SIJ Range of Motion
For many years, the sacroiliac joint was thought to be fused and immobile. The concept that the sacroiliac joint has any motion has been controversial until recent studies on cadavers, in-vivo, and biomechanical models have shown otherwise.
Cox , using cadavers, drove nails into the sacrum and ilium, flexed the thigh on the abdomen, and then hyper-extended the spine; both motions demonstrated separation of the nails. He stated, “This procedure definitely showed motion to exist in the joints normally both anteriorly and posteriorly.”
Using manual pressure on specially cut cadavers, Sashin  found an average of 4 degrees of motion in women under 30, more so in pregnant women.
Miller et al.  measured each direction from neutral in specimens within 12 hours after death. Lateral translation averaged 0.76 mm, anterior displacement averaged 2.74 mm, lateral rotation averaged 1.4 degrees, and axial rotation averaged 6.21 degrees. White and Panjabi p114 used Miller’s figures and noted that all motions were measured in older people and should be lower than in a young person due to reduced motion that occurs with age.
However, Vleeming p54 found “even in old age (over 72 years), the combined movement of nutation and counternutation can amount to about 4 degrees”.
Different, but similar, ranges of motion for the sacroiliac joint were found by Vukicevic et al. , using holographic analysis on cadavers, he found 2-7 mm, depending on the how much weight was loaded on the sacrum.
Weisl  stated that the greatest range of motion occurred when moving from recumbent to standing; the movement of the sacral promontory ranged from 5-6 mm. This did not take into account the additional lesser movement of the ilium.
Using Kirchner wires inserted into the pelvic bones of live subjects and locating them relative to a caliper while the subject went through various postures, Colachis et al.  found the sacral translation to be about 5 mm.
Egund et al. , using stereophotogrammetric analysis, in vivo, found a maximum of 2 degrees of sacral rotation about a sagittal axis and about 2 mm of linear translation.
In a study of the posterior superior iliac spines, using photostereogrammetry, Grieve  found a range of motion to be between 5 and 8 mm for the pain-free women and as little as 1mm to 16 mm, for women in pain, indicating hypo or hypermobility. This method should allow some, possibly significant, error because it used markers on the skin over the posterior superior sacroiliac spines and x-rayed the positions of the bones relative to the markers.
Sturesson et al. , also using stereophotogrammetric analysis, in vivo, found rotation varied from 1 to 3 degrees, depending on the movement. They also found a linear translation between 0.5 mm and 1.6 mm. It is interesting to note that they found no difference in movement between the symptomatic and non-symptomatic people.
In extreme reciprocal hip positions, Smidt  found motion at each sacroiliac joint of over 10 degrees in normal young subjects, and up to 18 degrees, per side, in young gymnasts. However, in a subsequent similar study using radiostereometric analysis on women with long term pain post-pregnancy, Sturesson found movements of less than 2 degrees. The difference between Smidt’s and Sturesson’s studies may be explained, in part, by the subjects studied. In Smidt’s study, the young subject’s sacroiliac joints would not have formed the restrictive ridge and groove, so their sacroiliac joints were still able to move in all directions . In addition, the strenuous movements involved in gymnastics may have stretched the ligaments considerably, significantly increasing range of motion. It should be noted that, in Sturesson’s study, the women may have developed the interlocking ridge and groove, which may have significantly reduced the sacroiliac joint’s range of motion.
The Musculoskeletal Integration Theory proposes that the true range of motion in a never-injured sacroiliac joint would be smaller than that found by Smidt, but possibly larger than that found by Sturesson. In another section of this theory (see Ridge and Groove), a mechanism is proposed that explains how the interlocking ridge and groove may develop as a result of injury. If this concept is correct, it suggests that an uninjured adult sacroiliac joint would have free movement in all directions but, after injury, the ridge and groove may limit the range of motion such that it will not occur freely in all directions. Thus, the overall motion may be well below what it would be if the joint was never injured. It follows that the true range of motion in a never-injured sacroiliac joint may be appreciably greater than that found by Sturesson. However, whether the joint is more mobile due to the sprained ligaments, or less mobile due to the interlocking of the ridge and groove, is yet to be determined. Finding adult subjects whose sacroiliac joints have never been injured may prove to be difficult since it appears that the ridge and groove are prevalent in our populace. However, at this point, we will use Sturesson’s measurements since they appear to represent the average adult.
Both In-Vivo and In-Vitro Studies
In addition, Goode  did a comprehensive search of the literature for the quantity of movement of the sacroiliac joint in both in-vivo and in-vitro studies. Of 118 manuscripts, he eliminated 111 based on concerns for transferability or validity due to missing elements of procedural design. His review of the remaining 7 well-designed studies demonstrated that “Rotation ranged between -1.1 to 2.2 degrees along the X-axis, -0.8 to 4.0 degrees along the Y-axis, and -.05 to 8.0 degrees along the Z-axis. Translation ranged between -0.3 to 8.0 millimeters (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.”
Scholten et al. , using biomechanical models of a pelvis, found rotation did not exceed 1.5 degrees and translation did not exceed 4 mm. With 500 Newtons of anterior shear force, the sacrum moved anteriorly and the ilia separated laterally, each by 1.4 mm. At the same time, the ilia twisted 1 degree.
- Cox, H., Sacro-iliac Subluxation as a Cause of Backache. Surgical Gynecology & Obstetrics, 1927. 45: p. 637-648.
- Sashin, D., A critical analysis of the anatomy and the pathologic changes of the sacro-iliac joints. The Journal of Bone and Joint Surgery, 1930. 12: p. 891.
- Miller, J.A., A.B. Schultz, and G.B. Andersson, Load-displacement behavior of sacroiliac joints. Journal of Orthopaedic Research, 1987. 5(1): p. 92-101.
- White, A. and M. Panjabi, Clinical Biomechanics of the Spine. 2nd ed. 1990, Philadelphia, PA: J.B. Lippincott Company.
- Vleeming, A., et al., The role of the sacroiliac joints in coupling between spine, pelvis, legs and arms., in Movement, Stability, and Low Back Pain, A. Vleeming, et al., Editors. 1997, Churchill Livingstone. p. 53-71.
- Vukicevic, S., et al., Holographic analysis of the human pelvis. Spine, 1991. 16(2): p. 209-14.
- Weisl, H., The movements of the sacroiliac joint. Acta Anatomica (Basel), 1955. 23(1): p. 80-91.
- Colachis, S.C., Jr., et al., Movement of the Sacroiliac Joint in the Adult Male: a Preliminary Report. Archives of Physical Medicine and Rehabilitation, 1963. 44: p. 490-8.
- Egund, N., et al., Movements in the sacroiliac joints demonstrated with roentgen stereophotogrammetry. Acta Radiologica: Diagnosis (Stockholm), 1978. 19(5): p. 833-46.
- Grieve, E.F., Mechanical dysfunction of the sacro-iliac joint. International Rehabilitation Medicine, 1983. 5(1): p. 46-52.
- Sturesson, B., G. Selvik, and A. Uden, Movements of the sacroiliac joints. A roentgen stereophotogrammetric analysis. Spine, 1989. 14(2): p. 162-5.
- Smidt, G.L., Interinnominate Range of Motion, in Movement, Stability & Low Back Pain. The essential role of the pelvis., A. Vleeming, et al., Editors. 1997, Churchill Livingstone: Edinburgh. p. 187-191.
- Bowen, V. and J.D. Cassidy, Macroscopic and microscopic anatomy of the sacroiliac joint from embryonic life until the eighth decade. Spine, 1981. 6(6): p. 620-8.
- Goode, A., et al., Three-dimensional movements of the sacroiliac joint: a systematic review of the literature and assessment of clinical utility. The Journal of Manual and Manipulative Therapy, 2008. 16(1): p. 25-38.
- Scholten, P.J., et al., Motions and loads within the human pelvis: a biomechanical model study. Journal of Orthopaedic Research, 1988. 6(6): p. 840-50.