220. The cross-sectional area of psoas muscle impacts functional outcomes of MI-TLIF for lumbar degenerative diseases

Abstract

BACKGROUND CONTEXT The decrease of psoas cross-sectional area has been used as a parameter of sarcopenia and reported to be a predictor of increased risk of mortality and complications in various surgeries, including spine surgery. However, it is unclear whether psoas size impacts postoperative functional outcomes in spine surgery. PURPOSE To investigate the impact of psoas cross-sectional area on short-term clinical outcomes of MI-TLIF for degenerative diseases. STUDY DESIGN/SETTING Retrospective study. PATIENT SAMPLE A total of 108 patients who underwent minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) at a single level for degenerative lumbar diseases. Patients with previous anterior-approached lumbar surgery history were excluded. OUTCOME MEASURES Oswestry Disability Index (ODI), Visual Analog Scale at Back (VAS Back) and at leg (VAS Leg), Short Form 12 Physical Component Summary (SF-12 PCS) and Mental Component Summary (SF-12 MCS) and Patient-Reported Outcomes Measurement Information System Physical Function (PROMIS PF) at pre-op, 2 weeks, 6 weeks, 3 months and 6 months, intra- and postoperative complications, length of stay (LOS). METHODS The cross-sectional area of psoas muscle was measured at the level of L3/4 on T2-weighted axial images of preoperative MRI by 2 observers. Normalized total psoas area (NTPA) was calculated as total psoas area normalized to patient height. Outcomes in patients with the lowest sex-specific quartile of NTPA (Low NTPA group) were compared to the other 3 quartiles (High NTPA group). RESULTS A total of 108 patients (age [58.5±13.4], gender [62 males, 46 female], diagnosis [68 lumbar degenerative spondylolisthesis, 30 lumbar canal stenosis, 8 lumbar disc herniation]) were included in this study. The lowest quartile of NTPA threshold was 780 mm2/m2 in male and 486 mm2/m2 in female. The inter-rater reliability for NTPA was excellent. (ICC = 0.989, 95% CI 0.984-0.993) There were no significant differences between the two cohorts regarding demographics (age, gender, race, diagnosis, type of surgery, surgical level) including factors affecting clinical outcomes of lumbar surgery (BMI, smoking status, mental disorders, worker's compensation, previous lumbar surgery history). At 2- and 6-weeks preop, there was no significant difference between cohorts in all parameters. At 3 and 6 months, all parameters for the Low NTPA group showed a tendency for worse outcomes compared to those in the High NTPA group. In particular, ODI at 6 months (Low NTPA group 30.1 vs High NTPA group 16.4, P=0.011), VAS back at 6 months (Low NTPA group 3.6 vs High NTPA group 1.9, P=0.022), SF-12 MCS at 3 months (Low NTPA group 48.8 vs High NTPA group 54.0, P=0.043) and at 6 months (Low NTPA group 49.0 vs High NTPA group 55.2, P=0.016) were significantly worse in the Low NTPA group. There was no significant difference in intra- and postoperative complications and LOS in this study. CONCLUSIONS The decrease of psoas cross-sectional area had a negative impact on short-term functional outcomes of MI-TLIF. This parameter is highly reliable and easy to measure with preoperative MRI. Along with the progress of the aging society, this sarcopenia-related parameter may play an important role in preoperative decision making in the treatment for degenerative lumbar diseases. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.