Comparison of human lumbar facet joint capsule strains during simulated high-velocity, low-amplitude spinal manipulation versus physiological motions

Abstract

Background context: Spinal manipulation (SM) is an effective treatment for low back pain (LBP), and it has been theorized that SM induces a beneficial neurophysiological effect by stimulating mechanically sensitive neurons in the lumbar facet joint capsule (FJC).

Purpose: The purpose of this study was to determine whether human lumbar FJC strains during simulated SM were different from those that occur during physiological motions.

Study design/setting: Lumbar FJC strains were measured in human cadaveric spine specimens during physiological motions and simulated SM in a laboratory setting.

Methods: Specimens were tested during displacement-controlled physiological motions of flexion, extension, lateral bending, and axial rotations. SM was simulated using combinations of manipulation site (L3, L4, and L5), impulse speed (5, 20, and 50 mm/s), and pre-torque magnitude (applied at T12 to simulate patient position; 0, 5, 10 Nm). FJC strains and vertebral motions (using six degrees of freedom) were measured during both loading protocols.

Results: During SM, the applied loads were within the range measured during SM in vivo. Vertebral translations occurred primarily in the direction of the applied load, and were similar in magnitude regardless of manipulation site. Vertebral rotations and FJC strain magnitudes during SM were within the range that occurred during physiological motions. At a given FJC, manipulations delivered distally induced capsule strains similar in magnitude to those that occurred when the manipulation was applied proximally.

Conclusions: FJC strain magnitudes during SM were within the physiological range, suggesting that SM is biomechanically safe. Successful treatment of patients with LBP using SM may not require precise segmental specificity, because the strain magnitudes at a given FJC during SM do not depend upon manipulation site.

Fig. 1

Schematics of the experimental setups. For all testing protocols, vertebral kinematics and facet joint capsule strains were measured by optically tracking infrared reflective markers using the two charge coupled device (CCD) cameras. The orientation axes of the system are shown for each view. (a) Specimens were tested during physiological motions of extension, flexion, and lateral bending using a displacement-controlled linear actuator motor. A load cell was in series with the motor to measure the applied load. (b) Spine specimens were tested during physiological motions of axial rotations using a torque motor, which was in series with a torque sensor to measure the applied torque. (c) Spine specimens were tested during simulated spinal manipulation (SM) using both the torque motor and linear actuator motor. The torque motor was used to apply a pre-torque to the specimen to simulate patient position, and a custom-built spine fixation apparatus was used to hold the specimen in place during mechanical testing. During SM simulations, the linear actuator motor was used to deliver the impulse load to L₃, L₄, and L₅. The direction of the pre-torque and the manipulation are shown. (d) During simulated SM, the linear actuator motor was attached to the anterior aspect of the vertebral body of interest using a Synthes Small Fragment Locking Compression Plate (LCP). The LCP was attached to a joint (allowing 30° of rotation), which was connected to the linear actuator via a rod.

Fig. 2

Representative data from a simulation of spinal manipulation applied to the anterior aspect of L₄, which simultaneously produced rotation (+Y-axis) and translation (−X-axis) of the vertebrae (see Fig. 1 for orientation axes). (a) A single trial consisted of 7 mm total displacement, which was comprised of a preload (maintained for 500 ms) and peak impulse. In the trial shown, the impulse was delivered at 50 mm/s. (b) Facet joint capsule maximum (max) and minimum (min) principal strains (left L_3–4 capsule strains shown) were typically opposite in sign. (c) Vertebral kinematics (Y-axis rotations and X-axis translations of L₃ and L₄ are shown) were measured using six degrees of freedom, and the dominant vertebral motions occurred in the direction of the applied manipulation. Load–time, strain–time and vertebral motion–time relationships closely resembled displacement–time relationships.

Fig. 3

Load magnitudes during simulated manipulations of the lumbar spines (n=7) were site-specific (manipulation sites: (a) L₃, (b) L₄, (c) L₅). Both preload and total load magnitudes at L₄ and L₅ were significantly larger than those that occurred at the respective more superior vertebrae (3-way ANOVA, p<.001). Preload and total load magnitudes did not vary significantly with speed (ANOVA, p=.075). ^*Both preload and total load magnitudes were larger with 5 Nm and 10 Nm pre-torque versus 0 Nm pre-torque (3-way ANOVA, p<.001).

Fig. 4

Preload and total moment magnitudes during simulated manipulations of the lumbar spines (n=7) were site-specific (manipulation sites: (a) L₃, (b) L₄, (c) L₅). L₄ and L₅ moments (both preload and total) were significantly larger than L₃ moments (3-way ANOVA, p<.001). Preload and total moment magnitudes did not vary significantly with speed (ANOVA, p>.07). ^*Both preload and total moment magnitudes were larger with 10 Nm pre-torque versus 0 Nm pre-torque (3-way ANOVA, p<.001).

Fig. 5

Vertebral translation (trans) magnitudes during simulated manipulations of lumbar spines (n=6) were not site-specific. Compared with the translations along the Y- and Z-axes, translations were larger in absolute magnitude along the X-axis (the direction of the applied impulse). Total vertebral translations were computed as the vector sum of the translations that occurred along the three axes. Total vertebral translations and the translations that occurred along a given axis were of similar magnitude, regardless of whether the manipulation was applied locally or distally (ANOVA, p>.05). Vertebral translations also did not vary with pre-torque magnitude (ANOVA, p>.05).

Fig. 6

Site-specific lumbar spine manipulations (n=6) induced vertebral rotations both locally and distally. X-axis rotations (see Fig. 1 for orientation axes) were relatively small in absolute magnitude and were highly variable. At a given vertebra, and for a given combination of manipulation site and pre-torque magnitude, rotations were typically largest in absolute magnitude about the Y-axis, which was the direction of the applied pre-torque and impulse load. Z-axis rotations were relatively small; at L₃ and L₄ the magnitude and direction of Z-axis rotations were dependent upon pre-torque magnitude and manipulation site. ^*5 Nm pre-torque significantly larger than 0 Nm pre-torque (ANOVA, p<.015). ^**10 Nm pre-torque significantly larger than 0 Nm pre-torque (ANOVA, p<.015). ^ Significantly different versus L₃ manipulation site (ANOVA, p<.03). ♦ Significant interactions between pre-torque and manipulation site (ANOVA, p<.035).

Fig. 7

Facet joint capsule (FJC) maximum (max) principal strains ( ${\widehat{E}}_1$, n=6) (a) during simulated spinal manipulation (SM) were within the range that occurred (b) during physiological motions of extension (E), flexion (F), lateral bending (CB=compressive bend; TB=tensile bend), and axial rotations (TA=tensile axial; CA=compressive axial). During SM, FJC strains on both sides of the spine were induced regardless of whether the manipulation was applied distally or locally (ANOVA, p>.13). On the left side of the spine, FJC strain magnitudes were larger with 5 Nm (^*) and 10 Nm (^**) pre-torque versus 0 Nm pre-torque (ANOVA, p<.03).

Fig. 8

Facet joint capsule (FJC) minimum (min) principal strains ( ${\widehat{E}}_2$, n=6) (a) during simulated spinal manipulation were within the range that occurred (b) during physiological motions of extension (E), flexion (F), lateral bending (CB=compressive bend; TB=tensile bend), and axial rotations (TA=tensile axial; CA=compressive axial). During SM, FJC strains on both sides of the spine were induced, regardless of whether the manipulation was applied distally or locally (ANOVA, p>.14). ^**10 Nm pre-torque significantly larger than 0 Nm pre-torque (ANOVA, p<.05).