Objective:

To evaluate the effect of the total psoas area index [TPAI = total psoas muscle area (cm²)/height² (m²)] on neurological complications and clinical outcomes following lateral lumbar interbody fusion (LLIF) and identify the appropriate TPAI to achieve a substantial clinical benefit (SCB).

Methods:

A consecutive series of 123 patients who underwent single-level LLIF at a single center with at least two years of follow-up were retrospectively reviewed. Patient characteristics and operative data were evaluated. Neurological complications were classified as transient and persistent symptoms. The visual analog scale (VAS) score for back pain was assessed preoperatively and at one and two years postoperatively.

Results:

This study included 31 men and 92 women. The mean TPAI was 8.97 cm²/m² for males and 5.04 cm²/m² for females. The mean TPAI was not significantly different between patients with and without perioperative neurological complications. Multiple logistic regression analysis showed that solid interbody fusion was the most significant factor for achieving an SCB regarding back pain in males (odds ratio [OR]: 2.453, p = 0.019) and females (OR: 2.906, p = 0.042). The TPAI was one of the predictors for achieving an SCB in males (OR: 1.251, p = 0.038) and females (OR: 1.795, p = 0.023). The optimal cutoff point of the TPAI for an SCB was 8.18 cm²/m² in males and 4.43 cm²/m² in females.

Conclusion:

The TPAI has little effect on perioperative neurological complications. However, the TPAI was identified as one of the predictors for achieving an SCB regarding back pain.