Classification of chronic back muscle degeneration after spinal surgery and its relationship with low back pain

Abstract

Study Design: Retrospective case series. Purpose: To classify back muscle degeneration using magnetic resonance imaging (MRI) and investigate its relationship with back pain after surgery. Overview of Literature: Back muscle injury and degeneration often occurs after posterior lumbar surgery, and the degeneration may be a cause of back pain. However, the relationship between back muscle degeneration and back pain remains controversial. Methods: A total of 84 patients (average age, 65.1 years; 38 men, 46 women) with lumbar spinal stenosis underwent posterior decompression surgery alone. MRI (1.5 tesla) was evaluated before and more than a year after surgery in all patients. Muscle on MRI was classified into three categories: Low intensity in T1-weighted imaging, high intensity in T2-weighted imaging (type 1), high intensity in both T1-and T2-weighted images (type 2), and low intensity in both T1-and T2-weighted imaging (type 3). The prevalence of the types and their relationship with back pain (determined on a visual analog scale) were evaluated. Results: MRI revealed muscle degeneration in all patients after surgery (type 1, 6%; type 2, 82%; and type 3, 12%). Type 2 was significantly more frequent compared with types 1 and 3 (p < 0.01). Low back pain was significantly improved after surgery (p < 0.01). Low back pain was not associated with any MRI type of muscle degeneration after surgery (p > 0.05). Conclusions: Various pathologies of back muscle degeneration after posterior lumbar surgery were revealed. Type 2 (fatty) change was most frequent, and other patients had type 3 (scar) or type 1 (inflammation or water-like) changes. According to the Modic classification of bone marrow changes, Modic type 1 change is associated with inflammation and back pain. However, no particular type of back muscle degeneration was correlated with back pain after surgery.