Magnetic resonance imaging zygapophyseal joint space changes (gapping) in low back pain patients following spinal manipulation and side-posture positioning: a randomized controlled mechanisms trial with blinding

Abstract

Objective: The purpose of this study was to quantify lumbar zygapophyseal (Z) joint space separation (gapping) in low back pain (LBP) subjects after spinal manipulative therapy (SMT) or side-posture positioning (SPP).

Methods: This was a controlled mechanisms trial with randomization and blinding. Acute LBP subjects (N = 112; four n = 28 magnetic resonance imaging [MRI] protocol groups) had 2 MRI appointments (initial enrollment and after 2 weeks of chiropractic treatment, receiving 2 MRI scans of the L4/L5 and L5/S1 Z joints at each MRI appointment. After the first MRI scan of each appointment, subjects were randomized (initial enrollment appointment) or assigned (after 2 weeks of chiropractic treatment appointment) into SPP (nonmanipulation), SMT (manipulation), or control MRI protocol groups. After SPP or SMT, a second MRI was taken. The central anterior-posterior joint space was measured. Difference between most painful side anterior-posterior measurements taken postintervention and preintervention was the Z joint "gapping difference." Gapping differences were compared (analysis of variance) among protocol groups. Secondary measures of pain (visual analog scale, verbal numeric pain rating scale) and function (Bournemouth questionnaire) were assessed.

Results: Gapping differences were significant at the first (adjusted, P = .009; SPP, 0.66 ± 0.48 mm; SMT, 0.23 ± 0.86; control, 0.18 ± 0.71) and second (adjusted, P = .0005; SPP, 0.65 ± 0.92 mm; SMT, 0.89 ± 0.71; control, 0.35 ± 0.32) MRI appointments. Verbal numeric pain rating scale differences were significant at first MRI appointment (P = .04) with SMT showing the greatest improvement. Visual analog scale and Bournemouth questionnaire improved after 2 weeks of care in all groups (both P < .0001).

Conclusions: Side-posture positioning showed greatest gapping at baseline. After 2 weeks, SMT resulted in greatest gapping. Side-posture positioning appeared to have additive therapeutic benefit to SMT.

Figure 1

Theoretical model of one of the beneficial effects of spinal manipulative therapy (SMT, spinal adjusting). This project assessed Step 3 of the model, separation of the Z joint articular surfaces (therapeutic gapping).

Figure 2

Flowchart showing the overview of the project. VAS = visual analog scale, BQ = Bournemouth Questionnaire of functional impairment, and VNPRS = verbal numeric pain rating scale.

Figure 3

Enrollment and exclusion of study subjects. Exclusions are listed along the right side of the flowchart. Withdrawals during the 2-week treatment period and second MRI scan are summarized in the last row of boxes (Protocols 1–4). The following abbreviations are used in the bottom row of boxes: neutral = supine position, side = side-posture positioning (SPP), SMT = spinal manipulative therapy. All SMT was performed with the most painful side (primary treatment side, PTS) as the up-side.

Figure 4

Procedures used for each of the 4 study protocol groups. The protocols are described in the “MRI Scanning” subsection of the Material and Methods. Notice that all protocols began with an MRI scan in the neutral position (first row). Subjects were then randomized into one of 4 protocol groups (second and third rows) and were then scanned a second time in either the neutral or side-posture position (third row). Although subjects are shown receiving spinal manipulative therapy (SMT) or SPP with the left side as the up-side, the up-side was the subject’s most painful side (primary treatment side, PTS) at the examination appointment, which was frequently the right side (see Table 3).

Figure 5

Illustration (A) and MRI scan (B) showing the central anterior to posterior (A-P) measurement of the Z joints that were made from the left and right L4/L5 and L5/S1 Z joints in this study.

Figure 6

Gapping differences (in mm, Y-axis) between the A-P Z joint space measurements of the first and second MRI scans (value from the first scan was subtracted from the value of the second scan) at the second MRI appointment (M2). The greatest gapping differences of the primary treatment side (PTS) are presented here. Protocol 3 [spinal manipulative therapy (SMT) protocol groups] showed more gapping (therapeutic gapping) than the other protocol groups, followed by Protocol 1 [side-posture positioning (SPP) protocol group].

Figure 7

Pre-intervention and post-intervention scans for each of the 4 study protocol groups. The box on each scan indicates the up-side Z joint during side-posture-positioning or side-posture SMT. This was also the most painful side of low back pain. L4 indicates the L4/L5 segmental level and L5 indicates the L5/S1 segmental level. Notice the low signal line within the center of the Protocol 3 “Post” R L4/L5 Z joint. This may be gas (most likely carbon dioxide) within the joint secondary to cavitation during SMT.