What Is the Fate of the Adjacent L3-L4 and L5-S1 Disk Angles Following a L4-L5 Decompression-only Surgery?

Although decompression without fusion is widely performed for lumbar stenosis, the segmental behavior of adjacent disks following decompression alone remains poorly defined. Most prior studies have focused on adjacent segment mechanics after fusion, yet it is unclear whether similar reciprocal changes occur when motion is preserved. This pilot study evaluated changes in sagittal alignment at adjacent segments and lower lumbar lordosis following single-level L4-L5 decompression for lumbar spinal stenosis.

A retrospective review of 46 patients (21 males, 25 females) undergoing L4-L5 laminectomy, diskectomy, or combined procedures was performed. Standing lumbar radiographs were obtained preoperatively and 6 months postoperatively. Measurements included L1-S1 lumbar lordosis (LL) and disk angles at L3-L4, L4-L5, and L5-S1. Univariate regression analysis identified predictors of cranial (L3-L4) and caudal (L5-S1) changes, including age, sex, body mass index, surgical approach, procedure type, and LL and L4-L5 changes.

Among 46 patients (23 laminectomy, 15 diskectomy, 8 combined), mean LL change was 1.39° (P = .372) and the change in L4-L5 disk angle correlated significantly with change at L3-L4 (β = 0.241, P = .0407), but no predictors met criteria for multivariate inclusion. Subgroup analysis showed consistent L4-L5 to L3-L4 coupling across procedures, strongest for laminectomy (β = 0.236, R² = 0.129, f2 = 0.148, power = 42.1%).

L4-L5 laminectomy demonstrated the strongest association between operated and cranial segment motion, suggesting biomechanical coupling after decompression. Larger, prospective studies are warranted to validate these preliminary findings.