The combined anterior cruciate and medial collateral ligament replacement by various materials: a comparative animal study.

On 30 sheep, a combined replacement of the anterior cruciate and medial collateral ligament of the right knee was performed with four different materials. Dacron prostheses and glutaraldehyde-preserved bovine tendon prostheses as well as braided ligament prostheses made of carbon fibers and braided resorbable polydioxanone fibers surrounded by lyophilized dura in their intra-articular part were used. Ten unoperated sheep served as a control group. After 1 year the animals were sacrificed and the knee joints were explanted and biomechanically as well as histomorphologically investigated. The gross inspection of the joints showed no ruptured medial collateral ligament replacement but did show partially and totally ruptured anterior cruciate ligament replacements. The Dacron prosthesis was broken in 50% of the cases, whereas for the other materials one ruptured ligament replacement each (12.5%) could be observed. The anterior drawer test and the determination of the tensile stiffness of the remaining ligament replacements revealed that none of the operated knees achieved the properties of the normal control knees. However, the carbon fiber implants had the best result of all prostheses tested. For all materials except the resorbable polydioxanone, abrasion particles could be found in the anterior cruciate ligament and in the synovial membrane. The tissue reaction to these particles was a mild synovitis for carbon fragments, a strong synovitis for Dacron particles, and a chronic inflammatory response to bovine tendon fragments with macrophage granulomas and fibrosis.