A 72-year-old woman with osteoporosis presents with a fall at home. X-ray confirms a femoral neck fracture. Which clinical feature best distinguishes an intracapsular (subcapital) femoral neck fracture from an extracapsular (intertrochanteric) fracture?

Explanation

## Distinguishing Intracapsular from Extracapsular Femoral Neck Fractures ### Vascular Anatomy: The Key Discriminator **Key Point:** The critical difference between intracapsular and extracapsular femoral neck fractures lies in the blood supply to the femoral head. Intracapsular fractures occur proximal to the hip joint capsule attachment. The femoral head receives its blood supply primarily from: - Medial and lateral femoral circumflex arteries (branches of profunda femoris) - These vessels run along the femoral neck within the joint capsule - Fracture disrupts these vessels → **avascular necrosis (AVN) risk of 10–30%** Extracapsular (intertrochanteric) fractures occur distal to the capsule. The blood supply remains largely intact because: - The circumflex vessels are not disrupted - Periosteal blood supply is preserved - AVN risk is negligible (<1%) ### Comparison Table | Feature | Intracapsular | Extracapsular | | --- | --- | --- | | **AVN Risk** | High (10–30%) | Minimal (<1%) | | **Blood Supply Disruption** | Yes (medial/lateral FCFA) | No | | **Union Rate** | Lower (delayed/non-union) | Higher (better healing) | | **Treatment** | ORIF or hemiarthroplasty (displaced) | ORIF with plate/nail | | **Deformity** | Flexion, adduction, internal rotation | External rotation | ### Clinical Pearl **High-Yield:** The vascular anatomy is the fundamental reason intracapsular fractures carry worse prognosis. This is why: - Intracapsular fractures in young patients → ORIF urgently (preserve femoral head) - Intracapsular fractures in elderly → hemiarthroplasty (accept loss of head) - Extracapsular fractures → ORIF with plate/nail (good healing potential) ### Why Intracapsular Fractures Have Worse Outcomes 1. **Immediate vascular compromise** → bone necrosis begins within hours 2. **Delayed union/non-union** → 10–20% non-union rate (vs. 2–5% extracapsular) 3. **AVN** → late collapse and arthritis even if union occurs [cite:Rockwood & Green's Fractures in Adults Ch 48]