Biological response to a new composite polymer augmentation device used for cruciate ligament reconstruction.

A resorbable composite augmentation cord braided of poly(L-lactide) and poly(L-lactide-co-glycolide) fibers was designed for the temporary protection of repaired cruciate ligaments. This study examined the biocompatibility of the new device and the influence of augmentation duration on ligament healing in a sheep model. The anterior cruciate ligament (ACL) was cut close to the femoral insertion and reinserted with sutures. The repaired ACLs were augmented with the slowly degrading new composite cord and alternatively with a faster degrading polydioxanone cord (PDS). A tendon graft group (gold standard) served as control. Histological evaluation and biomechanical testing were performed after 6 months. The composite cord showed no signs of degradation, whereas the PDS was intra-articularly resorbed. Both devices showed only minor foreign body reactions, proving their good biocompatibility. However, 9 of 11 composite cords had ruptured too early because of fatigue at the bone tunnel entrances. All operated knees were less stable than the nonoperated collateral joints. Knees equipped with the composite cord showed the largest anterior instabilities, whereas the PDS-augmented group exhibited in some cases knee instabilities comparable with that of the tendon group. A positive effect of a longer mechanical protection by a slowly degrading augmentation could not yet be shown. The fatigue strength of the device still needs improvement.

Biocompatibility and functionality of the degradable polymer alkylene bis(dilactoyl)-methacrylate for screw augmentation in vivo.

Recently, a new degradable polymer has been developed on the basis of alkylene bis(dilactoyl)-methacrylate as an alternative material for screw augmentation. The polymer has been investigated in vitro and in a short-term experiment in rabbits exhibiting promising results. The aim of the present study was to investigate its long-term biocompatibility and mechanical functionality in a large animal model. The polymer was used for screw augmentation in the cancellous bone of the femoral condyle and tibia epiphysis of 12 sheep and was compared to polymethylmethacrylate (PMMA) augmented and nonaugmented screws. After an implantation period of 6 months, bone, regional lymph nodes, and several organs were histologically evaluated. The mechanical efficacy was investigated by a biomechanical pullout test. A lot of mononuclear macrophages and multinuclear foreign body giant cells with incorporated polymer particles indicate strong inflammatory reactions. Large osteolysis zones with osteoclasts were found in the surrounding polymer. The polymer was fragmented but not substantially degraded. Polymer particles were also found in the regional lymph nodes. Lung, liver, kidney, and spleen did not show any pathological signs. The pullout force of screws augmented with the new polymer was significantly reduced in comparison to PMMA augmented and nonaugmented screws, respectively. It was concluded that the material has poor biocompatibility and cannot be recommended for clinical application as screw augmentation material.