Acute Single Joint Pain

This is a very common problem in primary care. Usually, there are few physical signs, although occasionally a genuine monoarthritis with all the classical signs of inflammation will present. Overall, the most likely aetiological factor is trauma, though other conditions may already affect a joint. In the elderly, an exacerbation of osteoarthritis is common; this condition may also cause multiple joint pain. The knee is probably the single most frequently affected joint.

Published: 2nd August 2022 | Updated: 15th August 2022

Differential diagnosis

Common Diagnoses

  • Acute Exacerbation of Osteoarthritis (OA)
  • Traumatic Synovitis
  • Gout/Pseudogout
  • Chondromalacia Patellae (CP) and Other Anterior Knee Pain Syndromes
  • Traumatic Haemarthrosis (e.g. after Cruciate Ligament Injury)

Occasional Diagnoses

  • Fracture
  • Reiter’s Disease
  • Psoriatic Arthritis
  • Rheumatoid Arthritis (RA)
  • Patellar Tendinitis, Osgood–Schlatter’s Disease

Rare Diagnoses

  • Septic Arthritis (SA)
  • Haemophilia
  • Local Tropical Infections (e.g. Madura Foot [Mycetoma Pedis], Filariasis)
  • Malignancy (Usually Secondary)
  • Avascular Necrosis
  • Recurrent Joint Subluxation

Ready reckoner

Key distinguishing features of the most common diagnoses

OACP/Anterior Knee PainTraumatic SynovitisGout Traumatic Haemarthrosis
Sudden OnsetPossibleNoYesPossibleYes
History of Acute TraumaPossibleNoYesPossibleYes
Recurrent ProblemYesYesNoYesNo
Several Joints PainfulPossibleNoNoPossibleNo
Hot, Red JointNoNoNoYesPossible

Possible investigations

Likely: None.

Possible: FBC, ESR/CRP, uric acid, X-ray, joint aspiration (in monoarthritis of large joint).

Small Print: Rheumatoid factor/anti-CCP antibodies, clotting studies/factor VIII assay, arthroscopy.

  • FBC/ESR/CRP: WCC and ESR/CRP raised in infection, systemic inflammatory conditions; Hb may be reduced in the latter.
  • Uric acid: Once attack has subsided, useful to add weight to clinical diagnosis of gout (especially if considering treatment with allopurinol).
  • Rheumatoid factor may be useful if symptoms suggest possible RA (consider anti-CCP antibodies if rheumatoid factor is negative).
  • X-ray: Essential if fracture suspected. May also reveal OA, avascular necrosis, malignancy and help to distinguish between RA and psoriatic arthritis.
  • Sterile aspiration of joint fluid: To look for pus (septic arthritis), blood (haemarthrosis) and crystals (gout/pseudogout).
  • Clotting studies/factor VIII assay: If haemophilia a possibility.
  • Arthroscopy: May be required urgently in secondary care if trauma has resulted in a haemarthrosis.

Top Tips

  • Autoimmune blood tests can be misleading in possible arthritis. The diagnosis should be clinical; blood testing simply adds weight and prognostic information to the clinical assessment. Positive tests can be found in normal patients – beware of inappropriately labelling an insignificant problem as a significant arthritis on the basis of a blood test.
  • Gout is very painful, will limit movement and may cause a slight fever. Septic arthritis gives a similar picture but with marked restriction of movement and, usually, a high fever. If in doubt, arrange urgent assessment.
  • In obscure cases, question and examine the patient carefully. For example, in Reiter’s disease, symptoms of urethritis or conjunctivitis may have been minimal or forgotten; in psoriatic arthritis, there may only be insignificant skin lesions.

Red Flags

  • If one joint is red, very hot, intensely painful with marked limitation of movement and systemic illness, septic arthritis must be excluded – admit.
  • Haemarthrosis usually develops rapidly after trauma and indicates significant damage requiring immediate referral; effusion due to synovitis usually takes a day or longer to accumulate and is less urgent.
  • Septic arthritis is notoriously easy to miss in a patient with coexisting RA. The systemic signs may be absent and the diagnosis may mistakenly be viewed as a flare-up of rheumatoid arthritis.
  • A young adult male with a monoarthritis of the knee not caused by trauma is likely to have Reiter’s disease.
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Website disclaimer

Pulse Reference is based on the best-selling book Symptom Sorter.

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.