Joints
Sacroiliac joint
Load transfer between trunk and legs runs through here. The joint barely moves but has to carry enormous forces, and does so through form closure (the rough, interlocking surfaces) plus force closure (tension in muscles and ligaments).
- Joint type
- Partly synovial, partly syndesmosis (amphiarthrosis), very small excursion
- Body region
- Pelvis
- Latin name
- Articulatio sacroiliaca
Movements, axes and normal values
| Movement | Plane | Axis | Normal range | End feel |
|---|---|---|---|---|
| Nutation (forward tilt of the sacrum) | sagittal | transverse through S2 | 2-4 degrees | hard-elastic |
| Counternutation | sagittal | transverse through S2 | 1-2 degrees | hard-elastic |
- Close-packed position
- Nutation: the position in which form closure is maximal
- Resting (loose-packed) position
- Counternutation
- Capsular pattern
- No classic capsular pattern; pain on provocation rather than loss of movement
- Arthrokinematics
- Minimal translation and rotation over rough, interlocking surfaces. Form closure comes from the shape of the bone itself, force closure from the gluteus maximus with the contralateral latissimus dorsi through the thoracolumbar fascia, and from the transversus abdominis and the pelvic floor.
- Stability
- Anterior, posterior and interosseous sacroiliac ligaments (the strongest ligaments in the body), plus the sacrotuberous and sacrospinous ligaments, which limit nutation.
- Palpation
- Posterior superior iliac spine as a dimple; the joint lies directly medial and deep to it.
- Clinical
- Pelvic girdle pain during and after pregnancy; the diagnosis rests on a cluster of provocation tests (Laslett: distraction, compression, thigh thrust, sacral thrust and Gaenslen), of which three out of five must be positive; sacroiliitis in axial spondyloarthritis.
- Source
- Vleeming et al., Movement, Stability and Lumbopelvic Pain; Laslett, Evidence-Based Diagnosis and Treatment of the Painful SI Joint