Strategies to Minimize Invasiveness and Optimize Success: Cervical Front/Back Surgery for Deformity Correction

48 Strategies to Minimize Invasiveness and Optimize Success: Cervical Front/Back Surgery for Deformity Correction

Lee A. Tan and K. Daniel Riew

Summary

Surgical treatment of cervical spine deformity can be challenging. In this chapter, we provide a detailed narrative review of preoperative evaluation, surgical planning, and surgical techniques for cervical deformity correction with an illustrative case. Various strategies for minimizing surgical invasiveness and complication avoidance in cervical deformity surgery were also discussed.

Keywords: cervical spine deformity anterior osteotomy Smith-Petersen osteotomy pedicle subtraction osteotomy complication avoidance

48.1 Introduction

Cervical spine deformities can have significant negative impact on patients’ quality of life. Many different surgical techniques exist for operative treatment of cervical spine deformities, including anterior cervical discectomy and fusion (ACDF), cervical corpectomy, anterior osteotomy with bilateral uncinate resection (ATO), posterior cervical instrumentation and fusion with or without laminectomy, Smith-Petersen osteotomy (SPO), and pedicle subtraction osteotomy (PSO). For flexible cervical deformities, anterior or posterior approach alone may be adequate for deformity correction. However, rigid cervical deformity correction often requires a multistage surgery utilizing a combination of anterior and posterior techniques.

In this chapter, we provide an illustrative case to demonstrate the decision algorithm for selecting the appropriate and least invasive approach for cervical spine deformity correction that minimizes surgical morbidity and optimizes clinical outcome.

48.2 Surgical Planning for Cervical Spine Deformity

An essential part of any successful surgery requires a sound surgical plan based on clear understanding of the pathology and well-defined goals of surgery. In the setting of cervical spine deformity, the surgeon must consider how much correction of the deformity is required and if any neural decompression is needed. The main goals for cervical spine deformity surgery should include adequate deformity correction in order to restore horizontal gaze and lessen spinal cord tension, and decompress the neural elements if needed, achieving a biomechanically sound construct with meticulous arthrodesis technique to minimize the risk of pseudarthrosis and other surgical complications. Several important factors must be considered preoperatively, including: (1) presence of any spinal cord or nerve root compression, (2) flexibility of the deformity, (3) presence of bony fusion, (4) location of the deformity, (5) prior cervical surgery, (6) degenerative changes at adjacent spinal levels, and lastly (7) the patient’s general health status and medical comorbidities.

Preoperative dynamic X-rays, magnetic resonance imaging (MRI), and computed tomography (CT) of the cervical spine must be carefully studied. If significant ventral compression of the spinal cord is present, then an anterior approach usually needs to be included in the overall treatment strategy to ensure adequate spinal cord decompression. However, if an indirect decompression can be achieved via deformity correction, the posterior-only approach may be adequate. Furthermore, if the structural integrity of the anterior spinal column is compromised, such as in the setting of infection or neoplasm, then the anterior approach is usually necessary to address the anterior pathology and reconstruct the anterior spinal column.

The flexibility of the deformity is also an important factor in determining the overall treatment strategy and can be assessed on dynamic cervical X-rays. If the deformity is flexible and corrects on extension, then a posterior-only approach may be possible to obtain adequate deformity correction. If the deformity is stiff, then thin-cut CT should be obtained to evaluate for presence and location of possible existing bony fusion. If the facet joints are not fused, then anterior-only correction may be possible, although some surgeons may still prefer backing up the construct posteriorly if the anterior instrumentation spans more than three levels (anterior-posterior). If the facet joints and the anterior spinal column are fused, then posterior release may need to be performed prior to anterior correction, followed by posterior instrumentation and fusion with or without additional osteotomy (posterior-anterior-posterior), depending on the extent of correction needed.

The location of kyphotic deformity is also an important factor in formulating the overall treatment plan. A focal kyphotic deformity in the mid-cervical spine usually can be corrected via anterior corpectomy; a severe focal kyphotic deformity at the cevicothoracic junction can be treated with either a C7 or T1 PSO. In patients with cervical spinal deformity and concurrent severe thoracic kyphosis, additional osteotomies in the thoracic spine may be required to obtain the necessary correction.

If the patient had prior cervical spine surgery, prior operative reports should be obtained and reviewed to gain information regarding the type of surgery performed, the specific instrumentation used, and any pertinent intraoperative findings. Prior fusion mass should be assessed with CT to check for pseudoarthrosis. If a prior anterior cervical approach is used, it is preferable to go through the contralateral side to avoid scar tissues; however, otolaryngology consultation must be obtained preoperatively to confirm vocal cord motility bilaterally. If the recurrent or superior laryngeal nerve has been injured or ear, nose, and throat (ENT) evaluation is unable to be obtained for any reason, then the ipsilateral side should be used to avoid possible bilateral recurrent laryngeal nerve injuries. If a prior posterior cervical spine surgery was performed, the wound should be inspected for the integrity of soft tissues. If the muscles are dehisced and there is a large cavity in the center of the wound or poor soft tissue coverage, then wound-related complications are much more common. Dehisced muscles have to be mobilized from their lateral position and reattached in the midline. If the surgeon does not have experience with such techniques, a plastic surgery consultation should be obtained.

To formulate a sound surgical plan, the desired amount of correction must be calculated to determine the specific surgical techniques required. Although there is no universally accepted “normal values” for cervical alignment parameters, current limited literature suggests that T1 slope minus C2–C7 lordosis < 15 degrees, C2–C7 sagittal vertical axis (SVA) < 40 mm, and chin-brow vertical angle (CBVA) between −10 degrees and +20 degrees are generally acceptable ranges.1^,²^,³^,⁴ Of course, each patient is unique and the optimal surgical correction needs to be determined on individual basis. As a general rule, the amount of lordosis (kyphosis correction) obtained is about 5 degrees for a single-level ACDF, 10 degrees for an SPO, 17 degrees for an ATO, and up to 35 degrees for a C7 PSO.⁵^,⁶

48.3 Surgical Technique to Minimize Invasiveness

Anterior cervical surgery is already a relatively minimally invasive approach. One can perform even an eight-level anterior operation from C2 to T3 through a cosmetically pleasing single or double transverse incisions. To minimize trauma to the trachea and esophagus, we dissect as though we are performing two levels more than what is required (e.g., to perform a C3–C7 operation, we dissect to expose C2 to T1). When this exposure wide, less retraction force is required and therefore, less trauma to the midline structures. We also move the retractor to expose one to two levels at a time so that the retraction time is minimized at each level. We work as quickly as possible and make every attempt to keep the retraction time to less than 3 hours. If the retraction time is greater than 3.5 to 4 hours, we usually keep the patient intubated at least overnight and check a cuff leak test prior to extubating.

In contrast to the anterior exposure, the posterior exposure for a circumferential procedure for a deformity correction would hardly qualify as a “minimally invasive” procedure. However, much can be done to minimize the exposure. We utilize a muscle-sparing approach to the posterior cervical spine. This involves finding the avascular and amuscular midline, which is more difficult than it sounds. As someone so aptly put it, “the midline is rarely in the middle and there is no line.” The easiest way to find this is to palpate the C7 spinous process and cut down to it. Then, we carefully dissect cranially from that point under the microscope. The spinous processes are palpated repeatedly to maintain a midline dissection. Deep to the fascia, we use blunt dissection with the index finger to separate the two halves. If that proves ineffective, we use monopolar electrocautery or Metzenbaum scissors. Meticulous dissection helps to optimize healing, prevent bleeding, and decrease postoperative pain associated with the procedure. If the exposure has been done correctly, the muscles should still be enveloped in their fascia and there should be minimal bleeding. After exposing the spinous processes, we use electrocautery, without power, as a dissector to identify and widen the raphe between the two halves of the interspinalis muscle, which connects one spinous process to the next. Note that there is no interspinous ligament in the cervical spine. The interspinalis muscle is found in its place. We then cut each half of the bifid spinous process with a bone cutter, leaving the muscle attached to each side. If the spinous process is not bifid, we cut a thin sliver of bone on each side of the monofid process. During the closure, we will place sutures lateral to these bony fragments, so that the closure is bone-to-bone, instead of muscle-to-muscle. This helps to minimize muscle trauma during closure and also helps to prevent dehiscence.

We continue the deep dissection with an electrocautery set to 20, minimizing the burn and lightly dissecting the muscles subperiosteally off the lamina. There is minimal bleeding until one gets just lateral to the beginning of the lateral mass, where there are bony bleeders. These can be controlled with bone wax. The dissection stops at the lateral border of the lateral mass because further laterally, there is a venous plexus that bleeds profusely.

Just as important as the dissection is the closure. We place a deep drain and leave hemostatic agents superficial to the drain, so long as the lamina is intact to protect the cord. If there has been a laminectomy, one cannot leave hemostatic agents in the wound, as they will expand and cause cord compression. We then put in approximately 500 mg of vancomycin powder and sprinkle another 500 mg at every layer during closure. We typically use 120–150 pop-off sutures (placed every 7–10 mm) to close the wound. This leaves no dead space in which fluid, which can be a nidus for an infection, can accumulate. We have not had an infection in the posterior cervical spine in the last 2,000+ cases. The first layer of closure is the bone-to-bone spinous process re-approximation. Then, if the dissection was done correctly, the fascial covering of the muscles should be undisturbed and this fascia is used to close the wound. It takes three to four layers to close this layer. The next layer is the supraspinous and nuchal ligament complex. Above that, the fat layer is closed with 2–0 pop-off sutures with no dead space. We close the skin with subcuticular sutures to enhance cosmesis.

48.4 Case Illustration

48.4.1 Presentation

A 20-year-old male patient presented with progressive gait imbalance and worsening right upper extremity weakness. His pertinent past medical history included achondroplasia and multiple craniospinal surgeries including suboccipital craniectomy with C1–C2 laminectomies, and spinal fusion from C5 to L4. Physical examination was remarkable for diffuse right arm weakness (4/5), as well as overt myelopathic signs including hyperreflexia in bilateral upper and lower extremities, positive Hoffmann’s reflex bilaterally, clonus, and unsteady gait.

48.4.2 Imaging studies

The cervical spine X-rays revealed a kyphotic cervical deformity with C2–C7 kyphosis measuring 36.1 degrees; the apex of the kyphosis was located at C2–C3 and C3–C4 above the prior fused levels (Fig. 48.1). Dynamic cervical X-rays showed that the deformity was rigid without any movement on flexion and extension (Fig. 48.2). The MRI of the cervical spine demonstrated severe cervical stenosis and anterior cord compression at C2–C3 and C3–C4 (Fig. 48.3). The C2–C7 SVA was measured to be 37.2 mm. Given the patient’s worsening neurological status, surgical correction of the fixed cervical deformity with spinal cord decompression was deemed the most appropriate management strategy.