Knee injection

Why might this treatment be considered?

A knee injection may be considered to reduce symptoms for a defined period, support participation in exercise or rehabilitation, or help identify the source of pain. The appropriate injection depends on the diagnosis, purpose, medical history and current guidance. An injection does not reverse osteoarthritis or regrow lost cartilage.

What does the procedure involve?

The skin is cleaned and a needle is passed into the knee joint, sometimes using ultrasound guidance. Excess fluid may be removed first when appropriate. Corticosteroid is used for short-term anti-inflammatory relief; NICE describes benefit in osteoarthritis as typically lasting around 2 to 10 weeks. Local anaesthetic may provide immediate temporary relief and can have a diagnostic role. Platelet-rich plasma (PRP) is prepared from a sample of the patient’s own blood before injection. Hyaluronic acid is a manufactured gel-like substance injected into the joint; current NICE osteoarthritis guidance advises that it should not be offered routinely.

Potential benefits

• Temporary reduction in pain and inflammation, particularly after corticosteroid injection
• A period in which exercise, physiotherapy or everyday activity may be easier
• Immediate but short-lived relief from local anaesthetic, which may also provide diagnostic information
• Some patients report symptom improvement after PRP or hyaluronic acid, although response is variable and evidence differs between treatments
• An outpatient option that does not commit the patient to later surgery

Reasonable alternatives

• Education, activity modification and pacing
• Physiotherapy and an individual exercise programme
• Weight optimisation where appropriate
• Pain relief or anti-inflammatory medication when medically suitable
• A walking stick, brace or other aid
• Continuing without an injection
• Knee replacement when symptoms and arthritis are sufficiently advanced and non-operative measures no longer provide acceptable relief

Important risks and limitations

Every procedure carries risk. The likelihood and importance of each risk vary between individuals.

• Little, brief or no improvement
• A temporary increase in pain or swelling after injection
• Bleeding or bruising, particularly with anticoagulant or antiplatelet medication
• Rare infection within the joint, requiring urgent medical assessment
• Temporary numbness or weakness from local anaesthetic
• A temporary rise in blood glucose, flushing or skin change after corticosteroid
• Discomfort or bruising when blood is taken for PRP
• A local inflammatory reaction after PRP or hyaluronic acid
• Allergic reaction to an injected medicine or dressing
• Rare injury to a nearby nerve or blood vessel
• Repeated corticosteroid injections may have additional local and systemic effects, so frequency is considered individually
• An injection close to planned knee replacement may affect surgical timing and should be disclosed to the treating surgeon

Recovery and expectations

• Follow the treating unit’s advice about transport and driving after the procedure.
• Avoid strenuous activity for 24 to 48 hours, then return gradually to the agreed exercise plan.
• Local anaesthetic relief wears off within hours; other injections may take longer to have an effect.
• People with diabetes should monitor blood glucose more frequently after corticosteroid injection.
• Seek urgent medical assessment for increasing pain after 48 hours, redness, heat, marked swelling, discharge, fever or feeling unwell.
• Record the amount and duration of any improvement, as this helps guide future treatment decisions.