Abstract
INTRODUCTION:
In varus knee, posterior cruciate ligament (PCL) release has been reported to result in the increase of the flexion gap without significant effect on the extension gap. However, the effect of release on gap angle is still obscure. On the other hand, gap angle and distance measured with the tension devices may vary due to different distraction forces. In this study, difference of gap angle and distance before and after PCL resection in knee extension and 90° flexion was inspected. Effect of different distraction force on gap was also assessed.
OBJECTIVES:
Fifty cases with medial osteoarthritis undergoing PS-TKA were included in the study. PCL of all the cases were identified intact before resection.
METHODS:
After distal femoral and proximal tibial cuts were initially performed and anterior cruciate ligament (ACL) was excised, joint gap angle and distance in full extension and at 90° flexion were obtained by means of a tensioning device, Balancer under 10, 20 and 30 inch-pounds distraction. The gap angle and distance were measured 3 times at each step. Then PCL was excised and the same measurement was performed.
RESULTS:
The gap distances significantly enlarged following the increased distraction forces in both knee extension and 90° flexion, before and after the PCL resection (p < 0.0001). The distances were the same before and after the PCL resection in extension under each force. However, after the PCL was resected, the joint distance at 90° flexion significantly enlarged at 10, 20 and 30 inch-pounds for 1.2, 1.6 and 1.8 mm, respectively (p < 0.001). All measured joint gap angles showed varus results. The gap angles significantly increased following the increased distraction forces in both knee extension and 90° flexion, before and after the PCL resection (p < 0.0001). The mean gap angles in extension were 1.9°, 2.9° and 3.6° for 10, 20 and 30 inch-pounds, respectively. The angles significantly decreased after PCL resection in extension at different forces for 0.6°, 0.4° and 0.3°, respectively (p < 0.05). In 90° flexion, the mean angles were 2.9°, 5.5° and 7.3°, respectively, and were decreased after the resection for 0.3° (p = 0.9), 0.6° (p = 0.01) and 1.1° (p = 0.00024)
CONCLUSION:
In this study, all the distances and angles had a correlation with the distraction powers of the tensioner. For the joint gap distance, the distance in extension was not influenced by the release of the PCL, but was enlarged at 90° flexion after the release. We found that the varus gap angles were decreased at both extension and flexion. Thirty inch-pounds seem to have more effect on the gap angle than 20 inch-pounds at 90° flexion after the release. It indicated that the evaluation of the joint gap might not be accurate if the distraction power of the tension device is not appropriate. Our study indicated that in varus deformity osteoarthritic knees, PCL resection may have influence on the correction of deformity. The means of modified gap control method and measured bone resection method, and the character of joint gap in CR, CS or PS TKA should be considered independently.
