Name a primary external rotator of the hip and its nerve.

Name a primary external rotator of the hip and its nerve.

• A. Piriformis; sacral plexus (L5-S2)
• B. Gluteus medius; superior gluteal nerve
• C. Tensor fasciae latae; superior gluteal nerve
• D. Obturator externus; obturator nerve

Answer: (A)

External rotation of the hip is produced by several deep lateral rotator muscles, with the piriformis being a classic example. The piriformis runs from the anterior surface of the sacrum to the superior border of the greater trochanter, and its action is to rotate the thigh laterally when the hip is extended (it can also abduct the thigh when the hip is flexed). Its nerve supply comes from the sacral plexus via the nerve to the piriformis, typically carrying fibers from L5–S2. This combination—a primary external rotator with innervation from the sacral plexus—fits the description. Gluteus medius and tensor fasciae latae are mainly abductors and medial rotators, innervated by the superior gluteal nerve, not the primary external rotator. Obturator externus is an external rotator innervated by the obturator nerve, but it’s not the classic example cited for a primary external rotator with sacral-plexus innervation.

External rotation of the hip is produced by several deep lateral rotator muscles, with the piriformis being a classic example. The piriformis runs from the anterior surface of the sacrum to the superior border of the greater trochanter, and its action is to rotate the thigh laterally when the hip is extended (it can also abduct the thigh when the hip is flexed). Its nerve supply comes from the sacral plexus via the nerve to the piriformis, typically carrying fibers from L5–S2. This combination—a primary external rotator with innervation from the sacral plexus—fits the description. Gluteus medius and tensor fasciae latae are mainly abductors and medial rotators, innervated by the superior gluteal nerve, not the primary external rotator. Obturator externus is an external rotator innervated by the obturator nerve, but it’s not the classic example cited for a primary external rotator with sacral-plexus innervation.