KneeSchool/Imaging Academy/Post-operative Imaging
Post-operative Imaging
Page 5.12.8 · Patellofemoral MRI · imaging page
The knee after patellofemoral surgery, where the images show what was done and cannot show whether it worked.
The same topic at 4 depths
Each tier deepens the one below it and never repeats it. Choose the level you want.
Post-operative Imaging
Choose a depthFor Medical Students
What It Shows
Post-operative imaging of this joint shows the altered anatomy after a soft tissue reconstruction, a bony realignment or a procedure on the groove. 2.12.6 covers the surgical anatomy.
Radiographs show the implants, the tunnels and the position of the bone. 5.3.2 covers the lateral view.
It matters because the altered anatomy becomes the new baseline, and a reader without the operative detail reports it as abnormal. 5.20.7 covers reporting the post-operative knee.
How It Is Acquired
Start with radiographs, since they show the implants and the bone position with least artefact. 5.3.3 covers the skyline view.
Use a post-operative magnetic resonance protocol when soft tissue is the question. 5.5.3 covers the post-operative protocol.
Find out which operation was done before reporting, because the expected appearance differs completely between them. 5.20.7 covers reporting the post-operative knee.
Repeat the measurements that led to the operation rather than looking at the repair alone. 5.12.1 covers trochlear dysplasia.
Compare with the pre-operative study wherever one exists. 5.20.1 covers structured reporting.
What Normal Looks Like
Implants in their intended position with no loosening at the bone interface. 5.5.6 covers the bones.
A graft running in a continuous line from its femoral attachment to the medial patella. 5.17.6 covers imaging after MPFL reconstruction.
A united osteotomy with the tubercle in its new position. 5.16.5 covers osteotomy planning.
A patella engaged in the groove at the imaged angle. 5.12.4 covers patellar subluxation.
Signal change around the tunnels and the graft, which is expected for months after surgery. 5.5.3 covers the post-operative protocol.
What Abnormal Looks Like
A graft that is discontinuous, absent or pulled off its attachment. 5.17.6 covers imaging after MPFL reconstruction.
Fixation that has moved, backed out or loosened. 5.5.6 covers the bones.
An osteotomy that has not united or has displaced. 5.16.5 covers osteotomy planning.
A patella still displaced or tilted after the procedure. 5.12.3 covers patellar tilt.
New cartilage loss where the load was moved onto an unprepared surface. 5.12.6 covers cartilage injury.
A fracture through a tunnel or an osteotomy, which is the complication radiographs are requested for. 5.3.12 covers patellar fractures.
Key Learning Points
- Radiographs come first because they carry least artefact.
- The operation performed has to be known before reporting.
- Signal change around a graft is expected for months.
- The original measurements should be repeated.
- The altered anatomy is the new baseline.
MRCS Level
How It Is Acquired
In a viva the expected answer asks what was done before describing an appearance.
The expected points are the radiographs first, the operation performed, the expected post-operative appearance, the artefact, and the repeated measurements.
Say that metal reduces what a magnetic resonance study can show nearby. 5.5.3 covers the post-operative protocol.
Say that a graft remodels, so its appearance changes with the time since surgery. 5.17.6 covers imaging after MPFL reconstruction.
Say that instability recurring after surgery sends you back to the bony measurements. 5.16.4 covers the TT-TG measurement.
What Abnormal Looks Like
The reasoning expected is that an operated knee carries three separate questions: whether the repair is intact, whether the fixation is sound, and whether the original problem was addressed. 3.12.8 covers patellar instability.
Metal artefact is worst next to the implant, which is where the fixation question sits, so the radiograph answers that one better. 5.3.3 covers the skyline view.
Computed tomography answers the bone position and the union where artefact defeats magnetic resonance imaging. 5.16.8 covers the 3D reconstructions.
An intact graft in a patella that still displaces is a failure of indication rather than of fixation. 5.12.4 covers patellar subluxation.
How Good It Is
Imaging after patellofemoral surgery is a good test of structural integrity and no test of clinical outcome.
Its best contribution is the fixation, the union and the graft continuity, with the radiograph carrying most of it. 5.3.3 covers the skyline view.
It is limited by metal artefact, by the absence of an agreed normal post-operative appearance, and by findings that are expected rather than wrong. 5.5.3 covers the post-operative protocol.
No figures appear for accuracy on this page, under decision 028, and no tunnel positions, correction values or union intervals appear either: those are published quantities tied to particular techniques and this environment cannot check them.
Key Learning Points
- An operated knee carries three separate questions.
- Artefact is worst where the fixation question sits.
- Computed tomography answers union and bone position.
- An intact graft with a displacing patella is an indication failure.
- Structural integrity is not clinical outcome.
FRCS Level
How Good It Is
At decision level the imaging after a failed patellofemoral operation has to separate a technical failure from a wrong operation, and the two look different. 3.12.8 covers patellar instability.
A displaced graft or a non-union is technical and is visible. 5.16.5 covers osteotomy planning.
An intact construct with persistent instability points at an unaddressed bony factor. 5.12.1 covers trochlear dysplasia.
The pre-operative measurements should be repeated on the post-operative study using the same convention. 5.12.2 covers patella alta.
New pain with an intact construct raises the cartilage and the load distribution rather than the repair. 5.12.6 covers cartilage injury.
Where It Misleads
The commonest error is reporting the expected post-operative appearance as a complication. 5.20.7 covers reporting the post-operative knee.
Signal around a tunnel months after surgery is read as infection or loosening. 5.5.3 covers the post-operative protocol.
Metal artefact obscuring a structure is reported as absence of that structure. 5.1.6 covers imaging pitfalls.
A measurement made on an operated knee is compared with a threshold derived from unoperated ones. 5.16.4 covers the TT-TG measurement.
Hardware that has done its job and is now prominent is read as failure. 5.16.5 covers osteotomy planning.
Key Learning Points
- Expected appearances are reported as complications.
- Signal around a tunnel is read as infection.
- Artefact is reported as absence.
- Operated knees are measured against unoperated thresholds.
- Prominent hardware is not failed hardware.
Fellowship Level
Where It Misleads
At fellowship level the patient arrives after surgery done elsewhere, with no operative note and a report written without one. 5.20.7 covers reporting the post-operative knee.
The construct on the images rarely identifies the technique used, and the technique decides what the appearance should be. 5.17.6 covers imaging after MPFL reconstruction.
A procedure on the groove alters it permanently, so every later measurement of the groove describes the operation rather than the patient. 5.12.1 covers trochlear dysplasia.
A tubercle transfer moves the reference point the original measurements were made from, which leaves a serial comparison meaningless. 3.12.12 covers the tibial tubercle position.
Cartilage assessment near metal is the least reliable part of the study and is where a revision decision often rests. 5.12.6 covers cartilage injury.
The useful report states the operation if known, the construct seen, the integrity of each part, the repeated measurements with their conventions, and what the artefact prevented. 5.20.1 covers structured reporting.
Key Learning Points
- The technique used is rarely identifiable from the images.
- A procedure on the groove makes later measurements describe the operation.
- A tubercle transfer moves the reference point for serial comparison.
- Cartilage near metal is the least reliable part of the study.
- The report should state what the artefact prevented.
Explore Further
Where this topic came from and where it goes next in the spiral.
- 5.17.6MPFL Reconstruction
- 5.5.3Post-operative Protocol
- 5.16.5Osteotomy Planning
- 5.20.7Reporting Post-operative Knees
- 5.12.1Trochlear Dysplasia
- 5.12.6Cartilage Injury
References
No reference list is attached to this draft. Evidence verification has not run, because source retrieval was unavailable at generation time. Under the Operations Handbook a missing reference is acceptable and an invented one is a critical failure, so nothing has been cited and no citation marker appears in the text. This page carries no diagnostic accuracy figure, which is decision 028 rather than an omission: the comparative standing of the modalities is standard teaching and a specific sensitivity written from memory is the same class of claim as an invented citation, so ACC-001 refuses the number and the page states the comparison. A reviewer with the literature can add the figures into How Good It Is without restructuring the page. Any measurement here, including a sequence parameter, an angle or a millimetre, is written from standard teaching, has not been checked, and is registered under decision 006 in pipeline/config/figures with a verification state of UNVERIFIED_FROM_MEMORY.
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