Recurrent Knee Pain
Differential Diagnosis
Common Diagnoses
- Ligament Sprain/Minor Soft Tissue Injury
- Osteoarthritis
- Cartilage Injury
- Chondromalacia Patellae/Patellofemoral Pain
- Osgood–Schlatter’s Disease
Occasional Diagnoses
- Recurrent Monoarthritis (e.g. Gout, Pseudogout, Reiter’s)
- As Part of Polyarthritis (e.g. Rheumatoid, Ankylosing Spondylitis, Psoriatic Arthritis)
- Iliotibial Tract Syndrome
- Bursitis
- Referred from Hip or Back
- Ligament Rupture
- Patellar Tendonitis
- Baker’s Cyst
- Loose Body
- Bone Disease (e.g. Paget’s)
- Recurrent Dislocation of the Patella
- Medial Shelf Syndrome
- Osteochondritis Dissecans
Rare Diagnoses
- Haemochromatosis
- Recurrent Haemarthroses (e.g. Coagulation Disorder)
- Osteosarcoma
Ready Reckoner
Key distinguishing features of the most common diagnoses
| Ligament Sprain/ Soft Tissue | Osteoarthritis | Cartilage Injury | Chondromalacia Patellae/Patellofemoral Pain | Osgood– Schlatter’s | |
|---|---|---|---|---|---|
| Effusion | No | Possible | Possible | Possible | No |
| Specific Injury | Yes | No | Yes | No | No |
| Locking | No | Possible | Possible | No | No |
| Both Knees Affected | No | Possible | No | Possible | Possible |
| More Common in Women | No | No | No | Yes | No |
Possible Investigations
Likely:X-ray.
Possible:FBC, CRP, uric acid, MRI, autoantibodies.
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.
Top Tips
- 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.
Red Flags
- 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.