GPAtlas🧭 When to suspect
Knee pain is one of the commonest musculoskeletal presentations in primary care. The core skill is pattern recognition – separating acute trauma from chronic degenerative, inflammatory, crystal, infective and referred causes, because each follows a different pathway. Age is a useful pointer: injury and patellofemoral pain dominate in younger adults, while osteoarthritis (OA) becomes increasingly likely over 45.
Two priorities override everything else: never miss a septic joint, and never miss a fracture or referred hip pathology. A hot, swollen, acutely painful joint is septic arthritis until proven otherwise, and knee pain with a limp in a child must prompt examination of the hip.
| Clinical pattern | Consider |
|---|---|
| Acute trauma with rapid, tense effusion (haemarthrosis within hours) | Anterior cruciate ligament (ACL) rupture, intra-articular fracture, patellar dislocation |
| True locking – knee fixed, cannot fully extend | Displaced meniscal tear or loose body |
| Giving way / instability | Ligamentous injury (especially ACL), patellar instability |
| Anterior knee pain, worse on stairs and prolonged sitting | Patellofemoral pain |
| Activity-related pain just below the patella in an active adolescent or athlete | Osgood–Schlatter disease, patellar tendinopathy |
| Hot, swollen, acutely painful joint with restricted movement, feeling unwell | Septic arthritis (emergency) or crystal arthritis (gout, pseudogout) |
| Gradual pain with short-lived stiffness (< 30 min), worse with use, age > 45 | Osteoarthritis |
| Prolonged early-morning stiffness, multiple joints, systemic features | Inflammatory arthritis (e.g. rheumatoid arthritis) |
| Knee pain with a limp in a child or adolescent | Referred hip pathology – slipped upper femoral epiphysis (SUFE), Perthes' disease, transient synovitis |
| Posterior knee fullness or swelling | Baker's (popliteal) cyst |
Source: NICE NG226 · NICE NG219 · BSR
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