What is the ACL?
The anterior cruciate ligament (ACL) is a dense structure of connective tissue (type I and III collage) located within the knee joint. Simply put, the ACL connects the femur (thigh bone) to the tibia (shin bone). Its proximal attachment point is on the posterior aspect of the medial surface of the lateral femoral condyle (the thigh bone). The ACL then runs anteriorly, medially, and distally to its distal attachment, at the anterior and lateral point of the tibia (shin bone).
The ACL exists to control knee joint kinematics and primarily to resist anterior tibial translation (forwards movement of the shin) and rotation. A secondary function is to also stabilise the knee near full extension.
What causes ACL injury?
Injury to the ACL is most common in sports that involve movements such as high intensity deceleration, cutting and curving, jumping and landing. Some of the most common sports involving ACL injuries are soccer, basketball and American Football.
There are two major types of ACL injury provoking mechanisms:
- Contact (less frequent)
- Non-contact (most frequent)
What are the risk factors for ACL injuries?
Visible features exhibited during ACL injury incidences include:
- Reactive decision making (in response to external stimuli)
- High speed movement (acceleration or deceleration)
- Reduced balance (internally or externally driven)
- Majority weight distribution over standing leg
- Lack of control of centre of mass
- Poor foot and standing leg placement
- Knee valgus and associated hip internal rotation
- Foot pronation
- Pelvic instability
- Lateral and/or rotational trunk sway towards plant leg
Knowing the above, training to improve physical and biomechanical risk factors such as strength, power, coordination and movement skills is key for safe deceleration, cutting, jumping and landing.
How do you check for an ACL injury?
If you think you may have sustained an ACL injury, seeking professional medical advice is crucial! Signs and symptoms of a positive ACL sprain include:
- Pain and on the outside or back of the knee
- Swelling around the knee in the first few hours post-injury
- Limited range of motion in the knee
- Discomfort when weight bearing and walking
However, medical professionals will be able to provide greater confidence on the presence of injury with clinical tests like the “anterior drawer” test, of which the ACL accounts for approximately 85 % of the resistance to laxity. Finally, an MRI scan will provide a specific indication on the extent of the sprain.
What does ACL injury rehabilitation look like?
It is advised that ACL injury rehabilitation is treated on a case-by-case basis, as the individual recovery and progression through such injuries is varied. However, rough guidelines presented within literature and practice can provide medical professionals, coaches and athletes with a suitable framework to work from.
Conservative routes (no surgery) for ACL rehabilitation are followed in some cases, but generally sporting athletes are advised to take surgical intervention, ACL reconstruction (ACLr). During this surgery a graft is taken from either the patella or hamstring tendon, and the time course for returning to competitive sport is 6 to 9 months.
However, in recent years a new reconstruction procedure has been introduced, the Internal Brace. This procedure has been shown to accelerate return times to as short as 5 months.
The ACLR rehabilitation timeline is typically made up from several phases, with progression through each being criteria-based. This means that progression is only made when specific qualitative and quantitative tests are successfully completed and all individuals within the decision making process are satisfied. A brief overview of these sections can be found below:
Pre-ACLR. Pre-op phase – Injury recovery and preparation for surgery
Aim – reduce swelling, restore range of motion and improve physical capacity
Phase 1 – Recovery from surgery
Aim – reduce swelling, restore range of motion and improve quadriceps function
Phase 2 – Strength and neuromuscular control
Aim – regain balance, muscle strength and single leg control
Phase 3 – Running reintroduction
Aim – restore normal gait pattern and improve running volume tolerance
Phase 4 – Multidirectional movement reintroduction
Aim – improve sport-specific biomechanics and technical action capabilities
Phase 5 – Return to training
Aim – increase exposure to competitive sport-specific scenarios and achieve competitive training volume and intensity
Phase 6 – Return to competition and performance
Aim – progressively introduce competitive matches and monitor performance levels
Look out for future articles to follow with greater detail on each phase of the ACLR process!