This post comes from Fred Nelson, MD, an orthopaedic surgeon in the Department of Orthopedics at Henry Ford Hospital and a clinical associate professor at Wayne State Medical School. Some of Dr. Nelson’s tips go out weekly to more than 3,000 members of the Orthopaedic Research Society (ORS), and all are distributed to more than 30 orthopaedic residency programs. Those not sent to the ORS are periodically reposted in OrthoBuzz with the permission of Dr. Nelson.
Nearly 200,000 Americans have bariatric surgery each year, so it’s important to understand the long-term musculoskeletal consequences of those procedures. Gastric bypass constitutes the most common bariatric surgery and is believed to lead to bone loss. However, fracture risk in gastric-bypass patients has been insufficiently studied. Given that diabetes is an independent risk factor for fractures, any gastric bypass–fracture association should be studied in patients with and without diabetes.
That’s what Swedish researchers did in a retrospective cohort study1 of 38,971 obese patients who underwent gastric bypass—7,758 of whom had diabetes and 31,213 of whom did not. The patients in each of the two groups were propensity-score matched with controls (1 to 1). The researchers evaluated the overall risk of fracture and fall injury, along with fracture risk according to amount of weight loss and degree of calcium and vitamin D supplementation during the first year after surgery.
After a median follow-up of 3.1 years, gastric bypass was associated with an increased risk of any fracture, both in patients with diabetes (HR, 1.26) and without diabetes (HR, 1.32). Fracture risk appeared to increase with time. The risk of fall injury without fracture also increased after gastric bypass. (The increased risk of fall injury may explain some of the increased fracture risk.) Surprisingly, neither higher amounts of weight loss nor poor calcium and vitamin D supplementation during the first year after surgery were associated with increased fracture risk.
The metabolic consequences of surgically induced weight loss are significant for the obese population. Those consequences probably reach beyond bone to affect many aspects of musculoskeletal and possibly neurological homeostasis.
- Axelsson KF, Werling M, Eliasson B, Szabo E, Näslund I, Wedel H, Lundh D, Lorentzon M. Fracture Risk After Gastric Bypass Surgery: A Retrospective Cohort Study. J Bone Miner Res. 2018 Jul 16. doi: 10.1002/jbmr.3553. [Epub ahead of print] PMID: 30011091
The two numbers that you’ll want to remember from the computer model-based cost-effectiveness study by McLawhorn et al. in the January 20, 2016 Journal of Bone & Joint Surgery are $13,910 and $100,000. The first number is an incremental cost-effectiveness ratio (ICER). Here, it’s the estimated added cost per quality-adjusted life year (QALY) for morbidly obese patients (BMI ≥35 kg/m2) with end-stage knee osteoarthritis who undergo bariatric surgery two years prior to total knee arthroplasty (TKA), compared with similar patients who undergo immediate TKA.
The $100,000 is the threshold “willingness to pay” (WTP) that the authors used in their evaluation. Willingness to pay reflects the amount society and healthcare payers such as Medicare and private insurers are willing to pay for a patient to accrue one year lived in perfect health.
Here’s another way to view these findings: Morbidly obese patients who undergo TKA are at increased risk for wound-healing problems, superficial and deep infections, early revision, and poor function. The authors estimated that if bariatric surgery reduces the TKA risks in these patients by at least 16%, on average, the combination of bariatric surgery followed by TKA is more cost-effective than immediate TKA alone.
Because the ICER was much less than the WTP in this model, the authors conclude that “bariatric surgery prior to total knee arthroplasty may be a cost-effective option for improving outcomes in motivated patients with a BMI of ≥35 kg/m2 with end-stage knee osteoarthritis.” However, they are quick to add that “decision modeling cannot simulate reality for every clinical situation.” While this rigorously developed model may provide a decision-making framework for surgeons and policymakers, the authors say, “this approach may be impractical for an individual patient…desiring immediate symptomatic relief from knee osteoarthritis.”