top of page

Anterior Cruciate Ligaments (ACL) Injuries

One of the most common knee injuries is a sprain or tear to the anterior cruciate ligament (ACL).

Athletes who participate in multi directional sports such as football, rugby, basketball and netball are more at risk of an injury to the ACL.

If you injure your ACL you may require surgery to regain full mobility. However, this is not always essential. This will depend on the severity of the injury to the ACL, as well as the activity levels you wish to return to, and how quickly you want to return to them.

Anatomy of the knee

The knee is formed of 3 bones; the thigh bone (femur), the shin bone (tibia) and the kneecap (patella). The tibia and femur come together to form the hinge of the joint whilst the patella sits in front to both protect the knee and improve the efficiency of the muscles surrounding it.

There are 4 main ligaments within the knee. They act like ropes to hold the bones together and stabilise the knee joint.

Collateral Ligaments

The collateral ligaments are found either side of the knee. The medial collateral ligament (MCL) sits on the inside of the knee. The lateral collateral ligament (LCL) sits on the outside of the knee. These control any sideways movements.

Cruciate Ligaments

The cruciate ligaments are found within the knee. There are two cruciate ligaments, the anterior cruciate ligament (ACL) which sits at the front, and the posterior cruciate ligament (PCL) which sits at the back. These cross over to form an X shape within the joint. These ligaments control any forwards and backwards movement of the tibia and femur.

Levels of injury

All ligament injuries are considered as 'sprains' and are graded depending on the severity.

Grade 1: The ligament is mildly damaged but still intact. It has been slightly overstretched but still able to function and stabilise the knee joint.

Grade 2: The ligament has been stretched to a point where there is a partial tear. The ligament becomes loose and cannot function as effectively.

Grade 3: This is also referred to as a ligament rupture/complete tear. The ligament has completely torn into two pieces and is unable to stabilise the joint.

Partial tears of the ACL ligament are very uncommon. Often the ACL completely tears when injured.

Roughly half of all ACL injuries result in damage to another structure within the knee joint such as the meniscus, articular cartilage or other ligaments of the knee.

What causes ACL injuries?

The ACL can be injured in several different ways:

  • Rapidly changing direction

  • Landing incorrectly from a jump

  • Direct impact or trauma to the knee

  • Suddenly stopping when running


At the time of injuring your ACL you may hear a popping noise and your knee suddenly feeling unstable like it will give way underneath you. You may also experience:

  • Pain/difficulty walking

  • Significant swelling. This often comes up within the first 24 hours of the injury

  • Pain when touching the knee joint

  • Loss of range of movement of the knee

Diagnosing an ACL injury

Physical examination and history taking

When being seen by a physiotherapist or doctor they will initially ask for details surrounding your injury and medical history.

When physically examining your knee they will complete a number of test to not only assess the damage to your ACL, but the other structures within the knee as well.

Further investigations

Further investigations may be required to confirm a diagnosis. These may include:

  • X-rays: These do not show any ligament or muscle injury but are very effective to rule out any bone related trauma.

  • Magnetic resonance imaging (MRI) scan: These provide an in depth image of the soft tissue structures within the knee such as the ACL. An MRI is not essential to diagnose a ruptured ACL.

Treatment options

The treatment approach for an injured ACL will vary depending on the individuals patients needs. For example a young professional athlete looking to return to sport quickly may require surgery. However, a middle aged or elderly person with a sedentary lifestyle may be able to return to their regular activities without surgery.

Non surgical treatment

Although a torn ACL will not heal without surgery it may not be necessary to repair the ruptured ligament. If the rest of the knee is in good health a non surgical approach may be the most effective for you.

Bracing: Initially after the injury you may be required to wear a brace. This will help manage the swelling and pain. You may also be given crutches to assist with walking.

Physiotherapy: After the initial swelling has gone down a careful rehabilitation program can be started to strengthen the muscles surrounding the knee to support it.

Surgical treatment

Most ACL tears cannot be repaired and therefor a graft must be taken from another area of the body and implanted into the knee. This graft will act as a scaffolding for a new ligament to grow on.

Grafts can be taken from various areas of the body:

  • Hamstring graft: The most common graft is the hamstring graft. The hamstring muscles sit at the back of the thigh.

  • Patella graft: A patella tendon graft can also be used. The patella tendon runs from the knee cap to the shin bone in front of the knee

  • Quadriceps graft: This tendon runs from the kneecap into the front thigh muscle.

There are pros and cons to each graft and this should be discussed with your orthopaedic surgeon before the procedure.

The procedure to reconstruct an ACL is done via arthroscopy. This involves very small incisions and is often referred to as keyhole surgery. It is a less invasive form of surgery resulting in less pain afterwards and a quicker recovery.


Whether your treatment was surgical or non surgical rehabilitation is essential to returning to your daily activities.

Initially physiotherapy will focus on restoring range of movement. This will then be followed by exercises to strengthen the muscles surrounding the knee. These exercises gradual progress to expose the ligament to more and more stress.

The final phase of rehabilitation individually tailored to work towards your goals such as returning to sports.

74 views0 comments

Recent Posts

See All


bottom of page