Clinical Significance of Difference in Lumbar Lordosis (DiLL) as a Dynamic Spinal Alignment Parameter: A Narrative Review.

Abstract

Background: Lumbar lordosis (LL) varies with posture due to spinal mobility. The difference in LL (DiLL) between supine and standing positions (DiLL: supine LL - standing LL) is a novel dynamic parameter reflecting functional spinal alignment. Recent studies suggest its potential utility in predicting outcomes after lumbar spine surgery.

Methods: A narrative review of the literature was conducted to examine posture-related changes in LL, with a particular focus on DiLL. Recent studies assessing LL in different postures and its association with postoperative outcomes following lumbar decompression and fusion surgeries were included.

Results: Standing LL is typically greater than supine LL in healthy individuals, resulting in negative DiLL. However, elderly individuals and patients with adult spinal deformity (ASD) often show positive DiLL, indicating reduced ability to maintain lordosis when standing. Patients with a positive DiLL value (DiLL [+]) tend to have worse postoperative outcomes than DiLL (-) patients after short-segment fusion or decompression surgeries. Among DiLL (+) patients, those with mild or no vacuum phenomena in non-fused intervertebral discs (retaining postoperative mobility) exhibited better surgical outcomes than those with severe vacuum phenomena in such discs.

Conclusions: DiLL is an easily obtainable dynamic parameter using standard imaging and may serve as a useful predictor of surgical outcomes, particularly in procedures that preserve lumbar mobility. While static parameters like pelvic incidence-LL mismatch remain essential in long-segment fusions, DiLL provides additional insight into functional alignment. In lumbar decompression or short-segment fusion surgeries, DiLL (+) patients who are expected to have non-fused intervertebral discs with severe disc vacuum phenomena postoperatively may experience poorer surgical outcomes. Therefore, if such patients present with severe ASD-specific symptoms, such as fatigue-induced low back pain when standing, we recommend considering long-segment fusion surgery or informing patients about the potential for residual postoperative symptoms and postoperative kyphosis.