Anterior Cruciate Ligament (ACL) Injuries

Anterior Cruciate Ligament (ACL) Injuries

What and where is the ACL?

Your knee is made up of Collateral (Medial and lateral collateral ligaments) and Cruciate (anterior and posterior cruciate) ligaments. The ACL is one of two collateral ligaments in your knee, the other being the posterior collateral ligament.

These two ligaments control the forward and backward movement in your knee. It serves this function due to its position, the two collateral ligaments cross each other in the form of a “X”. The ACL is located diagonally in the middle of knee and attaches to the tibial tuberosity (top of your shin).

ACL Function

  • Its prime purpose is to prevent the tibia from shearing forward during knee flexion.
  • It provides rotational stability.

Mechanisms that Injure the ACL

  • Non – Contact (Chappell, Yu, Kirkendall, Garrett, 2002)
  • Sports that have a high volume of cutting, pivoting (change of direction) with high jumping and landing involvement. Soccer has been reported to have the highest number of incidents reported (Pollard, Sigward, and Powers, 2010).
  • Forced extension of the knee from direct blow.
  • Mechanics of decelerating during landing (Decker, Tony, Wyland, Sterett & Steadman, 2003)
  • Gender differences, females suggested to be more susceptible due to a number of theories in research. Research argues the landing mechanics, joint angles at pelvis and lower extremity, hormonal and anthropometric differences (Anderson et al, 2001) are suggested to make women more likely to injure their ACL.

Types of Tears

Most muscular or ligamentous injuries are graded by orthopedic specialists and medically trained professionals using a Grade 1-3 (severity scale) approach. When the ACL is damaged it usually ruptures nearby structures such as meniscus, articular cartilage or other ligaments, sometimes referred to the unhappy triad (Damaged ACL, MCL, medial meniscus)

Grade 1: Mild ligament tear, slight stretching and microscopic tears of fibres.

Grade 2: Moderate ligament tear, partial tearing

Grade 3: Severe/complete ligament tears.

Signs and Symptoms

  • Audible crack at the time of Injury (hearing a pop or crack)
  • Immediate pain, inability to continue activity
  • Marked swelling within few hours of injury
  • Decreased range of motion at knee – impaired walking and weight bearing
  • Unstable sensation – feeling of giving way.


  1. Immediate care: The aim is to decrease swelling immediately by using cryotherapy (ice) and keeping the leg elevated. This will aid lymphatic drainage and encourage healing properties to the area. Seek medical advice as soon as possible, Imaging in the form of an MRI would be required to ensure correct diagnosis of ACL involvement is present. Anti-inflammatory and painkillers may also be taken to help with pain management.
  2. Conservative treatment (Non-Operative): Your physiotherapist or sports therapist will follow this rough guideline in the management of your ACL injury. During your treatment plan your therapist may suggest that a brace may be beneficial. This is simply another way to stabilise the knee without surgery, there are ACL specific braces that can be worn during sports such as tennis and squash.

Rehabilitation – Key aims (2 weeks – 6 months post surgery)

  • Reduce swelling
  • Restore active range of motion. Knee extension in particular post surgery (Isometric exercises)
  • Correct muscle imbalances. Regain quadricep/hamstring strength safely.
  • Progress from non-weight bearing exercises, to partial and fully weight bearing.
  • Balance and proprioception, varying double/single leg and the surfaces training on.Corrective gait analysis.
  • Plyometric exercises whereby muscles exert maximum force in short intervals of time to increase power.
  • Speed work from linear planes of movement, to cambered runs.
  • Agility from cambered to sudden change of direction/cutting exercises.
  • Sport specific drills, return to play.

3. Surgical treatment: arthroscopic ACL reconstruction. It is important to understand that graft choices and surgery are dependant on a number of factors, age, lifestyle, surgeon to name a few. The damaged ACL will be partially or completely removed and replaced by a graft.

Graft types:

  • Autografts- this is where the surgeon will use other parts of your body to create the new ligament. The most popular choices are using the patella tendon (knee cap) or a hamstring graft (semimembranosus, gracilis tendon).
  • Allografts- is the least common due to success rates, it uses a ligament from a deceased donor

Step by Step Surgery outline:

  • The chosen/graft tendon will be removed and stitched together to make the correct thickness for the new ACL
  • Small tunnels are drilled into the Tibia (top of shin) and Femur (thigh bone).
  • The graft will be pulled through the holes and secured in place close to the original ACL.


Injuring your ACL is fairly common and needs to be managed with care to prevent further damage. Seeking medical advice from a health professional is important to understand the options that you may have. Every individual is different and therefore the care required needs to be tailored to what you need.

If you need any help or advice regarding an ACL injury then please contact the clinic to speak with one of our therapists.

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Reference List:

Anderson, A, F., Dome, D, C., Gautam, S., Awh, M, H. & Rennirt, G, W. (2001). Correlation of
Anthropometric Measurements, Strength, Anterior Cruciate Ligament Size, and Intercondylar Notch Characteristics to Sex Differences in Anterior Cruciate Ligament Tear Rates. The American Journal of Sports Medicine, 29 (1), 58-66.

Chappell, J, D., Yu, B., Kirkendall, D, K. & Garrett, W, E. (2002). A Comparison of Knee Kinetics
between Male and Female Recreational Athletes in Stop-Jump Tasks. The American Journal
of Sports Medicine. 33 (2), 261-267.

Decker, M, J., Torry, M, R., Wyland, D, J., Sterett, W, I. & Steadman, J, R. (2003). Gender differences
in lower extremity kinematics, kinetics and energy absorption during landing. Clinical
Biomechanics, 18(7), 662-669.

Pollard, C, D., Sigward, S, M. & Powers, C, M. (2010). Limited Hip Knee Flexion During Landing is Associated with Increased Frontal Plane Knee Motion and Moments. Clinical Biomechanics.25 (2), 142.

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