INTRODUCTION: The purpose of the current study was to determine the effect of varying spinal manipulative therapy (SMT) vector on vertebral accelerations in an in vivo ovine model.
METHODS: Twelve healthy, young Merino sheep (mean 24 kg, s.d. 3 kg) were examined. Ten‐g piezoelectric, tri‐axial accelerometers were attached to intraosseous pins rigidly fixed to the L2 and L4 spinous processes under fluoroscopic guidance following general anesthesia. SMT was applied to the L3 spinous process using a hand‐held Impulse Adjusting Instrument. In each of three trials, thirteen SMTs (˜200 N peak force) were randomly applied over 2.5 seconds (˜6 Hz) at input force vectors of 90 degrees (z‐axis), 60 degrees (cephalad), and 120 degrees (caudal). During the SMTs, vertebral accelerations at L2 and L4 were recorded at a sampling frequency of 5000 Hz using a 16‐bit data acquisition system. Peak‐peak acceleration responses at L2, L4, and L2‐L4 were computed for each trial. A one‐way ANOVA compared the mean acceleration responses between the three applied force vectors.
RESULTS: A significant increase in mean L2, L4, and L2‐L4 vertebral accelerations were observed for all SMTs directed caudal (p<.01). For SMTs directed cephalad, mean L2 vertebral accelerations were significantly greater than L4 vertebral accelerations (p<.01), and conversely, for caudal thrusts L4 vertebral accelerations were significantly greater than accelerations observed at L2 (p<.01). SMTs applied perpendicularly to the spine caused larger vertebral accelerations at L2 compared to SMTs directed cephalad, however L4 accelerations were significantly greater for cephalad SMTs compared to those delivered at 90 degrees (p<.01).
DISCUSSION: The vector that SMT is delivered has a significant effect upon vertebral accelerations. Enhancing vertebral motions by modulating applied vector is an important biomechanical consideration for clinicians whom are attempting to improve inter‐segmental mobility during SMT.