Education And Debate

ABC of Emergency Radiology: THE KNEE

BMJ 1994; 308 doi: (Published 08 January 1994) Cite this as: BMJ 1994;308:121

Most knee injuries are confined to the soft tissues and are invisible in plain radiographs

The exposed position of the knee and its functional demands make it one of the most vulnerablejoints to injury, especially in athletes. In most cases, however, the plain films look normal andclinical examination does not show any disruption of ligaments. This article describes the commo types of bony injury that are found and advises how to assess plain radiographs.

Important anatomical considerations

Fractures of the fibular neck and head may be associated with damage to the common peroneal nerve and collateral ligament complex and may be part of a pronation lateral rotation ankle injury.


The knee is a synovial joint formed by the femoral condyles articulating with the tibial condyles (figs 1 and 2). The patella lies within the quadriceps tendon. The posterior surface of this sesamoid bone has a steep sloping medial articulating facet and a shallower lateral facet for articulation with the femoral condyles.

The arterial blood supply can be compromised in fractures near the adductor canal and popliteal fossa because of impingement of fracture fragments. Tibial and fibular fractures can cause compression of vessels because of haematoma in the leg compartments.

The common peroneal nerve runs close to the neck of the fibula and is prone to injury. Posteriorly, the popliteal artery is closely related to the tibial plateau and may be damaged by fracture fragments or in dislocation of the knee.

There is a complex arrangement of ligaments around the knee including the medial, lateral, and cruciate ligaments. Part of the lateral ligament complex is attached to the fibular head. Injury to any of these complexes causes instability of the knee. The anterior cruciate ligament is attached to the medial tibial spine so avulsion fractures of thisspine or of the base of the intercondylar …

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