Gluteal region and hip joint
Gluteal region and hip joint anatomy: sciatic foramina, Trendelenburg, injections
Gluteal region and hip joint for FCPS Part 1: sciatic foramina, gluteal muscles, Trendelenburg sign and the safe injection site. Also covers hip ligaments, femoral head blood supply and dislocation positions, each tied to a gait, fracture or misplaced needle.
Greater and lesser sciatic foramina
The sacrospinous and sacrotuberous ligaments convert the greater and lesser sciatic notches into foramina. Piriformis passes out through the greater sciatic foramen and is the key landmark of the buttock.
| Route | Structures |
|---|---|
| Greater foramen, above piriformis | Superior gluteal nerve, artery and vein (only these) |
| Greater foramen, below piriformis | Sciatic nerve, inferior gluteal nerve and vessels, posterior cutaneous nerve of thigh, nerve to quadratus femoris, pudendal nerve, internal pudendal vessels, nerve to obturator internus |
| Out of the greater, back in through the lesser foramen | Pudendal nerve, internal pudendal vessels, nerve to obturator internus (they hook round the ischial spine and sacrospinous ligament into the perineum) |
| Lesser foramen, outwards | Tendon of obturator internus |
- Spasm or hypertrophy of piriformis can compress the sciatic nerve (piriformis syndrome): buttock pain radiating down the back of the thigh, worse on sitting.
- Buttock claudication on walking points to atheroma of the internal iliac artery, the source of the gluteal arteries.
Gluteal muscles
| Muscle | Action | Nerve |
|---|---|---|
| Gluteus maximus | Extends and laterally rotates the hip; powerful in rising from sitting, climbing stairs and running | Inferior gluteal (L5–S2) |
| Gluteus medius and minimus | Abduct and medially rotate the hip; in walking they hold the pelvis level when the opposite foot is off the ground | Superior gluteal (L4–S1) |
| Tensor fasciae latae | Abducts, medially rotates; tightens the iliotibial tract | Superior gluteal |
| Piriformis, gemelli, obturator internus, quadratus femoris | Lateral rotation; hold the head in the acetabulum | Small nerves from the sacral plexus |
- Trendelenburg sign: stand on the affected leg; the pelvis drops on the opposite (unsupported) side because the hip abductors on the standing side cannot hold it. Causes: superior gluteal nerve injury (for example a knife wound or hip surgery), weak gluteus medius and minimus, a dislocated hip, or a short femoral neck (coxa vara, old neck fracture) that shortens the abductor lever.
- Trendelenburg (waddling) gait: the trunk lurches over the weak side at each step; if both sides are affected the gait waddles.
- Gluteus maximus gait: the trunk is thrown backwards at heel strike to keep the hip extended.
Safe intramuscular injection
- Divide the buttock into quadrants by a vertical line through the iliac crest's highest point and a horizontal line through the greater trochanter. Inject into the upper outer quadrant, into gluteus medius, or at the ventrogluteal site between the ASIS and the iliac tubercle.
- The sciatic nerve curves through the lower medial part of the buttock, midway between the greater trochanter and the ischial tuberosity. Injections given too low and medially cause sciatic palsy, usually seen as foot drop because the peroneal fascicles suffer most.
Hip joint
- A ball-and-socket synovial joint, very stable because of the deep acetabulum, the fibrocartilaginous acetabular labrum and strong capsular ligaments.
| Ligament | Attachment | Role |
|---|---|---|
| Iliofemoral (Y-shaped, of Bigelow) | AIIS to intertrochanteric line | Strongest ligament; prevents hyperextension; taut when standing, relaxed when sitting; lets us stand with little muscle work |
| Pubofemoral | Superior pubic ramus to capsule | Limits abduction and extension |
| Ischiofemoral | Ischium to capsule | Limits medial rotation and extension |
| Ligamentum teres (of the head) | Acetabular notch to fovea | Carries a small artery; little mechanical role |
- Close-packed position: extension, slight abduction and medial rotation (all ligaments tight).
- Flexion is limited by contact of the thigh with the anterior abdominal wall when the knee is bent, and by tension in the hamstrings when the knee is straight. Extension is limited by the iliofemoral ligament.
- Relations: iliopsoas and its bursa in front; obturator externus directly below; the short lateral rotators and sciatic nerve behind; gluteus minimus above.
- Capsule volume is greatest with the hip flexed, abducted and externally rotated. A child with a septic or inflammatory effusion holds the hip this way to reduce capsular pressure and pain. Septic arthritis is an emergency because the pressure can block flow in the retinacular vessels and cause avascular necrosis.
- Nerve supply (Hilton's law): femoral, obturator, sciatic (nerve to quadratus femoris) and superior gluteal branches. Because the obturator and femoral nerves also supply the knee, hip disease in children (Perthes disease, slipped upper femoral epiphysis) often presents as knee pain.
Blood supply of the femoral head
| Source | Importance |
|---|---|
| Retinacular arteries, mainly from the medial circumflex femoral artery (via the trochanteric anastomosis), running up the neck under the synovial reflection | Main supply in adults |
| Lateral circumflex femoral | Minor, mainly to the anterior neck |
| Artery of the ligamentum teres (from the obturator artery) | Important in children; small in adults; still reaches the head if the circumflex and cruciate vessels are ligated |
| Nutrient artery of the shaft | Little contribution to the head |
- Intracapsular (subcapital, transcervical) neck fracture tears the retinacular vessels, causing avascular necrosis and non-union; displaced fractures in the elderly are treated by hemiarthroplasty or total hip replacement.
- Extracapsular (intertrochanteric) fractures leave the head supply intact and heal well with a dynamic hip screw.
- Elderly women with neck of femur fractures usually have postmenopausal osteoporosis; calcium and vitamin D (with bone-protective drugs) reduce further fractures.
Positions after injury
| Injury | Leg position | Why |
|---|---|---|
| Posterior dislocation (dashboard injury) | Shortened, flexed, adducted, medially rotated | Head forced back over the posterior acetabular rim; sciatic nerve at risk |
| Anterior dislocation | Abducted, laterally rotated, slightly flexed | Head lies over the obturator foramen or pubis |
| Neck of femur fracture | Shortened and laterally rotated | Shortening by muscles crossing the fracture (gluteals, hamstrings, adductors, rectus femoris); lateral rotation by iliopsoas acting on the lesser trochanter, with the short lateral rotators |
Remember Posterior dislocation: flexed, adducted, internally rotated; fractured neck: shortened and externally rotated.
Two-joint muscles of hip and knee
| Muscle | Hip | Knee |
|---|---|---|
| Rectus femoris | Flexes | Extends (so injury stops you flexing the hip and extending the knee together, as in a kick or high jump) |
| Sartorius | Flexes, abducts, laterally rotates | Flexes (the muscle that flexes both hip and knee) |
| Hamstrings (semitendinosus, semimembranosus, long head of biceps) | Extend | Flex |
| Gracilis | Adducts | Flexes |
Exam trap Only the superior gluteal nerve and vessels pass above piriformis.
Exam trap In a Trendelenburg sign the pelvis drops on the side opposite the weak abductors.
How FCPS asks about this
- Structures above versus below piriformis: superior gluteal nerve and vessels above; sciatic, inferior gluteal and pudendal below.
- Waddling gait, pelvis sagging after a buttock wound: superior gluteal nerve; gluteus medius and minimus.
- Safe injection site: upper outer quadrant, to avoid the sciatic nerve.
- Ligament taut on standing, relaxed on sitting, prevents hyperextension: iliofemoral (Y) ligament.
- Septic hip held flexed, abducted, externally rotated: capsule has its largest volume in that position.
- Shortened, externally rotated leg after a fall: neck of femur fracture; intracapsular fractures risk avascular necrosis via torn retinacular vessels.
- Foot drop after posterior hip dislocation: peroneal part of the sciatic nerve is the most vulnerable.
Test yourself on this topic
5 of the 28 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
After a car crash in which his knee struck the dashboard, a 28-year-old man has severe hip pain. His leg is shortened, flexed, adducted and internally rotated. Which of the following is the most likely injury?
Answer: Posterior dislocation of the hip
In a dashboard injury, force is transmitted along the femur with the hip flexed and adducted, driving the femoral head out of the back of the acetabulum. The posteriorly displaced head leaves the leg shortened, flexed, adducted and internally rotated. Anterior dislocation gives an abducted, externally rotated limb, and femoral neck fractures give shortening with external rotation.
Posterior hip dislocation
- Dashboard injury
- Shortened, flexed, adducted, internally rotated
- Check the sciatic nerve
Remember Posterior dislocation: the leg turns in; fracture: it turns out.
Exam trap Reduce within 6 hours to reduce the risk of avascular necrosis.
Why the other options are wrong
- Anterior dislocation of the hip Leg lies abducted and externally rotated.
- Intracapsular fracture of the femoral neck Leg is shortened and externally rotated.
- Intertrochanteric fracture Leg is shortened and markedly externally rotated.
- Central fracture-dislocation of the acetabulum Leg position is often near normal.
After reduction of a posterior hip dislocation, a 30-year-old man has foot drop and numbness over the dorsum of the foot, but calf power and sole sensation are nearly normal. Why is the peroneal component mainly affected?
Answer: Peroneal fascicles are more vulnerable
In the sciatic nerve, the common peroneal division lies laterally, has fewer and larger fascicles with less protective connective tissue, and is tethered at the sciatic notch and at the neck of the fibula. It is therefore stretched and damaged more easily than the tibial division. Most sciatic injuries from hip dislocation or hip surgery thus present mainly as foot drop with numbness of the dorsum of the foot.
Peroneal division vulnerability
- Lies laterally in the sciatic
- Fewer, larger fascicles
- Tethered at notch and fibular neck
- Injury looks like foot drop
Remember Sciatic injury at the hip often looks like a peroneal palsy.
Exam trap Check and record foot dorsiflexion before reducing a dislocated hip.
Why the other options are wrong
- The tibial nerve leaves the sciatic in the pelvis Both divisions leave the pelvis together in one sheath.
- Peroneal fibres run separately through piriformis The peroneal division sometimes pierces piriformis, but this is not the reason.
- The tibial fibres lie lateral in the nerve The tibial division lies medially.
- Only the peroneal fibres cross the hip joint Both divisions are equally close to the joint.
A nurse gives a ventrogluteal intramuscular injection by placing her palm on the greater trochanter, index finger on the ASIS and middle finger along the iliac crest, injecting into the V between the fingers. Into which of the following muscles is the drug deposited?
Answer: Gluteus medius
The ventrogluteal site lies in the triangle formed by the anterior superior iliac spine, the iliac tubercle on the crest and the greater trochanter. Here the needle enters gluteus medius (with gluteus minimus deep to it), which is thick and lies well away from the sciatic nerve and the main gluteal vessels. It is therefore preferred to the dorsogluteal site, where a misplaced needle can injure the sciatic or superior gluteal nerve.
Ventrogluteal site
- Palm on greater trochanter
- Fingers on ASIS and iliac crest
- Drug into gluteus medius
- Far from the sciatic nerve
Remember Ventrogluteal is safest: gluteus medius, no big nerves.
Exam trap In the dorsogluteal site, inject in the upper outer quadrant only.
Why the other options are wrong
- Gluteus maximus Used in the dorsogluteal upper outer quadrant, closer to the sciatic nerve.
- Piriformis Lies deep, near the sciatic nerve.
- Tensor fasciae latae Lies more anteriorly and laterally on the thigh.
- Quadratus femoris Lies low, near the sciatic nerve.
In a child, which small artery, running in the ligament of the head of the femur, gives a minor blood supply to the femoral head?
Answer: Branch of the obturator artery
The femoral head is supplied mainly by retinacular branches of the medial circumflex femoral artery (and lateral), running up the neck under the capsule. A small artery to the head runs in the ligamentum teres, usually from the acetabular branch of the obturator artery; it matters in children but supplies little in adults. Displaced intracapsular neck fractures tear the retinacular vessels, risking avascular necrosis.
Femoral head supply
- Main: medial circumflex femoral (retinacular)
- Also: lateral circumflex
- Minor: artery of ligamentum teres (obturator)
- Neck fracture: avascular necrosis
Remember The ligament's artery is small; the circumflex does the work.
Exam trap In adults the ligamentum teres artery cannot keep the head alive after neck fracture.
Why the other options are wrong
- Superior gluteal artery Supplies the gluteal muscles.
- Inferior epigastric artery Supplies the anterior abdominal wall.
- Profunda femoris directly Gives the circumflex arteries; not directly.
- Popliteal artery Supplies the knee.
A paraplegic man stands in calipers by leaning back so his hips hang on their ligaments. Which ligament stops further hip extension?
Answer: Iliofemoral ligament
The iliofemoral (Y-shaped) ligament runs from the anterior inferior iliac spine to the intertrochanteric line in front of the hip. It is the strongest ligament in the body and becomes taut in extension, preventing hyperextension. This lets a person stand with the trunk balanced behind the hips with little muscle effort, as paraplegic patients in calipers do. The pubofemoral and ischiofemoral ligaments mainly limit abduction and internal rotation.
Iliofemoral ligament
- Y-shaped, in front of the hip
- Strongest ligament
- Taut in extension
- Lets us stand with little effort
Remember The Y ligament stops hip hyperextension.
Exam trap All three capsular ligaments tighten in extension, which is the close-packed position.
Why the other options are wrong
- Pubofemoral ligament Mainly limits abduction.
- Ischiofemoral ligament Mainly limits internal rotation and adduction in flexion.
- Ligament of the head of the femur Carries a small artery; adds little to stability.
- Transverse acetabular ligament Bridges the acetabular notch; does not limit extension.
Where this sits in the CPSP syllabus
- Paper 1: Lower limb, Gluteal region and hip joint; safe injection site
- Surgery & Allied, Paper 2: Lower limb, Gluteal region and hip joint; safe injection site