RA knees with severe flexion contracture usually present with posterior subluxation of the tibia, proximal tibial bone deficiency combined with valgus deformity, and external rotation of the tibia, which can be partially attributed to the contracture and the traction of the biceps muscle and iliotibial tract . The involvement of the periarticular soft tissues is part of the constellation of pathology in rheumatoid arthritis. Hence, it is critical to achieve correction of deformity, equalize the medial and lateral soft tissue tension, and implant the components accurately. Appropriate soft tissue balancing in the form of ligament and capsular release at the time of arthroplasty is essential to the success of the procedure [21, 22]. As to the remaining some flexion in operation, it was especially important to properly position the individual components and the resulting overall alignment of the lower extremity in RA knee with one-stage TKA . In the present study, successful TKA was performed in not only in moderate flexion contracture patients but also in severe flexion deformity of RA patients, and all cases had good clinical results. Once the correct bony alignment is achieved, it is very important for the success of TKA that the medial and lateral joint laxity does not exceed more than 2 mm in the stress test (varus and valgus stress testing) when prostheses are implanted.
Although TKA can be performed in this challenging patients [4, 5], complete intraoperative correction of severe flexion deformity presented a challenging situation for orthopedic surgeons [4, 6]. Various techniques of addressing these deformities have been described including additional bony resection, ligamentous releases, and the use of increasing constraint prosthesis . However, an ideal soft tissue balance is difficult to obtain during surgery . Appropriate soft tissue balancing in the form of ligament and capsular release at the time of arthroplasty is essential to the success of TKA procedures, which not only achieves an obvious correction of the flexion contracture but also effectively improves the range of motion and the functional recovery of the knee joint after TKA [9, 20]. However, indications of orthopedic procedure on the flexion contracture were complex and required special consideration of the adequate collateral stability and extensive experience in TKA surgery [2, 24–26]. In our early experience on severe flexion contractures in two RA patients, instability was caused by a massive release of soft tissue during TKA procedure. Therefore, appropriate soft tissue balancing in the form of ligament and capsular release at the time of arthroplasty is essential to the success of TKA procedures in severe flexion contractures of RA patients.
Flexion contracture is a common deformity encountered during total knee arthroplasty, and severe fixed deformities require surgical correction with release of the contracted soft tissues and appropriate management of the femoral bone resection . Traditional methods for correcting a severe flexion deformity of the knee during total knee arthroplasty can often lead to the excessive release of the posterior capsule and medial or lateral collateral ligament . As many reports on flexion contracture management in the RA knee are available in the literature, the peroneal nerve palsy in TKA was concerned previously [2, 3]. Preoperative severe flexion contracture was assumed as the risk factor for the development of the nerve palsy after TKA [29, 30]. In TKA, complete intraoperative correction of severe flexion deformity is dangerous, which can cause complications such as the peroneal nerve palsy . At present study, the surgical decompression of peroneal nerve was not performed and the transient peroneal nerve palsy had recovered after conservative therapy. Thus, the good result should be due to the appropriate soft tissue balancing other than a massive release at the time of arthroplasty.
The success of TKA in severe flexion deformity of RA patients depends on many factors, including the preoperative condition of the joint, surgical technique, and postoperative rehabilitation [32–34]. Splints are good supportive devices in flexion patients. The experience of Sarokhan et al.  has shown that the use of preoperative and postoperative serial casts aids greatly in the correction of severe flexion deformity of the knee. The use of dynamic extension splinting at night is beneficial to improve flexion contractures in this case studies. Physiotherapy is another important component of flexion patients . In this study, splints are supportive devices in flexion patients until the some residual flexion contractures were totally corrected. Rand  reported that the most important complication affecting the results of total knee replacement in patients with RA is infection. Rates of infection have been reported to be approximately three times greater in patients with RA than in those with OA [36, 37].