The Femur

Gross Anatomy

Proximal Femur

• Roughly spherical (~2.5 cm radius of curvature)
• Largely covered by hyaline articular cartilage except at the fovea capitis (a pit on the medial surface for attachment of the ligamentum teres / ligament of the head)
• Articulates with the acetabulum to form a ball-and-socket (spheroidal) joint

• Connects the head to the shaft
• Neck-shaft angle averages 127° in adults (begins at ~141° in the fetus; decreases with age)
• Femoral neck is anteverted approximately 14° relative to the femoral condyles (range 1-40°)
• Largely intracapsular; the posterior neck is only partially covered by the joint capsule (basicervical and intertrochanteric regions are extracapsular)

Shaft (Diaphysis)

• Cylindrical; directed obliquely downward and medially, so the knee lies near the body's midline
• The posterior surface bears a prominent longitudinal ridge, the linea aspera, which serves as attachment for adductor and other thigh muscles
• The linea aspera splits distally into the medial and lateral supracondylar lines, which form the floor and sides of the popliteal fossa
• The pectineal line runs from the lesser trochanter to the linea aspera (adductor longus and brevis, pectineus insert here)

Distal Femur

• Expands into two large articular masses: the medial condyle (larger) and lateral condyle (smaller)
• The condyles articulate with the tibial plateaus and with the patella (via the patellar/trochlear surface anteriorly)
• Between the condyles posteriorly lies the intercondylar (intercondyloid) fossa:
  • Lateral wall = attachment of the anterior cruciate ligament (ACL)
  • Medial wall = attachment of the posterior cruciate ligament (PCL)
  • The roof is demarcated by the intercondylar line
• Non-articular bony prominences above the condyles = medial and lateral epicondyles (attachment sites of collateral ligaments and muscles)
• The adductor tubercle sits above the medial epicondyle; it is the termination of the medial supracondylar line and receives the adductor magnus tendon

Blood Supply

1. Medial circumflex femoral artery (MFCA) - the dominant supply; a branch of the profunda femoris (deep artery of thigh). It runs posteriorly around the neck and its deep branch penetrates retinacular vessels under the joint capsule to supply the femoral head
2. Lateral circumflex femoral artery (LCFA) - contributes mainly to the anterior neck via ascending branch
3. Artery of the ligamentum teres - a branch of the obturator artery; relatively minor in adults but contributes to the foveal area

Clinical point: Femoral neck fractures and hip dislocations can rupture the MFCA retinacular vessels, interrupting the main blood supply and causing avascular necrosis (AVN) of the femoral head. In children, the piriformis fossa nail entry point for intramedullary nailing risks damage to the posterosuperior retinacular vessels off the MFCA - this is why lateral trochanteric entry is preferred.

Ossification

• The distal femur is responsible for the highest percentage of longitudinal growth in the lower extremity (~70% of femoral length; ~37% of total lower limb length)
• Slipped capital femoral epiphysis (SCFE) occurs through the femoral head physis at the zone of hypertrophy

Key Angles and Measurements

Proximal Femoral Trabecular Architecture

• Compression trabeculae - arching from calcar to superolateral femoral head cortex
• Tension trabeculae - from the lateral cortex, arching medially toward the femoral head
• The Ward triangle is a relatively weak area between the two systems where trabecular density is low - a common site for stress fractures and osteoporotic fractures

Muscle Attachments Summary

Clinical Correlations

• Femoral neck fractures: Commonest in elderly osteoporotic women (minimal trauma); risk of AVN and non-union due to tenuous blood supply. Classification: subcapital, transcervical, basicervical
• Intertrochanteric fractures: More vascular region, lower AVN risk; treated with intramedullary nail or dynamic hip screw
• Subtrochanteric fractures: High biomechanical stress; treated with intramedullary nail
• Femoral shaft fractures: High energy in young (MVA), lower energy in elderly; intramedullary nail is gold standard treatment
• Distal femur fractures: Up to 6% of all femur fractures; bimodal distribution (high energy in young, low energy in elderly); thin cortices and wide medullary canal make fixation challenging

The Femur

Overview: Anatomical Position in the Body

Anterior view showing both femora in standing position (oblique medial course), a mid-shaft cross-section (triangular with linea aspera posteriorly), and posterior surface of the proximal femur. - Gray's Anatomy for Students

1. Proximal Femur

Anterior (left) and posterior (right) views of the right hip joint showing proximal femoral landmarks. - THIEME Atlas of General Anatomy

Head of Femur

• Smooth, roughly spherical (~2.5 cm radius)
• Covered by hyaline articular cartilage over most of its surface
• Articulates with the acetabulum to form a ball-and-socket (spheroidal) joint
• The fovea capitis (fovea) is a small pit on the superomedial surface - it is non-articular and is the attachment for the ligamentum teres (ligament of the head of the femur)

Neck of Femur

• Approximately 5 cm long; connects the head to the shaft
• Projects in a superomedial direction
• Neck-shaft angle: averages 127° in adults (starts at ~141° in the fetus; decreases with age)
  • Coxa vara = angle < 120°; Coxa valga = angle > 135°
• Anteversion: the neck is rotated anteriorly 10-15° (range 1-40°) relative to the plane of the femoral condyles
• Capsular relationship: the anterior surface of the neck is fully intracapsular; the posterior neck is only partially covered by the capsule (the basicervical and intertrochanteric regions are extracapsular)

Greater Trochanter

• Large, lateral bony prominence at the neck-shaft junction
• Muscle attachments: gluteus medius (lateral facet), gluteus minimus (anterior facet), piriformis (superior border), obturator internus and gemelli (medial surface - trochanteric fossa), obturator externus

Lesser Trochanter

• Smaller, posteromedial prominence at the base of the neck
• Sole attachment: iliopsoas (psoas major + iliacus)

Intertrochanteric Line and Crest

2. Shaft (Diaphysis)

Posterior view of right proximal femur showing the fovea, trochanters, pectineal line (spiral line), gluteal tuberosity, and linea aspera. - Gray's Anatomy for Students

• The shaft is bowed anteriorly (slight anterior convexity)
• Mid-shaft cross-section is triangular: anterior surface, posteromedial surface, and posterolateral surface, with the posterior border forming the linea aspera

Linea Aspera

• Pectineal line (spiral line) - medial divergence, curves anteriorly under the lesser trochanter to join the intertrochanteric line. Attachment: pectineus
• Gluteal tuberosity - lateral divergence, broad roughening up to the greater trochanter. Attachment: gluteus maximus

• Medial supracondylar line - ends at the adductor tubercle on the medial condyle. The adductor magnus inserts here
• Lateral supracondylar line - forms the lateral edge of the popliteal surface
• The area between these two lines forms the popliteal surface (floor of the popliteal fossa)

Key Muscle Attachments to Shaft

3. Distal Femur

Distal femur: (A) anterior view with condyles, epicondyles, and adductor tubercle; (B) lateral profile; (C) end-on view showing trapezoidal shape - wider posteriorly - with intercondylar notch. - Rockwood & Green's Fractures in Adults 10th ed

Condyles

• Two large articular masses: medial condyle (longer, extends farther distally) and lateral condyle (shorter, broader, extends farther proximally)
• Anteriorly, the two condyles unite to form the patellar (trochlear) surface - a groove for the patella
• Intercondylar (intercondyloid) fossa separates them posteriorly
• The distal femur, viewed on end, is trapezoidal in shape: the posterior part of the condyles is wider than the anterior part (creating ~25° inclination medially, ~15° laterally)

Intercondylar Fossa

Epicondyles

• Medial epicondyle - bony non-articular prominence on the medial condyle; attachment for the medial (tibial) collateral ligament; medial head of gastrocnemius attaches just above it
• Lateral epicondyle - attachment for the lateral (fibular) collateral ligament and popliteus tendon (in an oblique groove just below it)
• Adductor tubercle - at the uppermost part of the medial condyle; where the medial supracondylar line terminates; adductor magnus inserts here

Femoral-Tibial Axis

• The anatomic axis of the femoral shaft makes ~6-7° of valgus relative to the knee joint line (range 2-10°)
• This valgus offset is factored into knee arthroplasty instrumentation

4. Blood Supply to the Femoral Head

Course of femoral neck vessels: the medial and lateral circumflex femoral arteries (branches of the deep artery of thigh/profunda femoris) supply the femoral head via retinacular vessels that run along the neck deep to the capsule. - THIEME Atlas of General Anatomy

1. Medial circumflex femoral artery (MFCA) - dominant supply. A branch of the profunda femoris (deep artery of thigh). Its deep branch passes posterior to the neck, then gives off superior retinacular arteries that run along the neck under the capsule → the main perfusion to the femoral head
2. Lateral circumflex femoral artery (LCFA) - contributes via ascending branch; mainly supplies the anterior neck and greater trochanter
3. Artery of the ligamentum teres - branch of the obturator artery; enters through the fovea; minor contribution in adults but important in children

Clinical: AVN risk - Femoral neck fractures can sever the retinacular vessels of the MFCA, cutting off the dominant blood supply and causing avascular necrosis (AVN) of the femoral head. The risk is highest with subcapital fractures (highest displacement, most proximal), lower with basicervical fractures (extracapsular, more vascular zone). This is why displaced femoral neck fractures in young adults are treated urgently with reduction and fixation (or hemiarthroplasty in elderly patients).

5. Ossification

• The distal femoral epiphysis contributes the highest proportion of longitudinal growth in the lower limb
• Slipped Capital Femoral Epiphysis (SCFE) occurs through the zone of hypertrophy of the femoral head physis
• In children, intramedullary nail insertion at the piriformis fossa risks damage to the posterosuperior retinacular vessels of the MFCA → AVN risk; trochanteric entry is preferred

6. Key Angles and Measurements

7. Thigh Compartments Related to Femur

8. Clinical Fracture Classification Summary

Femoral Neck Fractures

• Subcapital (across head-neck junction) - highest AVN risk
• Transcervical (through mid-neck)
• Basicervical (at base of neck) - lowest AVN risk; extracapsular

• Type I: < 30° from horizontal (compressive forces - more stable)
• Type II: 30-50°
• Type III: > 50° (shear forces dominant - highest non-union risk)

Intertrochanteric Fractures

• Run between greater and lesser trochanters
• Extracapsular - blood supply to femoral head preserved, AVN risk is low
• Treated with intramedullary nail or dynamic hip screw (DHS)

Femoral Shaft Fractures

• High energy in young (MVAs); lower energy in elderly
• Intramedullary nail is gold standard
• "Damage control" approach for polytrauma patients

Distal Femur / Supracondylar Fractures

• The supracondylar zone = distal ~15 cm of femur
• Bimodal: high energy in young, ground-level falls in elderly osteoporotic patients
• Thin cortices and wide medullary canal make stable fixation difficult
• Goals: anatomic articular reduction, restore limb alignment, early mobilization