The Journal of Bone and Joint Surgery, Vol 70, Issue 8 1182-1191, Copyright © 1988 by Journal of Bone and Joint Surgery, Inc
Biomechanical analysis of anterior and posterior instrumentation systems after corpectomy. A calf-spine model
KR Gurr, PC McAfee and CM Shih
Department of Orthopaedic Surgery, Johns Hopkins University School of Medicine, Baltimore.
To simulate the spinal instability that is found clinically after anterior
corpectomy for the treatment of a fracture or a neoplasm, twelve fresh
calf-spine segments, each containing five motion segments, were
destabilized using a complete anterior corpectomy at the third lumbar level
and anterior discectomies at the second and third and the third and fourth
lumbar levels. Mechanical non-destructive cyclical testing in axial
compression, rotation, and flexion was performed on each spinal segment
after stabilization was accomplished. The three anterior-stabilization
constructs that were compared were: (1) iliac strut grafting, (2)
polymethylmethacrylate and anterior Harrington-rod instrumentation (the
technique of Siegal and Siegal), and (3) the Kaneda anterior device. After
anterior iliac-crest strut grafting, four types of posterior
instrumentation were also tested sequentially: (1) Harrington distraction
rods, (2) Luque rectangular instrumentation, (3) Cotrel-Dubousset
transpedicular instrumentation, and (4) Steffee transpedicular screws and
plates. Rotation, torque, axial displacement, and axial loads were measured
during loading across the whole spinal segment between the grip points.
Using an anterior extensometer, intervertebral displacement at the second,
third, and fourth lumbar levels, and thus across the corpectomy defect at
the third lumbar level, was recorded "on line" during testing in flexion
and axial load. By recording the intervertebral displacement, the efficacy
of each spinal construct in minimizing motion across the corpectomy defect
could be quantified. The value for one-way analysis of variance for axial
intervertebral displacement across the site of the third lumbar corpectomy
was F = 10.5, p less than 0.001. The value for one-way analysis of variance
for flexural intervertebral displacement across the corpectomy defect was F
= 21.1, p less than 0.001. Homogeneous subsets of rigidity for torsional
stiffness revealed that the least rigid constructs were iliac grafting
alone, Harrington-rod instrumentation, and Luque rectangular
instrumentation. The most rigid constructs were the anterior Kaneda device,
transpedicular Cotrel-Dubousset instrumentation, and Steffee screws and
plates. CLINICAL RELEVANCE: After corpectomy, spinal reconstructive surgery
can restore axial, torsional, and flexural rigidity to normal levels. These
experimental conclusions applied to the acute restoration of stability,
rather than to rigidity after long-term cyclical loading. Using the most
rigid anterior system, the Kaneda device, the fixation extended only one
vertebral level cephalad and one level caudad to the corpectomy
defect.(ABSTRACT TRUNCATED AT 400 WORDS)
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