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At least 19 recordsLinked to original sources
PubMed1980

[Measurements of the transfer of force by bone screws].

Bone screws normally used for functionally stable osteosynthesis were subjected to marginal torque in a limited number of cadaver mandibles. Since the various manufacturers differ considerably in lead, form of thread, and relation of external and internal diameters, the experiments appeared to us to be revealing in terms of the practical application. The experimental set up was presented in addition to the findings.

Biomechanical Phenomena↗
PubMed2006

An in vitro biomechanical comparison between prototype tapered shaft cortical bone screws and AO cortical bone screws for an equine metacarpal dynamic compression plate fixation of osteotomized equine third metacarpal bones.

OBJECTIVES: To compare biomechanical properties of a prototype 5.5 mm tapered shaft cortical screw (TSS) and 5.5 mm AO cortical screw for an equine third metacarpal dynamic compression plate (EM-DCP) fixation to repair osteotomized equine third metacarpal (MC3) bones. STUDY DESIGN: Paired in vitro biomechanical testing of cadaveric equine MC3 with a mid-diaphyseal osteotomy, stabilized by 1 of 2 methods for fracture fixation. ANIMAL POPULATION: Adult equine cadaveric MC3 bones (n=12 pairs). METHODS: Twelve pairs of equine MC3 were divided into 3 groups (4 pairs each) for (1) 4-point bending single cycle to failure testing, (2) 4-point bending cyclic fatigue testing, and (3) torsional single cycle to failure testing. An EM-DCP (10-hole, 4.5 mm) was applied to the dorsal surface of each, mid-diaphyseal osteotomized, MC3 pair. For each MC3 bone pair, 1 was randomly chosen to have the EM-DCP secured with four 5.5 mm TSS (2 screws proximal and distal to the osteotomy; TSS construct), two 5.5 mm AO cortical screws (most proximal and distal holes in the plate) and four 4.5 mm AO cortical screws in the remaining holes. The control construct (AO construct) had four 5.5 mm AO cortical screws to secure the EM-DCP in the 2 holes proximal and distal to the osteotomy in the contralateral bone from each pair. The remaining holes of the EM-DCP were filled with two 5.5 mm AO cortical screws (most proximal and distal holes in the plate) and four 4.5 mm AO cortical screws. All plates and screws were applied using standard AO/ASIF techniques. Mean test variable values for each method were compared using a paired t-test within each group. Significance was set at P<.05. RESULTS: Mean 4-point bending yield load, yield bending moment, bending composite rigidity, failure load and failure bending moment of the TSS construct were significantly greater (P<.00004 for yield and P<.00001 for failure loads) than those of the AO construct. Mean cycles to failure in 4-point bending of the TSS construct was significantly greater (P<.0002) than that of the AO construct. The mean yield load and composite rigidity in torsion of the TSS construct were significantly greater (P<.0039 and P<.00003, respectively) than that of the AO construct. CONCLUSION: The TSS construct provides increased stability in both static overload testing and cyclic fatigue testing. CLINICAL RELEVANCE: The results of this in vitro study support the conclusion that the EM-DCP fixation using the prototype 5.5 mm TSS is biomechanically superior to the EM-DCP fixation using 5.5 mm AO cortical screws for the stabilization of osteotomized equine MC3.

Animals↗
PubMed1992

The use of power tools in the insertion of cortical bone screws.

Cortical bone screws are commonly used in fracture surgery, most patterns are non-self-tapping and require a thread to be pre-cut. This is traditionally performed using hand tools rather than their powered counterparts. Reasons given usually imply that power tools are more dangerous and cut a less precise thread, but there is no evidence to support this supposition. A series of experiments has been performed which show that the thread pattern cut with either method is identical and that over-penetration with the powered tap is easy to control. The conclusion reached is that both methods produce consistently reliable results but use of power tools is much faster.

Bone Screws↗
PubMed2006

Tapered orthodontic miniscrews induce bone-screw cohesion following immediate loading.

The aim of this study was to investigate the initial stability of tapered orthodontic miniscrews (T-type screws) after placement, the necessity of a healing period, and the propriety of immediate loading. Twenty male Wistar rats with a mean age of 20 weeks were divided into two groups. In the immediate-loading groups, straight orthodontic miniscrews (S-type screws) and T-type screws (five rats each) underwent experimental traction force for 2 weeks (W) immediately after placement. In the healing groups (S- and T-type, five rats each), force was applied for 2 W after a 6-W healing period. The right tibia in each rat was identified as the test limb, while the left tibia in each rat was used as the control group, and underwent no experimental force during the experimental period. The screw-to-bone contact was observed histologically and the bone-screw contact ratio was calculated. Scheffe's test was performed to compare the bone-screw contact ratio in each group using statistical software package (SPSS 8.0 for Windows). In the control group, the bone-screw contact ratio improved from 34.8 +/- 16.0 to 74.8 +/- 12.0 per cent with S-type screws in proportion to the experimental period (2 to 8 W, respectively). With the T-type screws in the test group, there was no significant difference between the immediate-loading and healing groups. In the immediate-loading group, the bone-screw contact ratio with T-type screws was significantly greater (82.3 +/- 15.0 per cent) than with the S-type screws (33.3 +/- 11.8 per cent; P < 0.05), suggesting that T-type screws can be used for orthodontic anchorage immediately after placement.

Animals↗
PubMed2006

Experimental evaluation of the holding power/stiffness of the self-tapping bone screws in normal and osteoporotic bone material.

OBJECTIVE: The goal of this study is to compare the holding power of the self-tapping bone screws in normal and osteoporotic bone materials. BACKGROUND: Self-tapping screws are increasingly being used in orthopaedic surgery due to their advantages over the other bone screws. METHODS: Screws were divided into five groups (six screws per group) based on the depth of insertion in the bone coupons that represented normal and osteoporotic bones. Screws were randomly inserted into the bone coupons with tips of the screws being -1 mm, 0 mm, 1 mm, 2 mm and 3 mm relative to the far cortex. Biomechanical testing was performed using an Instron 8,511 in accordance with the American Society for Testing and Materials standards for bone screws. Two-factor analysis of variance (ANOVA) was used to determine if the holding power of the screws were different with respect to insertion depths and bone materials. FINDINGS: The bone materials had a significant difference (P < 0.05) in the holding power and depths of insertion past the far cortex were significantly different from one another in holding power. The affect of the screw material on the holding power of the self-tapping screws in different bone materials was also examined. The performance of stainless steel screws was superior to that of titanium screws in the osteoporotic material. INTERPRETATION: Based on the results it can be concluded that the depth of insertion of the tip of the screw for adequate fracture fixation in normal bone is 1mm or more past the far cortex and in osteoporotic bone it is at least 2mm past the far cortex.

Bone Screws↗
PubMedDate not supplied

Strength comparison of allogenic bone screws, bioabsorbable screws, and stainless steel screw fixation.

Allogenic bone screws are new to the fixation market and have yet to be tested against current fixation materials. An in vitro comparison of the same sizes of stainless steel, bioabsorbable, and allogenic bone screws was undertaken to assess screw resistance to the forces of bending, pullout, and shear. Using aluminum plates to support the screws, forces up to 1000 Newtons were applied to six to eight samples of each type of screw. During each test, stainless steel screws withstood the maximum force that could be exerted by the testing apparatus without failing (bending, 113.9 +/- 11.8 N mean +/- SE; pullout 999.1 +/- 33.7 N; and shear, 997.5 +/- 108.8 N). In each test, compared to bioabsorbable screws, allogenic bone screws failed faster (pullout, allogenic: 12.4 +/- 1.1 seconds vs. bioabsorbable, 120.6 +/- 13.8 seconds; p = .001; bending, allogenic: 53.4 +/- 4.8 seconds vs. bioabsorbable, 201.9 +/- 11.1 seconds; p = .001; shear, allogenic 13.5 +/- 1.4 seconds vs. bioabsorbable, 43.8 +/- 0.9 seconds; p = .001) under equivalent (pullout: bioabsorbable, 385.0 +/- 18.4 N vs. allogenic, 401.0 +/- 35.9 N; p = .001) or lower (bending, allogenic: 4.7 +/- 0.2 N vs. bioabsorbable, 11.0 +/- 0.9 N; p = .675; shear, allogenic: 312.1 +/- 15.5 N vs. bioabsorbable 680.9 +/- 8.5 N; p = .001) loads, and in a highly variable fashion. Overall, the bioabsorbable screws withstood the forces of bending, pullout, and shear better than the allogenic screws, and stainless steel screws outperformed both bioabsorbable and allogenic screws. Despite these results, allogenic screws could still be useful in compliant patients who would benefit from their osteoconductive properties.

Absorbable Implants↗
PubMedDate not supplied

An in vitro biomechanical comparison of the insertion variables and pullout mechanical properties of ao 6.5-mm standard cancellous and 7.3-mm self-tapping, cannulated bone screws in foal femoral bone.

OBJECTIVE: To compare screw insertion variables and pullout mechanical properties between AO 6.5-mm cancellous and 7.3-mm cannulated bone screws in foal femoral bone. STUDY DESIGN: A paired, in vitro mechanical study. SAMPLE POPULATION: Seven pairs of femora from immature (1-7 months) foals. METHODS: The 6.5 cancellous and 7.3-mm cannulated screws were inserted at standardized proximal and distal metaphyseal, and mid-diaphyseal locations. Insertion torque, force, and time to drill, tap (6.5-mm cancellous), guide wire insertion (7.3-mm cannulated), and screw insertion were measured. Screw pullout properties (yield and failure load, displacement, and energy, and stiffness) were determined from mechanical tests. The effects of screw type and location on insertion variables and pullout properties were assessed with repeated measures ANOVA. Pairwise comparisons were examined with post hoc contrasts. Significance was set at P<.05 for all comparisons. RESULTS: Insertion torques for the 7.3-mm cannulated screws were significantly greater than for the 6.5-mm tap, but significantly lower than for the 6.5-mm cancellous screws. Total screw insertion times were similar. Pullout properties of both screws were similar at each femoral location. The holding power of both screws was significantly greater in the mid-diaphysis than in either metaphyseal location. Pullout failure occurred by bone shearing at the bone-screw interface in all specimens. CONCLUSIONS: The 6.5-mm cancellous and 7.3-mm cannulated screws vary in insertion properties, but have similar pullout properties in the mid-diaphysis, proximal, and distal metaphysis of foal femora. Both screw types have greater holding power at the mid-diaphyseal location compared with metaphyseal locations. Based on overall similar holding powers of 6.5-mm cancellous and 7.3-mm cannulated screws, it is unlikely that increasing the screw diameter beyond 6.5 mm will provide increased holding power in foal femoral bone. CLINICAL RELEVANCE: Use of the 7.3-mm cannulated screw should be considered for foal femoral fracture repair when greater accuracy is needed, or when bone threads for the 6.5-mm cancellous screw have been stripped.

Animals↗
PubMed2001

[In vivo studies of screw-bone contact of drill-free screws and conventional self-tapping screws].

Screw-bone contact (SBC) and bone remodeling of titanium drill-free screws or self-tapping screws should be compared. Each 10 titanium self-tapping miniscrews or microscrews, and each 10 titanium drill-free miniscrews or microscrews were inserted into the anterior wall of the frontal sinus of 5 Göttingen minipigs. Intraperitoneal injections of fluochromes (Xylenol, Calcein, Alizarincomplexon and Tetrazyklin) were performed between the 2nd and 9th postoperative week. The pigs were sacrificed after 6 months, the screw-bone blocks were resected and microradiographic, histologic and fluorescence microscopic examinations were carried out. In drill-free screws mean SBC was 88.4 (miniscrews) or 93.8% (microscrews). In self-tapping miniscrews mean SBC was 54.9, in microscrews 81%; the differences were significant in statistical analysis (t-test: p < 0.05). In fluorescence microscopy the amount of bone remodeling (ratio of residual versus newly formed bone) was measured. Significantly more of the residual bone was found in the region of the screw threads of drill-free screws (miniscrews: mean 71.8, microscrews: mean 67.9%) than in the region of screw threads of self-tapping screws (miniscrews: mean 33.1, microscrews: mean 42.4%; t-test: p < 0.05). The superior SBC of drill free screws in comparison to SBC of self-tapping screws and the higher amount of original bone in the threads of drill free screws explain the sufficient holding strength of drill free screws in clinical tests. Both results are important for osteosynthesis in regions where thin cortical bone is present, as in the central midface.

Animals↗
PubMed1987

Fixation of displaced femoral neck fractures. A comparison between sliding screw plate and four cancellous bone screws.

In a prospective, randomized trial, 104 consecutive patients with displaced femoral neck fractures were allocated either to fixation with a sliding screw plate or 4 ASIF cancellous bone screws. The patients were reexamined at fixed intervals to determine the time of union. The 2-year-cumulated rate of union was 64 per cent in the plate group and 84 per cent in the screw group.

Adult↗
PubMed2000

Mechanical performance of standard and cannulated 4.0-mm cancellous bone screws.

The mechanical performance of bone screws is determined by their pull-out strength (holding power), compressive force, stripping torque, yield bending moment, ultimate bending moment, and fatigue strength. These parameters are related to the parameters of the screw design, including major thread diameter, minor thread diameter, thread length, pitch, shaft diameter, cannulation diameter, and material properties. The goal of the study was to theoretically predict the static performance of five 4.0-mm, 45-46-mm-long, cancellous, partially threaded standard and cannulated bone screws and compare the predictions with experimental measurements. A secondary goal was to determine if cannulation of the bone screw diminished its mechanical performance. The predicted values for pull-out force, compressive force, and stripping torque were determined by the thread length, major thread diameter, and thread shape factor. The screws with the largest major thread diameter and longest thread length had the greatest pull-out force, compressive strength, and stripping torque. However, when correcting for the thread length, a higher thread shape factor compensated for a smaller major diameter. The coefficient of determination (r2) for the correlation between the predicted and measured pull-out force improved from 0.75 to 0.90 when the theoretical model included the thread shape factor. The yield and ultimate bending moments are a function of the section modulus and material properties of the screw. The Ace solid screw had the greatest section modulus and yield and ultimate bending moments. The experimental data support the theoretical models for predicting the mechanical performance of bone screws. The design of the bone screws can be optimized on the basis of theoretical modeling. The strong correlation between the predicted and measured parameters allows comparison between bone screws without repeated experimental tests. Theoretical and experimental results show that cannulation of the bone screw did not inherently diminish its mechanical performance.

Biomechanical Phenomena↗
PubMed2005

How pilot-hole size affects bone-screw pullout strength in human cadaveric cancellous bone.

OBJECTIVE: Screw failure of cancellous bone screws is not uncommon. To compare the effect of varying pilot-hole size on pullout strength of cancellous bone screws in human cadaveric bone, we designed and performed a biomechanical study to allow quantitative analysis. METHODS: Three pairs of distal femurs and 4 pairs of proximal tibias from embalmed human cadavers were stabilized in a mould, and the bone cortex was overdrilled. Four sites in a linear transverse plane were randomly assigned, anatomically matched with the paired bone and drilled with either pilot-hole size 3.2 mm or 2.5 mm. The cancellous screw (Synthes noncannulated 4.5-mm shaft, 6.5-mm external diameter) was guided into the pilot hole and pulled on by a test frame (Instron 8874 biaxial servo-hydraulic test frame) with increasing force to the point of failure, and the forces at which failure resulted were compared. RESULTS: A comparison of 25 anatomically paired sites with a 2-tailed paired t test and Wilcoxon matched-pairs signed rank test indicated significantly stronger pullout strength (p = 0.047 and p = 0.047) of the 2.5-mm compared with the 3.2-mm pilot hole. Subanalysis of the 4 studied locations indicated that 3 supported the above findings and 1 supported a reverse trend. CONCLUSIONS: Generally, cancellous screws demonstrated a significantly (p < 0.05) stronger hold using a smaller size pilot hole than the recommended standard diameter. All locations except the inner lateral site supported this finding.

Aged↗
PubMed1984

Small joint fusions of the hand using the Herbert Bone Screw.

The Herbert Bone Screw has a thread at both ends and was originally developed for internal fixation of fractured scaphoid bones. The two main advantages of compression and no head, make it most suitable for internal splinting of the small joints of the hand. The authors have used this device on thirty-nine joints in ten different sites of the hand, and it has proved to be an extremely successful method.

Arthrodesis↗
PubMed2005

Biomechanical and histomorphometric study on the bone-screw interface of bioactive ceramic-coated titanium screws.

The purpose of this study was to compare the osseointegration of 4 different kinds of bioactive ceramic-coated screws with uncoated screws by biomechanical and histomorphometric analysis. Calcium pyrophosphate (CPP), apatite-wollastonite 1:3 glass ceramic (W3G), apatite-wollastonite 1:1 glass ceramic (WAG) and bioactive CaO-SiO2-B2O3 glass ceramic (CSG) coatings were prepared and coated by the dipping method. Coated and uncoated titanium screws were inserted into the tibia of 18 adult mongrel male dogs for 2, 4, and 8 weeks. The insertion torques, radiographs, undecalcified histology, histomorphometric analysis, and extraction torques were evaluated. No difference of insertion torque was found among the five screw types. At 2 and 4 weeks after implantation, the extraction torque of ceramic-coated screws was significantly higher than that of uncoated screws (p < or = 0.0001). At 8 weeks, the extraction torques of CPP-, W3G-, and WAG-coated screws were significantly higher than those of CSG-coated and uncoated screws (p<0.0001). At 2, 4, and 8 weeks, the extraction torques of 4 different ceramic-coated screws were significantly higher than the corresponding insertion torque. Strong fixation was observed even at 2 weeks in the CPP-, W3G- and WAG-coated screws. The bone-screw contacts of the 4 different coated screws at 2 and 4 weeks were statistically higher than that of the uncoated screws, and the bone-screw contacts of the CPP-, W3G- and WAG-coated screws at 8 weeks were also statistically higher than that of the uncoated screws. The fixation strength was increased by the presence of osteoconductive coating materials, such as CPP, W3G, and WAG, which enabled to achieve higher fixation strength even as early as 2-8 weeks after the insertion.

Animals↗
PubMed1990

Design and testing of external fixator bone screws.

In external fixation, bone screw loosening still presents a major clinical problem. For this study, the design factors influencing the mechanics of the bone-screw interface were analysed and various experimental screws designed with the intention of maximizing the strength and stiffness of the inserted screw. Push-in, pull-out and bending tests were then carried out on the three experimental screws, and on two commercially available screws in both a synthetic material and in cadaveric bone; photoelastic tests on different screw threadforms were also performed. The results of the push-in and pull-out tests indicate that both the screw threadform and cutting head have a significant effect on the holding strength of the screw. The photoelastic tests show that most of the applied load is distributed over the first few threads closest to the load, and that the area between the thread crests is subjected to high shear stresses.

Biomechanical Phenomena↗