The most important finding of the present study is a new protocol for successfully treatment of severe flexion contractures (greater than 80°). To our knowledge, this is the first report of adult-onset Still’s disease with 90° knee flexion contracture. Our findings also suggest that residual flexion contracture following TKA should be corrected within a short time to obtain satisfactory clinical outcomes.
In contrast to our present case, other studies have reported that treatment of these patients leads to poor results following various soft tissue treatments. In a recent study, the iliotibial tract and biceps tendon were elongated by a Z-plasty procedure before performing TKA in a patient with a flexion contracture of 85°. However, on the 20th postoperative day, the tibia dislocated posteriorly. This may have occurred because the extension angle was achieved within a very short period [
6]. Another study indicated that severe flexion contracture greater than 90° could be treated with TKA, but that residual flexion contractures were observed postoperatively. The average residual flexion contracture was 7° after four years of follow-up [
5]. Those studies demonstrated that TKA should be performed before Z-plasty to avoid the development of serious complications in these patients. It is important to achieve full extension within a short time as residual flexion contracture will persist and pose a functional disability [
9].
TKA should be carefully performed in cases with 90° flexion contracture. All surgical techniques used during TKA to address preoperative flexion contracture were performed in the present case, including adequate bone resection, ligament releases, removal of posterior osteophytes, and posterior capsular releases [
3]. It is common to perform an additional resection of the distal femur when treating severe flexion contracture. One study showed that for every 10° of flexion contracture, 2 mm of additional bone resection would be needed [
10]. Therefore, a patient with an 80° flexion contracture would require 8 mm of distal bone resection. This is somewhat consistent with the current case, in which an additional 6 mm of bone was resected for the 90° flexion contracture. Some authors reported that a hinged implant may be necessary for preoperative flexion contractures greater than 30° [
3]. Our patient did not need a hinged implant that would result in a greater amount of bone removed than a posterior stabilized implant. Second, serial casting was used after surgery to treat the residual flexion contracture for four weeks. Serial casting has been shown to result in significant improvements in joint contracture in patients with hemophiliac arthropathy [
11]. In the current case, the goal of the serial casting after TKA was to achieve gradual and controlled extension as quickly as allowed, and then to maintain full extension for one to two weeks before removing the cast. These changes are thought to be the result of significant improvements in the tightening of the posterior capsule, the biceps femoris, the gatrocnemius muscles and tendons, as well as the collateral ligament [
11]. Although applying serial casting was somewhat time-consuming, its cost was comparatively low. Thermal injury should also be avoided when applying serial casting. Moreover, the casting should be done continuously for no more than five weeks to avoid the complication of knee stiffness [
12]. Various orthoses have been used in the past, including stretch splints to hold the joint in extension after TKA [
13,
14]. However, these splints can cost more than $2000 and require prolonged treatment (e.g., four to55 weeks) [
14]. In the current case, our patient achieved full extension in five weeks.