Diagnostic value of abduction angle and magnetic resonance imaging in dogs with arthroscopically confirmed medial shoulder instability.

Objective: Medial shoulder instability (MSI) is a frequent cause of thoracic limb lameness in dogs, yet its diagnosis remains challenging, with arthroscopic examination considered the gold standard. The objective of this study was to assess the diagnostic sensitivity of preoperative shoulder abduction angle measurements and MRI findings for detecting MSI in dogs with arthroscopically confirmed diagnoses. Animals and procedure: arthroscopy. Inclusion criteria included signalment and clinical history and clinical, orthopedic, and neurological examinations, followed by bilateral shoulder abduction angle measurements using the contralateral "healthy" limb as reference. Preoperative imaging included neutral lateral shoulder radiography and MRI examinations. Shoulder abduction angles and MRI findings were compared with arthroscopic diagnoses to assess sensitivity. Results: Seventeen dogs (9 males, 8 females) with a median age of 72.0 mo and a median weight of 25.0 kg were included. Median lameness grade was 2 (mild to moderate). Median shoulder abduction angles were 42° in affected shoulder and 28° in contralateral shoulder, with a median difference of 14°, ranging from 11 to 26°. The shoulder abduction angle test (threshold > 40°) showed 100% sensitivity (95% CI: 80.5 to 100%) for MSI detection, whereas the sensitivity of MRI examination (medial compartment pathology) was 23.5% (95% CI: 6.8 to 49.9%). Conclusion and clinical relevance: Bilateral shoulder abduction angle measurement is a practical, noninvasive, and apparently effective diagnostic tool for MSI that outperformed MRI with regard to diagnostic sensitivity in the study sample. Given the cost of MRI and need for anesthesia, shoulder abduction angle measurement may be preferable in clinical settings. Moreover, in cases of unilateral shoulder lameness, a difference > 10° in the abduction angles between the affected and contralateral "healthy" shoulders might be a simple, accessible indicator of MSI.