To investigate the progression of adult spinal process impingement (SPI) and provide a staging system through a retrospective long-term MRI-based longitudinal study. From April 2005 to April 2025, 132 patients who underwent at least four lumbar MRI scans prior to index lumbar surgery were enrolled. The mean follow-up duration was 11.7 ± 3.2 years. Patients were divided into two groups: group 1 (no SPI; n = 70, mean age 60.0 ± 6.4 years, F:M = 45:25) and group 2 (with SPI; n = 62, mean age 67.2 ± 7.1 years, F:M = 43:19). A novel SPI staging system and grading system for herniation of the interspinal ligament (HISL) was established. The analysis focused on the L3/S1 levels. Radiographic assessment included standing anteroposterior and flexion-extension lumbar radiography. Osteoporosis was evaluated using DEXA scans. In group 1, two interspinal ligament patterns were observed: normal MRI (76.7%) and fatty degeneration (23.3%). Group 2 showed 107 SPI levels: 25 at L3/L4, 61 at L4/L5, and 21 at L5/S1 levels. The SPI progresses through four stages: early (I), soft tissue (II), bone (III), and spinal stenosis (IV), with variable intervals. Osteoporosis is a key factor in the development of SPI. HISL appeared in 28 segments of group 2 but none in group 1 (p < 0.001). Of the HISL cases, 12 were mild, 9 were moderate, and 7 were severe. Lumbar decompression was performed in four moderate and five severe cases. This long-term longitudinal MRI study delineated the stages and natural progression of SPI. HISL was strongly associated with the SPI, and its size was the principal factor contributing to spinal stenosis.
Li et al. (Tue,) studied this question.