Outcomes of primary total hip arthroplasty in patients who have a BMI less than 20.

PURPOSE: Low body mass index (BMI) is an independent risk factor for morbidity and mortality, yet patients who have a BMI < 20 undergoing total hip arthroplasty (THA) have attracted little attention. This paper investigates the incidence of (1) mechanical complications (periprosthetic fracture (PPFX), aseptic loosening, and aseptic revision); (2) infectious complications (prosthetic joint infection (PJI) and surgical site infection (SSI)); and (3) venous thromboembolism (VTE) in this population up to two years postoperatively.

METHODS

A national all-payer database identified THA patients from 2010-2021 with low BMI (< 19.9) or normal BMI (20-24.9) (n = 25,578). Patients with trauma, malignancy, or rheumatoid arthritis were excluded. Propensity score matching yielded low BMI (n = 6372) and normal BMI (n = 14,025) groups. Chi-square analyses evaluated complication rates at 90 days, one year, and two years, with odds ratios (OR) and 95% confidence intervals (CI).

RESULTS

At 90 days, low BMI patients demonstrated higher rates of SSI (OR 1.64, 95% CI 1.04-2.60), PPFX (1.54, 95% CI 1.26-1.88), PJI (1.34, 95% CI 1.14-1.58), and aseptic revision (1.44, 95% CI 1.18-1.76). Elevated rates of PPFX, PJI, and aseptic revision persisted at one and two years (all P < 0.05).

CONCLUSION

Patients who had a low BMI and underwent THA demonstrated increased rates of PPFX, SSI, PJI, and aseptic revision at 90 days as well as increased rates of PPFX, PJI, and aseptic revision up to two years following surgery. Our findings suggest that patients who have a BMI < 20 may be particularly vulnerable to complications following THA.