Abstract
Introduction
New implants for total knee arthroplasty (TKA) are frequently introduced with the promise of improved performance. Infrequently there is accompanying data to document relative performance. The goal of this study was to evaluate the outcomes of an implant widely used for decades (Existing TKA), compared to a new implant (New TKA) from the same manufacturer.
Methods
From October 2011-March 2015, 19 sites prospectively enrolled and implanted 752 Subjects with Existing TKA. Between November 2012 and May 2015, 23 sites (18 sites had enrolled Existing TKAs), implanted 1131 Subjects with the New TKA. Demographics were similar between groups. Subjects were seen preoperatively, <1-year, 1-year, and 2-years to collect patient reported outcome measures (PROMs), radiographs and any complications. PROMs consisted of Knee Injury and Osteoarthritis Outcome Score (KOOS) (permits WOMAC scoring), Oxford Knee Score (OKS), Patient's Knee Implant Performance (PKIP) and EQ5D-3L and a p-value of 0.01 was established for statistical significance for PROMs comparisons. Kaplan-Meier (KM) implant survivorship (revision of any component for any reason) estimates were calculated.
Results
The mean follow-up for the Existing and New groups was 2.2 years (SD: 0.7) and 2.5 years (SD: 0.8), respectively. The difference in KM survivorship was not statistically significant (p=0.9727, Figure 1). In the Existing TKA group, 11/752 Subjects required component revision with 6 involving removal of metal components for the following reasons: infection (4), pain (5), loosening (1) and instability (1). In the New TKA group, 19/1137 Subjects required component revision with 7 involving removal of metal components for the following reasons: infection (6), joint stiffness (6), pain (3), bone fracture (2), crepitus (1), and loosening (1).
The 2-year PROMs were compared between groups and demonstrated similar or improved scores in favor of the New vs. Existing TKA. Mean outcomes for New TKA vs. Existing TKA at 2 years were: KOOS (ADL: 89.0 vs. 86.9, p=0.005; Pain: 89.0 vs. 87.1, p=0.018; Symptoms: 84.1 vs. 82.1, p=0.010; Sport/Rec: 63.9 vs. 58.8, p=0.001, QOL: 77.0 vs. 73.5, p=0.003), PKIP (Overall: 76.5 vs. 73.5, p=0.003; Confidence: 8.4 vs. 8.1, p=0.003; Stability: 8.6 vs. 8.3, p=0.006; Satisfaction: 8.3 vs. 8.1, p=0.053; Modify Activities: 6.6 vs. 6.4, p=0.335), OKS (42.0 vs. 41.1, p=0.023), and EQ5D-3L (0.88 vs. 0.88, p=0.906). There was no difference between the two groups in the percent of Subjects with immediate postop radiographic interface gaps or radiolucencies (metal-cement or the bone-cement interfaces).
Conclusion
The implant survivorship and radiographic assessments showed similar outcomes between the two groups. The New TKA demonstrated modest improvements in PROMs across a broad spectrum of measures.
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