Osteoarthritis of the coxofemoral joint in 24 horses : evaluation of radiography, ultrasonography, intra-articular anaesthesia, treatment and outcome

Background: Few case reports describe equine coxofemoral joint osteoarthritis (CFJOA).

Objectives: To evaluate diagnostic findings and outcome of horses with CFJOA and to provide a score facilitating radiographic assessment.

Study design: Retrospective case series.

Methods: History, clinical signs, ultrasonographic, radiographic and intra-articular anaesthesia findings, treatments, outcome, and necropsy results of horses with CFJOA presented between 2002 and 2023 were collated. Radiographic findings were categorised to develop a radiographic score which was applied by two masked
examiners. Intra- and inter-observer reliability was determined using weighted Cohen's kappa (Cκ) and the correlation between radiographic and ultrasound findings via Spearman correlation coefficient.

Results: The study included 24 horses (median age 14 years). Most of them (20/24) were chronically lame. Frequent clinical signs included unilateral gluteal muscle atrophy (18/21), lengthening of the stride of the affected limb (13/19) and locomotion on three tracks (13/20). Both imaging modalities enabled evaluation of periarticular
osteophytes (correlation coefficient r = 0.64; p = 0.003). Additionally, radiography allowed detection of irregular joint spaces, subchondral bone opacity changes and femoral head flattening/tapering. Inter-observer (Cκ = 0.846) and intra-observer (Cκ = 0.853 and Cκ = 0.842) agreement was excellent. If treated, mostly intraarticular
corticosteroids were administered (16/18). Nine horses were euthanised immediately or during follow-up examination. Post-mortem, the Ligamentum capitis ossis femoris was commonly found ruptured. All surviving horses remained lame.

Main limitations: Retrospective analysis of clinical records and subjective outcome assessment based on owner follow-up with potential recall bias. Due to overall disease severity, associations between different grades of clinical findings, radiographic
abnormalities and outcome could not be evaluated.

Conclusions: Typical clinical signs may indicate CFJOA. Standardised evaluation of ventrodorsal radiographs allows a comprehensive diagnosis. Postmortem findings suggest joint instability as a possible causative factor that may contribute to the poor prognosis and resistance to medical therapy of the disorder.