KneeSchool/Imaging Academy/Crystal Arthropathy
Crystal Arthropathy
Page 5.14.4 · Synovial and Inflammatory Disorders · imaging page
Deposits with an appearance of their own, where the radiograph outperforms the scan and an acute attack cannot be told from infection.
The same topic at 4 depths
Each tier deepens the one below it and never repeats it. Choose the level you want.
Crystal Arthropathy
Choose a depthFor Medical Students
What It Shows
Crystal arthropathy is joint disease caused by crystal deposition, chiefly urate and calcium pyrophosphate. 5.5.11 covers the synovium.
Radiographs show calcium pyrophosphate deposits in cartilage and menisci, and erosions with overhanging margins in gout. 5.3.1 covers the AP view.
It matters because the deposits are visible and specific, which is unusual in this chapter, and because an acute attack mimics infection. 5.14.7 covers septic arthritis.
How It Is Acquired
Start with radiographs, because calcification is the finding and they show it best. 5.3.1 covers the AP view.
Look at the menisci and the hyaline cartilage for calcification. 5.5.8 covers the menisci.
Look at the bone for erosion with a sclerotic overhanging margin. 5.5.6 covers the bones.
Use ultrasound where a tendon or a superficial deposit is the question. 5.4.5 covers the quadriceps tendon.
Aspirate when the knee is acutely hot, because the crystal and the organism are both found that way. 5.4.17 covers the aspiration.
What Normal Looks Like
Cartilage and menisci with no calcification. 5.5.8 covers the menisci.
No erosion with an overhanging margin. 5.5.6 covers the bones.
Joint space appropriate to age with no disproportionate pattern. 5.3.17 covers joint space narrowing.
No tophaceous soft tissue mass. 4.3.8 covers swelling.
What Abnormal Looks Like
Linear calcification in the hyaline cartilage and in the menisci. 5.5.8 covers the menisci.
Joint space loss in a pattern that does not fit the alignment, often patellofemoral predominant. 5.3.3 covers the skyline view.
Erosion with a sclerotic overhanging margin, which is characteristic of gout. 5.5.6 covers the bones.
A soft tissue mass of intermediate signal containing deposits. 5.13.7 covers bone tumours.
An acutely swollen joint with synovitis and nothing else to explain it. 5.14.1 covers synovitis.
Key Learning Points
- The deposits are visible on radiographs and are specific.
- Calcification sits in cartilage and in menisci.
- Gout erodes with an overhanging margin.
- An acute attack mimics infection.
- Aspiration finds both the crystal and the organism.
MRCS Level
How It Is Acquired
In a viva the expected answer asks for the radiograph and then the aspirate.
The expected points are the radiograph, the cartilage and meniscal calcification, the erosion pattern, ultrasound for a superficial deposit, and the aspiration.
Say that this is the chapter's exception, where the radiograph beats the scan. 5.1.3 covers choosing the correct investigation.
Say that an acute crystal attack and an infection cannot be separated by imaging. 5.14.7 covers septic arthritis.
Say that calcium pyrophosphate deposition produces a joint space pattern that does not match the alignment. 5.20.6 covers reporting osteoarthritis.
What Abnormal Looks Like
The reasoning expected is that a crystal has a density and a signal of its own, so unlike every other condition in this chapter the agent itself is directly visible. 5.2.22 covers the CT acquisition.
That visibility is why a plain film is informative, and why dual energy computed tomography has a role that urate in particular suits. 5.2.22 covers the CT acquisition.
Calcium pyrophosphate deposition produces arthritis in a distribution that mechanical wear does not, which is the clue on a radiograph reported as osteoarthritis. 5.20.6 covers reporting osteoarthritis.
Chondrocalcinosis also makes a meniscus look abnormal on magnetic resonance images, which is a direct cause of over-reported tears. 5.6.2 covers the meniscal signal grading.
How Good It Is
Radiography is the best available first test here and the aspirate is the diagnostic one.
Its best contribution is the calcification and the erosion pattern, both of which are specific when present. 5.5.6 covers the bones.
It is limited because absence of calcification excludes nothing, because the acute attack cannot be told from infection, and because magnetic resonance appearances mislead towards meniscal pathology. 5.6.2 covers the meniscal signal grading.
No figures appear for accuracy on this page, under decision 028, and no attenuation values or deposit dimensions appear either: those are published and protocol quantities and this environment cannot check them.
Key Learning Points
- The crystal itself is visible, unlike every other agent here.
- Dual energy computed tomography suits urate.
- The joint space pattern does not match the alignment.
- Chondrocalcinosis causes over-reported meniscal tears.
- Absence of calcification excludes nothing.
FRCS Level
How Good It Is
At decision level the finding changes whether an operation happens at all. 5.1.3 covers choosing the correct investigation.
Chondrocalcinosis with a reported meniscal tear is a reason to doubt the tear rather than to resect it. 5.6.2 covers the meniscal signal grading.
A crystal arthropathy pattern explains a knee whose wear does not fit its alignment. 5.20.6 covers reporting osteoarthritis.
An acute presentation is aspirated before anything else, and a scan delays that. 5.4.17 covers the aspiration.
Deposits around an implant complicate the assessment of loosening and infection together. 5.17.9 covers the revision arthroplasty.
Where It Misleads
The commonest error is resecting a meniscus that looks torn because it is calcified. 5.6.2 covers the meniscal signal grading.
An acute attack is treated as an infection, or an infection as an attack. 5.14.7 covers septic arthritis.
A tophus is reported as a soft tissue tumour. 5.13.7 covers bone tumours.
Calcification is read as an old injury. 5.5.8 covers the menisci.
A disproportionate joint space pattern is reported as osteoarthritis with no comment. 5.20.6 covers reporting osteoarthritis.
Key Learning Points
- A calcified meniscus is resected as a torn one.
- Attack and infection are mistaken for each other.
- A tophus is reported as a tumour.
- Calcification is read as an old injury.
- A disproportionate pattern deserves a comment.
Fellowship Level
Where It Misleads
At fellowship level these patients arrive after an arthroscopy that found calcified cartilage and did not change the symptoms. 5.1.2 covers clinical examination versus imaging.
The imaging was right and the inference was wrong, which is the pattern worth recognising rather than the appearance. 5.20.8 covers common reporting errors.
Deposition accelerates after meniscectomy and after arthroplasty, so a post-operative knee with new calcification is following a known course rather than developing a complication. 5.20.7 covers reporting the post-operative knee.
Dual energy computed tomography for urate is available in few centres and answers a question the aspirate already answers more cheaply. 5.1.5 covers the cost-effectiveness of imaging.
An acute crystal attack in a replaced knee is the diagnosis nobody wants to make without an aspirate. 5.17.9 covers the revision arthroplasty.
The useful report names the deposits, their sites, the joint space pattern, the erosion morphology, and that an acute presentation needs an aspirate. 5.20.1 covers structured reporting.
Key Learning Points
- The imaging was right and the inference was wrong.
- Deposition accelerates after meniscectomy and arthroplasty.
- Dual energy computed tomography answers what the aspirate does.
- An attack in a replaced knee still needs an aspirate.
- The report should direct an acute knee to aspiration.
Explore Further
Where this topic came from and where it goes next in the spiral.
- 5.14.7Septic Arthritis
- 5.6.2Meniscal Signal Grading
- 5.4.17Aspiration
- 5.3.1AP View
- 5.14.1Synovitis
- 5.20.1Structured Reporting
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.
Safety. KneeSchool is educational and does not give individual medical advice. Seek urgent assessment for a knee that cannot bear weight after an injury, a hot swollen knee with a fever, or new numbness, weakness or coldness in the leg or foot.