Size and position of a single condyle allograft influence knee kinematics

An optimal match for size and shape between the donor femur and the host kn ee is considered a critical factor influencing the outcome of a knee allogr aft implantation. An in vitro allograft model was developed to determine th e influence of the size and position of a lateral distal femoral condylar a llograft on knee kinematics. Functional knee motion was simulated in a cada ver host knee in the intact state after removing and reimplanting the nativ e lateral condyle of the distal femur and after serially replacing the nati ve condyle with eight donor allografts. Each allograft was first tested in an optimal position and subsequently shifted 3 mm proximal and 3 mm distal to the joint line to quantify changes in joint kinematics due to the positi on of the allograft. The intact knee and the knee with the ideally implante d native allograft followed similar kinematic trends. Decreasing the width of the allograft increased the valgus knee orientation at full flexion, tra nslated the tibia posteriorly at full extension, and externally rotated the tibia throughout knee flexion. The proximal shift in allograft position in creased the valgus orientation at full extension, translated the tibia post eriorly at mid-flexion, and externally rotated the tibia throughout flexion . The distal shift in position had the opposite effect on the kinematics of the proximal shift. These results indicate that improving techniques for p reoperative size-matching and intraoperative allograft placement may help t o reduce biomechanical complications following implantation of the allograf t.