Introduction: This ex vivo study evaluated the effects of sequential cranial cruciate ligament transection (CCLx), medial meniscal release (MMR) and CORA-based leveling osteotomy (CBLO) on canine stifle stability compared to intact status, and assessed the effect of stifle flexor loading on joint subluxation.

Materials and Methods: Seven left hind limb preparations were instrumented for constant quadriceps and gastrocnemius loads (15 kg and 5 kg, respectively) and an optional stifle flexor load (SFL) of 3 kg. Constructs were moved from full flexion to extension under fluoroscopic recording for intact, CCLx, MMR and CBLO situations, both with and without stifle flexor loading. Fluoroscopic landmarks were used to calculate tibial subluxation.

Results: With zero SFL, MMR caused more pronounced tibial subluxation compared to intact than CCLx alone at joint angles over 50°. CBLO restored stifle stability after MMR up to a joint angle of 115°. With a 3 kg SFL, tibial subluxation did not become significant until joint angles of 125° (CCLx) and 115° (MMR), while CBLO stifles remained stable throughout. Tibial subluxation differed significantly with SFL for CCLx and MMR across almost the full range of joint angles, whereas CBLO differed significantly only from 80°-145°.

Discussion/Conclusion: CBLO appears effective in eliminating cranial tibial subluxation until 140° in this model, with late subluxation possibly consistent with stated procedure aims. Simulated stifle flexor loading dramatically improved joint stability across a wide range of joint angles: delayed or inconsistent muscle activation might play a role in persistent instability in vivo noted in previous case studies.