Previous Imaging

For Medical Students

What It Tests

Asking about previous imaging tests what exists, what it showed, and what the patient believes it showed.

The third of those matters most, because the explanation a patient has been given becomes part of their problem and shapes everything they say afterwards. 4.1.3 covers the contamination.

It also tests how old the imaging is, since a knee changes and a scan from three years ago describes a knee that no longer exists.

How It Is Performed

Ask what imaging they have had: radiographs, ultrasound, magnetic resonance, computed tomography, or a scan they cannot name.

Ask when, and whether it was before or after any treatment.

Ask whether the images are available or only the report, because a report is a interpretation and the images can be reviewed.

Ask what they were told, in their words, and listen for the phrase that has stuck.

Take the history before reading the report wherever possible, which is awkward and is the only way to get an uncontaminated account. 4.1.3 covers the principle.

What a Positive Means

A scan showing a finding that matches the history supports the diagnosis.

A scan showing a finding that does not match the history is a finding and not a diagnosis, and degenerate changes in a middle aged knee are the commonest example. 4.9.11 covers it.

A normal scan in a patient with convincing mechanical symptoms does not exclude a cause, and small flap tears and chondral lesions are missable. 4.2.7 covers mechanical symptoms.

Imaging from before a treatment cannot describe the current knee, and this matters most after surgery.

A patient who has been told their knee is worn out carries that sentence into every consultation, and part of this history is finding out what they were told.

MRCS Level

What a Positive Means

The expected reasoning is about base rates. Degenerate meniscal change, cartilage signal change and small effusions are common in asymptomatic middle aged knees, so their presence carries limited weight alone. 4.1.6 covers the point.

In a young knee after a defined injury the base rate is lower and a finding means more.

An old radiograph is still useful for alignment and joint space, and a previous radiograph compared with a current one gives a rate of change that neither gives alone.

Imaging performed at another institution may use different sequences and different reporting conventions, which is a reason to review the images rather than the report.

A report is not the finding. The images can be reviewed and frequently should be.

How Good It Is

This history performs well for establishing what exists and poorly for establishing what it showed, since patients recall conclusions rather than findings.

The date is reliably recalled, which matters because it determines relevance.

The most useful question is what they were told, and it is useful for a reason that is about the consultation rather than the knee.

Comparing serial imaging is among the more useful things available in degenerative disease and depends entirely on knowing that the earlier imaging exists.

FRCS Level

How Good It Is

At decision level the imaging history determines whether anything further is needed, which is a question that should be asked more often.

A patient with recent adequate imaging that answers the clinical question needs no more, and repeating it is a cost without a benefit.

A patient with imaging that does not answer the question, or that predates a relevant change, needs it repeated and the history establishes which.

In planning, the imaging requirement follows from the operation rather than from the diagnosis: an osteotomy needs long leg alignment views, a revision reconstruction needs tunnel assessment, and neither is supplied by a standard scan. 4.20.4 covers osteotomy assessment.

Establishing what the patient has been told is also a planning matter, because the consent conversation has to start from where they are.

Where It Misleads

The commonest error is letting the imaging lead. A consultation that begins with the scan has already lost the uncontaminated history.

The second is accepting a report of a finding as a diagnosis, which this chapter returns to because it is the commonest error in knee practice. 4.1.1 covers it.

The third is repeating imaging because it was done elsewhere rather than because it does not answer the question.

And failing to correct a wrong explanation the patient is carrying, which is a clinical task rather than a courtesy, because that explanation will determine what they expect and therefore whether they are satisfied.

Fellowship Level

Where It Misleads

In referred practice the patient usually arrives with several scans and an explanation built from the most recent one.

The useful task is to establish the sequence of imaging against the sequence of operations and symptoms, which is the timeline 4.2.30 describes, with imaging added to it.

Post-operative imaging is difficult to interpret and a report written without the operative detail is frequently misleading, which is a reason to review images alongside the notes rather than reading reports.

In a painful arthroplasty or a failed reconstruction the imaging that answers the question is frequently not the imaging that has been done, and the history is what identifies the gap. 4.20.9 covers revision assessment.

The most important part of this history at this level is what the patient has been told by each previous clinician, because a referred patient is frequently carrying several incompatible explanations and the consultation has to address that before anything else.

No figure here supports these claims, under decision 023.