Comparative investigation on the biomechanical properties of ligament replacement in the sheep knee using six different ligament prostheses

Six different ligament prostheses were implanted in 40 sheep to replace the anterior cruciate and medial collateral ligament of the right knee. After one year the explanted knee joints were tested for stability by measurement of the anterior drawer. Tensile tests on the ligament replacements were performed to determine the stiffness and rupture force of the replacement. Gross inspection of the knee joint showed abrasion and partial ruptures for all types of prostheses after one year. Depending on the type of prosthesis total rupture rates between 0 and 66% of all implants could be seen. The anterior drawer for the operated knee was 3–4 times higher than for the non-operated contralateral side. Neither the stiffness nor the rupture strength of the replacements reached the biomechanical properties of the normal ligaments.