No apologies. This week’s blog contains an abundance of anatomical terms. The good news is that there is a summary at the end, so you can skip straight to that if you just want the gyst.
Mark Laslett – Identified that the SIJ can be implicated in dysfunction in two different ways:
1. pain derived from the joint, this has been proven to exist by injecting anaesthetic into the joint space which causes the pain to abate, showing it derives from there. Bussey and Milosavljevic found that there are nociceptors throughout the joint capsule, ligaments and potentially throughout the subchondral bone suggesting that trauma or tension to any of these structures could lead to pain and Vleeming et al propose that this pain could be driven by assymetric tension across the joint. Furthermore sacroiliac joints are prone to degenerative changes. A report delivered at the National Association of Spinal Surgeons suggested that in the studied cohort, with a mean age of 53, 35% of joints had serious degeneration and a further 30% minor and that it tended to occur more in men.
2. contribution, as a load bearing mechanical junction between the pelvis and spine, to dysfunction, leading to pain elsewhere. Mark Laslett was sceptical about how much a joint with little rotational or translational movement could influence other structures but let us see the avenues that other researchers are pursuing
A pelvic torsion will cause a functional leg length discrepancy, conversely a leg length discrepancy of 1 cm can cause increase a fivefold increase in pelvic forces.
Vleeming et al suggested that the sacroiliac joint can adopt a constantly braced force closure when there is load unpredictability or constant high loading and this can become a dysfunctional norm with muscular bracing and indeed muscular hypertonia and fatigue, furthermore, Iliacus can pull the ilium forward causing a relative counternutation of the sacrum in such positions as lying supine and straight leg raise, if the patient hasn’t braced and force closed adequately.
In pregnancy, pelvic girdle pain can be caused by insufficient bracing. People tend to brace the contralateral (good) SIJ using Biceps femoris and External Oblique when flexing bad sij, Sjödahl et al found evidence that, when performing an assymetric straight leg raise, women with pelvic girdle pain fail to tense their pelvic floor…is it also part of that force closure process? One muscle that doesn’t appear to be directly part of the process despite a longstanding belief it was involved is transversus abdominus, according to studies in vitro by Gnat et al.
McGrath et al have found another source of sacroiliac region pain. The posterior rami of the sacral nerves form a plexus (network) in the gluteal region close to the sacroiliac joints. They identified two potential places areas where it is proposed that entrapment may occur:
1. under Long Posterior Sacroiliac Ligament
2. where the medial branches of the posterior rami penetrate the deep fascial layer to innervate sacral multifidus and become cutaneous
You can think of this nerve entrapment as very similar to sciatica but much more localised.
So to sum up. The sacroiliac joints themselves have pain responsive nerves and may be responding to trauma or degeneration. The long-standing assumption that sacroiliac movement could lead to a pelvic torsion and contribute to dysfunction and pain elsewhere is now being questioned but new models involving uneven soft tissue tensions and bony plasticity may provide an alternative mechanism but a similar outcome and finally the area around the sacroiliac joints may be prone to sciatica type neuropathic pain, this may also be influenced by uneven forces and soft-tissue tensions.