Because of an iliac or sacrum lesion, the gluteus maximus may be disrupted between the iliac and sacral part at the level of the muscle origin.

The muscular fibers separate on a line from the conjoint origin towards the great trochanter.

This may even produce a trochanteric bursitis and pain down the iliotibial tract towards the lateral aspect of the knee.

This should not be confused with pain originating from the piriformis muscle.
Differentiation is done by palpation (the piriformis lies more caudal).

The iliac and sacral portions of the gluteus maximus have different functions. In standing on one leg during gait, the gluteus maximus pulls the ilium towards posterior. The sacral portion however is stretched because of the anterior rotation of S1 on the same side. This sacral portion then contracts isolytically while the iliac portion contracts isometrically.

With muscular separation of the gluteus maximus, the line between the iliac and sacral portion of the muscle is painful, especially when palpated under muscle contraction.

After osteopathic treatment, where the aim is to restore normal function of the whole pelvis, rest is absolutely necessary to let the separation heal.