Abstract
Background and purpose — The all-polyethylene tibial (APT) component, introduced in the early 1970s, was surpassed by metal-backed tibial (MBT) trays as the first choice for total knee arthroplasty (TKA). With improved polyethylene, the modern APT components can reduce costs, and have shown equivalent results in survivorship and early migration of the cruciate-retaining and cruciate-stabilizing designs. This study compares the 2-year migration of a similarly designed APT-posterior stabilized (PS) and a MBT-PS TKA, using radiostereometric analysis (RSA).Patients and methods — 60 patients were randomized to receive either an APT Triathlon PS or an MBT Triathlon PS TKA (Stryker, NJ, USA). Migration measured by RSA and clinical scores were evaluated at baseline and at 3, 12, and 24 months postoperatively. Repeated measurements were analyzed with a linear mixed model and generalized estimating equations.Results — The mean maximum total point movement (MTPM) at 3, 12, and 24 months was 0.41 mm (95% CI 0.33–0.50), 0.57 mm (0.44–0.70), and 0.56 mm (0.42–0.69) respectively in the MBT group and 0.46 mm (0.36–0.57), 0.61 mm (0.49–0.73), and 0.64 mm (0.50–0.77) in the APT group. 2 MBT and 1 APT implant were considered unstable at the 2-year follow-up. The KSS Knee score and KSS Function across 3, 12, and 24 months were comparable in both groups.Interpretation — For an APT-PS designed component, MTPM measured with RSA is comparable to the MBT-PS component after 2 years of follow-up. No differences in complications or clinical outcomes were found.
Highlights
Patients and methods — 60 patients were randomized to receive either an all-polyethylene tibial (APT) Triathlon posterior stabilized (PS) or an metal-backed tibial (MBT) Triathlon PS total knee arthroplasty (TKA) (Stryker, NJ, USA)
Despite the many advantages of the all-polyethylene tibial (APT) component, such as avoiding backside wear, preserving tibial bone, and lower costs, it accounts for only 0.1–13% of the total knee arthroplasties (TKA) registered (Norwegian Arthroplasty Register 2018, Swedish Knee Arthroplasty Register 2018)
When TKA was introduced in the early 1970s, implants included APT components, but this design was soon replaced by a metal-backed tibial (MBT) component due to disappointing survival rates of the APT (Steinberg and Steinberg 2000, Browne et al 2011)
Summary
This study was a randomized RSA trial comparing the APT-PS Triathlon Total Knee System with the MBT-PS Triathlon (Stryker, Warsaw, USA). Between November 2014 and June 2015, 60 consecutive patients were included and randomized to either an APT-PS or a MBT-PS component at the Hässleholm Hospital (Sweden). Patients were blinded to the treatment allocation and remained blinded throughout the study. Main exclusion criteria were BMI > 40, a flexion or varus/valgus contracture > 15°, preoperative knee score > 70, and patients who could not make the follow-up visits because of living far away from the hospital. The modular MBT component uses a highly cross-linked polyethylene insert (X3, Stryker Orthopaedics, Mahwah, NJ, USA). 8 well-scattered tantalum beads (ø 0.8 mm; RSA Biomedical, Umeå, Sweden) were inserted into the tibial bone as reference markers. The postoperative regime included immediate full weight-bearing and there were no differences in postoperative treatment between the 2 groups
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