ACI Imaging

For Medical Students

What It Shows

Autologous chondrocyte implantation seeds cultured cells into a defect under a cover, and the tissue they form matures over a long period. 5.11.8 covers cartilage repair procedures.

Imaging shows the fill, the surface, the repair tissue's signal and the bone beneath. 5.11.2 covers chondral defects.

It matters because the repair tissue starts unlike cartilage and becomes more like it over years, so the early appearance is expected to look poor. 5.11.10 covers MACI imaging.

How It Is Acquired

Establish the date of surgery, because the expected appearance changes over a timescale of years. 5.17.5 covers post-operative cartilage procedures.

Use a cartilage sensitive sequence and the same one at each follow up. 5.2.18 covers gradient echo imaging.

Assess the fill relative to the surrounding cartilage, including whether the repair is raised above it. 5.11.2 covers chondral defects.

Assess the repair tissue signal and expect it to differ from native cartilage. 5.11.1 covers normal cartilage.

Assess the subchondral bone, where overgrowth and marrow change both occur. 5.11.7 covers bone marrow lesions.

What Normal Looks Like

A filled defect with a surface roughly level with the surrounding cartilage. 5.11.2 covers chondral defects.

Repair tissue of signal unlike native cartilage, changing across successive studies. 5.11.1 covers normal cartilage.

Some subchondral marrow signal, expected in the early years. 5.11.7 covers bone marrow lesions.

A gradual trend towards a more cartilage like appearance. 5.11.8 covers cartilage repair procedures.

MRCS Level

How It Is Acquired

In a viva the expected answer names the maturation timescale before describing any appearance.

The expected points are the date, the consistent sequence, the fill and its level, the tissue signal, and the subchondral bone.

Say that the repair matures over years. 5.11.8 covers cartilage repair procedures.

Say that an early study looking poor is expected. 5.11.10 covers MACI imaging.

Say that graft overgrowth above the surrounding cartilage is a recognised appearance. 5.11.2 covers chondral defects.

What Normal Looks Like

The reasoning expected is that implanted chondrocytes have to produce and organise a matrix, which is a biological process taking years, so the signal follows the matrix's development rather than the surgery's success. 1.2.2 covers the articular cartilage.

That makes the trend the information and any single study a snapshot of an unfinished process. 5.11.8 covers cartilage repair procedures.

Overgrowth happens because the repair is not constrained by the native surface's geometry, which is a mechanical consequence of the technique rather than a complication of it. 3.5.1 covers the contact areas.

Subchondral change accompanies the procedure and settles, so early marrow signal has a different meaning from late marrow signal. 5.11.7 covers bone marrow lesions.

How Good It Is

Imaging follows this repair's maturation well and predicts its durability poorly.

Its best contribution is the serial trend, which is the only interpretable output given a years long process. 5.11.8 covers cartilage repair procedures.

It is limited because the matrix's mechanical quality is what determines durability and the signal reflects its water content. 5.18.2 covers T2 mapping.

No figures appear for accuracy on this page, under decision 028, and no maturation timescales or scoring values appear either: those are published quantities and this environment cannot check them.

FRCS Level

How Good It Is

At decision level the imaging supports the follow up conversation and rarely prompts a reoperation.

Progressive fill with a settling subchondral bone is the expected course, and confirming it reassures a patient in a long rehabilitation. 4.20.5 covers the post-operative cartilage examination.

Absent fill with a persistent defect is a failure, and that is a secure finding. 5.11.2 covers chondral defects.

Graft overgrowth causing mechanical symptoms is a specific treatable problem. 4.17.2 covers mechanical symptoms.

Progressive subchondral deterioration beneath a filled repair is the worrying pattern and is better evidence than the fill is. 5.11.7 covers bone marrow lesions.

Where It Misleads

The commonest error is reading an early study as a failed repair. 5.11.8 covers cartilage repair procedures.

Expected repair tissue signal is reported as degeneration. 5.11.1 covers normal cartilage.

Overgrowth is reported without reference to symptoms. 4.17.2 covers mechanical symptoms.

The date is absent and the appearance is read against no timeline. 5.17.5 covers post-operative cartilage procedures.

Sequences differ between follow ups, so the trend is not a trend. 5.2.18 covers gradient echo imaging.

Fellowship Level

Where It Misleads

At fellowship level this procedure is followed by imaging for years, and what the imaging follows is not what determines the result.

The maturation process is biological and slow, so the imaging follow up is long, and a long series of morphological studies accumulates cost without accumulating predictive power. 5.1.5 covers the cost effectiveness of imaging.

Compositional sequences are the natural tool for a maturing matrix and their thresholds do not transfer, so the technique best suited to this question is the one least available. 5.18.2 covers T2 mapping.

Scoring systems for this repair are numerous and built around fill and signal, and their relationship to patient reported outcome is weak, which is the finding that should govern how the imaging is used. 5.21.3 covers the cartilage imaging literature.

The procedure itself has largely been superseded by its matrix assisted successor, so the imaging literature describes a technique in decline while the appearances remain relevant to patients already treated. 5.11.10 covers MACI imaging.

The useful practice is to image on a schedule the decision actually needs rather than annually by habit, and to report the trend. 5.20.5 covers reporting cartilage lesions.