IntroductionPrimary patella resurfacing (PPR) in primary total knee arthroplasty (TKA) is a topic without clear clinical evidence. Using Patient Reported Outcome Measurements (PROM), previous work found TKA patients without PPR to have more pain postoperatively, but little is known whether this may impede patients from returning to their usual leisure sport. This observational study aimed at evaluating the treatment effect of PPR, with PROMs and return to sport (RTS).Materials and methods156 primary TKA patients were retrospectively included from August 2019 to November 2020, from a single hospital in Germany. PROMs were measured with the Western Ontario McMaster University Osteoarthritis Index (WOMAC) and the EuroQoL Visual Analog Scale (EQ-VAS), preoperatively and 1 year postoperatively. Leisure sport with three levels of intensity (never, sometimes, regular) were requested. The treatment effect of PPR was evaluated with a difference-in-difference (DiD) approach, with several confounders.ResultsDescriptively, the mean WOMAC total score and the mean WOMAC pain score were postoperatively better with PPR, ( – 4.8 points,  – 1.1 points), then without PPR. The mean improvements of the WOMAC total score were better with PPR ( – 7.8 points). Mean improvements for the WOMAC pain score were also better with PPR ( – 1.2 points). Mean EQ-VAS were postoperatively similar, and the mean improvements were better with PPR (3.4 points). Rate of RTS was 93% for patients with PPR and 95% for patients without PPR. The DiD revealed minor differences in PROMs and RTS, not to result in statistically significant treatment effects.ConclusionsThere was no treatment effect for TKA with PPR, regarding PROMs and RTS, and descriptive differences were below published thresholds for clinical relevance. Rate of RTS was high for all patients, regardless of PPR. For the two endpoint categories, there was no measurable advantage of TKA with PPR over TKA without PPR.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00402-023-04930-x.