Kinematic alignment in total knee arthroplasty.

Abstract

The objective of kinematic alignment in total knee arthroplasty is to implant the prosthesis according to the individual joint line, leg axis and ligament tension. Knee osteoarthritis with failure of nonsurgical treatment according to current guidelines. Severe deformity or instability requiring aconstrained knee prosthesis. Necessity of intramedullary stems. Medial parapatellar approach to the knee. Resection of the cruciate ligaments, the meniscus and the osteophytes. Femur-first technique with distal resection of the femur, the intramedullary guide is only used for the extension/flexion positioning of the femoral component. The positioning in varus-valgus is orientated according to the native joint line after correction of chondral wear. The distal resection should be equal to the thickness of the prosthesis considering the chondral wear (up to 2 mm) and the thickness of the saw blade (1 mm). The rotation of the femoral component is set according to the posterior condylar axis under consideration of chondral wear. The amount of resected dorsal bone should correspond to the thickness of the dorsal condyles of the prosthesis. The alignment of the tibia is parallel to the individual joint line. This enables reconstruction of the individual physiological slope, rotation and the varus-valgus axis. Extension and flexion gap are controlled. Asymmetries between the lateral and medial joint space are corrected through avarus or valgus recut of the tibia as long as the surgical planning has not been achieved. The hip-knee angle is controlled; however, the aim in kinematic alignment is to reconstruct the individual axes and ligament tensions and not astraight leg axis. Persisting asymmetries in ligament tension are adjusted by classical soft tissue balancing techniques. Differences between the extension and flexion spaces are corrected by adapting the tibial slope. Release of the ligaments is usually not necessary; sometimes astripping of the dorsal capsule is performed. After the trial implantation, the original prosthesis is implanted. Functional rehabilitation with weight bearing as tolerated. Randomized studies showed abetter function in the Knee Society Score and abetter range of motion with kinematically aligned prostheses compared to mechanical alignment. Available meta-analyses also showed better results for kinematically aligned knees. The first mid-term results of this new technique with afollow-up of 10years show asurvival rate of 97.5% of the prosthesis.