Assessment of a Novel Radiographic Index and Functional Outcomes After Secondary Patellar Resurfacing: A Matched Cohort Study

Background: This study evaluated the effectiveness of secondary patellar resurfacing (SPR) on clinical outcomes in patients who experienced anterior knee pain (AKP) following primary total knee arthroplasty (TKA) without concomitant patellar resurfacing. The study also investigated the association between radiographic parameters and postoperative AKP and explored whether a novel radiographic index was associated with postoperative AKP. Methods: A retrospective cohort of 246 patients was analyzed, including 82 patients who had idiopathic AKP following TKA and were treated with SPR, and 164 matched controls of those who underwent primary TKA without patellar resurfacing and did not develop postoperative AKP. Patient-reported outcome measures, including the visual analog scale, Knee Society Score, and Oxford Knee Score, showed statistically significant improvement in the SPR group (P < 0.005), whereas radiographic parameters demonstrated limited discriminative value. Results: A newly developed metric, the GC index, defined as the ratio of anterior femoral offset to anterior patellar displacement (APD), demonstrated good discriminative performance within the present cohort, with a sensitivity of 82.9% and specificity of 85.4%, and remained independently associated with postoperative AKP after adjustment for relevant confounding factors. Conclusions: These findings support the potential role of SPR in managing persistent AKP after TKA and suggest that the GC index may represent a potential adjunctive radiographic marker requiring further prospective validation.