An Innovative One-Stage Technique

Alberto Ponte

Goals of Treatment

1. Correct structural thoracic or thoracolumbar hyperkyphosis:

a. By a single-stage procedure.

b. By substantial shortening of the posterior spine.

2. Restore a normal sagittal profile and balance:

a. By correcting to optimal physiologic ranges of 30 to 40 degrees (without inducing junctional kyphosis).

b. By a harmonious distribution of correction over the entire curve.

3. Provide immediate and long-term stability of correction:

a. By avoiding anterior column disruption, thus preserving the immediate load sharing capacity.

b. By fusion and a fully segmental anchorage of instrumentation.

Diagnosis

The diagnosis of typical Scheuermann’s kyphosis is based on radiographic changes of irregular vertebral end plates, narrowing of intervertebral disc spaces, wedging of at least 5 degrees of three contiguous vertebrae, and Schmorl’s nodules. In more recent years the wedging of 5 degrees or more of only one vertebra has been considered sufficient for the diagnosis. A disease affecting a short segment of the spine induces a long segment deformity. In atypical forms there is an absence of end plate irregularities and/or vertebral wedging.

On clinical examination both forms present with a rigid thoracic or thoracolumbar kyphosis greater than 45 degrees, which appears in adolescence and resists forced extension. This differentiates these patients from flexible postural roundbacks. A lateral radiograph in hyperextension over a plastic wedge, placed just below the apex of the curvature, confirms a fixed deformity. There is a compensatory, nonstructural increase in lumbar lordosis, whereas cervical lordosis is usually decreased.

Mechanics of Kyphosis Correction

Surgical correction is obtained by combining anterior lengthening and posterior shortening of the spine. Each technique, however, either primarily lengthens the anterior spine or primarily shortens the posterior spine. The innovative posterior technique, developed in 1987 and described here, is the only one correcting almost entirely by shortening the posterior spine. This procedure also produces the longest moment arm for posterior corrective forces among all techniques. Much lesser forces are therefore needed to obtain the same bending moment, with consequently much smaller loads on the bone/metal interface. Anterior column integrity, with the anterior longitudinal ligament and anterior discs acting as a tension band, is essential for producing the mechanical advantage.

Essential Principles of the Innovative Posterior Technique

1. A substantial shortening of the posterior spine through the closure of wide intersegmental resections (osteotomies) at every level within the deformity.

2. A construct with bilateral, fully segmental (not multilevel) anchorage, capable of achieving a harmonious correction by proportionally modulated compression forces (no excessive stress concentrations).

3. An intact anterior column (see above).

Indications

1. Scheuermann’s kyphosis: Surgical treatment should be performed only in patients who have reached complete skeletal maturity. Before that a nonoperative treatment can provide satisfactory results, with severe deformities being corrected by plaster casts. Indications for surgery are more restrictive than in scoliosis and should be based on an individualized evaluation of the patient, and not on a numerical threshold of x-ray degrees. Indications include significant pain, adult progression, severity, prevention of further increase in deformity, and unacceptable appearance problems with psychological distress. There are no limits of severity for the innovative technique.