Small Print:HLA-B27, joint aspiration, hip or back investigations if referred pain suspected, alkaline phosphatase, serum ferritin, coagulation screen.
X-ray: May give clues to many of the possible causes, or confirmatory evidence when clinical suspicion is high – for example, with osteoarthritis, bony loose body, Paget’s, osteochondritis dissecans.
FBC, CRP: CRP elevated and Hb may be reduced in inflammatory polyarthritis.
Uric acid: Typically elevated in gout.
MRI: Useful to assess soft tissue such as cartilage, especially if surgery is being considered.
Autoantibodies: If inflammatory polyarthritis suspected.
HLA-B27: A high prevalence in spondoarthritides.
Joint aspiration: May be diagnostically useful if an effusion is present – for example, revealing positively birefringent crystals in pseudogout. In practice, usually performed after specialist referral.
Hip or back investigations: Appropriate radiology may be necessary if it is thought the knee pain is referred from these areas.
Alkaline phosphatase: Elevated in Paget’s.
Serum ferritin: Elevated in haemochromatosis.
Coagulation screen: If coagulopathy suspected.
Patients place great value on X-rays whereas, in practice, they may contribute little to management of straightforward recurrent knee pain. To prevent an unsatisfactory outcome, consider proactively broaching the fact that an X-ray may be unnecessary.
Insisting that the patient accurately localises the pain – if possible – may usefully limit the diagnostic possibilities.
‘Straightforward’ osteoarthritis can become quite suddenly more painful, often for no obvious reason – exacerbations and remissions are part of the natural history of the disease.
Keen sports people often present with recurrent knee pain and are unlikely to indulge in the GP’s time-honoured ‘wait and see’ approach. Earlier investigation or intervention may prove necessary.
Do not forget that knee pain may be referred – if the cause isn’t immediately apparent, examine the hip, especially in children.
Anterior cruciate ligament injury is quite easily missed in casualty in the acute stage. It may only present later with an unstable knee.
Osteosarcomas are rare: But most commonly occur near the knee. Beware of unexplained constant, increasing pain waking the patient at night. Swelling and inflammation will only appear later.
The experts behind Pulse Reference are Dr Keith Hopcroft who is the co-author of Symptom Sorter, a GP in Essex and Pulse’s editorial advisor and Dr Poppy Freeman, a GP in Camden and also a clinical advisor to Pulse.
This website is for clinical guidance only and cannot give definitive diagnostic information. Practitioners should work within the limits of their individual professional practice, seek guidance when necessary and refer appropriately.
The AI platform ChatGPT has assisted in the creation of some of the content published as part of Pulse Reference. Dr Hopcroft and Dr Freeman have then thoroughly reviewed the content to ensure its timeliness and reliability.