Minimally Invasive Approaches to the Cervical Spine

Minimally invasive approaches and operative techniques are becoming increasingly popular for the treatment of cervical spine disorders. Minimally invasive spine surgery attempts to decrease iatrogenic muscle injury, decrease pain, and speed postoperative recovery with the use of smaller incisions and specialized instruments. This article explains in detail minimally invasive approaches to the posterior spine, the techniques for posterior cervical foraminotomy and arthrodesis via lateral mass screw placement, and anterior cervical foraminotomy. Complications are also discussed. Additionally, illustrated cases are presented detailing the use of minimally invasive surgical techniques.

The surgical management of cervical radiculopathy has evolved considerably over the past decades; however, no surgical treatment is without associated morbidity or limitations. Traditional techniques of treating patients with radiculopathy from cervical spondylosis have relied on posterior, anterior, and now oblique-based approaches. Minimally invasive approaches and surgical techniques are becoming increasingly popular for the treatment of a variety of cervical spine disorders. Commonly accepted tenants of minimally invasive spine surgery include smaller incisions, paramedian approaches, less dissection and muscle stripping, the use of the operating microscope, specialized retractors and instruments, and an increased reliance on fluoroscopic guidance. The goals of minimally invasive spine surgery are decreased iatrogenic muscle injury, less postoperative pain, and faster recuperation.

The popularity of minimally invasive approaches to the spine has increased proportionally to our understanding of the benefits of these techniques. It is known that traditional open exposures cause iatrogenic muscle injury. Minimally invasive techniques were initially introduced to treat lumbar spine disorders and have been demonstrated to have equivalent outcomes to traditional open procedures.

Fessler and Khoo reported improved postoperative pain with decreased blood loss in a series of patients undergoing minimally invasive cervical foraminal decompression. Two recent prospective, randomized clinical trials comparing minimally invasive posterior cervical foraminotomy with traditional open foraminotomy or anterior cervical discectomy and fusion have demonstrated that minimally invasive techniques can result in smaller incisions, less postoperative pain, and equivalent clinical outcomes.

There is no prospective literature available comparing arthrodesis with lateral mass screws placed in a minimally invasive versus open manner. Wang and Levi reported the successful use of minimally invasive lateral mass screws in 18 patients; however, it is important to note that 2 of these patients required conversion to an open procedure because of an inability to visualize the caudal level.

Anterior cervical neuroforaminal decompression without fusion via a transuncal approach is a useful technique in the treatment of cervical radiculopathy while preserving the intervertebral disk and providing complete decompression of the exiting nerve root. Furthermore, anterior approaches offer a direct route to ventral radiculopathy, which can be difficult to address from a posterior approach. Anterior cervical foraminotomy without discectomy potentially leads to decreased operating time, no need for immobilization or hardware, and minimal hospital stay.

Patient interest in minimally invasive cervical spine surgery has expanded dramatically and at a greater rate than medical evidence in support of such techniques. Patient demand for minimally invasive surgery must be tempered by a careful evaluation of patient anatomy and an honest appraisal of a surgeon’s experience and ability. Ultimately, a well-performed, thorough open surgery will be more successful than an inadequate minimally invasive operation. In this article, the authors detail minimally invasive approaches to the posterior cervical spine with explanations of both minimally invasive posterior cervical foraminotomy and lateral mass screw placement and describe the technique of minimally invasive anterior cervical foraminotomy.

Indications

Minimally invasive approaches to the cervical spine have a variety of uses in the treatment of disorders of the cervical spine. Minimally invasive posterior cervical foraminotomy is indicated for the treatment of cervical radiculopathy associated with isolated foraminal stenosis with a soft disk herniation and for the treatment of persistent radicular symptoms following an anterior procedure. Moreover, minimally invasive lateral mass screw fixation can be used to achieve cervical arthrodesis in the setting of subaxial instability and to augment a contemporaneous or prior anterior cervical fusion. Indications for minimally invasive anterior cervical foraminotomy are limited to cervical radiculopathy but include both bilateral radiculopathy and multilevel foraminal stenosis.

Contraindications

Minimally invasive approaches to the cervical spine are contraindicated in patients with cervical myelopathy secondary to central canal stenosis. Additionally, patients with severely degenerative anatomy, an aberrant course of the vertebral artery (VA), or hypoplasia of the lateral masses are not candidates for minimally invasive lateral mass screw fixation. Minimally invasive approaches to the cervical spine for arthrodesis must be used with extreme caution in trauma patients. Anterior cervical foraminotomy is contraindicated for patients with ossification of the posterior longitudinal ligament, myelopathy, vascular abnormalities, or predominantly significant neck pain. A thorough review of patients’ preoperative imaging and knowledge of the course of the VA is mandatory for all anterior procedures. Surgeon inexperience with minimally invasive techniques is an absolute contraindication to minimally invasive cervical spine surgery.

Contraindications

Minimally invasive approaches to the cervical spine are contraindicated in patients with cervical myelopathy secondary to central canal stenosis. Additionally, patients with severely degenerative anatomy, an aberrant course of the vertebral artery (VA), or hypoplasia of the lateral masses are not candidates for minimally invasive lateral mass screw fixation. Minimally invasive approaches to the cervical spine for arthrodesis must be used with extreme caution in trauma patients. Anterior cervical foraminotomy is contraindicated for patients with ossification of the posterior longitudinal ligament, myelopathy, vascular abnormalities, or predominantly significant neck pain. A thorough review of patients’ preoperative imaging and knowledge of the course of the VA is mandatory for all anterior procedures. Surgeon inexperience with minimally invasive techniques is an absolute contraindication to minimally invasive cervical spine surgery.

Surgical technique

Approach and Technique for Unilateral Posterior Foraminotomy

A minimally invasive approach to the cervical spine can use either a paramedian or midline incision depending on the surgical plan. Paramedian skin incisions are ideal for unilateral foraminotomy but less suited for bilateral procedures or when lateral mass screws will be placed. In such instances, the authors recommend a midline skin incision with two separate paramedian fascial incisions.

To perform a unilateral, single level foraminotomy, patients are positioned prone with the head held in a Mayfield 3-point skull fixation clamp (Integra, Plainsboro, New Jersey). The authors do not typically use monitoring, such as transcranial motor-evoked potentials or somatosensory-evoked potentials, for foraminotomies. The skin is typically injected before incision with a solution of local anesthetic with epinephrine to decrease the inhalational anesthesia requirement and improve hemostasis. Intraoperative fluoroscopy is essential to ensure proper level selection. A 15-mm longitudinal paramedian skin incision is made 5 mm off midline toward the affected side directly centered over the operative level. Dissection is carried straight down to the fascia with electrocautery. A longitudinal fascial incision of equivalent length is then made, and the surgeon’s finger is used both to bluntly dissect directly down through the paraspinal muscles to the lateral masses and facet joint of the affected level and to preliminarily clear soft tissue from these structures.

Depending on the retractor system, an initial dilator is then inserted onto the lateral mass and fluoroscopy is used to again confirm the correct level. The dilator can be used as a wanded to help clear soft tissue from the lateral masses and facet joints and to create a potential space in the paraspinal muscles for the tubular retractor. Serial dilators are then inserted, and fluoroscopy is again used to confirm that they remain seated on bone over the operative level. The final dilator is then followed by the tubular retractor itself, which is placed over the final dilator and locked into place. The importance of confirming and reconfirming the correct level cannot be overemphasized because migration of the retractors is common, potentially leading to a wrong-level surgery.

The retractor is then connected to a flexible mounting system and expanded to provide access to the lateral masses and facet joint. At this point, the operative microscope or endoscope is brought in to facilitate visualization and illumination. Electrocautery is used to clear any remaining muscle off of the lateral masses and facet joint. The medial and lateral margins of the lateral masses are key landmarks that must be completely visualized. Dissection should not be carried beyond the lateral margin of the lateral masses because significant bleeding can be encountered, obscuring visualization and increasing the difficulty of the operation.

After the lateral masses and facet joint have been adequately exposed, a final intraoperative radiograph is taken to confirm the correct level before beginning the foraminotomy. The medial half of the inferior articular process of the cephalad vertebra is resected with a 2-mm matchstick high-speed burr. A small amount of lamina of both the superior and inferior vertebra is also routinely removed with the burr to facilitate the identification of the ligamentum flavum. A rent is made in the ligamentum flavum by inserting a short blunt nerve hook into the facet joint, thus, gaining access to the epidural space and then pulling up gently on the ligamentum flavum. A 1-mm Kerrison punch is then used to resect the lateral ligamentum flavum to expose the shining cartilage of the superior articular process of the caudad vertebra. The medial one-third to one-half of the superior articular process is then subtotally resected with the burr, leaving only a thin shell of ventral cortical bone. A short, blunt nerve hook is then inserted into the foramen to create space between the nerve root and this shell of bone. A Kerrison punch or fine curette can be used to remove the remaining cortex of the superior articular facet taking care to prevent injury to the exiting nerve root. Surgifoam (Ethicon, Somerville, New Jersey) or similar hemostatic agents are used liberally during the procedure to maintain a dry operating field and to optimum visualization.

If ventral soft disk material is to be removed, the exiting nerve root can be mobilized superiorly with a short, blunt nerve hook to expose the disk herniation. Great care must be taken to prevent injury to the anterior motor branch, which can be mistaken for disk material.

The described technique can also be used to perform unilateral foraminotomies at multiple levels. Up to 3 sequential foramina may be decompressed via a single paramedian skin incision of 30 mm in this fashion. Exposure is performed in a similar fashion to the technique described for a single-level foraminotomy with a few modifications.

For multilevel foraminotomies, the incision and tubular dilators should be centered on the lateral mass one level above the lowest operative level. The initial dilator should be more aggressively wanded in a cephalad-caudad direction to create a path for the tubular retractor through the paraspinal muscles. Although many retractors are available, a skirted retractor may be advantageous to facilitate visualization in the setting of multilevel surgery ( Figs. 1 and 2 ).