Research Summary

BMI Thresholds Predict Postoperative Risk After Total Hip Arthroplasty

Miranda Manier, BA

Key Highlights

  • Periprosthetic joint infection (PJI) risk rises sharply after a BMI of 37.4 kg/m².
  • Surgical complications increase beginning at a BMI of 32 kg/m².
  • Medical complications increase beginning at a BMI of 39 kg/m².
  • Patients with a BMI of 50 kg/m² are over twice as likely to experience PJI compared to those at the threshold BMI.

A recent study published in Bone & Joint Journal found that patients with a higher BMI who had undergone a total hip arthroplasty (THA) face increasing risks of postoperative complications, with the risk of periprosthetic joint infection (PJI) rising exponentially beyond a BMI of 37.4 kg/m². The odds of developing PJI at a BMI of 50 kg/m² are more than 2.5 times higher than at the threshold. Surgical complications begin to rise at a BMI of 32 kg/m², and medical complications at 39 kg/m².

Obesity has long been associated with elevated complication rates following THA, but the specific BMI thresholds at which risks increase have not been clearly defined. This study aimed to characterize the relationship between BMI and early postoperative outcomes, particularly PJI, as well as composite medical and surgical complications. Understanding these relationships can help tailor perioperative counseling and risk mitigation strategies in patients with elevated BMI.

Researchers analyzed data from the Premier Healthcare Database for elective, primary THAs performed between October 1, 2015, and December 31, 2021. BMI was treated as a continuous variable in logistic regression models using restricted cubic splines (RCSs) to assess its effect on postoperative outcomes. The primary endpoint was PJI within 90 days of surgery. Secondary outcomes included composite surgical and medical complications. Inflection points, or BMI values where risk significantly changed, were identified using bootstrap simulation applied to the RCS models.

The study revealed that PJI risk increases markedly past a BMI of 37.4 kg/m². Compared with this inflection point, patients with a BMI of 40 kg/m² had a 1.22-fold increased risk of PJI, while those with a BMI of 50 kg/m² faced a 2.55-fold increase. For surgical complications, risk rose beginning at a BMI of 32 kg/m², and for medical complications, at a BMI of 39 kg/m². At a BMI of 50 kg/m², the odds of experiencing a surgical complication were 2.07 times higher, and the odds for medical complications were 1.36 times higher, compared with patients at the respective threshold BMIs.

“The results of this study indicate a non-linear relationship between patient BMI and early postoperative risk of PJI, composite medical complications, and composite surgical complications following THA,” the study authors concluded. “The identified cut points with associated odds ratios can serve as tools to help risk-stratify and counsel patients seeking primary THA.”

Reference:
Orringer M, Palmer RC, Ball JR, Telang S, Lieberman JR, Heckmann ND. Effect of BMI on the risk of postoperative complications following total hip arthroplasty. Bone Joint J. 2025;107-B(5 Supple A):47-54. doi:10.1302/0301-620X.107B5.BJJ-2024-1098.R1