Effect of pure muscle retraction on multifidus injury and atrophy after posterior lumbar spine surgery with 24 weeks observation in a rabbit model.

Purpose: To evaluate the effect of pure muscle retraction on multifidus injury and atrophy.
Materials and Methods: Sixty-three adult New Zealand white rabbits were divided evenly into three groups: 1-h retraction (group R1), 2-h retraction (R2), and sham surgery (C). The multifidus muscle was evaluated using magnetic resonance imaging (MRI) and histology after 3 and 48 h, and 1, 3, 6, 12, and 24 weeks after surgery.
Results: Multifidus muscle injury and atrophy were not observed in group C, but were obvious in groups R1 and R2. Edema, necrosis, and inflammation mainly occurred in the first week postoperatively, and were more severe in R2 than in R1 (P < 0.01). Muscle fiber regeneration began at week 1, fibrotic changes mainly occurred at weeks 3 and 6, and fat degeneration became obvious at weeks 12 and 24 postoperatively. The fibrosis and fat degeneration scores of R2 were higher than those of R1 (P < 0.01). Decreased acetylcholine activity and granular degeneration of the neuromuscular junction were observed in both retraction groups, but was more severe in R2 than in R1 (P < 0.01).
Conclusion: Muscle retraction was an important factor not only for multifidus injury, but also for long-term multifidus atrophy after posterior lumbar surgery; a longer retraction time caused more severe multifidus injury and atrophy. Muscle fibers can be regenerated postoperatively, and denervation might be the reason for muscle atrophy.