Normalized total psoas area predicts early postoperative mobility and perioperative adverse events after adult spinal deformity surgery.

Background Context: Poor muscle health has been shown to predict poor perioperative outcomes following adult spinal deformity (ASD) surgery. Currently, there is limited data concerning the correlation between muscle health and recovery among patients undergoing ASD surgery.

Purpose: To determine the relationship between normalized total psoas area (NTPA), postoperative mobility and adverse events (AEs) among patients undergoing ASD surgery.

Study Design: Retrospective cohort study PATIENT SAMPLE: A retrospective analysis was performed at a single institution between January 2014 and December 2023 of patients undergoing ASD surgery by 10 board certified fellowship-trained orthopaedic spine surgeons.

Outcome Measures: Primary outcome measures were postoperative ambulation distance on postoperative day (POD) 1, 2, 3, and 4 as well as perioperative adverse events including postoperative anemia requiring transfusion, ileus, urinary retention wound complication including dehiscence and infection, delirium, atelectasis, urinary tract infection (UTI), deep vein thrombosis (DVT), and epidural hematoma. Secondary outcome measures were 30-day reoperation rates, 30-day readmission rates, and postoperative length of stay (LOS).

Methods: Patients that underwent ASD surgery at a single center (2014-2023) were included in the study. NTPA was analyzed at the L3 and L4 mid-vertebral body on preoperative magnetic resonance imaging (MRI). Receiver operating characteristic (ROC) curve analysis was used to determine gender-specific NTPA cut-off values for predicting perioperative AEs. Patients were categorized as having a low NTPA if both L3 and L4 NTPA were below the cut-off values. Multivariate logistic regression was conducted to identify confounding predictors of perioperative AEs.

Results: 279 patients (102 males, 177 females, mean age 61.2±15.2 years) were included. ROC curve analysis demonstrated L3 NTPA <805 mm/m for males and <505 mm/m for females and L4 NTPA <912 mm/m for males and <714 mm/m for females as cut-off values predicting perioperative AEs. 103 patients (36.9%, 42 males, 61 females) were below these cut-off values and were in the low NTPA cohort. The remaining 176 patients (63.1%, 60 males, 116 females) were in the normal NTPA cohort. The low NTPA group had a higher overall perioperative AEs (70.9% vs 39.2%, p<.001), and lower ambulation distances on postoperative day 1 and 2 compared to the normal NTPA group (p=.021, p=.028, respectively). On multivariate analysis, there were no other predictors of perioperative AEs.

Conclusions: Low L3 and L4 NTPA is associated with lower early postoperative mobility and higher rates of perioperative AEs among patients undergoing ASD surgery. These findings stress the importance of muscle health in recovery after ASD surgery.