Abstract
Introduction
Compared with the cruciate-retaining (CR) insert for total knee arthroplasty (TKA), the cruciate-substituting (CS) insert has a raised anterior lip, providing greater anterior constraint, and thus, can be used in cases of posterior cruciate ligament (PCL) sacrifice. However, studies have shown that the PCL maintains femoral rollback during flexion, acts as a stabilizer against distal traction force and aids knee joint proprioception; therefore, the argument for PCL excision in CS TKA remains controversial. The purpose of this study was to analyze CS TKA kinematics and identify the role of the PCL.
Methods
Seven fresh-frozen lower-extremity cadaver specimens were analyzed using Orthomap® Precision Knee Navigation software (Stryker Orthopaedics, Mahwah, NJ, USA). They were surgically implanted with Triathlon® components (Stryker Orthopaedics). The CS insert has a raised anterior lip, and the posterior geometry shares the same profile as the CR, so we can choose retaining or sacrificing the PCL. Six patterns were analyzed: (1) natural knee; (2) only anterior cruciate ligament excision; (3) CS TKA, PCL retention, and bony island preservation; (4) CS TKA, PCL retention, and bony island resection; (5) CS TKA and PCL excision; and (6) CR TKA and PCL excision. Center of the knee and center of the proximal tibia were registered using navigation system, and the magnitudes of the condylar translation were evaluated. And then, using trigonometric function, the magnitude of anterior-posterior translation of the femur was calculated.
Results
PCL excision patterns showed that the magnitude of anterior-posterior (AP) translation was higher in mid-flexion and lower in deep flexion than in other patterns (Fig. 1). Comparing two PCL excision patterns, in CS insert, the anterior translation magnitude was a little lower in extension and 30° flexion. Comparing two PCL retention patterns, the both posterior translation magnitudes in deep flexion were comparable to that of the natural knee.
Discussion
Very few studies have reported about comparison of PCL retention with PCL excision in CS TKA. Omori et al. evaluated the medial pivot type TKA, and found that the design showed no femoral rollback under the PCL-sacrificing condition. In our study, increased anterior translation magnitudes in mid-flexion indicated paradoxical roll-forward, and decreased posterior translation magnitudes in deep flexion indicated decreased rollback. In other words, PCL excision in CS TKA caused mid-flexion instability and decreased the femoral rollback, so raised anterior lip was not likely to contribute to TKA kinematics. Another research is necessary to evaluate the effects of the raised anterior lip. On the other hand, PCL retention in CS TKA maintained physiological femoral rollback. The AP translation magnitude was not dependents on the bony island.
Conclusions
We had better retain the PCL in raised anterior lip type CS TKA to ensure physiological knee kinematics.
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