Impact of Muscle Degeneration in Chronic Low Back Pain

This is a prospective cohort study. Patients with lumbar degenerative diseases and symptoms of nerve compression (radiculopathy or neurogenic claudication) who will undergo surgical treatment for neural decompression (discectomy, foraminotomy or laminectomy).

The cohort will be followed by a team researcher (not blinded to the purpose of the study) at preoperative (up to 1 month before surgery), immediate postoperative (12 to 24 hours after procedure), 06, 12 and 24 months after surgery. Imaging tests will be performed on the preoperative evaluation and at six months follow-up after the operation.

The treatment will consist of lumbar decompression surgery, which may consist of discectomy, foraminotomy or laminectomy, according to the type and location of the compression. The choice of surgical technique will be made by the assistant surgeon.

Patients will be divided into four groups regarding the type of soft tissue retractor and image magnification:

Group 1: (minimally invasive microdiscectomy): surgeries performed with loupes or microscope plus minimally invasive soft tissue retractors (tubular or "Caspar").

Group 2: (open microdiscectomy) surgeries performed with loupes or microscope plus conventional soft tissue retractors (auto static, "Taylor" or "McCulloch").

Group 3: (endoscopic discectomy): surgeries performed by means of the "full endoscopic" technique;

Group 4: (open discectomy "with the naked eye"): surgeries performed without image magnification. Use of conventional soft tissue retractors (auto static, "Taylor" or "McCulloch").

Image Evaluation:

1. X-Rays (anteroposterior, lateral, dynamic lateral films) - to evaluate and measure the presence of scoliosis, spondylolisthesis or Degenerative vertebral dislocations.

2. MRI: to detect and to grade the presence of fat infiltration of the Psoas and Multifidus muscles (Arabanas et al); to grade Modic Signal and facet joint degeneration (Weishaupt et al).

Sample size:

To calculate the sample size, we considered the main outcome of the study: proportion of patients with residual pain (VAS ≥ 2) six months after surgery, and we assumed that around 15% of patients with fat infiltration (grades 1, 2 or 3) should remain with residual pain and that the proportion of patients without fat infiltration (grade 0) who remain with residual pain should be less than 15%.

Considering a test power of 80%, significance level of 5%, and two-tailed test, 138 patients in each group (presence of pain and muscle degeneration and presence of pain without muscle degeneration) will be necessary, totaling 276 patients. That would be the number required to detect a 10% difference in the proportion of residual pain between the groups with and without fat infiltration.

Statistics:

Numerical variables with normal distribution will be described by means and standard deviations and variables with non-normal distribution by medians and interquartile ranges, in addition to the minimum and maximum values. The distributions of numerical variables will be verified by histograms, boxplots and, if necessary, Shapiro-Wilk normality tests. Categorical variables will be described by absolute frequencies and percentages. The analyzes will be performed with the SPSS26 program, considering a 5% significance level.