Distribution of cavitations as identified with accelerometry during lumbar spinal manipulation

Abstract

Objective: This project determined the location and distribution of cavitations (producing vibrations and audible sounds) in the lumbar zygapophyseal (Z) joints that were targeted by spinal manipulative therapy (SMT).

Methods: This randomized, controlled, clinical study assessed 40 healthy subjects (20 men, 20 women) 18 to 30 years of age who were block randomized into SMT (group 1, n = 30) or side-posture positioning only (group 2; control, n = 10) groups. Nine accelerometers were placed on each patient (7 on spinous processes/sacral tubercles of L1-S2 and 2 placed 3 cm left and right lateral to the L4/L5 interspinous space). Accelerometer recordings were made during side-posture positioning (groups 1 and 2) and SMT (group 1 only). The SMT was delivered by a chiropractic physician with 19 years of practice experience and included 2 high-velocity, low-amplitude thrusts delivered in rapid succession. Comparisons using χ(2) or McNemar test were made between number of joints cavitating from group 1 vs group 2, upside (contact side for SMT) vs downside, and Z joints within the target area (L3/L4, L4L5, L5/S1) vs outside the target area (L1/L2, L2/L3, sacroiliac).

Results: Fifty-six cavitations were recorded from 46 joints of 40 subjects. Eight joints cavitated more than once. Group 1 joints cavitated more than group 2 joints (P < .0001), upside joints cavitated more than downside joints (P < .0001), and joints inside the target area cavitated more than those outside the target area (P < .01).

Conclusions: Most cavitations (93.5%) occurred on the upside of SMT subjects in segments within the target area (71.7%). As expected, SMT subjects cavitated more frequently than did subjects with side-posture positioning only (96.7% vs 30%). Multiple cavitations from the same Z joints had not been previously reported.

Figure 1

Methods used in this study to accurately identify proper vertebral levels; a = high signal intensity MRI marker, which when taped to the subject (b) was used to verify palpated L4 spinous process (L4 spinous process was used as the major landmark for placement of all accelerometers); c = neutral supine MRI scan being performed; d = scout MRI showing correct placement of high signal marker at the spinous process of L4.

Figure 2

Placement of accelerometers and spinal manipulation; a = illustration showing placement of 9 accelerometers; b = close-up of accelerometer (actual size ~1.0 cm³); c = subject with the 9 accelerometers placed for recording (white dots placed over each accelerometer); d = spinal manipulation performed while recording from accelerometers.

Figure 3

Recordings from accelerometers; a = oscilloscope recording from accelerometers of a cavitation; b = the same recording shown in “a” with the timeline expanded to show the order in which the accelerometers recorded a vibration. Notice that the accelerometer located 3 cm to the left of L4/L5 fired first (“1” in 4b, this was the only accelerometer positioned to the left of the median plane). The next accelerometers to fire were those positioned over the L3 spinous process (SP, “2” in the figure) and L4 SP (“3” in the figure). These accelerometers fired almost simultaneously. Consequently, this recording indicated a cavitation of the left L3/L4 Z joint.

Figure 4

Study Enrollment: Of the 99 telephone screens for this study, 74 were eligible to participate and attended the baseline visit, 49 were eligible following the baseline visit and MRI screening, and 40 were analyzed as complete sets of data (Group 1 = adjustment, or spinal manipulative therapy, n=30; Group 2 = side-posture positioning without spinal manipulation, n=10).

Figure 5

Results of the recordings from 40 subjects. The illustrations of the posterior view of the spine in “a” and “b” show the individual Z joints and the numbers on the left and right of the illustration are the number of cavitations for each vertebral level (Note: Only 1 cavitation is recorded here in the cases of multiple cavitations from individual joints.); a = Group 1, side-posture spinal manipulation group; b = Group 2, control group (side-posture, but no spinal manipulation). The red brackets indicate the target area of the adjustments (L3/L4, L4/L5, and L5/S1). The results show that the left Z joints in the target area had significantly more cavitations than both right-sided joints and Z joints outside the target area. The results also show that Z joints of Group 1 subjects cavitated significantly more frequently than those of Group 2.

Figure 6

Flowchart showing a model of putative beneficial anatomical/biomechanical effects of spinal manipulation.