A suddenly painful, hot and swollen knee may be caused by calcium pyrophosphate crystal arthritis, often called pseudogout. It can also have other causes, including joint infection. Seek urgent medical assessment for sudden intense joint pain and swelling rather than booking an elective PRP injection on the assumption that this is ordinary osteoarthritis.
What CPPD means
Calcium pyrophosphate deposition, or CPPD, describes crystals deposited in cartilage and other joint tissues. Some people have deposits without symptoms. Others develop acute inflammatory attacks, chronic arthritis, or CPPD alongside osteoarthritis. These are related but different clinical situations.
The term pseudogout is commonly used for an acute attack because its symptoms can resemble gout. The crystals are different: CPP crystals are not the urate crystals responsible for gout. A previous gout diagnosis does not prove the cause of every new swollen joint.
Contact The Wellness about a non-urgent knee assessment once any acute symptoms have been assessed. Mention a history of crystal arthritis or chondrocalcinosis when discussing an elective treatment.
Why a new hot knee should not be self-diagnosed
Mayo Clinic's March 2026 patient guidance describes swelling, warmth, severe pain and difficulty moving or loading the affected joint. The knee is a common site. Attacks may last days or weeks, but the expected duration does not make it safe to wait without an assessment.
Joint infection can resemble crystal arthritis. Fever or feeling unwell adds concern, but its absence does not establish that infection is excluded. If you cannot bear weight, have severe sudden pain or are systemically unwell, seek urgent care. An article cannot distinguish these causes remotely.
What chondrocalcinosis on an X-ray tells you
Chondrocalcinosis means cartilage calcification seen on imaging. It can support a CPPD assessment in the right context, but a scan finding alone does not prove it is causing the current pain. Many people with crystal deposits do not have acute attacks.
If your report describes both osteoarthritis and chondrocalcinosis, ask which process best explains your symptoms. A gradual load-related ache and a new inflammatory flare may need different decisions, even in the same knee.
How clinicians investigate it
The history, examination, previous attacks, medicines and imaging all matter. A clinician may recommend aspiration, in which fluid is removed from the joint for analysis. Testing can look for crystals and assess for infection where appropriate. A 2024 Frontiers in Medicine review describes joint-fluid and imaging assessment as part of the diagnostic approach.
Finding crystals should not be treated as permission to ignore possible infection. The same review states that joint injection for an acute attack should be performed only once a septic joint has been ruled out. The exact investigations depend on the clinical situation.
Bring previous scan reports, joint-fluid results and a medicine list. Tell the clinician about recent procedures, infection, blood-thinning treatment and any kidney or stomach problems that may affect treatment choices.
Treatment is directed at inflammation and the person
The 2024 review describes anti-inflammatory approaches for acute CPP crystal arthritis, including clinician-selected medication and, in some circumstances, aspiration with a joint injection after infection has been excluded. The choice depends on the number of joints involved, medical history and risks.
Do not start, stop or borrow prescription treatment on the basis of this guide. Treatments suitable for one person can be unsuitable for another, particularly with kidney disease, other medicines or gastrointestinal problems. People with recurrent attacks may need a prevention discussion rather than repeated unplanned treatment.
Current treatment aims to control symptoms and inflammation. The review does not establish a disease-modifying treatment that removes the underlying calcium crystal deposits. A reassuring treatment response is useful, but it does not make every future flare safe to manage without review.
Where PRP fits, and where it does not
Evidence about PRP for knee osteoarthritis is not evidence that it treats an acute CPP crystal attack or clears crystal deposits. The CPPD management review does not establish PRP as a standard treatment for acute crystal arthritis.
NICE's guidance for PRP in knee osteoarthritis describes limited-quality efficacy evidence and calls for special arrangements for clinical governance, consent and audit or research. It should not be recast as an endorsement for CPPD. If PRP is considered later for coexisting osteoarthritis, clarify the working diagnosis, the expected benefit and the uncertainty first.
An elective injection should not displace investigation of a new inflammatory episode. Equally, an incidental calcification finding is not by itself a personalised verdict that no future treatment can be considered. The decision needs the history and examination.
A clearer plan after the flare
Ask what caused the episode, whether further review is needed and what to do if it recurs. For an elective appointment, confirm the full fee, what assessment is included and whether imaging or joint-fluid testing is separately charged. Do not assume that a PRP package includes investigation of an undiagnosed hot knee.
Enquire about a diagnosis-led review at The Wellness. Share previous findings and treatment history so the proposed appointment addresses the right question.
Sources
- Mayo Clinic. Pseudogout, symptoms and causes, March 2026
- Recent advances in therapeutic management of CPPD, Frontiers in Medicine, 2024
- NICE. PRP injections for knee osteoarthritis, HTG497
General information, not a diagnosis or individual treatment advice.