Acute knee injuries caused by sports - Sports Medicine

More interest in high-risk sports has led to an increase in knee injuries, says Mr Arvind Mohan.

Sporting injuries of the knee are seen more frequently in primary care as lifestyles are changing. There is an enhanced interest in high-risk sports such as football and skiing and biking which have a high risk of sports injuries.

The commonest knee injuries are medial meniscus injury, medial collateral ligament (MCL), anterior cruciate ligament (ACL), lateral meniscus, articular cartilage injury, posterior cruciate ligament (PCL) sprain and patellar dislocation.

History and examination
The history is extremely important in diagnosing knee injuries. The mechanism of injury is crucial in making a clinical diagnosis of the structures involved. Patients should be asked to explain the position of the limb at the time of the injury as this will give a good idea of the structures affected.

Timing of swelling gives information regarding the structures involved in the injury. ACL injuries result in swelling of the knee within the first two hours. Meniscal injuries usually swell after six to 24 hours.

Swelling is more profuse in collateral ligament injuries as opposed to meniscal injuries.

If the patient heard a 'pop' in the knee should alert, a diagnosis of ACL rupture should be suspected until proved otherwise. These patients also have symptoms of 'giving way' or instability in the knee.

Examination is sometimes difficult in a hot swollen knee after an acute injury. The key is to examine every structure in order so that none is missed.

Examination consists of look, feel, move, measure and special tests.

Examination should start with gait assessment followed by inspection for any effusion or wasting of muscles. Joint line tenderness with an effusion is highly suggestive of a meniscal injury. Sometimes, you come across a dislocated meniscus as a result of a large bucket handle tear of the meniscus that dislocates into the intercondylar notch with the knee locked in flexion.

Measurement involves assessing the range of movement of the knee and assessing any limitation of movement. Various special tests used in the assessment of the knee include the patellar tap for effusion, McMurray's test for meniscal injuries, the drawer/Lachmann's/pivot shift test for anterior collateral ligaments and the drawer test for posterior collateral ligaments.

Any acutely swollen injury of the knee should be X-rayed to exclude a fracture. A normal X-ray with a swollen and painful knee could be an indication for an MRI as this will help diagnose any soft tissue injury, ACL, articular cartilage, meniscus or even any oedema of the bone known as 'bone bruising'.

Meniscal injuries
Medial meniscus injuries are more common as they are attached to the MCL making them less mobile. The most common mechanism of injury is the twisting injury. The meniscal tear can vary from simple tears to the more complex bucket handle tears that can leave the knee locked.

The most important sign of a meniscal injury is joint line tenderness and effusion in the joint. The joint line can be palpated with the knee in approximately 45 degrees of flexion. With posterior horn tears patients complain of pain on squatting.

McMurray's test is performed by flexion and external rotation for the medial meniscus and internal rotation for the lateral meniscus. This can be painful to the patient, so do warn them. It is possible to have a torn meniscus with a negative McMurray's test.

Meniscal injuries can be managed conservatively or surgically depending on the symptoms and severity. The spectrum of meniscal injuries varies from simple peripheral tears to the more complex bucket handle tears dislocating into the intercondylar notch.

Effusion of the knee, which appears between 24 and 48 hours after an injury, with minimal effusion and little pain on weight bearing and a history of similar symptoms in the past resolving spontaneously usually implies a type of meniscal injury that can be managed conservatively.

These patients have pain in late flexion on McMurray's test. However, patients with pain in early flexion, with significant effusion, locked knee and a history of severe twisting injury will need a referral.

Physiotherapy is the cornerstone of effective management of meniscal injuries. This consists of a phased rehabilitation protocol. Analgesia can be given in the first few weeks of the injury along with rest.

MCL injuries
MCL injuries usually result from a valgus stress to a partially flexed knee. These can be graded from 1 to 3, with type 1 being a sprain, type 2 a partial rupture and type 3 a complete rupture. Clinically, there is pain on valgus stress to the knee in 30 degrees of flexion. There is opening of medial joint lines in complete ruptures of the ligament. These can be managed conservatively with rest and analgesia followed by a phased physiotherapy rehabilitation protocol. MCLs can be associated with medial meniscal and anterior cruciate ligaments.

Mr Mohan is an orthopaedic surgeon at Southampton General Hospital, Southampton

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