Interlaminar epidural injection refers to a procedure that involves the delivery of injectate to the epidural space by directing a needle between the laminae of two adjacent vertebrae. The goal of this interventional pain medicine procedure is the relief of radicular pain and are a therapeutic option in the cervical, thoracic, or lumbar spine. Injectate typically is composed of a combination of anesthetics and steroids. The interlaminar approach allows for medication spread over a larger area than transforaminal epidural injection and can be advantageous in patients with multi-level spinal pathology. However, the intrinsic nature of the dorsal approach of interlaminar injection results in a limited ventral spread of injectate compared to transforaminal epidural injections, which can limit efficacy in a pathology-dependent manner.
The vertebral column is composed of seven cervical vertebrae, twelve thoracic vertebrae, five lumbar vertebrae, five fused sacral vertebrae, and four fused coccygeal vertebrae. The typical osseous anatomy of a vertebra consists of a vertebral body, two pedicles extending posteriorly, and the posterior elements. The component parts of the posterior elements are the laminae with two superior and two inferior articular facets on either side, transverse processes extending laterally, and a spinous process. The synovial articulation of the superior and inferior articular facets of the adjacent vertebra is termed the zygapophyseal joint or facet joint. The spinal cord runs through the vertebral canal which has osseous boundaries of the vertebral body anteriorly, the pedicles laterally, and the laminae posteriorly. Ligamentous boundaries of the vertebral canal as the spinal cord descends include the posterior longitudinal ligament anteriorly and the ligamentum flavum between adjacent vertebral laminae posteriorly.
Intervertebral discs exist between adjacent vertebral bodies. The discs contain a central nucleus pulposus with surrounding annulus fibrosus. The composition of the nucleus pulposus is semifluid collagen mixed with ground substance while the outer annulus fibrosis is composed of densely layered collagen fibers which extend into the endplates of the vertebral bodies. When a disc herniation occurs, and disc contents are released, there is an increase in pro-inflammatory molecules which can irritate surrounding structures, including the nerve roots and spinal nerves.
The spinal cord begins caudally to the medulla at the C1 vertebra and terminates as the conus medullaris in the vicinity of the L1-L2 region of the spinal column. At each level, dorsal and ventral roots combine to form spinal nerves which exit through neuroforamina. The remaining lumbar and sacral roots descend with the filum terminale collectively forming the cauda equina. The spinal cord has a wrapping comprised of protective meninges – the innermost pia mater, the arachnoid, and the outermost dura mater. The epidural region is located in the region between the dura mater and the osseous/ligamentous boundaries of the vertebral canal previously described. Areolar fatty tissue, lymphatics, and connective tissue comprise the epidural region.
The interlaminar approach for epidural injection involves needle passage ultimately through the ligamentum flavum to deliver injectate to the epidural space.
The clinical findings of patients who are most likely to benefit from epidural injections are those who have back pain with a radicular component due to herniated nucleus pulposus. Radicular pain in the cervical spine may refer to pain radiating down the upper extremity, while in the lumbar spine classic radicular pain radiates down the lower extremity. Physical exam findings may include those which correspond to radiculopathy, including positive Spurling test for the cervical spine, or positive straight-leg-raise for the lumbar spine. Patients with spinal stenosis also may benefit from epidural injections; however, recent studies continue to delineate optimal injectate composition.
The contraindications to interlaminar epidural injection include local infection, systemic infection, allergy to injectate, and potentially bleeding disorders or anticoagulation. The American Society of Intervention Pain Physicians (ASIPP) and American Society of Regional Anesthesia and Pain Medicine (ASRA) guidelines vary in terms of recommendations regarding discontinuation of anticoagulant/antiplatelet medications. ASIPP guidelines suggest that interventional spinal techniques can classify as low, intermediate, or high-risk techniques. In terms of interlaminar epidural injections, the following classification suggestions:
Intermediate-risk: Lumbar interlaminar epidural injections at L5-S1High-risk: Cervical, thoracic, and all lumbar interlaminar epidural injections above L4-L5
Recommendations on the continuation of antithrombotics or anticoagulants, stopping, and restarting therapy following the procedure are agent-specific. Clinicians need to consider appropriate consideration of the risks-benefits of holding these agents for all patients. Use of steroid for injection also expands contraindications to include medical comorbidities such as poorly controlled diabetes/hypertension or congestive heart failure.
Physician/X-ray tech/nurse/medical assistant or allied healthcare provider.
Generally, magnetic resonance imaging (MRI) is necessary before performing any spinal epidural injection. This imaging allows for clear visualization of the pathology and can aid in procedure planning. Along with clinical findings, MRI also helps determine the procedure or approach most likely to benefit the patient and has been shown to influence management decisions. For example, radicular pain due to a far lateral disc herniation may respond better to a transforaminal epidural injection, while multi-level mild to moderate foraminal stenosis in the context of spondylosis may respond better to an interlaminar approach. Electromyography (EMG) may also be used in procedure planning to predict patient response.
Patient positioning is prone, with bolsters or pillows positioned to increase interlaminar space optimally. The skin is cleansed and prepared in a sterile fashion. Fluoroscopic anterior-posterior (AP) imaging is used to identify the targeted vertebral levels. Cephalad or caudal tilt is used to maximize or "open up" the interlaminar space and a 5 to 15-degree oblique angle is introduced to establish a trajectory view for a paramedian approach. A 25-gauge needle is used for anesthesia of the skin and projected approach. Then, a 17 to 20 gauge Tuohy spinal needle is inserted at the same site parallel to the image trajectory. The spinal needle is advanced with the stylet in place using intermittent imaging. From superficial to deep the skin, subcutaneous tissue, and paraspinal muscles are pierced until encountering resistance at the ligamentum flavum. Lateral imaging may be used to assess depth depending on clinician preference and spinal region. This assistance can be especially useful in cervical or thoracic procedures for safety. Upon feeling the ligamentous resistance, the stylet is removed, and the LOR syringe filled with 2 mL of preservative-free normal saline is connected.
The spinal needle is then advanced in millimeter increments with continuous gentle pressure on the plunger of the LOR syringe. When the ligamentum flavum has penetrated a loss of resistance is felt through the plunger, and the normal saline is injected due to negative pressure upon penetration into epidural space. Firm, careful control of needle depth is vital as syringes are exchanged at this stage to avoid the advancement of the needle. The LOR syringe is exchanged for syringe containing iodinated contrast, and a small amount is injected to ensure epidural placement. On AP view, an asymmetric, vacuolated contrast spread consistent with epidural placement view should be observed. If the placement is too dorsal due to a false loss of resistance, a dense blotch may is observable suggesting the needle needs to be advanced further using the LOR technique once again. Or, a rapidly dissipating vascular pattern implies arterial injection, and the placement should be adjusted. If the needle has been advanced too far ventrally, a symmetrical, smooth, and faint pattern may be observed suggesting subdural injection. In this case, the clinician should withdraw the needle and an alternative interlaminar site selected. Once optimal contrast spread is seen, the syringe is exchanged, and medication instilled into the epidural space. The needle is withdrawn, a sterile dressing is applied, and the patient should undergo monitoring for some time following the procedure.
Complications of interlaminar epidural injections may be related to needle placement, infection, or medications administered. Regarding placement, advancement too far ventrally may result in the dural puncture or spinal cord trauma. Patients may experience a vasovagal reaction, headache, singultus, transient blindness, nausea, vomiting, or dizziness. Infectious complications include epidural abscess, meningitis, or osteomyelitis. Steroid preparations should be non-particulate to avoid complications associated with vascular occlusion, including spinal cord infarction. Complications due to steroid medications include but are not limited to hyperglycemia, hypothalamic-pituitary-adrenal (HPA) axis suppression, avascular necrosis, Cushing syndrome, and myopathy.
Interlaminar epidural injections are an important non-surgical treatment option for patients with back pain with a radicular component. The natural history of disc herniation suggests that significant improvement can occur in 4 to 6 months. Appropriately performed by an experienced clinician, these injections provide a relatively low-risk option to improve quality of life, restore the performance of activities of daily living (ADLs), and avoid surgical intervention due to potentially temporary disabling conditions.
Before the procedure, the clinician should educate the patient on the risks/benefits, preventative measures, with patient expectations addressed. While a physician performs intralaminar epidural injections, there is a need for other personnel like the X-ray technician, nurse to monitor the patient, and a medical assistant to assist with the medications. During the procedure, the patient requires monitoring by the nurse. The intralaminar epidural injection is not a cure but a temporizing method of pain control. To improve outcomes, there should be coordination with physical/occupational therapy (PT/OT), primary care physicians, and neurosurgery/orthopedic surgery to determine which is the best method for more long term pain relief. Patients should receive instruction from the physical therapist on proper biomechanics, strengthening/stretching exercises, ergonomics, and lifestyle changes. Reasonable consideration and exclusion of differential diagnoses, as well as the appropriate trial of conservative measures - including PT/OT, oral medications, and modalities - should be performed before any invasive procedure. The dietitian should assist with education on a healthy diet, and the pharmacist should educate the patient on means of pain control, with a view towards avoiding opioids if at all possible. Only through such an interprofessional team approach can the morbidity of spinal radicular pain be decreased. [Level V]
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