The effect of applied spinal manipulation force vector on resultant vertebral accelerations: an in vivo animal model

Department of Kinesiology, Arizona State University, Tempe, Ariz.; Bone and Joint Research Center, Department of Orthopaedic Surgery, University of North Texas Health Science Center, Fort Worth, Texas; Department of Orthopaedic Surgery, John Peter Smith Hospital, Fort Worth, Texas; Department of Orthopaedic Surgery, Eeuwfeestkliniek Hospital, Antwerpen, Belgium; The Adelaide Centre for Spinal Research, Institute of Medical and Veterinary Science, Adelaide, South Australia      .

Abstract

Introduction

In the performance of spinal manipulative therapy (SMT) and/or chiropractic adjustment it is theorized that the application of force should be in a specific angle
to maximize efficiency of the therapeutic intervention. Recent research in an in situ porcine model found that SMT force vectors that were perpendicular to the spine maximized vertebral accelerations as opposed to directing forces vectored at 30 degrees cephalad or caudal.

The purpose of the current study was to determine the effect of varying SMT applied angle on vertebral accelerations in an in vivo ovine model.

Methods

Twelve healthy, young Merino sheep (mean 24 kilograms, s/d/ 3 kilograms) were examined using a protocol approved by the Institutional Animal Ethics Committee of the Institute for Medical and Veterinary Science in Adelaide, Australia. Prior to testing, anesthesia was induced with an intravenous injection of gram thiopentone and was maintained after endotracheal intubation by 2.5 percent halothane.

Throughout testing the animals were ventilated and the respiration rate was linked to the tidal volume keeping the monitored C02 between 40 to 60 mmHg.
To quantify the dynamic, vibration response of the spine 10g piezoelectric, triaxial accelerometers were attached to intraosseous pins rigidly fixed to the L2 and L4 spinous processes under fluoroscopic guidance (Figure 1). The X, Yand Zaxes of the accelerometers were oriented with respect to the mediallateral (ML), dorsoventral (DV) and cranialcaudal or axial (AX) axes of the vertebrae. Only AX acceleration responses are reported herein.