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Everything you need to know about ACL injuries and treatment


The anterior cruciate ligament (ACL) is a ligament in the knee. Sometimes this ligament can tear, especially during sports that involve sudden stops and changes in direction.

Here’s what you need to know about how ACL injuries occur, how they are diagnosed, and what you can expect from treatment and rehabilitation.

What is the ACL?

Three bones make up the knee joint – the femur (thigh bone), the tibia (shin bone), and the patella (kneecap). These bones are connected by ligaments – tough, flexible bands of tissue, which keep the joint stable while a person is moving.

There are four main ligaments in the knee, including the ACL, which helps to connect the femur to the tibia. The ACL helps to keep the knee stable by preventing the tibia from sliding out in front of the femur and providing stability during rotating movements.

The ACL is one of the most commonly injured ligaments of the knee.

How do ACL injuries occur?

ACL injury often occurs in younger people when they make a non-contact, twisting movement. ACL injuries are common in sports such as rugby and netball, where players change direction quickly.

Someone who has injured their ACL will feel pain, be unable to weight bear and in most cases, the knee will become swollen immediately. They may feel a pop or snap as the injury occurs.

If you suspect you’ve injured your ACL, it is vital that you elevate and rest the knee, apply ice and a compress, and take pain medication until you’re able to see your healthcare provider.

Diagnosing an ACL injury

When patients come to me with a potential ACL injury, I first take a detailed medical history before examining the knee. My patients usually arrive with an X-ray of the knee, which is taken to exclude bone fractures. I ask the patient whether they have had previous knee procedures such as an ACL reconstruction, arthroscopy or meniscectomy.

I also ask patients how their current injury occurred, whether it was swollen, and if the knee feels unstable or as though it wants to give way. I assess the patient’s movement, look for instability and swelling, and check for any neurovascular damage.

To determine whether the patient has associated injuries to the meniscus or other ligaments, I send them for an MRI.

Once all of this has been done, I can usually confirm a diagnosis. Patients who are unable to walk properly will be need to use crutches and possibly also a brace.

This article focuses on patients who have a first-time ACL injury without any associated injuries.

Does everyone with a torn ACL need to have surgery?

Most patients under the age of 40 will need an operation to reconstruct the ACL.

Patients who play sports such as rugby, especially on a professional level, usually will need ACL reconstruction surgery. These patients tend to find that without surgery, their knee buckles when they push off or side-step.

In many patients over the age of 40, the ACL can be treated conservatively without the need for surgery. However, these patients may encounter knee problems approximately 10 years after the injured occurred. This is because a healthy ACL prevents translation – the forward movement of the knee. Without a healthy ACL, the meniscus may become damaged and fail.

Pre-operative preparation

Before I can perform ACL reconstruction surgery on a patient, certain criteria need to be met. The patient needs to have what is known as a “quiet knee”. This means the knee should have good range of motion without pain, stiffness, and swelling. To achieve this, patients will need to rest the knee for a few weeks before surgery and pre-operative physiotherapy is vital.

If we do the surgery too soon, the patient may have stiffness in the knee and arthrofibrosis, or scarring.

Pre-operative physiotherapy

Physiotherapist Helene Swanepoel explains what patients can expect from physiotherapy before their ACL reconstruction surgery:

Patients who were physically active at the time of their injury often don’t need to undergo pre-operative physiotherapy. Those who do need to see a physiotherapist will usually do between 2 – 6 weeks of physiotherapy.

Patients who cannot stand or weight bear on the affected leg or have a very swollen or painful knee will have to use crutches until their surgery. If the knee is very unstable, they will also have to wear a brace.

What to expect from ACL reconstruction surgery

During arthroscopic ACL reconstruction surgery, I remove the torn ACL and replace it with a graft. There are two types of grafts that we can use: And autograft involves taking tissue from the patient’s own body and an allograft contains tissue from a donor.

Autograft: In the case of an autograft, we use the patient’s own tendons, harvested from the hamstrings, quadriceps, or the patellar tendon.

In girls, I typically harvest tissue from the hamstrings. Patients who have tissue harvested from the hamstrings will loose about 10% of their explosive power in deep flexion (jumping up from a squat).

In rugby players, I often use tissue from the quadriceps. This is a very strong graft and the patient won’t lose any explosive power.

I try to avoid using tissue from the patellar tendon for grafts as it can cause anterior knee pain (pain at the front of the knee) in the patient.

Allograft: For an allograft, we can use tendons from a cadaver. We try to avoid this as, in South Africa, cadavers are kept frozen, which reduces the quality of the tissues. Alternatively, a parent or relative can donate living tissue – usually from their hamstrings.

The benefit of using tissue from a donor is that, in young patients, they will still have good autograft options if they reinjure their ACL in the future.

Most ACL reconstructions are done as day cases, which means that the patient will arrive early in the morning and leave in the afternoon.

What to expect after surgery

After the operation, patients will experience discomfort which will be managed with medication and icing. Swelling is normal. A physiotherapist will see you straight after the surgery to make sure you are able to walk and climb stairs with crutches before you are discharged.

If you do your rehab properly, your knee should be as good as the other knee. However, you will be at a slightly higher risk of reinjuring the ACL than someone who has never torn their ACL.

Most patients with an ACL injury will need to avoid playing sport for nine months to a year, depending on their individual case. There is a 40% re-rupture rate for those who return to sport sooner than that.

The road to rehabilitation

Physiotherapist Helene Swanepoel describes what post-operative physiotherapy and rehabilitation entails:

Patients will come to me for their first rehabilitation physiotherapy session 10 days to two weeks after their ACL reconstructions. They will have physiotherapy every two weeks for four to six months and I provide exercises which the patient needs to do at home.

The aim of rehabilitation is to get good knee function and get the patient back to the level of activity they were at before surgery. We have to make the knee stable and strengthen all the muscles around the knee.

Initially the patient will still have to ice their knee to reduce inflammation.

From two weeks post-surgery, I will help the patient to fully extend their knee, establish a normal gait, and start strengthening muscles.

From six weeks, I work on balance and proprioception and add weight-bearing to the strengthening exercises.

After nine weeks, a patient progresses to more strenuous rehabilitation.

I also work on strengthening the stomach and hip muscles, as these support the knee.

After doing physiotherapy for four to six months, I refer patients to a biokineticist for further rehabilitation, especially if they play sports.

Patients can expect to use crutches for up to six weeks after their ACL reconstruction.

In my experience, ACL reconstruction surgery is very successful and patients who work hard during the rehabilitation period usually return to their previous level of function.


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