Device, protocol and measurement of regional spinal stiffness

Spinal stiffness is commonly assessed by manual therapists but the methodology varies widely. The current study presents a novel device - Therapeutic Spinal Mobilizer - to measure spinal stiffness safely and reliably. The methodology developed allows exertion of a force perpendicular to the spinal skin surface over a selected spinous process at a preselected frequency for predetermined duration cyclically in a repeatable manner. The loading rate is governed by the gravity feed. The force applied and displacements produced were used to calculate the spinal stiffness at that level. The results revealed a significant difference in stiffness due to magnitude of load (loading rate) (p<0.01) but no significant difference in stiffness between different cycles of loading with same load. The phase of respiration significantly affected stiffness, with total lung capacity being stiffest and residual functional capacity the least stiff (p<0.05). There was a significant difference in stiffness of the three spinal levels tested (p<0.05). In conclusion, the standardized methodology revealed that spinal stiffness of one region may be very different from another. Different loads yield significantly different stiffness (p<0.01).