Beyond BMI: L4-L5 visceral-to-subcutaneous fat ratio on CT predicts impaired wound healing after posterior lumbar fusion-A retrospective study.

BACKGROUND

Obesity is a recognized risk factor for postoperative complications after spine surgery, but body mass index (BMI) does not capture regional fat distribution. The visceral-to-subcutaneous fat area (VFA/SFA) ratio measured on CT reflects an unfavorable fat distribution pattern, yet its role in wound healing after posterior lumbar fusion (PLF) is unclear.

METHODS

We retrospectively analyzed 526 adults who underwent instrumented PLF for degenerative lumbar pathology and had preoperative non-contrast abdominal CT including the L4-L5 level. On a single axial slice at L4-L5, visceral fat area (VFA) and subcutaneous fat area (SFA) were segmented using a semi-automated protocol and the VFA/SFA ratio was calculated and grouped into quartiles. The primary outcome was impaired wound healing within 30 days, defined as persistent erythema or swelling, fat liquefaction, prolonged serous/serosanguinous exudation, partial wound edge necrosis or superficial dehiscence, or the need for negative-pressure therapy, delayed suture removal, additional antibiotics, or surgical debridement. Group comparisons used t tests and χ 2 tests. Univariable and multivariable logistic regression were performed, and discrimination of BMI, VFA, SFA, VFA/SFA, and clinical prediction models was assessed using receiver operating characteristic curves.

RESULTS

Impaired wound healing occurred in 59 patients (11.2%). Compared with patients with good healing, those with impaired wound healing had higher BMI (25.4 ± 4.0 vs. 23.1 ± 3.8 kg/m2, p < 0.001) and higher VFA/SFA ratio (1.063 ± 0.246 vs 0.895 ± 0.259, p < 0.001), whereas SFA did not differ. Each 0.1 increase in VFA/SFA ratio was associated with an adjusted odds ratio of 1.32 (95% CI 1.16-1.50; p < 0.001) for impaired wound healing, independent of age, sex, BMI, diabetes, ASA class, albumin, multilevel fusion, operative time, and blood loss. The AUC was 0.66 for BMI and 0.70 for VFA/SFA; adding VFA/SFA to a clinical model increased the AUC from 0.70 to 0.77.

CONCLUSION

The preoperative VFA/SFA ratio at L4-L5 is an independent predictor of impaired wound healing after PLF and provides incremental discriminative value beyond BMI and conventional clinical risk factors.