Spinal Deformities in Ankylosing Spondylitis: Surgical Management

CHAPTER PREVIEW

CHAPTER SYNOPSIS:

This chapter reviews the indications and techniques for surgical correction of kyphotic deformity in patients with ankylosing spondylitis involving the cervical, thoracic, or lumbar regions of the spine.

IMPORTANT POINTS:

•

Ankylosing spondylitis is a seronegative inflammatory arthritis of the spine.
•

The inflammatory phase is painful and eventually becomes less painful but results in an ossified, stiffened spine.
•

In most cases, the deformity is not severe enough to warrant surgical intervention and the functional handicap is tolerable.
•

Most common areas to require surgery are the cervical or lumbar spine.
•

Missed fractures can result in a progressive kyphotic deformity.

CLINICAL/SURGICAL PEARLS:

•

Surgery of the cervical spine requires special attention to the intraoperative positioning (sitting position) and anesthetic management.
•

To provide an adequate decompression, complete removal of the spinous process of C7, together with the majority of the spinous processes of C6 and T1, and the pedicle of C7 should be performed.
•

The use of intraoperative and postoperative Halo immobilization is imperative for cervical spine osteotomies.
•

Although rarely necessary, if surgical correction of a thoracic deformity is performed, it requires a multilevel anterior release followed by posterior osteotomies and compressive instrumentation for correction of the deformity.
•

If possible, the lumbar osteotomy is at L3-4, which is below the level of the conus and allows for multiple proximal and distal bony fixation points.

CLINICAL/SURGICAL PITFALLS:

•

C8 radiculopathy is the most common neurologic issue.
•

Attention should be paid to both the coronal and sagittal plane correction.
•

Ideally, final sagittal correction of a cervical spine osteotomy should leave approximately 10 degrees of residual flexion to allow for activities of daily living.
•

Regardless of the region, the osteoclasis should be performed in a controlled manner to reduce the risk for catastrophic neurologic injury.

VIDEO AVAILABLE:

N/A

Ankylosing spondylitis is a seronegative inflammatory arthritis of the spine that affects 0.2% to 0.3% of the population at any given time. It is more common in male individuals, and usually presents with early pain in the sacroiliac joints and lower back that can be confused with other causes of back pain. The characteristic pain at the onset is usually nonmechanical and more inflammatory in nature, and there can be early radiographic changes of the sacroiliac joints with erosion of the subchondral bony surfaces. Bone scan studies will also highlight early changes in the sacroiliac joints. Serologic tests that can be done include specific human leukocyte antigen-B27 tissue typing, which is almost always positive in these patients, as well as erythrocyte sedimentation rate and C-reactive protein level. The disease inflammatory process usually gradually affects the rest of the spine moving up through the lumbar, thoracic, and cervical regions. The last area to be affected is the upper cervical spine. The inflammatory phase is painful, and eventually this becomes less painful but results in an ossified, stiffened spine. Some loss of lumbar lordosis and slight kyphosing tendency usually occurs; however, in most cases, the deformity is not severe enough to warrant surgical intervention, and the functional handicap to the patient is usually tolerable. In some instances, the deformity can become more severe in the lumbar, thoracic, or cervical regions with resulting functional handicap to the patient that can be severe enough to warrant surgical treatment. The most common areas to require surgery are the cervical spine or lumbar spine. Rarely is surgery necessary in the thoracic spine. Severe deformities in the cervical spine are often the result of a missed fracture that had occurred with resultant gradual flexion of the neck and healing in a kyphotic position. The purpose of this chapter is to review the indications and techniques for surgical correction of kyphotic deformity in patients with ankylosing spondylitis involving the cervical, thoracic, or lumbar regions of the spine.

CERVICAL SPINE

The deformities that can be present in the cervical spine can be the most striking and functionally handicapping of all in this particular disease setting. Major cervical spine deformities that result in a chin-on-chest position are often the result of a missed fracture that had occurred. In this circumstance, a minor trauma occurs, such as a minor motor vehicle accident rear-end collision or a fall down some steps that results in some pain in the neck. The patient is often seen in a health-care facility and diagnosed with a “neck strain.” They are often provided with a soft cervical collar or some other type of orthosis. With the ossified spine and the heavy head, large lever arm force can produce a sheer type of fracture at the base of the cervical spine that is difficult to see on plain radiographic evaluation. If this is not seen at that point and immobilized in a halo vest, the fracture can go on to settle in the flexed position with gradual worsening of the kyphotic malalignment of the cervical spine that occurs over the ensuing months. The fracture will eventually heal in this flexed position with a kyphotic deformity. In a recent review of 131 patients who had undergone cervical osteotomy, a prior fracture could be confirmed in 35 cases. Early treatment of the fracture should be to realign the spine to the prefracture position with controlled halo traction and immobilization in a halo vest. An unrecognized fracture also presents the potential for severe neurologic injury. If the head and neck were in a certain degree of flexion before the fracture, no attempt should be made to increase the correction of the neck with traction because this may cause some displacement of the fracture resulting in neurologic injury. The safest approach is to realign the neck into the prefracture position and immobilize it in this position with the halo vest.

Major flexion deformities of the cervical spine present many functional handicaps to an individual. These include the inability to see ahead well while walking, climbing or descending stairs, or simply crossing a street, to mention a few. Difficulties with swallowing and eating properly often occur, as well as with personal hygiene such as shaving in the neck and lower chin. Most patients with a significant kyphotic deformity are unable to drive a vehicle. Assessment of the patient involves measurement of the chin-brow to vertical angle ( Fig. 30-1 ).

Surgical correction can be undertaken for the appropriate indications and has to be done in a carefully thought out and extremely controlled fashion to minimize risk. The technique I use is with the patient in a sitting position in a specialized chair, with a halo applied before and then after surgery connected to a vest ( Fig. 30-2 ). The procedure is undertaken under local anesthesia with some intravenous sedation. The sitting position of the patient allows for controlled correction to be performed in a safe fashion, whereas lying prone presents many difficulties such as proper positioning with marked cervical kyphotic deformity and adequate control of the head-neck axis during the osteoclasis and corrective procedure.

Surgical Technique

The patient is prefitted with a halo in the operating room and then positioned in a specialized dental-type chair. Gentle inline traction with 5 pounds is applied to an overhead support. The posterior neck is shaved and prepped, and draped with a translucent stick-on plastic drape as shown in Figure 30-2 . The patient is also fitted with a Doppler monitor on the chest to detect any air embolisms, which is one of the potential risks of performing surgery in the sitting position. To date, I have not had any major complications in relation to air embolism problems. A sponge immersed in saline is always kept available to be placed in the wound should any air embolism be detected on the Doppler imaging.

A midline incision is made, and local infiltration of 1% lidocaine is used in the skin and subcutaneous tissues right down to the deep fascial tissue and ligamentum nuchae before making the skin incision. Once the tips of the spinous processes have been identified, further infiltration with 1% lidocaine is used in the deep fascial periosteal plane along the posterior aspects of the laminae and tips of the spinous processes. Subperiosteal dissection and elevation of the paraspinal muscle mass can then be carried out. This is surprisingly well tolerated by most patients. If some pain is produced during the procedure, further infiltration is used and the procedure can be continued. It is paramount to keep the patient as comfortable as possible, and some intravenous sedation also helps in regard to this. Once the spine has been exposed, the correct levels must be ascertained.

The facet capsule tissue is completely cleared away on both sides. The facet joints will be ossified and landmarks distorted. A lateral x-ray film is obtained to confirm levels. The bony removal portion of the procedure does not usually cause pain because no pain nerve endings are within the bone itself. The spinous process of C7 is completely resected, and the majority of the C6 spinous process and the superior portion of the T1 spinous process. The entire C7 lamina is then removed with Kerrisons, together with the majority of the inferior portion of the C6 lamina and the majority of the superior portion of the T1 lamina. The posterior aspect of the spinal cord is now well visualized. The cord itself does not cause pain on gentle touch. The exiting C8 nerve roots are now uncovered by resection of the C7-T1 lateral mass joints. The opening is made as wide as possible to allow ample room for the C8 nerve roots, with the joints completely resected far laterally across on both sides.

The C7 pedicle is now removed. As I and my co-authors have described, the technique had originally involved leaving the C7 pedicles intact; however, at this time, I prefer to remove the C7 pedicles to diminish the incidence and potential of C8 radiculopathy after surgery. Adhesions between the dura and laminae are also observed in some patients and have to be carefully separated. The amount of bone to be excised can be determined before surgery based on measurements. The undersurfaces of the C6 and T1 laminae that remain have to be carefully beveled with a Kerrison to provide further room for the spinal cord during the extension/osteoclasis part of the procedure ( Fig. 30-3 ). During decompression of the C8 nerve roots and resection of the lateral mass joints, it will be noted that if the C8 dorsal root ganglia is touched, the patient will have symptoms of pain and/or numbness and tingling in the C8 distribution. Although it is not recommended that this be done more often than needed, it is a supporting indicator of the appropriate level.