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      Absorbable scaphoid screw development: a comparative study on biomechanics

      Therapeutics and Clinical Risk Management
      Dove Medical Press
      absorbable scaphoid screw, biomechanics, internal fixator, kirschner wires

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          Abstract

          Background The scaphoid is critical for maintaining the stability and movement of the wrist joints. This study aimed to develop a new internal fixator absorbable scaphoid screw (ASS) for fixation of the scaphoid waist after fracture and to test the biomechanical characteristics of ASS. Materials and methods An ASS was prepared using polylactic acids and designed based on scaphoid measurements and anatomic features. Twenty fractured scaphoid waist specimens were randomly divided into experimental and control groups (n=10/group). Reduction and internal fixation of the scaphoid were achieved with either Kirschner wires (K-wires) or ASS. A moving target simulator was used to test palmar flexion and dorsal extension, with the range of testing (waist movement) set from 5° of palmar flexion to 25° of dorsal extension. Flexion and extension were repeated 2,000 times for each specimen. Fracture gap displacements were measured with a computerized tomography scanning. Scaphoid tensile and bending strengths were measured by using a hydraulic pressure biomechanical system. Results Prior to biomechanical fatigue testing, fracture gap displacements were 0.16±0.02 mm and 0.22±0.02 mm in the ASS and K-wire groups, respectively. After fatigue testing, fracture gap displacements in the ASS and the K-wire groups were 0.21±0.03 mm and 1.52±0.07 mm, respectively. The tensile strengths for the ASS and K-wire groups were 0.95±0.02 MPa and 0.63±0.02 MPa, respectively. Conclusion Fixation using an ASS provided sufficient mechanical support for the scaphoid after fracture.

          Most cited references31

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          Preliminary report on the osteogenic potential of a biodegradable copolymer of polyactide (PLA) and polyglycolide (PGA).

          A biodegradable copolymer of 50 polylactide: 50 polyglycolide was prepared for implantation into experimentally created osseous defects in the tibias of 25 rats. Similarly prepared defects were made in the humeri of the same rats and these defects did not receive copolymer implants. Upon sacrifice, both the implant treated and untreated sites of the experimentally produced osseous defects were evaluated by gross appearance and by histomorphometric examination using a Zeiss Videoplan Image Analysis System with Osteoplan (version 4.1). The animals were evaluated in groups of five at 7, 14, 21, 28, and 42 days. When compared with bony defects that were not treated with the biocompatible, biodegradable copolymer implant, the implant sites displayed an accelerated rate of healing at 7, 14, 21, and 28 days (p less than 0.001). A similar healing response rate, however, was observed at 42 days (p less than 0.25-0.1). No adverse host tissue responses were observed histologically.
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            Management of scaphoid nonunion.

            The primary risk factor for nonunion of the scaphoid is displacement/instability, but delayed or missed diagnosis, inadequate treatment, fracture location, and blood supply are also risk factors. Untreated nonunion leads to degenerative wrist arthritis-the so-called scaphoid nonunion advanced collapse wrist. However, the correlation of symptoms and disease is poor; the true "natural history" is debatable because we evaluate only symptomatic patients presenting for treatment. It is not clear that surgery can change the natural history, even if union is attained. The diagnosis of nonunion is made on radiographs, but computed tomography or magnetic resonance imaging scans can be useful to assess deformity and blood supply. Treatment options vary from percutaneous fixation to open reduction and internal fixation with vascularized or nonvascularized bone grafting to salvage procedures involving excision and/or arthrodesis of carpals.
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              Biodegradable implants in fracture fixation: early results of treatment of fractures of the ankle.

              Biodegradable polylactide-glycolide copolymer implants for fracture fixation were developed and tested in rabbits. In a prospective clinical study 44 patients with a displaced fracture of the ankle were randomly allocated to two groups; one was treated with conventional metallic implants and the other with the biodegradable implants. There were no differences between the two groups in the early results, but the biodegradable fixation method is advantageous because the removal procedure associated with metallic implants is avoided.
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                Author and article information

                Journal
                27217756
                4853148
                10.2147/TCRM.S99024
                http://creativecommons.org/licenses/by-nc/3.0/

                Medicine
                absorbable scaphoid screw,biomechanics,internal fixator,kirschner wires
                Medicine
                absorbable scaphoid screw, biomechanics, internal fixator, kirschner wires

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