The ACL and knee stability
Both the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) are important for knee stability.
They tether the tibia to the femur in such a way as to allow bending and straightening while preventing forwards and backward movements of the two bones in relation to one another.
"....The ACL is an important rotational stabilizer of the knee joint...."
ACL injury
The ACL can rupture through the body of the ligament during a knee injury, or the ligament can pull off its attachment to the wall of the notch (avulsion).
The former is more common in adults, and the latter is more common in children. An ACL injury is very disabling and usually the person is immediately unable to continue with the activity that caused it. It is often acompanied by immediate joint swelling due to bleeding into the joint capsule (haemarthrosis), and the knee generally feels unstable when trying to bear weight.
"....The ACL is one of the most frequently injured ligaments of the inferior extremity, especially in young sportspersons, necessitating prompt and adequate medical and surgical care...."
Tests of ACL integrity
The most common test of the integrity of the ACL is the anterior drawer test.
The examiner will position the patient optimally, and then pull against the tibia, looking for excessive anterior translation.
The Lachman, pivot shift test and Slocum test are all also relevant.
Born without cruciate ligaments
Some people are born without cruciate ligaments.
This condition is rare.
"....congenital absence of the cruciate ligaments is usually associated with musculoskeletal diseases, in particular incomplete or stunted development of the lower limbs...."
"Congenital absence of the cruciate ligament is a rare condition with a prevalence of 0.017 per 1000 live births."
Forum discussions
- Born without ACL's in both knees?! - A youth soccer coach is astonished to find that some people are born without cruciate ligaments.
- Born without ACL's - A more detailed discussion about the problems people face who are born without ACLs.
- Do I need ACL surgery? - Discussion involving skiers about the merits or otherwise of initially following a conservative route after ACL injury in the hope that stability can be achieved without surgery.
- ACL injury - no reconstructive surgery - Another discussion about making the decision to proceed to reconstructive surgery after ACL injury.