Rethinking the Risks of Revision Associated With Obesity

What’s the Claim?

A large registry study from Australia — identified as one of the “Notable Articles of 2022” in JBJS — found the risk of revision after TKA to be very slightly greater in patients with obesity than those of normal BMI. Among patients whose BMI were between 30 and 39.99 (Class I and II obesity), the hazard ratio for all-cause revision compared to patients with a normal BMI was only 1.12 (95% CI 1.03 to 1.22). For patients whose BMI was ≥ 40, the risk was somewhat greater, with an HR of 1.3 for revisions beyond a year compared to patients with a normal BMI. Looking specifically at revision for infection, the risk increase was more severe than that. But sliced another way, which we believe is important, the absolute magnitude of increased risk really seems quite small — the cumulative percent risk of revision for any cause at 5 years was 2.5% for patients without obesity, 2.9% for those with Class I or II obesity, and 3.3% for those whose BMI was ≥ 40.

How’s It Stack Up?

In terms of the numbers, this study is in line with what others have found. Several systematic reviews and other registry studies suggest these estimates are right in the ballpark. The key here, as surgeons — and, we think, as physicians — is to reconsider what we should do with this information. The pendulum has swung hard one way, resulting in many surgeons refusing to offer joint replacement to patients with obesity and some individuals to advocate for hard BMI cutoffs rather than shared decision-making on this subtle and complicated topic. One major society’s guideline all but did so, as well.

What’s Our Take?

If any topic ever needed to be managed with shared decision-making rather than hard cutoffs, it is this one. Risk exists on a sliding scale, and that risk should be discussed with patients (and those conversations should be well-documented, for the protection of their surgeons), but taking the decision out of patients’ hands is wrong. There are many reasons for this, but space constraints allow us only to cover two. First, consider the magnitude of the risk we’re dodging and what dodging it does to patients — the absolute increase in risk of revision at 5 years was between 0.4% and 0.8% depending on BMI; this is a non-zero but very small increment. Over 40% of the US adult population has obesity, so using a BMI cutoff excludes a vast number of patients from a generally beneficial intervention in the hopes of preventing a small number of complications. Second, obesity is much less modifiable than is commonly believed; an Editorial in CORR® suggested that the odds of someone with obesity losing a substantial amount of weight and keeping it off are lower than someone staying off of heroin using methadone maintenance, and that we offer joint replacement to patients with other — more impactful — risk factors all the time. So the idea that we’re “deferring” surgery for this risk factor is, for most patients, an illusion. Hard cutoffs result in denying surgery, not deferring it. This seems unfair. More flexible decision-making on this topic is needed.

Source

Wall CJ, Vertullo CJ, Kondalsamy-Chennakesavan S, Lorimer MF, de Steiger RN. A Prospective, Longitudinal Study of the Influence of Obesity on Total Knee Arthroplasty Revision Rate: Results From the Australian Orthopaedic Association National Joint Replacement Registry. J Bone Joint Surg. 2022;104:1386-1392.