Revision ACL Imaging

For Medical Students

What It Shows

A revision study is done to plan a second reconstruction, so it describes the existing tunnels, the existing hardware and everything that might have caused the failure. 5.7.11 covers graft failure.

It covers more than the graft: the tunnels, the menisci, the cartilage, the collaterals, the corners and the alignment. 5.10.3 covers posterolateral corner injuries.

It matters because a revision fails for the same reasons a primary does, and the study is where those reasons are found before the operation rather than after. 6.8.1 covers graft failure.

How It Is Acquired

Establish the previous operations and the hardware in place, because the study cannot be planned without them. 5.17.1 covers post-operative cruciate reconstruction.

Use a protocol that accommodates metal, since hardware artefact sits over the tunnels. 5.5.3 covers the post-operative protocol.

Assess tunnel position and width, which decide whether the revision can be single stage. 5.7.12 covers tunnel assessment.

Assess the menisci and cartilage, because their state limits what a revision can achieve. 5.6.11 covers meniscal extrusion.

Obtain the alignment and slope from radiographs, which the magnetic resonance study cannot supply. 5.3.6 covers long leg alignment films.

What Abnormal Looks Like

Tunnels wider than their apertures, which is widening and affects the plan. 5.7.12 covers tunnel assessment.

Tunnels positioned where the new tunnel needs to go, which is the convergence problem. 6.8.2 covers tunnel malposition.

Meniscal loss, extrusion and cartilage loss in the compartments. 5.6.11 covers meniscal extrusion.

Injury or laxity in the collaterals and corners, which is a cause of failure rather than an incidental finding. 5.10.3 covers posterolateral corner injuries.

MRCS Level

How It Is Acquired

In a viva this is the study where the expected answer lists what the surgeon needs rather than what the scanner shows.

The expected points are the previous operations, the metal protocol, tunnel position and width, the compartments, and the alignment radiographs.

Say that you would ask for computed tomography for the tunnels. 5.16.8 covers three dimensional reconstructions.

Say that the secondary restraints are assessed as causes of failure. 5.10.3 covers posterolateral corner injuries.

Say that the tibial slope needs a lateral radiograph. 5.3.2 covers the lateral view.

What Abnormal Looks Like

The reasoning expected is that a revision has to put a graft somewhere the bone will hold it, so the existing tunnels are an obstacle with a geometry that must be known in advance. 5.7.12 covers tunnel assessment.

Converging or widened tunnels mean the new tunnel has no sound bone, which is why a staged bone graft exists as an option. 6.8.2 covers tunnel malposition.

An unaddressed secondary restraint or an abnormal slope reproduces the loading that failed the first graft, so correcting the cruciate alone repeats the experiment. 3.7.3 covers the secondary restraints.

Compartment state sets the ceiling on what the revision can deliver, which is a conversation with the patient rather than a technical point. 5.11.2 covers chondral defects.

How Good It Is

Magnetic resonance imaging supplies the soft tissue half of the revision plan and computed tomography supplies the bone half.

Its best contribution is the menisci, the cartilage and the secondary restraints, which are what no other study shows. 5.6.11 covers meniscal extrusion.

It is limited by hardware artefact over the tunnels, and by tunnel geometry being answered better elsewhere. 5.2.19 covers artefacts.

No figures appear for accuracy on this page, under decision 028, and no tunnel width threshold appears either, because the thresholds that separate single stage from staged revision are published quantities this environment cannot check.

FRCS Level

How Good It Is

At decision level the revision study decides the number of operations as well as the operation.

Widened or converging tunnels make the revision staged, and that is settled before the patient is listed rather than in theatre. 6.8.2 covers tunnel malposition.

An abnormal tibial slope or a varus limb makes the alignment part of the plan, and no cruciate revision alone addresses it. 5.3.7 covers the mechanical axis.

An unaddressed corner makes the revision a combined procedure. 5.10.3 covers posterolateral corner injuries.

Established compartment degeneration changes the conversation from a revision to what the knee can be expected to do. 5.3.16 covers Kellgren-Lawrence grading.

Where It Misleads

The commonest error is reading the study as a graft study, so the causes of failure go unreported. 5.7.11 covers graft failure.

Tunnel width is judged through hardware artefact instead of on computed tomography. 5.16.8 covers three dimensional reconstructions.

The slope and the alignment are not requested, so two recognised causes of failure are absent from the assessment. 5.3.2 covers the lateral view.

The corners are not examined, and a combined injury is revised as an isolated one. 5.10.3 covers posterolateral corner injuries.

The compartment state is noted without being connected to what the revision can achieve. 5.11.2 covers chondral defects.

Fellowship Level

Where It Misleads

At fellowship level the revision study is the point at which this chapter's argument becomes a practical failure rather than an academic one.

The information the surgeon needs is spread across three studies, magnetic resonance, computed tomography and standing radiographs, and no convention requires all three before a revision is planned. 5.16.8 covers three dimensional reconstructions.

The thresholds that decide staged against single stage revision come from small series with different measurement methods, so the decision is made on judgement dressed as a measurement. 5.21.2 covers the cruciate imaging literature.

Rotational laxity is the commonest failure mode and the least imaged, so the cause of the first failure is frequently unmeasured when the second operation is planned. 3.7.7 covers rotational stability.

Tibial slope's contribution to repeated failure is increasingly accepted and the lateral radiograph that measures it is still not routine with a revision work up. 5.3.2 covers the lateral view.

The honest summary is that revision planning asks more of imaging than any other decision in this chapter and receives the least organised answer. 5.20.1 covers structured reporting.