Obtaining satisfactory stability in the coronal plane is critical for the long-term success of TKA and requires precise rotational alignment of the femoral component. Malrotation of the femoral component has been associated with numerous undesirable conditions including patellofemoral and tibiofemoral instability, arthrofibrosis, knee pain, and disturbed knee kinematics [8–10]. Many utilize a measured resection technique to search correct femoral component rotation and subsequent coronal plane stability. There are two methods for osteotomy of posterior femoral condyle in flexion gap during total knee arthroplasty: gap balance and osteotomy measurement . The measurement of osteotomy is usually performed by osteotomy of the posterior femoral condyle based on 3°external rotation on the coronal plane of the distal femur (Fig. 3), but there is a large individual difference in the rotation angle [12–14]. In the measurement of osteotomy, there are also osteotomy methods marked by intraoperative surgical touch of the femoral epicondylar axis. However, not a few literatures reported that the internal epicondylar groove can only be identified in some patients, and the occurrence rate of patients with severe osteoarthritis is less, and the accuracy of intraoperative positioning of the transfemoral epicondylar axis is poor. As a result, the accuracy of intraoperative osteotomy mostly depends on the experience of the operator . Intraoperatively, it is often the case that accurate distal femur osteotomy is difficult due to the formation of an uneasily adjusted flexion gap. As our recommendation, this new osteotomy position measurement avoids an imbalance of the flexion and extension by measuring the accurate osteotomy gap at the distal femur.
Many studies[15-18 ]have reported the "osteotomy gap measurement technique" used in TKA procedures. It is generally believed in the orthopedic community that TKA surgery should be aimed at obtaining the same rectangular gap in knee flexion and extension, and achieving soft tissue balance before osteotomy is the optimized choice for the best surgical results. However, traditional operation techniques rely on soft tissue balance to achieve gap balance after osteotomy. During the operation, the osteotomy is completed by referring to the anatomical landmarks; once the gap is found to be unbalanced, the soft tissue release is continued, that is, first osteotomy and then release. Since the loosening of soft tissue increases the flexion gap and the extension gap by different amounts, it is difficult to achieve an accurate balance between the flexion gap and the extension gap at the same time. It is based on this that we introduced and used the self-made measurement module to accurately measure the flexion-extension gap before osteotomy in TKA procedures. The advantage of the new measurement of osteotomy location was the ability to measure the flexion gap before osteotomy of the distal femur, and the amount of osteotomy was determined according to the individual differences of patients during TKA.
We believe that the poor rotation axis of prosthesis by osteotomy is related to the individual difference of posterior condyle angle in the population. Therefore, the rotation angle of the osteotomy plate should take into account the individual differences of the femur. During TKA, equal rectangular space should be obtained when the knee joint is extended and flexed. Release the medial ligament in patients with varus and release the lateral ligament in patients with ectropion. The goal is to obtain the same rectangular gap regardless of the osteotomy method. The new technique uses the self-made gap gasket to measure the flexion gap before osteotomy of femur, so that the imbalance of postoperative space was avoided. The orthopedist can adjust the position of the osteotomy plate to improve the balance of extension and flexion gap according to the gap measured by the self-made gasket. However, the defect of this technique is the lack of observation of curative effect of large sample randomized controlled trial.