Evaluation of a radiological grading system for the early detection of total knee arthroplasties at risk for revision surgery.

Introduction: X-rays are regularly performed after primary total knee arthroplasty (TKA). While soft tissue management and ligament tension cannot be evaluated, important information, such as inadequate component positioning and loose cement location, as well as subsequent loosening, can be detected. The aim of this study was to correlate radiological findings, referring to the radiological grading system (previously published by the same study group, henceforth abbreviated as "RGS"), with long-term outcomes and implant survival.

Materials and methods: A total of 266 patients who underwent titanium-coated TKA were included. In addition to implant survival, visual analogue scale score, Tegner activity score, knee society score (KSS), Western Ontario and McMaster Universities Osteoarthritis Index, and short form-12 score as well as range of motion were evaluated. Clinical examination as well as anterior-posterior, lateral, full-length weight bearing, and patellar view radiographs were performed pre- and postoperatively, at the 3-, 6-, and 12-month postoperative follow-ups and at the final follow-up. The radiological grading system was evaluated and correlated with long-term outcome and survivorship.

Results: The revision-free survival rate was 88.4% at a median follow-up of 9.8 years (IQR: 9.3-10.3 years; range: 0.1-11.8 years). Revision surgery was required in 31 TKAs (11.7%). The multivariate Cox regression model showed a significant association between an RGS score ≥ 3 deviation points (DP) and an increased risk for revision (hazard ratio: 2.092; 95% CI: 1.020-4.290; p = 0.044). Moreover, the KSS for pain was significantly worse in patients with a RGS score ≥ 3 DP (median, 85 [74-92] vs. 90 [80-94]; p = 0.007).

Conclusions: This is the first study indicating that deviation in component positioning, having an inadequate long leg axis, the presence of free cement or residual bony structures on postoperative X-rays significantly correlate with TKA outcome and implant survival. Therefore RGS can be of high predicable value for the survivorship of the prosthesis.

Level of evidence: Level IV - retrospective cohort study.