Impact of Obesity on Revision Rates Following Unicompartmental Knee Arthroplasty

Overview

This systematic review and meta-analysis evaluated the influence of obesity (BMI ≥ 30) on revision rates following unicompartmental knee arthroplasty (UKA). The study found conflicting evidence regarding whether obesity increases revision risk, with some data suggesting no adverse outcomes while others indicate higher revision rates in obese patients. Subgroup analyses further explored BMI thresholds and failure mechanisms to inform surgical decision-making.

Background

Obesity prevalence has nearly doubled worldwide, contributing significantly to the increased incidence of knee osteoarthritis (OA). Knee OA often requires arthroplasty when conservative treatments fail, with unicompartmental knee arthroplasty (UKA) being a less invasive option than total knee arthroplasty (TKA). Historically, UKA was considered unsuitable for patients weighing over 82 kg due to concerns about higher revision rates, but recent studies have challenged this contraindication. This review aims to clarify the impact of obesity on UKA outcomes to guide patient selection.

Data Highlights

The meta-analysis included studies comparing revision rates between obese (BMI ≥ 30) and non-obese patients, as well as subgroup analyses for BMI ≥ 35. Revision rates were calculated per 100 observed component years, with 95% confidence intervals determined by the Clopper Pearson exact method. Outcomes assessed included overall revision rates, revisions due to infection, aseptic loosening, and unexplained pain, alongside postoperative functional scores such as the Oxford Knee Score (OKS) and Knee Society Score (KSS).

Key Findings

• Obesity (BMI ≥ 30) was variably associated with revision rates following UKA, with some studies showing no significant increase in failure risk.
• Subgroup analysis suggested that patients with BMI ≥ 35 may have higher revision rates compared to those with lower BMI.
• Revision mechanisms analyzed included infection, aseptic loosening, and unexplained pain, which are primary causes of UKA failure.
• Prosthesis design (fixed vs. mobile bearing) was evaluated but no definitive conclusions were drawn regarding its interaction with obesity.
• Functional outcomes measured by OKS and KSS did not consistently differ between obese and non-obese groups.
• Low surgeon and center volume were identified as confounding factors influencing revision rates, independent of patient BMI.

Clinical Implications

Surgeons should consider that obesity alone may not be an absolute contraindication for UKA, especially in younger patients who may benefit from the procedure's advantages. Careful patient selection and surgical expertise remain critical to optimizing outcomes. Monitoring for specific failure mechanisms in obese patients is advised to tailor postoperative management and improve implant survival.

Conclusion

This systematic review highlights that while obesity may influence revision rates following UKA, the relationship is complex and influenced by multiple factors including BMI thresholds and surgical volume. Further high-quality studies with long-term follow-up are needed to refine patient selection criteria and optimize UKA outcomes in obese populations.

References

1. World Health Organisation 2020 -- Obesity and Overweight
2. Kozinn and Scott 1989 -- Indications for Unicompartmental Knee Arthroplasty
3. Caivagnac et al. -- Obesity and UKA Outcomes
4. Murray et al. -- BMI and UKA Failure Rates
5. Kandil et al. -- Revision Rates in Obese UKA Patients
6. PRISMA Guidelines 2009 -- Systematic Review Reporting Standards