Assessment of the psoas muscle changes following the oblique lateral interbody fusion (OLIF) approach: A prospective observational study

Traditional open posterior fusion techniques involve stripping of the posterior paraspinal muscles with protracted retraction, which can lead to ischemia and denervation. This may result in poor clinical outcomes despite a well-performed surgery. Oblique lumbar interbody fusion (OLIF) is a minimally invasive modified retroperitoneal anterior approach in the corridor between the psoas major (PM) and great vessels. The purpose of this research was to study changes in psoas properties and clinical outcomes in terms of the loss of hip flexion in patients undergoing OLIF surgery. Patients with lumbar pathologies who underwent instrumented OLIF at our center were included. These patients were examined clinically at baseline and 6 months postoperatively. The Oswestry disability index (ODI) and visual analog scale (VAS) scores for back pain and leg pain were noted. Magnetic resonance imaging (MRI) scans were obtained preoperatively and postoperatively (minimum 6 months) to compare the cross-sectional areas (CSAs) of the PM. In total, 17 patients (male: female = 8:9) with a mean age of 46.06 ± 10.49 years were included. The operation time was 154.94 ± 32.33 min, estimated blood loss was 190 ± 56 mL, and mean CSAs of the right and left psoas were, respectively, 9.94 ± 3.19 and 10.65 ± 3.74 cm 2 preoperatively and 10.00 ± 3.06 and 8.53 ± 2.81 cm 2 at follow-up. Qualitative measurements revealed that muscle atrophy on the left side (approach side) was 19.12% ± 3.14% and fatty degeneration had occurred in 13 of 17 (76.5%) patients. Postoperatively, all patients had significant improvement in the VAS (back and leg) and ODI scores. Furthermore, 3 of 17 (17.6%) patients had mild hip weakness (4/5) on the left side immediately postoperatively, but it resolved in 6 months. Moreover, 2 of 17 (11.8%) patients complained of paraesthesia. OLIF does cause injury to the PM but it is clinically insignificant according to MRI scans and clinical evaluations.