GPs Dr Keith Hopcroft and Dr Vincent Forte kick off their new series, which looks at common presentations and offers guidance on likely causes, how to come to sensible conclusions and when alarm bells should ring
Recurrent knee pain is a very common presentation with a wide differential. Classification of causes isn't helped by changing and confusing nomenclature. As ever in general practice, a careful history and examination will provide useful clues – but management will often be dictated more by degree of disability and the patient's wishes than by making a precise diagnosis.
Differential diagnosis
Common
• Ligament sprain/minor soft tissue injury
• Osteoarthritis
• Cartilage injury
• Chondromalacia patellae
• Osgood–Schlatter's disease
Occasional
• Recurrent monoarthritis, for instance gout, pseudogout, Reiter's syndrome
• As part of polyarthritis, e.g. rheumatoid, ankylosing spondylitis, psoriatic arthritis
• Bursitis
• Referred from hip or back
• Ligament rupture
• Patellar tendonitis
• Baker's cyst
• Loose body
• Bone disease, for instance Paget's
• Recurrent dislocation of the patella
• Medial shelf syndrome
• Osteochondritis dissecans
Rare
• Haemochromatosis
• Recurrent haemarthroses, such as coagulation disorder
• Osteosarcoma
Possible investigations
Likely
• X-ray: may give clues to many possible causes, or confirmatory evidence when clinical suspicion is high – for example, with osteoarthritis, bony loose body, Paget's, osteochondritis dissecans.
Possible
• 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 is suspected.
Occasional
• HLAB27: a high prevalence in spondoarthritides.
• Joint aspiration: may be useful if an effusion is present – for example, revealing positively birefringent crystals in pseudogout. In practice, it is usually performed after specialist referral.
• Hip or back investigations: radiology may be necessary if it is thought the knee pain is referred from these areas.
• Alkaline phosphatase: elevated in Paget's disease.
• Serum ferritin: elevated in haemochromatosis.
• Coagulation screen: if coagulopathy suspected.
Top tips
• Patients place great value on X-rays, but in practice these may contribute little to management of straightforward recurrent knee pain. To prevent an unsatisfactory outcome, consider mentioning that an X-ray may be unnecessary.
• Insisting that the patient accurately localises the pain – if possible – may usefully narrow the diagnostic possibilities.
• Apparently 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 enthusiasts often present with recurrent knee pain and are unlikely to indulge the time-honoured ‘wait and see' approach. Earlier investigation or intervention may prove necessary.
Dr Keith Hopcroft is a GP in Basildon, Essex
Dr Vincent Forte is a GP in Gorleston, Norfolk
This is an extract from the fourth edition of Symptom Sorter – published by Radcliffe Publishing ISBN-978-1-84619-453-5.
Pulse readers can buy Symptom Sorter, Fourth Edition at the special price of £19.99 plus P&P (usual price £24.99 plus P&P). To claim the discount, please order direct from Radcliffe Publishing entering discount code DX62 at the checkout, or order by telephone on 10235 528820 quoting the same code. Offer ends 17 December 2010.
Red flags Red flagsDon't 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.
