Blood Supply of the Hip

What this anatomy decides. The femoral head is supplied by vessels that run outside the bone, on the surface of a neck that breaks — which is why one anatomical fact drives so much clinical practice, and why each consequence has its own page. Failure of that supply is avascular necrosis of the hip; the injury that most often causes it is a neck of femur fracture, and when the vessels fail without the bone uniting the result is femoral neck non-union. The same supply is what surgical hip dislocation (Ganz) is built to protect, what hip dislocation and acetabular fracture surgery must not tear, and what makes the paediatric hip vulnerable in Perthes disease and SUFE.

Retrograde and exposed. The supply to the femoral head is unusual because it is retrograde: the vessels travel up the femoral neck to reach the head at the articular margin. This precarious arrangement means that any fracture of the femoral neck is likely to sever these vessels, leaving the head without a valid blood supply.

The sources. The femoral artery gives off the profunda femoris, and from the profunda come the two circumflex femoral arteries that supply the neck and head. The obturator artery, from the internal iliac, reaches the head through the ligamentum teres, and the inferior gluteal artery, also from the internal iliac, makes a minor contribution to the posterior capsule.

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Medial femoral circumflex artery (MFCA). It usually arises from the profunda femoris, posteriorly, but can come directly from the common femoral. It winds medially around the femur, passing between pectineus and iliopsoas, then runs superior to adductor brevis and inferior to obturator externus, and the main trunk continues deep to quadratus femoris. Its terminal branch is the lateral epiphyseal artery, which reaches the head through the retinacular system below.

This is the critical vessel: 80% of the head's supply, covering the posterior, superior and lateral aspects of the head, which is the weight-bearing zone.

Lateral femoral circumflex artery (LFCA). It leaves the profunda femoris laterally and runs laterally deep to sartorius and rectus femoris. It has three branches:

• Ascending - anastomoses with the MFCA at the base of the neck
• Transverse - contributes to the cruciate anastomosis
• Descending - to the knee

Its share of the head is minor: anterior retinacular branches supply the anterior inferior aspect of the neck. Where the ascending branch meets the MFCA at the base of the neck the two form the extracapsular arterial ring of Crock.

The ascending cervical (retinacular) arteries. These arise from the extracapsular ring, pierce the capsule at the base of the neck and run up the neck primarily outside the bone, under the synovial reflection, in the retinacula of Weitbrecht. They enter the bone at the articular cartilage margin, in the subcapital region, and become the intra-osseous supply. There are three groups:

1. Posterior-superior - 2-4 vessels, branches of the MFCA; large and critical
2. Posterior-inferior - branches of the MFCA
3. Anterior - branches of the LFCA; smaller

Whatever the grouping, the anterior, inferior and medial contributions are small; the posterior-superior group is the main supply, and the one to protect or avoid.

Artery of the ligamentum teres. It comes from the posterior branch of the obturator artery (or from the medial circumflex) and travels within the ligament from the acetabular notch to the fovea; it is sometimes called the medial epiphyseal artery. In infants it is a vital supply and in children a variable one. In adults it is often patent but supplies only a small area around the fovea, which is insufficient to rescue the head if the neck vessels are cut.

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Thinking of the supply as three rings in series, from the base of the neck to the head, makes the vulnerability at each level easy to follow.

1. The extracapsular ring sits at the base of the neck, formed by the anastomosis of the MFCA posteriorly and the LFCA anteriorly, so it draws on both medial and lateral sources. It is the base station for everything above it: if a basicervical fracture disrupts it, the supply fails.

2. The ascending (retinacular) system runs on the surface of the neck, inside the capsule, and is the vulnerable link. Subcapital fractures almost universally disrupt it, and intracapsular tamponade from a haemarthrosis can compress these vessels even when they are not torn. Preserving them is the key to head viability.

3. The subsynovial intra-articular ring lies just below the cartilage junction and is the point of entry into bone. From here on the vessels are end-arteries with no further collaterals.

The sequence. Ischaemia kills osteocytes within 12-24 hours. The body then attempts to revascularise and remodel the necrotic bone by creeping substitution, laying new woven bone on the dead trabeculae. If resorption exceeds formation during that remodelling phase the weakened subchondral bone collapses, seen as the crescent sign, and the result is articular incongruity and secondary osteoarthritis.

The clock. The point of no return is often debated. Prompt reduction, variously put at 6 or 24 hours, is advocated for young patients; whether a hard cut-off is justified is taken up under Controversies.

Why the hip. Three features explain why:

• A retrograde supply with no collaterals
• An intracapsular space that can be pressurised
• High weight-bearing loads, which lead to collapse

The scaphoid, talus and humeral head share the retrograde arrangement.

Garden. The Garden classification of femoral neck fractures correlates directly with vascular integrity, and it is the predicted vascular survival that drives the fix-versus-replace decision:

• Grade I (valgus impacted) - trabeculae angulated, minimal displacement; vessels likely intact and the risk of AVN low (less than 15%)
• Grade II (complete, undisplaced) - the break is complete but anatomically reduced; vessels intact or kinked
• Grade III (complete, partially displaced) - vessels tethered or torn; the posterior retinaculum may still be intact
• Grade IV (complete, fully displaced) - the head is dissociated; vessels torn and the risk of AVN high

The caveat is that the Garden grade has only moderate interobserver reliability, and many surgeons collapse it to a binary undisplaced-versus-displaced decision in practice.

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The displaced neck fracture. A shortened and externally rotated leg means the fracture is displaced (Garden III or IV), and the rotation is the reason the posterior retinaculum is likely torn.

Posterior dislocation. A dashboard injury forces the head out of the acetabulum posteriorly, which tensions or tears the MFCA and the ligamentum teres. The hip is reduced immediately to restore flow, by relieving tamponade and kinking.

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Bone scan (technetium-99m). Uptake depends on blood flow and osteoblastic activity, so a cold spot in the early phase indicates an avascular head and a hot spot in the late phase indicates revascularisation and healing. It is useful for predicting head viability after a fracture but rarely changes acute management.

MRI. The gold standard for the diagnosis of AVN and the most sensitive modality, it can detect ischaemia within 24-48 hours. The signs are a serpentine line marking the demarcation between dead and living fatty marrow, the double-line sign on T2, and marrow oedema, which precedes collapse.

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When a young or middle-aged patient presents with hip pain and abnormal femoral head marrow on MRI, the following entities mimic or overlap with post-traumatic AVN. Distinguishing them changes management.

The decision. Two questions separate the rows of the table: is this head worth preserving, and can this patient survive a failed fixation and a second operation?

Read "young" and "older" physiologically, not off a birthday. A hard age line is the compressed version of this table and it is the wrong one: the cut-off is genuinely contested through the 50-65 band, where pre-injury mobility, cognition, bone quality and the patient's own priorities decide - see Controversies below.

Decompression and reduction. In young patients, releasing the capsule to let out the haematoma is thought to reduce intracapsular pressure and improve flow, though the evidence is mixed. Anatomic reduction is essential to un-kink the retinacular vessels, and that un-kinking is the primary rationale for urgent surgery.

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Cannulated screws. The goal is compression without rotation, and the configuration is an inverted triangle: one screw inferior, two superior. The inferior screw passes through the dense bone of the calcar. The posterior-superior screw is the risk zone: if its threads penetrate the posterior cortex they catch the lateral epiphyseal vessels where they run in the synovial reflection (Weitbrecht's retinacula) and tear them. Careful lateral viewing confirms that the threads are strictly intracapsular and intra-osseous.

The posterior approach. The MFCA runs superior to quadratus femoris and deep to the piriformis tendon. Taking quadratus femoris down too proximally, or extending the piriformis release into the capsule, can damage the main trunk, and the result is complete AVN of the head.

Surgical dislocation (Ganz). Through a trochanteric flip (digastric slide) - see surgical hip dislocation (Ganz) - the head is dislocated anteriorly while the MFCA is kept intact posteriorly with the obturator externus and quadratus femoris muscle flap. Done correctly it gives a full view of the head and acetabulum without AVN risk, and it demonstrates that the MFCA is tethered to the external rotators.

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Avascular necrosis declares itself as late segmental collapse, which is painful and requires total hip replacement; the collapse can occur up to 2-3 years after the injury. Non-union follows when vascular failure prevents healing. Hardware failure, screws backing out or cutting out, is the consequence of poor bone stock or non-union.

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After fixation the weight-bearing prescription is contested: touch or partial weight bearing to protect the reduction and the blood supply has its advocates, but most allow weight bearing as tolerated in stable constructs. After replacement the patient bears full weight immediately, because vascularity is no longer an issue.

Displaced fractures in young adults carry a non-union rate of roughly 10-30% and an AVN rate of roughly 15-30% even with anatomic fixation; the Upadhyay RCT reported overall AVN of 16.3%. For undisplaced fractures, non-union is approximately 5% and AVN under 10%. In children the risk follows the Delbet level set out above.

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Global Epidemiology

• Hip fractures are projected to reach 4.5-6 million annually worldwide by 2050, with the burden shifting toward Asia.
• Intracapsular (femoral neck) fractures account for roughly half of all proximal femoral fractures; in adults under 50 they are usually high-energy and carry a disproportionate AVN/non-union risk.
• AVN after displaced neck fracture in young adults is reported at roughly 15-30% even with optimal treatment; non-union at 10-30%.

Side-by-Side Guideline Comparison

Registry Evidence

• NJR (UK), AOANJRR (Australia), AJRR (US), SHAR (Sweden): Track arthroplasty done for failed fixation/AVN; total hip replacement generally outperforms hemiarthroplasty in younger, active patients for function and revision in displaced neck fractures.
• National Hip Fracture Databases (UK NHFD and similar): "time to theatre" is a quality metric, but the strongest modifiable driver of head salvage remains reduction quality, not the clock alone (see Upadhyay).

High- vs Limited-Resource Practice Variation

• High-resource: MRI for early AVN, dedicated trauma lists, choice of THR vs fixation, and surgical-dislocation expertise for select head/neck pathology.
• Limited-resource: Cannulated screws or DHS predominate because of cost and implant availability; muscle-pedicle bone grafting (e.g. quadratus femoris pedicle) is still used in some centres to biologically augment fixation in young patients.

Paediatric Note

• The artery of the ligamentum teres is important in infants; septic arthritis of the hip in this group causes a pressure tamponade that can infarct the epiphysis and is a surgical emergency.

Does timing really matter? The "hip attack" / 6-hour dogma is challenged by the Upadhyay RCT, which found delay beyond 48 hours did not increase AVN or non-union in young adults. Reduction quality and posterior comminution were the dominant predictors. Most still operate urgently, but the evidence for a hard time cut-off is weak.

Capsulotomy, aspiration or nothing. Intracapsular tamponade is real, but whether decompressing the haematoma improves head survival is unproven. It is biologically plausible and low-risk, so many surgeons do it for young patients despite the absence of high-level evidence.

Implant choice and vascular insult. FAITH showed higher AVN with the sliding hip screw than with parallel cancellous screws, raising the question of whether reaming and a single large central device add vascular or thermal insult to an already compromised head.

THR versus fixation in the 50-65 group. The "young" cutoff is contested. Below this band, head preservation is favoured; above it, registries and trials increasingly favour arthroplasty (often THR) for displaced fractures. The middle band remains an individualised decision.