A 34-year-old builder presents to the emergency department having injured his left knee earlier that afternoon while playing football. He describes being tackled and feeling his knee twist inwards. Immediately after the injury his knee began to swell and he was unable to continue playing. He now has only limited movement of his knee and is unable to walk.
He is otherwise fit and healthy and does not take any regular medication. He has a wife and two children and smokes 20 cigarettes a day. His average alcohol intake is 34 units a week.
The left knee is held in approximately 30° of flexion. It is swollen and there is an obvious effusion. Palpation elicits localized tenderness along the medial tibiofemoral joint line. It is not possible to fully extend the knee either passively or actively. The ligamentous stability of the knee appears normal. Neurovascular examination of the limb is normal.
• What is the likely injury?
• What are the other causes of a haemarthrosis?
• How should this patient be managed?
This man has sustained a meniscal injury. Most knee injuries result in swelling which develops over hours rather than minutes. The history of immediate knee swelling suggests that there is a haemarthrosis. (This can be easily confirmed by aspirating a few millilitres of fluid from the joint using an aseptic no-touch technique).
Causes of a haemarthrosis!
• Anterior cruciate tear: in 75 per cent of cases
• Meniscal tear
• Spontaneous haemarthrosis: haemophilia
It is not uncommon to sustain a simultaneous cruciate and meniscal injury. In practice it is often difficult to assess the ligamentous stability in the acutely injured knee and make a definitive diagnosis on clinical examination alone. However, in this case the findings of a ‘locked’ knee, and the fact there was thought to be no ligamentous deficiency, suggest
an isolated meniscal injury. The classical cause of an acutely ‘locked’ knee is a ‘buckethandle meniscal tear’. This refers to a longitudinal full-thickness tear of the meniscus. The flap which is created can flip into the joint on the other side of the femoral condyle,blocking full extension of the knee.
The blood supply of the meniscus is located at its periphery, the ‘red zone’. The inner ‘white’ portion is avascular. The importance of this relates to the location of any meniscal tear; if confined to the red zone then there is the potential for repair and subsequent healing. In this scenario the patient should be taken to theatre for an arthroscopy. As well as allowing the knee to be ‘unlocked’, it will provide a definitive diagnosis, with the potential to repair the meniscal tear.
• A history of immediate knee swelling suggests a haemarthrosis.
• A locked knee can be caused by a bucket-handle meniscal tear.