Lumbar Spine Alignment in Six Common Postures: An ROM Analysis With Implications for Deformity Correction

Study Design. A cross-sectional study of prospectively collected data. Objective. To compare lumbar spine alignment in six common postures, and estimate loss in range of motion (ROM) relative to standing. Summary of Background Data. Ideal position for fusion of lumbar spine remains unknown. Although surgical fusion is necessary for deformity correction and symptom relief, the final position in which the vertebrae are immobilized should provide maximum residual function. Methods. Data were collected prospectively from 70 patients with low back pain recruited over a year. All subjects had x-rays performed in slump sitting, forward bending, supine, half squatting, standing, and backward bending postures. ROM quantified in terms of sagittal global and segmental Cobb angles was measured from L1 to S1. Loss of ROM relative to standing was calculated for each posture. Analysis of variance and unpaired t tests were used to identify differences in alignment between postures. Results. Slump sitting gives the greatest lumbar flexion followed by forward bending, and supine postures (P < 0.001). Backward bending produces greater lumbar extension than standing (P = 0.035). Half-squatting and standing postures were not significantly different (P = 0.938). For all postures, L4–5 and L5-S1 segments remained in lordosis, with L4–5 having greater ROM than L5-S1. L1–2 turns kyphotic in lying supine, L2–3 at forward bending, and L3–4 at slump sitting in the form of a “kyphosing cascade.” Should the entire lumbar spine be fused in standing position from L1-S1, there would likely be a mean loss of 47.6° of lumbar flexion and 5.9° of lumbar extension. Conclusion. The present study demonstrates the extent of flexibility required of the lumbar spine in assuming various postures. It also enables comparison of the differences in degree of motion occurring in the lumbar spine, both across postures and across segments. Significant loss in ROM, particularly flexion, is anticipated with fusion modeled after the lordotic standing lumbar spine. Level of Evidence: 2

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