Objective To investigate the effects of body mass index (BMI) on mortality and perioperative complications in elderly patients with hip fracture.

Methods The medical records of hip fractures in elderly patients over 65 years old were collected in our hospital. According to BMI, the patients were divided into the underweight group (UW group) with 30 cases, normal weight group (NW group) with 183 cases, overweight group (OW group) with 65 cases and obese group (OB group) with 17 cases. The preoperative and intraoperative data of hip fractures in three groups were analyzed.

Results Among the 295 patients, 10.85% (32/295) cases died after one year, and 21.02% (62/295) cases developed perioperative complications. The differences in the age, operation time, perioperative complications and one-year postoperative mortality rate among three groups were statistically significant (P ＜ 0.05 to P ＜ 0.01). Taking patients in the NW group as the control, after controlling the confounding factors such as age, gender, ASA classification and operation time, the results of logistic regression analysis showed that the BMI was an independent influencing factor of perioperative complications and 1-year postoperative death in elderly patients with hip fractures (P ＜ 0.05 to P ＜ 0.01). The probability of perioperative complications in the OB group was 4.31 times that in the NW group (P ＜ 0.05, 95%CI: 1.28–7.67), and that in the UW group was 3.43 times that in the NW group (P ＜ 0.05, 95%CI: 1.23–6.56). The risk of death one year after surgery in the UW group was 3.75 times that in the NW group (P ＜ 0.05, 95%CI: 2.25–6.67).

Conclusions The mortality rate of patients with low body weight increases one year after surgery. Compared with patients with normal body weight, the patients with underweight or obese also have an increasing risk of perioperative complications.