Diagnosis and symptoms6 min read
Why do joints swell? What oedema means
Swelling after injury or overload is a natural part of healing. When it persists, however, it becomes a problem in itself: it restricts movement and inhibits muscle strength.
Two different types of swelling
Joint effusion collects inside the joint capsule. In joints such as the knee, fullness around the kneecap and a 'floating' kneecap are signs of this type.
Soft tissue oedema collects in tissues outside the joint. Leaving a dent when pressed with a finger is its typical finding.
The two point to different causes and are managed differently. Effusion indicates a problem within the joint, while soft tissue oedema relates more to circulation and the lymphatic system.
The effect of swelling on movement
Fluid within the joint reflexively inhibits the surrounding muscles. In the knee this effect is marked in the quadriceps, which weakens quickly.
That inhibition cannot be overcome by will. Strengthening done before swelling resolves does not produce the expected result, which is why oedema management is the first step of the programme.
Swelling also mechanically restricts range of motion. Prolonged restriction turns into capsular stiffness and becomes harder to reverse.
Warning findings
Tense swelling developing within minutes of injury suggests bleeding into the joint and requires early assessment.
Swelling with redness, warmth and fever raises the possibility of joint infection. This is urgent and not suitable for waiting.
Sudden swelling in one leg with calf pain and warmth requires urgent assessment for a blood clot.
Key points
- Joint effusion and soft tissue oedema point to different causes.
- Effusion reflexively inhibits the surrounding muscles.
- That inhibition cannot be overcome by will; swelling must resolve first.
- Prolonged restriction turns into capsular stiffness.
- Swelling with redness and fever is an urgent finding.
Frequently asked questions
Does swelling resolve on its own?
In simple injuries it usually recedes within days to two weeks. Swelling lasting weeks or recurring indicates an ongoing problem within the joint and requires assessment.
Should I move while swollen?
Yes, within the pain-free range. Movement supports fluid clearance and prevents stiffness. Complete rest does not reduce swelling and increases stiffness.
Should the fluid be drained?
Drainage can be considered where fluid is very tense and markedly restricts movement. It is not routine, and fluid refills if the underlying cause is unresolved.
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This content is for information only and does not replace medical diagnosis or treatment. Response to treatment varies between individuals. Please consult a healthcare professional about your symptoms.