Hip Muscles Anatomy: Flexors, Extensors, Abductors, Adductors and Clinical Tests

The muscles acting at the hip sort cleanly into five functional groups. FLEXORS: the iliopsoas (iliacus + psoas major) is the prime mover, aided by rectus femoris, sartorius, tensor fasciae latae, and pectineus. EXTENSORS: gluteus maximus (the powerful extensor for stairs and rising) and the hamstrings (biceps femoris, semitendinosus, semimembranosus). ABDUCTORS: gluteus medius and minimus, plus tensor fasciae latae — critically important for stabilizing the pelvis during single-leg stance. ADDUCTORS: adductor longus, brevis, and magnus, plus gracilis and pectineus. LATERAL ROTATORS: piriformis, obturator internus and externus, the gemelli, and quadratus femoris (mnemonic "Piece Goods Often Go On Quilts"). The single most clinically tested relationship is that the hip ABDUCTORS (gluteus medius/minimus), supplied by the SUPERIOR GLUTEAL NERVE, stabilize the pelvis — their failure produces the Trendelenburg sign.

The ILIOPSOAS is the most powerful hip flexor — psoas major arises from the lumbar vertebrae, iliacus from the iliac fossa, and they insert together on the lesser trochanter of the femur. It is innervated by the femoral nerve (and direct branches of L1-L3). The rectus femoris (femoral nerve) crosses both hip and knee, flexing the hip and extending the knee. On the extensor side, GLUTEUS MAXIMUS is the largest muscle of the body, supplied by the INFERIOR GLUTEAL NERVE (L5-S2); it is the key extensor for power activities like climbing stairs and rising from a chair, though it is relatively quiet during level walking. The HAMSTRINGS (sciatic nerve, tibial division) extend the hip and flex the knee. A clinical pearl: weakness rising from a seated position points toward gluteus maximus (inferior gluteal nerve), whereas difficulty with level-ground pelvic stability points toward the abductors.

The ABDUCTORS — gluteus medius and gluteus minimus, with the tensor fasciae latae — are supplied by the SUPERIOR GLUTEAL NERVE (L4-S1). During single-leg stance (every step of walking), they contract on the STANCE side to keep the pelvis level over the planted leg. The ADDUCTORS — adductor longus, brevis, and magnus, plus gracilis and pectineus — are supplied mainly by the OBTURATOR NERVE (L2-L4), with the adductor magnus having a dual supply (obturator plus the tibial division of the sciatic for its hamstring part) and pectineus often by the femoral nerve. The clinically vital fact is the superior gluteal nerve's control of the abductors: damage it (or the muscles), and the pelvis can no longer be stabilized in stance, producing the Trendelenburg sign.

Here is the high-yield clinical test. When you stand on one leg, the gluteus medius/minimus of the STANCE leg contract to hold the pelvis level. If those muscles (or the superior gluteal nerve supplying them) are weak, the pelvis DROPS on the opposite (unsupported, swing) side — a POSITIVE TRENDELENBURG SIGN. The drop is contralateral to the lesion, because the problem is the inability of the stance-side abductors to hold up the other side. To compensate while walking, the patient leans the trunk TOWARD the affected (stance) side to shift the center of gravity over the hip — producing the lurching TRENDELENBURG GAIT (a "gluteus medius gait"). With bilateral weakness, the result is a waddling gait. Remember the rule: the pelvis sags on the side OPPOSITE the weak gluteus medius, and the patient lurches TOWARD the weak side.

The superior gluteal nerve is vulnerable to poorly placed intramuscular gluteal injections — which is exactly why IM injections are given in the UPPER OUTER QUADRANT of the buttock (or the ventrogluteal site), avoiding the nerve and the sciatic nerve below. Hip osteoarthritis, total hip arthroplasty, and gluteus medius tendon tears can also cause abductor weakness and a Trendelenburg gait without nerve injury. Piriformis syndrome compresses the sciatic nerve as it passes near (or through) the piriformis, causing buttock pain and sciatica-like symptoms. Pairing the muscle group, its nerve, and the resulting gait abnormality is the framework that solves these vignettes.

Snap a photo of a clinical vignette or anatomy diagram and AnatomyIQ groups the hip muscles by action, names the nerve supplying each group, and walks through the gait interpretation — including which side the pelvis drops and which way the patient leans in a Trendelenburg gait. Practice cases come in three difficulty levels with labeled diagrams. This content is for educational purposes only and does not constitute medical advice.