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A ligament is a strong band of tissue that connects bone to bone. A ligament becomes sprained when it is over stretched. The anterior cruciate ligament (ACL) is one of the major ligaments inside the knee joint. It attaches from the thigh bone to the shin bone. Along with the posterior cruciate ligament (PCL) it keeps the knee joint stable.

How is the ACL injured?

In addition to keeping the knee joint stable, the ACL prevents the shinbone from sliding forwards beneath the thighbone and can be injured in several ways:

•    Changing direction rapidly
•    Slowing down when running
•    Landing from a jump
•    Direct contact, such as in a football tackle
•    Sudden stop in skiing or running

If the ACL is sprained it can then be described according to the severity of the sprain:

•    grade I sprain: pain with minimal damage to the ligament
•    grade II sprain: more ligament damage and mild looseness of the joint
•    grade III sprain: complete tearing of the ligament and the joint is very loose or unstable.

Symptoms of Anterior Cruciate sprain or tear

When the injury occurs a loud pop may be heard. There will be immediate pain and swelling that gradually increases over several hours. The swelling that occurs is made up of a collection of blood and fluid. Usually there is difficulty walking and pain increases with movement of the knee.

In the case where an ACL has been torn previously and reconstructive surgery has not been done the knee joint may often feel loose during activities that involve twisting of the knee joint.

Diagnosis and treatment

Your physiotherapist will be able to diagnose this condition. If there is a large amount of swelling your doctor may choose to drain this with a needle. X-rays are usually performed to rule out any bony damage and a scan may also be done to see the damage to the ligament as a full tear requires reconstructive surgery. It is also important to remember that in the case of severe sprains often other ligaments and tissues (e.g. nerves, bone and blood vessels) of the knee joint can be damaged.

The immediate treatment of the knee will depend on the severity of ligament damage. Where the ligament is still intact with or without laxity (grade I and II) physiotherapy is recommended. If the ligament is completely torn (grade III) then reconstructive surgery would be performed followed by physiotherapy.
In the management of ACL sprain initial physiotherapy would involve reducing pain and swelling. This may involve the use of electrotherapeutic modalities, ice, rest, wearing of a brace, the use of crutches and gentle massage. Following this treatment would move onto rehabilitation and return to sport. This may involve strengthening of knee stability muscles, stretching and decreasing activity of tight/overactive muscles, proprioceptive (balance) exercises and correction of any abnormal lower limb biomechanics. Your physiotherapist would also guide you in a gradual progression to sport.