The role of muscle forces on rotational and cranio‐caudal stability in the intact and CCL ‐deficient stifle: An ex vivo biomechanical study

OBJECTIVE: To investigate the effects of muscle activation on internal tibial rotation and cranio-caudal translation (CCT) in intact and cranial cruciate ligament (CCL) deficient stifles. STUDY DESIGN: Ex vivo biomechanical study. ANIMALS: Eight cadaveric, nonpaired canine stifles. METHODS: Stifles were tested intact and after arthroscopic CCL transection. Quadriceps, biceps femoris, and gastrocnemius forces were simulated with pneumatic actuators in single or cocontraction muscle activation (0%-100% bodyweight [BW]). The tibia was mounted to a linear-torsional tester; the femur to a six-degrees-of freedom fixture. Internal tibial rotation (5 Nm torque) and CCT (30% BW cranial and caudal translation) were recorded via motion tracking system. RESULTS: Without muscle activation, CCL transection increased internal tibial rotation (34.8 ± 11.8° CCL-deficient vs. 27.9 ± 10.8° intact; p = .041). Across 0%-100% BW activation, internal rotation decreased in both conditions, to 4.3 ± 2.3° (intact; p < .0001 vs. 0% BW) and 2.8 ± 1.3° (CCL-deficient; p = .001 vs. 0% BW) at 100% BW. At 100% BW, biceps femoris reduced internal rotation more than quadriceps and gastrocnemius in both CCL conditions. Muscle activation reduced CCT in CCL-deficient stifles; however, at 100% BW, CCT was 19.1 mm in CCL-deficient versus 2.8 mm in intact (+582%; p < .0001). CONCLUSION: Periarticular muscle activation mitigates axial plane rotational laxity but does not prevent CCT. CLINICAL SIGNIFICANCE: Targeted muscle strengthening may help manage rotational laxity; however, surgical stabilization remains necessary to address CCT after CCL rupture. Internal tibial rotation may require additional surgical stabilization in selected cases.