Anterior Cruciate Ligament (ACL)
What is an ACL?
The Anterior Cruciate Ligament, commonly known as the ACL, is an important ligament of the knee. Along with the posterior cruciate ligament (PCL) the ACL forms a cross (cruciate) between the shin bone (tibia) and to the thigh bone (femur). Together these ligaments provide stability of the knee joint, with the majority of ligamentous support of the knee coming from the ACL.
The ACLs two main roles are:
(A) Prevent the forward translation of the tibia on the femur
(B) Assist with rotational stability of the knee
The rate of ACL injury is highly common in the sporting population. It is often associated with sports that require cutting, pivoting and sudden deceleration such as Australian Rules Football, netball, basketball, soccer, gymnastics, hockey and downward skiing.
There are multiple risk factors that may influence the incidence of an ACL injury, as listed below:
Non-modifiable risk factors:
- Genetics: athletes with an ACL tear are twice as likely to have family history of ACL tears
- Females: There is approximately a x6 times greater incidence of ACL tears in females. This is likely attributed due to anatomical variations, hormonal involvement and neuromuscular deficits.
- Previous ankle or knee injury with residual joint laxity
Modifiable risk factors:
- Muscle strength imbalance (low hamstrings to quadriceps strength ratio)
- Poor neuromuscular control and coordination
- Bio-mechanical factors such as poor hip and ankle control, reduced core strength, reduced ankle range of motion and a deficit in lower limb strength
- Reduced sport specific fitness/conditioning
- In-proper technique and body positioning for sport specific skills
- Environmental conditions: playing surface and wet weather
- Inadequate shoe wear
- Increased Body Max Index (BMI)
Mechanism of injury:
Two thirds of ACLs injuries occur in a non-contact situation, which often involve the athlete landing in knee hyperextension, a side pivoting motion and/or decelerating suddenly. In footage of ACL ruptures, the knee is commonly seen to track inwards compared to the foot (valgus moment) and is accompanied by a knee inwards rotation motion.
During an ACL rupture, an athlete will often describe an audible “pop” or “crack” and a feeling of the knee giving way or instability. The majority of complete ACL tears are often followed by few minutes of severe pain and the sportsperson will be unable to continue their activity. Often the athlete will have a reduced range of knee motion, particularly extension, following the incident.
The best time to exam an ACL tear is within the first hour following the injury, as following the first 24-72 hours, hemarthrosis (bleeding into the joint space) and swelling occurs and may limit the examination findings.
It is important to present for medical assessment as soon as possible following an injury, even if significant swelling has occurred. Your physiotherapist will perform a comprehensive physical examination and perform special tests to diagnose your injury.
It is important to undergo a thorough physiotherapy assessment as other knee injuries such as damage to the meniscus and/or medial and lateral collateral ligaments of the knee may accompany an ACL tear.Often an investigation or imaging may be required to confirm an ACL tear and conversely rule out other injuries. You may be referred by your physiotherapist, doctor or surgeon for knee MRI scan. Occasionally an X-Ray may also be indicated if an avulsion fracture (small component of bone pulled away by ligament) is suspected during the mechanism of injury.
In the acute stage following an ACL tear it is advisable to follow the RICER principal for the first 48-72 hours. This involves Rest, Ice, Compression, Elevation, and a Referral for medical management. In addition to this it is advised you follow the No HARM protocol to further limit bleeding and swelling into the joint: No Heat, Alcohol, Running or Massage.
A torn ACL can be managed in several ways including conservatively, with bracing, or via a surgical reconstruction. The benefits and associated risks of all methods can be discussed with your treating physiotherapist or healthcare professional in order to tailor a treatment plan specific to your presentation and future goals. In short; young, active individuals aiming to return to a pivoting sport or activity are often candidates for ACL reconstruction surgery.
During ACL reconstruction surgery, the torn ACL is replaced with a graft that aims to replicate the normal functions of the ligament. Several graft options may be explored in discussion with your surgeon, most commonly including:
(A) Bone-patella-tendon-bone (BPTB): where part of the middle third of the patella tendon (knee tendon) and a piece of the tibial bone (shin bone) are taken to make the graft
(B) Hamstring tendon graft: where the semitendinosis (hamstring) tendon is bundled and looped (+/- gracilis (groin) tendon) to form the graft
(C) Quadriceps tendon graft (less common)
(D) Taking the above tendons from the uninjured leg
(E) Synthetic grafts such as the LARS ligament graft, however this is rarely utilised in modern practice.
Rehabilitation for a reconstructed or conservatively managed ACL tear should be under the direct supervision of a physiotherapist. This is integral as there is a 6-30% recurrence rate of ACL injury in the years following an ACL tear, and this risk can also affect the opposite knee.
The aims of physiotherapy are to:
(A) Restore knee joint range of motion
(B) Improve knee and lower limb strength
(C) Address poor biomechanics and improved jumping/landing strategies
(D) Skill retraining
(E) Facilitate return to sport or activity
(F) Prevent re-injury rate
At Total Physiocare we treat hundreds of knee injuries and work closely with multiple orthopaedic surgeons in order to accurately diagnose, manage and rehabilitate clients following an acute knee or ACL injury. Call us now to make an appointment!