Obesity and unicompartmental knee arthroplasty (UKA) are linked with durable results, confirming it does not affect implant longevity.
Unicompartmental knee arthroplasty outcomes in obese patients have been widely debated in orthopaedics. Many surgeons hesitate to recommend partial knee replacement to obese patients due to presumed higher risks of failure. However, a recent long-term study by Prof. Cavaignac and his peers provides new evidence that challenges this assumption.
This article summarises the main findings of that research: “Obesity has no adverse effect on the survival of unicompartmental knee arthroplasty in a long-term follow-up of 16 years”, and explains their implications for knee surgeons and patients considering unicompartmental arthroplasty.
Obesity and Partial Knee Replacement: Background and Rationale
Obesity and partial knee replacement are closely linked because excess body weight is one of the main contributors to medial compartment osteoarthritis. The unicompartmental knee arthroplasty procedure, also known as partial knee replacement, replaces only the damaged compartment of the knee, preserving healthy bone and ligaments.
Historically, obesity was considered a relative contraindication for UKA. Surgeons feared that increased body mass index (BMI) could accelerate implant wear and lead to premature failure. Yet, while obesity undoubtedly increases mechanical load on the joint, recent data suggest that improved implant materials, alignment accuracy and minimally invasive techniques have largely mitigated this risk.
Long-Term Study Design and Methodology
The referenced study analysed 1,000+ unicompartmental knee arthroplasties performed over a 16-year period. Patients were divided into BMI categories:
- normal (<25 kg/m²),
- overweight (25–30 kg/m²)
- obese (>30 kg/m²)
This division was made to compare the effect of obesity on knee prosthesis longevity.
Researchers evaluated both revision-free implant survival (the primary endpoint) and surgery-free survival (secondary endpoint), alongside functional outcomes assessed by the International Knee Society (IKS) score and range of motion (ROM).
Importantly, follow-up data extended beyond 10 years for most patients, making it one of the most robust datasets available on unicompartmental knee arthroplasty long-term results in obese patients.
Key Findings: Partial Knee Replacement Survival in Obese Patients
The study provides valuable long-term evidence on partial knee replacement survival in obese patients and how obesity influences implant performance.
1. Comparable Implant Longevity
The most significant finding is that unicompartmental knee replacement survival in obese patients did not differ from non-obese counterparts. Revision-free implant survival rates were statistically equivalent across BMI groups, even at the 16-year follow-up mark.
This demonstrates that obesity alone does not compromise implant durability. The prostheses showed excellent fixation, with no increase in mechanical loosening or polyethylene wear among obese individuals.
2. Similar Functional Outcomes
When examining clinical scores, the study reported no significant difference in postoperative IKS or ROM values between BMI categories. Patients with obesity regained comparable mobility and function to those with normal weight.
These results indicate that obesity and partial knee arthroplasty outcomes are primarily influenced by surgical precision and rehabilitation quality rather than BMI. With proper technique and structured physiotherapy, obese patients can expect similar long-term function.
3. Slightly Higher Early Complication Rate
The only minor distinction observed was a slightly higher rate of superficial wound complications in the obese group. However, these did not translate into increased revision rates or poorer long-term outcomes.
Understanding the Effect of Obesity on Unicompartmental Knee Prosthesis Longevity
To interpret these results accurately, it is essential to understand the effect of obesity on unicompartmental knee prosthesis longevity.
Mechanical vs. Biological Considerations
The effect of obesity on partial knee prosthesis longevity has both mechanical and biological dimensions. Mechanically, excess body weight increases axial loading, which can theoretically accelerate wear. Biologically, adipose tissue releases pro-inflammatory cytokines that may influence healing.
Despite these factors, the study’s findings show that modern implant designs and improved cementless or hybrid fixation systems effectively counterbalance these risks. By optimising component alignment and ligament balance, surgeons can achieve consistent and durable outcomes regardless of BMI.
Surgical Expertise and Robotic Precision
The integration of robotics into unicompartmental knee arthroplasty has been transformative. Systems now allow surgeons to simulate and adjust implant positioning intra-operatively, improving accuracy by fractions of a millimetre.
As shown in Professor Cavaignac’s practice in Toulouse, robotic guidance not only enhances precision but also standardises results between patients. This is particularly beneficial in complex cases such as obese or post-traumatic knees.
BMI and Unicompartmental Knee Arthroplasty Outcomes: What This Means for Patients
The correlation between BMI and unicompartmental knee arthroplasty outcomes is now clearer than ever. Surgeons can confidently recommend this procedure to well-selected obese patients suffering from isolated medial or lateral osteoarthritis.
Practical Recommendations
- Patient selection: Focus on knee morphology, ligament stability and cartilage distribution rather than BMI thresholds.
- Surgical planning: Use robotic assistance or computer navigation when available to ensure perfect implant alignment.
- Rehabilitation: Encourage weight management and muscle strengthening to support long-term success.
Conclusion & Findings
In conclusion, obesity should no longer be considered a contraindication for partial knee replacement. According to this 16-year study, obese and non-obese patients achieve comparable implant survival, function and satisfaction.
This research provides reassurance to both surgeons and patients: with modern techniques, proper patient selection and expert postoperative care, long-term results remain excellent regardless of BMI.
To explore other clinical research led by Professor Etienne Cavaignac visit his website’s publications section. For consultations or surgical planning, patients can book an appointment with Professor Cavaignac.