STUDY DESIGN: Postoperative back muscle injury was evaluated in rats by magnetic resonance imaging and histologic analyses. OBJECTIVE: To compare the magnetic resonance imaging manifestation of back muscle injury with the histologic findings in rats and to subsequently clarify the histopathologic appearance of the high intensity regions on T2-weighted images in human postoperative back muscles. SUMMARY OF BACKGROUND DATA: In a previous study, it was found that the signal intensity on T2-weighted images of the postoperative back muscles was increased in patients who had postsurgical lumbar muscle impairment, especially in those with a prolonged surgery duration. However, the specific histopathologic changes that cause the high signal intensity on T2-weighted images remain unclear. METHODS: Rats were divided into three groups: sham operation group, 1-hour retraction group, and 2-hour retraction group. Magnetic resonance imaging and histology of the multifidus muscles were examined before surgery and at 2, 7, and 21 days after surgery. RESULTS: T2-weighted imaging was more useful than T1-weighted imaging to estimate back muscle injury. The high signal intensity of the multifidus muscles on T2-weighted images remained 21 days after surgery only in the 2-hour retraction group. Histologically, the regeneration of the multifidus muscles was complete at 21 days after surgery in the 1-hour retraction group, but the regenerated muscle fibers in the 2-hour retraction group had a small diameter, and the extracellular fluid space remained large. CONCLUSION: The high signal intensity on T2-weighted images of the postoperative multifidus muscles in the regenerative phase may be due to an increased extracellular space and incomplete muscle fiber regeneration.
STUDY DESIGN:Postoperative back muscle injury was evaluated in rats by magnetic resonance imaging and histologic analyses. OBJECTIVE: To compare the magnetic resonance imaging manifestation of back muscle injury with the histologic findings in rats and to subsequently clarify the histopathologic appearance of the high intensity regions on T2-weighted images in humanpostoperative back muscles. SUMMARY OF BACKGROUND DATA: In a previous study, it was found that the signal intensity on T2-weighted images of the postoperative back muscles was increased in patients who had postsurgical lumbar muscle impairment, especially in those with a prolonged surgery duration. However, the specific histopathologic changes that cause the high signal intensity on T2-weighted images remain unclear. METHODS:Rats were divided into three groups: sham operation group, 1-hour retraction group, and 2-hour retraction group. Magnetic resonance imaging and histology of the multifidus muscles were examined before surgery and at 2, 7, and 21 days after surgery. RESULTS: T2-weighted imaging was more useful than T1-weighted imaging to estimate back muscle injury. The high signal intensity of the multifidus muscles on T2-weighted images remained 21 days after surgery only in the 2-hour retraction group. Histologically, the regeneration of the multifidus muscles was complete at 21 days after surgery in the 1-hour retraction group, but the regenerated muscle fibers in the 2-hour retraction group had a small diameter, and the extracellular fluid space remained large. CONCLUSION: The high signal intensity on T2-weighted images of the postoperative multifidus muscles in the regenerative phase may be due to an increased extracellular space and incomplete muscle fiber regeneration.
Authors: Leonard I Voronov; Georgios Vastardis; Julia Zelenakova; Gerard Carandang; Robert M Havey; Erik I Waldorff; Michael R Zindrick; Avinash G Patwardhan Journal: Int J Spine Surg Date: 2014-12-01