L1 slope: an overlooked spinal parameter

Area of Science:

• Spine biomechanics
• Radiographic analysis
• Spinopelvic parameters

Background:

• Lumbar lordosis is segmented into L1 slope and sacral slope.
• L1 slope (L1S) is a key spinopelvic parameter but is infrequently reported.
• Existing evidence suggests L1S exhibits relative constancy.

Purpose of the Study:

• To analyze the L1 slope (L1S) in relation to other spinopelvic parameters.
• To investigate the constancy of L1S across varying spinal alignments.
• To explore correlations between L1S and measures of lumbar lordosis and pelvic incidence.

Main Methods:

• Evaluated standing lateral lumbosacral x-rays (76 low back pain patients) and CT scans (116 asymptomatic subjects).
• Measured spinal and spinopelvic parameters, including L1 slope (L1S).
• Subgrouped patients by mean sacral slope (SS) or pelvic incidence (PI) and compared parameter means and correlations.

Main Results:

• L1S demonstrated consistent values across subgroups, irrespective of SS or PI.
• L1S remained unchanged in standing and supine positions, unlike other spinal parameters.
• Significant correlations were found between L1S and lumbar lordosis (LL), proximal LL (PLL), distal LL (DLL), and pelvic incidence-lumbar lordosis (PI-LL) mismatch.

Conclusions:

• L1S is a stable spinopelvic parameter, with typical values of 16°-18° (standing) and 8°-9° (supine).
• L1S shows significant correlations with LL, PLL, DLL, and PI-LL mismatch.
• L1S is strongly associated with health-related quality of life scores.