Thigh Bone
Femur
location_on Thigh, between the hip joint and knee joint
The femur is the longest, heaviest, and strongest bone in the human body, extending from the hip to the knee. The femoral head forms a nearly perfect sphere that articulates with the acetabulum, while the distal condyles form the upper surface of the knee joint. The femoral neck connects the head to the shaft at an angle of approximately 125 degrees and is a common site of osteoporotic fracture in the elderly.
Key Anatomical Features
- Head is a sphere covered with articular cartilage except at the fovea capitis for the ligamentum teres
- Neck connects the head to the shaft at a neck-shaft angle of approximately 125 degrees
- Greater trochanter is the large lateral projection at the junction of neck and shaft
- Lesser trochanter is a medial projection inferior to the neck for psoas major insertion
- Linea aspera is a vertical ridge on the posterior shaft for muscle attachment
- Medial and lateral condyles at the distal end form the upper surface of the knee joint
Muscle Attachments
| Muscle | Attachment | Action |
|---|---|---|
| Gluteus medius | Lateral surface of greater trochanter | Abducts the hip and prevents pelvic drop |
| Iliopsoas | Lesser trochanter | Flexes the hip (most powerful hip flexor) |
| Vastus lateralis | Lateral lip of linea aspera | Extends the knee |
| Vastus medialis | Medial lip of linea aspera | Extends the knee and stabilizes the patella |
| Vastus intermedius | Anterior and lateral shaft | Extends the knee |
| Adductor magnus | Linea aspera and adductor tubercle | Adducts and extends the hip |
| Gluteus maximus | Gluteal tuberosity | Extends and laterally rotates the hip |
| Gastrocnemius | Posterior surfaces of medial and lateral condyles | Flexes the knee and plantarflexes the ankle |
Joints and Articulations
| Joint | Type | Connects to |
|---|---|---|
| Hip joint | Synovial ball-and-socket | Acetabulum of hip bone |
| Knee joint (tibiofemoral) | Synovial modified hinge | Tibia |
| Knee joint (patellofemoral) | Synovial plane | Patella |
Common Pathologies
Femoral neck fracture
Common osteoporotic fracture in the elderly, classified as intracapsular (subcapital, transcervical) or extracapsular (intertrochanteric, subtrochanteric). Intracapsular fractures risk disrupting the blood supply to the femoral head.
Femoral shaft fracture
High-energy fracture that can cause significant blood loss (up to 1.5 liters into the thigh). May be associated with fat embolism syndrome.
Slipped capital femoral epiphysis (SCFE)
Adolescent condition where the femoral head slips posteriorly and inferiorly off the neck through the physis. Most common in obese adolescent males.
Avascular necrosis of the femoral head
Death of bone in the femoral head from disrupted blood supply, caused by fracture, corticosteroids, alcoholism, or sickle cell disease. Leads to femoral head collapse and hip arthritis.
Clinical Relevance
Hip fractures (femoral neck and intertrochanteric) have a one-year mortality rate of approximately 20-30% in elderly patients. Intracapsular fractures disrupt the retinacular vessels (branches of the medial circumflex femoral artery), the main blood supply to the femoral head, risking avascular necrosis. Displaced intracapsular fractures in the elderly are treated with hemiarthroplasty or total hip replacement rather than fixation. The femoral triangle contains the femoral artery, vein, and nerve (from lateral to medial: nerve, artery, vein, empty space, lymphatics = NAVEL).
Development and Ossification
The femur ossifies from five centers: one for the shaft (7th fetal week), and four secondary centers for the head (around 1 year), greater trochanter (around age 4), lesser trochanter (around age 12), and distal end (around 36th fetal week). The distal femoral epiphysis is the first secondary center to appear and is used as evidence of a full-term birth in forensic medicine. All epiphyses fuse by age 18-20.
Did You Know?
- The femur is the longest bone in the body, approximately one-quarter of a person's total height
- The femur can support up to 30 times the body weight during activities like running and jumping
- The presence of the distal femoral epiphysis on fetal X-ray indicates a gestational age of at least 36 weeks
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