The current study assessed the persistence of lumbar somatic dysfunction over 8 weeks and the association of that persistence with lumbar BMD T scores. Although the study population was a primarily asymptomatic group, specific patterns of persistent somatic dysfunction were observed. Persistent left lumbar rotational asymmetry occurred 10 to 30 times more often than persistent right rotational asymmetry. Left lumbar rotation is consistent with the common compensatory pattern defined by Zink and Lawson,
14 who reported that asymptomatic individuals frequently have common patterns of asymmetry throughout the body, including right pelvic rotation and left lumbar rotation. This pattern is also consistent with the most common lumbar scoliosis pattern, T12-L4 convex left, which is accompanied by left lumbar rotation.
18 Shaw et al
19 also noted a predominance of left lumbar rotational asymmetry in an assessment of 12 asymptomatic osteopathic medical students. In their study,
19 the rotational asymmetry was identified independently by means of both palpation and ultrasonography. In the previously published portion of the current study,
13 we found that participants with and without chronic LBP demonstrated a greater incidence of left rotational asymmetry than right rotational asymmetry. In addition, both groups had a significantly higher frequency of left moderate/severe rotational asymmetry than right moderate/severe asymmetry (
P<.001). A small percentage of the persistent left rotational asymmetry seen in the current study was moderate/severe. This low percentage of moderate/severe findings is likely a result of the inclusion of a low number of chronic LBP participants (ie, 2) who were followed up over the 8 weeks of the study, so the persistence of the somatic dysfunction could not be compared between groups.
Few studies have been performed that have assessed the persistence of vertebral somatic dysfunction over time. Motion restriction as assessed in the current study is also known as spinal stiffness or posterior-to-anterior spinal stiffness
20 and is commonly used as part of clinical assessment in physical therapy, chiropractic, and osteopathic manipulative medicine.
21 Latimer et al
8 assessed motion restriction over time by using a stiffness testing device in participants with LBP and without LBP. Over an average of 22 days, they found that stiffness stayed relatively constant in participants without LBP, but stiffness decreased as pain decreased in the LBP participants. Spinal motion restriction is multifactoral and is affected by the thickness of overlying tissues,
21 the participant's respiratory cycle,
22 the tension of the supporting structures such as the muscles and ribs,
23 and the range of motion of the vertebral elements.
24 Lee et al
21 noted a decrease in motion restriction at L4 in asymptomatic individuals who had a greater iliac crest skinfold thickness, a measurement probably proportional to the depth of the tissue overlying the spinous processes. (The average BMI in the Lee et al
21 study was 23.8, whereas ours was 26.3.) Owens et al
20 noted that the spinous processes of L4 and L5 were more difficult to palpate because of a greater depth of overlying tissues in their study participants. Greater tissue depth may be the reason that 10% of L4 vertebrae in the current study demonstrated persistent motion restriction, compared with 40% or more of L1-L3 vertebrae that had persistent motion restriction.
Although a small percentage of the persistent motion restriction seen in the current study was graded as moderate/severe, motion restriction was the only persistent somatic dysfunction element to show an association with the final vertebral BMD T score. Disk deformation commonly occurs with scoliotic curvatures, with osteophytes occurring more frequently on the concave side of the curve and disk herniations occurring more frequently on the convex side.
25 Persistence of lumbar group curves, such as those seen in scoliosis, is associated with a loss of the lumbar lordosis and reduced extension range of motion.
25 Lumbar degenerative joint disease and lumbar degenerative disk disease most commonly occur at the L4-L5 and L5-S1 levels.
26,27 Degenerative disk disease, which typically precedes degenerative joint disease, alters the mechanical loading of intervertebral disks and the facet joints
27,28 and may lead to changes in passive range of motion. The osteophytes, along with the endplate sclerosis that occurs in spinal degenerative joint disease, affect BMD values as measured with DXA.
29,30 Therefore, elevated BMD—as was seen with persistent motion restriction—may represent early degenerative changes.
In the previously reported data,
12 the presence of both rotational asymmetry and motion restriction were found to be related to the initial vertebral BMD T scores. When the association of persistent somatic dysfunction with the final BMD T scores in the current study was assessed, only persistent vertebral motion restriction was associated with the final vertebral BMD T scores. Persistent vertebral tenderness and moderate/severe vertebral TTA were associated with changes from the initial to the final BMD T scores. Because the occurrence of persistent tenderness and moderate/severe TTA in the participants was fairly low, the current study should be repeated with a larger sample size to determine the reproducibility of this finding.