DEFINITION

The precise definition of cervical kyphosis is not clearly described. Normal alignment from C2 to C7 in the sagittal plane is approximately 20 degrees of lordosis.

ANATOMY

With normal alignment, the load bearing axis of the cervical spine lies in the posterior third of the vertebral bodies.

The foramen transversarium of C7 generally contains only veins; however, vertebral artery anomalies do exist and careful examination of the preoperative magnetic resonance imaging (MRI) is necessary.4

As the C7 foramen transversarium is usually “empty,” this level is the most amenable to a pedicle subtraction osteotomy (PSO).

PATHOGENESIS

There are many etiologies of cervical kyphosis, including degenerative disease, trauma (acute and chronic onset), tumor, infection, inflammatory arthropathies, and iatrogenic causes.

Ankylosing spondylitis is the most common inflammatory cause.

Caused by contraction and ossification of the ligaments of the spine

Associated with the human leukocyte antigen B27 (HLA-B27) haplotype in 80% to 90% of patients. Iatrogenic causes include postlaminectomy kyphosis, pseudarthrosis, and postradiation syndromes.

NATURAL HISTORY

As there are many etiologies of cervical kyphosis, the natural history is quite variable.

In patients with fixed deformities, such as ankylosing spondylitis, the deformity may progress due to stress fracture or an unrecognized fracture, often indicated by an acute increase in the magnitude of the deformity or the level of pain.

As the axis of loading moves anterior to the vertebral body, the tendency is for progression of the deformity.

With more deformity, the spinal cord may become draped over the vertebral bodies, and the patient may become myelopathic, quadriparetic, or quadriplegic.

PATIENT HISTORY AND PHYSICAL FINDINGS

The chief complaint of the patient should be elicited. The patient may present with swallowing and/or

breathing difficulties. Forward gaze is often affected. Patients may also note low back pain, as they hyperextend the lumbar spine to maintain a horizontal gaze.

The patient should be asked to stand with hips and knees extended, allowing for an accurate assessment of the deformity and sagittal balance.

Any sudden change in deformity or pain should be considered a fracture until proven otherwise.

An accurate history of previous cervical procedures is needed, as this is essential for preoperative planning. The patient should be asked to lay supine to assess the rigidity of the deformity.

The gait should be observed for evidence of myelopathy. Other affected joints should be assessed to determine the need for treatment prior to addressing the cervical deformity.

The exam should include a full neurologic examination to check for evidence of myelopathy or spinal cord dysfunction.

All patients should undergo a full medical evaluation, as respiratory and gastrointestinal dysfunction are not uncommon in this population. In severe cases of respiratory compromise, a preoperative tracheostomy may be advisable.

IMAGING AND OTHER DIAGNOSTIC STUDIES

Radiographic evaluation should begin with anteroposterior (AP), lateral, and flexion/extension radiographs of the cervical spine (FIG 1A-F).

This allows for assessment of both the degree and flexibility of the deformity.

Standing AP and lateral radiographs of the entire spine, with the hips and knees in maximal extension, are obtained to assess global coronal and sagittal balance. We also obtain standing AP and lateral photographs to post in the operating room and to aid in planning correction.

A computed tomography (CT) scan with 1-mm cuts and sagittal, coronal, and three-dimensional reconstructions are obtained. This allows for assessment of the fusion mass and helps provide landmark guidance for instrumentation (FIG 1G).

If one is deciding between Smith-Petersen osteotomies (SPO) and a PSO, then careful evaluation of the disc spaces is necessary. If there is a circumferential fusion, a PSO is required.

An MRI is obtained to visualize the neural elements. If the patient cannot tolerate a closed MRI (sometimes precluded by the deformity), then an open MRI or CT myelogram may be obtained.

DIFFERENTIAL DIAGNOSIS

Degenerative disease Inflammatory arthropathy

Ankylosing spondylitis Rheumatoid arthritis

FIG 1 • A,B. Standing AP and lateral radiographs, respectively, of a 69-year-old man who presented with fixed coronal and sagittal plane deformities after multiple prior anterior and posterior procedures. The fixed deformity was confirmed by AP (C) and lateral (D), flexion (E), and extension (F) radiographs. G. Midsagittal CT scan shows a fixed cervical kyphosis at C4-C6.

Posttraumatic kyphosis Acute

Chronic

Infection

Tumor: includes intradural pathologies Iatrogenic

Postlaminectomy Pseudarthrosis Postradiation

NONOPERATIVE MANAGEMENT

Nonoperative management of symptomatic cervical kyphosis is limited, as the patient has minimal compensatory mechanisms to maintain horizontal gaze.

Pain may be controlled with anti-inflammatory and narcotic medications.

Bracing of flexible deformities is not ideal, as any improvement in symptoms will only occur when the brace is worn. Bracing of fixed deformities is not possible. Chronic brace use runs the risk of pressure ulcer formation.

SURGICAL MANAGEMENT

Surgical management is necessary when the patient is suffering from respiratory compromise, has difficulty eating, or has significant difficulty maintaining horizontal gaze.

In many cases, correction of cervical kyphosis is an elective procedure that is performed when the patient can no longer tolerate the symptoms, most of which are not life threatening.

Preoperative Planning

All joints should be evaluated prior to a cervical osteotomy because hip and knee flexion contractures may require intervention prior to addressing the cervical spine.

Patients may present with concomitant thoracolumbar (TL) kyphosis, and a corrective osteotomy of the TL spine may be necessary. In this case, the TL procedure should be performed first, as horizontal gaze may

correct with the TL osteotomy.8 If the cervical osteotomy is performed first, a subsequent TL osteotomy may leave the patient in a position with the head fixed in too much extension.

The chin-brow angle should be measured.

We also measure the angle of deformity with a midsagittal CT scan image. This allows for more accurate planning in severe deformities.

The goal of correction should be to create a chin-brow angle of approximately 10 degrees.

With the head in slight flexion, the patient is able to see both their feet and straight ahead.

We aim to align the posterior vertebral line of C2 with the anterior vertebral line of C7.

Although aesthetically pleasing to the layman, a neutral chin-brow angle is not well-tolerated by the patient, as they cannot see directly in front of their body.8

For smaller deformities, with only a posterior fusion, we may perform single or multiple SPOs. For larger deformities (>30 degrees) or circumferential fusion, we will perform a PSO.

Anterior osteotomies or a corpectomy, combined with a posterior approach, may offer impressive corrections, avoiding the increased risks associated with three column osteotomies.

Also, combined anterior/posterior approaches may be more appropriate for segmental kyphosis above C7.

Positioning

Gardner-Wells tongs are used to secure the head, and 15 pounds of traction is applied.

Bivector traction is applied through the frame. One vector pulls axially and is used to position the head until the osteotomy closure. At the time of closure, an extension moment is applied by switching the weight to the second rope which facilitates closure and holds the head in the appropriate position until the head is fixed in place (FIG 2).

FIG 2 • Bivector traction is achieved through two traction ropes. Rope A pulls longitudinally. Rope B is placed over the “H-bar” and pulls with an extension moment.

We position the patient prone on a Jackson frame with a chest bolster, anterior iliac crest pads, and a leg sling. In the case of severe deformity, the chest bolster may be built up with pillows to allow appropriate positioning of the surgical field.

Although historically performed in a seated position, we prefer the prone position, as upper cervical implant placement is easier.7

The arms are wrapped with blankets at the patient's side, and the elbows and wrists are padded. Gentle traction is applied to the shoulders with tape.

The patient is placed in a maximal reverse Trendelenburg position. This brings the operative site into the surgeon's field of view and allows for pooling of blood in the lower extremities.

Approach

A standard midline approach is used. We minimize blood loss by staying within the midline raphe down to the spinous processes.

The lateral masses are exposed in their entirety but not more laterally in an effort to minimize bleeding.

TECHNIQUES

Smith-Petersen Osteotomy

Osteotomy

This technique relies on open disc spaces or a prior anterior release/osteotomy.

The inferior facet of the cranial vertebra is removed using a matchstick burr. A chevron shape is created to maximize bony apposition after osteotomy closure and provide some increased stability.

The ligamentum flavum is excised with Kerrison rongeurs or curettes. If ossified, it is removed with a high-speed burr.

Ensure that the exiting nerve root passes freely, without the creation of iatrogenic foraminal stenosis.

Osteotomy Closure

At this point, the surgeon takes a firm hold of the Gardner-Wells tongs and the traction weight is shifted to the extension rope. The surgeon extends the neck, and the osteotomy is closed.

The rods are placed in the screw heads and fixed in place.

Intraoperative radiographs are obtained to check implant position and to check the correction of the deformity.

The wound is closed as described later.

Pedicle Subtraction Osteotomy

Placement of Instrumentation

Similar to the SPO. At C2, pedicle screws are placed if the anatomy allows. Laminar screws may also be used, although rod placement may require cross-connectors. A combination of laminar screws and pedicle screws may be used as well. We may extend to skull if the occipitocervical joint is already fused.

From C3 to C5, lateral mass screws are placed. Attention is paid to place the screws in line with one another, as this facilitates placement of the final rod.

Lateral mass screws are placed at C6 if T1 is not instrumented.

Pedicle screws are placed from T1 to T3 or T4, with T1 omitted if C6 is instrumented. The instrumentation is placed distally to T3 or T4 to ensure six to eight points of distal fixation (TECH FIG 1).

C7 Laminectomy

A laminectomy of C7 is performed using a high-speed burr. The lamina is removed in one piece and reserved for use as local bone graft (TECH FIG 2A).

The laminae of C6 and T1 are undercut to provide additional room for the neural elements following closure of the osteotomy.

The ligamentum flavum is excised with Kerrison rongeurs and/or curettes. If ossified, a burr is used.

The lateral masses of C7 are removed in piecemeal fashion, with a Leksell rongeur and a high-speed burr. A chevron-shaped cut is made so that there is rotational stability after closing the osteotomy (TECH FIG 2B).

The inferior facets of C6 and superior facets of T1 are excised. The inferior borders of the C6 pedicles and superior borders of the T1 pedicles must be visualized. This allows adequate room for the C7 and C8 nerve roots following osteotomy closure.

Decancellation

Cotton patties and Penfield retractors are place around the C7 pedicle to protect the C7 and C8 nerve roots. Resection of the C7 pedicle begins by passing the high-speed burr down the pedicle.

Care must be taken to preserve the walls of the pedicle.

TECH FIG 1 • Instrumentation has been placed.

The pedicle walls are then removed, piecemeal, with pituitary rongeurs and reverse angle curettes (TECH FIG 3A).

The pedicle walls must be removed entirely to prevent nerve root impingement following closure of the osteotomy.

A void is created in the posterosuperior portion of the vertebral body, with reverse angle curettes or small bone tamps (TECH FIG 3B).

Decancellation is completed with curettes and pituitary rongeurs, with the cancellous bone removed and preserved for local graft or pushed anteriorly within the vertebral body (TECH FIG 3C).

The same procedure is performed at the contralateral pedicle. Decancellation should continue until the pedicles freely communicate with each other.

An “egg shell” of C7 should now remain.

With a Woodson elevator or angled dural elevator, the posterior wall of the vertebral body is impacted, completing the osteotomy of C7. This should not require much force. If it does, then more decancellation of the body is necessary (TECH FIG 3D).

TECH FIG 2 • A. The laminectomy is performed en bloc and the bone is saved for use as bone graft. B. The lateral masses are removed with the Leksell rongeur, and the superior facets of T1 and inferior facets of C6 are removed.

TECH FIG 3 • A. Resection of the pedicle walls begins with a curette. B. A void is created within the vertebral body with a small bone tamp. C. The void has been expanded so that the pedicles communicate freely with each other. D. A Woodson elevator is used to impact the posterior aspect of the vertebral body, completing the osteotomy. This is performed on both sides of the body.

Osteotomy Closure

Prebent rods, or articulating rods (our preference), are placed in the distal screw heads (TECH FIG 4A).

The surgeon now grabs a hold of the Gardner-Wells tongs and the weight is switched to the extension moment rope. The neck is gently extended by the surgeon to the desired position (TECH FIG 4B).

If enough bone has been removed from C7, this action should take little force. The rods are fixed in place.

The C7 and C8 nerve roots are checked to ensure that there is no impingement.

The electrophysiologist checks the neuromonitoring signals to ensure there have been no changes during closure of the osteotomy.

If there are changes, we relax the closure and perform a rehearsed Stagnara wake-up test.

Radiographs are checked to assess implant position, deformity correction, and the integrity of the anterior column.

In some cases, the anterior column may book open. This usually happens when corrections greater than 40 degrees are attempted. In these cases, we will sometimes turn the patient supine and place a plate across the opening, with an allograft placed within the deficient area. We also do this in osteoporotic patients with poor fixation. If we instrumented to the skull and the screws have excellent

purchase, this is not necessary.

Bone Grafting

The laminae, spinous processes, and lateral masses/transverse processes of C6 and T1 are decorticated with a high-speed burr.

Irrigation is used to minimize thermal necrosis.

The C7 lamina, which had been preserved, is split in the sagittal plane. The two pieces are then placed along the decorticated spinous processes of C6 and T1 and then cabled into place.

The remainder of the local bone graft is packed around the closed osteotomy site.

Wound Closure

Meticulous attention is paid to wound closure to minimize dead space and to ensure a good cosmetic appearance.

TECH FIG 4 • A. An articulating or contoured rod is then placed. B. The head is extended, and the osteotomy site is closed.

We close the paraspinals in multiple layers, minimizing the amount of muscle within each suture bite. Prior to closure of the fascial layer, a thrombin-soaked Gelfoam sheet is placed in the wound.

Prior to closure, 500 mg of vancomycin powder is sprinkled in the wound.

Redundant skin is inevitable, but, with an accurate closure, the wound will smooth as it heals.

In the case of excessive redundancy, we will excise ellipses of full-thickness skin from the proximal and distal aspects of the wound.

Drains are placed deep and superficial to the fascia.

These drains are removed when over 8 hours output is less than 30 mL, usually on postoperative day 1.

Hemostasis is verified after the closure of each layer.

Pressure is applied for 30 seconds after the closure of each layer.

PEARLS AND PITFALLS

Preoperative ▪ The preoperative physical examination should evaluate other joints that may be planning affected by the disease process and require intervention before the cervical

spine.

TL kyphosis, if severe enough to warrant surgery, should be corrected before the cervical spine.
Careful examination of the vertebral artery using preoperative imaging will minimize the risk of injury (FIG 3).
A detailed pulmonary history and examination is necessary, as some extreme cases may require a preoperative tracheostomy.
The goal of correction should be to 10-20 degrees of flexion, allowing the patient to see directly in front of their body.
Use Gardner-Wells tongs and bivector traction to help with intraoperative positioning of the head.
Position the patient prone, in maximal reverse Trendelenburg. This brings the operative site into the field of view and minimizes blood loss through pooling in the lower extremities.

Implant ▪ Lamina screws may be placed at C2 if the anatomy is not amenable to pars placement screws. Lamina screws may also be placed as an adjunct to pars screws in

cases of poor bone stock.
Place the implants in a straight line so that contouring of the rods is minimized.

Osteotomy ▪ Remove the C7 lamina in one piece and reserve for use as local bone graft.
The inferior articular facet of C6 and superior articular facet of T1 must be removed entirely to reduce the risk of C7 or C8 nerve root impingement.
Protect the nerve roots with cotton patties and Penfield retractors.
Impaction of the posterior wall should proceed with minimal force. If significant force is required, then remove more bone from the body itself.

Wound ▪ Close the wound in many layers, with meticulous attention to tissue apposition. closure ▪ Achieve hemostasis with compression and pharmacologic means (thrombin,

Gelfoam, etc.) after closure of each layer.
Place drains deep and superficial to the fascia. This will minimize dead space.
In cases of extreme tissue redundancy, ellipses may be excised from the proximal and distal aspects of the wound.
A plastic surgery consultation may be appropriate in the most extreme cases (redundant skin, previous surgery, etc.).

Postoperative ▪ Immobilize the patient in a hard collar for 6-12 weeks. care ▪ Mobilize the patient on postoperative day 1.

FIG 3 • Axial T2-weighted MRI of a 34-year-old man with a fixed cervical deformity, showing intraforaminal vertebral artery at C7. For this reason, multiple SPO were performed.

POSTOPERATIVE CARE

Most patients can be extubated without difficulty immediately following the procedure. All patients are immobilized in a hard collar for 6 to 12 weeks.

All patients are out of bed and walking on postoperative day 1.

Patients are generally discharged to home on postoperative day 1 or 2.

OUTCOMES

With proper planning, horizontal gaze is reliably restored.1,2,5,6,7,9 (FIG 4).

Belanger et al1 reported improved neck pain scores in 88% (21/24) of ankylosing spondylitis patients.

Subjective dysphagia was improved in 95% (18/19).

Subjective satisfaction scores are often good to excellent.7,9

COMPLICATIONS

Neurologic injury, including paralysis, has been reported with extension osteotomies, with an overall rate of approximately 23%.3

The most commonly affected nerve root is C8, with transient palsies more common than permanent injury.9

In cases of osteoporosis and osteopenia, implant failure and pseudarthrosis are concerns. Pseudarthrosis rates with modern implants have been reported from 0% to 13%.1,5,6,9

The vertebral artery is at risk; however, performing the osteotomy at C7 and careful planning may

minimize the risk. Make sure that there is no anomalous vertebral artery in the foramen transversarium of C7.

As with any posterior procedure, wound infection and wound dehiscence are potential risks. A plastic surgery consultation is appropriate for the most extreme wounds.

FIG 4 • Postoperative radiographs of the patient in FIG 1. He underwent posterior osteotomies (C4-C5, C5-C6) and removal of instrumentation, anterior C5 corpectomy and C7-T1 anterior cervical discectomy and

fusion (ACDF), and posterior instrumentation C2-T3.

REFERENCES

Belanger TA, Milam RA, Roh JS, et al. Cervicothoracic extension osteotomy for chin-on-chest deformity in ankylosing spondylitis. J Bone Joint Surg Am 2005;87(8):1732-1738.
El Saghir H, Boehm H. Surgical options in the treatment of the spinal disorders in ankylosing spondylitis. Clin Exp Rheumatol 2002;20(suppl 28):S101-S105.
Etame AB, Than KD, Wang AC, et al. Surgical management of symptomatic cervical or cervicothoracic kyphosis due to ankylosing spondylitis. Spine 2008;33(16):E559-E564.
Hong JT, Park DK, Lee MJ, et al. Anatomical variations of the vertebral artery segment in the lower cervical spine: analysis by threedimensional computed tomography angiography. Spine 2008;33(22): 2422-2426.
Langeloo DD, Journee HL, Pavlov PW, et al. Cervical osteotomy in ankylosing spondylitis: evaluation of new developments. Eur Spine J 2006;15(4):493-500.
McMaster MJ. Osteotomy of the cervical spine in ankylosing spondylitis. J Bone Joint Surg Br 1997;79(2):197-203.
Simmons ED, DiStefano RJ, Zheng Y, et al. Thirty-six years experience of cervical extension osteotomy in ankylosing spondylitis: techniques and outcomes. Spine 2006;31(26):3006-3012.
Suk KS, Kim KT, Lee SH, et al. Significance of chin-brow vertical angle in correction of kyphotic deformity of ankylosing spondylitis patients. Spine 2003;28(17):2001-2005.
Tokala DP, Lam KS, Freeman BJ, et al. C7 decancellisation closing wedge osteotomy for the correction of fixed cervico-thoracic kyphosis. Eur Spine J 2007;16(9):1471-1478.

Cervical Osteotomies for Kyphosis