One of the most common causes of piriformis syndrome is external femoral rotator imbalance caused by pelvic obliquity. In most cases, a tight piriformis rubbing on the sciatic nerve’s tough dural sheath won’t elicit symptoms unless the nerve is compressed against another sciatic notch structure or has already suffered entrapment elsewhere. When a contractured piriformis presses an inflamed sciatic nerve backward against the sharp tendinous edges of the gemellus superior, obturator internus or sacrospinous ligament, the condition may easily become chronic, and debilitating (figure 1).
Rarely in my clinical practice do I find the piriformis muscle to be the primary lesion causing hip and leg pain. Typically, double or triple crush syndromes beginning in the low back and SI joint also contribute to neuronal breakdown of the sciatic nerve. As the surrounding capillary beds and dural membrane become tethered, noxious nociceptive messages flood the brain leading to protective muscle guarding which further closes off space in the sciatic notch.
The primary symptom of piriformis syndrome is buttock pain, with or without pain in the hamstring region that is exacerbated by sitting or overuse. In an isolated piriformis syndrome, the prominent findings include buttock region tenderness from the sacrum to the greater trochanter and reproduction of buttocks pain on the prolonged hip flexion, abduction, and internal rotation. Minor findings include leg length discrepancy, weak adductors, and painful hip abduction while sitting.
The Role of the Stirrup Spring System
Consider this counterintuitive structural explanation for piriformis pain and pelvic obliquity. July’s e-newsletter described the antigravity function of what I reference as the Stirrup Spring System (SSS).
Notice in figure 2 how the biceps femoris muscle fires just prior to heel strike and pulls on the tibialis/peroneal stirrup to elevate the arch. During heel strike, force is transmitted back up through the lateral thigh and sacrotuberous ligament. With the help of the piriformis and other hip rotators, they right rotate the pelvis causing reciprocal left rotation of the lumbar spine.
If the bones, muscles and fascia of the foot, ankle, and knee are aligned and functioning properly, kinetic energy is transmitted unimpeded though the pelvis and all is well. However, any kink along the kinetic chain such as a flat foot, displaced fibula or fixated hip capsule will diminish the pull on the sacrum.
This loss of energy from below causes the hip’s external rotators to overwork in an effort to rotate the pelvis. Soon, myospasm and contractures develop in all sciatic notch musculature setting the stage for nerve trunk impingement.
Obviously, athletes are more likely to develop sciatic symptoms due to increased activity levels. However, prolonged loss of function in the leg and foot can put anyone at risk of developing this common syndrome. Working where it hurts won’t solve the problem. Therapists must find and fix all ‘kinetic chain kinks’…not only in the lumbar spine and pelvis but in all lower quadrant structures.