Anterior Cruciate Ligament (ACL) Tear

The anterior cruciate ligament: location and anatomy

The anterior cruciate ligament plays a particularly important role in the stability of the knee. The knee joint is one of the most complex in the human body and involves three bones: the femur, the tibia and the patella.

There are four main ligaments in the knee:

• Medial collateral ligament – Located on the inner side of the knee, its role is to stabilise the joint along the inner, medial portion of the knee.
• Lateral collateral ligament – Located on the outer side of the knee, its role is to control outward lateral movement at the knee.
• Posterior cruciate ligament – Located inside the joint, it crosses the anterior cruciate ligament in the shape of an X and controls the posterior stability of the knee.
• Anterior cruciate ligament – Controls the anterior stability of the knee. This ligament runs diagonally through the centre of the knee, and its role is to prevent the tibia from sliding forwards and to provide rotational stability.

Anterior cruciate ligament tear: general information

An anterior cruciate ligament tear is, along with ligament sprains, one of the most common knee injuries. It may be complete or partial – the latter when one of the two bundles tears (the anteromedial or the posterolateral bundle).

Most anterior cruciate ligament tears are complete and occur together with injuries to other structures in the knee: the meniscus, the articular cartilage, or other ligaments.

Causes and risk factors for an anterior cruciate ligament tear

The anterior cruciate ligament can tear in a number of situations:

• Rapid changes of direction
• Sudden stops and deceleration while running
• Landing incorrectly from a jump
• Direct contact or impact, such as a tackle in American football or rugby

Anterior cruciate ligament injuries are common in performance athletes and in very active people who play sport frequently. Skiers, rugby players and athletes in jumping disciplines are generally more susceptible to an anterior cruciate ligament tear of the knee.

Symptoms of an anterior cruciate ligament tear

When an anterior cruciate ligament tear occurs, the patient feels the knee shift. The tear is also accompanied by a characteristic sound, like a pop. After that moment, the following symptoms appear:

• Pain and swelling. Within the first 24 hours the knee swells. The swelling and pain may subside abruptly at some point, but that does not mean the problem has resolved.
• When the patient resumes sporting activity, the knee will most likely be unstable and they will feel it shift during activity.
• Reduced range of motion in the knee joint.
• Discomfort when walking.

It has been shown that any patient with an untreated anterior cruciate ligament tear and meniscus tear develops knee osteoarthritis within 10 years.

Diagnosis and investigations

The diagnosis is made by the orthopaedic surgeon following specific examinations:

• Consultation – physical examination and medical history
• Knee X-ray (front and lateral views)
• Magnetic resonance imaging (MRI)

Treatment of an anterior cruciate ligament tear of the knee

Treatment for a torn anterior cruciate ligament varies according to the patient's needs and is individualised. A young patient needs ligament reconstruction surgery. Less active patients, usually older, can resume their lifestyle without surgery.

Surgical treatment

This is the only ligament that does not heal through immobilisation, so surgery is sometimes essential. The orthopaedic surgeon replaces the torn ligament with a tissue graft. The graft can be obtained from several sources:

• Autografts – the semitendinosus and gracilis tendons, the quadriceps tendon or the patellar tendon can be used.
• An artificial ligament of the LARS type (Ligament Advanced Reinforcement System)
• Allograft – a transplant from clinically deceased donors

Ligament reconstruction surgery is performed arthroscopically, through small incisions. The benefits include reduced pain, a shorter hospital stay and faster recovery.

Conservative (non-surgical) treatment

A completely torn anterior cruciate ligament will not heal without surgery, but that does not mean surgery is mandatory. Conservative treatment is suitable for older or sedentary patients. If the other structures of the knee are intact, the doctor may recommend simple, non-surgical treatment options, including:

• Wearing a brace – the doctor may recommend a brace to stabilise the knee.
• Physiotherapy (kinesiotherapy) – as the swelling subsides, the patient begins a rehabilitation programme of specific exercises aimed at strengthening the muscles.
• Physical therapy – several types are beneficial for patients with a ligament tear: ultrasound therapy, electrotherapy, magnetotherapy and others.

Postoperative recovery

The patient is discharged the following day and can resume sporting activity after roughly five months, depending on how recovery progresses. Stitches are removed about two weeks after surgery, at which point patients can return to office work.

Return to sport takes place approximately 5 months after surgery. Performance athletes are a distinct category of patient and, because of the intensive effort they put into rehabilitation, they return to sport sooner.

The concept of a safe return to sport involves carrying out a number of tests and measurements. When the operated leg demonstrates 90% of the capacity of the healthy leg, the patient can be considered to be returning to sport safely.