The aim of the present study was to investigate the effect of SMT on pain, functional disability and the results of clinical tests of SIJ function and LDH in patients with unilateral SLDD plus SIJ hypomobility. Our findings suggest that five sessions of lumbar and SIJ manipulation can lead to statistically significant improvement in pain and functional disability, which in turn may restore normal SIJ mobility in these patients.
Compared to common treatments for LDH, SMT is reported to be 37,000 to 148,000 times safer than nonsteroid antiinflammatory drugs and 55,500 to 444,000 times safer than surgery [28]. Neither worsening of symptoms nor cauda equine syndrome were observed in our participants after SMT. Epidemiologic data on the rate of injuries caused by manipulation are limited. The most common incidents are related to innocuous physiologic reactions or short-term discomfort generated at the treatment site. However, these are self-limiting events that usually resolve within 24 h after SMT [28].
In rotational side-posture lumbar manipulation, the impact of the facet joints limits axial rotation of the lower lumbar vertebrae and consequently prevents annulus fibrosus tearing [28]. In the present study, patients with sequestrated LDH who had neurological signs were excluded because these patients may have bowel and bladder disorders, and many (but not all) of them are thus candidates for surgery [29]. In the present study manipulation was applied in the neutral flexion–extension position to reduce the risk of injury.
The diagnosis and treatment of SIJ hypomobility in patients with SLDD are important issues that have not been adequately addressed in the literature. In 78.3% of our cases, the side of SIJ hypomobility was the same as the side of LDH. After treatment, 95% improvement was obtained in the results of SIJ hypomobility tests (Table 2).
The SIJ has been reported to be one of the main sources of low back disorders [5]. A recent study also found that SIJ dysfunction was a prevalent concomitant pathology in patients with LDH. Therefore, SIJ dysfunction should be considered in the treatment of these patients [4]. Pelvic asymmetry as well as hypermobility or hypomobility of the spinal or sacroiliac joints can cause low back pain [3, 30]. Any involvement of the SIJ can induce muscle spasm in the piriformis, which in turn can lead to sciatic irritation and a wide range of symptoms mimicking radiculopathy [5]. Increased tension in the quadratus lumborum, iliopsoas or hamstring muscles may also affect the SIJ mechanism of action. Presumably, SIJ manipulation can decrease tension in these muscles and consequently correct lumbar spine dysfunction [3, 31].
Several mechanisms have been theorized for the mechanical and neurophysiological basis of SMT, including stimulation or modulation of the somatosensory system to evoke neuromuscular reflexes [32]. Forceful stretching of the spinal muscles induces relaxation after SMT. Other mechanisms are induced hypoalgesia [33], kinematic correction [34, 35] and increased lumbar range of motion [36]. A brief reduction in intradiscal pressure during SMT in cadavers and return to baseline within less than 1 min was reported in one earlier study [37]. Another study showed reduced H-reflex amplitude in patients with unilateral disc herniation, which improved after SMT [11]. The improved outcomes in our patients can be attributed to two main factors. Firstly, SIJ manipulation may improve normal functioning of the lumbar spine and related muscles [38]. Secondly, lumbar side-posture rotational manipulation can induce spinal muscle relaxation [32], improve lumbar range of motion [36], and briefly decrease intradiscal pressure [37].
The results of the SIJ hypomobility tests (including the Gillet test, standing flexion and sitting flexion tests) improved significantly in the 5th session and after 1-month follow-up compared to baseline values, whereas no statistically significant improvement was observed in the SLR and slump tests. Spinal manipulative therapy may enhance mobility of the SIJ and lumbar vertebrae, and affect the muscles in these regions, thus accounting for the improvement in pain and functional ability. However, significant changes in the slump and SLR tests may require additional interventions such as soft tissue manipulation and nerve mobilization, which were not tested in this study.
In one controlled trial, SMT and sham manipulation were compared in 102 participants with MRI-confirmed LDH; the SMT group showed significantly greater improvement in back and leg pain after 6 months [12]. Nevertheless, the intervention in that study was a combination of soft tissue manipulation and thrust manipulation, and the diagnosis and treatment of SIJ hypomobility were not considered.
In a prospective cohort study, Leemann et al., investigated the effect of high-velocity, low-amplitude SMT in patients with acute or chronic MRI-confirmed LDH, and reported clinically significant improvement in back and leg NRS and ODI scores in both short-term and long-term assessments [13]. In a follow-up study, Ehrler et al., investigated the association of magnetic resonance imaging features, including axial location and type of herniation, with the outcomes of SMT in patients with LDH [14]. This study reported greater improvements in symptoms among patients with sequestrated SLDD who received SMT to the level of herniation. These studies, however, did not consider the treatment of the SIJ in patients with LDH.
Burton et al., also compared SMT with chemonucleolysis in the treatment of patients with SLDD, and reported greater improvements in back pain and disability in the first few weeks in the SMT group [39]. Their SMT, however, included a combination of thrust manipulation, mobilization and soft tissue stretching.
The results of previous studies have shown that SMT is effective in the treatment of LDH [40]. The study most similar to ours is the one by Galm et al., which included 150 patients with LDH, 46 of whom had SIJ dysfunction. All participants received routine physiotherapy, mobilization and SMT in the prone position. Significant improvements were reported in lumbar and ischiatic pain in the SIJ dysfunction group. These authors concluded that in the presence of lumbar and ischiatic symptoms, appropriate treatment for SIJ dysfunction should be considered regardless of intervertebral disc pathomorphology [3]. In this study, however, the number of treatment sessions and the results of SIJ and LDH physical tests were not reported.
Our study had some limitations which should be noted. The pre–post test design did not include a control group; consequently, the results cannot be considered evidence in support of the clinical efficacy of SMT for patients with LDH and SIJ hypomobility. A controlled trial is advisable in which combined manipulations are compared to lumbar or SIJ manipulation separately, to elucidate whether using both lumbar and SIJ manipulation together yields better outcomes than using a single type of manipulation. The small sample size and lack of long-term follow-up are other limitations. In addition, we are aware that measuring physiologic responses to SMT by recording electromyographic activity of the spinal muscles, the myotomes and dermatomes of the involved nerve roots, would strengthen the results of future studies. Also, more reliable tests for SIJ dysfunction are available and should be used in future studies. Despite these limitations, we addressed some shortcomings of previous studies. The strengths of the present study were matching of the physical examination findings with imaging findings, considering SIJ hypomobility in the treatment of patients with LDH, and the application of spinal thrust manipulation alone rather than a combination of therapeutic methods.