What is Garden's classification system for subcapital femoral fractures?

Garden's classification system for subcapital femoral fractures is based on displacement of the femoral head. It is useful for estimating the patient's risk of osteonecrosis.

Stage I: incomplete or impacted subcapital fracture; all patients achieve union.
Stage II: complete subcapital fracture without displacement; all patients achieve union.
Stage III: complete subcapital fracture with partial displacement; 95% of patients achieve union.
Stage IV: complete subcapital fracture with total displacement; only 55% of patients achieve union.