ABSTRACT: Injectable corticosteroids may be used for managing painful shoulder conditions, but there are no universally accepted guidelines for dosage and administration. Understanding the mechanisms of action is critical for knowing when they can be used effectively. The biggest absolute contraindication to intra-articular or extra-articular corticosteroid injections is evidence or probability of infection. Relative contraindications include anticoagulation therapy, hemarthrosis, and poorly controlled diabetes mellitus. Most complications result from frequent use and can be avoided with appropriate doses and dosing intervals. Intra-articular and periarticular corticosteroid injections may cause significant systemic effects. The misuse of corticosteroid injections often is overuse. Creation of uniform guidelines for injections would help reduce their deleterious effects and maximize pain relief. (J Musculoskel Med. 2008;25:78-98)
Injectable corticosteroids, popular in the 1950s because they relieved pain in arthritic joints,1,2 are used widely now for managing a variety of painful articular and nonarticular shoulder conditions.3 When 1 or more separate but adjacent regions may be the anatomical source of shoulder pain, corticosteroids often are used in combination with local anesthetics—the anesthetic provides immediate site-specific pain relief and helps confirm injection accuracy.
Corticosteroid/anesthetic injections are potentially curative as well as diagnostic for some subacromial (SA) impingement syndromes (Figure), such as bursitis and rotator cuff tendinitis (Table 1),4 and are beneficial in managing other painful shoulder conditions, such as osteoarthritis and adhesive capsulitis (Table 2).1,5-10 However, there are no univer
sally accepted guidelines for dosage and administration for the various shoulder conditions.11-13
Figure – Injectable corticosteroids often are used in combination with local anesthetics for relieving shoulder pain when 1 or more separate but adjacent regions may be the anatomical source of the pain. Corticosteroid/anesthetic injections may be both curative and diagnostic for some subacromial (SA) impingement syndromes, such as bursitis and rotator cuff tendinitis. We recommend beginning with the lateral or posterolateral approach to the SA space.
In our shoulder specialty clinic, for example,we observe considerable variance in the administration and medical-record doc
umentation of corticosteroid/anesthetic injections by our referring orthopedic surgeons, primary care physicians, and other nonsurgeon health car
e professionals. There is a common lack of clarity about where the injection or injections were given (were both the SA space and acromioclavicular [AC] joint injected?) and the estimated percent relief attributed to the rapid effect of the local anesthetic. In a survey of 169 physicians (orthopedic surgeons and nonsurgeons) in our greater referral area, we found that these 2 groups often differ in the amounts of local anesthetic and corticosteroid used to inject for the same shoulder condition.12
In this 3-part article, we describe the diagnostic and therapeutic uses and misuses of corticosteroid/anesthetic injections for painful shoulder conditions. This first part reviews the mechanism of action of corticosteroids, current preparations, indications and contraindications, adverse effects, misuses, and lack of uniform standards of care. In the second part, to appear in a later issue of this journal, we will discuss the physical examination and radiographic evaluation. The third part will illustrate techniques for administering injections for specific shoulder conditions. We hope that this discussion will encourage the development of more uniform guidelines for musculoskeletal specialists and general-practice professionals, help improve injection accuracy, and enhance communication about estimation and documentation of immediate percent relief resulting from the local anesthetic.
MECHANISMS OF ACTION
Understanding the mechanisms of action of corticosteroids is critical for knowing when they can be used for treatment and why they are more potent than NSAIDs for painful shoulder conditions. The inflammatory process begins with activation of phospholipase A2, which converts phospholipids to arachidonic acid. Mediators of inflammation are then produced from arachidonic acid, which is converted into endoperoxides by cyclooxygenase (COX) or into hydroperoxides by lipoxygenase. Endoperoxides and hydroperoxides are further converted into other inflammatory mediators.
Corticosteroids are potent anti inflammatory medications that inhibit phospholipase A2, which prevents the formation of arachidonic acid, blocking synthesis along the COX and lipoxygenase pathways. They reduce prostaglandin synthesis by up to 50% and decrease interleukin-1 secretion by synovial membranes.14,15
