Published 6/1/2018
Laura M. Bruse, MD

Sexual Dimorphism in Sacroiliac Joint Dysfunction

Do genetics and hormones influence the risk of sacroiliac joint pain?

The presentation of any patient with sacroiliac (SI) joint pain is complex. The unique nature of the anatomy of the junction of the sacrum and the ilium and surrounding soft-tissue layers, which are attached by strong ligaments, contributes to highly variable symptoms. In addition, SI joint pain may manifest differently in males and females. Sexual dimorphism in the anatomy, load-bearing response, hormonal influences on the ligamentous attachments (posterior sacroiliac ligament, sacrospinous ligament and sacrotuberous ligament), and prevalence of inflammatory arthritides contribute to the differences in presentation between males and females with SI joint pain.

SI joint pain may be mistaken for low back pain. Approximately 15 percent to 30 percent of patients report pain around the posterior iliac spine area and frequently point to the low back and buttocks. SI joint pain can also overlap or be mimicked by several other orthopaedic conditions such as nerve root compression, zygapophyseal joint pain, or myofascial pain of structures in and around the joint. Non-spinal disorders of other organ systems, including gastrointestinal, genitourinary, and gynecologic, may provoke pain symptoms that mimic SI joint pain.

Anatomy and innominate motion and load response

The male pelvis is larger than the female pelvis, and the articular surface of the base of the fifth lumbar vertebrae in males occupies more than a third of the width of the sacral base. In females, however, it is less than a third. The sacrum is relatively wider in females, more uneven, less curved, and tilted backward. The female pelvic cavity is shorter and more cylindrical. All this leads to a greater SI joint surface area in adult males than females.

One study found that male SI joint overall innominate range of motion (ROM) is 30 percent to 40 percent less than female ROM. The differing viscoelastic response to load in the pelvic ring is said to account for these differences. This supports the notion that males and females differ in both SI joint geometry and ligamentous laxity. Another study found a difference in load-bearing transfer patterns between the two sexes. Whereas females tended to respond with a unilateral pattern of motion about the vertical axis, males responded with a reciprocal pattern about both the vertical and sagittal-horizontal axes with loading. This may explain why females have greater range of motion about the vertical axis, as this unilateral motion takes stress off the pubic symphysis.

Anatomy and hormonal influence

The less-pronounced curvature of the SI joint surfaces in females allows for an increase in the mobility of the pelvic ring during labor. Under the influence of the hormone relaxin during pregnancy, the SI joint apparatus loosens, resulting in relative separation of the pubic symphyses. These two factors increase mobility in the SI joint, supporting increased complaints of pelvic pain.

This laxity during pregnancy contributes to a three-fold higher risk of patients with SI joint asymmetry developing pelvic girdle pain (PGP), which in some women may persist into the postpartum period. The prevalence of pregnant women with PGP is about 20 percent. Although females are at greater risk, PGP can develop in both males and females with low-back pain, previous trauma to the pelvis, and arthritis.

Ankylosis and inflammatory disease

Ankylosis of the SI joint, diagnosed by radiography or computed tomography, is more prevalent in males and directly affects lumbosacral mobility by causing stiffness. Ankylosis generally occurs in patients older than 50 years. A radiograph may reveal periarticular osteophytes in the cranial iliac aspect in males and more ventral caudal in females. SI joint bridging (osteophytosis) is more common in males than in females, 12.27 percent versus 1.83 percent, respectively. When present, 97.5 percent of the bridging is extra-articular in males; in females, it is intra-articular. Degenerative periarticular osteophytosis immobilizes the SI joint.

The highest degree of SI joint involvement occurs in patients with ankylosing spondylitis (AS), reactive arthritis such as Reiter’s syndrome, and psoriatic arthritis. These inflammatory arthropathies also result in intra-articular ankylosis, commonly in patients younger than 50 years. In AS patients, the symmetric sacroiliitis is almost 100 percent. The male-to-female ratio is 3:1 in patients younger than 40 years.

In AS, the ankylosis often involves both the SI joint and the spine. This further inhibits mobility and causes increased pain in the low back and SI joint. The SI joint can undergo both para/intra-osteophytosis and bridging osteophytosis causing stiffness and decreased mobility.

The other spondylarthropathies include asymmetric joint involvement in young to-middle-aged individuals. Although reactive arthritis is predominant in males, both sexes present equal asymmetric involvement in psoriatic arthropathy. Inflammatory disorders may be clinically diagnosed with laboratory findings such as an HLA-B27 blood test. An erythrocyte sedimentation rate test may help confirm the diagnosis.

Combination of load and inflammation

Load and inflammation may combine to affect ankylosis. AS is an inflammatory condition, but those inflammatory components may be influenced by mechanical inputs from SI joint loading. Just as AS is more common in men, rheumatoid arthritis is more common in women. In females, however, the frequency and severity of metatarsophalangeal joint destruction do not appear to be due to loading.

The development of SI joint dysfunction in males with AS is likely due to a combination of influences: an inflammatory component, a larger and different articular SI joint surface, and different viscoelastic properties with differing responses to load patterns. To determine the exact load application for sex-based dimorphism, however, a study would have to evaluate load per mm2.

To fully understand the sexual dimorphism, more studies are needed to determine if the combination of less ROM, differing articular surfaces, and differences in loading patterns may contribute to the SI joint ankylosis being more prevalent in males.

Physical exam and treatment

A thorough neurologic exam and assessment of the low back and bilateral hips (including ROM and strength testing), with a dedicated exam of the sacroiliac joint, is critical to diagnosing SI joint pathology in patients with low-back or SI joint pain. Some provocative tests of the SI joint include Patrick’s and Gaenslen’s tests, and SI joint compression and distraction tests may also be helpful. The highest predictive value for SI joint pain (60 percent) is maximum pain below L5, together with posterior superior iliac spine or sacral sulcus tenderness.

To support and establish a diagnosis of idiopathic intra-articular joint pain, confirm that the patient has no neurologic deficits, dural tension signs, or laboratory, imaging, or clinical evidence of medical causes of SI joint pain. Also confirm that the pain is maximal below L5, and there is no evidence of lumbar pain generators (e.g., a negative zygapophyseal joint block and diskography). Controlled dual fluoroscopically guided, contrast-enhanced intra-articular SI joint injections should provide, at minimum, 75 percent relief in patients with SI joint pain.

Once a diagnosis of SI joint dysfunction is made, treatment can include medication, physical therapy, bracing, manual therapy, injections in the SI joint (diagnostic or therapeutic), radiofrequency denervation, and arthrodesis (open or minimally invasive). The efficacy of these modalities has not been compared in prospective studies.


When treating patients with sacroiliac pain, keep in mind the following:

  • The SI joint is a challenging orthopaedic pain producer.
  • Specific differences exist in the anatomy, viscoelastic properties, and mechanism and pattern of loading of the innominate bone and may contribute to SI joint dysfunction and pain.
  • Consider SI joint dysfunction in patients with well-described pain in the SI joint or ill-defined nonradicular pain in the low back.
  • Pain that does not respond to the usual algorithm of treatment for low-back or hip pathology may be due to SI joint pathology.
  • Low-back pain or PGP in females with hormonal changes, such as those that occur during pregnancy, may be due to SI joint pain.
  • Males have a higher prevalence of SI joint bridging (osteophytosis) and inflammatory arthritis such as AS.


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Laura M. Bruse, MD, is a clinical instructor in the Orthopaedic Surgery Department, Clinical Community Faculty, University of Nevada School Medicine in Las Vegas. Dr. Bruse recently completed service as chair of the AAOS Women’s Health Issues Advisory Board and currently serves on the AAOS Research Development Committee.