Abstract
Introduction
Neither a surgeon's intraoperative impression or computer navigation parameters have been shown to be predictive of postoperative outcomes following TKA. The purpose of this study is to determine 1) whether a surgeon and a robot can predict the 1-year KOOS pain score (KPS) and 2) determine what factors correlate with poor KOOS scores in well aligned and balanced TKA.
Methods
The data of 131 consecutive patients enrolled in a prospective trial was reviewed. All TKAs were performed using a dynamic ligament tensioning robotic system with a tibial first resection technique and a cruciate sacrificing ultracongruent knee implant. Each TKA was graded based on the final recorded mediolateral ligament balance at 10° and 90°: A) <1mm with an implanted insert thickness equal to planned (n=74); B) <1mm (n=25); C) <2mm (n=26); D) >2mm (n=6) (Table-1). The 1-year KPS for each knee grade were compared and the likelihood of achieving an KPS > 90 was calculated. Finally, the factors associated with lower KPS despite achieving a high grade TKA (A/B) was performed. The Mann-Whitney U test and Chi-squared analysis was performed.
Results
Patients with a grade of A and B had higher 1-year KPS compared to knees rated C and D (p=0.031) (Fig-1). There was no difference in KPS in TKAs rated A or B, but 33% in this group did not report a KPS > 90. While there was no correlation with age, sex, preoperative deformity, and preoperative KOOS and PROMIS physical scores, patients with KPS < 90 despite a TKA rated A or B had lower PROMIS metal health scores compared to patients reporting KPS > 90 (54.1 vs. 50.8, p= 0.043). Finally, Grade A and B patients who scored KPS > 90 were more likely to respond with “my expectations were too low”, and they are performing better than expected compared to Grade A and B patients who scored KPS < 90 (40% vs 22%, p = 0.004).
Summary
A robotic balanced knee is correlated with higher KPS at 1 year but not predictive. Despite accurate alignment, rotation, and ligament balance information, a robotic system could not guarantee excellent pain relief. Patient expectations and mental status also significantly affect the perceived success of TKA.
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