Article
Unrestricted caliper-verified kinematic alignment has no learning curve effect for accuracy of femoral resections and results in consistent implant alignment and high clinical outcomes
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Published: | October 25, 2022 |
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Outline
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Objectives: The primary objective of this study was to determine the surgeon's learning curve for unrestricted caliper-verified kinematically aligned TKA through the accuracy assessment of the femoral resections. Secondary objectives were to compare accuracy of femoral resections, consistency of implant positioning and limb alignment, and clinical outcomes of a surgeon experienced (E) in kinematic alignment (KA) versus a surgeon less experienced (LE) in KA.
Methods: This retrospective study included the first 30 consecutive KA TKAs performed by one LE surgeon which were compared to 30 consecutive KA TKAs performed by one E surgeon. Using the TKAs of the LE surgeon, the learning curve was assessed by computing the error in the femoral resections documented in a verification sheet. The error was the resected thickness minus the target thickness. The 30 TKAs performed by the LE surgeon were divided into three groups by chronological order and the bias (i.e. mean error) and precision (standard deviation of error) of the femoral resections were compared between the groups. To assess the effect of surgeon experience, these same error quantities were computed for the E surgeon. In addition, alignment variables including the hip-knee-ankle angle (HKAA), distal lateral femoral angle (DLFA), proximal medial tibial angle (PMTA), femoral component flexion, posterior slope of the tibial component, and internal-external rotation deviation from target were measured for both the E and LE surgeons. Statistical analyses were performed to compare resection thickness errors, mean and variance of the alignment variables, and clinical outcome scores between the two surgeons.
Results and conclusion: A learning curve to perform the femoral resections to target was not evident; bias and precision of the four femoral resections did not change across the three groups (Table 1 [Tab. 1]).
Surgeon experience did not affect errors of femoral resections (n.s.), implant alignment in the coronal and sagittal planes (n.s.), and limb alignment (n.s.). However, the LE surgeon positioned the tibial component in 5° more external rotation than the E surgeon (p=0.001) (Table 2 [Tab. 2]).
Oxford Knee Score, KOOS Jr. Score, and Forgotten Joint Score were not different between patients operated by the E surgeon and the LE surgeon at final follow-up (n.s.) (Table 3 [Tab. 3]).
Transitioning to KA TKA can be achieved without a learning curve. This results in comparable pre-arthritic joint line and limb alignment restoration and similar outcome score between a E and LE surgeon. Surgeons exploring other alignment options might find these results helpful when deciding to change.