Knees

Knee Disorders

The Normal Knee

In order to understand internal injuries of the knee, it is first important to have an overall understanding of the anatomy and function of the knee. The knee functions much like a hinged joint (an opening or closing door) and allows movement in one direction. The knee has little in the way of bony stability and requires largely on the tendons and ligaments and other soft tissue structures around the knee to provide it with strength and support. This is one of the reasons that the knee is one of the most commonly injured joints in sporting injuries.

As can be seen in the diagram, the important structures to be considered within the knee are:-

1. Cruciate ligaments
2. Collateral ligaments
3. Menisci
4. Articular cartilage

Cruciate Ligaments

A normal knee has an anterior and posterior cruciate ligament. These provide stability to the knee and are especially important for the athlete in cutting or turning or stepping manoeuvres. The anterior cruciate ligament comprises about 90 to 95% of sporting ligament injuries. Injuries to the posterior cruciate ligament are much rarer and are not usually the result of isolated sporting activities. Posterior cruciate ligament injuries most commonly incur in motor vehicle accidents. Following an anterior cruciate ligament injury, the athlete may feel a sudden excruciating pain and notice the knee swells markedly over a number of hours. Once the immediate pain an swelling have settled over the first ten to fourteen days, physical examination will usually reveal some laxity (or sloppiness in the knee). Your doctor is often clinically able to tell whether or not the anterior cruciate ligament has been torn or severely stretched, purely from physical examination without radiographs or other investigations. Plain x-rays are usually performed to ensure no fracture has occurred at the same time.

The treatment of cruciate deficient knees usually begins with a physiotherapy and rehabilitation programme. Many patients are able to return to their normal level of sporting activity purely with conservative (all non-operative means). However, a certain percentage of patients will not return to normal function with purely physiotherapy and an exercise programme. If these patients wish to return to their previous level of sporting activity, they may require a cruciate ligament reconstruction.

Collateral ligament injuries

Collateral ligament injuries are usually the result of a solid impact force. They commonly occur in contact sports where the patient's knee is fixed with the foot firmly planted on the ground and the patient is hit from the inside or outside resulting in the knee bending in an abnormal fashion. Most of these injuries can be treated conservatively in a splint or plaster with a physiotherapy progamme post-operatively. However, the more serious injuries may require operative intervention.

Meniscal Injuries

Meniscal tears are one of the most common sporting injuries that occur. The menisci functions as a "washer" in the joint and allows appropriate force transmission within the knee joint that minimises wear and tear effects in the knee. Meniscal tears often present with clicking, catching and recurrent swelling of the knee but in more severe cases the patient may present with a locked knee (an inability to straighten the knee past a certain point without experiencing excruciating pain). Meniscal injuries frequently require surgical treatment and this is usually performed by arthroscopy or keyhole surgery. Arthroscopically the meniscal tear can be trimmed back to remove the unstable fragment of meniscus or in some large tears it may be appropriate to suture the menisci back together. This can be done with the arthroscope as a day procedure.

Articular cartilage injuries

Often with severe direct blows to the knee or severe shear forces that occur in motor vehicle accidents or contact sports, a segment of articular cartilage may be torn from the underling bone to which it is attached. This may result in a loose body within the knee joint or a flap that gives rise to pain. The articular cartilage is a very specialised tissue within the knee as it provides the smooth gliding surface to allow all joints to operate without friction or pain. The articular cartilage is also very special in that if damaged following birth it is never able to repair itself like skin or bone. Thus the loss of articular cartilage from the joint is the first stage of early wear and tear or early osteoarthritis.

How does damage to the knee occur ?

Damage to the knee may occur as a result of acute trauma or as a result of gradual wear and tear process. The acute trauma setting may be something as severe as a motor vehicle accident or fall from a height. It may or may not involve fracture of the bone. More frequently the soft tissues in or around the knee may be injured and this may not be picked up with plain x-rays.

Damage to the knee may also occur as a result of a gradual wear and tear process. This is more akin to the rubber on a car tyre that gradually wears out with repeated use. With the wear and tear process water is lost from the articular cartilage which makes it weaker and more viable. Often a small or minor trauma in a slightly or moderately worn knee can result in a tearing of the menisci or an acute exacerbation of the knee problem. Thus in many cases there is a combination of a minor acute event that exacerbates an underlying wear and tear process.

Sports knee injuries

Sport knee injuries occur in athletes of all ages and grades and in different types of sporting activities. Some different types of sport are associated with higher rates of particular injuries. Of particular note there is a higher incidence of cruciate ligament injuries in netball and meniscal injuries occur in contact sports and meniscal and cruciate ligament injuries occur in contact sports where direct impact on the knee or stepping off a fixed rim occurs frequently.

Probably the most important aspect of treatment of sports related knee injuries is prevention of the injury itself. The frequency of acute sports knee injuries can be significantly decreased by pre-season training and fitness programmes. The use of a sports trainer or physiotherapist to guide you in the appropriate training of your knee and surrounding muscles is extremely important as this strengthens the knee and all the associated ligaments. This will decrease the reliance of the knee on the fixed ligamentous structures and decrease the forces transmitted through the knee resulting in a decreased incidence of significant damage.

Meniscal Tears

As can be seen from the diagram there are two half moon shaped cartilages within the knee called the menisci. The one on the inside of the knee is called the medial meniscus and the one on the outside of the knee is called the lateral meniscus. These menisci may be torn as a result of acute sports injuries or may spontaneously occur in association with wear and tear and age related changes. Ultimately tears are a combination of both of these factors.

Cruciate ligament injuries

As previously stated approximate ninety-five percent of cruciate ligament tears involve the anterior cruciate. Operative reconstruction of the anterior cruciate ligament is often required when conservative means and physiotherapy have failed. The most commonly used techniques of operative reconstruction involve the substitution of the torn cruciate ligament with another equivalent piece of ligament from the knee. Both the patella tendon and hamstring tendons are successfully used in cruciate ligament reconstructions. They both involve the drilling of some tunnels within the proximal tibia and distal femur around the knee joint and anatomically substituting a new tendon for the old or damaged tendon. The new or reconstructed cruciate ligament usually requires one to two metal screws or other fixation devices to hold it in place while the bony and other soft tissue structures heal.