Abstract
Introduction
The role of the (PCL) in modulating knee kinematics has been well documented. We asked whether function of the (PCL) would be better preserved by incorporating a three-dimensional model for planning and placement.
Methods
We evaluated patients (n=59) enrolled into a, prospective, study of conventional instrumentation (25) vs. 3D modeling (34) for (CR) TKA from July 2016 to Feb 2018. Follow-up included clinical exams, PROMs, and serial radiographs up to 24 months after surgery. We measured kinematic patterns radiographically at two years postoperatively. Variables were compared using simple linear regression, one-way ANOVA, and Fisher's exact test. We hypothesized that: 1. well-preserved PCL would demonstrate a more normal kinematic pattern of increasing rollback with increasing knee flexion without paradoxical movement, and 2. this pattern would be associated with improved intra- and post-operative motion and function.
Results
The 3D group exhibited a monotonic pattern of increasing rollback in more than twice the proportion of patients as the conventional group (18/34 (53%) vs. 6/25(24%), p=0.034). Two yrs post-operatively, the maximum active flexion was 5 deg greater on average for the 3D group (mean(SD) 111.8(6.6) vs. 106.8 (8.8), p=0.015), and we saw positive linear correlation of femoral rollback with maximum active (r=.39, p=0.002) and passive (r=.45, p<0.001) flexion. Increased rollback was correlated with better Knee Society symptom scores during the early post-operative period (r=.37, p=0.003 and r=.39, p=0.002, respectively).
Discussion
This study demonstrates the value of 3D reconstructions to improve kinematics in TKA. In fact, PCL retaining TKA has been consistently linked to paradoxical rollback, predisposing the extensor mechanism to increased stress and reduced femoral clearance, limiting flexion.
Paradoxical movement was more prevalent in conventionally instrumented knees. There were notable differences in PROMS even at six weeks post TKR. More normal kinematics were associated with increased motion and improved patient reported outcomes.
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