Impact of Muscle Degeneration in Chronic Low Back Pain

Surgical interventions for the removal of intervertebral disc fragments or to enlarge a narrow spine canal are commonly performed worldwide and are considered efficient. Concomitant low back pain is not uncommon among patients with lumbar nerve compression and neurological symptoms. When present, controversy persists in the literature regarding its ideal management. Although neurological symptoms improve after decompressive surgery, the presence of residual chronic low back pain may worsen satisfaction scores and cause functional disability.

The hypothesis of the present study is that the presence of atrophy of the paraspinal and trunk muscles predicts chronic low back pain after lumbar neural decompression. If confirmed, this finding will aid in better planning of physical rehabilitation strategies for this group of patients, as well as a clearer prediction regarding surgical treatment outcomes for patients and health professionals.

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:

For the sample size estimation, we considered the main outcome of the study, a 1.5-point change in the pain scale (VAS) among patients with fat infiltration (grades 1, 2, or 3) and without fat infiltration (grade 0), after 6 months of spine surgery, with 80% power and 95% confidence, the sample required for the study is 28 patients in each group considering a two-tailed test. Similarly to the previous study, we observed that the first 14 patients in the pilot study, 20% of patients had without fat infiltration, therefore, as the admission of patients into the study is consecutive, we expect to find this same percentage of patients without fat infiltration in the final sample of patients, so 140 patients are needed to get 28 patients without fat infiltration. Predicting a loss of 20% of patients at 6 months of follow-up, the initial sample to be considered will be 168 patients to obtain the minimum number of patients required in each group.

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.

Eligibility Criteria:
Inclusion Criteria:

1. adults 18 years of age and older;
2. with symptoms of lumbosacral neural compression (radiculopathy or neurogenic lameness);
3. failed conservative treatment for at least 6 weeks;
4. undergoing surgery for neural decompression (discectomy and / or foraminotomy and / or hemilaminectomy);
5. with complete pre and postoperative medical records in all evaluations.

Exclusion Criteria:

1. need for lumbar arthrodesis;
2. deep infection requiring surgical cleaning;
3. patients submitted to joint facet rhizotomy;
4. active rheumatologic disease, including seronegative arthropathies.