Muscle balancing efforts should con

Muscle balancing efforts should concentrate on the powerful two-joint muscles around the sacroiliac joint (e.g., gluteus maximus and biceps femoris) as they exert shear and torsion loads proportional to the strength of their contraction. Vleeming et al.  have documented that muscles attached to the sacrotuberous ligament (i.e., gluteus maximus and, in some individuals, biceps femoris and piriformis) can significantly limit ventral rotation (i.e., nutation). The clinical relevance of Vleeming’s work may be seen in a patient with a flexed sacrum or ventral capsular tear, tight psoas muscles, and weak gluteus/hamstrings. This individual will require correction of the imbalance to impede aberrant sacroiliac motion and loading.