Physician-applied contact pressure and table force response during unilateral thoracic manipulation.

OBJECTIVE: To measure the applied loading to human subjects during the reinforced unilateral thoracic manipulation.
DESIGN: Biomechanical descriptive study.
SETTING: The National College of Chiropractic Clinical Biomechanical Laboratory in Lombard, Illinois.
SUBJECTS: Seven men, ages 24 to 47, with no positive responses regarding muscle relaxants or thoracic spinal fractures, surgeries, or pain. MAIN OUTCOME MEASURES: We measured the contact pressure distribution at the physician-subject contact region and extracted three biomechanical parameters. From the measured time-dependent support force magnitudes, we extracted five additional biomechanical parameters.
RESULTS: In the application of the reinforced unilateral manipulative treatment, the physician establishes contact and applies a near-static preload force of 250 to 350 N. The dynamic portion of the typical thrust is preceded by a 22% decrease in force magnitude, and the peak thrust magnitude is linearly related to the preload force magnitude. We estimate that the peak contact pressure beneath the chiropractor's pisiform can exceed 1000 kPa, with the highest pressures transmitted over areas as small as 3.6 cm2, depending on manipulative style.
CONCLUSIONS: This work represents the first attempt at performing simultaneous measurements of the physician-applied loading and table force response and measuring the contact pressure distribution at the physician-patient contact region during chiropractic manipulation. This type of work will lead to a better understanding of the relationship between the dynamic physician-applied normal forces and the resulting load response at the table and gives us additional outcome parameters to quantify manipulative technique.