Why does the ACL suddenly tear?

A question often asked is why the ACL tears in manoeuvres that the sportsperson has completed successfully many times in the past. The sportsperson could be off balance, be pushed/nudged by an opponent, have adopted an unusually wide foot position. Inadequate muscle protection, poor neuromuscular control, fatigue and loss of concentration may also be relevant factors. 

That’s one of the reasons why general conditioning in prehab programmes and ACL rehab is important. Roughly 70% of all ACL injuries are as a result of a noncontact mechanism of injury and usually occur as an individual is cutting, jumping or planting. Lower extremity movement patterns during these activities play a critical role in injury mechanisms because they influence the load and forces on ligaments, meniscus/cartilage, and bone (DiStefano, L.J., 2009). 

ACL injuries occur most frequently in field sports involving landing from jumps, side-stepping, turning sharply and decelerating, e.g GAA, soccer, rugby, basketball.

ACL Anatomy:

The ACL is one of the two cruciate ligaments. It is named in relation to its attachment to the tibia.

The two cruciates – ACL and PCL are crucial in providing knee stability. It is essential in controlling

pivoting movements. If the ACL is not functional the tibia may rotate under the femur when a person attempts to land from a jump, pivot, or stop suddenly.

The ACL has two primary functions:

• It prevents forward movement of the tibia under the femur
• It controls rotational movement of the tibia under the femur

Intrinsic Risk Factors:

• Gender
• Female have a wider pelvis and slightly knocked knee
• Biomechanics
• Body mass index
• Age
• Anatomy of the bones
• Dynamic risk factors
• How we move/ jump/ land
• Extrinsic Risk Factors:
• Sport type
• Basketball
• Football
• GAA

The level of exposure to risk factors:

• Weather conditions
• Surfaces
• Hard/ Soft
• Uneven / Even
• Footwear

Point of no Return:

Non-contact ACL injuries often exhibit a common body posture that involves a valgus collapse of the knee joint (knee falls inwards/ medially), with the knee near full extension (between 0 and 30 degrees), external tibial rotation with the foot planted during a deceleration manoeuvre. Approximately 85% of the knee joint’s total restraint to anterior tibial translation is provided by the ACL and as studies have shown that sagittal plane knee angles near full extension and large quadriceps muscle forces increase ACL loading (Quatman, 2009).

Sign & Symptoms of ACL Tear:

• A description of valgus knee position at time of injury, a landing, cutting manoeuvre.
• Patient can hear a ‘pop’ or ‘click’ or something ‘going out of place and then going back’.
• Tears are extremely painful.
• Players are usually unable to continue playing.
• There can be relatively immediate swelling (2hrs)
• Patients experience a feeling of instability in the knee.
• Sometimes we need to reduce certain exercises that may be aggravating our symptoms only to add them back in with time.

Grades of Ligament Tears:

A tear occurs when the force placed on the ligament is too much for the ligament to control.

Grade 1: Mildly Damaged

Grade 2: Partial Tear

Grade3: Complete Rupture