Peripheral injections are among the most common procedures performed in an outpatient musculoskeletal medicine practice. Such injections serve a valuable role in the diagnosis and treatment of peripheral joint–mediated pain. Proper training, preparation, and technique is paramount to the performance of safe and effective peripheral joint and musculoskeletal injections.

Peripheral soft tissue or intraarticular injections commonly involve the injection of a local anesthetic in conjunction with corticosteroid. The local anesthetic is used to minimize the post-traumatic pain associated with joint or tissue needle penetration. In addition, the use of local anesthetic can serve a valuable diagnostic role during the immediate postinjection period by evaluating the injected structure as a pain generator. The use of a pain diary in conjunction with an injection can be particularly valuable in evaluating the degree and duration of pain relief obtained from the injected anesthetic. Steroids act as potent antiinflammatories; they can serve a therapeutic role in diminishing joint or tissue inflammation and can provide pain relief of longer duration. While local anesthetics generally take effect on the order of seconds to minutes, steroid injections often take several days to reach maximum efficacy.

For many injections it has become increasingly evident that surface anatomy landmarks alone are often not reliable enough for accurate needle placement, particularly in patients with suboptimal anatomy or body habitus. The use of image guidance in the form of fluoroscopy or ultrasound has become essential for the safe and accurate performance of many injection procedures, and the discussion that follows includes recommendations and technical considerations.

The first part of this chapter reviews basic principles of peripheral joint injection procedures. The second half describes individual joint and soft tissue injection techniques. Techniques for nerve blocks, neurolysis, trigger point injections, and spinal injections, as well as the diagnosis and pathogenesis of musculoskeletal conditions, are reviewed and discussed elsewhere in this text. The reader is referred to the index for these topics. In addition, a separate chapter is dedicated to the emerging role of ultrasound in musculoskeletal medicine (see Chapter 39).

Medications

Musculoskeletal injections most often involve the injection of two classes of medications: corticosteroids and local anesthetics. The local anesthetic results in immediate post-procedure pain relief, which may be useful for diagnostic purposes, and the steroid reduces inflammatory-mediated pain with longer duration of effect. Other commonly injected substances for musculoskeletal disorders include hyaluronic acid and, more recently, autologous platelet-rich plasma (PRP) or conditioned serum (ACS).

A. Local Anesthetics

Local anesthetics act by reversibly blocking the axon sodium channels, preventing sodium ion influx and action potential generation. The degree and duration of neural blockade is dependent on the volume, concentration, and proximity to the targeted nerve. The addition of a sympathomimetic such as epinephrine reverses the inherent vasodilatory effect of local anesthetics and in doing so decreases systemic absorption and secondarily increases concentrations, hastening onset, prolonging duration of action, and reducing toxicity. Local anesthetics typically are prepared with a pH of 5–6. The addition of sodium bicarbonate raises the pH and in doing so increases diffusion through the axon membrane and hastens onset. In the presence of inflammation, tissue pH is often lowered, thereby slowing local anesthetic onset of action. In addition, by buffering the injected solution, sodium bicarbonate reduces the burning pain associated with injection.

Local anesthetics, when administered using proper technique at reasonable doses and concentrations, are extremely safe medications that are widely used and well tolerated. Toxicity is generally associated with high volumes or concentrations or inadvertent intravascular injection. Central nervous system toxicity may cause confusion, convulsions, respiratory arrest, seizures, or death. Other serious side effects include cardiodepression, anaphylaxis, and malignant hyperthermia. When injecting large volumes of local anesthetic, withdrawing the plunger after each milliliter to check for heme and injecting contrast under live fluoroscopy is recommended to reduce risk of intravascular injection.

The two groups of local anesthetics include the amino esters and the amino amides. The ester group has an ester linkage and is broken down rapidly by the plasma pseudocholinesterase. The ester anesthetics are less commonly used owing to their short half-lives, instability in solution, propensity to degrade at high temperatures, and higher rate of allergic reactions. The shorter half-lives of esters may lower risks of toxicity. The amide group has an amide linkage; these agents are hydrolyzed in the liver. Consequently, caution is advised in patients with impaired hepatic function due to decreased ability to metabolize these agents. Methyl-paraben, a preservative, is commonly used with local anesthetics and is a common allergen. Allergic reactions to amides are generally related to methyl-paraben preservatives. The use of preservative-free anesthetics is mandatory for injections in or near the epidural space or thecal sac.

Lidocaine is the most commonly used local anesthetic owing to its rapid onset, intermediate duration, and safety profile, which allows for a relatively high maximum dose in comparison to effective dose. Bupivacaine is another commonly used local anesthetic, particularly for neural blockade, because of its longer duration of action. However, bupivacaine is limited by its longer onset of action and greater cardiotoxicity. Caution is advised when performing intraarticular injection with bupivacaine, which has shown chondrotoxic effects in animal studies and human case reports. Table 40–1 reviews the pharmacokinetics associated with the most commonly injected local anesthetics.

B. Corticosteroids

Corticosteroids all demonstrate some degree of glucocorticoid as well as mineralocorticoid activity. Antiinflammatory and immunosuppressive effects are mediated by the glucocorticoids whereas salt and water balance is affected by mineralocorticoids. The corticosteroids used in musculoskeletal injections have primarily glucocorticoid effects. Corticosteroids are commonly mixed with local anesthetics for musculoskeletal injections. The use of local anesthetics in conjunction with the injected steroid serves dual roles, diluting the steroid to permit greater spread of injectate across inflamed structures, as well as aiding in diagnosis.

Table 40–2 describes the common indications for glucocorticosteroid injections. The degree and duration of pain relief depend on many factors; in general, greater improvement is seen in inflammatory diseases as compared with degenerative diseases. Short-acting corticosteroids are rarely used for intraarticular injection as they are rapidly metabolized by the hypervascularized synovium of inflamed joints. Typically, systemic absorption following injection of intermediate- to long-acting corticosteroids begins at 48 hours and continues for several weeks. The most commonly used corticosteroids include methylprednisolone, triamcinolone, betamethasone, dexamethasone, and hydrocortisone. Glucocorticosteroids and their potencies are compared with hydrocortisone in Table 40–3. Dexamethasone and betamethasone demonstrate the greatest degree of glucocorticoid (antiinflammatory) activity, whereas hydrocortisone demonstrates the greatest degree of mineralocorticoid ­properties.

Adverse effects of corticosteroids include elevation in blood glucose, predisposition to local infection, osteonecrosis, tendon rupture, and postinjection pain flare. Other side effects include psychosis, facial flushing, injection site hypopigmentation, subcutaneous fat atrophy, increased appetite, dyspepsia, malaise, and insomnia. Serious side effects may include fluid retention leading to renal or congestive heart failure. The adverse effects of corticosteroids should be carefully considered in patients with uncontrolled blood glucose, active infection, ulcerative disease, uncontrolled hypertension, congestive heart failure, renal failure, or preexisting psychiatric illness or mood instability. For diabetic patients, a plan for blood glucose monitoring and glycemic coverage should be in place prior to injection.

C. Hyaluronic Acid

Another option for intraarticular injection involves the use of viscosupplementation for the treatment of osteoarthritis (OA)–related pain. Viscosupplementation involves the injection of hyaluronic acid, a glycosaminoglycan composed of repeating disaccharides of glucuronic acid and N-acetylglucosamine found naturally in synovial fluid. In the United States, the injection of hyaluronic acid is approved by the Food and Drug Administration (FDA) only for the treatment of pain associated with knee OA. Currently, there is limited evidence for the use of hyaluronic acid in the treatment of hip OA, and future indications are pending.

The concentration and molecular weight of hyaluronic acid are reduced in joints with OA. This reduction may be responsible for the decreased viscosity and elasticity noted in osteoarthritic joints. Although the mechanism of action of hyaluronic acid is not known completely, it is thought that these injections help in restoring the depleted hyaluronic acid in synovial fluid and within cartilage. Interestingly, although the half-life of hyaluronic acid is only 8.8 days, the onset of effect and duration of effect are actually much longer, with peak effects in pain and function scores occurring 5–13 weeks post-treatment. Therefore, there may be other mechanisms of action.

Hyaluronic acid may have additional antiinflammatory and antinociceptive effects. Several formulations are available, ranging from low molecular weight (Hyalgan) to high molecular weight (Synvisc). A Cochrane review on viscosupplementation that compared hyaluronic acid to steroid injection identified statistically significant differences in pain at 5–13 weeks postinjection. In addition, hyaluronic acid injection was found to have fewer systemic side effects with more prolonged effects than intraarticular corticosteroids. The safety of repeated exposure to hyaluronic acid injection has been well established, and repeat cycles of injection are recommended in patients who have previously responded favorably. The most common side effect is a local mild and self-limiting inflammatory response. Cross-linking of hyaluronic acid may also be related to a severe inflammatory response (commonly referred as pseudosepsis) that occurs within 24–72 hours of the injection, and it is important to rule out septic or acute inflammatory arthropathy.

D. Sterile Dextrose

Sterile dextrose at a concentration of 12.5–25% is a commonly used prolotherapy agent. In vitro studies on human chondrocytes and fibroblasts exposed to dextrose solution showed an increase in growth factor production. Sterile dextrose injections are generally performed with a 4-week interval between treatments and are repeated until at least 80% pain relief or plateau in clinical improvement is achieved. Postinjection antiinflammatory medications are avoided to allow the inflammatory healing phase to proceed unimpeded. There are indications from limited weak clinical trials that sterile dextrose has beneficial effects in pain relief and functional outcomes, with a good safety profile, in patients with knee OA.

E. Autologous Platelet-Rich Plasma

Autologous PRP, a concentration of human platelets in a small volume of plasma, is a regenerative form of therapy that is thought to augment tissue healing through natural healing cascades via growth factors released from the platelets. PRP has been used in the treatment of muscle, tendon, and cartilage injury. The use of PRP has been found to enhance production of hyaluronic acid and angiogenic growth factors in in-vitro studies of human synovial cells. The administration of PRP is generally performed with at least a 2-month interval between treatments and is repeated until at least 80% pain relief or plateau in clinical improvement is achieved. As with sterile dextrose injection, postinjection antiinflammatory medications are often avoided to allow the inflammatory healing phase to proceed.

F. Autologous Conditioned Serum

ACS (Orthokine, Regenokine) is an immunomodulator that has been available for use in Germany since 2003 but is not yet approved by the FDA. It is produced by removing 60 mL of a patient’s own blood, incubating the sample at 37 °C for 24 hours, and then centrifuging it to extract what is thought to be a potent interleukin-1 receptor antagonist. This substance, termed ACS, is then injected into an affected area with the goal of reducing pain and inflammation. The treatment is repeated a total of six times over 3 weeks. Limited studies thus far have shown ACS to be an effective and well-tolerated option in the treatment of early knee OA.

Adverse Effects

Complications following intraarticular injections include systemic toxic reactions; epinephrine reactions; allergic reaction; vasovagal response; nerve injury; infection; postinjection acute synovitis; ligament, tendon, or cartilage injury; tissue atrophy; and bleeding. Although the incidence of such complications is very low, several factors may increase patients’ risk. Patients who are receiving anticoagulant or antiplatelet agents, and those with a history of coagulopathy, are at greatest risk of hemarthrosis. Patients with diabetes mellitus are at greater risk for infection, which can lead to septic arthritis. The incidence of infection following joint injection ranges from 1 in 3000 to 1 in 50,000. Complications related to intraarticular injection are described in Table 40–4. Other complications that are unique to specific procedures are discussed in the context of each injection technique later in the chapter.

Arthrocentesis

Arthrocentesis can be performed for diagnostic and therapeutic purposes in patients with joint effusions. By decreasing mechanical pressure associated with joint effusions and in turn reducing inflammatory mediators, joint aspiration in isolation can be a therapeutic procedure. The aspirate can be sent for fluid analysis and cytology to differentiate infectious, hemorrhagic, inflammatory, and noninflammatory forms of arthritis. Table 40–5 provides details on characteristics of the joint aspirate in each of these four conditions. The techniques for arthrocentesis are the same as the intraarticular injection techniques described next and should precede the injection of medication into a joint with significant effusion.

Procedure Basics

A. Preinjection Care

Prior to every injection procedure, informed consent should be obtained; this includes the discussion of benefits, limitations, risks, and alternatives. The patient should then be positioned to provide optimum exposure to the area of interest, and surface anatomy landmarks should be palpated and marked. Both patient comfort and physician comfort should be considered as well for optimal positioning. Recumbent positioning is preferred over sitting or standing positioning in the event that a patient develops a vagal response or syncopal episode as a result of the injection. Clinicians should be aware that some exquisitely sensitive patients may develop vagal responses even during informed consent or during early preparations for the injection procedure.

After landmarks are appropriately palpated, the injection site should be marked using a skin marker or skin impression. Next, the skin should be thoroughly cleansed with antiseptic agents (povidone–iodine, chlorhexidine, or alcohol) and allowed to dry. Evidence suggests that a chlorhexidine preparation may be more effective than alcohol or povidone–iodine. In addition, when using povidone–iodine, it is essential to allow a drying time of at least 90–120 seconds to maximize its bacteriocidal effects. In patients with low pain thresholds, topical anesthetics or vapocoolant sprays may be used to minimize pain. Prior to injection, aspiration should be performed to reduce the risk of intravascular injection.

Universal precautions and sterile technique should be used and maintained throughout the procedure. The choice of sterile versus nonsterile gloves remains physician dependent for peripheral joint and soft tissue injections. If the region to be injected is to be palpated following skin preparation, then sterile gloves should always be used. If nonsterile gloves are to be used, full sterile precautions must be maintained at the site of injection. Patients should always be queried regarding latex allergies if latex gloves or dressings are to be used.

The choice of needle length and gauge is dependent on the type of injection performed, potential need for joint aspiration, and patient’s body habitus. The choice of needle, syringe, and injectate are dependent on the structure being injected and are discussed later in the chapter.

B. Postinjection Care

After the injection, a sterile adhesive bandage should be applied and the patient monitored for any immediate postinjection reaction or bleeding. If local anesthetic is being injected and the injection is serving a diagnostic role, a pain diary should be provided to the patient to more objectively evaluate numerical pain scores during the immediate postinjection period. Patients should be monitored for 15–20 minutes following injection and, if treated in an outpatient setting, should be advised ahead of time to have another person come with them in the event that significant paresthesia, proprioceptive loss, or focal weakness develop that would impair their ability to drive themselves home.

Patients should be advised of the possibility of short-term symptom aggravation, consisting of postinjection acute synovitis within the first 24–48 hours, which usually resolves spontaneously. To minimize postinjection inflammation, patients are advised to apply ice to the site for 15–20 minutes two to three times a day for the first 24–48 hours and use nonsteroidal antiinflammatory drugs as needed for postinjection discomfort. Patients should be instructed that a baseline level of pain may return for a period of time as the local anesthetic wears off, before the steroid starts to act. They should further be instructed to limit usage of the joint, at least for the first 24 hours, particularly for the weight-bearing joints. Activity restriction has been shown to prevent injury and prolong the effect of the injected steroid. In addition, patients should be informed of potential “red flags” and given instructions to call the treating physician if any of the following are noted: temperature exceeding 100.3°F, erythema, drainage, or ­effusion.

Injection frequency should be determined based on degree and duration of response to previous injections, the nature of disease process, medical comorbidities, symptom severity, and clinical judgment. Injection of large joints should not be performed more than three to four times per year and not more than 10 times cumulatively. Injections of small joints should not be performed more than two to three times per year and not more than four times cumulatively.

Temporomandibular Joint Injection

A. Indications

Common indications for temporomandibular joint (TMJ) injection include TMJ syndrome or arthritis. Patients usually present with pain and stiffness localized to the TMJ. The pain may also radiate to nearby facial structures, and commonly patients experience headaches in association. TMJ imaging should be obtained prior to injection.

B. Relevant Contraindications

There are no specific contraindications.

C. Equipment and Medication

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  Equipment: 27-gauge, 1-inch needle; 3-mL syringe for ­medication.

  
  
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  Image guidance: computed tomography (CT), fluoroscopy, or ultrasound guidance is optional.

  
  
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  Medication: 40-mg of methylprednisolone and 0.5 mL of 2% lidocaine.

D. Patient Preparation

The patient is placed in a supine or lateral recumbent position. The skin should be thoroughly cleansed with antiseptic agents (povidone–iodine, chlorhexidine, or alcohol) and allowed to dry.

E. Technique and Relevant Anatomy

The joint is localized below the zygomatic arch, 1–2 cm anterior to the tragus. The landmark is the inferolateral margin of the mandibular condyle. The joint is easily localized by opening and closing the mouth. The needle is inserted perpendicularly, with the tip angled slightly superiorly into the joint. Studies have demonstrated greater efficacy with ultrasound-guided approaches in children with juvenile idiopathic arthritis.

F. Potential Complications

The temporal artery lies posterior to the joint and should be avoided. The facial nerve may also be inadvertently blocked, causing facial muscle weakness.

Shoulder Joint Injections

Shoulder injections are among the most common injection procedures performed in a musculoskeletal medicine practice. Shoulder pain is often poorly localized, and physical examination findings can overlap widely among disorders. Therefore, these injections are often equally valuable for both diagnostic and therapeutic roles.

Sternoclavicular Joint Injection

A. Indications

Pain secondary to arthritis is the most common indication for intraarticular injection of the sternoclavicular (SC) joint. Other indications include post-traumatic pain associated with subluxation. OA of the SC joint is a relatively uncommon pathologic finding. The SC joint acts as a fulcrum for the shoulder and serves as an attachment site for the axial to appendicular skeleton. Patients may experience pain localized to the sternum, and pain may be increased with shoulder range of motion. The medial clavicle, manubrium of the sternum, and first rib articulate to form the SC joint, which is a true synovial joint. The joint is stabilized by the anterior and posterior SC ligaments. The SC joint may be subluxed, elevating the proximal clavicle in relation to the sternum and serving as a pain generator. Imaging should always be obtained prior to injection, and CT is the preferred imaging modality for the SC joint.

B. Relevant Contraindications

Acute trauma or dislocation is a contraindication to injection.

C. Equipment and Medication