Posterior decompressive procedures are a fundamental component of the surgical treatment of symptomatic cervical degenerative disease. Posterior approaches have the appeal of avoiding complications associated with anterior approaches such as esophageal injury, recurrent laryngeal nerve paralysis, dysphagia, and adjacent-level disease after fusion. Although open procedures are effective, the extensive subperiosteal stripping of the paraspinal musculature leads to increased blood loss, longer hospital stays, and more postoperative pain, and potentially contributes to instability. Minimally invasive access has been developed to limit approach-related morbidity. This article reviews current techniques in minimally invasive surgical management of cervical myelopathy and radiculopathy.
Key points
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Patients with radiculopathy caused by a lateralized osteophyte or disc herniation without cord compression, evidence of instability, or those for whom an anterior approach is contraindicated, are candidates for minimally invasive cervical discectomy or foraminotomy (MICD/F).
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Minimally invasive decompression of cervical stenosis (MIDCS) may be offered to patients who have less than 3 levels of disease, lack evidence of instability, and have normal cervical lordosis.
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In addition to equivalent efficacy, MICD/F and MIDCS offer the advantages of reduced blood loss, length of stay, postoperative pain, and muscle spasm; preservation of motion segments; and decreased risk of iatrogenic sagittal plan deformity.
Introduction
Several degenerative abnormalities of the cervical spine can be successfully treated with posterior decompressive techniques. Although anterior cervical procedures represent a well-established treatment for cervical disc herniation, posterior cervical laminoforaminotomy consistently shows symptom improvement of 90% to 97% for patients with foraminal stenosis or lateral disc herniation. Likewise, posterior decompression with either laminectomy or laminoplasty for patients with myelopathy from cervical stenosis shows clinical improvement in 62.5% to 83% of cases. Posterior decompressive procedures avoid the complications associated with anterior approaches such as esophageal injury, recurrent laryngeal nerve paralysis, dysphagia, and adjacent-level disease after fusion.
Although standard open approaches are effective, minimally invasive approaches have been developed to avoid the extensive subperiosteal stripping of paraspinal musculature that can result in significant postoperative pain, muscle spasm, and dysfunction in 18% to 60% of patients. Furthermore, preoperative loss of lordosis combined with long-segment decompression can contribute to the risk of sagittal plane deformity, a known complication that often obliges fusion at the time of decompression. The use of a posterior fusion technique increases operative time, blood loss, surgical risk, and early postoperative pain, and potentially contributes to adjacent-level disease.
The principal tenet of minimal-access techniques is to reduce approach-related morbidity. To this end, the advent of muscle-splitting tubular retractor systems and associated instruments have allowed for the application of minimally invasive techniques to posterior cervical decompressive procedures. Minimally invasive cervical discectomy/foraminotomy (MICD/F) was first described in a cadaver model, and has subsequently been shown to have clinical efficacy equal to that of open procedures in addition to having less blood loss, shorter hospital stay, and decreased postoperative pain.
Whereas the goal of MICD/F is nerve-root decompression, minimally invasive decompression of cervical stenosis (MICDS) is performed with the aim of decompressing the spinal cord. MICDS is a familiar modification of minimally invasive techniques that have been applied extensively to the lumbar spine. By preserving much of the normal osteoligamentous anatomy of the cervical spine, the MIDCS procedure reduces the risk of postlaminectomy kyphosis and avoids the need for prophylactic posterior fusion. The use of minimally invasive laminoplasty has been reported with positive results, although investigators have encountered technical difficulties and prolonged operative times.
Introduction
Several degenerative abnormalities of the cervical spine can be successfully treated with posterior decompressive techniques. Although anterior cervical procedures represent a well-established treatment for cervical disc herniation, posterior cervical laminoforaminotomy consistently shows symptom improvement of 90% to 97% for patients with foraminal stenosis or lateral disc herniation. Likewise, posterior decompression with either laminectomy or laminoplasty for patients with myelopathy from cervical stenosis shows clinical improvement in 62.5% to 83% of cases. Posterior decompressive procedures avoid the complications associated with anterior approaches such as esophageal injury, recurrent laryngeal nerve paralysis, dysphagia, and adjacent-level disease after fusion.
Although standard open approaches are effective, minimally invasive approaches have been developed to avoid the extensive subperiosteal stripping of paraspinal musculature that can result in significant postoperative pain, muscle spasm, and dysfunction in 18% to 60% of patients. Furthermore, preoperative loss of lordosis combined with long-segment decompression can contribute to the risk of sagittal plane deformity, a known complication that often obliges fusion at the time of decompression. The use of a posterior fusion technique increases operative time, blood loss, surgical risk, and early postoperative pain, and potentially contributes to adjacent-level disease.
The principal tenet of minimal-access techniques is to reduce approach-related morbidity. To this end, the advent of muscle-splitting tubular retractor systems and associated instruments have allowed for the application of minimally invasive techniques to posterior cervical decompressive procedures. Minimally invasive cervical discectomy/foraminotomy (MICD/F) was first described in a cadaver model, and has subsequently been shown to have clinical efficacy equal to that of open procedures in addition to having less blood loss, shorter hospital stay, and decreased postoperative pain.
Whereas the goal of MICD/F is nerve-root decompression, minimally invasive decompression of cervical stenosis (MICDS) is performed with the aim of decompressing the spinal cord. MICDS is a familiar modification of minimally invasive techniques that have been applied extensively to the lumbar spine. By preserving much of the normal osteoligamentous anatomy of the cervical spine, the MIDCS procedure reduces the risk of postlaminectomy kyphosis and avoids the need for prophylactic posterior fusion. The use of minimally invasive laminoplasty has been reported with positive results, although investigators have encountered technical difficulties and prolonged operative times.
Preoperative planning
A preoperative radiographic evaluation follows a detailed history and physical examination, and should include magnetic resonance imaging (MRI) or postmyelographic computed tomography (CT), and anteroposterior (AP), lateral, and flexion/extension cervical radiographs. Preoperative electromyography (EMG) and nerve conduction studies may also assist in the neurologic localization of specific radiculopathy. Those patients with radicular symptoms that correlate with electrophysiologic and radiographic findings may be well suited for MICD/F, depending on the underlying pathologic profile. Fig. 1 A shows a lateralized disc herniation without spinal cord compression on preoperative MRI scan. By contrast, Fig. 1 B shows moderate cord and nerve-root compression arising from a herniated disc. The former would be an ideal candidate for MICD/F, whereas MICDS or an anterior approach would be safer and more effective in the latter. Regardless of the abnormality, whether a soft disc or an osteophyte, it must be lateralized without significant canal stenosis to be amenable to MICD/F. MIDCS may be indicated for patients presenting with myelopathy or myeloradiculopathy caused by central spondylotic stenosis (eg, ligamentum flavum or facet hypertrophy). Those patients with moderate canal stenosis, normal cervical lordosis, primarily posterior disease, and without instability may be considered for MIDCS or traditional laminectomy or laminoplasty.
Patient positioning
General endotracheal anesthesia is induced with fiberoptic intubation utilized in patients with chronic spinal cord compression. If the patient is placed in the sitting position a precordial Doppler may be used to monitor for air embolism, although the risk of air embolism is very low. Foley catheterization is generally not needed. Routine perioperative antibiotics are administered, as is an intravenous corticosteroid at the surgeon’s discretion. Paralytic agents are minimized after induction to allow for physical intraoperative feedback of nerve-root irritation. The patient is placed in Gardner-Wells tongs or Mayfield head holder, and placed prone on a Jackson table with the head gently flexed ( Fig. 2 ). Alternatively, the patient may be placed in the sitting position. For the sitting position, the Mayfield 3-point head fixator is attached and the table progressively flexed to bring the patient into a semisitting position, such that head is flexed but not rotated and the posterior neck is perpendicular to the floor. Some prefer the sitting position because of the decreased blood pooling in the operative field and the gravity-dependent positioning of the shoulders for better lateral fluoroscopic images. Regardless of the position, the legs, hands, and arms are well padded, particularly over the cubital tunnel, to prevent positional ulnar neuropathy. The fluoroscopic monitor is placed opposite the side of the approach so that the surgeon can look directly at the monitors while standing next to the patient and operating through the tubular retractor. The C-arm is placed beneath or anterior to the patient depending on available space. The neck is checked a final time to ensure the position allows adequate jugular venous drainage and airway patency.
Surgical approach
This section outlines the technique for posterior MICD/F and MIDCS. The procedures described here use the METRx retractor (Medtronic Sofamor Danek, Memphis, TN); however, the principles are the same regardless of the retractor system used.
Before draping, an initial fluoroscopic image is acquired to confirm adequate visualization and to plan the initial entry point. The posterior neck is shaved, scrubbed, prepared, and draped in the usual manner. It is helpful to use adhesive lined drapes and/or an antibacterial adhesive layer such as Ioban (3M Health Care, St. Paul, MN) to maintain the orientation and position of the drapes during the procedure. Suction tubing, cautery lines, and the drill are typically draped over the top or side of the field and secured against the drapes. The operative level(s) is once again confirmed on lateral fluoroscopy while a long Kirschner (K)-wire or Steinman pin is held over the lateral side of the patient’s neck. For lower cervical levels (eg, C6–7, C7–T1) or in patients with high-riding shoulders in whom the operative level cannot be adequately visualized on lateral fluoroscopy despite maneuvers to push the shoulders down, both oblique and AP fluoroscopy can be used to localize the level and carefully dock as described below. A 2-cm longitudinal incision over the operative level is marked out approximately 1.5 cm off the midline on the operative side, and this is injected with local anesthesia. For 2-level procedures the incision should be placed midway between the targeted levels. For bilateral procedures, a midline skin incision can be used and the skin retracted to each side for independent dilations. After an initial stab incision, the K-wire is advanced slowly though the musculature under fluoroscopic guidance and docked at the inferomedial edge of the rostral lateral mass of the level of interest ( Fig. 3 ). It is critical to engage bone and not to penetrate the interlaminar space where the laterally thinned ligamentum flavum may not protect against iatrogenic dural or spinal cord injury. At this point the incision is completed about 1 cm above and below the K-wire entry point, and the wire is removed. The axial forces that are applied during muscle dilation in the lumbar spine are more hazardous in the cervical spine. Therefore, the cervical fascia is incised equal to the length of the incision using monopolar cautery or scissors so that muscle dilation can proceed in a safe and controlled fashion. The K-wire is replaced under fluoroscopy again, and the tubular muscle dilators are serially inserted. Alternatively, a larger skin incision can be made and, once the fascia is incised, the muscle can be spread with Metzenbaum scissors and the first dilator then placed. This method avoids potential complications associated with the K-wire, and may be attractive for the novice practitioner. After dilation, the final 16-mm or 18-mm tubular METRx retractor is placed over the dilators and fixed into place over the laminofacet junction with a table-mounted flexible retractor arm, and the dilators are removed (see Fig. 3 ). The microscope is then brought into the operative field, or a 25° angled glass-rod endoscope is attached to a camera and then secured to the retractor system.
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