Fig. 4.1
Posterior view of the sacroiliac joint and its associated ligaments
Although the structure of the SIJ is well defined, its exact role has been contentious from being considered of minimal functional significance (due to its limited movement) to being of important primary movements (that can be assessed clinically like any other large joints in the body). Both extreme views prove to be problematic [9]. According to one study, the SIJ ranges of movements are limited to translational and rotational motions along six degrees of freedom [6]. In a more recent in vivo analysis, even smaller degrees of movements in all planes (mean rotation of 2.5°, mean translation of 0.7 mm) exist among symptomatic and nonsymptomatic joints [10]. In essence, SIJ is a stress-relieving joint with limited motion. The joint complex helps buffer the torsional stress to prevent the sacrum and pelvic ring to fracture and transmit the longitudinal stress between the vertebral column and the lower limbs during movements [9].
Developmentally, the SIJ begins to appear during the second month of fetal development and a synovial membrane manifests by 37 weeks [3]. During the first 10 years of life, the joint grows in size but its surfaces remain flat [3]. During the second decade, the joint surfaces start to become irregular with a depression along the articular surface of the sacrum and a reciprocal ridge along the ilium. Degenerative changes in the SIJ start in puberty and continue throughout life. They accelerate during the third and fourth decades of life and are manifested by increasing surface irregularities, osteophyte formation, eroded cartilage, and accumulation of fibrous plaques. The iliac surfaces tend to age faster than the sacral side. By the sixth decade, sinuous corrugations are well established, the capsule becomes collagenous and the joint mobility becomes further restricted [3]. By the eighth decade, fibrous ankylosis and the thinning of the articular cartilage with less than 1 mm on the sacrum and 0.5 mm on the ilium are inevitable [3].
Despite increasing literature on the innervation of the SIJ, the subject continues to draw great debate. It is still undecided to which extent the anterior and posterior joints are innervated and by which neural segments. Studies were conducted in the late nineteenth and early twentieth centuries to assert that the joint was innervated anteriorly by branches of the lumbosacral trunk, the superior gluteal, and obturator nerves, and posteriorly by branches of the S1 and S2 dorsal rami [11, 12]. Yet modern studies provide conflicting conclusions. A German study reported a posterior innervation exclusively from the S1 and S2 dorsal rami but denied an anterior innervation from the sacral plexus or the obturator nerve [13]. However, a Japanese study reported a posterior innervation from the L5 and sacral dorsal rami and an anterior innervation from the L5 and S2 ventral rami [14]. Overall, the posterior joint is well understood and more clinically relevant for interventional pain specialists; its innervation appears to arise mainly from the dorsal rami of S1–3, with contributions from L5 (or L4 in case of sacralization of L5) and S4 in many individuals [15, 16]. Both intra-articular (IA) and extra-articular (EA) structures can be sources of pain. An electrophysiological study in cats identified nociceptive receptors in both the joint capsule and the adjacent muscles, with most residing within the capsule [17]. Immunohistochemical studies in human cadavers have demonstrated calcitonin-gene-related peptide and substance P immunoreactive nociceptors in both capsular and interosseous ligaments [18]. Clinical studies in asymptomatic volunteers and pain patients prove that pain can be reproduced with both capsular distension and ligamentous provocation [19–23].
Epidemiology
The SIJ was first described as a potential pain source in 1905 [24]. However, it was not precisely defined until 1994, when Fortin et al. demonstrated the pain syndrome in asymptomatic volunteers by distending the SIJ with a contrast medium and diagnosed by analgesic responses to image-guided IA local anesthetic injections [25, 26]. The lack of standardization in methodology and patient population led to a wide range of prevalence rates. Furthermore, the data on the prevalence of SIJC pain have been derived mostly from patients with nonspecific LBP.
In seven prevalence studies using concordant pain relief with lidocaine and bupivacaine as the diagnostic criterion, the prevalence rates for SIJ pain varied between 10 and 45 % with the false-positive rates ranging between 0 and 43 % [27–33]. In an early study in patients with LBP below L5–S1 (n = 43), Schwartzer et al. found the prevalence rate of 30 % (CI: 16–44 %) based solely on the analgesic response (≥75 %) to a single lidocaine block, 21 % based on pain relief and a ventral capsular tear on computed tomography, 16 % based on a combination of analgesic response, concordant pain provocation, and imaging findings [27]. In another study in patients with unilateral LBP (n = 54) who failed epidural steroid and facet injections, Maigne et al. reported an 18.5 % prevalence rate using an analgesic response to two different local anesthetics [29]. Manchikanti et al. reported a low prevalence rate of 10 % in 20 pts who underwent double confirmatory blocks [30]. Laslett et al. reported a 26 % prevalence rate in 48 patients with buttock pain [31]. In a retrospective review of 158 patients with LBP and/or leg pain, Irwin et al. calculated a similar prevalence rate of 26.6 % [29]. Both van de Wurff et al. and Liliang et al. reported high prevalence rates of 45 and 40 %, respectively [32, 33]. All these studies relied solely on IA injections as the diagnostic criterion; as a result, they likely exclude patients with EA pathology. In summary, SIJ complex (SIJC) pain seems to have a bimodal distribution, with higher rates in younger athletes and the elderly, and it appears fairly common in patients with chronic axial LBP below L5 [34, 35].
Etiology
The causes of SIJC pain are numerous. Essentially, the pain is a result of a combination of axial loading and abrupt rotation [36]. Immunohistological studies have indicated nociceptors throughout the joint capsules, ligaments, and subchondral bone, implying that these structures can be potential sources of pain [37, 38]. Furthermore, clinical studies have demonstrated pain provocation in asymptomatic volunteers using both capsular distension and ligamentous probing [25, 39]. Because both IA and periarticular SIJ injections have resulted in significant pain relief, the etiologies of SIJC pain can be divided into IA and EA sources (Table 4.1). Among IA causes, arthritis and spondyloarthropathies (Table 4.2) are the two most common ones, though the latter may also be associated with EA pathology [40]. For EA causes, myofascial and ligamentous injury manifest most frequently [41]. Distinguishing IA and EA pain generators is clinically relevant. Dreyfuss et al. found that multisite lateral branch blocks provided more pain relief for ligamentous probing than for capsular distension [42]. In contrast to IA pathology, EA sources likely occur in younger individuals with more prominent and unilateral tenderness, following a specific inciting event.
Table 4.1
Causes of intra-articular and extra-articular SU complex pain
Intra-articular | Extra-articular |
|---|---|
Arthritis | Ligamentous injury |
Spondyloarthropathy | Myofascial pain |
Trauma | Trauma/fractures |
Infection | Enthesopathy |
Cystic disease | Pregnancy |
Cystic disease |
Table 4.2
SIJ involvement in adult spondyloarthropathies
Ankylosing spondylitis | Reactive arthritis | Psoriatic arthritis | Enteropathic arthritis |
|---|---|---|---|
Almost 100 %, symmetric/alternating | 20–30 %, mostly asymmetric | 20–30 %, mostly asymmetric | 15–25 %, mostly asymmetric |
M:F = 3:1, <35 years of age | M:F = 5:1, young to middle-aged | M:F = 1:1, young to middle-aged | M:F = 1:1, young to middle-aged |
20–30 % PJ | 90 % PJ | Almost 100 % PJ | 15–30 % PJ |
SIJC pain tends to occur following a triggering event. Up to 50 % of patients with injection- confirmed SIJC pain can identify a specific trigger. The most frequent inciting events in descending order for trauma-induced SIJC pain are motor vehicle accidents, falls onto the buttock, pregnancy, athletic injuries, prolonged lifting and bending, and torsional strain [27, 43–46]. Other recognized rare-precipitating events include pyogenic infection and malignancy [47, 48].
A variety of risk factors can predispose patients to SIJC pain. These include true and apparent leg length discrepancy [49], gait and biomechanical abnormalities [50], prolonged vigorous exercise [51], scoliosis [52], pregnancy [53], and spine surgery [54]. True and functional leg length discrepancies can increase stress and abnormal force vectors on the ipsilateral lower extremity [55]. Patients with chronic LBP were significantly (75 %) more likely to have a leg length discrepancy of >5 mm than a matched asymptomatic cohort (44 %) [56]. Pregnancy can predispose women to SIJC pain via weight gain, exaggerated lordotic posture, hormone-induced ligamentous laxity, and the pelvic trauma of parturition [57, 58]. Spine surgery may be a trigger of SIJC pain, especially fusion to the sacrum. Ivanov et al. found the greatest increase in SIJ stress after L4–S1 fusion [59]. Ha et al. reported a nearly twofold increase in SIJ degeneration in the fusion cohort compared with the control group (75 % vs. 38.2 %), with the highest incidence in patients with fusions to the sacrum [60]. These findings are consistent with prevalence studies reporting 32–61 % of post-fusion patients experience SIJC pain [61, 62].
History and Physical Exam
Given its heterogeneous presentation from patient to patient, the SIJ-mediated pain cannot be reliably diagnosed by history and physical examination alone. Several investigators have attempted to map pain-referral patterns associated with the SIJ. By injecting contrast and lidocaine in asymptomatic volunteers, Fortin et al. generated a composite map on the patient’s buttocks, inferior from the posterior inferior iliac spine [25]. This mapping was later confirmed in a clinical study that found that those with buttock pain radiating into the posterolateral thigh reported pain with SIJ provocation and had negative facet blocks and discography [26]. Two studies found that if the most painful area is located within 10 cm of the posterior superior iliac spine, it is most likely caused by SIJ-based pain [26, 63]. In another study using >80 % pain relief following single SIJ blocks in 50 patients, the distribution patterns are: 94 % buttock pain, 72 % lumbar pain, 50 % pain extending into the lower extremity, 28 % pain below the knee, and 14 % pain radiating to the groin [64]. SIJ pain is more likely to be located laterally [34, 65]. A cross-sectional prevalence study found that pain referral to the groin was the only pain distribution that could reliably distinguish SIJ pain from other sources of LBP [27]. Yet another study suggested that pain arising from sitting, unilateral pain, and absence of lumbar pain were the most reliable symptoms to separate SIJ pain from facetogenic and discogenic pain [66].
Like the history, physical examination maneuvers cannot reliably diagnose SIJC pain [67]. One study of 50 patients who had three or more provocation maneuvers reported 60 % positive-predictive value for response to a single SIJ injection; as a result, it concluded that provocative tests should not be considered sole diagnostic criteria [68]. However, several investigators have found that the presence of three or more positive provocative tests appears to have reasonable sensitivity and specificity in identifying patients who will positively respond to diagnostic injections (Fig. 4.2). In a double-blind, placebo-controlled study, FABER (flexion, abduction, and external rotation), posterior shear, and resisted abduction tests had a sensitivity ranging between 77 and 87 %, and all with 100 % specificity [68] (see Fig. 4.2). In a blinded validity study performed in 48 patients, a battery of three out of six provocation tests had 94 % sensitivity and 78 % specificity in predicting a positive response to a single diagnostic SIJ injection [31]. Another study using double blocks as the diagnostic standards in 60 patients reported similar finding, the presence of three out of five positive provocation tests had 85 % sensitivity and 79 % specificity [32]. In a recent systematic review, the authors concluded that three positive provocation tests had significant diagnostic odds ratio of 17.16 using two positive blocks [69]. Lastly, research has found provocation tests to be more reliable than motion measurement tests [70, 71].
Fig. 4.2
Flexion, abduction, and external rotation (FABER) test of the right sacroiliac joint
In summary, a thorough history and physical examination may reveal important clues to etiologies to guide diagnostic workup and treatment plan. A combination of symptoms and signs can be utilized to select right candidates for SIJ blocks. For example, the SIJC pain is likely relieved from diagnostic injections when pain is located predominantly below L5, exacerbated by rising from a sitting position, most tender over the joint and associated with at least three or more provocative signs.
Diagnostic Imaging
A number of diagnostic imaging studies including CT, MRI, and radionuclide bone scanning have attempted to correlate radiological findings with the results of diagnostic blocks with varying success. CT is considered to be the gold standard for identifying bony pathology. In a retrospective study performed in 112 patients using diagnostic blocks as the reference standard, the investigators found that CT was associated with 58 % sensitivity and 69 % specificity [72, 73]. MRI can be useful in detecting early spondyloarthropathic SIJ pathologies with greater than 90 % sensitivity but is not effective in identifying noninflammatory etiologies [74].
Radionuclide bone scanning has been reported to have low sensitivity. In a clinical trial performed in 50 patients who underwent radionuclide imaging and diagnostic SIJ injections, the sensitivity and specificity were reported to be 13 and 100 %, respectively. In another similar study, nuclide imaging was found to have 46 % sensitivity and 90 % specificity (see Table 4.3).
Table 4.3
Imaging modalities
MRI | Modality of choice: 85 % sensitivity for active sacroiliitis. Cannot detect noninflammatory causes. STIR and contrast-enhanced preferred |
CAT | 58 % sensitivity and 69 % specificity. Cannot detect inflammation |
Bone scans | Low sensitivity, >90 % specificity |
X-rays | Very low sensitivity, high specificity |
Ultrasound | Can detect posterior ligamentous pathology. Can be useful during pregnancy |
Diagnostic Injection
SIJ injections are generally considered the most reliable means to diagnose SIJC pain. They have been used as the reference standard in most clinical studies investigating the predictive value of history and physical examination, referring pain patterns and imaging modalities. In almost all cases, these injections have been IA which may underestimate the true prevalence of SIJC. The false-positive rate of uncontrolled SIJ blocks is estimated to be 20 %, making controlled blocks with two different local anesthetic drugs or placebo-controlled blocks the best way to identify a painful SIJ and to predict treatment response to radiofrequency denervation. However, this methodology may be prone to a higher false-negative rate and may be less cost-effective.
Treatment
Conservative Treatment
Conservative management can serve as a first-line option with fewer risks to address the underlying pathology. True and functional leg length discrepancy can be treated with shoe lifts and physical therapy. Strength and flexibility training can help correct the maladaptive biomechanical imbalance [75]. Most studies on physical therapy focused on core strengthening and were conducted in peri- and postpartum women who routinely suffer from SIJ dysfunction [76].
A study evaluating three different physical modalities in pregnant women diagnosed with SIJC pain based on provocation maneuvers found that nonelastic SI belts, home exercise, and a structured clinical exercise are equally effective at 38 weeks gestation and 12 months postpartum [77]. A physical rehabilitation and exercise program should be individualized based on clinical findings, physical capacity, and anticipated compliance [56].
Manipulation such as osteopathic and chiropractic adjustments has been reported to be of value, although prospective controlled studies are lacking [78, 79]. Uncontrolled or inadequately controlled trials using different techniques and methodology have shown significant clinical benefits of pain originating from SIJ [53, 80–82]. SIJ bony asymmetries have been shown to resolve with manipulation [53, 83]. However, an early study showed no significant correlation between joint motion and response to diagnostic blocks [67], and a later study found no change in SIJ bony positioning after manipulation [79]. There are anecdotal reports of improved tone and pain involving SIJ-related soft tissues (quadriceps, abdominal musculature, and hamstrings after manipulation [83–86]). A well-designed study failed to demonstrate an association between spinal manipulation success and the presence of SIJ provocation maneuvers [78].
Pharmacotherapy should be considered as part of a multimodal treatment paradigm. In patients with acute nonneuropathic pain, oral or topical anti-inflammatory and muscle relaxants may be effective, though the treatment effect is relatively small. For patients with spondyloarthropathies, cytokine inhibitors and methotrexate may limit disease progression, improve pain relief, and increase function.
Interventional Treatment
Prolotherapy (Aka Proliferative Therapy)
It is hypothesized that the injection of nonpharmacological and nonactive irritant solutions such as dextrose and platelet-rich plasma into the joint, tendons, or ligaments will initiate an inflammatory process that may lead to enhanced blood flow and accelerated tissue repair. As a result, the injection may strengthen connective tissue and relieve musculoskeletal pain. In one randomized study comparing four biweekly IA prolotherapy with dextrose of 25 % to the IA steroid for injection-confirmed SIJ pain, both groups experienced significant but similar improvement at 2 weeks, but at 15 months post treatment, positive outcome sustained in 58.7 % of patients in the prolotherapy group versus 10.2 % in the steroid group [87]. An observational study evaluating three injections of hypertonic dextrose into the SIJ ligaments reported success rates of 76, 76, and 32 % at 3-, 12-, and 24-month follow-up visits, respectively. Despite these results, placebo-controlled studies are needed to establish the efficacy of prolotherapy for SIJC pain.
EA Steroid Injections
Two randomized controlled trials evaluated single periarticular injections with 3 mL of steroid and local anesthetic or 3 mL of saline and local anesthetic. The first study done in patients with seronegative spondyloarthropathy demonstrated that the steroid cohort experienced better pain relief than the control group at 2-month follow-up [40]. The second study done in patients with nonspondyloarthropathic SIJC pain showed similar result at 1-month follow-up [41]. In a nonrandomized study comparing IA and EA injections in patients with pain in the SIJ region and three positive provocative tests, pain improvement was observed in 100 % of EA group and 36 % of IA group [88]. In a retrospective study comparing IA blocks and combination of IA and EA blocks (to include the lateral branches and posterior ligaments), 50 % or greater pain relief was seen in 42.5 versus 27.5 % at 3 weeks and 31.2 versus 12.5 % at 3 months for the combination group and IA group, respectively [80]. Further studies with larger sample size with long-term follow-ups are needed to identify the subgroups that most benefit from EA injections.
IA Steroid Injections (Fig. 4.3)
Fig. 4.3
Anteroposterior and lateral fluoroscopic images demonstrating a right-sided sacroiliac joint block with an appropriate spread of contrast in the joint (arrowheads)
A prospective study in children with juvenile spondyloarthropathy who failed to respond to nonsteroidal anti-inflammatory drugs (NSAIDS) found CT-guided IA steroids to be effective with a mean duration of benefit of 12 months [90]. Another investigation evaluated the effect of IA steroid injections in patients with inflammatory spondyloarthropathy and MRI evidence of sacroiliitis and that in patients without radiologic-confirmed SIJ inflammation. Significant but similar improvements in pain scores and function were reported in both groups between 1 and 3 months [91]. In a randomized trial, ten patients with spondyloarthropathy and sacroiliitis received either IA steroids or saline [92]. Five of six steroid-injected joints had >70 % improvement compared to zero out of seven saline-injected joints at 1-month follow-up. Six of seven saline-injected joints were then injected with steroids, resulting in an overall 87.5 % with positive outcome at 1 month. The positive outcome declined to 62 and 58 % at 3 and 6 months, respectively. Overall, the evidence supporting IA steroid injections is more robust for spondyloarthropathy than for nonspondyloarthropathy.
Other IA Injections
Investigators have looked into phenol and hyaluronic acid solutions in an attempt to prolong the intrinsic short-term relief with corticosteroid injections. One report of IA phenol in patients who had short-term relief with IA steroid injections, nine out of ten patients experienced a median 20.5-week pain relief [93]. Given the high rates of ventral capsular tears and uncontrolled spread of injectate into the epidural space or sacral foramina [27, 94], IA phenol is considered high risk and therefore rarely done clinically. In a case series, four patients who underwent a series of three IA hyaluronic acid injections experienced 12–16 months of significant pain relief [95]. However, this treatment effect size is considered modest at best and may benefit a subgroup of patients with degenerative SIJ osteoarthritis.
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