Function of the cruciate ligament
In Germany there are about 100,000 cruciate ligament tears a year, more than 80% of them during sport. Each knee joint has two cruciate ligaments, an anterior and a posterior one. They are ligaments about 4 cm long and up to the thickness of a little finger that cross each other.
The anterior cruciate ligament, which lies behind the kneecap, braces the thigh bone and the shin bone against each other. It cannot be felt from the outside and withstands loads of up to 200 kg. When it works normally, it ensures that the movements between the cartilage surfaces of the knee joint are smooth, and thus prevents premature joint wear.
Causes of injury
A tear of the anterior cruciate ligament is a typical injury and usually happens when the knee is twisted while running. A typical example is skiing, when the ski tip gets stuck in the snow and the lower leg is abruptly stopped relative to the thigh. This usually puts enormous strain on the cruciate ligament, which then gives way. A cracking sound in the knee is often noticed. Swelling (effusion) almost always follows. After an initial painful phase, the patient can often put weight on the injured leg again without pain. This carries a great risk of underestimating the injury and overlooking the tear. In many patients, the diagnosis is therefore only made after many years.
Dangerous sports are therefore all sports with one-on-one situations and contact with opponents. The sport with the most anterior cruciate ligament tears in Germany is football, but only because it is the most widely played sport in Germany. A relatively higher risk exists in alpine skiing, as well as in handball, basketball, judo and wrestling. However, most cruciate ligament tears occur without contact with an opponent. During sudden changes of direction, the forces involved can be enough to tear the anterior cruciate ligament. Grippy sports hall floors, well-gripping soles and modern football studs are a possible additional source of danger.
There is no scientifically sound evidence that specific measures, for example braces or special warm-up exercises, can prevent a cruciate ligament tear. However, well-trained muscles help to stabilise the knee joint. Dangerous sports should therefore only be practised when you are sufficiently fit (think of pre-season ski training!).
Treatments
The consequence of an anterior cruciate ligament tear is instability of the knee, i.e. under load the shin bone and thigh bone can shift considerably against each other. This can, but need not, lead to acute symptoms. A cruciate ligament tear may cause no significant noticeable symptoms for many years and go unrecognised. Nevertheless, there is a risk that increased shear forces in the joint will damage the meniscus or the joint cartilage over time. Even after several years, the knee may then feel unstable or hurt under load. Over time, premature joint wear (osteoarthritis) can develop. To prevent this, an early diagnosis should be made by clinical examination and/or MRI.
Which treatment is best for which patient depends on many details. A patient with an isolated tear of the anterior cruciate ligament (without other injuries), little instability of the knee, aged over 50 and with low sporting demands is the ideal patient for non-surgical treatment.
In contrast, for patients with a complicated injury (for example an associated meniscus injury or cartilage damage), marked instability of the knee, aged under 50 and with high sporting demands, surgery is certainly the better option. Overall, however, the decision must always be made case by case, weighing up the individual aspects.
In general, surgery should only be performed once the swelling of the knee has gone down sufficiently and the joint can move largely freely. If surgery is carried out while the knee is still swollen and movement is clearly restricted, the risk that restricted movement will remain after the operation is considerably higher. During surgery, a tendon is taken from the affected leg and inserted under tension between the shin bone and the thigh bone. During a healing phase of several months, the tendon grows into the bone and gradually turns into a living new cruciate ligament. Rehabilitation takes 10–12 weeks; sporting strain should not be resumed before six months.