Bone Tumours

For Medical Students

What It Shows

A bone tumour around the knee may be benign or malignant, primary or secondary. 5.5.5 covers the tumour protocol.

Imaging shows a lesion's position in the bone, its margin, what it is doing to the cortex, and whether a soft tissue component is present. 5.5.6 covers the bones.

It matters because the knee is a common site for primary bone malignancy in young people, and the presenting complaint is knee pain. 4.2.13 covers night pain.

How It Is Acquired

Start with radiographs, which carry most of the diagnostic information for a bone lesion. 5.3.1 covers the AP view.

Note the lesion's position: epiphysis, metaphysis or diaphysis, and central or eccentric. 5.5.6 covers the bones.

Note the margin: sharp and sclerotic against ill defined and permeative. 5.3.19 covers subchondral sclerosis.

Note the cortex and any periosteal reaction. 5.3.2 covers the lateral view.

Use a tumour protocol magnetic resonance study covering the whole bone where a lesion is suspicious. 5.5.5 covers the tumour protocol.

What Normal Looks Like

Trabecular and cortical bone with no focal lesion. 5.5.6 covers the bones.

Marrow following fat on the T1 weighted images. 5.2.13 covers the T1 imaging.

A sharp sclerotic margin where a benign lesion is present, which is reassuring rather than normal. 5.3.19 covers subchondral sclerosis.

No periosteal reaction and no soft tissue mass. 5.3.2 covers the lateral view.

What Abnormal Looks Like

Marrow replacement on the T1 weighted images rather than marrow oedema. 5.2.13 covers the T1 imaging.

Cortical destruction or expansion. 5.3.2 covers the lateral view.

An aggressive periosteal reaction. 5.3.1 covers the AP view.

A soft tissue mass continuous with the bone lesion. 5.5.11 covers the synovium.

A pathological fracture through an abnormal area. 5.3.11 covers tibial plateau fractures.

MRCS Level

How It Is Acquired

In a viva the expected answer gets the radiograph and then stops.

The expected points are the radiograph first, the position, the margin, the cortex and periosteum, and the whole bone study.

Say that marrow replacement on a T1 weighted sequence is the finding separating this from everything else in the chapter. 5.13.1 covers bone marrow oedema.

Say that a suspicious lesion is referred before any intervention. 5.1.3 covers choosing the correct investigation.

Say that an arthroscopy or a biopsy before referral can change the definitive operation. 5.20.7 covers reporting the post-operative knee.

What Abnormal Looks Like

The reasoning expected is that the imaging features map onto how fast a lesion is growing, so the margin and the periosteal reaction report the biology rather than the histology. 5.5.6 covers the bones.

Replacement of marrow fat is the key discriminator, because every other condition in this chapter leaves fat somewhere in the lesion. 5.2.13 covers the T1 imaging.

Staging needs the whole bone and the chest, which takes the investigation out of the knee entirely. 5.5.5 covers the tumour protocol.

A biopsy tract becomes part of the resection, which is why the biopsy belongs to the team that will operate. 5.1.3 covers choosing the correct investigation.

How Good It Is

Radiography with magnetic resonance imaging is the best available assessment of a bone lesion and is a referral tool rather than a diagnostic endpoint in a knee clinic.

Its best contribution is identifying a lesion as suspicious, which is all a knee specialist needs from it. 5.3.1 covers the AP view.

It is limited because the diagnosis is histological, the staging is systemic, and the features a knee specialist sees least often are the ones that matter. 5.1.7 covers evidence-based imaging.

No figures appear for accuracy on this page, under decision 028, and no lesion sizes or staging thresholds appear either: those are published quantities from particular systems and this environment cannot check them.

FRCS Level

How Good It Is

At decision level there is one decision, whether to refer, and the imaging exists to make it. 5.1.3 covers choosing the correct investigation.

An aggressive margin, cortical destruction, a soft tissue mass or marrow replacement each answers it alone. 5.5.6 covers the bones.

A benign lesion with a sharp sclerotic margin at a typical site can be left, and that judgement is made with the radiograph in front of you. 5.3.19 covers subchondral sclerosis.

Any planned knee operation stops until the lesion is explained. 5.20.8 covers common reporting errors.

The imaging has to be complete before any intervention, because an operation changes everything after it. 5.20.7 covers reporting the post-operative knee.

Where It Misleads

The commonest error is reading a malignant lesion as a stress injury, since both give marrow change and pain in a young athlete. 5.13.2 covers stress reactions.

Marrow replacement is reported as marrow oedema. 5.13.1 covers bone marrow oedema.

A pathological fracture is reported as a stress fracture. 5.13.3 covers stress fractures.

A soft tissue mass is reported as a bursa or a cyst. 5.5.11 covers the synovium.

A lesion is biopsied or arthroscoped by the team that found it. 5.1.3 covers choosing the correct investigation.

Fellowship Level

Where It Misleads

At fellowship level these present as a knee that was treated for something else first. 5.20.7 covers reporting the post-operative knee.

A previous arthroscopy or biopsy has contaminated the compartments, which changes the resection and the prognosis. 5.1.3 covers choosing the correct investigation.

The prior imaging is the only record of the untouched anatomy and has to be obtained rather than repeated. 5.20.1 covers structured reporting.

Night pain, rest pain and a short history outweigh any reassuring imaging feature, and the history is the part referrals omit. 4.2.13 covers night pain.

Automated detection is trained on datasets where these lesions are rare, so a negative output carries little weight. 5.18.8 covers artificial intelligence in imaging.

The honest position is that a knee specialist's job here is recognition and referral, and that every page in this chapter exists partly so this one is not missed. 5.13.1 covers bone marrow oedema.