ACL tear (anterior cruciate ligament): diagnosis, surgery and rehabilitation

An NHS physiotherapy leaflet describes the ACL as a tough band of tissue running diagonally within the knee. It helps prevent forward movement and twisting of the shin bone on the thigh bone and, with the muscles, provides most of the knee's stability. It also gives the brain information about knee movement and balance, a sense called proprioception. An ACL injury can be a full tear (rupture) or a partial tear or sprain.

A North Tees and Hartlepool NHS Foundation Trust leaflet says ACL injuries occur most commonly during sports or activities involving twisting, sudden deceleration or landing from heights, and can also happen in a contact injury if the knee is twisted by an opponent. It adds that you can rupture your ACL outside sport by severely twisting or landing awkwardly. A leaflet from East Kent Hospitals University NHS Foundation Trust describes a sudden stop, change of direction or bump from another player as typical, followed by a swollen, painful knee that may later feel unstable or give way.

When the ligament tears there is usually bleeding into the knee, and swelling may be immediate or develop after a few hours. Other structures are often hurt at the same time: the East Kent leaflet lists meniscal tears, collateral ligament injuries and cartilage damage, and notes that meniscal tears can cause pain, swelling, locking and clicking.

According to the East Kent leaflet, a surgeon or knee specialist takes the history of the injury, examines the knee and arranges scans. Most people have an X-ray at the time of injury, but the diagnosis is confirmed with an MRI scan, which is usually organised by a surgeon or knee specialist rather than the emergency department. The specialist then explains any associated injuries and the next steps.

If you injure a knee and it swells quickly, you cannot put weight on it, it looks misshapen, or it is numb or tingling, seek urgent help. The NHS advises calling 999 or going to A&E if you heard a crack, or if the limb changes shape or the skin changes colour, because a bone may be broken.

The North Tees leaflet recommends the POLICE principles: protection (you may be offered a knee brace), optimal loading (you may be given crutches), ice, compression and elevation. It says these should allow you to regain almost full movement and walk normally, which it calls a quiet knee, before a physiotherapist progresses rehabilitation. The East Kent leaflet says that unless a specialist tells you otherwise you can walk fully weight-bearing and begin gentle exercises, using pain relief or a knee support if needed.

The East Kent leaflet says the body cannot repair a fully ruptured ACL, but not everyone needs reconstruction: some people do not have a knee that keeps giving way, some are happy to change activities, and some have not damaged other structures. The North Tees leaflet notes that a partial tear has a chance of healing, that a complete tear has less chance, and that new evidence suggests some complete tears may heal.

The North Tees leaflet lists the factors considered when deciding on surgery: age, wish to return to sport involving jumping, pivoting or fast deceleration, occupation (it gives firefighting as an example), how unstable the knee is and whether other repairs are needed. It also says surgery may not be offered if it appears someone is not committed to the demands of rehabilitation. If non-surgical treatment does not work you can have surgery later, though the East Kent leaflet warns that continued instability could lead to early osteoarthritis.

The East Kent leaflet describes ACL reconstruction as a keyhole procedure, usually a day case under general anaesthetic. Because only a small number of ligaments are suitable for repair, most operations rebuild the ligament using a graft: a tendon from the person (autograft), from the hamstring or the patella tendon, or from a donor (allograft). The graft is threaded through the shin bone and thigh bone and fixed with screws or a button.

Both leaflets stress rehabilitation. East Kent says physiotherapy is needed whether or not you have surgery and advises doing it before surgery too: the stronger you are going in, the stronger you will be afterwards. Early goals are regaining full range of movement, walking without a limp, and rebuilding strength and balance. The leaflet suggests that mild exercise discomfort up to 4 out of 10 is acceptable but that increased pain or swelling means easing off.

Recovery time depends on age, other knee damage, bracing, complications and how consistently you rehabilitate. East Kent advises not fully returning to sport until at least 12 months after surgery and says outcomes are better when return is delayed beyond 12 months. North Tees says that for sports involving pivoting or jumping, rehabilitation is likely to take at least a year, and that no test can say you are absolutely safe to return, so it is important to have the go-ahead from your rehabilitation specialist. Surgery also raises the risk of deep vein thrombosis, and teams assess this and may use medicines or compression stockings.

On the NHS an ACL injury is usually seen in a fracture clinic or by an orthopaedic or knee specialist, who refers you for physiotherapy whether or not you have surgery. Private orthopaedic and sports medicine services can arrange MRI and surgery more quickly. Ask who will supervise your rehabilitation, what the plan is if you choose not to operate, and how return-to-sport decisions will be made.