Comparative evaluation of posterior cruciate ligament in total knee arthroplasty

It has been realized that for osteoarthritis (OA) knee with varus deformity, posterior cruciate ligament (PCL) release resulted in the increase of the flexion gap without significant effect on the extension gap. While the effect of release on gap angle is still obscure. On the other hand, gap distance and varus angle measured under different distraction forces suggest different patterns.

In the current study, mechanical gap balance in displacement and angular alternation of extension and flexion gaps will be evaluated, with PCL fully retained or resected under different distracting forces in varus knees.

Fifty cases with medial OA undergoing posterior-stabilized (PS) total knee arthroplasty (TKA) were included in the study. PCL of all the cases were identified intact before resection. After distal femoral and proximal tibial cuts were initially performed and anterior cruciate ligament was excised, joint gap angle and distance in full extension and at 90° flexion were obtained by means of a tensioning device with 10, 20 and 30 inch-pounds (in-lbf) of distraction force. The gap angle and distance were measured three times at each step. After the excision of PCL, the same measurement was performed.

Both the distance and the varus angles of the knee gap enlarged accordingly with the augment of distraction forces at both extension and flexion with or without PCL resection. As to the gap distance, it remained the same after PCL resection at extension; while at flexion, the gap distance significantly ( p < 0.001) enlarged - 1.2, 1.6 and 1.9 mm - under 10, 20 and 30 in-lbf, respectively, after PCL resection. As to the varus angles, it significantly ( p < .050) decreased 0.6°, 0.3° and 0.4° at extension; while at flexion, the varus angles decreased 0° (not significant), 0.6° ( p < 0.050) and 1.1° ( p < 0.001) with 10, 20 and 30 in-lbf, respectively, after PCL resection.

Our study indicated that the sacrifice of PCL will decrease the varus deformity at both extension and flexion, but with the exception under low distraction force at flexion. A proper distraction tension is of great importance in gap balancing during TKA. Sufficient attention of varus differences should be paid to the gap balance technique when choosing from different techniques, PCL-retained TKA or PCL-sacrificed TKA, as well as and an appropriate distract tension during measurement.