Obesity is one of the most serious public health problems in the 21st century, and body weight is becoming an important consideration in orthopaedic procedures, especially joint arthroplasty. Two new studies in the February 3, 2016 Journal of Bone & Joint Surgery illuminate the relationship between body mass index (BMI) and hip-arthroplasty outcomes.
In a prognostic study based on registry data (21,361 consecutive hip replacements), Wagner et al. analyzed postsurgical complications and reoperations using BMI as a continuous variable. They found strong associations between increasing BMI and increasing rates of reoperation, implant revision or removal, early hip dislocation, and both superficial and deep infections. Although researchers are just starting to examine the efficacy of preoperative interventions to reduce BMI (see related OrthoBuzz post), Wagner et al. suggest that “collaborative interventions between care providers and patients may be undertaken to modify risk factors, such as BMI, before elective procedures.” A commentary on this study lauds the authors for analyzing BMI with a “dose-response” perspective, but the commentators note that “BMI neither remains constant nor follows a predictable trend over time.”
In a separate therapeutic study by Issa et al., clinical and patient-reported outcomes of primary THA were lower in super-obese patients (BMI ≥ 50 kg/m2) than in matched patients with normal BMI (<30 kg/m2). Specifically, after a mean follow-up of six years, compared with the normal-BMI group, the super-obese group had:
- A 4.5 times higher odds ratio (OR) of undergoing a revision
- A 7.7 times higher OR of surgical complications, including superficial and deep infections
- Significantly lower mean values on the Harris hip score, the physical and mental components of the SF-36, and the UCLA activity score.
Despite these between-group findings, super-obese patients still experienced significant clinical improvements compared with their preoperative status. However, they saw an average of 2.5 previous surgeons who refused to perform the procedure prior to being referred to the authors.
The relationships between body weight and joint replacement are debated often in the orthopaedic community. Some surgeons are so concerned about perioperative complications related to obesity that they recommend delaying arthroplasty in obese patients until weight loss is achieved.
But what are the likelihood and implications of weight changes after joint replacement? For those answers, in the June 3, 2015 edition of JBJS, Ast et al. tracked differences in body mass index (BMI) among nearly 7,000 patients for two years after total hip arthroplasty (THA) or total knee arthroplasty (TKA). Establishing a 5% BMI change as “clinically meaningful,” the researchers found that:
- Most patients (73% of those undergoing THA and 69% of those undergoing TKA) experienced no weight change.
- Female patients, patients with a higher preoperative BMI, and those undergoing TKA were most likely to lose weight after surgery.
- Weight loss was associated with improved clinical outcomes after THA, but not after TKA. However, weight gain in general was associated with inferior clinical outcomes.
- Those with better preoperative functional status were less likely to gain weight after THA or TKA.
Countering conventional wisdom that weight loss after total joint arthroplasty is unlikely, Ast. Et al. emphasize that “obese patients who undergo total joint arthroplasty are more likely than non-obese patients to lose weight after surgery.”