Resting Supine for 45 Minutes Yields Consistent Baseline Lumbar Intervertebral Disc Height in Asymptomatic Participants.

Purpose: Intervertebral disc (IVD) height fluctuates diurnally as the spine is exposed to periods of high and low loading. Therefore, accounting for loading history prior to measuring in vivo IVD height is important when investigating IVD mechanics. However, there is a lack of consensus in the literature on in vivo lumbar IVD height recovery times under low loads. Therefore, we sought to determine whether a 45-minute supine rest period yields a consistent baseline for measuring in vivo lumbar IVD height across different times of day.

Methods: Nine asymptomatic participants underwent magnetic resonance (MR) imaging following a 45-minute supine rest, beginning at 7:00 AM on one visit day and mid-day (10:30 AM-12:30 PM) on a separate day. MR images were manually segmented, and the mean heights of the L1-L2 through L5-S1 IVDs were measured. Three MR scans were segmented in triplicate to evaluate segmentation repeatability.

Results: Intraclass correlation coefficients (ICCs) and root mean squared error (RMSE) were calculated for different times of day (ICC: 0.96; RMSE: 0.08 mm) and for segmentation repeatability (ICC: 0.97; RMSE: 0.08 mm).

Conclusion: ICCs indicated excellent reliability, and RMSEs were below 1% of IVD height, suggesting that a 45-minute supine rest period provides a consistent baseline for measuring lumbar IVD height between 7:00 AM and 12:30 PM.