Revision Arthroplasty

For Medical Students

What It Shows

Post-operative imaging of a revision arthroplasty shows the components, the bone that remains, and the interfaces between them. 5.16.6 covers arthroplasty planning.

Radiographs, computed tomography and magnetic resonance imaging each contribute, and each is degraded by metal. 5.2.19 covers the artefacts.

It matters because the revision's difficulty is set by the bone that remains, which the imaging measures imperfectly. 5.5.6 covers the bones.

How It Is Acquired

Obtain radiographs in consistent projections and a standing alignment film. 5.3.6 covers the long leg alignment films.

Use computed tomography for bone loss, component position and any previous osteotomy. 5.16.8 covers the 3D reconstructions.

Accept that artefact is worst at the bone implant interface. 5.2.19 covers the artefacts.

Aspirate the joint, because infection decides whether the revision is one stage or two. 5.4.17 covers the aspiration.

Assess the extensor mechanism, which decides what the knee can do afterwards. 5.3.12 covers patellar fractures.

What Normal Looks Like

Components in position with no interface change over serial films. 5.3.19 covers subchondral sclerosis.

Bone stock adequate on both sides with no contained defect. 5.5.6 covers the bones.

Alignment appropriate to the implant in place. 5.3.7 covers the mechanical axis.

An intact extensor mechanism. 5.3.3 covers the skyline view.

What Abnormal Looks Like

Bone loss, contained or uncontained, which decides the reconstruction. 5.5.6 covers the bones.

Progressive lucency or component migration. 5.3.19 covers subchondral sclerosis.

Osteolysis extending away from the interface. 5.16.1 covers the fracture assessment.

A periprosthetic fracture, which changes the construct needed. 5.16.1 covers the fracture assessment.

Extensor disruption, which changes what any revision can achieve. 5.3.12 covers patellar fractures.

MRCS Level

How It Is Acquired

In a viva the expected answer names bone stock and infection.

The expected points are the consistent radiographs, the standing film, computed tomography for bone, the aspirate, and the extensor mechanism.

Say that the two deciding questions are bone and infection. 5.14.7 covers septic arthritis.

Say that imaging understates bone loss, because artefact hides the interface. 5.2.19 covers the artefacts.

Say that the examination reports the extensor mechanism and the stability. 4.20.9 covers the revision knee surgery examination.

What Abnormal Looks Like

The reasoning expected is that a revision reconstructs what is missing, so the plan depends on a quantity imaging measures least well, which is why the surgeon plans for more loss than the images show. 5.5.6 covers the bones.

Classification systems for bone loss were defined on radiographs, and a computed tomography study reclassifies them upward. 5.16.8 covers the 3D reconstructions.

Infection changes the whole operation and is a laboratory diagnosis, so no imaging finding substitutes for the aspirate. 5.4.17 covers the aspiration.

The extensor mechanism is the one structure whose loss cannot be reconstructed well, which makes it the most consequential soft tissue finding. 5.3.12 covers patellar fractures.

How Good It Is

Imaging is the best available assessment of a knee for revision and systematically understates the bone loss the surgeon will meet.

Its best contribution is the component position, the alignment and the pattern of loss. 5.3.6 covers the long leg alignment films.

It is limited by artefact at the interface, by classification systems that shift with the modality, and by being no test for infection. 5.14.7 covers septic arthritis.

No figures appear for accuracy on this page, under decision 028, and no defect classifications, bone loss volumes or survival figures appear either: those are published quantities from particular systems and this environment cannot check them.

FRCS Level

How Good It Is

At decision level the imaging decides the implant, the constraint and whether the revision is staged. 5.16.6 covers arthroplasty planning.

Bone loss decides the fixation and whether augments or a hinge are needed. 5.5.6 covers the bones.

Alignment and the limb's overall geometry decide the reconstruction's target. 5.3.7 covers the mechanical axis.

Infection decides the staging, and the imaging contributes nothing to it. 5.4.17 covers the aspiration.

A previous osteotomy or a retained implant elsewhere in the limb belongs in the plan. 5.17.4 covers the osteotomy.

Where It Misleads

The commonest error is planning from the imaging's estimate of bone loss. 5.5.6 covers the bones.

Artefact at the interface is read as loosening or as intact fixation, in either direction. 5.2.19 covers the artefacts.

A normal looking scan is read as excluding infection. 5.14.7 covers septic arthritis.

Osteolysis is read as a fracture, or a fracture as osteolysis. 5.16.1 covers the fracture assessment.

The extensor mechanism is omitted from the report. 5.3.12 covers patellar fractures.

Fellowship Level

Where It Misleads

At fellowship level the knee has been revised before and the records are partial. 5.20.7 covers reporting the post-operative knee.

Identifying the components from the images is often necessary and is unreliable, which makes obtaining the records part of the imaging task. 5.20.1 covers structured reporting.

Serial films across departments in different projections compare radiography rather than the implant. 5.3.1 covers the AP view.

Metabolic imaging is proposed for the infection question and cannot answer it, which is worth stating to referrers. 5.18.7 covers the PET-MRI.

Imaging after a staged revision has no agreed expected appearance at any interval. 5.5.3 covers the post-operative protocol.

The honest position is that this page's imaging supports a plan whose two deciding facts come from the operating theatre and the laboratory. 5.4.17 covers the aspiration.