TITLE: Postoperative weight loss and its clinical significance in patients with adolescent idiopathic scoliosis who undergo spinal fusion INTRODUCTION Several studies demonstrate a comparably lower preoperative weight and body mass index (BMI) in adolescents with idiopathic scoliosis (AIS); however, no study has quantified unintentional postoperative weight loss, or established its impact on outcomes, in this already ‘thin’ patient population after major spinal deformity surgery. METHODS Seventy seven consecutive and eligible patients with AIS who underwent posterior spinal fusion (PSF) were prospectively follow-up from hospital admission (Jan 2010-April 2012). Pre- and postoperative anthropometric measurements were collected (weight, height, BMI) and unintentional weight loss from admission to hospital discharge recorded. Clinically severe involuntary weight loss during the hospital stay was defined as >10% loss of initial body weight from admission to hospital discharge. Sociodemographic, nutritional and perioperative complication data were obtained. Descriptive statistics using SPSS® were performed. RESULTS Mean age of the cohort was 15 years (SD 1.89). Clinically severe postoperative weight loss >10% was identified in 22 patients (30.6%). Of clinical importance, >10% weight loss was associated with a significantly increased incidence of superficial wound infection (13.6% vs. 2%, P = 0.047). A non-significant trend towards increased minor (81.8% vs. 70%, P = 0.449) and major (9.1% vs. 4%, P = 0.756) complications and a slightly longer hospital stay (median 9.5 days vs. 9 days, P = 0.608) in patients who lost > 10% body weight, was also found. CONCLUSION A high prevalence (30.6%) of clinically severe postoperative weight loss >10% in this AIS cohort, was demonstrated. Significantly increased superficial wound infection rates were observed in patients who lost >10% weight during the hospital stay. While these data require further confirmation, this study suggests that 1) severe postoperative weight loss >10% may be a valuable marker of wound infection risk, and 2) surgical strategies to optimise nutritional status, early detect and prevent severe postoperative weight loss may prove beneficial to modifying wound infection risk in patients with AIS who undergo spinal fusion.