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At least 145 records · Page 8Linked to original sources
PubMed1996

Mason type II radial head fractures fixed with Herbert bone screws.

The management of radial head fractures remains controversial. Accurate classification of the fracture (Mason) may necessitate the use of special X-ray views (45 degrees arterior oblique or radio-capitellar). We present the results of 19 cases of Mason type II fractures treated operatively by open reduction and internal fixation with the Herbert bone screw. All patients achieved 'good-to-excellent' outcome at follow-up. Our results compare favourably with other forms of treatment for this injury.

Adolescent↗
PubMed1991

Three cancellous bone screws versus a screw-angle plate in the treatment of Garden I and II fractures of the femoral neck.

A consecutive clinical series of 33 patients with either an undisplaced (Garden I) or minimally displaced (Garden II) femoral neck fracture was randomly divided into two operative protocols. Half of the fractures were treated with three cannulated cancellous bone screws, while the other half were treated with a standard screw-angle plate device. After a mean follow-up of 2 years, 4 patients had died, while 20 of the remaining 29 hips showed excellent or good, 3 fair and 6 poor functional results. The three-screw fixation seemed to yield more technical complications as compared to the screw-angle plate fixation. However, the differences in functional end-results were of no clear statistical significance. We conclude that the screw-angle plate device gives acceptable results in this group of fractures. The use of cannulated hip screws may be more advantageous in the treatment of dislocated femoral neck fractures, where the torsional strength of fracture fixation and femoral head viability are more critical.

Adult↗
PubMed1980

Single crystal alumina for dental implants and bone screws.

When ground to a suitable form, flexural strength of single crystal alumina (Al2O3) decreases to as low as one third the strength of the intact crystal. This flexural strength decrease is, however, recovered by chemical etching at a high temperature to eliminate surface defects caused by grinding. By using this strength recovery treatment, various types of single crystal implants with fine structure were able to be designed. Four kinds of single crystal bone screws and single crystal dental implants of screw and anchor type were designed. Flexural strength and impact strength of the implants were measured.

Aluminum↗
PubMed1996

The strength of plate fixation in relation to the number and spacing of bone screws.

Our purpose was to study the relationship between the number of plate holes filled and the spacing between the screws and the resultant strength of plated constructs. Broad regular DC plates were anchored with 4.5-mm cortical screws to blocks of polyurethane foam. Six constructs were tested: (a) screws in holes 1, 2, and 3; (b) screws in holes 1 and 3; (c) screws in holes 1 and 4; (d) screws in holes 1 and 5; (e) screws in holes 1 and 6; (f) screws in holes 1, 3, and 5. The strength was quantified using a material-testing system. In cantilever and four-point bending, the constructs were loaded in both gap-closing and gap-opening modes. Screws in holes 1, 2, and 3 were tested against other constructs. For cantilever bending (gap opening and gap closing), construct (a) was stronger than construct (b), as strong as construct (c), but weaker than the constructs with more widely spaced screws (p < 0.0001). In terms of four-point bending, for gap opening, the standard fixation (construct (a) was stronger than construct (b) but weaker than the more widely spaced constructs. For gap closing, construct (a) was stronger than constructs (b) and (c) but weaker than the rest. Regardless of the spacing of screws and the plate length, strength in torsion was dependent on the number of screws securing the plate. In a laboratory fracture model of plate-bone constructs tested to failure by screw pullout, wider spacing of bone screws increases the bending strength of screw-plate fixation and can be more effective than increasing the number of screws. Torsional strength is independent of screw placement in plates of a given width and depends on the number of screws used.

Bone Plates↗
PubMed1996

Methylmethacrylate and bone screw repair of seventh lumbar vertebral fracture-luxations in dogs.

Fracture-luxations of the seventh lumbar vertebrae in two large dogs were stabilised with bone screws and methylmethacrylate. Screws inserted bilaterally into the bodies of the lumbar vertebrae and ilial wings were left protruding by about 2 cm, and embedded in methylmethacrylate bone cement. Implant failure occurred in one dog six days after surgery, necessitating a revision of the fixation. Fracture healing and return of normal ambulation occurred in both dogs. Implants were removed in one dog because of screw loosening and discomfort.

Animals↗
PubMed1981

In vitro evaluation of the loosening characteristics of self-tapped and non-self-tapped cortical bone screws.

The heads of self-tapping and non-self-tapping screws in dog femurs were exposed to a cyclic shearing force of 110 N for 200 loading cycles. This cyclic shear loading created a decrease in pull-out strength for both screw types of approximately 11% (p less than 0.01). No statistically significant difference in pull-out strength was found between screw types either before or after cyclic loading. A linear relationship between pull-out force and cortical thickness was observed for both screw types. These tests corroborated past work which showed equal holding power for the self-tapping and non-self-tapping screw. The progressive loosening of the screws with cyclic shear loading was accompanied by increasing load-displacement hysteresis and screw head migration. Greater hysteresis suggested that the non-self-tapping screw might have loosened more than the self-tapping screw from this applied loading schedule. Bone microcracking around screw threads before and after cyclic loading was observed by scanning electron microscopy. Photomicrographs of one non-self-tapping screw type and two self-tapping screw types showed microcracks at the tip of the outer diameter of the screw thread. More microcracks were observed after application of cyclic shear loading.

Bone Screws↗
PubMedDate not supplied

Biomechanical study of canine spinal fracture fixation using pins or bone screws with polymethylmethacrylate.

Five configurations of pins or screws interconnected with polymethylmethacrylate (PMMA) were applied to isolated canine lumbar spines (L2 to L5) in which a complete fracture-luxation had been produced at L3 to L4. Twenty-five repaired spines and five intact control spines were subjected to four-point bending and tested once to failure in ventral flexion. The purpose of this study was to determine the effects of pin number, pin angle, and use of 3.5-mm cortical bone screws instead of smooth 3.2-mm diameter pins on rigidity and ultimate strength of spinal fractures repaired by the implant-PMMA fixation technique. Bending moment versus the angular deformation curves were recorded. Rigidity, bending moment at 10 degrees angular deformation, moment at failure, and deformation at failure of each type of fixation were compared using analysis of variance. Spinal segments stabilized with eight pin-PMMA fixation had significantly greater rigidity and strength at failure than four pin-PMMA fixations (P < .05). Furthermore, spinal segments stabilized with eight pins angled away from the fracture failed at significantly greater bending moment than those with eight pins angled toward the fracture (P < .05). However, for four-pin fixation, greater strength was achieved by angling pins in the bone toward the fracture site (P < .05). Screw-PMMA fixations failed by screw bending and were less rigid and weaker at failure than the corresponding configuration of pin-PMMA fixation (P < .05).

Animals↗
PubMedDate not supplied

[Comparative biomechanical studies of conventional and self-tapping cortical bone screws].

In normal cortical screws the thread must be cut by a separate thread-cutter. So a high stability of the connection is achieved. On the other hand thread cutting needs time, which may be assumed to several minutes during a plate osteosynthesis. To avoid thread-cutting, self-tapping screws were used 20 years ago. These old self-tapping screws had a reduced stability and a lower torque at the final screw driving so that they tended to destroy the thread. By a modification of the cutting edges at the tip of the screw the tapping quality is increased decisively. The microscopic examination showed a better cutting of the new screws with little difference to a thread-cutter. In biomechanical tests the final torque and the maximum tension force of the self-tapping screws were at the same level as in usual pre-cut screws. In the practical use the new self-tapping screws have a good handling and save time during operation. In osteoporosis, they should be used carefully in order to meet the opposite corticalis' hole and not to destroy the ipsilateral corticalis' thread.

Biomechanical Phenomena↗
PubMed2003

Biological assessment of the bone-screw interface after insertion of uncoated and hydroxyapatite-coated pedicular screws in the osteopenic sheep.

The sheep seems to be a promising model of osteoporosis and biomaterial osteointegration in osteopenic bone. The long-term ovariectomized sheep model was used for the biological investigation of bone healing around uncoated and hydroxyapatite (HA)-coated pedicle screws in osteopenic bone. Four sheep were ovariectomized and four sheep were sham-operated. Twenty-four months after surgery, the animals were implanted with uncoated and HA-coated stainless steel screws in the lumbar vertebral pedicles. Four months later, bone-to-implant contact, bone ingrowth, and bone hardness were measured around screws. Uncoated stainless steel presented significantly (p < 0.0005) lower bone-to-implant contact in healthy and osteopenic bone compared with HA-coated stainless steel. HA significantly improved bone ingrowth in healthy bone (p < 0.05) compared with uncoated stainless steel. Osteopenia significantly (p < 0.05) reduced the area of bone ingrowth around the screw threads for both types of implants. In the inner thread area, bone microhardness significantly increased (p < 0.05) in HA-coated surface versus uncoated for healthy and osteopenic bone. HA coating significantly enhances bone-to-implant contact also in osteopenic bone in comparison with uncoated stainless steel surfaces. Bone ingrowth and mineralization are ameliorated by the osteoconductive HA coating. However, osteopenia seems to greatly influence bone ingrowth processes around the implanted screws regardless of the characteristics of the material surface.

Animals↗