41. Hook Patterns for the Preservation of Lumbar Lordosis

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rea of superior lamina and facet removed to sublux wire laterally

Figure 40–4

Drawings show wire placement (A), rod insertion (B), wire tightening (C), and placement of right-sided rod (D).

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190

SECTION II THE THORACIC SPINE

Eurostile

ABC

The sequence of wire placement, rod insertion, and wire tightening is shown in Figure 40–4.

Hook Patterns for the Preservation of Lumbar Lordosis

Joseph W. Dryer, Emile Cheung, and Gordon Lee Engler

Goals of Surgical Treatment

To create lumbar lordosis when using hook and rod instrumentation of the lumbar spine, and to preserve motion segments in the lumbar spine by limiting the caudal extent of the fusion.

Diagnosis

Whenever fusion is required far the treatment of scoliosis, the surgeon

must consider correction of the deformity in both the frontal and sagittal planes. Although the original Harrington instrumentation produced excellent correction in the frontal plane, the posterior distraction required to obtain such correction often distorted the sagittal plane. Thus, the term Harrington flat-back deformity described the loss of physiologic lumbar lordosis when Harrington instrumentation was used in the lumbar spine; long-term follow-up of these patients has shown extensive disc degeneration below the fusion, particularly in those patients fused to L3, L4, and L5.

A 36-inch standing lateral x-ray is required to properly assess the sagittal plane and plan the appropriate hook pattern so as to maximize lumbar lordosis. This is chiefly achieved by derotation of the lumbar spine as well as compression

Indications for Surgery

Idiopathic scoliosis with structural lumbar curves in excess of 40 degrees.

Contraindications

Any congenital abnormalities that result in absent or dysplastic posterior spinal elements such as spina bifida and congenital spinal stenosis, which may preclude hook placement in the spinal canal.

Advantages

Hook placement is rapid and does not require extensive x-ray control compared with pedicle screws. Patients younger than 10 years old often have small pedicles, making hook instrumentation safer and easier.

Disadvantages

Posterior instrumentation cannot correct the lumbar curve as well as ante-

rior instrumentation. Lumbar scoliosis that requires posterior instrumentation to L4 can often be better treated by anterior instrumentation that ends at L3.

Procedure

A standard subperiosteal exposure is performed. The importance of meticulous elevation of the soft tissues cannot be over emphasized. For fusion to reliably occur, the spinous process, laminae, pars, and facet joint at each level must be free of soft tissue and fully decorticated in preparation for bone grafting. Decortication of the facet joints is especially important because it allows increased segmental motion and, therefore, increased correction at each vertebra. In general, compression of the lumbar spine posteriorly by the appropriate hook pattern results in anterior gaping of the disc spaces, which is equivalent to lordosis. Correction of the frontal plane deformity is also achieved by derotation. A hook at every level of the thoracolumbar junction is required to provide stability for both derotation and lumbar compression. Additional stability and resistance to instrumentation pullout are provided by having hooks at every level of the lumbar spine as well.

The hook patterns shown for fusion to L1, L2, L3, and L4 (Fig. 41–1) were originally developed by Drs. Gordon Lee Engler and Harry L. Shufflebarger.

Suggested Readings

Barr SJ, Schuette AM, Emans JB. Lumbar pedicle screws vs. hooks: results

in double major curves in adolescent idiopathic scoliosis. Spine 1997;22:1369–1379.

Bridwell KH, Betz R, Capelli A, Huss G, Harvey N. Sagittal plane analysis

in idiopathic scoliosis patients treated with Cotrel-Dubousset instrumentation. Spine 1990;15:644–649.

Brown J. Cotrel-Dubousset instrumentation and the treatment of adoles-

cent idiopathic scoliosis. In: Bridwell KH, DeWald RL, eds. The Textbook of Spinal Surgery. 2nd ed. Philadelphia: Lippincott-Raven; 1997.

Lenke LG, Bridwell KH, Baldus C, Blanke K, Schoenecker PL. Cotrel-

Dubousset instrumentation for adolescent idiopathic scoliosis. J Bone Joint Surg Am 1992;74:1056–1067.

Sweet FA, Lenke LG, Bridwell KH, Blanke K. Maintaining lumbar lordosis

with anterior single solid rod instrumentation in thoracolumbar and lumbar adolescent idiopathic scoliosis. Spine 1999;24:1655–1662.

Eurostile

41 HOOK PATTERNS FOR THE PRESERVATION OF LUMBAR LORDOSIS

195

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Hook pattern for fusion to L1

For fusion to L1 after derotation, compression, distraction

Supralaminar

Laminar

Pedicle

T12

T11

T10

Laminar or pedicle

Supralaminar

Offset supralaminar

Pedicle

Distraction #2

Distraction #1

Compression

T10

T11

T12

Compress claw

Compress

Distract

Hook pattern for fusion to L 2

Pedicle

Supralaminar

T11

Supralaminar

T12

Laminar

T10

Laminar

Supralaminar offset

Pedicle or laminar

External body long body

Pedicle

For fusion to L2 after derotation, compression, distraction

Compress

Distraction

T10

T11

T12

Compression

to set

claw then

Compress

Distract

Distract mildly then

Figure 41–1

(A) Hook pattern for fusion to L1. (B) Hook pattern for fusion to L2. (C) Hook pattern for fusion to L3. (D) Hook pattern for fusion to L4.

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196

SECTION III THE LUMBAR SPINE

Eurostile

Hook pattern for fusion to L 3

For fusion to L3 after derotation, compression, distraction

Pedicle

Supralaminar

Pedicle

Supralaminar

Laminar

T12

T11

T10

Supralaminar offset

Pedicle

Pedicle or laminar

Laminar

L3 requires special “extended” hook, also called long body

Distraction

Compression

Distraction

Compression

T10

T11

T12

Compress

with claw

then

Compression

Distraction

Distract mildly then

Hook pattern for fusion to L 4

Supralaminar offset

Pedicle

Supralaminar

Pedicle

Supralaminar

T12

Supralaminar

T11

Pedicle

T10

Pedicle or laminar

Pedicle

For fusion to L4 after derotation, and selective compression, distraction

Compress

claw then

Compress

Distract

T10

T11

T12

Distraction #2

Laminar

Eurostile

Supralaminar

Compress #2

Compress

then

Distraction

41 HOOK PATTERNS FOR THE PRESERVATION OF LUMBAR LORDOSIS

197

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Apical Overcorrection and Lordosis Reconstruction of Thoracolumbar Idiopathic

Scoliosis

Joseph Y. Margulies, Lawrence I. Karlin, and Marc A. Asher

Goals of Treatment

To establish control and correction of the curve with less blood loss and shorter fusion levels.

Diagnosis/Indications for Surgery

Anterior apical overcorrection of idiopathic scoliosis is an accepted treatment for adolescent patients with thoracolumbar and upper lumbar scoliotic curves of 40 to 65 degrees.

Contraindications

Contraindications to anterior instrumentation include kyphosis above the planned level of instrumentation, and a compensatory thoracic curve that does not bend out to 20 degrees or less on a supine forced-bend film.

Advantages

It is preferable to do a posterior correction in some cases because it can utilize a shorter fusion section. The implant assembly is used as a correcting tool during surgery, and remains in the body as part of the fixation-stabilization mechanism until bone healing occurs.

Disadvantages

Stiff curves may require posterior facet joint resection or a different plan, such as anterior discectomy followed by posterior instrumentation.

Preoperative Planning

End vertebrae are selected on the basis of standard deformity radiographs,

including 36-inch posteroanterior (PA) and lateral x-ray and right and left

bends. The regional apex is determined on the standing x-ray. It is the most laterally displaced portion of the Cobb curve from a line joining the center of the Cobb end vertebral bodies. If the regional apex is a vertebra, further apparent as the single most rotated vertebra, the apex vertebra plus one

vertebral body above and one vertebral body below are included in the fusion. As the scoliosis reaches approximately 55 degrees or greater, it is generally necessary to add two vertebrae above and two vertebrae below the apex vertebrae. If the regional apex is a disc, then two vertebral levels above and below the apex are fused. The first caudal disc space, which

reverses coronal plane angulation on convex bending, can usually be excluded.

Procedure

The patient is positioned in a lateral decubitus position so that PA and lateral x-rays can be obtained. No bolster is placed under the patient as this has a tendency to block full correction. The usual anesthetic and padding precautions are necessary.

1. The spine is approached through a transthoracic retroperitoneal (or

retropleural/retroperitoneal) approach, resecting the rib two vertebral levels above the upper-instrumented vertebra. The sympathetic chain is mobilized laterally with the psoas. The segmental vessels are temporarily occluded and ligated, provided there are no monitoring changes. The discs are exposed to the far side to allow for a full annulectomy. The bodies, however, are not exposed much beyond the midline. A full 360-degree discectomy and annulectomy are done, exposing the posterior longitudinal ligament.

2. The proximal end screw is placed first, horizontal to the frontal plane

of the vertebral body, thus parallel to the end plate, and at the apex of the body. Placement is aided by visualization of the end plate, and the width of the body is measured at the exposed end plate.

3. A rod of proper length is cut and contoured to re-create the sagittal

plane angular position of the normal spine. A slight additional sagittal

plane contour is added. As described in Dr. Hall’s technique, the rod is bent to almost 30 degrees to produce overcorrection of the curve and some lordosis when the rod is rotated.

4. Once the rod is within the closed or capped vertebral screws and the set screws are loose, it is ready to be maneuvered. The rod is held either by the hex ranch at the hex end of a titanium rod, or with two rod-holding clamps at 90 degrees to each other and is rotated to place its sagittal plane contour in the true sagittal plane. The rod is slightly overrotated to provide for overcorrection of the curve and some lordosis and is secured by tightening one of the middle vertebral set screws to secure the new rod position (Fig. 42–1).

5. It is essential that the disc spaces be opened completely. The Cobb elevator or the PLIG instruments placed into the depth of the disc space are a helpful method for prying the disc space open, especially on the concave side. Additionally, some careful distraction can be applied between the screw connector bodies. Once the disc spaces are opened, the set screws are tightened.

6. To aid in overcorrection of the curve, the disc spaces must be completely filled. This can be achieved either with corticocancellous bone graft or with well-packed titanium mesh cages, which can be trimmed to a trapezoidal shape to accommodate the asymmetrical intervertebral spaces. The bone graft of choice is rib corticocancellous autograft. For two disc spaces, one rib is adequate; for three disc spaces, two ribs are needed; and for four discs, three ribs are necessary. The 10th rib can be taken at the site of entry, the 12th rib is taken from inside the chest, and the eighth rib is taken from outside the chest. The titanium mesh cages are filled maximally with rib corticocancellous autograft. The cages are then inserted to completely fill the distracted disc spaces. The disc spaces are then compressed toward the apex, and the set screws are tightened. Additional bone graft is added around the titanium mesh cages to completely fill the distracted disc spaces. The set screws should be revisited to ensure a tight fit (Fig. 42–2).

7. Closure is in the standard manner, utilizing chest tubes if the chest cavity is entered, or a retropleural Hemovac if a retropleural/retroperitoneal exposure is utilized.

Postoperative Care

Postoperative care begins in the intensive care unit approximately one night, with the patient sitting out of bed the next morning. A cast or brace is used at the physician’s discretion. The ambulatory patient is discharged at about 1 week postoperative. Children may return to class activity 5 to 6 weeks later, after a follow-up visit. Activities are restricted for 6 to 12 months, until there is clear indication of graft incorporation.