In vivo measurement of intradiscal pressure changes related to thrust and non-thrust spinal manipulation in an animal model: a pilot study

Abstract

Background: The intervertebral disc is a known back pain generator and is frequently the focus of spinal manipulative therapy evaluation and treatment. The majority of our current knowledge regarding intradiscal pressure (IDP) changes related to spinal manual therapy involves cadaveric studies with their inherent limitations. Additional in vivo animal models are needed to investigate intervertebral disc physiological and molecular mechanisms related to spinal manipulation and spinal mobilization treatment for low back disorders.

Methods: Miniature pressure catheters (Millar SPR-1000) were inserted into either the L4-L5 or L5-L6 intervertebral disc of 3 deeply anesthetized adult cats (Oct 2012-May 2013). Changes in IDP were recorded during delivery of instrument-assisted spinal manipulation (Activator V® and Pulstar®) and motorized spinal flexion with/without manual spinous process contact.

Results: Motorized flexion of 30° without spinous contact decreased IDP of the L4-L5 disc by ~ 2.9 kPa, while physical contact of the L4 spinous process decreased IDP an additional ~ 1.4 kPa. Motorized flexion of 25° with L5 physical contact in a separate animal decreased IDP of the L5-L6 disc by ~ 1.0 kPa. Pulstar® impulses (setting 1-3) increased IDP of L4-L5 and L5-L6 intervertebral discs by ~ 2.5 to 3.0 kPa. Activator V® (setting 1-4) impulses increased L4-L5 IDP to a similar degree. Net changes in IDP amplitudes remained fairly consistent across settings on both devices regardless of device setting suggesting that viscoelastic properties of in vivo spinal tissues greatly dampen superficially applied manipulative forces prior to reaching deep back structures such as the intervertebral disc.

Conclusions: This study marks the first time that feline in vivo changes in IDP have been reported using clinically available instrument-assisted spinal manipulation devices and/or spinal mobilization procedures. The results of this pilot study indicate that a feline model can be used to investigate IDP changes related to spinal manual therapy mechanisms as well as the diminution of these spinal manipulative forces due to viscoelastic properties of the surrounding spinal tissues. Additional investigation of IDP changes is warranted in this and/or other in vivo animal models to provide better insights into the physiological effects and mechanisms of spinal manual therapy at the intervertebral disc level.

Keywords: Chiropractic; Intervertebral disc; Intradiscal pressure; Lumbar; Spinal manipulation.

Fig. 1

Experimental methodology & manipulation devices. Xray of miniature pressure sensor inserted in the L4-L5 intervertebral disc (A) with an enlargement showing the sensor (*) projecting from the tip of a 18 gauge needle (B). Photos of commercially available Activator V® and Pulstar® devices that deliver spinal manipulative impulses of 2-3 ms duration. C. Photos of anesthetized feline on a hinged motorized flexion device in the horizontal and 20° flexion position

Fig. 2

L4-L5 Intradiscal Pressure Changes with the Pulstar Device. Intradiscal pressure (IDP) recordings from the L4-L5 disc during three consecutive Pulstar impulses delivered at device setting 1 (A), setting 2 (B), and setting 3 (C). Note the relatively constant baseline IDP and similar magnitudes of IDP changes across device settings despite a slight increase in peak IDP occurring with the third impulse on settings 1 and 2

Fig. 3

L4-L5 intradiscal pressure changes with the activator V device. Intradiscal pressure (IDP) recordings from the L4-L5 disc during three consecutive Activator V impulses delivered at device setting 1 (A), setting 2 (B), setting 3 (C) and setting 4 (D). Note the relatively constant baseline IDP with the exception of setting 1 which was lower and similar magnitudes of IDP changes across device settings. Figures 2, 3 and 4 are from the same experimental preparation

Fig. 4

L5-L6 intradiscal pressure changes with pulstar & flexion manipulation devices. Intradiscal pressure (IDP) recordings from the L5-6 disc during three consecutive Pulstar impulses delivered at device setting 1 (A), setting 1, 2, 3 (B), and 25° motorized flexion with manual thumb contact applying mild cranialward forces to the L6 spinous process (C). Note these recordings are from a separate preparation from Fig. 2

Fig. 5

IDP during 30° of motorized flexion with and without manual contact. Intradiscal pressure (IDP) recordings from the L4-L5 disc during motorized flexion of 30° without manual contact (A) and with manual thumb contact applied cranialward to the L4 spinous (B). Note the additional ~ 1.4 kPa decrease in IDP with applied physical contact