseal screws, the outcome would have been different, considering the statement by Ruggles (2025). Reviewing the cases 1 and 3 (Müller et al. , 2025), where transphyseal screws were inserted at the distal radii, the following comments can be made: In case 1, the implants had little or no effect, as the inserted screws were still straight 6 months post-insertion. Also, as expected by the first author of this Clinical Commentary, the deviation angles were unchanged. In case 3, the two transphyseal screws were considerably bent at six weeks post-insertion. This means that the screws were effective. Screw removal may turn out to be problematic, as the chance exists that the severely stressed screws may break during this procedure. References Auer J.A., Martens R.J., Williams H.E.: Periosteal Transection and Periosteal Stripping for Correction of Angular Limb Deformities in Foals. A Clinical Study. J. Amer. Vet. Med. Assoc. 181, 459-466, 1982. Auer JA, Martens RJ, Morris EL: Angular limb deformities in foals: Part 1. Perinatal factors. Comp Cont Educ Pract Vet 4:330-339, 1982 Auer, J.A. (1992) Angular limb deformities. In : Equine Surgery . Ed: Auer, J. WB Saunders, Philadelphia. pp 940-956. Bischofberger, A.S. and Auer, J.A. (2019) Angular limb deformities. In: Equine Surgery, 5th ed. Eds: Auer, J.A., Stick J.A., Kümmerle J.M. and Prange T. St. Louis, MO. Pp. 1471-1489. Bhattacharjee, S. (2023). The osseous fusion patterns in an equine limb: A theoretical deconstruction of the evolutionary mechanisms. www.elsevier.com/locate/biosystems 225 , 104871, pp 1-9. Bramlage, L.R. and Auer, J.A. (2006) Diagnosis, assessment and treatment strategies for angular limb deformities. Clin. Techn. Equine Pract. 5 , 259-269. Carlson ER, Bramlage LR, Stewart AA, et al: Complications after two transphyseal bridging techniques for treatment of angular limb deformities of the distal radius in 568 Thoroughbred yearlings. Equine Veterinary Journal 44:416-419, 2012. Dubuc, J: and Da Silveira E.A. (2019). Case Report: Partial resection of bilateral ulnar remnants for treatment of carpus valgus in a 3-week-old Hanoverian foal. Can. Vet. J. 60 , 864-868. Gray, A., Randleff-Rasmussen, P. and Lepage, O.M. (2017) Single transphyseal screws for the correction of moderate to severe angular limb deformities in 28 Thoroughbred foals. Equine Vet. Educ. 30 , 88-93. Hall, B.K. (2010) Atavisms. Curr. Biol. R 871. Hermans, W.A. 1969. Een hereditaire anomlie in in big Shetland Ponies. Vijschr. Diergeneesk. 94 , 16: 989-996 Hunt, R.J. (2000) Management of angular limb deformities. Proc. Am. Ass. Equine Practnrs. 46 , 128-129. Kay, A.T. and Hunt, R.J. (2009) Single Screw transphyseal bridging of the distal metacarpus and metatarsus for correction of angular limb deformities in the foal. Equine Vet. Educ. 22 , 671-672 Müller, A.C., Ehrle, A., Bartmann, C.,Lischer, C. and Röcken, M. (2025) Surgical management of carpus valgus deformity caused by persistent unla in three large breed foals. Equine Vet. Educ. tbd Rafati, N., Anderson, L.S., Mikko, S., Chungang, F., Raudsepp, T., Petterson, J., Janeka, J., Wattle, O., Ameur, A., Thyreen, G., Eberth, J., Huddleston, J., Malig, M., Baile, E., Eicher, E.e:, Dalin, G., Chowdary, B., Andersson, L., Lindgren, G. and Rubin, C.J. (2016) Large Deletions at the SHOX Locus in the Pseudoautosomal Region Are Associated with Skeletal Ativism in Shetland Ponies. G3; Genes/Genomes/Genetics. 6, 2213-2223. Ruggles, A.J. Rood and Riddle Equine Clinic. (2025) Personal communication. Shamis, L.D. and Auer J.A. (1985). Complete ulnas and fibulas in a pony foal. J Am. Vet. Med. Assoc. 186: 802-804. Speed, J.G. (1958). A cause of malformation of the limbs of Shetland ponies with a note on its physiologic significance. Brit. Vet. J. 114, 18-22. Tyson, R., Graham, J.P., Colahan, P.T. and Berry, C.R. (2004), Skeletal atavism in a Miniature Horse. Vet. Radiol. Ultras. 45. 315-317. Von Rechenberg, B., Tanner, S., Hilbe, M., Zlinsky, K., Kämpf, K., von Wedel, F., Kümmerle, J., Picek, S., Vogt, R . Auer, J.A . (2010) Molecular signalling within growth plates of the radius and tibia after periosteal stripping: an experimental study in lambs. Pferdeheilkunde 26 (4), 484-494. Figure Legends Fig. 1: A 3-day-old Arabian Horse filly showing a carpal valgus deformity in the right- and a carpal varus deformity in the left fore limb. The right fetlock region also shows a varus deformity. The conformation in the fore limbs is also called “wind swept”. B Dorsopalmar radiographic views of both carpal regions showing incomplete ossification of all cuboidal carpal bones. All bones show endochondral ossification, but there is still excessive precursor cartilage surrounding the ossification centers of the cuboidal bones. The angular limb deformities are readily recognizable on the radiographs. The right radius shows a “bend” in the bone, which means that the radiograph was not taken at a right angle to it. On such a radiographic view it is not possible to draw the bisecting lines correctly. The radiograph of left carpal region was not taken orthogonally, whereas the radius was shot at a right angle. Dotted lines were drawn along the joint spaces and the physes. Ideally all four lines should be parallel. The red lines in the right carpal region are not all parallel, most likely caused by squeezing the precursor cartilage t the lateral aspect, leading to a valgus deformity aggravated by the asymmetric growth of the distal radius. The varus deformity of the left limb was caused by a deformity in the proximal metaphysis of the third metacarpal bone (blue crossing lines). Fig. 2. A A 3-week-old Quarter Hoers filly showing marked valgus deformities in the froe limbs. Note, the bony proliferations at both distal radii. B Dorsopalmar radiographic views of both carpi show wedge-shaped distal radial physes and physeal ectasia (arrows). Both problems were treated by means of HCPTE laterally as well as screw and small bone plate temporary growth retardation. The progress was evaluated at 3 and 7 weeks. C Follow-up radiographs of the same foal 3 1 / 2 months post op show adequate correction. The physeal and epiphyseal region as enlarged but no physitis had developed. Note, the marked bend in the epiphyseal screws, demonstrating the forces that were exerted upon them. At that time the implants were removed carefully to avoid potential breaking of the distal screws. Figure 1A Figure 1B Figure 2A Figure 2B Figure 2CL Figure 2CR Supplementary Material File (figures.docx) Download 4.62 MB Information & Authors Information Version history V1 Version 1 30 October 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Collection Equine Veterinary Education Authors Affiliations Joerg Auer 0000-0002-4062-9802 Vetsuisse Faculty, University of Zurich View all articles by this author Carlotta Valletti [email protected] Vetsuisse Faculty, University of Zurich View all articles by this author Thomas Schmitz Vetsuisse Faculty, University of Zurich View all articles by this author Metrics & Citations Metrics Article Usage 268 views 212 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Joerg Auer, Carlotta Valletti, Thomas Schmitz. The significance of rudimentary ulnas and fibulas in the development of angular limb deformities in horses and some other comments.. Authorea . 30 October 2025. 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