A post-injection flare is a short-lived increase in pain or soreness at the site of a corticosteroid injection. Many patients describe this as a dull ache, swelling, or stiffness that appears a few hours after the procedure. It is a normal reaction to the steroid medication or the solution used in the injection, including local anaesthetic and saline, as it interacts with the tissues in the joint or tendon.
Why Does It Happen?
The exact cause is not fully understood, but research suggests several factors may contribute:
- Crystallisation of the steroid: Some corticosteroid formulations can form tiny crystals when injected. These crystals can irritate the surrounding tissue temporarily before dissolving.
- Tissue reaction to the injection: The act of inserting a needle and injecting fluid can cause local irritation or stretching of the joint capsule.
- Inflammatory rebound: A small, temporary increase in inflammation may occur as the body responds to the medication.
Studies indicate that up to 10-25% of patients may experience a post-injection flare, with symptoms generally resolving within 24-48 hours (Habib, 2004; Bannuru et al., 2015).
How to Manage Discomfort
Most post-injection flares are mild and self-limiting. Evidence-based strategies include:
- Rest the affected joint: Avoid heavy lifting, strenuous activity, or repetitive movements for the first 24 hours.
- Ice application: Apply a cold pack for 10-15 minutes to reduce pain and swelling.
- Pain relief if needed: Over-the-counter painkillers such as paracetamol can help.
- Monitor symptoms: Seek medical advice if pain worsens after 48 hours, is accompanied by fever, or there is significant swelling.
When to Resume Activity
After the initial flare period, gentle movement and rehabilitation exercises can be restarted. Ultrasound-guided injections target the inflamed tissue precisely, so once the short flare resolves, most patients notice rapid improvement in pain and mobility. Following your clinician’s advice is key to maximising long-term benefit and preventing stiffness or recurrence of discomfort.
Final Thoughts
A post-injection flare is a normal and temporary reaction following corticosteroid therapy. Understanding that this short-term discomfort is part of the body’s response can help you approach recovery with confidence. At The Ultrasound Injection Clinic, we deliver every injection with precision under ultrasound guidance to reduce risk and optimise outcomes. Your clinician will provide personalised advice on activity, symptom management, and follow-up care.
References
- Habib GS. Systemic effects of intra-articular corticosteroids. Clin Rheumatol. 2004;23(3):189–196.
- Bannuru RR et al. Comparative effectiveness of pharmacologic interventions for knee osteoarthritis. Ann Intern Med. 2015;162(1):46–54.
- McAlindon TE et al. OARSI guidelines for the non-surgical management of knee osteoarthritis. Osteoarthritis and Cartilage. 2014;22(3):363–388.
- Day R, Hornicek FJ. Intra-articular corticosteroid injections. J Am Acad Orthop Surg. 2006;14(10):599–607.