Comparative evaluation of radiographic and computed tomographic findings in dogs with bilateral medial coronoid disease (MCD) presenting with unilateral forelimb lameness

**Background:** Medial coronoid disease (MCD) is the most common manifestation of elbow dysplasia in medium to large breed dogs, frequently presenting with forelimb lameness. However, up to 50% of dogs with CT-confirmed MCD abnormalities may show no clinical lameness. The factors explaining why some affected elbows become symptomatic while others remain clinically silent are poorly understood. This study aimed to identify radiographic and CT differences between lame and non-lame limbs in dogs with bilateral MCD and unilateral lameness.

**Methods:** Medical records from the Small Animal Teaching Hospital at the University of Veterinary Medicine Hannover (February 2014–April 2019) were retrospectively reviewed. Forty-two dogs (84 elbow joints) with bilateral MCD confirmed by CT and unilateral forelimb lameness met inclusion criteria. Dogs with concurrent elbow pathology (ununited anconeal process, OCD, flexor tendon enthesiopathy) were excluded. Radiographs (mediolateral flexed and craniocaudal views) were scored using a modified IEWG system (0–3 based on osteophyte size) and trochlear notch sclerosis (TNS) ratio was calculated. CT imaging (Philips brilliance 64 slice scanner, 1mm slice thickness) evaluated pathology type, fragment type, shape, dislocation, and fragment size (cm²). Statistical analysis used t-tests, Wilcoxon rank sum tests, Kruskal-Wallis tests, and χ² independence tests as appropriate, with p<0.05 considered significant.

**Key Results:** The study population included 42 dogs (21 males, 9 neutered males, 8 females, 4 neutered females; median age 36.7 months, SD 31.3; median weight 33.6 kg, SD 10.5). Radiographically, the modified IEWG score was higher in group II (lame limb) than group I (non-lame limb) in 31% of cases. Group I had IEWG 0 in 57.1% and IEWG 1 in 33.3%; group II had IEWG 0 in 52.4% and IEWG 1 in 23.8%. Group II had IEWG score 2 almost twice as often and IEWG score 3 almost three times as often as group I. TNS ratio showed no significant difference (group I mean 0.460 vs. group II mean 0.481; p=0.072). On CT, single fragment was the most common pathology in both groups (69% group I, 73.8% group II). Fissures were more common in group I (21.4% vs. 4.8%), while multiple fragments were more common in group II (19% vs. 4.8%). Tip fragment/fissure was dominant in group I (66.7%), while group II showed a more even distribution (radial incisure fragment/fissure 38.1%, tip fragment/fissure 38.1%, combination 23.8%; p=0.019). Fragment dislocation was significantly more frequent in group II (59.5% vs. 19%; p<0.001). Fragment size was nearly twice as large in group II (median 0.16 cm², mean 0.202 cm², SD 0.134) compared to group I (median 0.09 cm², mean 0.112 cm², SD 0.106; p=0.001). Larger fragments were significantly more likely to dislocate (p=0.001).

**Clinical Implications:** This study provides evidence that fragment size and dislocation are key factors differentiating clinically symptomatic from asymptomatic elbows in dogs with bilateral MCD. The finding that larger fragments are more likely to dislocate and are associated with lameness suggests that CT assessment of fragment characteristics should inform clinical decision-making. However, the modified IEWG score and TNS ratio were less discriminative. The authors note that a definitive treatment decision tree could not be established, and that individual patient assessment remains essential. Limitations include the lack of arthroscopic correlation, absence of objective gait analysis (ground reaction forces), and the non-loaded nature of CT imaging which may affect assessment of radioulnar incongruence. The study reinforces the complexity of MCD and the need for further research to guide therapy.