2019 年 38 巻 4 号 p. 485-492
Objective: It is increasingly important to reproduce the patient's native joint line orientation when performing unicompartmental knee arthroplasty (UKA). Posterior tibial slope (PTS) also plays an important role in achieving excellent postoperative knee function. In preoperative planning, plain lateral radiographs have been used to evaluate native PTS (XP-PTS). However, it is unclear which part of the tibial articular surface the XP-PTS indicates, and it is not easy to accurately reproduce the intraoperative XP-PTS angle. The purpose of this study was to explore the useful intraoperative landmark for patient's native PTS during medial UKA.
Methods: Preoperative computed tomography (CT) data from 49 lower limbs of 40 Japanese patients who were to undergo scheduled medial UKA were used. Five PTS angles were obtained from different parts of the tibial surface; PTS in the center of the medial and lateral plateau, the inner one quarter of the medial plateau, and in the peri-medial and lateral tibial eminences, were measured using 3-dimensional preoperative planning software. Then, the XP-PTS angle was reconstructed from the same CT data and were measured and compared with those five PTS angles.
Results: The mean XP-PTS was 7.6°±3.0° (± SD). The PTS in the center of the medial and lateral plateaus were 8.9°±3.2° and 7.0°±2.8°, respectively. The PTS in the inner one quarter of the medial plateau was 7.6°±3.4°, and in the peri-medial and lateral tibial eminences were 9.9°±3.4° and 6.3°± 3.4°, respectively. The strongest positive correlation was observed between the XP-PTS and the PTS in the inner one quarter of the medial plateau (R＝0.78, P<0.001).
Conclusion: The PTS obtained from preoperative plain radiographs represented the PTS in the inner one quarter of the medial plateau. During operation, this part possibly be visible even before the femoral posterior resection by external rotation of the leg and removal of the medial meniscus. It can be an intraoperative landmark for native PTS during medial UKA.
