Ununited Medial Humeral Condylar Ossification Centre in the Cat

August 2, 2023

As part of our endeavour to advance knowledge in the field of veterinary orthopaedics  and ultimately improve the outcome for our patients we perform a critical review of all surgeries we undertake. In addition to this clinical audit we publish in peer reviewed journals reports of animals we have seen that may help colleagues who face similar cases. This month we were delighted to have our case report, detailing an unusual fracture in a wonderful cat called Salem, published in the renown journal Veterinary Comparative Orthopaedics and Traumatology (VCOT). My thanks to Thomas Maddox at Liverpool University and Kerstin Erles of Bridge Pathology for their assistance with writing the article.

Displacement of an Ununited Medial Humeral Condylar Ossification Centre in the Cat

Andy Morris1 Kerstin Erles2 Thomas W. Maddox3

1VetFix, Bournemouth, Dorset, United Kingdom

2Bridge Pathology Ltd, Bristol, United Kingdom

3School of Veterinary Science, Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, United Kingdom

Vet Comp Orthop Traumatol 2018;31:153–157.

Address for correspondence Andy Morris, BVSc, BSc (Hons), CertAVP(GSAS), MRCVS, VetFix, Bournemouth, Dorset, BH6 5BP, United Kingdom (e-mail: info@vetfix.co.uk).


Salter Harris fractures of the distal humeral physis are rare in the cat with type-IV fractures occurring most often.1 These have been reported only in very young cats with physeal closure of the distal humerus expected by 16 to 18 weeks of age.2 Delay or failure of physeal closure has been proposed to increase the risk of Salter Harris–like fractures in mature animals.3 This report documents a Salter Harris type-III–like fracture of the medial condylar ossification centre of the distal humerus in a mature cat. This cat also had delayed physeal closure of the medial aspect of the distal humeral growth plate with no osseous union of the medial condylar ossification centre in the contralateral elbow. Previously reported elbow disorders affecting cats without a history of significant trauma include degenerative joint disease,4–6 fragmentation of the medial coronoid process,7 medial humeral epicondylitis8 and synovial osteochondromatosis.9 To the authors’ knowledge, this is the first report of traumatic displacement of an ununited medial condylar ossification centre.

Case Report

A 2-year-old, 3.3-kg male neutered Domestic Shorthair cat was investigated for the complaint of a non–weight-bearing right forelimb lameness of 2-week duration. The cat was predominantly a house pet. Lameness occurred immediately after the cat jumped from a kitchen counter. No improvement was observed with cage rest and the administration of meloxicam (0.05 mg/kg orally) given once daily for 5 days. Upon examination, the lameness was localized to the right elbow joint with signs of pain and crepitation evident on manipulation. A short stature and crouched hindlimb gait were observed. There were signs of discomfort with left and right hip extension. Gross conformational deformity of both stifleswas apparent with spontaneousmedial luxation of the patellae occurring with stifle flexion. In addition to direct assessment by a veterinarian, an owner-completed clinical metrology tool, the feline musculoskeletal pain index (FMPI), was used as an assessment of musculoskeletal pain where a higher percentage possible score indicates less impairment.10 The FMPI score at presentation was 63%. A retrospective, owner-evaluated FMPI score prior to injury of 81% suggested the cat’s previous ability to perform certain activities was not normal, with the owner reporting an inability or reluctance to jump (►Supplementary Material, online-only). The results of routine haematology, biochemistry, and urine analyseswere unremarkable. The patient was premedicated with acepromazine (0.02 mg/kg IM) and methadone (0.3 mg/kg IM). General anaesthesia was induced with propofol (4 mg/kg IV) and maintained with isoflurane. Lactated Ringer’s solution was infused at 5 mL/kg/hour. Orthogonal radiographs of the right and left elbows demonstrated an absence of the most distal part of themedial portion of the right humeral condyle,with no normal humeroulnar articulation and sclerosis of the remaining lateral part of the condyle (►Fig. 1). A welldefined, smoothly marginated, ossified fragment (4  6  6 mm) was present craniomedial and slightly proximally, partly superimposed over the distomedial humerus. The fragment had a rounded cuboidal shape with a trabecular pattern and evidence of cortices. A much smaller, mineralized, approximately triangular fragment was present more distally, partially overlying the medial coronoid process of the ulna. The medial humeral epicondyle had a normal appearance and no significant soft-tissue swelling was evident. An ossified fragment of similar appearance and size was present in the left elbow (►Fig. 2). This was not significantly displaced from its position within the medial portion of the humeral condyle. Well-defined new bone formation was present on the cranioproximal aspect of the left radius. The proximal humeral physes were not fully closed. Additional findings included bilateral coxofemoral subluxation with mild periarticular osteophyte formation (►Fig. 3). There was also bilateral medial patellar luxation with abnormal stifle conformation with medial deviation of the proximal tibiae and slight lateral deviation of the distal femora. Based on the radiographic appearance, bilateral ununited medial condylar ossification centres of the distal humerus, with displacement of the medial condylar ossification centre on the right,was diagnosed. The short stature and finding of multiple abnormal joints suggested a possible underlying chondrodysplasia. Amedial surgical approach with the incision centred over themedial humeral epicondyle11 permitted careful isolation and then excision of the bone fragment. Upon gross examination, the articular surfaces of the distal humerus and proximal ulnawere considered normal. The jointwas flushed thoroughly with physiological saline. The joint capsule, fascia, and subcutaneous fascia were closed separately with metric 1.5 polydioxanone in a simple continuous pattern. Skin was closed with metric 1.5 nylon. A modified Robert Jones bandagewas placed for 24 hours. Postoperative analgesia was provided with the administration of Fig. 1 Preoperative radiographs of the right elbow. (a) Craniocaudal, (b) mediolateral and (c) craniolateral-caudomedial oblique radiographic projections demonstrate a well-defined ossified fragment located craniomedial and slightly proximal to the distal humerus (arrows). A smaller, mineralized, fragment overlies the medial coronoid process of the ulna (small arrows). There is absence of the most distal aspect of the medial part of the humeral condyle from its normal location. Fig. 2 (a) Craniocaudal and (b)mediolateral radiographic projections of the left elbow. The most distal and medial aspect of the humeral condyle is separated by a well-defined radiolucent line from the remainder of the humeral condyle, but the resultant ossified fragment is not significantly displaced from its normal location (arrows). New bone formation is apparent on the cranioproximal radius (small arrow). buprenorphine (0.02 mg/kg IV) three times daily for 24 hours and meloxicam (0.05 mg/kg orally), once daily for 14 days. The cat was discharged from hospital 24 hours after surgery and the owner informed to cage confine the cat for 7 days. After 14 days, oral meloxicam dose was reduced to 0.03 mg/ kg. The cat was also fed a prescription mobility diet (Hill’s Prescription Diet j/d). Free access around the house was permitted and environmental modifications, including ramps and walkways, were instigated. Histopathological analysis of the bone fragment demonstrated well-organized and mature bone lined by hyaline cartilage. The surface of the cartilage exhibited extensive fibrillation and areas of erosion and ulceration (►Fig. 4A). Regions of thebone fragment showed almost complete resorption of the subchondral bone plate with little overlying articular cartilage (►Fig. 4B). Small foci of subchondral fibrosiswere observed. Multifocal remodelling of the underlying bone was suggested by scattered osteoclasts within marrow cavities. Clinical reassessment 12 months postoperatively revealed mild intermittent right forelimb lameness. There was no obvious sign of pain on elbow flexion and extension by veterinary assessment. Elbowrange of motionwas considered similarbetween forelimbs. The FMPI scorewas84%, suggesting a return of function to approximately preinjury levels (►Supplementary Material). Further evaluation of the hip dysplasia and patellar luxation was declined by the owner.



Pathologic conditions affecting growth plates can result in severe orthopaedic problems. This case report demonstrates traumatic displacement of an ununited medial condylar ossification centre of the distal humerus in a mature cat. The bilateral symmetry and precise location of the bone fragments suggest a failure of physeal closure of the medial aspect of the distal humeral epiphyseal growth plate with nonunion of the medial condylar ossification centre. ►Fig. 5 demonstrates the radiographic appearance of the medial condylar ossification centre in a normal 8-week-old kitten. The humeral condyle arises from two separate ossification centres. The lateral ossification centre is the first to form, and in the cat it is radiographically apparent from 2 weeks of age and themedial centre from3 weeks of age.12 Physeal closure with union of the lateral and medial condylar centres is expected by 18weeks of age.2 A failure of physeal closure and nonunion of the medial condylar ossification centre in the cat is not reported in the veterinary literature. Mechanisms that govern normal physeal growth and closure are not well known. Systemic factors which affect many or all physes include genes, hormones, nutrition, and general health.13 In male cats, delayed physeal closure subsequent to neutering is reported at the distal radial physis,14 greater trochanter, distal femur and tibial tuberosity.15 The influence of neutering on the distal humeral physis is unknown; however, this growth plate is considered part of the early group of physes Fig. 4 (a) Histopathology of the excised fragment. Severe cartilage fibrillation (arrow) with cartilage necrosis (asterisk) and ulceration is present. Haematoxylin and eosin (H&E): 40 magnification. (b) Detail of the centre shown in a. There is extensive loss of articular cartilage. The subchondral bone exhibits resorption with occasional osteoclasts present (arrow). Replacement of the bone by fibrous tissue is present in the centre of the image (arrowheads). H&E: 200 magnification. Fig. 3 Ventrodorsal radiographic projection of the pelvis. There is mild bilateral coxofemoral subluxation, with flattening of the femoral heads and periarticular osteophyte formation at the margins of the acetabula. Femoral/tibial conformation is also abnormal bilaterally, with slight lateral deviation of the distal femur andmedial deviation of the proximal femur andmedial displacement of the patellae, although external rotation of both stifles compromises assessment of this. From evidence to date, it appears neutering may have a greater impact on specific physes fromthemiddle and late-closing growth plates.14,15 It has been proposed that physes that close prepuberty may close in response to lower levels of gonadal steroids, or, alternatively in response to some other, as yet undefined signal.15 The lateral aspect of the distal humeral epiphyseal growth plate was closed in this cat, suggesting an etiology specific to themedial humeral compartment of the elbow. It is generally agreed that the most severe disease seen in the feline elbow affects the medial compartment, including the medial coronoid process and medial aspect of the humeral condyle.16 Local factors that may affect a single physis include disturbance to blood supply, mechanical forces acting on the physis, trauma, and infection.13 Repetitive strain nonunions and fracture nonunions of the physes are reported in humans.13 Though early trauma with bilateral nondisplaced Salter Harris type-III–like fractures cannot be ruled out in this cat, no known traumatic event earlier in life was reported. The cat’s short stature and multiple joint abnormalities did suggest an underlying chondrodysplasia. Chondrodysplasia is a disturbance in the development of the long bones, especially of the epiphyseal growth plate. Complications and degenerative joint disease can be common sequelae of dysplasias because of altered bone shape and joint conformation. The altered elbow joint conformation in this catmay have affected mechanical forces acting on themedial compartment of the elbowimpeding the normal union of the medial condylar ossification centre. Delay or failure of physeal closure has been proposed to increase the risk of Salter Harris–like fractures in mature animals.3 Histopathologic features of the excised fragment showed a focus of severe degenerative joint disease and underlying resorption of the subchondral bone plate (►Fig. 3B). This was probably the result of an abnormal loading focus. The failure of unification of the humeral condyle plus abnormal loading forces and remodeling of the medial portion of the humeral condyle probably resulted, or contributed, to the traumatic displacement of the medial condylar ossification centre in this cat. Elbow degenerative joint disease with osteochondral fragments associated with disease of the medial coronoid process is reported in the cat.7 However, intra-articular osteochondral fragments have been found in cat elbow joints with apparently intact medial coronoid processes.17,18 Osteochondral fragments were shown to be composed of poorly organized bone, hyaline cartilage and fibrocartilage, consistent with synovial chondromatosis.17 Visual inspection of themedial coronoid process of the ulna in this catwas considered normal. Histological analysis of the excised fragment revealed mature and organized bone lined by articular cartilage. This was consistent with the displaced portion of the humeral condyle. The smaller mineralized fragment overlying the medial coronoid process of the ulna evident on preoperative orthogonal radiographs of the right elbow (►Fig. 1) was not identified during surgical excision of the bone fragment. This lesion was considered to represent an osteochondral fragment or mineralized free body in the area of the supinator sesamoid bone. Anatomic reduction and lag screw fixation of the displaced fragment was not attempted in this cat. This was due to the small fragment size, concerns of blood supply to the isolated fragment and complication risk (with client finances limiting the possibility of repeat surgery). There was also a delay from presumed injury to diagnosis of the displaced fragment. Because of the rarity of the disease and unknown risks of prophylactic screw placement, a decision was made not to attempt to protect the contralateral medial condylar ossification centre from future displacement. A combination of pharmaceutical, nutraceutical, and environmental modifications were chosen for the management of the arthritic pain in this cat. Meloxicam has proven to be effective for treating chronic pain in arthritic cats.5,19,20 Certain therapeutic dietsmay also be beneficial.21 Nonetheless, the owner was counselled that the long-term outcome for the right elbow joint was guarded and of the unknown future risk of displacement of the medial condylar ossification centre in the left elbow. Future surgical options including elbow arthrodesis were also discussed. Fig. 5 (a, b) Craniocaudal and (c, d) mediolateral radiographic projections of the left elbow demonstrating the appearance of ossification centres of the distal humerus in an 8-week-old kitten. The kitten was normal on orthopaedic examination of this limb with radiographs taken to allow surgical planning of a contralateral humeral fracture. ME, medial epicondyle ossification centre; MCOC, medial condylar ossification centre; LE, lateral epicondyle ossification centre; LCOC, lateral condylar ossification centre; MLCO, medial and lateral condylar ossification centres superimposed. Veterinary and Comparative Orthopaedics and Traumatology Vol. 31 No. 2/2018 Displacement of an Ununited Medial Humeral Condylar 156 Ossification Centre in the Cat Morris et al. The FMPI is a clinicalmetrology instrument employing an owner-completed questionnaire with appropriate readability, reliability and proven ability to discriminate normal cats from cats with chronic arthritic pain.10 The FMPI has not been shown to discriminate between disease severity subgroups. As such, the ability of the FMPI to assess the outcome of this case is untested. In addition, the retrospective use of the FMPI to assess arthritic pain and activity prior to fracture is not validated. Despite these limitations, the FMPI information was considered useful and as such included in the case report. Additional objective measures including peak vertical reaction force, collar mounted activity monitors and goniometry would have provided further assessment of outcome. This case is an interesting addition to the group of already known elbow diseases affecting the medial compartment of the elbow in the cat. Clinicians should be aware of the possibility of nonunion of the medial condylar ossification centre of the distal humerus in the mature cat. Although surgical excision of the displaced medial condylar ossification centrewas considered successful in this case, the benefit of fragment excision over surgical fixation is uncertain. The long-term impact of the loss of normal humeroulnar articulation is unknown and future progression of elbow arthritis was considered likely. Financial Support None. Conflict of Interest The authors have no conflict of interests with regard to this manuscript. Author Contributions All authors contributed to the study conception, the study design, the acquisition of data, data analysis and interpretation, drafting or revising of the manuscript, and approved the submitted manuscript. Acknowledgements The authors wish to thank Keith Moore for preliminary assessment and radiographs, Manuel Pinilla and Olga Travetti for the initial diagnostic imaging report. References 1 Vannini R, Olmstead ML, Smeak DD. An epidemiological study of 151 distal humeral fractures in dogs and cats. J Am Anim Hosp Assoc 1988;24:531–536 2 Smith RN. Fusion of ossification centres in the cat. J Small Anim Pract 1969;10(09):523–530 3 McGlennon NJ, Matic SE, Houlton JEF. Physeal closure in cats. In: WSAVA/BSAVA Congress, Paper Synopses. BSAVA, Gloucester. UK 30 March–2 April, 1989:228 4 Godfrey DR. Osteoarthritis in cats: a retrospective radiological study. 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J Vet Intern Med 2010;24(03):487–495 Veterinary and Comparative Orthopaedics and Traumatology Vol. 31 No. 2/2018 Displacement of an Ununited Medial Humeral Condylar Ossification Centre in the Cat Morris et al. 157