Intrinsic (not controllable)

• physiologic rotatory laxity
• ACL size
• valgus alignment
• hyperextension
• proprioception
• neuromuscular firing order
• hormonal influences
• gender

Extrinsic (partially controllable)

• strength
• conditioning
• shoes
• motivation
• deceleration forces during injury

Both (partially controllable)

• skill
• coordination

Arnheim stated that the knee is most vulnerable when the tibia is externally rotated and the knee is in a valgus position. Fu and Stone noted that same position as the most frequent injury mechanism in soccer, football, and skiing, but that the most common ACL injury mechanism in basketball is hyperextension with tibial internal rotation.