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      Impact of Different Screw Designs on Durability of Fracture Fixation: In Vitro Study with Cyclic Loading of Scaphoid Bones

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          Abstract

          Purpose

          The use of new headless compression screws (HCSs) for scaphoid fixation is growing, but the nonunion rate has remained constant. The aim of this study was to compare the stability of fixation resulting from four modern HCSs using a simulated fracture model to determine the optimal screw design(s).

          Methods

          We tested 40 fresh-frozen cadaver scaphoids treated with the Acumed Acutrak 2 mini (AA), the KLS Martin HBS2 midi (MH), the Stryker TwinFix (ST) and the Synthes HCS 3.0 with a long thread (SH). The bones with simulated fractures and implanted screws were loaded uniaxially into flexion for 2000 cycles with a constant bending moment of 800 Nmm. The angulation of the fracture fragments was measured continuously. Data were assessed statistically using the univariate ANOVA test and linear regression analysis, and the significance level was set at p < 0.05.

          Results

          The median angulation of bone fragments φ allowed by each screw was 0.89° for AA, 1.12° for ST, 1.44° for SH and 2.36° for MH. With regards to linear regression, the most reliable curve was achieved by MH, with a coefficient of determination of R 2 = 0.827. This was followed by AA (R 2 = 0.354), SH (R 2 = 0.247) and ST (R 2 = 0.019). Data assessed using an adapted ANOVA model showed no statistically significant difference (p = 0.291) between the screws.

          Conclusions

          The continuous development of HCSs has resulted in very comparable implants, and thus, at this time, other factors, such as surgeons’ experience, ease of handling and price, should be taken into consideration.

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          Most cited references27

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          A prospective randomized trial comparing nonoperative treatment with volar locking plate fixation for displaced and unstable distal radial fractures in patients sixty-five years of age and older.

          Despite the recent trend toward the internal fixation of distal radial fractures in older patients, the currently available literature lacks adequate randomized trials examining whether open reduction and internal fixation (ORIF) with a volar locking plate is superior to nonoperative (cast) treatment. The purpose of the present randomized clinical trial was to compare the outcomes of two methods that were used for the treatment of displaced and unstable distal radial fractures in patients sixty-five years of age or older: (1) ORIF with use of a volar locking plate and (2) closed reduction and plaster immobilization (casting). A prospective randomized study was performed. Seventy-three patients with a displaced and unstable distal radial fracture were randomized to ORIF with a volar locking plate (n = 36) or closed reduction and cast immobilization (n = 37). The outcome was measured on the basis of the Patient-Rated Wrist Evaluation (PRWE) score; the Disabilities of the Arm, Shoulder and Hand (DASH) score; the pain level; the range of wrist motion; the rate of complications; and radiographic measurements including dorsal radial tilt, radial inclination, and ulnar variance. There were no significant differences between the groups in terms of the range of motion or the level of pain during the entire follow-up period (p > 0.05). Patients in the operative treatment group had lower DASH and PRWE scores, indicating better wrist function, in the early postoperative time period (p < 0.05), but there were no significant differences between the groups at six and twelve months. Grip strength was significantly better at all times in the operative treatment group (p < 0.05). Dorsal radial tilt, radial inclination, and radial shortening were significantly better in the operative treatment group than in the nonoperative treatment group at the time of the latest follow-up (p < 0.05). The number of complications was significantly higher in the operative treatment group (thirteen compared with five, p < 0.05). At the twelve-month follow-up examination, the range of motion, the level of pain, and the PRWE and DASH scores were not different between the operative and nonoperative treatment groups. Patients in the operative treatment group had better grip strength through the entire time period. Achieving anatomical reconstruction did not convey any improvement in terms of the range of motion or the ability to perform daily living activities in our cohorts.
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            Shear movement at the fracture site delays healing in a diaphyseal fracture model.

            This study tested the hypothesis that interfragmentary axial movement of transverse diaphyseal osteotomies would result in improved fracture healing compared to interfragmentary shear movement. Ten skeletally mature merino sheep underwent a middiaphyseal osteotomy of the right tibia, stabilized by external fixation with an interfragmentary gap of 3 mm. A custom made external fixator allowed either pure axial (n=5) or pure shear movement (n=5) of 1.5 mm amplitude during locomotion by the animals. The movement of the osteotomy gap was monitored weekly in two sheep by an extensometer temporarily attached to the fixator. After 8 weeks the sheep were killed, and healing of the osteotomies was evaluated by radiography, biomechanical testing, and undecalcified histology. Shear movement considerably delayed the healing of diaphyseal osteotomies. Bridging of the osteotomy fragments occurred in all osteotomies in the axial group (100%), while in the shear group only three osteotomies (60%) were partially bridged. Peripheral callus formation in the shear group was reduced by 36% compared to the axial group (p<0.05). In the axial group bone formation was considerably larger at the peripheral callus and in between the osteotomy gaps but not in the intramedullary area. The larger peripheral callus and excess in bone tissue at the level of the gap resulted in a more than three times larger mechanical rigidity for the axial than for the shear group (p<0.05). In summary, fixation that allows excessive shear movement significantly delayed the healing of diaphyseal osteotomies compared to healing under axial movement of the same magnitude.
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              Management of the fractured scaphoid using a new bone screw.

              A new and simple operative technique has been developed to provide rigid internal fixation for all types of fractures of the scaphoid. This involves the use of a double-threaded bone screw which provides such good fixation that, after operation, a plaster cast is rarely required and most patients are able to return to work within a few weeks. A classification of scaphoid fractures is proposed. The indications for operation included not only acute unstable fractures, but also fractures with delayed healing and those with established non-union; screw fixation was combined with bone grafting to treat non-union. In a prospective trial, 158 operations using this technique were carried out between 1977 and 1981. The rate of union was 100 per cent for acute fractures and 83 per cent overall. This method of treatment appears to offer significant advantages over conventional techniques in the management of the fractured scaphoid.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                7 January 2016
                2016
                : 11
                : 1
                : e0145949
                Affiliations
                [1 ]Department of Orthopaedics and Traumatology, University Medical Center of Johannes Gutenberg University, Mainz, Germany
                [2 ]Physics Division, RheinMain University of Applied Sciences, Wiesbaden, Germany
                University of Sheffield, UNITED KINGDOM
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: DG HH DK PR. Performed the experiments: DG RH PH. Analyzed the data: DG RH PH HH. Contributed reagents/materials/analysis tools: HH AH DK PR. Wrote the paper: DG RH HH.

                Article
                PONE-D-15-26173
                10.1371/journal.pone.0145949
                4704798
                26741807
                dabb11dd-d5ed-48b3-8cad-eea4a8f7ed2f
                © 2016 Gruszka et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 16 June 2015
                : 10 December 2015
                Page count
                Figures: 6, Tables: 2, Pages: 11
                Funding
                Support to an Investigator Initiated Study was provided to The University Medical Center of Johannes Gutenberg University from the Stryker SA in the amount under 10.000 Euros. No benefits of any kind have been received or will be received directly by the authors from a commercial party. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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