Hypothesis for the pathophysiology of humeral intracondylar fissure

Analysis of humeral condylar morphology in dogs with and without humeral intracondylar fissure

Emily Frapwell 1, Moira Watkins 2, Bryony Halcrow 3, Heather Goodrum 3, Neil J Burton 1, Daniel M Ogden 4, Steve Bright 5, Bill Oxley 3

Background:
Humeral intracondylar fissure (HIF) is a condition observed primarily in spaniel breeds, characterized by a fissure through the humeral condyle. While initially attributed to incomplete ossification (IOHC), current theories suggest it may result from stress fractures due to abnormal loading. Prior findings of fissures in mature dogs with previously normal imaging have prompted investigation into whether elbow joint conformation contributes to HIF development.

Methods:
This retrospective case-control study evaluated 171 elbow CT scans divided into three groups: non-chondrodystrophic controls (n=44), unaffected older Springer Spaniels (n=27), and HIF-affected dogs (n=100). Morphological assessment of the humeral condyle was conducted using 3D surface-rendered models, with 10 distance and angular measurements analyzed. Observers were blinded to the HIF status of models. Inter- and intraobserver reliability was established prior to full data collection.

Results:
HIF-affected dogs showed significantly steeper axial angulation of both the medial (angle A) and lateral (angle B) humeral condyle surfaces, and greater vertical condylar heights (distances a and b) compared to controls. These patterns were consistent across overall comparisons, as well as subgroup analyses of Springer Spaniels and non-spaniels. The wedge-shaped articular surface between medial and lateral condyles was more acute in HIF dogs, suggesting altered shear force vectors may predispose to fissure development.

Limitations:
The study population was heterogeneous regarding age and breed, though age ranges were similar between most comparison groups. Morphological changes were inferred rather than directly correlated with force transmission. Additionally, while HIF was associated with distinct morphology, causality cannot be confirmed without biomechanical modeling.

Conclusions:
Dogs with HIF exhibit distinct differences in humeral condylar morphology, notably increased angulation and condylar height. These alterations may contribute to abnormal shear forces within the joint, supporting the theory that joint conformation influences HIF pathogenesis. Further studies, including biomechanical modeling and assessment of associated elbow structures, are needed to elucidate causal relationships and support screening or preventive interventions.

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