Fatty Infiltration of the Paraspinal Muscles Is Associated with Postoperative Leg Pain in Lumbar Spinal Stenosis

Purpose or Learning Objective: To evaluate the prognostic value of magnetic resonance imaging (MRI) assessment of preoperative fatty infiltration of the paraspinal muscles in postoperative pain or disability in lumbar spinal stenosis (LSS).

Methods or Background: We used prospective imaging and clinical data from the Norwegian Degenerative Spondylolisthesis and Spinal Stenosis-Spinal Stenosis Trial study. A musculoskeletal radiologist evaluated the preoperative lumbar MRI examination of 300 patients with LSS scheduled for decompression surgery. Only axial T2-weighted images covering the paraspinal and the psoas muscles bilaterally were considered.

Fatty infiltration of the paraspinal muscles was assessed by a muscle fat index (MFI). Signal intensity of the multifidus and the erector spinae at the most stenotic level of lumbar spine was divided by the signal intensity of the psoas major muscle at the same level and side of spine. Pain and disability 2 years after surgery were assessed using patient-reported outcome measures: the Oswestry Disability Index (scores: 0–100), the Zurich Claudication Questionnaire for symptom severity (scores: 1–5) and function (scores: 1–4), and numeric rating scales for leg and back pain (scores: 1–10).

Multivariate linear and logistic regression analyses assessed the relationship between the MFI and patient-reported clinical outcomes. In the logistic regression models, odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for associations between the MFI and ≥ 30% improvement of the postoperative outcomes (dichotomized into yes or no).

Results or Findings: After excluding 57 patients because axial images did not cover the muscles bilaterally, images from 243 patients were evaluated. Mean age of the patients was 66.6 (± 8.5) years; 119 were women (49%). Preoperative MFI and postoperative leg pain were significantly associated, both when leg pain was analyzed as a continuous parameter (coefficient: − 3.2; 95% CI, − 5.6 to − 0.8; P = 0.009) and dichotomized score (OR: 62.8; 95% CI, 4.8–817.8; P = 0.002). These findings suggested that increased fatty infiltration in the paraspinal muscles is associated with a higher risk of persistent leg pain after decompression surgery for LSS. The associations between the MFI and the other outcome measures were not statistically significant.

Conclusion: Increased preoperative fatty infiltration in the paraspinal muscles on MRI was associated with persistent leg pain 2 years after decompression surgery for LSS. This preoperative MRI finding may be useful as a prognostic factor in patients with LSS undergoing decompression surgery.

Publication History

Article published online:
26 May 2023