Abstract
Objective
The goal of total knee arthroplasty (TKA) is to achieve a stable and well-aligned tibiofemoral and patello-femoral (PF) joint, aiming at long-term clinical patient satisfaction. The surgical principles of both cruciate retaining (CR) and posterior stabilized (PS) TKA are accurate osteotomy and proper soft tissue balancing. We have developed an offset-type tensor, and measured intra-operative soft tissue balance under more physiological joint conditions with femoral component in place and reduced PF joint.
In this study, we measured intra-operative soft tissue balance and assessed the early post-operative knee joint stability quantitatively, and compared these parameters between CR and PS TKA.
Material and Method
Seventy patients with varus osteoarthritis of the knee underwent TKAs (35 CR TKAs: CR and 35 PS TKAs: PS). Mean varus deformity in standing position was 9.8 degrees in CR, and 10.7 degrees in PS (p = 0.45). All TKAs were performed by a single surgeon with measured resection technique. The external rotation of posterior femoral condyle osteotomy was performed according to surgical epicondylar axis (SEA) in pre-operative CT. We measured intra-operative soft tissue balance using an offset-type tensor with 40 lbs of joint distraction force at 0, 10, 30, 45, 60, 90, 120 and 135 degrees of flexion. The joint component gap (mm) and varus angle (degrees) were measured at each flexion angle.
Four weeks after operation, we evaluated the knee stability at extension by varus and valgus stress radiography using Telos (10 kg) and at flexion by epicondylar view with 1.5 kg weight at the ankle. We measured joint separation distance at medial as medial joint looseness (MJL) and at lateral as lateral joint looseness (LJL). Joint looseness was defined as the average of MJL and LJL.
Intra-operative measurements and post-operative joint stabilities were compared between CR and PS using unpaired t-test.
Result
Joint gap kinematics was different between CR and PS (figure 1). Joint component gap in PS were significantly higher than CR from 30 to 120 degrees of flexion.
Post-operative joint looseness were 2.7 mm and 3.7 mm at extension (p = 0.001, figure 2), and 1.1 mm and 1.9 mm at flexion (p = 0.021, figure 3) in CR and PS TKAs each respectively. At both extension and flexion, PS showed significantly higher joint looseness, especially with the higher MJL in PS comparing with CR.
Discussion
We found significant differences in gap kinematics and also in the early post-operative joint stability between CR and PS. In the PS TKAs, component gaps were significantly larger than those in CR TKAs at mid-flexion to deep flexion of the knee. These different characteristics of the intra-operative soft tissue balance would be a possible reason for the differences in the post-operative joint stability between CR and PS TKAs.
Our results suggested that TKAs performed by measured resection technique have significantly higher joint stability with CR than PS. These findings would be important issues in choosing prosthesis and operative technique.
Conclusion
With measured resection technique, CR TKAs had more consistent joint gap kinematics and higher joint stability after surgery comparing to PS TKAs.
