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ABSTRACT: Five different reconstructions of the atlantoaxial complex were biomechanically compared in vitro in a nondestructive test.
To determine whether non-bone graft-dependent one-point fixation affords stability levels equivalent to three-point reconstructions.
Previous investigations have demonstrated that three-point fixation, using bilateral transarticular screws in combination with posterior wiring, provide the most effective resistance to minimize motion around C1-C2. However, placement of transarticular screws is technically demanding. Posterior wiring techniques affording one-point fixation have failure rates of approximately 15%, with failure considered to be secondary to structural bone graft failures. One-point, non-bone graft-dependent fixations have not been tested.
Eight human cervical specimens, C0-C3 were loaded nondestructively. Unconstrained three-dimensional segmental motion was measured. The reconstructions tested were two one-point fixations, one two-point fixation, and two three-point fixations.
Under axial rotation two and three-point reconstructions provided better stiffness than the one-point reconstructions (P < 0.05). During flexion-extension, higher stiffness levels were observed in one- and three-point fixations when compared with the intact spine (P < 0.05). In lateral bending no significant differences were observed among the six groups, although the trend was that reconstructions including transarticular screws provided greater stability than one-point fixations.
The current findings substantiate the use of three-point fixation as the treatment of choice for C1-C2 instability. [l: atlantoaxial fixation, biomechanics, cervical spine, instability, spinal instrumentation, transarticular screws]
Spine 11/2000; 25(22):2877-83. · 2.08 Impact Factor
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ABSTRACT: Three types of anterior thoracolumbar multisegmental fixation were biomechanically compared in construct stiffness and rod-screw strain.
To investigate the effects of rod diameter and rod number on construct stiffness and rod-screw strain in anterior thoracolumbar multisegmental instrumentation.
No studies have been undertaken to investigate the biomechanical effects of rod diameter and rod number in thoracolumbar anterior instrumentation.
Ten fresh-frozen calf spines (T13-L5) were used. After intact analysis, a total discectomy and transection of the ALL and PLL were performed at L1-L2, L2-L3, and L3-L4 with intervertebral reconstruction using carbon fiber cages. Three types of anterior fixation were then performed at L1-L4: 1) 4.75-mm diameter single-rod, 2) 4.75-mm dual-rod, and 3) 6.35-mm single-rod systems. Single screws at each vertebra were used for single-rod and two screws for dual-rod fixation. These systems share the same basic design except rod diameter. Nondestructive biomechanical testing was performed and included compression, torsion, flexion-extension, and lateral bending. Construct stiffness and rod-screw strain of the three reconstructions were compared.
The 6.35-mm single-rod fixation significantly improved construct stiffness compared with the 4.75-mm single rod fixation only under torsion (P < 0.05). The 4. 75-mm dual rod construct resulted in significantly higher stiffness than did both single-rod fixations (P < 0.05), except under compression. No statistical differences were observed in rod-screw strain between the two types of single rods, whereas dual-rod reconstruction exhibited less rod-screw strain (P < 0.05).
For single-rod fixation, increased rod diameter neither markedly improved construct stiffness nor affected rod-screw strain, indicating the limitations of a single-rod system. In thoracolumbar anterior multisegmental instrumentation, the dual-rod fixation provides higher construct stiffness and less rod-screw strain compared with single-rod fixation.
Spine 09/2000; 25(18):2303-11. · 2.08 Impact Factor
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ABSTRACT: This is a review of 20 patients who experienced failure of threaded interbody fusion cages and underwent surgical correction.
To review the causes and possible treatment strategies for failed cylindrical cages.
Intraoperative complications have been described in the past; however, management of the postoperative patient with failure of interbody fusion devices has not been described.
In 20 patients with failed threaded titanium fusion cages (18 Bagby and Kuslich Devices [BAK; Sulzer-Spine Tech, Minneapolis, MN], 2 Ray Threaded Fusion Cages [Ray TFC; Surgical Dynamics, Norwalk, CT) who underwent revision surgery, all had failure before successful arthrodesis was achieved. Eight of the original titanium cages had been inserted anteriorly (7 laparoscopically), and 12 had been inserted for posterior interbody lumbar fusion. Before the revision surgery, five of the implants were thought to be solid by the referring surgeon, but pseudarthrosis was clearly present in all. In addition, 14 other explanted BAK devices were subjected to undecalcified histologic preparation, quantitative histomorphometry, and histopathologic analysis.
The average length of time before revision surgery (implant duration) was 31.8 weeks (range, 1-156 weeks). The most common revision procedure was posterior exploration of the symptomatic nerve root with foraminotomy for unrecognized lateral recess stenosis (11 cases) or excision of iatrogenically herniated intervertebral disc fragments (4 cases). However, four cages inserted through posterior exposure during an interbody lumbar fusion procedure had to be removed because of migration into the spinal canal. In nine cases posterior pedicle screw instrumentation was necessary in addition to posterolateral fusion using iliac crest bone grafting.
All 20 cages failed because of surgical technique rather than an intrinsic defect in fusion cage technology. The factors associated with failure of the original insertion procedure were failure to achieve adequate distraction of the anulus fibrosis; undersized cages, especially when placed through the posterior interbody lumbar fusion approach; cerebrospinal fluid leakage or pseudomeningocele; Type 2 diabetes mellitus; the use of local bone graft rather than iliac crest inside the cage; anterior insertion in an excessively lateral position resulting in symptoms of a far lateral disc herniation; and failure to identify the spinal midline during an anterior approach.
Spine 11/1999; 24(20):2147-53. · 2.08 Impact Factor
