Orthopedic Manual Physical Therapy for Sacroiliac Joint Pain, Part 2 - Anatomy & Kinematics
This is Part 2 of a series of blogs on the evidence-based examination and treatment of sacroiliac joint dysfunction. To review the evidence on the prevalence of sacroiliac joint pain, read Part 1 about the prevalence of sacroiliac joint pain.
Does the sacroiliac joint even move at all?
Some believe that the sacroiliac joint moves well and that excessive motion or asymmetrical positions can be responsible for pain; others feel that the sacroiliac joint is incapable of any movement at all and therefore isn’t relevant to the patient’s pain or worthy of examination.
Before considering the research on sacroiliac movement, let’s set the stage with a brief overview of sacroiliac anatomy:
One third of the sacroiliac joint consists of a synovial joint covered with smooth hyaline cartilage on both surfaces – features typical of other joints capable of movement (shoulder, knee, hip, etc). While there is considerable variability in the amount of total surface area between individuals (5-20cm2), the average has been observed to be approximately 12cm2 for adult females and 13cm2 for adult males. Interestingly, these synovial joint surfaces are ear-shaped and have portions of the same surfaces positioned in different planes – appearing to limit motion rather than facilitate it.
The remaining two thirds of the sacroiliac joint consist of a cartilaginous joint that is composed primarily of the posterior sacroiliac ligament with flexible, yet tough fibrocartilage (think annulus fibrosis of the intervertebral disc, menisci, pubic symphysis) on the bone surfaces.
The entire sacroiliac joint is then stabilized by a complex cluster of some of the strongest ligaments in the body that, by their varying alignments, appear to limit movement in every plane of motion. How strong are they? Clinically speaking, severe trauma to this region of the body results more frequently in pelvic or hip fractures than to ruptures of the ligaments stabilizing the sacroiliac joint.
Many of these features have led some to conclude that the sacroiliac joint is designed more for stability than mobility: “The SIJ should be classified anatomically as a symphysis [an immovable joint where two bones are closely joined] with some characteristics of a synovial joint.”
Interesting. So, the next logical question is, ‘Does the sacroiliac joint even move at all?’
Yes, it does.
Sturesson et al studied 25 patients with suspected SIJ disorders using roentgen stereophotogrammetry [RSA] in physiologic positions as well as in the extreme of physiologic positions. RSA is a highly accurate assessment of three-dimensional migration and micromotion of a joint by placing small markers percutaneously into relevant structures within the body and then taking a stereo image with two synchronized x-ray foci. In this study, markers were implanted into the sacrum and the ilium, and x-rays were taken in end-range positions.
The results? They found that the degrees of rotation were small with a mean of 2.5 degrees (0.8-3.9). The translation was a mean of 0.7 mm (0.1-1.6 mm).
This study by Sturesson et al was later validated in a systematic review by Goode et al: “Rotation ranged between –1.1 to 2.2 degrees along the X–axis, –0.8 to 4.0 degrees along the Y-axis, and –0.5 to 8.0 degrees along the Z-axis. Translation ranged between –0.3 to 8.0 mm along the X-axis, –0.2 to 7.0 mm along the Y-axis, –0.3 to 6.0 mm along the Z-axis.”
So, the sacroiliac joint does indeed move – just not very much. However, as we’ll next consider, in some persons it may not move at all:
Rosatelli et al studied the anatomy of the interosseous region of the sacroiliac joint and stumbled across a remarkable finding: “Surface characteristics of the SIJ complex observed in specimens 55 years of age or older included moderate to extensive ridging of the interosseous region of the sacrum and ilium in 100% of specimens and ossification of the central interosseous region of the sacroiliac ligament in 60% of specimens.”
Their conclusion: “Central region ossification of the interosseous SI ligament and the presence of ridges and depressions over the opposing interosseous surfaces of the sacrum and ilium are features common to specimens that are in or beyond their sixth decade. These findings further support the contention that there is little to no movement available at this joint in older individuals.”
So, while some professionals believe that the sacroiliac joint moves well and others feel that the sacroiliac joint is incapable of any movement at all, the truth isn’t as black-and-white. The sacroiliac joint does indeed move in most persons. However, there is only minute movement of the sacroiliac joint in younger individuals and little to no movement in the majority of individuals 55 years of age and older.
However, the questions still remain: How can we determine whether or not the sacroiliac joint is a relevant component of a patient’s low back pain? What is the latest evidence-based treatment for sacroiliac joint dysfunction once established? Future blogs will discuss the best available research in guiding the examination and treatment of suspected sacroiliac joint dysfunction.
Dr. Damon Bescia is a fellowship-trained Doctor of Physical Therapy, board certified in orthopedics and sports physical therapy, who specializes in Orthopedic Manual Physical Therapy and serves Naperville and its surrounding communities by way of his Concierge Practice, providing private one-to-one orthopedic manual physical therapy for his clients. For more information, please visit https://www.napervillemanualphysicaltherapy.com.
 Jesse MK et al. 3D Morphometric Analysis of Normal Sacroiliac Joints: A New Classification of Surface Shape Variation and the Potential Implications in Pain Syndromes. Pain physician. 2017 Jul;20:E701-9.
 Puhakka KB, Melsen F, Jurik AG, Boel LW, Vesterby A, Egund N. MR imaging of the normal sacroiliac joint with correlation to histology. Skeletal radiology. 2004 Jan 1;33(1):15-28.
 Sturesson B, Selvik G, UdEn A. Movements of the sacroiliac joints. A roentgen stereophotogrammetric analysis. Spine. 1989 Feb;14(2):162-5.
 Goode A, Hegedus EJ, Sizer P, Brismee JM, Linberg A, Cook CE. Three-dimensional movements of the sacroiliac joint: a systematic review of the literature and assessment of clinical utility. Journal of Manual & Manipulative Therapy. 2008 Jan 1;16(1):25-38.
 Rosatelli AL, Agur AM, Chhaya S. Anatomy of the interosseous region of the sacroiliac joint. Journal of Orthopaedic & Sports Physical Therapy. 2006 Apr;36(4):200-8.