Tibial displacement with stifle joint flexion and cranial cruciate ligament transection in the dog. An ex vivo study using a robotic simulator.

Objective: The aim of this study was to investigate the biomechanical effects of cranial cruciate ligament (CrCL) transection on stifle stability at three different stifle joint flexion angles using a robotic system. Methods: This was an ex vivo biomechanical study. Stifles (n = 6) were collected from the cadavers of Beagles weighing 10.5-12.0 kg. Six stifle joints were dissected, potted, and secured to the manipulator arms of a robotic simulator. With the stifle joint angle maintained at either hyperextension (151°), 135° or 90°, stability was assessed by application of a 50 N load in either the cranial-caudal (CrCd test) or proximal-distal (PD test) directions. The stifle was given a cranial-caudal load of 50 N (CrCd test). A proximal-distal compression load of 50 N was then administered by the manipulator (proximal-distal test: PD test). The change in three-dimensional kinematics of the intact and the CrCL-transected stifles was compared between hyperextension, and 135° and 90° flexion for the CrCd and PD load conditions. A value of p <0.05 was considered statistically significant. Results: The cranial tibial displacements in the PD tests of the CrCL-transected stifles at 135° (8.4 ± 1.2 mm) and at 90° (8.1 ± 1.9 mm) were significantly greater than the displacement at 151.5° (5.1 ± 1.6 mm) (p = 0.004 and p = 0.012 respectively). Clinical significance: The canine stifle exhibited the most instability when the stifle flexion angle was 135°.