Does Elevated BMI Justify Denial of Knee-Replacement Surgery?

A substantial number of  people living with obesity in need of knee-replacement surgery will have either been flatly denied surgery, or told to lose weight prior to qualifying for surgery. This common practice is largely based on the notion that outcomes in people with elevated BMI are generally poor, operations are riskier, and the life of the prosthesis due to loosening or wear may be drastically shortened. 

But, is this really the case?

Not, according to a large observational cohort study by Jonathan Thomas Evans and colleagues, just published in PLOS.

The researchers examined data from over 490,000 total knee replacements collected in the National Joint Registry (NJR) for England, Wales, Northern Ireland, and the Isle of Man from 2005 to 2016.

While individuals with higher BMI were slightly more likely to undergo revision surgery within 10 years of receiving their prosthesis, revision rates in all BMI classes remained well withing the accepted 10-year benchmark of 5%. 

Moreover, all BMI categories saw important improvements in function scores, which were only marginally (below the minimal detectable change) compared to patients with “normal” BMI.

Finally, there was no indication of increased mortality risk in higher BMI patients. In fact, 90-day mortality rates were significantly lower in patients with overweight and class I obesity than  in those with “normal” BMI. 

Thus, the authors suggest that policies limiting access to knee-replacement surgery based on BMI may no longer be justifiable. 

On the other hand, it may be important to note that this cohort most certainly represents a substantial selection bias with surgeons perhaps selecting fitter patients with raised BMI for surgery (“healthy-patient effect”). 

Or, as the authors put it,

“It appears that even if some patients with raised BMI are at risk of poorer outcomes, the outcomes remain acceptable by contemporary standards, and the selection process of orthopaedic surgeons is effective at identifying the correct patients to operate on at a population level.

Be that as it may, I would probably predict that if a staging system like the Edmonton Obesity Staging System (EOSS) were to be applied to this cohort, any residual effect of BMI will likely disappear – I would expect outcomes to be poorer the higher the EOSS stage, irrespective of BMI. 

For now, these data can certainly be used to initiate discussions on official or unofficial policies that restrict access to knee replacements based on BMI.

Berlin, D