Anterior Cruciate Ligament Injuries

Anatomy & Biomechanics

• completely intraarticular

• anteromedial fibres - tight in flexion - limits anterior translation of tibia on femur

• posterolateral fibres - tight in extension - limits anterior translation PLUS external rotation

• ACL strength = 50% PCL strength

• Load to failure = 1700N

• strain rate plays a role in the location of ligament failure
  • midsubstance tears occurring at higher rates
  • bone ligament complex tears occurring at lower rates

• Blood supply - middle genicular artery (post) & synovial vessels (ant)

• Mechanoceptors with a proprioceptive role

Examination:

• See Knee Examination

Mechanism of Injury:

• substantial anterior tibial shear forces that stress ACL are produced from quadriceps contraction, esp in 0-30 deg of extension

• Typically, the ACL is torn in a noncontact deceleration situation that produces a valgus twisting injury - when the athlete lands on the leg and quickly pivots in the opposite direction. 

Associated Injuries: ( Noyes, 1980 )