🍑 Muscular System Lesson

"Max Med Min": gluteal muscles — big, medium, small

Three muscles named literally by their size — and one of them has a specific clinical sign named after its weakness.

Max

Largest

Med

IM inject.

Min

Deepest

📖 Full Breakdown

Three muscles, three sizes, one important clinical sign

The names themselves (Maximus, Medius, Minimus) directly describe their relative size, making this an easy group to remember.

Gluteus Maximus

The largest, most powerful muscle in the body

Extends and externally rotates the hip — essential for climbing stairs and rising from a seated position.

Gluteus Medius

Hip abduction, and a key injection site

Abducts and internally rotates the hip. Notably, it is the PREFERRED intramuscular injection site in adults, due to its size and reduced risk of hitting major nerves compared to other sites.

Gluteus Minimus

The deepest and smallest

Lies deep to gluteus medius and performs a similar action — abduction and internal rotation of the hip.

Trendelenburg sign

A specific clinical test for gluteus medius weakness

When a patient stands on one leg and their pelvis drops on the OPPOSITE (unsupported) side, this indicates weakness in the gluteus medius on the side they're standing on — a classic physical exam finding.

🩺 Clinical / Exam Application

A patient with hip pain is asked to stand on one leg during a physical exam, and their pelvis visibly drops on the side they are NOT standing on. This positive Trendelenburg sign specifically points to weakness in the gluteus medius on the leg they ARE standing on — because gluteus medius's job is to stabilize the pelvis during single-leg stance, its weakness allows the opposite side of the pelvis to sag unsupported. This single observable sign, tied directly to knowing gluteus medius's specific function, can localize a nerve or muscle problem without any imaging.

⚠️ Exam Alert

The Trendelenburg sign is a frequently tested physical exam finding — know specifically that the pelvis drops on the side OPPOSITE to the weak gluteus medius, since this seems counterintuitive to some students at first (the weakness is on the standing leg, not the side that drops).

🚧 Common Trap

Don't assume gluteus medius and gluteus maximus serve the same function just because they're part of the same muscle group. Maximus primarily extends the hip (powering stair climbing); medius primarily abducts the hip (stabilizing the pelvis during walking) — these are functionally distinct roles.

✅ Quick Check

A patient has a positive Trendelenburg sign when standing on their right leg. Which muscle is weak, and on which side?

📝 Exam Prep

Common Exam Questions

❓ What is the Trendelenburg sign and what does it indicate?

✅ The Trendelenburg sign is when the pelvis drops on the unsupported side while standing on one leg — it indicates weakness of the gluteus medius on the side the patient is standing on.

❓ Why is gluteus medius the preferred site for intramuscular injections in adults?

✅ Gluteus medius is large, easily accessible, and located away from major nerves and blood vessels, making it a safer and more reliable IM injection site compared to other muscle groups.