Ben L. Allen

A mechanistic classification of closed, indirect fractures and dislocations of the lower cervical spine

Closed, indirect fractures and dislocations of the lower cervical spine occur in families or groups within which there is a spectrum of anatomic damage to a cervical motion segment. This study of 165 cases demonstrates the various spectra of injury, called phylogenies, and develops a classification based on the mechanism of injury. The common groups are compressive flexion, vertical compression, distractive flexion, compressive extension, distractive extension, and lateral flexion. The probability of an associated neurologic lesion relates directly to the type and severity of cervical spine injury. With use of the classification, it is possible to formulate a rational treatment plan for injuries to the cervical spine.

The Galveston technique of pelvic fixation with L-rod instrumentation of the spine.

From April 1978 to October 1982, the authors performed 44 pelvic fixations as part of L-rod Instrumentation of a spinal deformity. Thirty scoliosis and revision scoliosis cases with a minimum of 1 year follow-up were analyzed for changes of the instrumentation with respect to the pelvis, angular changes at the lumbosacral junction, radiolucency about the portions of the rods providing pelvic fixation, and success of lumbosacral fusion. The technique for fixation was different among three groups of patients. A pelvic fixation technique in which the pelvic segments of the rods were longer than 6 cm, completely intraosseous through their iliac course, and within 1.5 cm of the sciatic notch, yielded the best results.

The Galveston Technique for L Rod Instrumentation of the Scoliotic Spine

Many small details of technique are important for achieving an excellent quality L-rod instrumentation of the scoliotic spine. Herein the authors report specifics gleaned from their experience and discuss the basis for them. The optimum approach establishes correctability of the deformity prior to spinal instrumentation, provides secure internal fixation of the spine, and strives for a massive arthrodesis.

A mechanistic classification of thoracolumbar spine fractures.

Thoracolumbar spinal injuries are classified on the basis of the mechanical mode of failure of the vertebral bodies. The fractures are presented in seven categories. Emphasis is placed on the injury component causing the fracture patterns. The choice of instrumentation for surgery is based on the surgeons understanding of these injury patterns.

Biomechanical comparisons of spinal fracture models and the stabilizing effects of posterior instrumentations

In this study, the authors evaluated the stiffness of motion segments in intact spines in two spine fracture models, and with each of five implant systems used for posterior fixation of thoracolumbar spine fractures. The devices represented a cross-section of types, including those employing sublaminar wires with and without laminar hooks, pedicle screws, plates, and rods. Two spine fracture models, one partially and one totally destabilized, were used in the tests of the instrumentation. Stiffness, or the magnitude of load needed to produce a unit displacement of the construct in the direction of the applied load, was measured in flexion, extension, lateral bending, and torsion in combination with a compressive force. Both horizontal plane shear and angular displacements were measured in the two fracture patterns. All evaluations were made by testing the difference in stiffness for statistical significance among groups. The results showed significant differences in stiffness without Instrumentation among intact spines, partly destabilized spines (anterior two-thirds of disk and posterior ligaments removed), and totally destabilized spines (only anterior longitudinal ligament intact). The implant/spine constructs were least stiff relative to the intact spine in torsion, followed in increasing order of stiffness with flexion, lateral bending, and extension. In the Roy-Camille plate with six-screw fixation was found to produce the stiffest construct, followed by wired Harrington rods, C-rods and J-rods, and the Vermont internal fixator. Cyclic loading with stiffness measured before and after cycling indicated that most spinal implants lost stiffness in torsion and lateral bending, and that those tested maintained their initial flexion stiffnesses.

Surgical management of ankle valgus in children: use of a transphyseal medial malleolar screw.

Valgus deformity of the ankle in children is associated with a wide variety of clinical conditions. A retrospective review was performed of 17 children (29 involved extremities) with ankle valgus deformity who had been managed by use of a percutaneously placed, transphyseal medial malleolar screw. Median age at the time of surgery was 11 years, 2 months. Median postoperative follow-up was 2 years, 2 months. Tibiotalar axis and ankle mechanical axis were the best radiographic indicators of ankle valgus deformity. Fibular station and epiphyseal wedging were poor predictors of ankle alignment. Significant improvement in the tibiotalar axis (median, 12 degrees) was noted at follow-up, and the median rate of correction was 0.59 degree/month. Resumption of physeal growth and recurrence of deformity (rate of 0.60 degree/month) was seen when the screws were removed before skeletal maturity. The transphyseal medial malleolar screw is a minimally invasive, minimally morbid, technically simple method of reversible partial epiphysiodesis at the ankle and is an effective technique for the correction of ankle valgus deformity associated with a wide variety of clinical conditions in children.

A biomechanical study of thoracolumbar spine fractures with bone in the canal. Part III. Mechanical properties of the dura and its tethering ligaments.

Experiments were performed to determine some mechanical properties of the spinal cord-meningeal (SCM) complex and its tethering elements with reference to factors contributing to contact pressure of an anterior mass on the SCM complex with spinal fracture and the development of some means to relieve the pressure. Measurements were made using a combined microload cell and displacement transducer that was passed posteriorly through a hole drilled in vertebra T12 through the interpedicular space and contacted the cord. Loss of nerve roots and anterior ligaments as dural tethers in the lumbar region permitted the SCM complex to fall out of the lordosis of the canal and fail to resist transverse loading. Head and neck flexion increased contact force for a given depth of penetration, particularly in the cervical region. This was consistent with measurements of strain along the dura that was greatest in the cervical region. The dura was found to be elastic, having a failure strain averaging 34% but was uniform in thickness, stiffness, and elastic modulus along its length. The study did not delineate any surgical manipulation other than removal of the anterior mass that would be beneficial when there is anterior compression of the spinal cord.

Comparison of neurologic deficits with atlanto-dens intervals in patients with Down syndrome

Eighty-four patients with Down syndrome had flexion-extension lateral roentgenograms of the C1-C2 articulation for the purpose of dividing the group into subluxators (> or = 4 mm atlanto-dens interval and 2 mm translation) and nonsubluxators (those who did not meet these criteria). Neurologic examinations and chart review were carried out on all patients to ascertain those with a positive neurologic finding or history. Seventeen (20%) were defined as subluxators and 67 (80%) as nonsubluxators. Five (29%) of the subluxators were found to have positive neurologic findings and 18 (27%) of the nonsubluxators had similar types of positive neurologic findings. These percentages are not significantly different. This led us to conclude that positive neurologic findings and an abnormal atlanto-dens interval are not alone adequate criteria to judge need for surgical stabilization of the C1-C2 articulation in patients with Down syndrome.

Staged correction of neuromuscular scoliosis.

Summary Anterior release and fusion, combined with tong gravity traction and second stage L-rod instrumentation, establishes correctability and accomplishes circumferential arthrodesis of the spine in neuromuscular scoliosis. From March 1979 through April 1982, nine patients with neuromuscular scoliosis, with an average age of 16.4 years, underwent this two-stage surgical procedure. The parameters investigated included correction of scoliotic deformity, correction of pelvic decompensation, and spinal arthrodesis. The preoperative scoliotic curvature measured 81° and the postoperative curve measured 29.3°, an average correction of 63.8%. Pelvic obliquity was significant in five of nine patients, averaging 36.2° preoperatively. Postoperatively the pelvic obliquity averaged 11.8°, an average correction of 67.4%. One of two pelvic fixation rods rotated out of the pelvis of one patient; roentgenographically he appears to have fused without loss of correction. A second patient has a poor fusion mass by roentgenographic criteria, although she has lost no correction and has had no pain. This technique offers results comparable to other series reporting arthrodesis for neuromuscular scoliosis. It has the advantages of requiring no anterior instrumentation and no postoperative immobilization.

Outcomes in surgical treatment of "idiopathic-like" scoliosis associated with syringomyelia

Patients with “idiopathic-like” spinal deformities associated with syringomyelia were retrospectively reviewed. Ten patients had surgical stabilization of their curvatures with at least a 2-year follow-up, and an additional five patients were evaluated for deformity pattern with <2 years of follow-up. Paralytic curve patterns, scoliosis associated with spina bifida, congenital scoliosis, or other associated syndromes were discarded. All 10 patients with surgery who were followed for an average of 46 months lost 10° correction above, through, or below the instrumented segments. A total of 50% lost correction through the instrumented segments. Anterior fusion stabilized the instrumented portion of the spine better than posterior instrumentation alone. Eighty percent of the 15 patients had thoracic kyphosis >40°. Only one patient was lordoscoliotic. Syringomyelia deformities tend to be kyphoscoliotic in 80% of cases and behave more like paralytic curvatures postoperatively. MRI is recommended for apparent idiopathic scoliotic curvatures that are kyphoscoliotic and not lordoscoliotic.