Biomedical subjects

B W Cunningham

Publications and source records attributed to B W Cunningham.

41 records · Page 3Linked to original sources

PubMed1992

Biomechanical analysis of lumbosacral fixation.

Flexion testing was performed until failure on 66 lumbosacral bovine spinal segments comparing ten different lumbosacral instrumentation techniques. Maximum flexion moment at failure, flexural stiffness, and maximum angulation of the lumbosacral joint at failure were determined as well as strain measurements across the anterior aspect of the lumbosacral intervertebral disc using an extensometer. The maximum moment at failure was significantly greater for the only two devices that extended fixation into the ilium anterior to the projected image of the middle osteoligamentous column: ISOLA Galveston and ISOLA iliac screws (F = 12.2, P less than 0.001). The maximum stiffness at failure reinforced these findings (F = 23.7, P less than 0.001). A second subset of stability showed the advantages of S2 pedicle fixation by increasing the flexural lever arm (Cotrel-Dubousset butterfly plate, and Cotrel-Dubousset Chopin block, P less than 0.05). This exhaustive in vitro biomechanical study introduces the concept of a pivot point at the lumbosacral joint at the intersection of the middle osteoligamentous column (sagittal plane) and the lumbosacral intervertebral disc (transverse plane). A spinal surgeon can increase the stability of lumbosacral instrumentation by extending fixation through the anterior sacral cortex (Steffee plate group with pedicle screws that medially converge in a triangular fashion). A means of enhancing this fixation was to achieve more inferior purchase by extending the fixation down to the S2 pedicle (Cotrel-Dubousset Chopin and Cotrel-Dubousset butterfly groups). However, the best fixation was achieved by obtaining purchase between the iliac cortices down into the superior acetabular bone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

The effect of spinal implant rigidity on vertebral bone density. A canine model.

An animal model of anterior and posterior column instability was developed to allow in vivo observation of bone remodeling and arthrodesis following spinal instrumentation. After an initial anterior and posterior destabilizing lesion was created at the L5-L6 vertebral levels in 63 adult beagles, various spinal reconstructive surgical procedures were performed--with or without bilateral posterolateral bone grafting, with or without bilateral oophorectomies, and with or without spinal instrumentation (Harrington distraction, Luque rectangular, Cotrel-Dubousset pedicular, or Steffee pedicular implants). Observation 6 months after surgery revealed a significantly improved probability of achieving a spinal fusion if spinal instrumentation had been used (X2 = 5.84, P = .016). Nondestructive mechanical testing after removal of all metal instrumentation in torsion, axial compression, and flexion revealed that the fusions performed in conjunction with spinal instrumentation were more rigid (P less than .05). Quantitative histomorphometry showed that the volumetric density of bone was significantly lower (ie, device-related osteoporosis occurred) for fused versus unfused spines. In addition, a linear correlation occurred between decreasing volumetric density of bone and increasing rigidity of the spinal implant (r = .778); ie, device-related osteoporosis occurred secondary to Harrington, Cotrel-Dubousset, and Steffee pedicular instrumentation. Oophorectomized dogs became more osteoporotic than their surgically matched controls (posterolateral bone grafting alone, Cotrel-Dubousset pedicular instrumentation, and Steffee pedicular instrumentation); device-related osteoporosis added to the degree of hormonally induced osteoporosis (t = 5.0, P less than .0001). This is the first study to date documenting the occurrence of stress shielding in the spine secondary to spinal instrumentation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Triangulation of pedicular instrumentation. A biomechanical analysis.

Tensile load-to-failure pullout tests were performed on 54 cadaveric spinal segments. The vertebrae were grouped by adjacent levels and matched for bone mineral density (g/cm2), which was measured by dual-photon absorptiometry. Triangulation of Steffee screws and CD pedicle screws was accomplished by transverse plates specifically designed to increase fixation within the same vertebra before the longitudinal Steffee plate or CD rod was applied. A transverse plate with adjustable length was also tested to accommodate variable interpedicular distances. Comparative pullout load-to-failures were as follows: laminar hook, 809 SE 99.4 N; single CD pedicular screws, 863 SE 108 N; single Steffee pedicular screw, 1245 SE 75.3 N; adjustable transverse plate, 1341 SE 114; triangulated Steffee pedicle screws with a transverse plate, 1701 SE 151 N; and triangulated CD pedicle screws with a transverse plate, 2096 SE 115 N. Three triangulated constructs with pedicle screws and a transverse plate (CD, Steffee, and Kirschner) provided significantly greater fixation than conventional pedicular or laminar hook based instrumentation systems (P less than 0.05). Improved treatment of spinal deformities in the elderly and osteoporotic population is dependent on improving the fixation at the metal-bone interface of spinal implants Particularly in osteoporotic vertebrae, the strength of fixation of two triangulated pedicle screws is better than either laminar hooks or single pedicle screws. The strength of fixation of triangulated pedicle screws connected by a transverse plate is superior to a single pedicle screw because it is dependent on the mass of bone between the screws rather than simply the amount of bone within the screw thread.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1989

1989 Volvo Award in basic science. Device-related osteoporosis with spinal instrumentation.

An animal model of anterior and posterior column instability was developed to allow in vivo observation of bone remodeling and arthrodesis after spinal instrumentation. After an initial anterior and posterior destabilizing lesion was created at the L5-L6 vertebral levels in 42 adult beagles, various spinal reconstructive surgical procedures were performed--with or without bilateral posterolateral bone grafting, and with or without spinal instrumentation (Harrington distraction; Luque rectangular, or Cotrel-Dubousset transpedicular methods). After 6 months' postoperative observation, there was a significantly improved probability of achieving a spinal fusion if spinal instrumentation had been used (P = 0.058). Nondestructive mechanical testing after removal of all metal instrumentation in torsion, axial compression, and flexion revealed that the fusions performed in conjunction with spinal instrumentation were more rigid (P less than 0.05). Quantitative histomorphometry showed that the volumetric density of bone was significantly lower (ie, device-related osteoporosis occurred) for fused versus unfused spines; and Harrington- and Cotrel-Dubousset-instrumented dogs became more osteoporotic than the other three groups. The rigidity of spinal instrumentation led to device-related osteoporosis (stress shielding) of the vertebra. However, as the rigidity of spinal instrumentation increased, there was an increased probability of achieving a successful spinal fusion. The improved mechanical properties of spinal instrumentation on spinal arthrodesis more than compensate for the occurrence of device-related osteoporosis in the spine.

Animals↗

PubMedDate not supplied

A comparative mechanical analysis of the pointe shoe toe box. An in vitro study.

Dancing en pointe requires the ballerina to stand on her toes, which are protected only by the pointe shoe toe box. This protection diminishes when the toe box loses its structural integrity. The objectives of this study were 1) to quantify the comparative structural static and fatigue properties of the pointe shoe toe box, and 2) to evaluate the preferred shoe characteristics as determined by a survey of local dancers. Five different pointe shoes (Capezio, Freed, Gaynor Minden, Leo's, and Grishko) were evaluated to quantify the static stiffness, static strength, and fatigue properties (cycles to failure) of the shoes. Under axial loading conditions, the Leo's shoe demonstrated the highest stiffness level, and the Freed shoe exhibited the least strength. Under vertical loading conditions, the Leo's and Freed shoes demonstrated the highest stiffness levels, and the Gaynor Minden and Freed shoes exhibited the highest strength. Fatigue testing highlighted the greatest differences among the five shoes, with the Gaynor Minden demonstrating the highest fatigue life. Dancers rated the top five shoe characteristics, in order of importance, as fit, comfort, box/platform shape, vamp shape, and durability and indicated that the "best" shoe is one that "feels right" and permits artistic maneuvers, not necessarily the strongest or most durable shoe.

Adult↗