Gluteal Region, Hip and Thigh

Part 3 · The lower limb

The hip as the shoulder’s opposite, the abductor mechanism, and the femoral triangle

The shoulder’s mirror image

Set the hip beside the shoulder and every difference is a consequence of the same design decision.

Both are triaxial ball-and-socket joints. One was optimised for reach, the other for load. Understanding the hip as the shoulder inverted makes both easier to remember.

Learning outcomes

• Describe the hip joint: surfaces, labrum, capsule, ligaments, blood supply and movements.
• Explain hip stability and the significance of the close-packed position.
• Describe the gluteal region: muscles, nerves, vessels and the intramuscular injection site.
• Explain the abductor mechanism and the Trendelenburg sign quantitatively.
• Describe the three compartments of the thigh with attachments, nerve supply and actions.
• Describe the femoral triangle, adductor canal, and their contents and clinical importance.
• Describe the course of the femoral, obturator and sciatic nerves and predict lesion effects.
• Explain hip joint reaction forces and the effect of a walking stick and of body mass.
• Describe hip osteoarthritis, femoroacetabular impingement, gluteal tendinopathy, hamstring injury and groin pain, with their rehabilitation implications.

The hip joint

Articular surfaces

• Head of the femur: two-thirds of a sphere, articular except at the fovea capitis.
• Acetabulum: the horseshoe-shaped lunate surface, deficient inferiorly at the acetabular notch (bridged by the transverse acetabular ligament), with the non-articular acetabular fossa containing the pulvinar and the ligamentum teres.
• Acetabular labrum: fibrocartilaginous rim deepening the socket, increasing coverage to more than half the head, and creating a fluid seal that maintains intra-articular fluid pressurisation. Labral tearing destroys the seal, allowing fluid to extrude under load and accelerating cartilage degeneration — the mechanism linking FAI to early osteoarthritis.

Capsule and ligaments

The capsule runs from the acetabular margin to the intertrochanteric line anteriorly and to the medial two-thirds of the neck posteriorly (so the lateral posterior neck is extracapsular). Its deep circular fibres form the zona orbicularis, which grips the neck like a buttonhole and resists distraction.

Longitudinal retinacular fibres (retinacula of Weitbrecht) run along the neck carrying the retinacular vessels — the femoral head’s dominant blood supply.

All three capsular ligaments spiral in the same direction, tightening in extension and unwinding in flexion. Hence:

• Close-packed position: full extension with internal rotation and abduction — the position of maximum stability, in which the ligaments alone can hold the joint.
• Resting (loose-packed) position: ~30° flexion, 30° abduction, slight external rotation — the position an irritable hip adopts, the position of least intra-articular pressure, and the position for mobilisation. A patient lying with the hip flexed, abducted and externally rotated is telling you the joint is distended.
• Capsular pattern: internal rotation > flexion > abduction (external rotation and extension also restricted; sources differ on the exact order — the reliable finding is that internal rotation is lost first and most).

Movements and range

Functional ranges for activities of daily living are worth knowing when full range is not achievable: approximately 110–120° flexion (for shoe-tying and squatting), 20° abduction and 20° external rotation. This is the basis of the “hip precautions” advice after posterior-approach arthroplasty — avoid flexion beyond 90°, adduction past midline, and internal rotation — though many units have relaxed these as evidence for their necessity has weakened.

Blood and nerve supply

Arteries: the medial circumflex femoral (dominant, via the retinacular vessels), the lateral circumflex femoral, and the artery of the ligamentum teres (from the obturator; negligible in adults). The cruciate anastomosis — from the medial and lateral circumflex femoral, the inferior gluteal and the first perforating artery — provides collateral flow.

Nerves (Hilton’s law in action): femoral (via the nerve to rectus femoris), obturator, superior gluteal, and the nerve to quadratus femoris — L2 to S1. The obturator supply is why hip pathology refers pain to the medial knee, and why any child with knee pain and a limp must have the hip examined.

Dislocation

Posterior dislocation (~90%) — from an axial force through a flexed, adducted, internally rotated hip: the classic dashboard injury. The limb lies flexed, adducted, internally rotated and shortened. The sciatic nerve is injured in ~10–20% (usually the common fibular division). Test and document nerve function before and after reduction; the risk of avascular necrosis rises sharply if reduction is delayed beyond 6–12 hours.

Anterior dislocation (~10%) — the limb lies abducted, externally rotated and extended; the femoral nerve and vessels are at risk.

Congenital / developmental dysplasia (DDH) — see Chapter 8.

The gluteal region

Figure 1 · The gluteal region and the sciatic nerve

Figure 2 · The abductor mechanism in single leg stance

The muscles

The short external rotators from above down: Piriformis, Gemellus superior, Obturator internus, Gemellus inferior, Quadratus femoris, Obturator externus — “Play Golf Or Go On Quaaludes” or simply P-GO-G-Q-O.

Structures leaving the pelvis

The safe injection site

The gluteal region is a standard intramuscular injection site, and the sciatic nerve is the reason precision matters. Inject into the upper outer quadrant of the buttock, dividing the buttock by a vertical and a horizontal line through its centre. Better still, use the ventrogluteal (von Hochstetter) site: palm on the greater trochanter, index finger on the ASIS, middle finger spread toward the iliac crest. Inject into the triangle so formed, which is over gluteus medius and minimus and safely away from the sciatic nerve, superior gluteal vessels and subcutaneous fat.

Injection into the lower medial quadrant risks sciatic nerve injury — a classic, entirely avoidable, and still-occurring cause of foot drop, particularly in children.

The abductor mechanism — the most important biomechanics in the chapter

In single-leg stance (which occupies ~60% of the gait cycle on each side), body weight acts medial to the hip and would drop the unsupported side of the pelvis. The abductors (gluteus medius and minimus, with TFL) must generate a counterbalancing moment.

The geometry is brutally unequal: the body-weight moment arm is roughly 2.5 times longer than the abductor moment arm. To balance, the abductors must generate about 2.5 times body weight of force. Add that to body weight, and the hip joint reaction force in single-leg stance is approximately 2.5–3 × body weight — rising to 4–5 × in stair climbing and 6–8 × in running.

Three clinical conclusions follow directly:

• A walking stick in the CONTRALATERAL hand provides a very long counterbalancing moment arm across the body. A modest downward force through the stick therefore reduces the abductor force required substantially, cutting hip joint reaction force by roughly 20–30%. Held in the same hand as the affected hip, it does almost nothing. Patients are frequently taught this the wrong way round.
• Trendelenburg gait: with abductor weakness, the patient either drops the contralateral pelvis (positive Trendelenburg sign) or, more commonly in practice, lurches the trunk over the affected side (compensated Trendelenburg / gluteus medius lurch) to bring the centre of mass over the hip, shortening the body-weight moment arm.
• Weight loss reduces hip load by a multiple of the mass lost, because the reduction acts through the long moment arm.

Causes of a positive Trendelenburg sign: abductor weakness or inhibition (superior gluteal nerve lesion, L5 radiculopathy, post-arthroplasty via a lateral approach, pain inhibition, gluteal tendinopathy), a shortened femoral neck or coxa vara reducing the abductor moment arm, dislocation, and severe pain.

The thigh: three compartments

Figure 3 · Compartments of the thigh

Divided by the medial, lateral and posterior intermuscular septa arising from the fascia lata, whose lateral thickening is the iliotibial tract.

Anterior compartment

The pes anserinus (“goose’s foot”) is the conjoined insertion of Sartorius, Gracilis and Semitendinosus — “Say Grace before Tea” — each from a different compartment and a different nerve (femoral, obturator, tibial respectively). It is a common site of bursitis and of medial knee pain that mimics MCL or meniscal pathology.

Medial compartment

Posterior compartment — the hamstrings

All hamstrings extend the hip and flex the knee (except the short head of biceps, which only flexes the knee). Because they are biarticular, active and passive insufficiency (Chapter 6) apply — which is why hamstring length is tested with the hip flexed, and why they cramp when the hip is flexed and the knee flexed simultaneously.

The femoral triangle and adductor canal

Figure 4 · The femoral triangle

Femoral triangle

Contents, lateral to medial — “NAVEL”: Nerve (femoral) · Artery (femoral) · Vein (femoral) · Empty space (femoral canal) · Lymphatics (deep inguinal nodes, including the node of Cloquet)

The femoral sheath — a prolongation of transversalis and iliac fascia — encloses the artery, vein and canal, but NOT the nerve, which lies outside it. The femoral canal, the medial compartment, permits venous distension and is the site of femoral hernia (below and lateral to the pubic tubercle — versus inguinal hernia, above and medial).

Clinical uses: femoral pulse palpation at the mid-inguinal point; femoral vein cannulation and arterial access (the vein is medial to the artery — remembered by the fact that you aim medially for the vein); femoral nerve block; and lymph node assessment.

Adductor (subsartorial, Hunter’s) canal

A fascial tunnel in the middle third of the thigh, from the apex of the femoral triangle to the adductor hiatus.

Contents: the femoral artery and vein, the saphenous nerve, and the nerve to vastus medialis.

At the adductor hiatus in adductor magnus, the femoral vessels pass into the popliteal fossa and become the popliteal artery and vein. The saphenous nerve does not — it pierces the fascia to become subcutaneous, supplying the medial leg and foot. Adductor canal block, now widely used after knee arthroplasty, targets the saphenous nerve while sparing quadriceps motor function — which is why it has largely replaced the femoral nerve block, whose quadriceps weakness caused falls.

Nerves

Femoral nerve (L2–L4)

Formed in psoas, emerges at its lateral border, passes under the inguinal ligament lateral to the femoral artery and outside the femoral sheath, then divides.

• Motor: iliacus, pectineus, sartorius, quadriceps.
• Sensory: anterior and medial cutaneous nerves of the thigh; saphenous nerve to the medial leg and foot.
• Lesion: loss of knee extension (the patient’s knee buckles; they may lock it by leaning the trunk back), weak hip flexion, absent knee jerk, sensory loss over the anterior thigh and medial leg. Causes: pelvic surgery, retroperitoneal haematoma (particularly in anticoagulated patients — a classic cause), lithotomy positioning, femoral nerve block, diabetic amyotrophy.

Obturator nerve (L2–L4)

Descends on the lateral pelvic wall, through the obturator canal, dividing into anterior and posterior divisions on either side of adductor brevis.

• Motor: the adductor compartment.
• Sensory: a small patch on the medial thigh — and articular branches to both the hip and the knee, which is the anatomical basis of hip pathology referring to the knee.
• Lesion: weak adduction, a wide-based gait; rare in isolation, seen after pelvic surgery, in obstetric injury, and in obturator hernia (Howship–Romberg sign — medial thigh pain on hip extension and internal rotation).

Sciatic nerve (L4–S3)

The largest nerve in the body, ~2 cm wide at its origin. Leaves the pelvis through the greater sciatic foramen below piriformis (in ~85–90%; variants exist in which the common fibular division pierces piriformis, and these are cited in discussions of piriformis syndrome), descends midway between the ischial tuberosity and the greater trochanter, and runs on adductor magnus deep to the hamstrings.

It is two nerves in one sheath from the outset:

It divides at the apex of the popliteal fossa (variably higher).

Sciatic nerve lesions: posterior hip dislocation, misplaced gluteal injection, hip surgery, pelvic tumour, prolonged sitting. A complete lesion produces total loss below the knee plus hamstring weakness — with preserved knee extension and hip flexion (femoral) and preserved sensation over the medial leg (saphenous).

“Sciatica” is a symptom, not a diagnosis, and in the great majority of cases it originates at the lumbar nerve root, not the sciatic nerve itself. Piriformis syndrome as a cause is controversial, over-diagnosed, and best regarded as a diagnosis of exclusion; deep gluteal syndrome is the broader modern term for extrapelvic sciatic entrapment.

Lateral femoral cutaneous nerve (L2, L3)

Passes under the inguinal ligament near the ASIS. Entrapment causes meralgia paraesthetica — burning, numbness and dysaesthesia over the anterolateral thigh, with no motor deficit. Associated with obesity, pregnancy, tight belts and waistbands, and prolonged hip extension. Recognising it prevents a great deal of unnecessary lumbar imaging.

Vessels

The femoral artery continues from the external iliac at the inguinal ligament, gives the profunda femoris (the main supply to the thigh, itself giving the medial and lateral circumflex femoral arteries and four perforating arteries), and passes through the adductor hiatus to become the popliteal artery.

The cruciate anastomosis (inferior gluteal, medial and lateral circumflex femoral, first perforating) and the trochanteric anastomosis provide collateral circulation around the hip — clinically important when the femoral or external iliac artery is occluded.

The great saphenous vein — the longest vein in the body — ascends from the anterior to the medial malleolus (a reliable cut-down site), up the medial leg and thigh, to pierce the cribriform fascia at the saphenous opening and join the femoral vein at the saphenofemoral junction, ~3–4 cm inferolateral to the pubic tubercle.

Clinical conditions

Hip osteoarthritis

• Presentation: groin pain (the most specific location), often referred to the anterior thigh and medial knee via the obturator nerve; morning stiffness under 30 minutes; difficulty with socks, shoes and getting in and out of a car.
• Sign: the capsular pattern, with internal rotation lost first and most. Loss of hip internal rotation in flexion is one of the more useful clinical findings in medicine — it is also a marker for FAI and, notably, is associated with low back pain.
• Management: first-line is exercise therapy, education and weight management (NICE, OARSI); progressive strengthening of abductors and extensors, range restoration, gait aid prescription in the contralateral hand, and activity pacing. Arthroplasty for those with persistent, function-limiting symptoms — one of the most successful operations in medicine.

Femoroacetabular impingement (FAI) syndrome

Abnormal contact between the proximal femur and the acetabular rim during movement, producing labral and chondral damage.

The Warwick Agreement definition requires all three of symptoms, clinical signs and imaging findings — morphology alone is not FAI, and cam morphology is present in a large proportion of asymptomatic athletes. Clinical: groin pain, the FADIR/anterior impingement test (flexion–adduction–internal rotation), and reduced internal rotation in flexion. First-line management is physiotherapist-led rehabilitation; arthroscopy for those who fail it, with trials (FASHIoN, UK FASHIoN) showing a modest advantage for surgery over physiotherapy at 12 months, and continuing debate about longer-term outcomes.

Greater trochanteric pain syndrome (gluteal tendinopathy)

Formerly called “trochanteric bursitis” — the pathology is predominantly tendinopathy of gluteus medius and minimus at the trochanteric insertion, with secondary bursal involvement.

• Presentation: lateral hip pain, worse on lying on the side, on single-leg loading, on stairs, and after prolonged sitting with the legs crossed. Peak in women aged 40–60.
• The mechanism is compression. The ITB compresses the tendon against the trochanter in hip adduction — so the aggravating positions are side-lying, crossing the legs, standing “hanging on one hip”, and stretching into adduction. Therefore: ITB stretching and adduction stretches are contraindicated, which is precisely the treatment patients are most often given.
• Management (the LEAP trial evidence): load management and education about avoiding adduction, plus progressive abductor strengthening in neutral to slight abduction, outperform corticosteroid injection and wait-and-see at 8 weeks and 12 months.

Hamstring injury

The commonest injury in running and kicking sports.

• Mechanism: eccentric loading at long muscle length during terminal swing, when the hamstrings decelerate the extending knee.
• Site: most often the long head of biceps femoris at the proximal musculotendinous junction / intramuscular tendon.
• Risk factors: previous hamstring injury (much the strongest), age, reduced eccentric strength, short biceps femoris fascicle length.
• Prevention: the Nordic hamstring exercise has the strongest evidence of any single injury-prevention intervention, roughly halving hamstring injury rates when adherence is adequate (Chapter 6).
• Proximal hamstring tendinopathy is distinct: deep buttock pain at the ischial tuberosity, worse with sitting and with hill running; also a compressive tendinopathy, aggravated by hip flexion — so, again, aggressive stretching into hip flexion makes it worse.

Groin pain

The Doha agreement classification is now standard, and it is worth using because “groin strain” as a label is useless:

• Adductor-related (the commonest)
• Iliopsoas-related
• Inguinal-related
• Pubic-related
• Hip-related (FAI, labral tear, osteoarthritis)
• Other causes — including hernia, referred lumbar pain, stress fracture of the femoral neck or pubic rami, and, importantly, non-musculoskeletal causes (urological, gynaecological, intra-abdominal). A femoral neck stress fracture presenting as groin pain in a runner is a limb-threatening miss.

Other conditions

Where students consistently go wrong

• Forgetting the ischiofemoral ligament is the weakest. Hence posterior dislocation.
• Confusing close-packed and resting positions. Close-packed = extension, internal rotation, abduction. Resting = ~30° flexion, 30° abduction, slight external rotation.
• Missing the two nerve supplies of adductor magnus.
• Forgetting the short head of biceps femoris is the only hamstring supplied by the common fibular division and the only one not crossing the hip.
• Putting the femoral nerve inside the femoral sheath. It is outside.
• Teaching the walking stick on the wrong side. Contralateral hand.
• Calling greater trochanteric pain “bursitis” and stretching the ITB. It is a compressive tendinopathy; adduction stretches aggravate it.
• Injecting into the lower medial gluteal quadrant. Upper outer quadrant or ventrogluteal.
• Treating cam morphology on imaging as a diagnosis of FAI. Symptoms + signs + imaging, all three.
• Not examining the hip in a child or adolescent with knee pain. Perthes, SCFE, septic arthritis.

Check yourself

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

Quick review

Further reading

Chapter 14 of 24 · Human Anatomy · Physiotherapist India Next: Chapter 15 — Knee and Leg: the knee joint, menisci and cruciates, and the compartments of the leg.

Reviewed by the Physiotherapist India Team. · Human Anatomy contents