ACL Injury Mechanisms and Risk Factors

What are the key mechanisms of injury for ACL injuries?

1. Dynamic Knee Valgus: Involves hip adduction, hip internal rotation, tibial abduction, tibial rotation, foot pronation, and can include ipsilateral trunk flexion and contralateral pelvic drop if unilateral. 2. Poor Landing Form: Involves asymmetrical landing, placing greater stresses on one extremity. 3. Deceleration: Occurs with sudden stops or changes in direction, requiring significant quadriceps force, which can lead to increased anterior shear if not counterbalanced by hamstring co-contraction. 4. Knee Hyperextension: Directly increases ACL strain.

What percentage of ACL injuries occur in isolation versus in combination with other injuries?

25% occur in isolation, 25% with MCL injury, 20% with lateral meniscus injury, and 30% with medial meniscus injury.

What are some risk factors for ACL injuries?

1. Prior ACL injury 2. Participation in pivot or cutting sports 3. Female gender 4. Core or lower extremity strength deficits 5. Poor single limb balance 6. Fatigue.

What are the common symptoms of an ACL injury?

Acute onset of pain, usually after cutting or landing a jump, often accompanied by a pop or snap sound. Most individuals are unable to walk without help or exhibit a significant limp. Swelling occurs within hours, often with hemarthrosis.

What is contraindicated for the first few months after ACL surgery?

Resisted knee extension between 45 and 0 degrees causes anterior tibial shear and is contraindicated.

What alternative exercise is suggested post-ACL surgery?

Avoid resisted open kinetic chain knee extension and instead work in the 90-45 degree range.

Which special test is used to rule in an ACL injury?

The Lachman test.

What are the differential diagnoses for ACL injuries?

ACL isolation or positive findings for meniscus, MCL, or LCL injuries, which can also include more than two injuries.

Which movement pattern best describes "dynamic knee valgus"?

Hip ADD, Hip IR, Tibial ABD, Foot Pronation

3 multiple choice options

Poor landing form often involves:

Asymmetrical landings stressing one extremity

3 multiple choice options

Deceleration injuries usually involve:

Sudden stop or change of direction requiring high quad force

What action directly increases ACL strain?

Knee hyperextension

1 multiple choice option

What percentage of ACL injuries occur in isolation (without other structures injured)?

25%

ACL and medial meniscus injuries occur together approximately:

30%

Which history finding is most common after ACL rupture?

Hearing or feeling a pop at time of injury

3 multiple choice options

Which condition typically develops within hours of ACL injury?

Hemarthrosis

3 multiple choice options

Why is resisted knee extension between 45 and 0 degrees contraindicated early after ACL surgery?

It causes anterior tibial shear

Which special test is most sensitive for ruling in ACL injury?

Lachman test

Which factor is NOT associated with dynamic knee valgus?

Foot supination

3 multiple choice options

What sport type is most associated with higher ACL injury rates?

Cutting and pivoting sports

3 multiple choice options