Anterior Cruciate Ligament

 

What is it?

The Anterior Cruciate ligament (ACL) is one of four main knee ligaments. It is situated deep within the knee joint with its partner the Posterior Cruciate ligament (PCL). Ligaments are tough inelastic structures that span from bone to bone across a joint and provide that joint’s inherent stability. Damage to ligaments in the form of a tear or full rupture undermines the joint’s stability and normal function. The ACL connects the underside of the thigh bone (femur) to the top of the shin bone (tibia) and its primary role is to prevent unwanted forward translation of the tibia on the femur.

The key signs that may indicate whether the ACL has been injured are an audible snap or pop together with a feeling that the knee joint has become unstable. It is common for the knee to swell grossly, usually quite quickly and the individual would likely avoid taking any weight through the painful leg. Clinical tests by a Physiotherapist would determine whether the ACL and/or other structures had been damaged. Commonly other knee structures are damaged together with the ACL depending on the mechanism of injury, namely the medial collateral ligament (MCL) and the medial meniscus (cartilage). If the ACL is significantly damaged then it is usual for an onward referral to be made to a knee Orthopaedic Surgeon for further investigations (MRI scan) and perhaps surgical reconstruction.

 

Causes

The ACL can be damaged either through direct contact i.e a force directed into the outside of the knee which folds the knee inwards (imagine being rugby tackled at knee height from the side!) but can commonly be injured in non-contact situations. Changing direction rapidly whilst bending and twisting the knee or landing from a jump and twisting or perhaps over straightening (hyper extending) the knee joint can lead to ACL ruptures.

There are some predisposing anatomical features which may lead to an increased risk of ACL rupture. For example the strength relationship between the front thigh muscles (Quadriceps) and the back thigh muscles (Hamstrings) is important especially in female athletes. Females are said to be eight times more likely to damage their ACL in a non-contact injury as their quadriceps and hamstring strength are less evenly matched compared with males. If a quadriceps contraction is particularly strong, without the correspondingly even contraction of the hamstrings, then the force generated can be significantly greater than that required to cause failure of the ACL tissue. Appropriately, significant emphasis is placed on hamstring rehabilitation following ACL reconstruction surgery.

 

Treatment

Following a thorough examination and assessment of the presenting problem, advice and treatment may include the following:
 

Partial tears of the ACL which do not present with significant rotational instability issues can be managed conservatively (non-operatively).

For more acute injuries early management is focused on the PRICE principles:

• Protection – Strapping and/or knee brace

• Rest – from aggravating activities

• Ice – to reduce swelling and pain

• Compression – to reduce swelling and offer support

• Elevation – to aid swelling reduction

   

Commencement of an active rehabilitation programme as soon as the acute symptoms have settled. Emphasis on proprioception and hamstring strength retraining.

ACL Reconstruction Management:

Adherence to the Surgeon’s post operative protocol which will vary depending on the Surgeon and type of reconstruction performed.

Typical guidelines state:

 

• Early 0-2 weeks – reduce pain, swelling, work on maintaining full leg straightening, gentle leg exercises and normal walking practice in order to dispense with crutches

• 2-6 weeks – Increase knee bending, progress exercises to include closed chain strengthening (foot in contact with the floor), normalize walking pattern

• 6-12 weeks – progression of above exercises, straight leg swimming

• 3-4 months – jogging – progress to running

• 6 months – specific training for contact sports, tennis

• 9 months+ - Contact sports, skiing.