Keywords
sacroiliac pain - physical examination - differential diagnosis - low back pain
Introduction
Low back pain is the main cause of non-oncological chronic pain in Chile.[1]
[2] Its consequences affect not only the individual with pain, but also the general
population, since low back pain is an important factor for absenteeism from work and
medical leaves,[3] generating a significant economic cost. Within low back pain etiologies, sacroiliac
pain (SIP) is reported in 15% to 30% of the cases.[4] However, despite the impact on the quality of life of patients with this condition,[5] SIP is usually underdiagnosed in the presence of low back pain.[6]
Today, either in primary care or at a general trauma consultation, it is a real challenge
to identify the sacroiliac joint (SIJ) as the cause of low back pain. This is due
to its low index of suspicion by medical personnel, and to the low specificity and
high rate of false-positive results on the anamnesis and physical examination.[7] Other reasons include the following:
-
1) Heterogeneous clinical manifestation of pain, with variable location, radiation,
and intensity.[8]
[9]
-
2) Wide range of special physical tests, since none has sufficient diagnostic applicability.[10]
[11]
[12]
[13]
-
3) The highly prevalent coexistence with other degenerative lumbar conditions, with
imaging findings which are non-symptomatic or constitute potential sources of pain.[14]
-
4) The wide list of differential diagnoses that could explain such pain.[15]
-
5) The lack of clinical recommendations or guidelines in Chile to propose a uniform
confrontation.
This article presents a review of the literature with the intention of proposing a
diagnostic approach to the patient with SIP, in order to optimize resources and improve
diagnostic performance. The review was made based on a search on PubMed for “sacroiliac
joint pain” associated with the keywords “physical examination” and “Diagnosis”, filtering
by Review, Systematic review, clinical trial and Meta-Analysis type articles, obtaining
139 articles, of which they were selected for their impact and relevance according
to the criteria of the authors. We will review the anatomy, etiology, anamnesis, physical
examination, and supplementary tests to finally propose a diagnostic algorithm to
approach the patient with low back pain.
Anatomy and Biomechanics
The SIJ is the largest axial joint in our skeleton, and it distributes the axial load
of the spine to both lower extremities. It is a mixed joint, since the anterior third
of the articular surface consists of hyaline cartilage and presents a joint capsule,
whereas the posterior two thirds are composed of fibrocartilage and a dense network
of ligaments, acting as a syndesmosis,[16] as shown in [Figure 1].
Fig. 1 Sacroiliac joint (SIJ) anatomy. 1: Posterior view; 2: anterior view; 3: cross-section
in superior view.
Innervation of the SIJ is a matter of debate.[17] Posteriorly, it is innervated by lateral bundles from the dorsal branch of L4-S3;
anteriorly, it is postulated to be innervated by L2-S2. However, since the SIJ is
close to the lumbosacral plexus and certain muscles, including the piriformis, gluteus
maximus and biceps femoris, SIJ inflammation can irritate these structures, resulting
in radiation of the joint pain.[18]
[19]
The range of motion of the SIJ is extremely limited and varies according to gender
and age. In children and adolescents, its stabilizing ligaments are more flexible;
in older subjects, however, SIJ ankylosis is common, especially in males.[19] Its main movements are nutation and counternutation. Nutation refers to sacral rotation
in the sagittal plane, bringing the distal end of the sacrum posteriorly. This movement
is scarce under normal conditions, around 1 mm to 4 mm, but it increases considerably
in pregnant women to favor vaginal delivery.[20] In counternutation, the sacrum rotates in such a way that its distal portion approaches
the symphysis pubis, while its upper portion is directed posteriorly ([Figure 2]).
Fig. 2 Sacroiliac joint (SIJ) movement. 1: Nutation and counternutation movements; 2: view
of the sacral and iliac articular surface.
Bones and ligaments account for SIJ stability. Vertical stability is supported by
the bone structure transmitting axial load forces in lateral compression to the iliac
bones and then to the hips, making the sacrum into the cornerstone of pelvic architecture.
The reinforced sacroiliac ligament complex provides stability at the anteroposterior
plane,[21] as shown in [Figure 1].
Sacroiliac Pain Etiology and Differential Diagnosis
Sacroiliac Pain Etiology and Differential Diagnosis
When faced with a patient with low back pain, the doctor must determine if this is
a true case of SIP or pain from another source. During evaluation, all non-sacroiliac
causes of low back pain must be considered, both musculoskeletal, especially lumbar/hip
conditions, and visceral or intrapelvic causes, since all of them are part of the
list of differential diagnoses.[4]
[22]
[23]
[24]
[Table 1] summarizes the causes of low back pain.
Table 1
|
Lumbar pathology:
|
|
Lumbar discopathy
|
|
Facet syndrome
|
|
Myofascial syndrome
|
|
Lumbar spine arthrosis
|
|
Hip pathology:
|
|
Hip arthrosis
|
|
Femoroacetabular impingement
|
|
Gluteal tendinitis
|
|
Trochanteric bursitis
|
|
Sacroiliac joint pain
|
|
Intrapelvic causes:
|
|
Pelvic inflammation
|
|
Endometriosis
|
|
Retrocecal appendicitis
|
|
Diverticulitis
|
|
Tubo-ovarian abscesses
|
|
Renal colic
|
|
Neoplasia
|
The SIJ can be affected by numerous conditions, which can either be primary pathologies
or secondary systemic pathologies. For the primary conditions, the causes are eminently
mechanical or infectious.[24]
[25] Sacroiliac pain can result from a phenomenon similar to that observed in transitional
syndrome after spinal surgeries, in which hypermobility of a vertebral segment develops
secondary to the fixation of adjacent segments. The SIJ may present such hypermobility
after lumbosacral arthrodesis, resulting in pain.[26]
[27]
[28] The secondary causes of SIP are systemic diseases, some of them with an inflammatory
origin, such as ankylosing spondylitis, or metabolic conditions, including hyperparathyroidism.[15]
[29] The primary and secondary causes of SIP are summarized in [Table 2].
Table 2
|
Primary causes
|
|
Previous fracture
|
|
Microtrauma
|
|
Microinstability due to pregnancy-related hypermobility
|
|
Infectious sacroiliitis
|
|
Chronic osteomyelitis
|
|
Hypermobility after lumbosacral arthrodesis
|
|
Iliac condensing osteitis
|
|
Idiopathic sacroiliac pain
|
|
Secondary causes
|
|
Ankylosing spondylitis
|
|
Psoriatic arthritis
|
|
Arthritis associated with inflammatory bowel disease
|
|
Reactive arthritis
|
|
Chondrocalcinosis
|
|
Hyperparathyroidism
|
|
Reiter disease
|
Clinical History
The proper pain identification requires important historical elements, such as onset,
temporal profile, character, triggering or mitigating factors, radiation, and location.
Sacroiliac pain usually manifests as mechanical lumbar pain, below L5, specifically
lower than the posterior-superior iliac spine (PSIS).[9]
[12] Studies with sacroiliac infiltration in asymptomatic patients show areas of pain
10 cm caudal and 3 cm lateral to the PSIS,[8] but pain may arise in the unilateral or bilateral gluteal territory, the thigh,
the groin, the leg, and the foot.[9]
[30] In addition, low back pain has been associated with changes in position, such as
sitting down or standing up.[31]
During anamnesis, the doctor must ask about some SIP-predisposing elements, including
history of pelvic trauma, surgical history, especially lumbosacral arthrodesis,[26] current or recent pregnancy, and sports or manual work activities resulting in pelvic
shear or twist, such as weightlifting, contact sports, or skating.[32]
General anamnesis must be thoroughly performed to uncover other morbid or surgical
data, or even a family history of autoimmune diseases. Since sacroiliitis can occur
as a manifestation of an underlying disease, the concomitant presence of general symptoms,
such as fever and weight loss, or specific symptoms, including polyarthralgia, and
abdominal, gynecological, or urological symptoms, must be determined.[24]
[Table 3] shows a series of questions as a first approach to the patient in an attempt to
rule out different differential diagnoses for low back pain. If any answer is affirmative,
non-sacroiliac causes of pain must be considered, since SIP may result from a systemic
condition.
Table 3
|
Pain in an atypical location? (Cephalic to L5, anterolateral, deep, or non-objective)
|
|
Pain with non-mechanical characteristics? (Nocturnal, at rest, not responding to non-steroidal
anti-inflammatory drugs)
|
|
Presence of constitutional symptoms? (Fever, weight loss, fatigue)
|
|
Presence of gastrointestinal, urological, and/or gynecological symptoms?
|
Physical Examination
The physical examination in a patient with suspected SIP must be complete and accurate.
Since the length of the consultation is often short, the physical examination is limited
to the suspicion based on elements from the anamnesis. However, a complete physical
examination of the hip and lumbar spine is essential when the medical history is doubtful.
The physical examination must start with a general examination, evaluating gait, analgesic
postures, and obvious deformities, such as significant asymmetry in the length of
the lower limbs or lumbar scoliosis.[24] Next, bone and muscle structures at the hip and lumbar levels must be palpated to
detect tenderness; palpation may include the abdomen, looking for abdominal tenderness,
if a referred pain of abdominopelvic origin is suspected.
After palpation, it is important to evaluate the ranges of motion of the lumbar spine
and the hip, assessing active and passive movements, and comparing them with the contralateral
side. A systematic motor and sensory evaluation of each nerve root is critical so
as not to miss any deficit unnoticed by the patient.
Finally, tests must be performed to rule out specific conditions that are part of
the list of differential diagnoses, including those to provoke radicular pain or assess
femoroacetabular impingement.[23]
[Table 4] proposes elements of the physical examination that, if altered, indicate a cause
of pain other than the SIJ.
Table 4
|
Presence of mass or pain during abdominal palpation.
|
|
Limited or painful hip range of motion, pain at musculoskeletal palpation.
|
|
Tenderness on palpation of paravertebral lumbar or spinous processes. Painful lumbar
range of motion.
|
|
Positive signs on provocative tests, impaired strength or sensitivity in lower limbs.
|
Specific SIJ tests are useful when the physical examination does not indicate a hip
or lumbar condition. Because of the high rate of false-positive results regarding
some SIJ tests, it is important to use them with discretion. This is especially true
in the presence of hip disease, because some SIJ tests also diagnose hip conditions,
sometimes with greater diagnostic effectiveness.[33]
Various specific tests have been described for the diagnosis of SIP.[7]
[10]
[12]
[13]
[34]
[35]
[36] When three of these tests are positive, the negative predictive value (NPV) for
SIP reaches 87%.[37] The tests most used in the clinical practice are described below. [Table 5] summarizes the sacroiliac tests available, and their sensitivity, specificity, reliability,
NPV and positive predictive value (PPV); these tests are shown in [Figure 3].
Table 5
|
Test*
|
Sensitivity
|
Specificity
|
Reliability
|
Positive predictive value
|
Negative predictive value
|
|
Pelvic distraction
|
23–60%
|
81–98%
|
82%
|
60–93%
|
57–81%
|
|
Pelvic compression
|
26–69%
|
69–100%
|
82–87%
|
52–100%
|
59–82%
|
|
Thigh thrust
|
36–88%
|
69%
|
84%
|
58%
|
92%
|
|
Gaenslen test
|
31–71%
|
71–94%
|
82–88%
|
47–81%
|
60–77%
|
|
Sacral thrust
|
53%
|
75%
|
66–78%
|
56%
|
80%
|
|
Patrick test (flexion, abduction, external rotation – FABER)
|
34–69%
|
92%
|
74–80%
|
81%
|
60%
|
|
Drop test
|
–
|
–
|
88–97%
|
–
|
–
|
|
Posterior superior iliac spine distraction test[37]**
|
100%
|
89%
|
94%
|
90%
|
100%
|
Fig. 3 Sacroiliac pain provocation tests. 1: Thigh thrust; 2: Patrick test (flexion, abduction,
external rotation – FABER); 3: Gaenslen test; 4: pelvic distraction; 5: sacral thrust;
6: pelvic compression.
Gaenslen test: the patient is placed in supine position and asked to flex the hip
and knee on the affected side, bringing the knee towards the chest and supporting
it with the arms. The contralateral leg should hang over the edge of the table. The
examiner presses the bent knee toward the chest and exerts counterpressure on the
other knee. The test is considered positive if it reproduces the exact pain reported
by the patient.
Sacral thrust: with the patient in prone position, the examiner pressures the sacrum.
The test is considered positive when it reproduces the exact pain reported by the
patient.
Thigh thrust: with the patient in supine position, the hip on the affected side is
flexed at 90°, and the ipsilateral knee is also flexed. The examiner places one hand
on the patient's sacrum and supports the flexed knee with the other hand. The hip
is adducted slightly while the examiner exerts force through the main axis of the
femur, towards the sacrum. The test is considered positive when it reproduces the
exact pain reported by the patient.
Pelvic compression: the patient is placed in lateral recumbency, with the affected
side up, hips flexed at 45°, and knees flexed at 90°. The examiner exerts downward
pressure on the iliac crest. The test is considered positive when it reproduces the
exact pain reported by the patient.
Pelvic distraction: With the patient in supine position, the examiner applies force
to both anterior superior iliac spines (ASISs) in a posterolateral direction. The
test is considered positive when it reproduces the exact pain reported by the patient.
Patrick test (flexion, abduction, external rotation – FABER): with the patient in
supine position, the ankle on the affected side is placed on the contralateral thigh
with knee flexion and abduction and external rotation of the ipsilateral hip. Then,
the examiner pressures the flexed knee, containing both ASISs. The test is considered
positive if the patient reports the same pain in the ipsilateral side.
Fortin finger test: the patient stands up and is asked to point twice with one finger
at the spot where they feel the greatest amount of pain. The test is positive when
the patient indicates a spot 2 cm inferomedial to the PSIS both times.
Drop test: the patient stands up on the foot of the affected side and is asked to
perform metatarsal support (tiptoe) and drop the heel. The test is considered positive
when it reproduces the pain.
Gillet test: the examiner stands behind the patient, who is standing up. The examiner
places one thumb on the PSIS on the affected side and the other thumb on the spinous
process of S2, at the same level, and then asks the patient to flex the ipsilateral
hip. Normally, the PSIS descends 1 or 2 cm. The test is considered positive if the
spine does not descend, reflecting SIJ hypomobility.
PSIS distraction test:[35] With the patient standing up or in prone position, both thumbs are placed on the
PSIS, exerting medial to lateral pressure. The test is considered positive if the
pain is reproduced.
Imaging
The use of imaging for SIP diagnosis is a controversial topic. On the one hand, SIJ
conditions may not have radiological manifestations, and the same disease may result
in different manifestations.[29] On the other hand, different anatomical structures may present altered imaging findings
but not cause pain, leading to diagnostic errors. In a study carried out by Boden
et al.,[14] 67 assymptomatic individuals were examined through magnetic resonance imaging (MRI),
and substantial lumbar spine abnormalities were found in 1/3 of them; this proportion
reached 57% among subjects older than 60 years of age. Similarly, in 2015, Eno et
al.[38] retrospectively analyzed computed tomography scans of 373 patients without low back
pain or pelvic girdle pain. They found that 65.1% of the patients had signs of SIJ
degeneration, and that this prevalence increased with age, reaching 100% in those
older than 90 years of age.
In case of uncertainty as to whether the patient's pain comes from the SIJ, some authors
suggest requesting an anteroposterior hip radiograph, which, together with the clinical
history and physical examination, can guide the differential diagnosis.[24] However, this test is not very sensitive, and there is no quality evidence to support
it. In case of alarming symptoms, including extreme age, chronic pain, disabling pain,
recent trauma, neurological deficit, cancer history, and use of corticosteroids, an
MRI scan must be requested according to the diagnostic suspicion, with higher sensitivity
and specificity.[2] Magnetic resonance imaging scans enable a more precise evaluation of the SIJ, with
early identification of inflammatory changes and structural alterations, especially
in patients with hip spondylopathy.[39] Lumbar MRI is useful to search for a different source of pain.[24] Another imaging test used in the clinical practice is bone scintigraphy.[40] Since it shows the whole body, scintigraphy is useful in nonspecific conditions
with broad diagnostic hypotheses. It has been described to be especially helpful in
cases with no access to a diagnostic infiltration, or when the diagnosis is unclear;
in addition, it may indicate a mechanical origin for the pain.[41]
Diagnostic Infiltration
Since imaging and specific sacroiliac provocation tests lack diagnostic precision,
some cases require diagnostic infiltration, which is considered the gold standard
for the diagnosis of SIP.[42] Diagnostic infiltration has several advantages. First, it enables the confirmation
or exclusion of the source of pain, which in turn enables the examiner to determine
if the patient would benefit from sacroiliac arthrodesis. In addition, it is a simple
procedure with few complications. Lastly, not only it helps in the diagnosis, but
it can play a therapeutic role. Despite the lack of quality evidence to warrant its
use, therapeutic sacroiliac infiltration is performed with increasing frequency in
the United States.[43]
To be effective and valid or interpretable, this procedure requires that two fundamental
conditions are met: 1) the infiltration must be performed in the operating room with
intraoperative radiography to assure, under direct visualization, the deposition of
the anesthetic agent with contrast media in the intra-articular space, since blind
punctures present a success rate as low as 22%;[44] and 2) the infiltration of a maximum volume of 1 mL to 1.5 mL of local anesthetic
agent and corticosteroids, since larger volumes can diffuse into other territories
and generate false-positive results.[8]
The procedure must be carried out with the proper technique.[45] First, specific tests are performed, and the patient is asked to rate the intensity
of the pain evoked in each test from 1 to 100. The patient is then placed in prone
position, and an anteroposterior radiograph is taken. The puncture is oriented toward
the lower SIJ recess, 1 cm to 2 cm superior to the lowest aspect of the joint. The
puncture is performed with the needle directed from medial to lateral, confirmed with
oblique variations of the anteroposterior radiograph with cephalad, caudal, or lateral
angulations. Once it has been confirmed that the tip of the needle is in an intra-articular
position in two orthogonal projections, the contrast media solution with the anesthetic
agent is injected; the infiltration of the corresponding space with no leak is confirmed
radiologically. Finally, the same specific tests are repeated, and the intensity of
the pain in each test is recorded.
To minimize the number of diagnostic infiltrations, several authors[31]
[37] have proposed to perform them in patients with three or more positive provocation
tests, since there is a low probability of a sacroiliac origin for the pain when less
than three tests are positive. Postinjection pain provocation tests help to distinguish
whether or not the pain is originated from the SIJ.[46] An infiltration is considered positive if the postprocedure pain relief exceeds
50% or even 75%[37]
[47]
Discussion
The clinical diagnosis of SIP is not easy due to its several etiologies and the complex
anatomy of the joint. Adequate anamnesis and physical examination guide the diagnostic
study, indicating different anatomical or systemic causes for SIP, and defining whether
or not to perform sacroiliac tests. Such tests have been the subject of research due
to their controversial diagnostic role.
In 1994, Fortin et al.[8]
[9] demonstrated the location pattern of SIP in two studies. In a later study, Fortin
y Falco[12] described the “Fortin finger test” as a successful test for SIP diagnosis. However,
some authors[34]
[48] have postulated that SIP provocation tests are more reliable than palpation. Robinson
et al.,[34] in a 2007 study of 61 patients with suspected SIP, concluded that palpation tests
have interexaminer agreement rates significantly lower than those of the provocation
tests. On the other hand, the usefulness of SIP provocation tests performed in isolation
has also been questioned due to their low specificity and sensitivity and high rate
of false-positive results.[49]
[50] Until now, no maneuver alone reportedly had some diagnostic applicability, and several
specific tests with various indicators of sensitivity, specificity and predictive
values have been described.[10]
[11]
[12]
[13]
[34]
[35]
[36]
Several authors[13]
[34]
[37]
[51] have postulated that performing more than one test and interpreting a combination
of tests would result in a reliable SIP diagnosis. In 2006, a study carried out by
van der Wurff et al.[37] with 60 patients with a history of low back pain using articular blocks in symptomatic
patients and pain provocation tests demonstrated that the performance of less than
3 positive tests had a high NPV (87%), while 3 or more specific positive provocation
tests had a high PPV for SIP (from 65% to 93%). Kokmeyer et al.,[13] in a study with 78 patients, reached similar conclusions. The authors pointed out
that if three out of a set of five pain provocation tests were negative, the NPV would
be higher compared to an isolated test and present greater agreement between examiners.
These last two studies enabled the validation of the clinical usefulness of specific
sacroiliac tests, and it was concluded that they fulfill their role when performed
together.
Sacroiliac tests must be correctly interpreted in each individual patient, according
to the diagnostic suspicion suggested by the anamnesis and the physical examination.
This is why proposing the performance of an anamnesis and systematic physical examination
prior to specific tests is critical, for it enables the proper selection of patients
with SIP who would benefit from more invasive procedures, such as infiltration. [Figure 4] shows an algorithm summarizing the diagnostic approach to low back pain in a context
of suspected SIP. [Table 6] lists supplementary tests that can be requested according to the clinical suspicion.
Fig. 4
Table 6
|
Imaging
|
|
Sacroiliac magnetic resonance imaging
|
|
Lumbosacral magnetic resonance imaging
|
|
Hip magnetic resonance imaging
|
|
Pelvic and hip radiography
|
|
Lumbar spine radiography
|
|
Bone scintigraphy
|
|
Lab tests
|
|
General blood work: complete blood count, erythrocyte sedimentation rate, C-reactive
protein, serum biochemistry panel, renal function
|
|
Rheumatological tests: human leukocyte antigen (HLA) B27, antinuclear antibody (ANA),
extractable nuclear antibody (ENA), rheumatoid factor (RF), antibody anti-cyclic citrullinated
peptide (CCP)
|
Conclusion
Sacroiliac pain is an important cause of low back pain. It can result from several
conditions, and it is often underdiagnosed. Its specific diagnosis is a challenge
for doctors, so an orderly and sequential approach to these patients is essential.
An accurate diagnosis requires a detailed anamnesis and physical examination to help
rule out the main differential diagnoses. Several specific sacroiliac tests are useful
in subjects with a clear suspicion of SIP, provided that other potential sources of
pain are ruled out because they have a high rate of false-positive results. This is
why the combined use of these tests optimizes their diagnostic performance, which
may reach negative predictive values of up to 87%. Imaging is not usually required
for the diagnosis, but it should be considered to investigate other causes of pain,
especially in the presence of alarming signs. Diagnostic infiltration of the joint
is the gold standard technique, and it must be reserved for patients in whom the suspicion
of SIP persists. In addition, it can play both diagnostic and therapeutic roles in
SIP.
