The effect of high, medium and low mobilization forces applied during a hip long-axis distraction mobilization on the strain on the inferior ilio-femoral ligament and psoas muscle: A cadaveric study.

Background: Several studies have suggested that the changes in elasticity of the joint capsule and surrounding muscles during a hip long-axis distraction mobilization (LADM) could explain the pain-relieving and mobility-improving effects of the technique.

Objective: To compare the strain on the inferior ilio-femoral ligament and psoas muscle when applying three different magnitudes of force during LADM.

Design: Repeated measures controlled laboratory cadaveric study.

Methods: Eleven hip joints were mobilized from six fresh-frozen cadavers (mean age, 73.4 ± 5.7 years). Three magnitudes of force (low, medium and high) were applied during a hip LADM in open-packed position according to grades of joint mobilization. Strain on the inferior ilio-femoral ligament and psoas muscle were measured with strain gauges. The magnitude of the force applied during LADM was recorded.

Results: Strain on the inferior ilio-femoral ligament during a high-force LADM was significantly higher than strain on the inferior ilio-femoral ligament during low (p < 0.001) and medium-force LADM (p < 0.001). The strain on the inferior ilio-femoral ligament during a medium-force LADM was significantly higher than during a low-force LADM (p = 0.004). No changes in strain on psoas muscle were observed. The magnitude of force applied during LADM showed a significant progressive increase from low to high-force LADM.

Conclusion: The different magnitudes of forces applied during LADM produce different strains on the inferior ilio-femoral ligament but not on the psoas muscle. The strain on the inferior ilio-femoral ligament during LADM depends on the magnitude of the mobilization force.