Reliability of Ultrasonography to Assess Spinal Compression During Heavy Load Carriage

Back pain and spinal injury are leading contributors to premature retirement, particularly in physically demanding occupations. Direct and practical methods of spinal assessment are needed to evaluate interventions aimed at reducing spinal loading and injury risk. Ultrasonography has been reliably used to estimate spinal compression via intervertebral disc height, but its reliability for measuring inter-transverse process distances under load has not been established.

Eleven healthy adults underwent ultrasonographic measurement of inter-transverse process distances at each lumbar level (L1-L5), and the total lumbar distance under four loading conditions: (1) immediately on standing while unloaded, (2) after 15 min of unloaded standing, (3) after 15 min of standing loaded with a 25 kg weighted vest, and (4) after 30 min of loaded standing. These procedures were repeated after 1-7 days. Inter-rater, within-visit, and between-visit reliability were assessed using intraclass correlation coefficients (ICCs) and coefficients of variation (CV). Bland-Altman plots were used to assess agreement. A one-way analysis of variance was used to determine the effects of each loading condition on inter-transverse process distances.

Inter-rater, within-visit, and between-visit reliability was good to excellent with ICCs between 0.81 and 0.99 and CVs between 5.24% and 13.0% for all measurements. Inter-transverse process distances were reduced at L2/3 (p = 0.007), L3/4 (p = 0.006), and across the total lumbar distance (p = 0.02) following 15 and 30 min of loaded standing.

Ultrasonography is a reliable, low-cost method for quantifying changes in lumbar spine geometry during loaded standing. This technique may have value in occupational and clinical settings for assessing spinal compression in response to mechanical load.