Biomechanical cyclic loading test of a synthetic ligament fixation system used for intra-articular stabilization of deficient canine stifles

Abstract

Background: Cranial cruciate ligament rupture (CCLr) is the most common cause of hindlimb lameness in dogs. Currently, surgical management of CCLr is mostly performed using tibial osteotomy techniques to modify the biomechanical conformation of the affected stifle. These surgical techniques have a significant complication rate, associated with persistent instability of the stifle which may lead to chronic postoperative pain. Over the last decade, studies have been published on various techniques of anatomical CCL reconstruction in veterinary practice, using physiological autografts or woven synthetic implants. Aim: The aim of this ex vivo biomechanical study is to investigate the ex vivo dynamic biomechanical behavior of a synthetic implant (ultra-high molecular weight polyethylene implant) fixed with interference screws for the treatment of cranial cruciate ligament rupture in dogs, according to a fatigue protocol (48h per test). Methods: Seven stifles from four skeletally mature canine cadavers were implanted with the synthetic implant. It was fixed with four interference screws inserted in transversal and oblique tunnels in both the distal femur and the proximal tibia. For each case, 100 000 cycles were performed at 0.58Hz, with traction loads ranging from 100N to 210N. Results: Neither screw-bone assembly rupture nor a pull-out issue were observed during the dynamic tests. The linear stiffness of the implants associated with a fixation system with four interference screws increased over time. The final displacement did not exceed 3mm for five of the seven specimens. Five of the seven synthetic implants yielded to a lengthening in functional range [0: 3 mm]. Linear stiffness was homogeneous among samples, showing a strong dynamic strength of the interference screw-based fixations of the UHMWPE implant in the femoral and tibial bones. Conclusion: This study completes the existing literature on the biomechanical evaluation of passive stifle stabilization techniques with a testing protocol focused on cyclic loading at a given force level instead of driven by displacement. These biomechanical results should revive interest in intra-articular reconstruction after rupture of the cranial cruciate ligament in dogs.