The development of cervical spine deformity may be secondary to advanced degenerative disease, trauma, neoplastic disease, or surgery.¹ It may also occur in patients with systemic arthritides, such as ankylosing spondylitis and rheumatoid arthritis.

The most common cause of cervical kyphosis is iatrogenic (postsurgical).² This most commonly occurs after laminectomy. The surgical procedure involves disruption of the dorsal tension-band. The incidence of clinically significant kyphosis in this situation may be as high as 21%.³ Kyphosis may also occur following ventral cervical surgery. This may be due to pseudarthrosis or failure to restore the anatomic cervical lordosis during surgery.^4,5

Whatever the cause, the development of cervical deformity should be avoided and corrected when appropriate. Axial loading tends to further the kyphosis, thus creating a vicious cycle and progression of the deformity.⁶ The deformity tends to cause neck pain, which is mechanical in nature.⁷ The pain is due to a biomechanical disadvantage placed on the cervical musculature and degeneration of the adjacent cervical discs. In advanced cases, forward gaze, swallowing, and respiration may be adversely affected.

Ventral versus Dorsal Approach

Sagittal plane deformity in the cervical spine may be corrected ventrally,^8–11 dorsally,^12,13 or ventrally and dorsally (in combination).^12,14–16 The ventral approach is one that is familiar to most spine surgeons and may be performed with minimal morbidity.

Many patients with cervical kyphosis have had a prior cervical operation, often a laminectomy (Fig. 222-1). A dorsal revision strategy is associated with increased morbidity with regard to wound complications, pain, and the risk of neurologic injury. A ventral approach is advantageous in that “virgin” surgical territory is entered. If a prior ventral approach had been performed, the same approach may be used without difficulty, or the opposite side of the neck may be entered for the revision. These factors decrease the morbidity associated with revision cervical surgery.

FIGURE 222-1 Lateral cervical radiograph. The patient has a prior cervical laminectomy and also has a solid fusion mass at C4-7. The radiograph demonstrates significant kyphosis.

In the majority of cases of cervical kyphosis, there exists ventral compression of the spinal cord along with the deformity. This ventral compression must be addressed prior to deformity correction. A ventral decompression may not be adequately performed from a dorsal approach; therefore, a ventral decompression should be included with dorsal instrumentation, which increases the morbidity of the operation. A ventral approach permits adequate spinal cord decompression via multiple intervertebral discectomies or corpectomies. We favor leaving intermediate vertebral bodies and not performing multiple adjacent-level corpectomies (i.e., C5, C6, and C7). A safe intermediate vertebral body is one in which there is cerebrospinal fluid signal dorsal to the body on a T2-weighted MRI. Adequate ventral decompression may be performed with this strategy, and the intervening body is used as an intermediate point of fixation (see subsequent discussion).

Using a dorsal-alone strategy, one is most often unable to correct cervical kyphosis significantly. Only if the deformity is “flexible” and is able to be corrected with cervical traction may a dorsal alone strategy be used. This finding is not at all common. More often, a ventral release procedure is required prior to the dorsal deformity correction procedure. A dorsal deformity correction procedure, with or without a ventral release, may not fully correct the deformity. Even with the use of cervical pedicle screws, Abumi et al. were able to correct cervical deformity only from 28.4 to 5.1 degrees of kyphosis, with all patients achieving a solid arthrodesis.¹² A ventral strategy provides a better surgical leverage for deformity correction while providing very solid fixation points if intermediate points of fixation are used.⁶

As mentioned previously, using multiple points of intermediate fixation is optimal with ventral deformity correction strategies. This is accomplished by leaving intermediate vertebral bodies in place, instead of performing multiple adjacent corpectomies. These intermediate bodies provide solid fixation points for intermediate points of screw fixation. These intermediate points facilitate the “bringing of the spine” to a contoured implant to achieve further lordotic correction. They also provide three- or four-point bending forces to prevent deformity progression and construct failure.⁶ These intermediate fixation points may also be provided with dorsal lateral mass fixation, but entail the addition of a dorsal procedure, in addition to a ventral decompression procedure.

Axially dynamic cervical implants further add to the success of a ventral deformity correction procedure.¹⁷ These constructs are able to provide for the placement of multiple intermediate points of fixation. The dynamic aspect of the implant is able to off-load stresses at the screw/implant interface, which aids in the prevention of nonunion and construct failure, and also provides solid fixation for the prevention of cervical deformity progression.

Clinical Experience

We use a ventral-only approach for the correction of cervical kyphosis in specific clinical scenarios. This technique is optimally used when the kyphosis is fixed (i.e., rigid) and the facet joints are not ankylosed. If the facet joints or other dorsal elements are fused, a dorsal osteotomy is required. Ankylosis may easily be determined by fine-cut CT scanning. The clinical technique has been previously described,^17,18 and surgical steps will be briefly outlined here.

The patient is positioned supine on the operating table. A roll or “bump” is placed under the shoulders, and the head is supported on a “doughnut” built up by enough blankets to keep the cervical spine neutral. Multiple discectomies or corpectomy(ies) combined with discectomies are used for decompression, yet leaving vertebral bodies that may be used for points of intermediate fixation. Distraction points may be placed in a convergent manner, and when distraction is applied, segmental lordosis is attained at each level. Following decompression, a lordotic interbody graft may be placed to maintain segmental lordosis. After complete decompression, the blankets are removed from the “doughnut” and maximal cervical extension is attained; this may be performed prior to interbody graft placement. Lastly, a lordotic plate may be applied to the spine and initially affixed to the proximal and distal vertebral bodies only. Next, screws are placed into the intermediate vertebral bodies. Tightening the screws then brings the “spine to the implant.”

We have reported our experience with this technique with 12 patients. A dynamic implant was us in most patients.¹⁷ The majority of patients presented with mechanical neck pain as part of their symptom complex. The average magnitude of deformity correction (preoperative to postoperative) was 20 degrees of lordosis. The average postoperative sagittal angle was 6 degrees of lordosis. The average change in the sagittal angle during the follow-up period was 2.2 degrees of lordosis.

Using this ventral technique, lordosis was attained in all but one patient (Fig. 222-2). This posture was effectively maintained during the follow-up period. All patients demonstrated improvement postoperatively, and three had complete resolution of their preoperative symptoms.

FIGURE 222-2 Lateral cervical radiograph following surgery (same patient as in Fig. 222-1). A ventral-alone strategy using multiple intermediate points of fixation. The kyphosis is effectively reduced.

Cervical spondylotic myelopathy (CSM) is a chronic spinal degenerative condition characterized by progressive symptoms of neck pain, upper extremity numbness and motor weakness, spastic gait disturbance, urinary dysfunction, hyperreflexia, and impotence. The primary pathophysiologic mechanism is a progressive narrowing of the sagittal diameter of the spinal canal due to a host of mechanical factors.¹ White and Panjabi have subdivided the mechanical factors into two groups: static factors (congenital spinal canal stenosis, disc herniation, osteophytosis, and ligament hypertrophy) and dynamic factors (abnormal forces placed on the spinal cord during normal range of motion of the cervical spine).² As the degenerative spinal elements compress the spinal cord, blood vessels can simultaneously be compressed, causing chronic cord ischemia and myelomalacia.³ Several studies have demonstrated that early surgical intervention can improve prognosis and prevent continued neurologic decline, as well as decrease the risk of sudden spinal cord injury from minor events.^4–7

There has been much debate as to the most optimal surgical approach for a patient with CSM, and once the recommendation has been made for surgery, often the approach is tailored to the individual patient. Assessment of the sagittal alignment of the patient’s cervical spine is of utmost importance when considering the best surgical approach, because CSM is often associated with loss of cervical lordosis (so-called “spine straightening”) or cervical kyphotic deformity. In the case of cervical kyphotic deformity, the spinal cord shifts ventrally in the canal and abuts the ventral spinal elements at the apex of the deformity. As the deformity progresses, the static and dynamic mechanical stresses applied to the spinal cord increase, leading to worsening neurologic function.⁸ To most effectively manage patients with this pathologic variation, surgical intervention must be targeted at adequate decompression of the neural elements and prevention of progression, if not outright correction, of the cervical kyphosis.

There are three major options for surgical management of CSM: the ventral approach, dorsal approach, or a combination of the two. Several studies have demonstrated the effectiveness of the ventral approach in treating CSM.^9,10 The ventral approach is heavily favored by many surgeons who treat CSM, especially in the presence of a cervical kyphotic deformity.¹¹ The ventral approach can be used to treat pathology limited to one or two levels (via ventral cervical discectomy and fusion) and over three or more levels (via subtotal cervical corpectomy and strut graft, usually in conjunction with dorsal instrumentation). Unfortunately, long-segment ventral procedures have been associated with a high rate of pseudarthrosis, graft dislodgement and subsidence, or construct failure.^9,12 Several options are available if the surgeon chooses to use solely a dorsal approach. However, because the source of the pathology in CSM with kyphotic deformity is ventral to the spinal cord, the chosen dorsal approach must not only effectively decompress the neural elements, but also correct the kyphotic deformity to allow the spinal cord to migrate dorsally away from the ventral compressive elements. In this chapter, the focus is placed on the major dorsal approaches available to treat CSM and the pros and cons of each.