Internal bracing with an artificial ligament for superficial medial collateral ligament injury impairs the mechanical property of repaired native ligament: A porcine study.

Abstract

Superficial medial collateral ligament (sMCL) injury is common, but there are no in vivo studies describing the biomechanical efficacy of anatomic repair with internal bracing for grade 3 injuries. We used a porcine model to evaluate the efficacy of internal bracing using an artificial ligament for the early repair of acute, grade 3 sMCL injuries. Sixteen male castrated pigs were randomly assigned to a repair group: (1) anatomic repair using two suture anchors (Group R; n = 9) or (2) anatomic repair with internal bracing augmentation (Group IB; n = 7). The left knees were allocated to a sham surgery group (Group S; n = 16). All animals were sacrificed 4 weeks after surgery. The right and left femur-sMCL-tibia complexes were mounted on a tensile tester and stretched to failure using the same conditions as preconditioning at a cross-head speed of 50 mm/min. The internal bracing in Group IB was removed prior to the biomechanical testing. The failure mode and structural properties (upper yield load, maximum load, linear stiffness, and elongation at failure) were determined. Significant differences in failure mode were observed among the three groups. All sMCLs repaired with just the suture anchors (Group R) were avulsed from the femoral attachment, while most of the sMCLs repaired with internal bracing augmentation (Group IB) exhibited mid-substance tears (Group R vs Group IB, P = 0.0023). In Group S, 14 sMCLs were avulsed from the femoral attachment and two were avulsed from the tibial attachment (Group IB vs Group S, P < 0.001). No significant difference was observed between Group R and Group S. There were no significant differences in the upper yield load, maximum load, linear stiffness, or elongation at failure among the groups. Loading of an artificial ligament for internal bracing did not result in better structural properties of the repaired sMCL itself.