Multifidus innervation and muscle assessment post-spinal surgery.

PURPOSE: Assessment of the integrity of the multifidus muscles and corresponding nerve roots, post-open (OSS) versus minimally invasive spinal surgery (MISS) for lumbar spine fractures.

METHODS

We investigated the first six patients undergoing MISS in our institution and age- and sex-matched them with 6 random patients who previously had OSS. All had a similar lumbar fracture configuration without evidence of spinal cord injury. All were assessed using ultrasound muscle quantification and electromyographic studies at a minimum of 6 months post-operatively. Mean cross-sectional area (CSA) was measured at sequential levels within and adjacent to the operative field. Concentric needle electromyography was performed at instrumented and adjacent non-instrumented levels in each patient.

RESULTS

Mean CSA across all lumbar multifidus muscles was 4.29 cm(2) in the MISS group, 2.26 cm(2) for OSS (p = 0.08). At the instrumented levels, mean CSA was 4.21 cm(2) for MISS and 2.03 cm(2) for OSS (p = 0.12). At non-instrumented adjacent levels, mean CSA was 4.46 cm(2) in the MISS group, 2.87 cm(2) for OSS (p = 0.05). Electromyography at non-instrumented adjacent levels demonstrated nerve function within normal limits in 5/6 levels in the MISS group compared to 1/6 levels in the OSS (p = 0.03). Instrumented levels demonstrated nerve function within normal limits in 5/12 levels in the MISS group compared with 4/12 in the OSS group, including moderate-severe denervation at 5 levels in the OSS group (p = 0.15).

CONCLUSIONS

Posterior instrumented MISS demonstrates a significantly superior preservation of the medial branch of the posterior ramus of the spinal nerve and less muscle atrophy, particularly at adjacent levels when compared to OSS.