superior gluteal nerve
The superior gluteal nerve is formed from posterior divisions of L4, L5 and S1 nerve roots of the sacral plexus. The nerve supplies branches to the gluteus minimus and medius muscles and terminates by innervating the tensor fasciae latae muscle.
The superior gluteal nerve arises from the posterior divisions of the sacral plexus along with the sciatic nerve, inferior gluteal nerve, and coccygeal plexus. It is formed from the L4-S1 nerve roots and shortly after forming exits the pelvis through the greater sciatic foramen.
Of all the nerves that exit through the greater sciatic foramen, the superior gluteal nerve is the only nerve to pass above the piriformis muscle.
After exiting the pelvis the superior gluteal nerve enters the gluteal region and spirals up over the inferior border of the gluteus minimus muscle. The nerve then travels anteriorly and laterally in a plane between the gluteus medius and gluteus minimus muscles.
The superior gluteal nerve ramifies between the gluteal minimus and maximus muscles and distributes branches to both of these muscles. The superior gluteal nerve terminates by piercing and innervating the tensor fasciae latae muscle.
The superior gluteal nerve is the only nerve which departs the pelvis through the greater sciatic foramen above the piriformis muscle. It is accompanied by the superior gluteal artery and vein. The other nerves that exit the though the greater sciatic foramen, including the pudendal nerve, inferior gluteal nerve and sciatic nerve, exit below the piriformis muscle.
Variations of the superior gluteal nerve have been noted in cadaveric studies, particularly in the more inferior branch of the superior gluteal nerve. The most common variation was distribution of the nerve around the greater trochanter and a variable location of the superior gluteal nerve piercing the tensor fasciae latae muscle. Case studies have also shown isolated cases of entrapment of the superior gluteal nerve between an aberrant piriformis muscle with two muscle bellies.
Injury to the superior gluteal nerve results in characteristic motor loss that manifests as a disabling gluteus medius limp more commonly known as a Trendelenburg or gluteal gait. Weakness of the gluteus medius muscle shifts the center of gravity to the non-affected limb producing the gait. The Trendelenburg’s sign is able to determine a unilateral impaired gluteus medius muscle. Bilateral lesions to the superior gluteal nerve may result in a waddling gait.
Superior gluteal nerve entrapment can also occur as a result of compression by the anterosuperior tendinous fibers of the piriformis muscle and may result in claudication type back pain, weakness of abduction of the affected hip and tenderness of the greater sciatic notch.