What are the risks of knee replacement surgery in obese individuals?

Risks of Knee Replacement Surgery in Obese Individuals

Obese patients should not delay knee replacement surgery to meet arbitrary weight thresholds, but must be thoroughly counseled about their significantly higher risks of complications including infections, wound complications, and implant failure.

Increased Risks in Obese Patients

Obesity significantly impacts outcomes following total knee arthroplasty (TKA) in several important ways:

Medical Complications

• Strong evidence shows obese patients have less improvement in outcomes with TKA 1
• Morbidly obese patients (BMI >40 kg/m²) experience:
  • Higher rates of overall complications (32% vs 0% in non-obese) 2
  • 3-9 times higher risk of deep prosthetic infections 3
  • Significantly more wound complications 4
  • Higher revision rates (7% vs 2% in non-obese patients) 4

Functional Outcomes

• Lower post-operative functional Knee Society Scores compared to non-obese patients 3, 2
• Only 57% of morbidly obese patients achieve excellent or good results compared to 86% in non-obese patients 5
• While functional scores do improve after TKA in obese patients, they remain inferior to those of non-obese patients 4

Implant Longevity

• Higher incidence of radiolucent lines on post-operative radiographs (29% vs 7%), suggesting potential loosening 2
• Inferior survivorship using revision and pain as endpoints (72.3% vs 97.6%) 2

Current Guidelines on Obesity and TKA

The 2023 American College of Rheumatology and American Association of Hip and Knee Surgeons guideline specifically addresses this issue:

• For patients with obesity and moderate-to-severe symptomatic OA who are indicated for TKA, they conditionally recommend against delaying surgery to meet a rigid weight or BMI threshold 1
• Instead, patients should be educated about their increased risks of medical and surgical complications due to obesity and counseled on weight loss 1

This recommendation acknowledges that while obesity increases surgical risk, there is insufficient evidence that delaying surgery until a specific BMI target is achieved leads to better outcomes.

Special Considerations for Morbidly Obese Patients

For patients with morbid obesity (BMI >40 kg/m²):

• The technical challenges of surgery are greater due to anatomical factors 4
• Cardiovascular evaluation is particularly important as obesity can mask cardiac pathology 1
• Physical examination often underestimates cardiac dysfunction in severely obese patients 1
• Electrocardiographic signs of right ventricular hypertrophy suggest pulmonary hypertension, an important surgical risk factor 1

Preoperative Risk Assessment

When evaluating obese patients for TKA:

1. Cardiovascular assessment is crucial as obesity can mask cardiac symptoms 1
2. Respiratory evaluation is important due to increased ventilatory demands and risk of sleep apnea 1
3. Diabetes screening is essential as diabetic patients have higher risk of complications with TKA 1
4. Chronic pain assessment is needed as patients with chronic pain conditions have less improvement in outcomes 1
5. Depression/anxiety screening is valuable as these conditions are associated with poorer outcomes 1

Important Counseling Points for Obese Patients

When discussing TKA with obese patients:

• TKA does not result in weight loss and therefore has no benefit on weight-related medical conditions 3
• While outcomes are inferior compared to non-obese patients, obese patients still experience significant pain relief and functional improvement 6
• The risks of complications increase with higher BMI, with morbidly obese patients at greatest risk 4
• Patients should understand that obesity may affect implant longevity and increase the likelihood of revision surgery 2

Conclusion

While obesity significantly increases the risks associated with knee replacement surgery, current guidelines do not support mandatory weight loss before proceeding with surgery. Instead, a thorough risk assessment and comprehensive patient counseling about the specific increased risks should be conducted, allowing patients to make informed decisions about their care.