Qualitative Evaluation of Paraspinal Musculature After Minimally Invasive Lumbar Decompression: A Prospective Study

Abstract

Background: To quantify fatty infiltration and degree of paraspinal muscle degeneration in patients submitted to tubular microdiscectomy and conventional open microdiscectomy.

Methods: A prospective cohort of patients was submitted to microdiscectomy for lumbar disc herniation after failure of conservative treatment. Selection of the technique was based on the surgeon's preference. Analysis of the multifidus muscle was performed using the Goutallier system and the percentage of fat in the muscle. Preoperative and 1-year postoperative T2-weighted magnetic resonance imaging was used, and statistical analysis was carried out using the Wilcoxon test and Spearman correlation test using a significance level of 5%.

Results: Thirty-two patients were included in the study. The percentage of fatty infiltration in the muscle increased on both sides of the spine 1 year after surgery, although only the ipsilateral side presented statistical significance in patients submitted to conventional microdiscectomy (43.3% preoperative and 57.8% postoperative). Muscular degeneration increased significantly ipsilateral to the disc herniation according to the Goutallier classification (grades 1-2) for both interventions. No statistically significant difference was found for fatty infiltration scores or for the degree of muscular degeneration of the multifidus in the comparative analysis of the methods.

Conclusions: Muscular damage resulting from surgery of lumbar disc herniation significantly increases fatty infiltration and degeneration of the multifidus. Muscular degeneration was associated with worsening back pain.

Clinical relevance: While no significant difference was found between the techniques, the tubular minimally invasive approach shows a tendency for less muscle damage. These findings highlight the importance of minimizing muscle injury during surgery to improve postoperative recovery and long-term outcomes.

Keywords: Goutallier classification; comparative analysis; fatty infiltration; microdiscectomy; minimally invasive surgical procedures; muscle injury atrophy.

Figure 1

Image representation of the modified Goutallier scale: grade 0 indicates no intramuscular fat; grade 1 indicates some fatty streaks present; grade 2 indicates fat that is evident but less than muscle tissue; grade 3 indicates amounts of fat that are equal to the amount of muscle; and grade 4 indicates more fat than muscle tissue.

Figure 2

Selection of the multifidus muscle (represented in the yellow circle) using ImageJ software. The obtained image was then converted to an 8-bit scale. The standard calibration was determined using the psoas muscle as the lower limit and the subcutaneous fat as the upper limit. The relative amount of fat is represented by the number of pixels present, expressed as a percentage. A comparison of the 2 sides was made between the 2 groups and participants, using the nonoperated side as a control.

Figure 3

. Boxplots of the clinical variables of the research participants, by time point.