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

Abstract 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 &lt; .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 &lt; .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.