[What is the influence of the approach to intraoperative measurement of the knee joint on total knee arthroplasty? A navigation-controlled study on a cadaver knee].

Correct postoperative leg alignment and stability of the total knee prosthesis over the full range of movement is one critical factor for successful TKA. The anatomic approach is still the subject of controversy. The aim of our study was to elucidate the influence of the surgical approach on the ligament balancing and the anterioposterior limb axis.On five cadaver knees we studied the influence of the subvastus, midvastus, medial parapatellar, rectus snip, and tuberosity osteotomy approaches on the anterioposterior leg axis in extension and the rotation of the femoral component in flexion. Measurements were performed and documented by CT-free Ci-Navigation-System. Ligament tension was measured with a tensor device. We found that the subvastus approach leads to less widening of the medial compartment than all other approaches in extension. In 90 degrees flexion we found a similar influence. The consecutive release from subvastus to midvastus to medial parapatellar approach leads to a further opening of 0.5-1 degrees valgus in extension as well as in flexion. An everted patella amplifies this influence. The surgeon has to be aware of the impact on the ligament situation in regard to the anatomic approach when ligament balancing and soft tissue releases are carried out. Patella eversion should be avoided when managing soft tissues.