Intervertebral kinematics of the cervical spine before, during, and after high-velocity low-amplitude manipulation.

BACKGROUND CONTEXT: Neck pain is one of the most commonly reported symptoms in primary care settings, and a major contributor to health-care costs. Cervical manipulation is a common and clinically effective intervention for neck pain. However, the in vivo biomechanics of manipulation are unknown due to previous challenges with accurately measuring intervertebral kinematics in vivo during the manipulation.

PURPOSE: The objectives were to characterize manual forces and facet joint gapping during cervical spine manipulation and to assess changes in clinical and functional outcomes after manipulation. It was hypothesized that patient-reported pain would decrease and intervertebral range of motion (ROM) would increase after manipulation.

STUDY DESIGN/SETTING: Laboratory-based prospective observational study.

PATIENT SAMPLE: 12 patients with acute mechanical neck pain (4 men and 8 women; average age 40 ± 15 years).

OUTCOME MEASURES: Amount and rate of cervical facet joint gapping during manipulation, amount and rate of force applied during manipulation, change in active intervertebral ROM from before to after manipulation, and numeric pain rating scale (NPRS) to measure change in pain after manipulation.

METHODS: Initially, all participants completed a NPRS (0-10). Participants then performed full ROM flexion-extension, rotation, and lateral bending while seated within a custom biplane radiography system. Synchronized biplane radiographs were collected at 30 images/s for 3 seconds during each movement trial. Next, synchronized, 2.0-milliseconds duration pulsed biplane radiographs were collected at 160 images/s for 0.8 seconds during the manipulation. The manipulation was performed by a licensed chiropractor using an articular pillar push technique. For the final five participants, two pressure sensors placed on the thumb of the chiropractor (Novel pliance system) recorded pressure at 160 Hz. After manipulation, all participants repeated the full ROM movement testing and once again completed the NPRS. A validated volumetric model-based tracking process that matched subject-specific bone models (from computed tomography) to the biplane radiographs was used to track bone motion with submillimeter accuracy. Facet joint gapping was calculated as the average distance between adjacent articular facet surfaces. Pre- to postmanipulation changes were assessed using the Wilcoxon signed-rank test.

RESULTS: The facet gap increased 0.9 ± 0.40 mm during manipulation. The average rate of facet gapping was 6.2 ± 3.9 mm/s. The peak force and rate of force application during manipulation were 65 ± 4 N and 440 ± 58 N/s. Pain score improved from 3.7 ± 1.2 before manipulation to 2.0 ± 1.4 after manipulation (p <. 001). Intervertebral ROM increased after manipulation by 1.2° (p = .006), 2.1° (p = .01), and 3.9° (p = .003) at the C4/C5, C5/C6, and C6/C7 motion segments, respectively, during flexion-extension; by 1.5° (p = .028), 1.9° (p = .005), and 1.3° (p = .050) at the C3/C4, C4/C5, and C5/C6 motion segments, respectively, during rotation; and by 1.3° (p = .034) and 1.1° (p = .050) at the C4/C5 and C5/C6 motion segments, respectively, during lateral bending. Global head ROM relative to the torso increased after manipulation by 8º (p = .023), 10º (p = .002), and 13º (p = .019) during lateral bending, axial rotation and flexion-extension, respectively, after manipulation.

CONCLUSIONS: This study is the first to measure facet gapping during cervical manipulation on live humans. The results demonstrate that target and adjacent motion segments undergo facet joint gapping during manipulation and that intervertebral ROM is increased in all three planes of motion after manipulation. The results suggest that clinical and functional improvement after manipulation may occur as a result of small increases in intervertebral ROM across multiple motion segments. This study demonstrates the feasibility of characterizing in real time the manual inputs and biological responses that comprise cervical manipulation, including clinician-applied force, facet gapping, and increased intervertebral ROM. This provides a basis for future clinical trials to identify the mechanisms behind manipulation and to optimize the mechanical factors that reliably and sufficiently impact the key mechanisms behind manipulation.