Musculoskeletal injections in general
Devendra Mahadevan and Euan Stirling
Introduction
Pain from musculoskeletal problems is an increasing cause for poor quality of life and is putting increased demands on the healthcare system. The chronicity of symptoms may impact on the physical, psychological and socio-economic status of patients (Video 1.1).
Management strategies should focus on the individual needs of these patients (localised versus systemic pain, co-morbidities, physical status and functional requirements). There are a multitude of treatment options employed by healthcare providers. These include non-medicinal treatments (self-management education, physical/exercise therapy, manual therapy and psychosocial interventions), complementary therapies (acupuncture, ultrasound, TENS [transcutaneous electrical nerve stimulation]), pharmacological interventions (analgesics, anti-inflammatories, corticosteroid injections) and surgery. In order to provide optimal care to patients with musculoskeletal pain and ensure efficient use of healthcare resources, evidence-based practice is essential.
This chapter discusses the use of corticosteroid injections in the management of musculoskeletal pain and the practicalities of providing this treatment. Like all other procedures, the efficacy of this treatment depends on appropriate use, i.e. correct indication, selecting the appropriate pharmacological agent and performing the procedure correctly and safely.
What are corticosteroids?
Corticosteroids are steroid hormones that are either naturally produced by the adrenal cortex in vertebrates or synthetically made to mimic the naturally occurring variant. Corticosteroids regulate a wide range of physiologic processes, including stress and immune responses, regulation of inflammation, carbohydrate metabolism, protein catabolism, blood electrolyte levels and behaviour [1].
They can be given topically, orally or by injection, and may produce a local or systemic response. Examples of synthetic corticosteroids used as pharmacological agents include betamethasone, prednisone, triamcinolone and dexamethasone.
How do steroid injections work?
Corticosteroids have a combined anti-inflammatory and immunosuppressive effect. When injected into joints, they reduce synovial blood flow and vascular permeability [2], and lower leukocyte and inflammatory mediators including prostaglandins and leukotrienes [3–5]. They also alter local collagen synthesis [6] and increase the hyaluronic acid concentration within the joint [3,4]. The mechanism of action is complex: The steroids act directly on nuclear steroid receptors and interrupt the inflammatory and immune cascade at several levels. The net effect is reduction in pain and inflammation locally.
The esterification (reaction between alcohols and carboxylic acids to make esters) of corticosteroids enhances their pharmacokinetic properties. The alteration of the parent steroid chemical properties can improve metabolic and water solubility and lipophilicity, thus potentially increasing bioavailability and prolonging duration of efficacy [7]. For example, branched esterification reduces the solubility of the drug and enhances its duration of action, as it remains longer at the injection site [2].
What are the indications and contraindications of corticosteroid injections?
Corticosteroid injections play an important role in the management of musculoskeletal conditions. They can be used as a definitive treatment (e.g. trochanteric bursitis, De Quervain’s tenosynovitis); provide a pain-free window for rehabilitation (e.g. subacromial impingement, epicondylitis, plantar fasciitis); or to provide episodic pain and symptom relief (e.g. osteoarthritis).
When used appropriately for the correct indication, corticosteroids will provide good relief (Table 1.1). One must be aware that corticosteroids are contraindicated in several conditions that produce a ‘painful and swollen’ joint (Table 1.2). Physicians need to be astute in establishing the diagnosis prior to instilling corticosteroid injections. If the intra-articular diagnosis is not obvious, a diagnostic aspiration should be performed prior to injecting the joint with corticosteroids. The aspirated fluid may be visually analysed (cloudy synovial fluid or haemarthrosis) and if it looks abnormal, should be sent for microscopy and cultures.
Table 1.1 Indications for corticosteroid injections
