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Human Anatomy · Lower limb

Gluteal Region, Hip and Thigh

The hip is the opposite bargain to the shoulder. A deep socket, a strong capsule and heavy ligaments make it stable enough to carry you for a lifetime. What it asks in return is a set of muscles strong enough to hold the pelvis level every time you take a step.

8Sections
3Diagrams
1Illustrations
7Tables
10Questions

What you will be able to do

  • Compare the hip with the shoulder and explain the opposite design compromises.
  • Name the hip ligaments and say which movement each checks.
  • Explain why the hip is most vulnerable to dislocation in flexion.
  • Name the gluteal muscles with their actions and nerve supply.
  • Explain the abductor mechanism and interpret a Trendelenburg sign correctly.
  • Describe the relationship of the sciatic nerve to piriformis, and its clinical importance.
  • Name the three thigh compartments with their muscles, nerve and action.
  • Name the boundaries and contents of the femoral triangle in order.
  • Reason through the common hip problems from the anatomy that produces them.

The hip joint

A ball and socket joint between the head of the femur and the acetabulum. Compare it with the shoulder and the design decision is obvious.

ShoulderHip
SocketShallow, holding about a third of the head Deep, enclosing more than half of it
CapsuleLax, contributing little Thick and strong, reinforced by three named ligaments
Stability fromMuscle, continuously Bone and ligament, passively
CommonlyDislocates Fractures. Dislocation needs major force.
LigamentRunsChecks
Iliofemoral
the Y-shaped ligament of Bigelow		 From the ilium above the acetabulum to the intertrochanteric line Extension. The strongest ligament in the body. It is what lets you stand with the hip muscles almost silent.
PubofemoralFrom the pubic part of the rim Abduction and extension
IschiofemoralFrom behind, spiralling upwards Medial rotation and extension
Ligament of the head From the acetabular fossa to the pit on the head Little mechanically, but it carries a small artery to the head — which matters most in children.

All three ligaments tighten in extension

This is why standing costs so little muscular effort: the ligaments do the work. It is also why the hip is most vulnerable in flexion, when they are slack. A dashboard injury drives a flexed hip backwards and dislocates it posteriorly, and that position is why the sciatic nerve is so often involved.

The gluteal region

Figure 1 · The gluteal region and the sciatic nerve

Illustration to be added

A posterior dissection of the right gluteal region with the skin and fat removed. Show gluteus maximus reflected laterally to reveal the deeper layer: gluteus medius above, piriformis emerging from the greater sciatic foramen, then superior gemellus, obturator internus, inferior gemellus and quadratus femoris in order from above downwards. Show the sciatic nerve emerging below piriformis and descending into the posterior thigh, with the superior gluteal nerve and vessels above piriformis and the inferior gluteal nerve below it. Mark the greater trochanter and ischial tuberosity. Add a small inset showing the buttock divided into four quadrants with the upper outer quadrant shaded as the safe injection site and the sciatic nerve's course drawn beneath. Muscle in brick, bone warm ivory, nerves gold, arteries red.

MuscleDoesNerve
Gluteus maximus Powerful hip extension and lateral rotation. Used for stairs, rising and running rather than level walking. Inferior gluteal
Gluteus medius and minimus Abduct the hip, and hold the pelvis level in single leg stance. Their anterior fibres rotate medially. Superior gluteal
Tensor fasciae latae Assists abduction; tightens the iliotibial bandSuperior gluteal
Piriformis and the deep group
obturator internus, the gemelli, quadratus femoris		 Lateral rotation, and steadying the head of the femur in the socket Branches from the sacral plexus

The abductor mechanism

Figure 2 · The abductor mechanism in single leg stance

The hip abductor mechanism in single leg stance Two figures in single leg stance, one with working abductors holding the pelvis level and one with weak abductors letting the opposite side drop. WHY A WEAK HIP SHOWS UP IN THE OTHER SIDE OF THE PELVIS Normal The abductors on the standing side pull down on the pelvis, holding the opposite side level. Weak abductors They cannot hold it. The opposite side of the pelvis drops as soon as the other foot leaves the ground. The sign appears on the side OPPOSITE the weakness, which is why it is so often read the wrong way round.
The sign appears on the side opposite the weakness. The abductors of the standing leg are what hold the other side of the pelvis up.

Every step you take is a moment of single leg stance, and in that moment the whole weight of the body tries to tip the pelvis down on the unsupported side. What prevents it is gluteus medius and minimus on the standing side, pulling the pelvis down towards their own femur.

The consequence catches students out every year: when these muscles are weak, the pelvis drops on the opposite side. A positive Trendelenburg sign on the left means the right abductors have failed. Watch the pelvis, not the leg the patient is standing on.

Why the abductors have to be so strong

The abductors attach close to the hip and body weight acts far from it, through the centre of the body. It is a third class lever again, so the muscle must produce a force several times body weight simply to hold you level. That is why abductor weakness shows up so quickly, and why hip pain of any cause tends to produce a limp that shifts weight over the painful side.

The sciatic nerve and piriformis

The sciatic nerve is the thickest nerve in the body. It leaves the pelvis through the greater sciatic foramen and, in most people, passes below piriformis. In a minority it passes through or above the muscle, and those variations are one proposed explanation for buttock pain with a normal spine.

Its position matters practically. It lies deep in the buttock, and an injection placed carelessly can reach it — which is why intramuscular injections are given in the upper outer quadrant of the buttock, well away from its course.

The thigh

Figure 3 · Compartments of the thigh

Compartments of the thigh Compartments with their muscles, nerve supply and shared action. COMPARTMENTS OF THE THIGH Anterior extends the knee, flexes the hip Quadriceps femoris, in four parts Sartorius Iliopsoas, entering from above NERVE Femoral Medial adducts the hip Adductor longus, brevis and magnus Gracilis Pectineus NERVE Obturator Posterior extends the hip, flexes the knee Biceps femoris Semitendinosus Semimembranosus NERVE Sciatic, tibial part Three compartments, three nerves, three actions. Learn the pattern and the muscles follow.
The same pattern as the arm. One compartment, one nerve, one action — which turns a long muscle list into three ideas.

Three compartments, and the pattern that ran through the arm and forearm holds again: each compartment has one nerve and one broad action.

DetailWorth knowing
Rectus femoris The only part of quadriceps crossing the hip as well as the knee. Its length therefore depends on hip position, which is why knee extension is weaker with the hip extended.
Sartorius The longest muscle in the body. Flexes, abducts and laterally rotates the hip and flexes the knee — the tailor's cross-legged position.
Iliopsoas The most powerful hip flexor. Crosses the lumbar spine as well, so it links trunk and limb directly.
Adductor magnus Has two parts with two nerves: an adductor part (obturator) and a hamstring part (sciatic). It behaves like both muscles.
Hamstrings All cross both hip and knee except the short head of biceps femoris. This is why they are so often strained, and why hip position changes knee flexion strength.

The femoral triangle

Figure 4 · The femoral triangle

The femoral triangle The contents of the femoral triangle from lateral to medial, with its boundaries. FEMORAL TRIANGLE CONTENTS, LATERAL TO MEDIAL N Nerve femoral nerve A Artery femoral artery V Vein femoral vein L Lymphatics and the femoral canal Remember it as N A V Y, running lateral to medial. BOUNDARIES Above the inguinal ligament Laterally sartorius Medially adductor longus Floor iliopsoas and pectineus Roof fascia lata
Nerve, artery, vein, lymphatics — lateral to medial. The nerve lies outside the sheath holding the vessels, which is why a nerve block and a vascular puncture aim at different points.

A hollow at the top of the thigh, and the route through which everything reaches the lower limb. The femoral pulse is felt here, at the midpoint of the inguinal ligament, and it is where a femoral line is placed.

Note that the nerve lies outside the sheath that contains the artery and vein. That is why a femoral nerve block and a femoral vascular puncture are aimed at slightly different places.

Distally the vessels leave the triangle and run in the adductor canal, a tunnel between the anterior and medial compartments, before passing behind the knee to become the popliteal vessels.

What goes wrong here

ProblemAnatomy behind itWhat you find
Hip osteoarthritis Loss of articular cartilage in a joint that carries several times body weight Groin pain, often referred to the knee by Hilton's law. Medial rotation is usually lost first.
Femoral neck fracture The retinacular vessels run along the neck to supply the head Shortened, laterally rotated limb. Displaced fractures risk the head's blood supply.
Trendelenburg gait Weak or inhibited gluteus medius and minimus Pelvis drops on the swing side, or the trunk lurches over the stance side to compensate.
Greater trochanteric pain Gluteal tendons and a bursa where they cross the trochanter Tenderness over the trochanter, pain lying on that side, pain on single leg stance.
Hamstring strain Two-joint muscles working eccentrically at long length during swing Sudden posterior thigh pain while sprinting. Bruising tracks distally over days.
Posterior dislocation Ligaments are slack in flexion; force drives the head backwards Limb short, flexed, adducted and medially rotated. Check the sciatic nerve.

Where students get this wrong

Reading Trendelenburg on the wrong side

The pelvis drops opposite the weak muscle. Name the side of the weakness, not the side of the drop.

Thinking gluteus maximus is the main walking muscle

It is relatively quiet in level walking. It comes into its own on stairs, in rising from a chair and in running.

Forgetting the hip is vulnerable in flexion

All three capsular ligaments tighten in extension and slacken in flexion. That is when dislocation happens.

Testing quadriceps without noting hip position

Rectus femoris crosses both joints. Knee extension strength changes with the hip, and a test that ignores this is not repeatable.

Assuming groin pain is a groin problem

Hip pathology refers to the groin and often to the knee. A child limping with knee pain needs the hip examined.

Injecting into the wrong part of the buttock

Upper outer quadrant only. The sciatic nerve runs deep through the lower and medial parts.

Check yourself

Ten questions on this chapter. Tap one to see the answer and the reasoning.

Q1. The strongest ligament in the body, checking hip extension, is the:
  1. (A) Pubofemoral
  2. (B) Ischiofemoral
  3. (C) Iliofemoral
  4. (D) Ligament of the head of the femur

Answer: (C) The iliofemoral, or Y-shaped ligament of Bigelow. Its strength is why standing upright costs so little muscular effort.

Q2. The hip is most vulnerable to dislocation when it is:
  1. (A) Extended and laterally rotated
  2. (B) Flexed
  3. (C) Abducted
  4. (D) In the anatomical position

Answer: (B) All three capsular ligaments tighten in extension and slacken in flexion, which is why a dashboard injury to a flexed hip dislocates it posteriorly.

Q3. A patient's pelvis drops on the left when standing on the right leg. This indicates:
  1. (A) Weak left hip abductors
  2. (B) Weak right hip abductors
  3. (C) Weak right hip adductors
  4. (D) Weak left quadriceps

Answer: (B) The abductors of the standing leg hold the opposite side of the pelvis up. A drop on the left means the right abductors have failed.

Q4. Gluteus medius and minimus are supplied by the:
  1. (A) Inferior gluteal nerve
  2. (B) Superior gluteal nerve
  3. (C) Obturator nerve
  4. (D) Femoral nerve

Answer: (B) The superior gluteal nerve. Gluteus maximus is supplied by the inferior gluteal nerve.

Q5. In most people, the sciatic nerve leaves the pelvis:
  1. (A) Above piriformis
  2. (B) Through piriformis
  3. (C) Below piriformis
  4. (D) Through the lesser sciatic foramen

Answer: (C) Below piriformis, in the majority. Variations passing through or above the muscle exist and are one proposed cause of buttock pain with a normal spine.

Q6. The muscles of the medial compartment of the thigh are supplied by the:
  1. (A) Femoral nerve
  2. (B) Sciatic nerve
  3. (C) Obturator nerve
  4. (D) Superior gluteal nerve

Answer: (C) The obturator nerve. Anterior compartment is femoral, posterior is the tibial part of the sciatic.

Q7. The contents of the femoral triangle, from lateral to medial, are:
  1. (A) Vein, artery, nerve
  2. (B) Nerve, artery, vein, lymphatics
  3. (C) Artery, vein, nerve
  4. (D) Nerve, vein, artery

Answer: (B) Nerve, artery, vein, lymphatics - remembered as NAVY. Note the nerve lies outside the femoral sheath containing the vessels.

Q8. Knee extension strength changes with hip position because:
  1. (A) The knee capsule tightens in hip flexion
  2. (B) Rectus femoris crosses both the hip and the knee
  3. (C) The patella moves with hip position
  4. (D) Vastus medialis is a two-joint muscle

Answer: (B) Rectus femoris is the only part of quadriceps crossing the hip. Its length, and therefore its force, depends on hip position.

Q9. Intramuscular injections are given in the upper outer quadrant of the buttock to avoid the:
  1. (A) Superior gluteal artery
  2. (B) Femoral nerve
  3. (C) Sciatic nerve
  4. (D) Obturator nerve

Answer: (C) The sciatic nerve runs deep through the lower and medial parts of the buttock. The upper outer quadrant is well clear of its course.

Q10. A child limps and complains of knee pain, but the knee examines normally. You should:
  1. (A) Reassure and review in a month
  2. (B) Examine the hip
  3. (C) Treat as a hamstring strain
  4. (D) Assume it is growing pain

Answer: (B) Hip pathology commonly refers pain to the knee through shared nerve supply. A child with knee pain and a normal knee needs the hip examined.

Quick review

Everything on this page, in one screen

  • The hip is the shoulder's opposite: deep socket, strong capsule, passive stability. It fractures rather than dislocates.
  • Iliofemoral ligament is the strongest in the body and checks extension. All three tighten in extension.
  • The hip dislocates in flexion, when the ligaments are slack. Check the sciatic nerve afterwards.
  • Gluteus maximus = stairs, rising, running. Medius and minimus = holding the pelvis level.
  • Trendelenburg: the pelvis drops opposite the weak side. Name the weakness, not the drop.
  • The abductors work through a third class lever, so they must produce several times body weight.
  • The sciatic nerve usually passes below piriformis. Inject in the upper outer quadrant only.
  • Thigh: anterior femoral, medial obturator, posterior sciatic.
  • Rectus femoris and the hamstrings cross two joints, so hip position changes knee strength.
  • Femoral triangle contents: N A V Y, lateral to medial. The nerve is outside the sheath.
  • Hip pathology refers to the groin and the knee. A child with knee pain needs the hip examined.

Further reading

BookWhat it adds here
B D Human Anatomy, Volume 2: Lower Limb, Abdomen and Pelvis
Chaurasia		Regional detail at examination level.
Anatomy and Human Movement
Palastanga, Field and Soames		 The abductor mechanism and hip mechanics, treated properly.
Clinical Anatomy by Regions
Snell		 The femoral triangle and the clinical consequences of injury here.
Gray's Atlas of Anatomy
Drake, Vogl and Mitchell		 Keep the gluteal and thigh plates open alongside.

Reviewed by the Physiotherapist India Team. · Human Anatomy contents