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INTRODUCTION: To determine stifle joint stability following centre of rotation of angulation-based levelling osteotomy (CBLO) of stifles with transected cranial cruciate ligament (CCL) in a novel limb press model.MATERIALS & METHODS: Ten feline hindlimbs were prepared by coxofemoral disarticulation. Quadriceps and gastrocnemius muscles were replaced with turnbuckles in series with load cells. Limbs were mounted in a frame and axially loaded with 30% body weight, and turnbuckles adjusted aiming for a femoral angle of 60° ±2°, and stifle and tibiotarsal angles of 120° ±5°. Limbs were radiographed and contemporaneous load cell measurements taken. This was repeated after CCL transection and again after CBLO to a target tibial plateau angle of 10°. Angles, quadriceps:gastrocnemius force ratios and cranial tibial subluxation were analysed using repeated-measures ANOVA. RESULTS: Cranial tibial subluxation was observed after both CCL transection and CBLO: both were significant compared to the intact joint (p<0.001, 7.1 mm ± 1.2 mm, and p<.001, 6.1 mm ±1.3 mm, respectively). Stability situation did not affect either limb angulation (p>0.4) or force ratios (p=0.2). Mean quadriceps:gastrocnemius force ratio was 2.0 ±0.3. CBLO reduced mean tibial plateau angle from 23.8° to 9.4°.DISCUSSION/CONCLUSION: CBLO failed to restore stifle joint stability despite relatively realistic simulated force ratios.The model has some inadequacies (only two muscles, incorrect muscle force ratios), biomechanical features (muscle-joint lever arms, force orientation), or anatomical differences from the dog (tibial plateau topography). Positioning was repeatable and consistent, and muscle forces were more consistent with in vivo reports than previous feline limb press models.ACKNOWLEDGEMENTS: Institutional funding was received. The authors declare no conflict of interest.

INTRODUCTION: Current feline limb press models have indicated poor ex vivo stability for tibial tuberosity advancement and tibial plateau leveling osteotomy despite promising clinical reports, and good ex vivo stability in canine models. We questioned whether model validity rather than species differences might be an explanation.MATERIALS & METHODS: A custom limb press was constructed to test cadaver hind limbs under three conditions: intact hip joint (IHJ, n=8), fixed femur (FF, n=8), and extension-flexion femur (EFF, n=12). Limbs were prepared by hemipelvectomy or coxofemoral disarticulation, extraneous soft tissues were removed, and quadriceps and gastrocnemius muscles simulated using turnbuckles and load cells in series, attached using bone tunnels and screws. Turnbuckles were adjusted to set femoral angle to 60±2°, and stifle and tarsal angles to 120±5° under an axial load of 30% body weight. Load cell forces were recorded, normalized to body weight and force ratios calculated.RESULTS: Normalized gastrocnemius forces (N/N) were 0.79±0.10, 1.11±0.48 and 0.7±0.12 for IHJ, FF and EFF respectively: normalized quadriceps forces (N/N) were 1.80±0.16, 0.90±0.55 and 1.50±0.23. Only quadriceps load varied significantly between models (Welch P=.001, ω_p^2=0.495). Mean quadriceps:gastrocnemius (Q:G) ratios were 2.3±0.4, 1.2±1.2 and 2.1±0.3 for the three models.DISCUSSION/CONCLUSION: The FF model produced highly variable loads and Q:G force ratios: the majority of Q:G ratios were <1 and consistent with relative gastrocnemius overload. In contrast, IHJ and EFF models produced consistent Q:G force ratios which better approximate literature values in vivo. Earlier stability results using the FF model may be incorrect due to construct invalidity.ACKNOWLEDGEMENTS: No conflict of interest is declared. Departmental financial support was received.