Impact of surgical approaches on the lumbar multifidus muscle: an experimental study using sheep as models.

OBJECT In this paper, the authors assessed the effects of different surgical approaches and reconstructive methods on the spinous process after lumbar surgery in sheep. METHODS A total of 41 healthy, adult sheep weighing 38-40 kg were used in this study. The animals were randomly divided into 4 groups (10 animals per group and 1 control). Animals in Group A underwent a spinous process-splitting procedure to expose the lamina. Animals in Group B had bilateral multifidus muscles stripped and the spinous process excised. All animals in Group C underwent unilateral stripping of the multifidus muscle from the spinous process (Group C1) as well as spinous process splitting at the bottom to expose the contralateral lamina attached to the multifidus muscle (Group C2). To mimic the laminoplasty procedure, the multifidus muscles were stripped bilaterally in Group D. For all groups, the surgical level (L-6), length of incision (4 cm), the retracting distance, and time (40 minutes) remained constant. Ten months after surgery, the atrophy rate of the cross-sectional areas (CSAs) of the multifidus muscle, MR imaging findings, and histological changes of the muscle tissue were evaluated. Normal multifidus muscles taken from a healthy sheep at the L-6 level and the preoperative data of MR imaging in experimental animals provided control data (Group E). RESULTS The MR imaging and histological scores of multifidus muscles from sheep in Groups A, B, C1, C2, and D were significantly decreased, and the atrophy rates were significantly higher than those from sheep in Group E (p < 0.05). The postoperative MR imaging and histological scores obtained in Groups A and C2 were highest and the atrophy rates were lowest, while animals from Group B had the highest atrophy rate and lowest MR imaging and histological scores among all experimental groups (p < 0.05). The scores for animals in Groups A and C2, in which the muscles were not stripped from the spinous process, achieved lower atrophy rates and higher MR imaging and histological scores than those for sheep in Groups C1 and D, in which the muscles were stripped (p < 0.05). The groups in which the spinous process was reconstructed after detachment of the muscles (Groups C1 and D) had lower atrophy rates and higher MR imaging and histological scores than Group B (p < 0.05). CONCLUSIONS The multifidus muscle can be effectively protected by reducing the extent of muscle detachment and reconstructing the posterior bone-ligament complex. A spinous process-splitting procedure is a useful method to reduce postoperative muscle atrophy.