The Cruciate Ligaments of the Knee: Your Questions Answered

Most of us only hear about the cruciate ligaments (ACL and PCL) of the knee when we injure them. But why do we need them? What happens in case of injury? Beijing United Family Hospital (BJU) Orthopedic Sports Medicine Specialist Prof. Thomas Nau explains.

What is the function of the cruciate ligaments (ACL and PCL) and why do we have them?

The cruciate ligaments are the central stabilizing structures of the knee joint. We have an anterior cruciate ligament (ACL), which is more commonly injured, and a posterior cruciate ligament (PCL). These two ligaments are positioned in the center of our knee joint and cross over each other. This cross structure is what gives cruciate ligaments their names (‘crux’ is the Latin word for ‘cross’). The ACL is the main stabilizer against forward-directed forces, but it also plays an important role in controlling rotational movements. In contrast, the PCL provides stability in the posterior direction (backward), but it also has a similar function when it comes to controlling rotational forces.

What are the most common ways that people injure their cruciate ligaments?

Injuries to the cruciate ligaments are usually caused by sports with sudden stops and/or changes in direction (so-called high-pivoting sports, such as skiing, football, basketball, tennis, etc.). Many people report feeling a pop in their knee. The knee may swell and feel unstable, although these symptoms vary from case to case. Symptoms may occur immediately after the injury or a few hours later. In any case, a swollen knee after injury is always a warning sign and should be seen by an orthopedic specialist.   

If I injure my ACL, will I definitely need surgery?

We know today that a completely torn ACL does not heal by itself, making this ligament considerably different compared to other ligaments. A direct repair by suturing the torn ends of the ligament together also does not lead to reasonably good results and usually fails. Therefore, the current gold standard in the treatment of a torn ACL is surgical reconstruction, in which some tendon material from your own body is used to reconstruct a new ligament. The tendons usually are taken from the back (hamstrings) or the front (patellar or quadriceps tendon) of your thigh. This procedure is routinely done in a minimally invasive fashion.

When should I have this procedure? Does it need to be done right away or can I plan and do it later?

In principle, both ways are an option. Ideally, I like to operate within the first week of the injury, especially in cases with accompanying injuries. We always do a magnetic resonance imaging (MRI) study of the injured knee first, in order to see the full extent of all injuries and to be able to plan the surgical procedure better. In case an early surgery is not possible, we start with physiotherapy and schedule the procedure at a later time. Sometimes, patients have their ACL  reconstruction months or even years after the initial injury. 

If I can wait to have this surgery done later, does it really need to be done at all? I have heard that some people live without an ACL!

If you decide that you do not want your ACL reconstructed, other structures around the knee joint, mainly muscles, will take over the function of the ACL temporarily. Nobody can predict if or how long this will work, as this usually takes a very individual course. If you continue to be active and do all sorts of sports, then sooner or later you will experience episodes of instability (so-called giving-way attacks). These attacks are uncomfortable and painful and may sometimes result in permanent injuries and damage to other structures of the knee (cartilage, meniscus, etc.). Thus, for active patients, regardless of their age, I usually recommend surgical reconstruction.

What is the rehabilitation process like? When can I go back to my sport?

An ACL reconstruction can be done as a day case or with a short in-hospital stay (one to three days). I usually prescribe a temporary brace for two to three weeks and allow immediate mobilization with full weight-bearing. The right physiotherapy is crucial and starts directly after the surgery. I am in constant contact with the therapist and we try to create a rehab program that is as individual as possible. As a landmark, after six weeks, my patients usually start to use a bike and begin controlled strengthening training. So-called high-pivoting sports, such as skiing or football, are strictly forbidden for six months, as the newly reconstructed ligament needs this time to become fully biologically incorporated into the knee joint.

Prof. Thomas Nau is a Consultant Orthopedic Surgeon and Sports Medicine Specialist at Beijing United Family Hospital. He has more than 20 years of experience in treating sports injuries. To make an appointment with him, please call the BJU Service Center at 4008-919191. 

• Want to hear more from Prof. Nau? Read his tips for skiing safely. 

• Looking to sneak more physical activity into your daily life? Learn some life hacks here. 

• Want to pick up a new sport? Know what the common injuries are and how to avoid them!