The influence of severe knee varus and patellofemoral joint degeneration on outcomes following fixed-bearing medial robotic-assisted unicompartmental knee arthroplasty: a minimum of 18-month follow-up.

backgroundThis study aimed to investigate whether preoperative severe varus deformity, patellofemoral joint (PFJ) osteoarthritis severity, or PFJ alignment influenced the early outcomes following primary fixed-bearing medial robotic-assisted unicompartmental knee arthroplasty (RA-UKA) in carefully selected patient cohort.

methodsOne-hundred-fifty patients undergoing primary fixed-bearing medial RA-UKA with a mean 23.7-month follow-up (SD 2.1; range: 18-26) were prospectively enrolled. Outcomes were compared based on knee varus and PFJ osteoarthritis severity. Radiographic evaluation included the Altman score, patellar tilt and congruence angles as well as the hip-knee-ankle, coronal femoral component, and coronal tibial component angles (HKA, c-FCA, and c-TCA, respectively). Clinical evaluation included Knee Society Knee and Function Scores (KSS knee, KSS function), Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS-JR), Oxford Knee Score (OKS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Forgotten Joint Score-12 (FJS-12), and 5-point Likert scale. Furthermore, the association between PFJ alignment and outcomes following RA-UKA at the last follow-up was investigated.

resultsPostoperative HKA was significantly higher in the severe varus than in the control group (P < 0.001). However, no differences were observed in postoperative c-FCA, c-TCA, laxity measurements in the medial compartment, or PFJ OA progression between the groups. No significant differences were found in early functional outcomes or complications between severe varus and control groups (P > 0.05). No differences in early functional outcomes were observed between patients with and without radiographic evidence of PFJ OA. Pearson's correlation test revealed no association between preoperative PFJ alignment and functional outcomes at the last follow-up.

conclusionThis is the first study demonstrating that preoperative radiographic severe knee varus, mild-to-moderate PFJ OA, and malalignment of the PFJ do not adversely influence early outcomes after fixed-bearing medial RA-UKA. However, the relatively short follow-up period limits the assessment of complications, implant survivorship, and mid- to long-term functional outcomes, particularly in patients with severe varus deformity. Therefore, the current findings apply only to early postoperative outcomes.