Posterior cruciate ligament removal contributes to abnormal knee motion during posterior stabilized total knee arthroplasty

Abstract

Abnormal anterior translation of the femur on the tibia has been observed in mid flexion (20-60 degrees ) following posterior stabilized total knee arthroplasty. The underlying biomechanical causes of this abnormal motion remain unknown. The purpose of this study was to isolate the effects of posterior cruciate ligament removal on knee motion after total knee arthroplasty. We posed two questions: Does removing the posterior cruciate ligament introduce abnormal anterior femoral translation? Does implanting a posterior stabilized prosthesis change the kinematics from the cruciate deficient case? Using a navigation system, we measured passive knee kinematics of ten male osteoarthritic patients during surgery after initial exposure, after removing the anterior cruciate ligament, after removing the posterior cruciate ligament, and after implanting the prosthesis. Passively flexing and extending the knee, we calculated anterior femoral translation and the flexion angle at which femoral rollback began. Removing the posterior cruciate ligament doubled anterior translation (from 5.1 +/- 4.3 mm to 10.4 +/- 5.1 mm) and increased the flexion angle at which femoral rollback began (from 31.2 +/- 9.6 degrees to 49.3 +/- 7.3 degrees). Implanting the prosthesis increased the amount of anterior translation (to 16.1 +/- 4.4 mm), and did not change the flexion angle at which femoral rollback began. Abnormal anterior translation was observed in low and mid flexion (0-60 degrees) after removing the posterior cruciate ligament, and normal motion was not restored by the posterior stabilized prosthesis.

Figure 1

Intraoperative experimental setup. An optical tracking system recorded knee motions using the positions and orientations of trackers affixed to the femur and tibia. At four surgical stages, knee motions were recorded as the surgeon moved the knee through its range of flexion and extension. (see methods for details)

Figure 2

Anterior femoral position throughout the range of knee flexion for one subject after removal of the ACL and PCL. Experimental data represent three trials of flexion extension. Data were fit with a fifth-order polynomial.

Figure 3

Anterior femoral position throughout the range of knee flexion for one subject at the four surgical stages (Intact, No ACL, No ACL No PCL, TKA. Arrow indicates anterior femoral translation.

Figure 4

Anterior femoral translation at the four surgical stages (mean±SD). The mean anterior femoral translation significantly increased with PCL removal (No ACL No PCL) and with prosthesis implantation (TKA). *p < 0.05.

Figure 5

Knee flexion angle at which femoral rollback began at the four surgical stages (mean±SD). Femoral rollback angle occurred in deeper flexion after removal of the PCL (No ACL No PCL). Normal femoral rollback angle was not restored with the prosthesis (TKA). *p < 0.05.