The intermaxillary screw: a dedicated bicortical bone screw for temporary intermaxillary fixation.
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Bone Screws↗
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Comparison of insertion time and pullout strength between self-tapping and non-self-tapping AO 4.5-mm cortical bone screws in adult equine third metacarpal bone.
OBJECTIVE: To compare screw insertion characteristics and pullout mechanical properties between self-tapping (ST) and non-self-tapping (NST) AO 4.5-mm cortical bone screws in adult equine third metacarpal bone (MC3). STUDY DESIGN: In vitro biomechanical experiment. ANIMALS OR SAMPLE POPULATION: Seven pairs of adult equine MC3. METHODS: Bicortical holes were drilled transversely in proximal metaphyseal, diaphyseal, and distal metaphyseal locations of paired MC3. NST screws were inserted in pre-tapped holes in 3 sites of one bone pair, and ST screws were inserted in non-tapped holes of contralateral MC3. Tapping and screw insertion times and maximum torques were measured. Screw pullout mechanical properties were determined. RESULTS: Screw insertion time was longer for ST screws. Total time for tapping and insertion (total insertion time) was over twice as long for NST screws. Statistically significant differences were not observed between screws for any pullout mechanical property. From pullout tests, diaphyseal locations had significantly stiffer and stronger structure than metaphyseal locations. Pullout failure more commonly occurred because of screw breakage than bone failure. Bone failure and bone comminution were more commonly associated with ST screws. Bone failure sites had pullout failure loads that were 90% of screw failure sites. CONCLUSIONS: NST and ST 4.5-mm-diameter cortical bone screws have similar pullout mechanical properties from adult equine MC3. ST screws require less than half the total insertion time of NST screws. CLINICAL RELEVANCE: Use of ST 4.5-mm-diameter cortical bone screws should be considered for repair of adult equine MC3 fractures; however, bone failures at screw sites should be monitored.
Animals↗
Apparatus to test insertion and removal torque of bone screws.
This paper describes affordable equipment for testing bone screw torque, corresponding to ASTM standard F543-00 for testing metallic medical bone screws. Correct testing of thin and long bone screws is essential due to screw failures during insertion and removal of the screws. Furthermore, insertion torque is an important factor in predicting fixation strength, screw pull-out force and effects of surface treatment of screws. The capability of the custom-built tester was determined using polytetrafluoroethylene and wood disc samples and bone screws. Bovine cortical bones allowed testing to the failure limit, i.e. the torque increased in long screws to the fracture limit. For 2.7 and 3.5 mm thick self-tapping cortical bone screws, the failure torques were 30-50 per cent higher than the minimum values required by the standard (1.0 and 2.3 N m respectively). The equipment provided reproducible results and fulfilled the ASTM standard very well. Preliminary testing with amorphous diamond coated bone screws showed good durability of the coating and on average 10-15 per cent lower torque values compared with uncoated screws. The equipment can be used to measure insertion and removal torques as described in the standard. Furthermore, it also allows testing of normal screws and bolts.
Animals↗
Biomechanical comparison of the Herbert and AO cortical bone screws for compression of an equine third carpal bone dorsal plane slab osteotomy.
OBJECTIVE: To assess feasibility of insertion of 4.5-mm Herbert cannulated bone screws (HS) using fluoroscopic guidance and compare the mechanical shear strength of these HS and 4.5-mm AO cortical bone screws (AO) for fixation of dorsal plane slab osteotomies in equine cadaver third carpal bones (C3). ANIMALS OR SAMPLE POPULATION: Eight equine cadavers. METHODS: Bone mineral composition and density of contralateral C3 were confirmed to be equivalent using dual-energy x-ray absorptiometry. A standard 10-mm C3 slab osteotomy was reduced using HS or AO instrumentation under fluoroscopic guidance. Specimens were loaded in shear until failure, using a materials testing apparatus. RESULTS: HS and AO instrumentation allowed accurate reconstruction of the osteotomy, but there was difficulty encountered seating the HS proximal self-tapping threads. There was no significant difference in maximal load to failure, stiffness, or mode of failure of constructs created with the HS and AO screws. CONCLUSIONS: Use of 4.5-mm HS for repair of C3 radial facet, dorsal plane slab fractures may result in a mechanically comparable fixation to a repair using a 4.5-mm AO. Equine dorsal C3 may be too dense, however, to allow placement of the proximal self tapping threads of the HS without potentially excessive application of torque to the screw itself. CLINICAL RELEVANCE: Dorsal plane, radial facet slab fractures of the equine C3 are a significant clinical problem. Accurate reconstruction and stabilization are necessary for return to athletic function.
Absorptiometry, Photon↗
Alendronate inhibits bone resorption at the bone-screw interface.
In the current study, we investigated whether the systemic administration of alendronate, a third-generation bisphosphonate, suppressed the loosening of screws at the bone-screw interface. We systemically administered alendronate to rats fitted with external fixators. External fixators with two half pins were applied to the right femurs of rats, and alendronate was administrated once a week during a 5-week postoperative period. Radiographic, histologic, and immunohistochemical findings subsequently were analyzed. Treatment with alendronate reduced the width of the fibrous loosening membrane and the number of osteoclasts at the bone-screw interface. These findings indicate that systemic treatment with alendronate exerts an inhibitory effect on local bone resorption at the bone-screw interface.
Acid Phosphatase↗
Biomechanical comparison of the screw-bone interface: optimization of 1 and 2 screw constructs by varying screw diameter.
STUDY DESIGN: In vitro biomechanical investigation of 1 and 2-screw anterior scoliosis constructs with varying screw diameters. OBJECTIVE: To determine a possible optimal configuration of screw number and diameter at varying levels within the thoracic spine for anterior vertebral body fixation. SUMMARY OF BACKGROUND DATA: Single-rod systems are typical in anterior thoracic and thoracolumbar correction of adolescent idiopathic scoliosis; although dual rod systems may offer more flexural stability. Loss of fixation remains problematic, particularly in the proximal thoracic vertebrae, and it remains unclear how screw diameter or the number of screws within the vertebrae affect fixation. METHODS: Individual vertebral levels from 10 cadaveric thoracic spines were randomly assigned to either 1 or 2 screws of 5, 6, or 7-mm diameter. Bone-screw interface failures were created in coronal plane cantilever plow, and failure loads were compared across vertebral levels for each instrumentation method. RESULTS: Two-screw constructs had significantly higher failure loads than single-screw constructs, while increasing screw diameter also produced significant changes in fixation strength. Two-screws had improved performance in the mid and lower thoracic spine, while a single screw was more stable in the upper thoracic spine. CONCLUSIONS: Failure modes for 1-screw constructs almost entirely (89%) showed gradual plowing through the bone, whereas acute fracture through the vertebral body or pedicles were common forms of failure (85%) for 2-screw constructs.
Aged↗
Relation of vertebral bone screw axial pullout strength to quantitative computed tomographic trabecular bone mineral content.
Noninvasive prediction of the maximum axial load that a spinal bone screw will be able to withstand after anterior surgical placement would be highly useful. To investigate if this is feasible, we first performed preliminary experiments to distinguish the trabecular and cortical contributions to overall stiffness; the trabecular component was found to dominate. We then used a commercial computed tomography bone mineral package to determine the mineral density of the trabecular region of 41 porcine vertebrae in terms of equivalent K2HPO4 concentration; values ranged from 104 to 343 mg/cm3. A 6.5-mm diameter cancellous bone screw was then inserted laterally in each vertebra, and the ultimate tensile strength (UTS) of the screw/bone interface was measured using a tensile testing machine. The UTS values ranged from 589 to 2,620 Newtons. A superlinear relation was found between UTS and the projected K2HPO4 concentration in the direction of the screw axis, expressed in units of mg/cm2.
Animals↗
Optimizing bone screw pullout force.
Stability of internal fixation by plate and screw depends on the interface of bone and screw threads. Bone-screw thread design was tested in a synthetic bone model to determine maximum bone-screw pullout force. The model was confirmed to provide reproducible results in a clinically relevant range. Consistent material properties were reflected in the relatively small standard deviations in pullout force, which were less than 10% of mean values. As expected, major diameter was an important determinant of pullout force in a roughly linear manner. Pitch was important with a finer thread giving greater purchase. Minor diameter and the ratio of major to minor diameter had a small but significant effect on pullout force. This study was significant for establishing a good bone-screw testing model and suggesting important thread parameters in selecting or manufacturing a bone screw to optimize its holding power.
Biomechanical Phenomena↗
Histologic study of the bone adjacent to titanium bone screws used for mandibular fracture treatment.
PURPOSE: Titanium miniplates have been widely used in mandibular fracture fixation because of their strength and excellent biocompatibility. However, the condition of the bone adjacent to titanium bone screws has not been clarified. This study histologically examined the bone-screw interface in patients treated for mandibular fractures. PATIENTS AND MATERIALS: Specimens were obtained from 14 patients, and the undecalcified sections were stained by the toluidine blue and Levai Laczko methods and examined with light microscopy. The mean ratio of direct contact between the bone and the titanium bone screw surface was also analyzed using a computer-aided image analyzer. RESULTS: The formation of new bone was observed around the titanium bone screws in all cases. In areas of cortical bone, partial interposition of soft tissues was rarely observed. However, in areas of cancellous bone, partial interposition of soft tissues was seen, and bone resorption between the bone and soft tissues was noted. The mean ratio of direct contact between all of the adjacent bone and the surface of the titanium bone screws was 64.4%. The mean ratio of direct contact between cortical bone and the titanium bone screws was 82.4%. Black particles were observed in the bone and soft tissues around the titanium bone screws, and multinuclear giant cells resembling macrophages were observed near these particles. CONCLUSION: Titanium bone screws used for mandibular fracture fixation develop almost complete contact with new bone. Some metalosis is present.
Adolescent↗
Comparison of bone screw holding strength in healthy bovine and osteoporotic human cancellous bone.
Pushout tests were carried out on two different diameter, self-tapping, cancellous bone screws (4 mm and 6.4 mm) inserted in bovine cancellous bone sections taken perpendicular and at 45 degrees to the long axis of the bone. Comparison was made with the same type of screws inserted into sections taken from osteoporotic and/or osteoarthritic human femoral heads. The results showed no significant difference in the holding strength of different diameter screws in bovine bone sections of given orientation but significant differences when the trabecular orientation of the section was changed. By comparison, the holding strengths of the same screws in diseased femoral heads were found to be both significantly different from each other and significantly lower than for the same screws inserted in healthy bovine bone. The screw diameter, trabecular orientation, mineral content and the health of the bone all need to be considered in order to optimise the holding strength of the screws in cancellous bone.
Animals↗
Axial cyclic behavior of the bone-screw interface.
Screw fixation strength is investigated by using a pullout test. Despite many screw pullout studies, the effects of loading rate on the pullout behavior of pedicle screws are not known. The objective of this study was to assess the effects of loading rate on the pullout stiffness and strength of pedicle screws. Sixty pedicle screws were inserted in foam blocks and pulled out at four different rates: 0.1, 1, 5 and 50 mm/min. Twenty of these 60 screws were cycled non-destructively at four different rates sequentially, i.e., 0.1, 1, 5 and 50 mm/min prior to pullout. Ten additional pedicle screws were inserted in five calf lumbar vertebrae, cycled as in foam group, and pulled out at a rate of either 0.1 or 50 mm/min. The results showed that the stiffness was higher at all rates compared to 0.1 mm/min in foam model but in bone model only 1 and 5 mm/min groups were higher compared to 0.1 mm/min. The pullout strength in 50 mm/min group was higher than that in 0.1 mm/min group in both foam and bone model. The results suggested that loading rate influenced the mechanics of the bone-screw interface. Therefore, a fair comparison between the pullout studies can be achieved under same loading rate conditions. Moreover, the cycling of the pedicle screws in axial direction within a pre-yield region showed an unusual hysteresis curve. Further studies are needed for a better understanding of the mechanics of the screw-bone interface.
Animals↗
[Verification of an ultrasound measuring procedure for evaluating screw-bone fusion based on mechanical parameters].
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Animals↗
Improvement of the bone-screw interface strength with hydroxyapatite-coated and titanium-coated AO/ASIF cortical screws.
OBJECTIVE: To evaluate whether coating AO/ASIF screws with osteoconductive materials can improve bone-screw fixation. DESIGN: Ninety-six AO/ASIF 4.5-millimeter cortical screws were divided into four paired groups and implanted in the femurs and tibiae of six sheep: Group A = standard stainless steel screws; Group B = stainless steel screws coated with highly crystalline hydroxyapatite; Group C = stainless steel screws coated with low crystalline hydroxyapatite; Group D = titanium screws coated with titanium. The screws were implanted according to the standard AO technique to an insertion torque of 2,000 Newton-millimeters. Sheep were killed at one, three, and twelve months after surgery. MAIN OUTCOME MEASURES: Extraction torque was measured on six screws from each group selected at random at time of each euthanization. Morphologic analysis of the bone-screw interface was performed on the remaining screws. RESULTS: At each euthanization the extraction torque of Group A was lower than that of the other groups (p < 0.0001). At three and twelve months the extraction torque of Group B was higher than that of Group D (p = 0.002). Morphologic results showed extensive bone-screw gap in Group A. Optimal osteointegration was observed in Groups B and C. Osteointegration of Group D was higher than that of Group A and lower than that of Groups B and C. CONCLUSIONS: It was demonstrated that AO/ASIF screws coated with osteoconductive materials achieve optimal fixation strength, even in the early phase. This fixation strength was significantly higher than that of the standard screws.
Animals↗
A biomechanical comparison of headless tapered variable pitch compression and ao cortical bone screws for fixation of a simulated midbody transverse fracture of the proximal sesamoid bone in horses.
OBJECTIVE: To compare mechanical properties and failure characteristics of 2 methods of fixation for repair of a transverse, midbody fracture of the proximal sesamoid bone (PSB): 4.5-mm AO cortical bone screw (AO) placed in lag fashion and 4/5-mm Acutrak (AT) self-compressing screw. STUDY DESIGN: An in vitro biomechanical evaluation of intact forelimb preparations and forelimb preparations with a simulated midbody PSB fracture stabilized by a bone screw. SAMPLE POPULATION: Sixteen paired and 8 unilateral cadaveric equine forelimbs. METHODS: A midbody transverse osteotomy was created in the medial PSB of bilateral forelimbs of 8 equine cadavers. The osteotomized PSB in 1 forelimb from each cadaver was repaired with an AO screw. The osteotomized PSB in each contralateral limb was repaired with an AT screw. Eight unilateral intact control limbs were also studied. Mechanical properties were determined from axial compression, single cycle to failure, load-deformation curves. Failure characteristics were determined by evaluation of video images and radiographs. RESULTS: No statistically significant differences were found between repair groups. Both AO and AT groups had significantly lower mechanical properties than intact limbs except for stiffness. CONCLUSION: AO and AT constructs were mechanically comparable when used to stabilize a simulated midbody fracture of the medial PSB. Both constructs were mechanically inferior to intact limbs. Clinical Relevance- The AT screw should be considered for clinical use because of the potential for less soft tissue impingement and superior biocompatibility compared with the stainless-steel AO screw. However, postoperative external coaptation is necessary to augment initial fracture stability for either fixation method, and to maintain a standing metacarpophalangeal joint dorsiflexion angle between 150 degrees and 155 degrees.
Animals↗
Modifications of the distal metaphyseal osteotomy to better facilitate use of the Herbert bone screw for fixation.
The Herbert bone screw was initially developed for management of fractures of the carpal scaphoid. Due to its unique features, the applications of this rigid internal fixation device have been expanded. The most common use of the Herbert screw in podiatric surgery has been for fixation of the Austin osteotomy of the first metatarsal head, for correction of hallux abducto valgus. Technical difficulties encountered in this procedure may have discouraged its use or led to discontinuance. These problems are addressed, and modifications in technique are suggested. The most important modification involves a change in the angle and orientation of the osteotomy.
Bone Screws↗
Pull-out strengths of bone screws at various sites about the pelvis--a preliminary study.
The pull-out strength of both cortical and cancellous screws from bone at various sites about cadaveric pelves was examined. No significant differences were seen between cortical or cancellous screws at similar sites with the possible exception of the sacroiliac joint. Pull-out strengths were best correlated to the depth of bone at a particular screw hole. For practical purposes, the strongest sites are in the thick buttress of bone along the iliopubic column.
Acetabulum↗
The Herbert differential pitch bone screw in displaced radial head fractures.
The Herbert bone screw (Herbert and Fisher, 1984) has been used in the treatment of ten segmental fractures of the radial head. This differential pitch bone screw provides rigid fixation with compression, has no protruding head, is easily introduced and is of such a small diameter that more than one screw can be used. The early results achieved are reported.
Adolescent↗
Compression forces generated by Mini bone screws--a comparative study done on bone model.
The compressive forces generated by the AO/ASIF 3.0 mm cannulated cancellous and 2.0 mm cortical screws, Mini-Acutrak and Herbert/Whipple small bone cannulated screws were measured in the laboratory with the use of simulated cancellous bone and a load cell washer as a means of quantifying their fixation capabilities. The Herbert/Whipple screw and the Mini-Acutrak screw were found to have nearly identical compression capabilities and provided more compression than the cortical screw. The AO/ASIF cannulated screw when used with a support screw demonstrated a compressive capacity twice that of the 2.0 mm cortical screw and higher than the headless Mini-Acutrak and Herbert/Whipple screws. The Mini-Acutrak screw produced about 70% of compression of the cancellous screw in spite of having a diameter almost half that of the cancellous screw. The Herbert/Whipple screw in spite of its larger size compared to the Mini-Acutrak produced almost the same amount of compression.
Biomechanical Phenomena↗