What Role Does Patello-Femoral Joint Degeneration Have on Pain and Function After Unicompartmental Knee Arthroplasty? A Prospective Observational Cohort Study

Background Influences on anterior knee pain, stair climbing limitations, and function such as rising from sitting are poorly understood in unicompartmental knee arthroplasty. Original indications for unicompartmental knee arthroplasty (UKA) excluded patients who had patello-femoral disease, while more recent studies have expanded the indications to include these patients. This study examined the influence of the patello-femoral joint degeneration on patient reported outcome measures (PROMs) relating to anterior knee pain and function after UKA. Methods Between October 2017 and August 2021, Knee Injury and Osteoarthritis Outcome Score of Joint Replacement (KOOS, JR.) PROMs were collected preoperatively and at 12 months follow-up for 678 medial UKAs. Patello-femoral joint (PFJ) status was visually graded intraoperatively. Radiographic or intraoperative medial patellar facet and trochlear patello-femoral arthritis and pre-operative anterior knee pain were not considered contraindications for UKA, while grade IV lateral patello-femoral arthritis was considered a contraindication for UKA. Multivariable ordinal logistic regressions were performed, using the KOOS, JR questionnaire assessing pain during stair climbing, standing upright, and function during rising from sitting. Independent regressions were performed for each targeted KOOS, JR question, with adjustments for age at surgery, sex, and baseline pain and function scores. Results No association was observed between 12-month postoperative anterior knee pain (P=0.575) or function (P=0.854) with patellar osteoarthritis grading after UKA. Similarly, when comparing fixed and mobile bearing UKA designs, no association was observed between bearing type and pain (P=0.663) or functional outcomes (P=0.758). Conclusions Pain and function improved significantly following medial UKA and was independent of medial patellar and trochlear degenerative status.