10 things you should know about the anterior cruciate ligament

What is it and what does it do?

The anterior cruciate ligament (ACL) is one of the four major stabilisers of the knee, forming the ‘central pivot’ along with the posterior cruciate ligament (PCL).

It is the main anterior stabiliser of the knee, preventing the tibia from sliding forward on the femur, as well as controlling hyperextension and internal rotation.

How do ACL injuries occur?

Although they can occur in various everyday activities, anterior cruciate ligament injuries are usually related to practicing sports: especially those that require pivoting, such as football, basketball, skiing and rugby.

They tend to occur through self-injury, meaning that the individual’s own movement is the only factor involved. ACL injuries can happen when landing from a jump or changing direction, and when performing any movement that involves contraction of the quadriceps, valgus motion, flexion or external rotation.

What are the symptoms of an ACL tear?

In an acute setting, the individual often experiences intense inflammation of the knee or hemarthrosis (accumulation of blood in the knee), accompanied by pain and a limited range of motion.

After this acute process, the pain decreases and the symptoms of ‘failure’ (joint instability) set in when rotating the knee, doing routine movements or carrying out everyday activities. This is the consequence of tearing one of the knee’s major stabilisers.

What are the risks associated with an ACL tear?

After tearing the ACL, the individual may experience episodes of instability or a sensation of ‘knee failure’ (this is how many of our patients describe it). This results in an increased risk of meniscal tears and cartilage damage, which can lead to the development of arthrosis in the long term.

Do all ACL injuries require surgery?

Surgery is necessary in most cases, as it is the only way to normalise the knee’s stability. However, for patients with low physical demands who do not experience episodes of instability during everyday activities, a conservative or non-surgical treatment may be prescribed.

What techniques are used to reconstruct the ACL?

There are various techniques for anterior cruciate ligament reconstruction (ACLR). Today, ‘anatomical’ techniques are used. They have replaced the earlier ‘transtibial’ techniques, which were unable to control the knee’s rotational stability.

What is the best type of graft?

Reconstruction of the anterior cruciate ligament requires the use of a graft, which is selected on a case-by-case basis depending on each patient’s age, height and weight. The choice is also influenced by the type of sport and the frequency and intensity with which it is practiced, as well as certain biomechanical characteristics of the joint.

The most commonly used grafts are:

  • Hamstring tendon: Its main advantage is reduced morbidity in the area from which the graft is taken, and the possibility of its regeneration. It is also aesthetically favourable, since the scar is smaller (approx. 25 mm) and is located on the anterointernal part of the knee. As for disadvantages, the main issue is the time it takes for the tendon to attach to the bone (10-12 weeks).
  • Patellar tendon: The greatest advantage is that the graft attaches faster (4-6 weeks), but in exchange, there can be greater anterior knee pain after surgery. It is also less aesthetically pleasing, since the graft is obtained by making an incision of 5-6 cm on the front part of the knee.
  • Quadriceps tendon: This is similar to the patellar tendon technique. The graft is obtained along with a bone fragment from the superior pole of the patella, but there is no bone fragment on the opposite end. The main advantages are rapid attachment to the femur and less anterior knee pain than is generated by patellar tendon grafting. The disadvantage is that it requires the same amount of time to attach to the tibia as the hamstring tendon does.

These are the main options in the case of primary surgery. Other tendon structures or allografts are usually reserved for revision or multiligamentary surgeries.

Which patients have a greater risk of re-tearing after an ACL reconstruction?

There is sufficient evidence to suggest that some patients have a greater rate of failure or re-tearing after reconstruction of the anterior cruciate ligament. They include:

  • Patients younger than 18
  • Athletes with a high level of pivoting in the knee
  • Hypermobile patients
  • Patients with a high degree of preoperative rotational instability
  • Patients who undergo revision surgeries

For patients who have one or more of these characteristics, anterolateral tenodesis is usually performed in order to reduce residual instability and/or the rate of re-tearing.

When should surgery be performed?

The ideal moment is when the joint is no longer inflamed, mobility has been completely regained and the pain has subsided. To help make this happen, the patient is prescribed a series of rehabilitation guidelines to follow before the operation, such as performing exercises to strengthen muscles or undergoing cryotherapy. Keep in mind that doing a good job before the operation will optimise postoperative results.

What is the postoperative period like, and how long is the recovery time?

The patient tends to remain hospitalised until the day after the surgery. A brace is used to protect the knee for the first two weeks and to help keep it extended at night.

During the first days and weeks, pain control (through cryotherapy and specific medication) and muscle activation (through isometrics exercises) are prioritised. Mobility is progressively regained, adding muscle-building exercises according to each patient’s level of tolerance.

At this stage, it is essential to have a personalised rehabilitation process, which requires a coordinated effort between the surgeon and the physiotherapist.

All patients who undergo ACL surgery should resume practicing sports gradually, following a ‘return to play’ programme in accordance with each patient’s specific athletic activity.

During this part of the process, working together with the rehabilitator is vital in order to carry out a programme that involves functional activities, improvement and correction of athletic movements and muscle strengthening. This will not only allow the patient to achieve a high level of satisfaction when it comes to resuming sports, but also decrease their likelihood of suffering a new injury.