Reliability and minimal detectable change for measuring segmental lumbar spine flexion and extension in the sidelying...

There is no imaging gold standard for measuring segmental spinal motion that can serve as a criterion measure to compare with manual assessment or evaluate mechanical changes following spinal manipulative therapy (SMT).

This study aimed to determine intra-rater and inter-rater reliability, as well as the minimal detectable change (MDC), for measuring segmental lumbar spine flexion and extension in the sidelying position using ultrasound imaging.

Ultrasound images of the spinous processes of the lumbar spine and base of the sacrum were acquired from 30 asymptomatic subjects positioned in sidelying. Two independent examiners took two measurements of the interspinous distance at each lumbar segment using digital calipers during a single session.

Inter-rater reliability using intraclass correlation coefficient (ICC_(2,1)) for lumbar flexion ranged from 0.87 to 0.97. The 95% limits of agreement (LOA) for flexion inter-rater reliability were -0.26 to 0.30 cm. For extension, ICC_(2,1) ranged from 0.81 to 0.96. Intra-rater reliability was higher, with ICC_(3,1) >0.90 for all segments in both directions. The 95% LOA for flexion intra-rater reliability was -0.17 to 0.17 cm. Standard error of measurement (SEM) ranged from 0.074 to 0.280 cm, and MDC at the 95% confidence level ranged from 0.204 to 0.498 cm, with flexion showing greater precision.

The results suggest ultrasound imaging is a reliable and precise method for assessing segmental lumbar motion in the sidelying position. Future research employing this ultrasound imaging method may inform debates on manual assessment of segmental spinal motion and the mechanical mechanism underlying SMT.