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Isador H Lieberman

Publications and source records attributed to Isador H Lieberman.

24 records · Page 2Linked to original sources
PubMed2002

In vitro stability of FRA spacers with integrated crossed screws for anterior lumbar interbody fusion.

STUDY DESIGN: Mechanical testing of human lumbar functional spine units was carried out after instrumenting the disc space with femoral ring allografts (FRAs) with and without integrated crossed anterior screws applied into the adjacent bodies. OBJECTIVES: To assess the stability of FRA construct with and without the integrated crossed anterior screws and to compare that with the intact specimen. SUMMARY OF BACKGROUND DATA: Most modern methods of achieving anterior lumbar intervertebral fusion rely on the use of interbody spacers to restore and maintain intervertebral height, overall alignment, and stability while facilitating arthrodesis. The FRAs have the advantage of biologic compatibility but may not have enough stability when used as stand-alone devices. FRA spacers alone are less stiff in torsion and extension compared with other instrumented constructs. Increased motion could lead to higher failure rates because of graft migration and pseudarthrosis. This makes the use of supplementary anterior or posterior fixation necessary. The current authors hypothesized that the addition of anterior integrated crossed screws applied through the FRA spacer into the adjacent vertebral bodies would increase the stability of the FRA spacer in extension and torsion in the absence of further posterior instrumentation. METHODS: Seven fresh-frozen human cadaveric lumbar spine functional spine units were tested applying cantilever bending moments in flexion, lateral bending, torsion, and extension. The specimens were tested in the following sequence: intact, with FRA spacer alone and with FRA spacer and integrated crossed screws. The stiffness of each construct was then compared with the intact specimen. Specimens with obvious deformity on radiographs or dual-energy radiograph absorptiometry t score values <-1.2 were excluded. RESULTS: The addition of the integrated crossed metal screw system improved the stiffness of the construct by 53% over the intact (P = 0.02) and by 31% over the FRA alone in extension (P = 0.01), whereas it improved the stiffness by 40% over the intact (P = 0.03) and by 18% over the FRA alone in torsion (P = 0.21). The crossed screw system did not improve the stiffness compared with intact in either flexion or lateral bending modes. CONCLUSIONS: Although there is a trend toward improved stability of the FRA spacers in torsion with the addition of the metal screws, this is not statistically significant. The integrated crossed anterior metal screw system significantly improves the stability of the FRA spacers in extension when used for anterior lumbar interbody fusion.

Adult↗
PubMedDate not supplied

Distribution of anterior cortical shear strain after a thoracic wedge compression fracture.

BACKGROUND CONTEXT: Vertebral compression fractures (VCFs) are a common clinical problem and may follow trauma or be pathological. Osteoporosis increases susceptibility to fracture by reducing bone mass and weakening bone architecture. Approximately 2.5 million osteoporotic fractures occur worldwide annually, usually involving the vertebrae, wrist and hip. In the United States 700,000 VCFs occur annually, causing significant morbidity, mortality and economic burden. An initial VCF often leads to subsequent VCFs. The strain distribution along the anterior cortex, the major load-bearing pathway in flexion, may be predictive of impending VCF. Regions of high strain distribution are likely to experience secondary fracture. PURPOSE: To investigate the distribution of anterior cortical strain at, above and below an experimentally created index VCF to determine the vertebral body at risk of secondary fracture. STUDY DESIGN: In vitro experimental study using cadaveric thoracic spinal segments. METHODS: Seventeen thoracic spines underwent dual-energy X-ray absorptiometry (DEXA) to assess bone mineral density and were divided into T1-T3 (Subsegment 1), T4-T6 (Subsegment 2), T7-T9 (Subsegment 3) and T10-T12 (Subsegment 4). Rectangular rosette strain gauges were applied to the anterior cortices of the vertebrae of each subsegment (vertebrae in each specimen were denoted V1-superior, V2-intermediate and V3-inferior). V1 and V3 were partially embedded into polyester resin blocks, which were used to mount the specimens in a materials testing machine. Nondestructive predefect testing was performed in compression at 125 N and 250 N, followed by flexion at 1.25 Nm and 2.5 Nm. To ensure fracture reproducibility, V2 of each specimen had a trabecular defect created to a volume of 21.3+/-4.4% of the V2 centrum. Postdefect nondestructive compression and flexion were then performed in a manner similar to the predefect tests, followed by destructive testing in flexion. Anterior cortical shear strain on V1, V2 and V3, applied moments and applied flexion angle were all measured and analyzed. RESULTS: A VCF occurred in 55 of the 59 subsegments. Fifty-one VCF (93%) were seen in V2 and 4 VCF (7%) were seen in V1. After the creation of the trabecular defect, the shear strain on V2 increased, but a comparison of the postdefect with the predefect nondestructive tests showed no significant differences. The pre- and postdefect shear strain distribution in compression and flexion was V1strain>V3strain>V2strain. Shear strain at failure was highest on V2, and in all subsegments there were significant differences between V2 and V3 (p<.05). In all subsegments there were no significant differences between V2 and V1 (p>.05) at failure with the exception of Subsegment 1 where V2 and V1 were significantly different (p<.05). The predominant strain pattern at failure was (V2strain>V1strain>V3strain V2strain>>V3strain). Using shear strain as the codeterminant of peak moment with bending stiffness and applied angle at failure, the strain on V1 was the greatest predictor (p=.0084; R2=0.78). These findings suggest that the events leading to a secondary fracture probably start before the index VCF occurs and continue with loading beyond the index VCF. CONCLUSION: Anterior cortical strain is concentrated at the apex of a thoracic kyphotic curve. The vertebral body immediately above the index VCF has the next highest amount of strain and therefore the highest risk of secondary fracture.

Absorptiometry, Photon↗
PubMedDate not supplied

Biomechanical changes after the augmentation of experimental osteoporotic vertebral compression fractures in the cadaveric thoracic spine.

BACKGROUND CONTEXT: Osteoporotic compression fractures are an important public health concern, leading to significant morbidity, mortality and economic burden. Cement augmentation procedures used to treat these fractures alter the biomechanics of the fractured segment, which could promote adjacent failure. However, if alignment is improved or restored, there will be less risk of adjacent failure. PURPOSE: To determine the effects of load (compression/flexion), adjacent vertebral location (superior/inferior) and augmentation on vertebral segment stiffness and adjacent vertebral strain in the upper and lower thoracic spine. STUDY DESIGN: Human cadaveric thoracic spine segments were tested under load control before and after the creation of experimentally augmented vertebral compression fractures. METHODS: Six T1-T5 and six T8-T12 segments were obtained from eight thoracic spines with known bone mineral density (BMD). Rosette strain gauges were applied to T2, T4, T9 and T11 to measure strain adjacent to the experimental fracture sites T3 and T10. Two compression fractures were created in succession, the first in flexion preceded by a weakening defect in T3 and T10 and the second created in an adjacent vertebra in compression without prior weakening. The first fracture was reduced with the inflatable bone tamp (IBT) and augmented with cement. Compression and flexion tests were performed before and after the first fracture while measuring vertebral cortical shear strain on T2, T4, T9 and T11 and stiffness of the entire segment. Strain and stiffness were compared by using a repeated measures analysis using adjacent vertebral location (superior/inferior), augmentation and load (compression/flexion) as factors. RESULTS: The mean BMD was 0.61+/-0.11 g/cm(2) (T1-T5) and 0.78+/-0.07 g/cm(2) (T8-T12). Stiffness in compression and flexion increased with load (p<.05, and p>.27, respectively). Augmentation reduced compressive and bending stiffness (p=.23, and p=.19, respectively), whereas the adjacent vertebral strain increased (p>.11). The adjacent strain in flexion was much greater than in compression (p<.03). Cement augmentation caused greater amounts of inferior than superior adjacent strain (p>.19). The applied moment at first fracture was 2.98+/-1.28 Nm (T1-T5) and 8.44+/-1.02 Nm (T8-T12). The compressive load at second fracture was 1122+/-993 N (T1-T5) and 2906+/-1008 N (T8-T12). Adjacent vertebral strain during the second compression and flexion tests exceeded that during the first compression and flexion tests (p=.11). Adjacent vertebral strain at second fracture exceeded that at first fracture (p=.007) and was greater on the superior adjacent vertebra than the inferior (p=.47). CONCLUSION: With axial compressive loads, the addition of flexion increases fracture risk. Cement augmentation of a fractured vertebral segment reduces stiffness while increasing both the superior and inferior adjacent cortical strain. This increment in strain that is greatest on the inferior adjacent vertebra effectively redistributes loads from the superior adjacent vertebra to the inferior adjacent vertebra, sparing the superior adjacent vertebra from failure.

Adult↗
PubMedDate not supplied

Vertebroplasty and kyphoplasty: filler materials.

Over 700,000 osteoporotic compression fractures occur each year in the United States, twice the number of hip fractures. These vertebral fractures, most of which occur in the elderly, represent significant personal and societal burdens. Percutaneous vertebroplasty (PVP) is a minimally invasive method that involves the percutaneous injection of polymethylmethacrylate (PMMA) into a collapsed vertebral body to stabilize the vertebra. Kyphoplasty is an advanced minimally invasive technique with a number of potential advantages over PVP, including lower risk of cement extravasation and better restoration of vertebral body height and spinal biomechanics. The filling materials used for both these techniques require good biocompatibility, good biomechanical strength and stiffness, and good radiopacity for the fluoroscopy guided procedures. New filler materials (synthetic bone substitutes, e.g., composite resin materials, calcium phosphate or calcium sulfate cements) in addition to new PMMA formulations are now available for clinical use. In this review paper, we will focus on the issues and characteristics of these filler materials as they pertain to vertebral augmentation procedures.

Animals↗