The sacrum has two unique roles. In the vertical direction it lies at the base of the vertebral column and thus supports the lumbar spine. In the horizontal direction it forms an integral part of the pelvic complex. It is wedged between two bones known as the iliac bones and forms the posterior wall of the pelvis. This arrangement allows forces to pass from the lumbar spine (low back) to the pelvis and into the legs and vice versa.
However the sacrum is not fused with the rest of the pelvis. Instead it forms a joint on each side with the corresponding ilium (iliac bones) thus forming the sacro-iliac joints. The sacro-iliac joints in essence are stress relieving joints i.e. if they did not exist the pelvis would be a solid ring and thus would be exposed daily to twisting forces that would eventually lead to the pelvis snapping.
The exact source of sacro-iliac dysfunction is unknown. It is believed though that mechanical dysfunction in the pelvic girdle (e.g. changes in alignment) causes pain due to stretching of the surrounding soft tissues. The mechanical changes may then result in a secondary inflammation at the sacro-iliac joint also causing pain.
Signs and symptoms of Sacro-iliac dysfunction
• Low back pain below L5 (the last lumbar vertebrae)
• Pain is usually one sided but can be bilateral
• Pain can refer to the groin, buttock and antero-lateral thigh
• Difficulty and pain with stairs, rolling in bed and standing on one leg
• Tenderness over the sacro-iliac joint
• Associated muscle spasm
Diagnosis and treatment
Your physiotherapist will be able to diagnose and treat this condition. On examination there will be mechanical dysfunction (e.g. asymmetry of the ilia, rotation of the sacrum). With these mechanical dysfunctions there will be associated muscle imbalances (e.g. muscle tightness and muscle weakness) and changes in posture.
Treatment initially would involve reducing pain and inflammation. This may involve the use of electrotherapeutic modalities, soft tissue therapy, ice, and heat. Depending on the mechanical dysfunction your physiotherapist will choose the appropriate technique to correct this. Added to this they will correct any muscle imbalances. Muscle tightness would be treated with massage and appropriate stretches and muscle weakness would be treated with specific strengthening exercises (e.g. retraining and strengthening of the muscular corset of the low back and pelvis).
In some cases taping may be used in the short term to hold the corrected alignment of the pelvis while muscle imbalances are corrected. Your physiotherapist would also asses and correct any postural abnormalities, poor working habits and sporting techniques that may be predisposing the condition.