Mechanics of pelvic girdle stability and self-bracing in SIJ-related pelvic girdle pain: a review, by Bussey, in Physical Therapy Reviews (2015)
The sacroiliac joints (SIJ) are a pair of synovial joints situated between the sacrum of the spine and ilium on the left and right sides of the pelvis. They are surrounded by a number of strong ligaments that hold them firmly together. The sacrum is comprised of the five lowest vertebrae of the spine, which are all fused together and do not move against one another like the cervical, thoracic, or lumbar vertebrae. The SIJ are capable of only a small range of motion, although exactly how much movement they can perform is currently unclear. The SIJ have been identified as a common cause of low back pain (LBP), which is a very prevalent musculoskeletal complaint affecting a large proportion of society.
Researchers have estimated that as many as 15 – 30% of cases of LBP might be attributable to the SIJ, although given that diagnosis of the precise cause of low back pain is very difficult, such estimates must necessarily be highly uncertain. The underlying reasons for this potential contribution of the SIJ to cases of low back pain are unclear. It has been suggested that the basic biomechanical functions of the SIJ might well be contributory, given that they appear to play a role during both upright standing and in normal gait. Specifically, it is thought that the SIJ function as shock absorbers during gait and that repeated impacts might cause damage to the overlaying cartilage and consequently osteoarthritis, just as at other load-bearing joints in the body. Osteoarthritis is a chronic, progressive, degenerative joint disorder. It is characterised by constellation of damaging structural changes in a joint, including the areas of articular cartilage and subchondral bone, which can be observed on X-ray imaging scans. Such changes are thought to be instrumental in the development of pain and functional impairment. Originally, osteoarthritis was thought to be entirely a disease of the articular cartilage but more recently research has revealed that the condition is a multifactorial disease of the whole joint and has a very complex pathogenesis involving interactions between various joint tissues. In order to understand the potential for osteoarthritis in the SIJ in addition to its possible contribution to low back pain, many studies performed biomechanical analyses on the SIJ either in standing or during gait. Unfortunately, observations of the SIJ position and movement are very difficult to carry out reliably because of the complex anatomy and surrounding tissues, the very small ranges of motion through which the SIJ move, and large degrees of inter-individual variability.
OBJECTIVE:To review the literature regarding mechanical and motor control factors that might affect pelvic girdle stability and consequently influence the development of chronic posterior pelvic girdle pain.
The reviewer asserts that the pelvis is the link that permits load to be transferred between the axial skeletal of the spine and the primary bones of the lower body. The transmission of force from the lumbar spine to the head of each femur occurs via the bones of the pelvis and the sacrum. Consequently, stability of this lumbopelvic complex under loading is important for effective, pain-free force transmission.
The reviewer explains that the mechanical stability of the pelvis and the lumbopelvic complex can be sub- divided into two sets of factors: static stability, arising from the passive support provided by bones, joint structures, and ligaments, which can be termed “form closure” and dynamic stability, arising from tension provided by and through the surrounding muscles and fascia that compress the joints of the pelvis, which can be termed “force closure”. Form closure is primarily therefore a function of anatomy. Force closure is a function of both muscular strength and co-ordination. Specifically, the reviewer notes that muscular forces exerted by the biceps femoris, erector spinae, gluteus maximus and latissimus dorsi have all been found to increase stiffness of the SIJ, which is indicative of increased force closure. Only the gluteus maximus is directly able to act to close the SIJ, however, with fibers crossing from the sacrum to the ischium of the pelvis, while the actions of the other muscles on the SIJ likely occur through their connection to the thoracolumbar fascia or to the posterior ligamentous structures of the SIJ.
The precise co-ordination of the individual muscles around the pelvis may alter the stability of the SIJ. The reviewer notes that individuals with pain have been found display altered control mechanisms in lumbopelvic movements. In particular, it has been noted that the normal (stable) anticipatory postural adjustment strategies that are seen in healthy people are replaced by compensatory postural adjustment strategies in individuals with pain, which are only usually observed in healthy individuals in the act of performing high-load tasks.
What did the researchers conclude?
The researcher concluded that load transfer through the pelvis requires both both form closure and force closure and is therefore a function of anatomical features, muscular strength, and co-ordination.
This narrative review was limited in that it was not performed systematically and is therefore heavily dependent upon the opinions of the reviewer.