Femur Anatomy
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Direct answer
The femur is the longest, heaviest and strongest bone in the body and contributes roughly a quarter of standing height. Its neck meets the shaft at about 125–130 degrees, with roughly 15 degrees of anteversion, and its head survives on retinacular branches of the medial circumflex femoral artery that ascend the neck beneath the synovial reflection — so an intracapsular neck fracture threatens avascular necrosis. Attachments map the surface: glutei on the greater trochanter, iliopsoas on the lesser trochanter, adductors along the linea aspera. Fracture patterns carry exam-favourite correlations, from the externally rotated limb of an elderly neck fracture to the popliteal artery behind a supracondylar break.
What you must remember
- Neck-shaft angle: about 125–130 degrees in adults, near 150 at birth, drifting towards 120 in the elderly; coxa vara shortens the abductor lever arm and causes a Trendelenburg limp.
- Anteversion: about 15 degrees; excess (dysplasia, cerebral palsy) causes intoeing and predisposes to anterior dislocation.
- Greater trochanter, with nerves: gluteus medius and minimus (superior gluteal nerve); piriformis (S1–S2), gemelli and obturator internus (nerve to obturator internus) into the trochanteric fossa; obturator externus (obturator nerve) below it.
- Lesser trochanter and shaft: iliopsoas (L1–L2); quadratus femoris (nerve to quadratus femoris) on the quadrate tubercle; gluteus maximus (inferior gluteal nerve) on the gluteal tuberosity; short head of biceps femoris (common peroneal division of sciatic) on the lateral lip of the linea aspera — the only hamstring so supplied.
- Nutrient artery: usually the second perforating branch of the profunda femoris; its foramen on the linea aspera points upwards, away from the distal end that provides about 70 per cent of growth.
- Blood supply of the head: medial circumflex femoral retinacular branches (dominant), a lateral circumflex contribution, and the artery of the ligamentum teres from the obturator — negligible in adults.
- Fracture-site nerve correlations: sciatic nerve palsy in posterior hip dislocation or acetabular fracture; popliteal artery and tibial nerve behind a supracondylar fracture; superior gluteal nerve at risk beyond 5 cm above the greater trochanter.
- Rotation pearl: classically about 45 degrees of external rotation with an intracapsular neck fracture, about 90 with an intertrochanteric one — a favourite bedside discriminator.
One fracture, two fates
Picture a 72-year-old woman who slipped in the bathroom and cannot stand; her right leg lies shortened and externally rotated. Nearly all blood reaching the femoral head ascends the neck in retinacular branches of the medial circumflex femoral artery, and a transcervical break tears them at the moment of injury; the ligamentum teres artery perfuses only a small central sector in adults, so a displaced Garden III–IV fracture leaves the head ischaemic. That one fact splits treatment: a young patient's fractured neck is an orthopaedic emergency — urgent reduction and fixation to salvage the head — while the frail elderly often receive hemiarthroplasty, replacing the doomed head. An intertrochanteric fracture behaves oppositely, wrapped in muscle and perforating vessels: it unites reliably but can bleed a litre or more, so a dynamic hip screw, not a replacement, is planned.
Holding the bone in a viva
Handed a dried femur, expect the opening question first: which side, and which end is up. Three features settle it — the nutrient foramen points upwards towards the hip, the head faces medially and slightly upwards, and the linea aspera marks the back. The classic slip is reciting the slogan "the nutrient foramen points towards the growing end"; in the femur that end is the distal one, so the foramen points away from it, upwards. Rapid fire follows: candidates who place piriformis, the gemelli and obturator internus "on the greater trochanter" lose the mark, for they insert into the trochanteric fossa; obturator externus sits alone below. Close with the clinical hook — the elderly woman's trivial fall, the limb rolled outward by iliopsoas and the short rotators.
Frequently asked questions
Which artery is the chief blood supply of the head of the femur?
Retinacular branches of the medial circumflex femoral artery, especially the superior group, ascending the neck beneath the synovial reflection. The ligamentum teres artery contributes little in adults.
How do you clinically distinguish an intracapsular from an intertrochanteric fracture?
Classically the intracapsular fracture holds the limb in about 45 degrees of external rotation, the intertrochanteric in about 90 with greater shortening and swelling. Radiographs with Garden grading settle the classification.
Which nerve is injured in posterior dislocation of the hip?
The sciatic nerve, which runs directly behind the joint. Test dorsiflexion, eversion and sole sensation before and after reduction.
From which artery does the femur receive its nutrient supply?
Usually the second perforating branch of the profunda femoris. Its foramen points away from the distal growing end — upwards, towards the hip — the detail that orients an unmarked femur in a viva.
Why does a supracondylar fracture endanger the popliteal artery?
The artery lies against the popliteal surface, tethered above at the adductor hiatus. Gastrocnemius tilts the distal fragment backwards, lancing the vessel — absent distal pulses demand urgent vascular assessment.