Ultrasound assessment of lumbar disc height in physical therapy exercises

Purpose. Lumbar stabilisation exercises assume that body positions load or unload the intervertebral disc (IVD) predictably, yet several of these positions cannot be reproduced inside a magnetic resonance scanner, so in vivo evidence is scarce. This study established whether ventral lumbar IVD height can be measured by transabdominal ultrasound in six physical therapy positions. Materials & Methods. Adescriptive, within-participant repeated-measures study was conducted. Ten healthy adults (9 men, 1 woman; 18–50 years; BMI 18.4–25.7 kg/m², from retrospectively self-reported height) assumed six positions in one session: supine, standing, bird-dog, modified Biering-Sørensen, standing with an axial barbell load (50 kg men, 30 kg women) and overhead-bar traction. Ventral IVD height at L3–L4 and L4–L5 was measured by a single experienced sonographer. Estimates are reported as means with SD and 95% CI. Results. All 120 disc–position combinations were measured (100%; 95% CI 97–100%; participant level 10/10, 95% CI 69–100%), including under load and suspension. Mean height ranged from 6.08 to 6.83 mm. Stable between-participant differences accounted for 56% and 49% of total variability; the mean within-participant SD was 0.56–0.58 mm. At L3–L4 the largest mean reduction from supine occurred under axial load (−0.74 mm) but varied widely between participants, whereas the modified Biering-Sørensen position gave a smaller but far more consistent reduction (−0.45 mm). No such pattern appeared at L4–L5. Conclusions. Transabdominal ultrasound measured ventral lumbar IVD height in all six positions, including those inaccessible to conventional imaging, with within-participant variability of about 0.6 mm. Position-related differences were small relative to this variability, and no position, including overhead-bar traction, increased ventral disc height.