Clinical evaluation of the spacer technique in cruciate-retaining total knee arthroplasty: secondary analysis of a study terminated early for safety reasons

During cruciate-retaining total knee arthroplasty (CR-TKA) the contact point (CP) of the femur on the tibia is determined by balancing the posterior cruciate ligament (PCL). This can be done with the spacer technique. The aim of this secondary analysis was to analyze the position, of the medial and lateral CP in CR-TKA and to assess the association of CP with clinical outcome. 23 patients received CR-TKA with intraoperative PCL balancing performed with the spacer technique. At 3, 12, and 24 months postoperative, a pair of standing radiographs was made of the flexed knee using a radiostereometric analysis (RSA) setup. The 3D positions of femur and tibia components were used to calculate the medial and lateral CPs, defined as the point with the smallest distance between femoral condyle and tibia plateau. Positions of CPs and tibial slope were compared between patients with/without flexion limitation. Patients with flexion limitation (n=6) showed a more posterior medial CP and higher tibial slope, compared with patients with no flexion complaints (p=0.022, and p=0.027, respectively). Besides less flexion, patients with flexion limitation reported more pain, less function and less satisfaction. The medial CP seems to relate to clinical outcome; patients with flexion limitation had a more posterior medial CP. This might be an indication for a too tightly balanced PCL, resulting from a suboptimally functioning spacer technique for this implant.