Correspondence

I would like to submit a letter to the Editors in response to a recent article by Vleeming A, Schuenke MD, Masi AT, Carreiro JE, Danneels L, and Willard Fh entitled: ‘Sacroiliac joint: an overview of it anatomy, function and potential clinical implications’, published in the September 2012 issue of Journal of Anatomy.

Although for the most part this is a nice review of the anatomy of the sacroiliac joints (SIJs) I am concerned that a number of important points were not considered on how the SIJs behave from a kinesiological perspective.

The authors intimate to the reader that the most convincing studies regarding the amount of motion occurring at the sacroiliac joints are in agreement; the fact of the matter is that this is an illusory number that is still unclear despite the articles cited. The author's conclusion that very little motion (< 2°) develops at this anatomically large synovial joint while conceding the fact ‘that motion plays a large part in maintaining the health of the joint’ is puzzling. Motion must occur at the SIJs with its hyaline articular cartilage occupying 17.5²-cm surface area (Brooke, 1923). The SIJ articular cartilage, like any hyaline cartilage, cannot survive without repeated joint compression and motion on its surfaces. Although how much motion occurs at the SIJs is a much debated issue, this really is not that important from a clinical perspective. This is because at this time we really don't know if too much or too little motion at the sacroiliac joint is may cause sacroiliac joint pain.

I believe the most important omission in this review is what is known about how the sacroiliac joints move. A seminal overlooked point is that together the two sacroiliac joints behave as one functional unit, even though they are two structurally different joints. The renowned anatomist M. A. MacConnail noted that all of the spinal joints, except the atlanto–axial articulation, are bicondylar joints where movement of the left joint is always paired with an equal and correlative movement of the right joint (MacConnail & Basmajian, 1977). The sacroiliac joints behave in exactly this way (Lavignolle et al. 1983; Cibulka et al. 1988; Smidt et al. 1995, 1997; Sturesson et al. 2000). As for the symphysis pubis, for all practical purposes, except during pregnancy, it acts as a fused joint and does nothing more than insure that movement at the left sacroiliac joint is equally and correlatively imparted to the right sacroiliac joint (Meissner et al. 1996). This type of paired joint motion is the key to understanding the problems that develop in this joint and is also likely why so many studies have failed in their attempt to explain how the sacroiliac joints really move.

I agree with the authors that that the sacroiliac joint is an overlooked cause of low back pain and although I don't disagree with the concepts of form and force closure and motions of sacral nutation/counter nutation, I believe this notion cannot fully explain all of the problems that occur at these two joints. Obviously, much more research is needed here.