Infection

The incidence of infectious complications after spinal injections is reported as 1%–2%. Most infections are minor, but severe complications, such as epidural abscess, meningitis, osteomyelitis, septic z-joint arthritis, and discitis, have been reported. The predominant mechanism for infections is considered to be the introduction of Staphylococcus aureus from the skin to the spinal structures, although cases have been reported in which gram-negative aerobes and anaerobes were identified, presumably after accidental intestinal penetration.

Apart from meticulous sterile technique for preventing infectious complications after spinal injections, the standard use of prophylactic antibiotics has been recommended, but only for discography.

Early diagnosis and treatment are essential to minimize the chance of a poor outcome. General signs of infection may include severe back pain, fever, chills, and malaise. Other signs may vary depending on the underlying pathology, such as meningeal irritation for meningitis or progressive neurologic deficit for an epidural abscess. Diagnostic tests should be chosen based on the suspected pathology and often include magnetic resonance imaging (MRI) and blood tests, such as complete blood count, erythrocyte sedimentation rate, and C-reactive protein. Specific tests, such as cerebrospinal fluid (CSF) analysis, may be indicated.

Appropriate treatment, such as administration of antibiotics or surgery, should be initiated as soon as possible.

Allergy

Allergic and anaphylactic reactions to commonly used medications for spinal injections are very rare. However, such reactions have been described after the administration of contrast media, local anesthetics, and corticosteroids, most often in the 2 hours after the epidural injection. Symptoms may vary from mild ones, such as light-headedness and nausea, to convulsions and compete cardiovascular and respiratory collapse.

A careful history of previous allergic reactions should be taken before all spinal injections. Hemodynamic and respiratory monitoring and full resuscitation equipment, including antihistamine medication, should be readily available.

Corticosteroids

Corticosteroids injected into spinal structures have systemic side effects. These include flushes, facial erythema, rash, pruritus, headache, dizziness, insomnia, elevated temperature, irregular menses, mood swings, gastrointestinal discomfort, epidural lipomatosis, and fluid retention.

A significant effect of a spinal injection with corticosteroids is adrenal suppression, which usually lasts 4 to 7 days after a single epidural injection but the effects can last for up to 5 weeks.

Hyperglycemia after spinal corticosteroid injections is rarely of clinical importance. However, in diabetic patients, the elevation of blood glucose is usually more pronounced. There are reports that the severity of glucose increase is related to the level of hemoglobin A1c at the time of injection. Diabetic patients should be informed of the possible blood glucose increase, which may require adjustment of their insulin dose.

Current evidence seems to favor the use of nonparticulate preparations for spinal injections over particulate ones, especially for epidural injections. The use of particulate steroid preparations in lumbar and cervical spinal injections has been shown to be associated with severe morbidity, such as spinal cord infarction presumably by arterial embolisation. In an animal study, direct injection with particulate steroid into the vertebral artery resulted in severe neurologic deficits, whereas no deficits were found when nonparticulate steroids were used. Furthermore, a comparative study showed no statistical or clinical difference in pain relief effectiveness between cervical transforaminal particulate triamcinolone and nonparticulate dexamethasone.

Bleeding

The spine, particularly the epidural space, is a densely vascularized structure. Therefore, all spinal injections carry an inherent risk of bleeding complications. The incidence of clinically significant spinal hematomas is very low, but they have been shown to be associated with severe morbidity.

An increased bleeding tendency is associated with a higher risk of epidural hematoma, but epidural hematoma can develop in any patient after spinal procedures. An increased bleeding tendency is often encountered in patients with coagulation disorders, such as hemophilia or von Willebrand disease, in those taking anticoagulants, or in those with liver or renal disease. It is essential that patients with an increased bleeding tendency are identified by taking a complete history on coagulation disorders, use of anticoagulants, easy bruising, and prolonged bleeding after dental procedures.

Appropriate blood tests are required once a coagulation disorder is suspected. Based on the outcome of these tests, referral to a hematologist for further analysis and treatment may be necessary.

Guidelines for patients on anticoagulants who are proposed for spinal procedures have been described elsewhere. Generally, anticoagulants are put on hold, and with warfarin, an international normalized ratio of 1.4 is the general standard. However, when injections have a low associated risk of bleeding, there is some controversy regarding the discontinuation of nonsteroidal anti-inflammatory medications (NSAIDs) or even therapeutic anticoagulation.

Early diagnosis and treatment of spinal hematoma is important, because the outcome is highly dependent on the time interval between the onset of symptoms and the initiation of treatment. Symptoms include unexpected duration or spread of sensory or motor deficit, unexplained spinal or radicular pain, and bladder or bowel dysfunction. Symptoms may present immediately postprocedure or be delayed for several days.

MRI is the preferred imaging modality if a spinal hematoma is suspected. Once the diagnosis of spinal hematoma is made, immediate referral to a neurosurgical facility is mandatory, because treatment generally involves surgical decompression.