Introduction
Anatomy
Cause
Symptoms
Diagnosis
Non-surgical treatment
Surgical treatment
Rehabilitation
Prevention
Knee injuries are a common reason for an orthopaedic visit. Among the injuries of the major ligaments of the knee, the most common is anterior cruciate ligament tear.
The knee joint is the largest joint in our body, and is indispensable for walking and moving. The joint is stabilised by two sets of ligaments – the cruciate ligaments and the collateral ligaments.
Cruciate ligaments are located within the knee joint, connecting the knee to the tibia (shin bone) and the femur (thigh bone). The cruciate ligaments contain many layers of fibre, which help to hold the knee in place whether it is bending (flexing) or straightening (extending). This stabilising function is crucial to the normal movement of the knee.
The term “cruciate” refers to the cross shape of the ligaments. The ligament that lies in the front is called “anterior cruciate ligament”, or ACL. It helps the keep the tibia from sliding too far forward. The ligament that lies in the back is called “posterior cruciate ligament”, or PCL. It helps maintain the position of the tibia below the femur.
ACL injuries can strike anyone, but some individuals are more prone to ACL injury, such as athletes participating in high-demand sports that involve such manoeuvers as cutting, pivoting and sudden turns. Examples are football, basketball, skiing, gymnastics, hockey, wrestling and rugby. An ACL tear most often occurs during sporting activities when an athlete suddenly pivots, causing excessive rotational forces on the ligament. Other mechanisms that can cause an ACL tear include severe trauma and work injuries.
Injuries to the posterior cruciate ligament are not as common. When that occurs, it usually is due to the over-stretching of the ligament when an object forcefully hits the tibia backwards while the knee is bent. This action pushes the tibia back and causes a PCL tear. The other mechanism of injury is hyperflexion of the knee, with the foot held pointing downwards. These movements stress the PCL, and if the force is high enough, a PCL tear will result.
Injuries to the ACL may not present any immediate symptoms at all. But you may hear a loud popping sound and have the sensation that the knee is giving away. Within two to 12 hours, the knee will be swollen and you will experience excruciating pain when trying to stand up and walk.
Injuries to the PCL usually do not cause the knee to be unstable. However, serious injuries would cause the femur to slide back, so that the articulating surfaces of the femur and the tibia grind against each other directly. This could eventually cause arthritis.
Medical history is taken and a thorough examination of the knee is performed for both ACL and PCL injuries. For ACL injury, the physician will test the stability of the knee by exerting pressure from different points. A useful test is the Lachman Test, in which the physician pulls the shin bone forward to see if it moves too far forward. If so, it confirms an ACL tear. An X-ray may be taken to see if there are any associated bone fractures, and an MRI may be ordered to evaluate if there is any damage to the cartilage and ligament. An arthroscopic exam may be performed only under special circumstances.
As for the PCL, a posterior drawer test will be performed. With the patient’s knee bent, the doctor will push the tibia backward. If the PCL is deficient or torn, the tibia will slide too far backwards and indicate an injury. X-rays and MRIs are helpful in clarifying the diagnosis and detecting any other damages. It is common to find other ligament injuries or cartilage damage when a PCL tear is found.
Immediately after you have detected the injury, ice the knee to control the swelling and elevate your knee. Do not try to walk as this would further damage the cartilage in the knee.
Partial rupture of the ACL does not require surgery. Physical therapy combined with stabilising devices to support the knee joint is usually enough to produce satisfactory results.
As for injuries to the PCL, surgeries are usually not needed. Upon completing physical therapy sessions, the patient can return to normal activities and athletes can resume their sporting activities.
If the ACL is completely ruptured, especially in the cases of young athletes and athletes who wish to return to their high-demand sports, a reconstruction surgery is recommended. Surgery can take the form of arthroscopy or open surgery. An incision is made on the patella or the muscles around the knee. A tendon will be selected from within the knee and tied to the tibia and the femur.
If the PCL is seriously injured, so that a part of the femur (thigh bone) has been torn off together with the ligament, then a surgery can restore the original position of the ligament and the bone. The result of this type of surgery is usually satisfactory. As for surgical reconstruction of the PCL, it is technically difficult to perform due to the position of the ligament in the knee. Generally, this type of surgery is reserved for patients who have injured several major knee ligaments or for those who cannot perform their activities because of persistent knee instability.
Rehabilitation for non-surgical treatment:
Non-surgical rehabilitation for a torn ACL typically lasts six to eight weeks. Treatments include electrical stimulation and ice to reduce pain and swelling. Range-of-motion and strengthening exercises of the knee help improve functions gradually. A brace may be used to provide some initial protection.
When the swelling has subsided, the muscles will get back to nearly their full strength and control, and you will no longer have the sensation of the knee giving way. You can then return to your regular sports activities.
Post-surgery rehabilitation:
A progressive rehabilitation programme usually lasts for four to six months after surgery to ensure the best outcome of your ACL reconstruction. A physiotherapist will help you perform quadricep and hamstring muscle exercises and some range-of-motion exercises for the knee.
Adequate warm-up is necessary before participating in any athletic activities and competitions. The limb muscles should undergo a period of stretching and relaxation before performing rigorous movements, as it takes time for joints and muscles to reach their optimal level of performance. As much as possible, avoid unaccustomed impact and motions beyond one’s limit.
Adapted from AAOS patient information pamphlets