Investigation of acute knee injury

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James Teh, consultant musculoskeletal radiologist1,
Gregoris Kambouroglou, consultant trauma surgeon2,
Julia Newton, sports medicine physician3

¹Radiology Department, Nuffield Orthopaedic Centre, Oxford University Hospitals NHS Trust, Oxford OX3 7LD, UK
²Trauma Service, John Radcliffe Hospital, Oxford University Hospitals NHS Trust, Oxford OX3 9DU
³Oxsport, Nuffield Orthopaedic Centre, Oxford University Hospitals NHS Trust, Oxford OX3 7LD

Correspondence to: James Teh jamesteh1{at}googlemail.com

Radiography may be inadequate for evaluating the knee injury; other imaging techniques may be needed, especially magnetic resonance imaging

Learning points

Plain radiographs often show no fractures after acute knee injuries; even serious internal derangements of the knee may be occult on radiographs
The Ottawa rule is recommended for deciding whether to do radiography after knee injuries
Magnetic resonance imaging is the technique of choice for evaluating internal derangement of the knee
Computed tomography has an important role in evaluating fractures shown on radiographs, and for delineating fractures before surgery

A 24 year old man, who was previously fit and well, presented to the emergency department after a footballing injury to his right knee. He had twisted his knee with his foot planted to the ground. He had felt a “pop” at the time of injury and experienced immediate pain and swelling. Clinical examination showed a swollen knee with tenderness over the fibular head. The patient was unable to flex to more than 90° and unable to weight bear. The results of the Lachman test (modified anterior drawer test) and the McMurray test were considered equivocal, but the degree of pain and swelling made examination difficult.

What is the next investigation?

Acute knee injury in adults is one of the most common and clinically challenging musculoskeletal disorders that present to emergency departments and general practitioners. A clear imaging rationale is important so that unnecessary radiography is avoided. Clinicians also need to know when to request further imaging and which modalities are most appropriate.

Initial imaging should be directed at detecting acute knee injuries that need immediate treatment, such as fractures and dislocations. Most soft tissue injuries, including internal derangements of the knee, although potentially disabling, do not usually need emergency treatment.