All-polyethylene unicompartmental knee arthroplasty is associated with increased risks of poorer knee society knee score and lower satisfaction in obese patients

Background Although metal-backed tibial component (MB) is biomechanically superior to all-polyethylene (AP) implants in fixed-bearing unicompartmental knee arthroplasty (UKA), recent studies have shown comparable functional outcomes between the two. However, no study has examined this comparison in obese patients (BMI ≥ 30 kg/m 2 ). We investigated whether functional outcomes between the two implants differ among obese patients, and whether the extent of obesity influences these outcomes. Patients and methods Four hundred twenty-two UKA implants from 347 obese patients were reviewed retrospectively. Patients were assessed using the Knee Society Knee Score (KSKS) and Function Score (KSFS), the original Oxford Knee Score (OKS), and SF-36 Physical Component Summary (PCS) and Mental Component Summary (MCS). Minimal clinically important difference (MCID) attainment was recorded. Patients’ fulfillment of expectations and satisfaction with the surgery outcome was also graded. Patients were further divided into lower obesity (BMI 30–34.9 kg/m 2 ) and higher obesity (BMI ≥ 35 kg/m 2 ) to examine effect modification. Results There were no differences in functional outcomes and quality-of-life scores, MCID attainment of functional scores, as well as satisfaction and expectation fulfillment between AP and MB. Among higher obesity patients, AP was associated with a poorer KSKS ( p = 0.031) and lower proportion of satisfaction fulfillment ( p = 0.041) 2 years postoperatively compared to MB. Conclusion We found no differences in functional and quality-of-life outcomes between fixed-bearing AP and MB tibial components among obese patients who underwent UKA. However, among higher obesity patients (BMI ≥ 35 kg/m 2 ), patients with AP tibial component were associated with lower KSKS score and a lower proportion of attaining satisfaction fulfillment 2 years postoperatively.