Posterior Scoliosis Correction of King II Curves: Hooks and Rods

30 Posterior Scoliosis Correction of King II Curves

Hooks and Rods

Lawrence G. Lenke

Goals of Surgical Treatment

To balance, correct, and stabilize the curvature.

Diagnosis

True King II curve identification:

1. The King II curve is one where both thoracic and lumbar curves cross the midline, with the thoracic Cobb greater than the lumbar Cobb and the percent thoracic side bending being less than the percent lumbar side bending correction. It is now well known that a thoracolumbar junctional kyphosis (T10-L2 sagittal Cobb of greater than or equal to +20 degrees) is a relative contraindication to a selective thoracic fusion because one must stop near or at the apex of the sagittal plane malalignment.

2. I found that a selective thoracic fusion can be performed when the thoracic to lumbar (T:L) Cobb and AVT ratios were greater than 1.2, and the T:L AVR was greater than 1.0. In addition, there had to be an absence of any thoracolumbar junctional kyphosis, and a maximum lumbar Cobb measurement of 60 degrees on the upright film.

3. For a true King II curve definition, I feel the lumbar apex should completely deviate from a vertically oriented center sacral line (as designated a Lenke type C lumbar modifier).

Selection of Fusion Levels

In a true King II curve treated with posterior hook-rod instrumentation, fusion levels normally extend from the neutral vertebra proximally (T4 or T5) to the stable vertebra distally at the thoracolumbar junction (usually T12 or L1).

The proximal thoracic region should also be evaluated in the coronal and sagittal planes as well as clinically for a structural proximal thoracic curve. If this is noted, then the instrumentation proximally should extend up to T2 or T3 for inclusion of the structural proximal thoracic curve. It is important to determine the stable vertebra off a vertically oriented center sacral line that does not have any accommodation for mild pelvic obliquity. When pelvic obliquity is greater than 2 cm, the radiograph should be performed with an appropriate shoe lift under the short leg to level the pelvis.

The stable vertebra is the most proximal lower thoracic or upper lumbar vertebra most closely bisected by this vertically oriented center sacral line (CSVL). For most true King II curves, the stable vertebra is either T12 or L1. If the T12-L1 disc is the “stable” segment, then I prefer to end the instrumentation at T12 as long as there is absolutely no thoracolumbar junctional kyphosis. If there is any hint of thoracolumbar junctional kyphosis or in a larger thoracic curve (> 70 degrees), I would recommend extending the instrumentation and fusion to L1 instead when using hooks.

Instrumentation Techniques

Following adequate subperiosteal exposure out to the tips of the transverse processes of the intended vertebra to be fused, appropriate inferior facet joint osteotomies for hook placement and fusion purposes is performed. Hooks are then placed (assuming a T4-T12 instrumentation construct). The left-sided concave hook pattern will normally begin proximal with a oneor two-level pedicle-transverse process (or supralaminar) claw of T4 or T4-T5. Another up-going pedicle hook is placed two levels below the upper most pedicle hook usually at T6, and then a down-going supralaminar hook is placed three levels above the lowest instrumented vertebra (LIV), at T9. A two-level supralaminar-infralaminar claw at T11-T12 completes the concave hook pattern.

The right-sided hook pattern begins with a two-level pedicle-transverse process claw at T4-T5, two up-going pedicle hooks at T7 and T9, and then a supralaminar hook at the LIV (T12) (Fig. 30–1). The left-sided concave rod is placed first. It is contoured to the appropriate coronal and sagittal planes, engaged in the hooks proximally and cantilevered into the hooks successively from proximal to distal. Hooks are seated from distal to proximal with the distal compression claw seated first, apical supralaminar hook seated second, the apical pedicle hook third, and the proximal pedicle claw last. Thus, compression forces are performed across the thoracolumbar junction ensuring appropriate lordotic contour of the thoracolumbar junction, prior to any distraction forces at the apex and above. Mild translational forces can be applied with in situ rod benders to further correct the scoliosis.

Next, the right or convex rod is placed with hooks being seated proximally first at the upper level claw and proceeding distally down to the supralaminar hook placed at the LIV. Thus, compression forces are placed from the apical pedicle hooks to the upper claw over the convexity of the convex spine, then a distraction force is directed against the relative concavity of the lower right-sided thoracic spine. These forces are directly opposite to those that have been placed on the left-sided concave spine, as one would expect.

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