A 79-year-old woman with a hip fracture presents with a shortened left lower extremity. Which muscle is primarily responsible for lateral rotation of the thigh?

• A. Pectineus
• B. Gluteus minimus
• C. Rectus femoris
• D. Piriformis

Answer: (D)

The piriformis muscle is primarily responsible for the lateral rotation of the thigh. This deep muscle, located in the posterior pelvic region, originates from the sacrum and inserts into the greater trochanter of the femur. When the thigh is in an extended position, the piriformis plays a significant role in laterally rotating the hip joint. Additionally, when the thigh is flexed, it can assist in abduction.

Understanding the specific actions of the muscles around the hip is critical, especially in older patients who may present with conditions such as hip fractures. The other muscles listed have different primary functions. For instance, the pectineus is mainly involved in hip flexion and adduction, while the gluteus minimus primarily acts as a hip abductor and medial rotator. The rectus femoris, part of the quadriceps group, is mainly involved in knee extension and also contributes to hip flexion but does not play a significant role in lateral rotation. Hence, the piriformis stands out as the muscle predominantly responsible for lateral rotation of the thigh.