I finished my first year exams 2 days ago and I would figure I should be decompressing and staying as far away from anything relating to Osteopathy for a while…well, I have come to the conclusion that I am lost without Osteopathy so I am about to dive back in and keep trying to understand what is really going on with the human body (if that is even possible).
Let me start by defining a sacral shear. A sacral shear theoretically occurs in the coronal plane which means that the axis of rotation would be anterior to posterior. That is all well and good and looks like it could happen when viewing an anatomical diagram in 2 dimensions on a piece of paper but take another look at the diagrams. There is no connective tissue that will provide any impetus for movement of the sacrum/coccyx directly through the coronal plane. The majority of the muscular tissue looks like it goes from midline (sacrum/coccyx) and travels laterally but there is an obvious posterior to anterior direction to these muscles (gluteus maximus, piriformis, and coccygeus being the ones with direct attachment to the sacrum/coccyx). Considering the fact that these muscles have posterior to anterior pulls (the gluteus maximus also having a superior to inferior direction) it should now start to seem difficult for a sacral shear to exist alone. To throw a little more anatomy at you, consider that the ischiocavernosus travels from the ischial tuberosity to the pubic symphysis with both medial to lateral and inferior to superior pulls. Looking back at the gluteus maximus it should also be noted that the superior to inferior and posterior to anterior directions of pull will create primarily oblique rotations of the sacrum.
When looking at the sacrum/coccyx it is important to note that they exist between the innominates and that considering Wolff’s Law the innominate as a whole shows that there is a primary rotation that occurs obliquely through all planes (sagittal, coronal, and transverse). The simplest way to trace this arc is to start at the right posterior sacroiliac ligament, follow the iliac crest anterior to the the right inguinal ligament, the right inguinal ligament connects at the pubic symphysis and we can now follow the line through the left ischiocavernosus to the the left ischial tuberosity (this can also simply be the bony arch between the pubis and ischium) and then pick up the left sacrotuberous ligament. Now that we are at the left sacrotuberous ligament we follow its oblique direction through the sacrum back to the right posterior sacroiliac ligament. This arc is mirrored on the opposite side and when all of the soft tissue of the pelvic/sacrum/coccyx are considered as a unit it can be posited that there are no clearly delineated lines of strain that exist in one plane and that the body has responded by building rotational structures to disperse the multitude of forces experienced in the pelvic complex.
As meandering as anyone can get when consciously investigating the body all of the above hopefully highlights why the sacrum can not simply shear. Look at the pelvic complex with Wolff’s Law in mind and trace the arc I have outlined. Nothing in the body exists in isolation and the sacrum is obviously not an exception.
Considering the fact that it is not possible for the sacrum to simply shear it should always be considered that sacral correction needs to be performed with the oblique rotations that it generally gets caught in as the primary consideration. When using the long lever the sacrum is corrected by following the arc I outlined above and reversing the primary rotation of the innominate (note that the innominate has much more movement potential than the sacrum as can be proven by the amount of muscular investment it displays). Students at the CAO should be aware that, barring any contraindications, this is most directly achieved through supine leg rotation and that the barriers you need to be paying attention to are created within the arc I have posited (as always the technique is not the important part as this correction can be performed differently – it can be done short lever with myofascial principles if necessary as when a patient has no leg to use as a long lever). Correction of the sacrum is made possible only when the innominates have been corrected as they are the structure that creates sacral dysfunction through articular surfaces and soft tissue connections. Correction is created by reversing the rotational direction of dysfunction through the long lever as achieved by supine leg spinning (again, don’t simply get caught on the technique, use the anatomical structure to determine the most appropriate method for the patient on the table).
There are obviously more considerations that I have not highlighted here (such as the influence of the iliacus or gluteus medius and minimus) but that is why the waters of Osteopathy are so deep. It is impossible to measure the body in a finite fashion. Even with the arc I have defined to help understand sacral dysfunction there are no directly straight lines in the arc, it is not a perfect circle. The fact that it is not a perfect circle is why it can be said that Osteopathy exists in the grey area and why paying attention to barriers is so important as there are infinite amounts and directions of pull. I am putting this idea out there and I welcome feedback as I am very new to Osteopathic thinking and would be grateful for any corrections that may be offered!