Introduction
Corticosteroid injections, often referred to as ‘cortisone shots,’ are a cornerstone in the non-surgical management of numerous inflammatory musculoskeletal conditions, including arthritis, bursitis, and tendinitis. [1, 2] These injections deliver potent anti-inflammatory medication (glucocorticoids) directly to a localized area, providing targeted pain relief and swelling reduction. [3] While highly effective for short-term symptom control, like any medical intervention, steroid injections carry a risk of side effects. These can range from common, mild local reactions to rare, serious systemic complications, and a distinct, temporary increase in pain known as the “flare” reaction. [4] Understanding the mechanisms and management of these effects is crucial for both practitioners and patients.
Why Steroids Work and What Goes Wrong
Corticosteroids are synthetic versions of cortisol, a hormone naturally produced by the adrenal glands. [2] Their primary function is to suppress the immune system’s inflammatory response.5
1.1 The Anti-Inflammatory Effect
Once injected into a joint or surrounding soft tissue, the corticosteroid molecules pass into the local cells, where they bind to specific receptors. [5] This binding action effectively shuts down the production of several key inflammatory chemicals, such as prostaglandins and leukotrienes.6 The result is a profound reduction in localized swelling, heat, and pain. [2, 6]
1.2 The Local Delivery Trade-Off
To prolong the anti-inflammatory effect, most injectable steroids (like Triamcinolone or Methylprednisolone) are prepared as a particulate suspension. This means the drug is in the form of microcrystals that dissolve slowly over days or weeks, ensuring a sustained release. [7] This slow-release feature, however, is directly linked to the most common post-injection side effect: the steroid flare.
The Post-Injection Flare Reaction
The “steroid flare” or “post-injection flare” is a phenomenon where pain temporarily worsens after the injection, rather than improving.7
2.1 Clinical Presentation and Incidence
A flare is clinically defined as a significant exacerbation of pain at the injection site that is notably higher than the patient’s baseline pre-injection pain. [8]
- Incidence: Studies estimate the flare reaction occurs in approximately 1% to 30% of patients following a corticosteroid injection, though the rate is highly dependent on the type of steroid used and the location of the injection. [4, 9]
- Timing and Duration: The reaction almost always begins within the first 6 to 48 hours after the procedure, often as the immediate effect of the co-injected local anesthetic wears off. Crucially, the flare is short-lived, resolving spontaneously within 1 to 3 days. [1, 10]
2.2 The Mechanism of the Flare
The most widely accepted scientific theory for the steroid flare relates directly to the particulate nature of the medication. [8, 11]
- Crystal-Induced Synovitis: When the microcrystals of the steroid suspension are deposited into the synovial fluid (the fluid in the joint) or surrounding soft tissue, they can act as foreign bodies.13
- Immune Response: These microcrystals are recognized by the body’s local immune cells (macrophages and leukocytes). This leads to a temporary, localized inflammatory cascade—the opposite of the steroid’s intended effect. [11]
- Clinical Overlap: The resulting clinical picture (pain, warmth, swelling) can be very similar to other crystal-induced joint disorders, such as acute gout, though it is a sterile (non-infectious) inflammatory event [8].
2.3 Management of the Flare
It is vital for both patients and clinicians to recognize that a flare is a self-limiting reaction and not a sign of treatment failure or a serious complication like infection. [1] Management focuses on symptom relief:
- Rest: Restricting activity and avoiding strenuous exercise of the affected area for 24-48 hours. [10]
- Cryotherapy: Applying ice or a cold compress to the injection site for 1810−15 minutes every few hours. [1]
- Analgesics: Over-the-counter pain medications, such as acetaminophen or non-steroidal anti-inflammatory drugs (NSAIDs, if cleared by a physician), are often recommended to manage discomfort. [1, 10]
Skin and Tissue Changes
Beyond the flare, other side effects can occur at or near the injection site, primarily with more superficial injections [4].2
3.1 Skin Hypopigmentation
- Description: A lightening or whitening of the skin (hypopigmentation) occurs due to the local effect of the steroid on melanocytes (the cells that produce pigment). [4, 12]
- Incidence: This effect is more noticeable in individuals with darker skin tones and is a temporary cosmetic concern. [12] It typically resolves, though it may take several months to a year. [13]
3.2 Subcutaneous Fat Atrophy
- Description: The steroid can cause a localized breakdown of fat cells just beneath the skin, resulting in a dimpling or depression (atrophy) at the injection site. [4]
- Mechanism: This effect is thought to be a direct catabolic (tissue-breaking down) effect of the corticosteroid on local adipocytes. [14]
- Resolution: Like hypopigmentation, this is often temporary but can be cosmetically distressing. [13]
3.3 Tendon and Ligament Damage
This is a critical, though rare, complication. Direct injection of corticosteroids into a weight-bearing tendon (e.g., Achilles or patellar tendon) is associated with an increased risk of tendon weakening and subsequent rupture [15]. For this reason, injections are typically administered around a tendon (peritendinous) rather than directly into the tendon body, and patients are advised to limit strenuous activity for a period post-injection [15].
Absorption and Hormonal Impact
While local injections are designed to minimize systemic exposure, the medication is still absorbed into the bloodstream. This can lead to temporary, mild systemic effects, and in some cases, more serious hormonal imbalances [4].
4.1 Transient Hyperglycemia and Flushing
- Hyperglycemia: Corticosteroids are known to increase insulin resistance and stimulate glucose production in the liver. [16] This results in a temporary elevation of blood glucose levels, which is particularly important for patients with diabetes.24 Blood sugar should be monitored closely for several days post-injection. [1]
- Facial Flushing: Many patients report a sensation of warmth and redness, particularly in the face and chest, which is generally harmless and resolves within a few days. [1, 4]
4.2 Hypothalamic-Pituitary-Adrenal (HPA) Axis Suppression
This is arguably the most significant systemic risk, even from a local injection. [17]
- Mechanism: The HPA axis regulates the body’s natural production of cortisol. When a high concentration of synthetic steroid is absorbed into the bloodstream, it creates a powerful negative feedback loop on the hypothalamus and pituitary gland. [17] This signals the adrenal glands to stop or dramatically reduce their own cortisol production.
- Clinical Risk: This adrenal suppression is usually short-lived, but it has been documented to persist for 2 to 4 weeks after a single injection. [17] In a physiologically stressed state (e.g., severe illness, major surgery, or trauma), the body may be unable to produce the necessary surge of natural cortisol.29 This can lead to a life-threatening condition called adrenal crisis, characterized by low blood pressure and shock. [17]
4.3 Risks of Repeated and Frequent Injections
While guidelines vary, the consensus recommends limiting the number of injections into a single joint, often to no more than three or four per year. [18] Frequent use is associated with a greater risk of:
- Accelerated Joint Deterioration: Some studies suggest that repeated corticosteroid injections into weight-bearing joints (like the knee) may have detrimental effects on cartilage health and could potentially accelerate the progression of osteoarthritis. [19] The exact clinical significance of this effect is still under investigation, but it underscores the need for judicious use. [19]
- Bone Mineral Density Loss: While less a concern than with oral steroids, high cumulative doses from repeated injections can contribute to a decrease in bone mineral density (osteoporosis). [4]
Conclusion and Patient Education
Corticosteroid injections remain a highly effective tool for providing short-term, localized relief from inflammatory pain, which can be critical for enabling physical therapy and rehabilitation.33 However, their use requires a thorough understanding of potential side effects.
The most common reaction, the steroid flare, is a transient, self-resolving event caused by the steroid’s microcrystalline structure. More serious complications, though rare, include infection, tendon rupture, and HPA axis suppression.34 Patient education on recognizing the signs of infection (pain/swelling lasting more than 48 hours, fever) and the importance of adhering to injection frequency limits are essential components of a safe and successful treatment plan. [20] Clinicians must weigh the short-term benefit of pain relief against the potential long-term risks, particularly those related to joint degeneration from repeated use. [19]
