Changes in Femoral Posterior Condylar Offset, Tibial Posterior Slope Angle, and Joint Line Height after Cruciate-Retaining Total Knee Arthroplasty

PURPOSE: Changes in the femoral posterior condylar offset (PCO), tibial posterior slope angle (PSA), and joint line height (JLH) after cruciate-retaining total knee arthroplasty (CR-TKA) were evaluated to determine their influence on the flexion angle. MATERIALS AND METHODS: A total of 125 CR-TKAs performed on 110 patients were retrospectively reviewed. Pre- and postoperative PCO, PSA, and JLH were compared using correlation analysis. Independent factors affecting the postoperative flexion angle of the knee were analyzed. RESULTS: The PCO was 28.2+/-2.0 mm (range, 24.5 to 33.1 mm) preoperatively and 26.7+/-1.8 mm (range, 22.2 to 31.2 mm) postoperatively (r=0.807, p0.291). CONCLUSIONS: Although the PCO and JLH did not change significantly after CR-TKA, the PSA decreased by 5.5degrees with a small range of variation. Restoration of the PCO and JLH could promote optimization of knee flexion in spite of the decreased PSA after CR-TKA.

The Effect of Tibial Posterior Slope on Contact Force and Ligaments Stresses in Posterior-Stabilized Total Knee Arthroplasty-Explicit Finite Element Analysis

PURPOSE: The purpose of this study is to evaluate the effect of change in tibial posterior slope on contact force and ligament stress using finite element analysis. MATERIALS AND METHODS: A 3-dimensional finite element model for total knee arthroplasty was developed by using a computed tomography scan. For validation, the tibial translations were compared with previous studies. The finite element analysis was conducted under the standard gait cycle, and contact force on ultra-high molecular weight polyethylene (UHMWPE) and stresses on lateral and medial collateral ligaments were evaluated. RESULTS: The tibial translations showed similarity with previous studies. As the tibial posterior slope angle increases, the contact stress area increased and was well distributed, and the contact force on UHMWPE decreased overall. However, the maximum contact force in the case for 10degrees case was greater than those for others. The stresses on ligaments were the greatest and smallest in 0degrees and 10degrees cases, respectively. CONCLUSIONS: The higher tibial posterior slope angle leads to the lower contact stress and more extensive stress distribution overall in posterior-stabilized total knee arthroscopy. However, it does not absolutely mean the smallest contact force. The stresses on ligaments increased with respect to the smaller tibial posterior slope angle.

Relationship Between ground Surface and Tibial Posterior Slope at Erect Posture in Total Knee Arthroplasty

PURPOSE: To evaluate the perioperative changes of the relationship between tibial posterior slope and ground surface and the factors which influence the perioperative changes of the relationship between tibial posterior slope and ground surface following total knee arthroplasty. MATERIALS AND METHODS: Between Sept. 2005 and Feb. 2006, 94 consecutive primary total knee arthroplasty with posterior cruciate ligament-retaining type performed in 50 patients by one surgeon. Posterior slope of the proximal tibia resection in extramedullary guide was fixed at 5degrees. All the retrieved patients wore a 90degrees ankle brace and stood on the ground during radiographic examination. We prospectively analyzed the measurement of tibial posterior slope angle, the angle between tibial posterior slope and ground surface and the angle between a midline from 1st metatarsal shaft to talus and ground surface on preoperative and postoperative 2-weeks radiographs. RESULTS: On preoperative radiograph, average of tibial posterior slope angle is 11.3degrees and 11.5degrees in right and left knee, respectively. Angle between tibial posterior slope and ground surface is an average of 8.8degrees and 9.5degrees in right and left knee, respectively. On postoperative 2-weeks radiograph, tibial posterior slope angle is an average of 9.3degrees and 9.1degrees in right and left knee, respectively. Angle between tibial posterior slope and ground surface is an average of 6.2degrees and 6.4degrees in right and left knee. There are significant differences between tibial posterior slope angle and the angle between tibial posterior slope and ground surface on preoperative and postoperative 2-weeks radiograph (p<0.05). CONCLUSION: According to ankle lateral angle, it is possible that tibial posterior slope associated with the ground surface may decrease at erect posture in total knee arthroplasty. This may lead to overly decrease tibial posterior slope associated with the ground surface at comfortable erect posture in total knee arthroplasty.