View of ACL from the front of the bended knee. The anterior cruciate ligament is one of the two large ligaments which cross over each other right inside the knee joint notch.
View of the ACL from the side, with the knee cut in half.
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.
Peer-reviewed papersQuote from peer-reviewed paper:
"....The ACL is an important rotational stabilizer of the knee joint...."
Citation: Shom P, Varma AR, Prasad R. The Anterior Cruciate Ligament: Principles of Treatment. Cureus. 2023 Jun 11;15(6):e40269. doi: 10.7759/cureus.40269. PMID: 37448400; PMCID: PMC10336184.
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.
Peer-reviewed papersQuote from peer-reviewed paper:
"....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...."
Citation: Shom P, Varma AR, Prasad R. The Anterior Cruciate Ligament: Principles of Treatment. Cureus. 2023 Jun 11;15(6):e40269. doi: 10.7759/cureus.40269. PMID: 37448400; PMCID: PMC10336184.
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.
Quick linksBorn without cruciate ligaments
Some people are born without cruciate ligaments.
This condition is rare.
Peer-reviewed papersQuote from peer-reviewed paper:
"....congenital absence of the cruciate ligaments is usually associated with musculoskeletal diseases, in particular incomplete or stunted development of the lower limbs...."
Citation: Lu R, Zhu DP, Chen N, Sun H, Li ZH, Cao XW. How should congenital absence of cruciate ligaments be treated? A case report and literature review. World J Clin Cases. 2019 Oct 6;7(19):3082-3089. doi: 10.12998/wjcc.v7.i19.3082. PMID: 31624758; PMCID: PMC6795736.
Quote from peer-reviewed paper:
"Congenital absence of the cruciate ligament is a rare condition with a prevalence of 0.017 per 1000 live births."
Citation: Benassi AB, Guerreiro JPF, de Oliveira Queiroz A, Gasparelli RG, Danieli MV. Anterior and posterior cruciate ligament agenesis. J Surg Case Rep. 2018 Aug 15;2018(8):rjy216. doi: 10.1093/jscr/rjy216. PMID: 30151108; PMCID: PMC6101568.
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.