Spinal Tissue Loading Created by Different Methods of Spinal Manipulative Therapy Application

Abstract

Study design: Comparative study using robotic replication of spinal manipulative therapy (SMT) vertebral kinematics together with serial dissection.

Objective: The aim of this study was to quantify loads created in cadaveric spinal tissues arising from three different forms of SMT application.

Summary of background data: There exist many distinct methods by which to apply SMT. It is not known presently whether different forms of SMT application have different effects on spinal tissues. Should the method of SMT application modulate spinal tissue loading, quantifying this relation may help explain the varied outcomes of SMT in terms of effect and safety.

Methods: SMT was applied to the third lumbar vertebra in 12 porcine cadavers using three SMT techniques: a clinical device that applies forces through a hand-held instrument (INST), a manual technique of applying SMT clinically (MAN) and a research device that applies parameters of manual SMT through a servo-controlled linear actuator motor (SERVO). The resulting kinematics from each SMT application were tracked optically via indwelling bone pins. The L3/L4 segment was then removed, mounted in a parallel robot and the resulting kinematics from SMT replayed for each SMT application technique. Serial dissection of spinal structures was conducted to quantify loading characteristics of discrete spinal tissues.

Results: In terms of load magnitude, SMT application with MAN and SERVO created greater forces than INST in all conditions (P < 0.05). Additionally, MAN and SERVO created comparable posterior forces in the intact specimen, but MAN created greater posterior forces on IVD structures compared to SERVO (P < 0.05).

Conclusion: Specific methods of SMT application create unique vertebral loading characteristics, which may help explain the varied outcomes of SMT in terms of effect and safety.

Level of evidence: N/A.

Figure 1

Rectangular flags with four infrared light-emitting diode markers attached to bone pins drilled into L3 and L4 vertebrae.

Figure 2

Three methods used to apply spinal manipulative therapy: (A) mechanical force manually assisted instrument (Activator V-E); (B) manual spinal manipulative therapy application; (C) linear actuator motor.

Figure 3

Robotic testing. (A) Potted specimen with L4 mounted to the six-axis load cell and L3 fixed to a stationary cross beam. (B) Parallel robot platform with load cell and specimen attached.

Figure 4

Representative example of contact surface area (1 cm² each sensor) at peak force magnitude during (A) mechanical force manually assisted instrument (Activator V-E) and (B) manual spinal manipulative therapy application.

Figure 5

Average peak and mean forces experienced by the intact specimen during the application of spinal manipulative therapy with different methods. Red bars indicate significant comparisons (P < 0.05).

Figure 6

Average of normalized peak and mean forces experienced by supra- and interspinous ligaments during the application of spinal manipulative therapy with different methods. Red bars indicate significant comparisons (P < 0.05).

Figure 7

Average of normalized peak and mean forces experienced by bilateral facet joints, capsules and ligamentum flavum during the application of spinal manipulative therapy with different methods. Red bars indicate significant comparisons (P < 0.05).

Figure 8

Average of normalized peak and mean forces experienced by intervertebral disc, anterior and posterior longitudinal ligaments during the application of spinal manipulative therapy with different methods. Red bars indicate significant comparisons (P < 0.05).

Figure 9

Loading rate representation of different methods of spinal manipulative therapy application. INST indicates mechanical force manually assisted (Activator V-E); MAN, manual SMT; SERVO, linear actuator motor.