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Lowen GB, Garrett KA, Moore-Lotridge SN, Uppuganti S, Guelcher SA, Schoenecker JG, Nyman JS. Effect of Intramedullary Nailing Patterns on Interfragmentary Strain in a Mouse Femur Fracture: A Parametric Finite Element Analysis. J Biomech Eng 2022; 144:051007. [PMID: 34802060 PMCID: PMC8822464 DOI: 10.1115/1.4053085] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Revised: 11/17/2021] [Indexed: 11/08/2022]
Abstract
Delayed long bone fracture healing and nonunion continue to be a significant socioeconomic burden. While mechanical stimulation is known to be an important determinant of the bone repair process, understanding how the magnitude, mode, and commencement of interfragmentary strain (IFS) affect fracture healing can guide new therapeutic strategies to prevent delayed healing or nonunion. Mouse models provide a means to investigate the molecular and cellular aspects of fracture repair, yet there is only one commercially available, clinically-relevant, locking intramedullary nail (IMN) currently available for studying long bone fractures in rodents. Having access to alternative IMNs would allow a variety of mechanical environments at the fracture site to be evaluated, and the purpose of this proof-of-concept finite element analysis study is to identify which IMN design parameters have the largest impact on IFS in a murine transverse femoral osteotomy model. Using the dimensions of the clinically relevant IMN as a guide, the nail material, distance between interlocking screws, and clearance between the nail and endosteal surface were varied between simulations. Of these parameters, changing the nail material from stainless steel (SS) to polyetheretherketone (PEEK) had the largest impact on IFS. Reducing the distance between the proximal and distal interlocking screws substantially affected IFS only when nail modulus was low. Therefore, IMNs with low modulus (e.g., PEEK) can be used alongside commercially available SS nails to investigate the effect of initial IFS or stability on fracture healing with respect to different biological conditions of repair in rodents.
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Affiliation(s)
- Gregory B. Lowen
- Vanderbilt University, Department of Chemical and Biomolecular Engineering, 2201 West End Ave, Nashville, TN 37235
| | - Katherine A. Garrett
- Vanderbilt University Medical Center, Department of Orthopaedic Surgery, 1215 21 Ave. S., Suite 4200, Nashville, TN 37232
| | - Stephanie N. Moore-Lotridge
- Vanderbilt University Medical Center, Department of Orthopaedic Surgery, 1215 21 Ave. S., Suite 4200, Nashville, TN 37232;Vanderbilt University Medical Center, Vanderbilt Center for Bone Biology, 1211 Medical Center Dr., Nashville, TN 37212
| | - Sasidhar Uppuganti
- Vanderbilt University Medical Center, Department of Orthopaedic Surgery, 1215 21 Ave. S., Suite 4200, Nashville, TN 37232;Vanderbilt University Medical Center, Vanderbilt Center for Bone Biology, 1211 Medical Center Dr., Nashville, TN 37212
| | - Scott A. Guelcher
- Vanderbilt University, Department of Chemical and Biomolecular Engineering, 2201 West End Ave, Nashville, TN 37235; Vanderbilt University, Department of Biomedical Engineering, 5824 Stevenson Center, Nashville, TN 37232; Vanderbilt University Medical Center, Vanderbilt Center for Bone Biology, 1211 Medical Center Dr., Nashville, TN 37212; Vanderbilt University Medical Center, Division of Clinical Pharmacology, 1211 Medical Center Dr, Nashville, TN 37217
| | - Jonathan G. Schoenecker
- Vanderbilt University, Department of Pharmacology, 465 21 Ave South, 7124 Medical Research Building III, Nashville, TN 37232; Vanderbilt University Medical Center, Vanderbilt Center for Bone Biology, 1211 Medical Center Dr., Nashville, TN 37212; Vanderbilt University Medical Center, Department of Pathology, Microbiology, and Immunology, 1161 21 Ave S C-3322 Medical Center North, Nashville, TN 37232; Vanderbilt University Medical Center, Department of Pediatrics, 2200 Children's Way, Suite 2404, Nashville, TN 37232
| | - Jeffry S. Nyman
- Vanderbilt University, Department of Biomedical Engineering, 5824 Stevenson Center, Nashville, TN 37232; Vanderbilt University Medical Center, Department of Orthopaedic Surgery, 1215 21 Ave. S., Suite 4200, Nashville, TN 37232; Vanderbilt University Medical Center, Vanderbilt Center for Bone Biology, 1211 Medical Center Dr., Nashville, TN 37212; Tennessee Valley Healthcare System, Department of Veterans Affairs, 1310 24 Ave. S, Nashville, TN 37212
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Meeson R, Moazen M, Sanghani-Kerai A, Osagie-Clouard L, Coathup M, Blunn G. The influence of gap size on the development of fracture union with a micro external fixator. J Mech Behav Biomed Mater 2019; 99:161-168. [PMID: 31357063 PMCID: PMC6715773 DOI: 10.1016/j.jmbbm.2019.07.015] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2019] [Revised: 05/31/2019] [Accepted: 07/18/2019] [Indexed: 02/02/2023]
Abstract
Increasingly, the rat femoral fracture model is being used for preclinical investigations of fracture healing, however, the effect of gap size and its influence on mechanobiology is not well understood. We aimed to evaluate the influence of osteotomy gap on osteotomy healing between the previously published extremes of guaranteed union (0.5 mm) and non-union (3 mm) using this model. A femoral osteotomy in 12–14 week old female Wistar rats was stabilised with a micro fixator (titanium blocks, carbon fiber bars) with an osteotomy gap of 1.0 mm (n = 5), 1.5 mm (n = 7), 2.0 mm (n = 6). After five weeks, the left femur was retrieved. The osteotomy gap was scanned using X-ray microtomography and then histologically evaluated. The radiographic union rate (complete mineralised bone bridging across the osteotomy) was three times higher for the 1.0 mm than the 2.0 mm gap. The 1.0 mm gap had the largest callus (0.069μm3) and bone volume (0.035μm3). Callus and bone volume were approximately 50% smaller within the 2.0 mm gap. Using cadaveric rat femurs stabilised with the external fixator, day 0 mechanical assessment of construct stiffness was calculated on materials testing machine displacement vs load output. The construct stiffness for the 1.0, 1.5 and 2.0 mm gaps was 32.6 ± 5.4, 32.5 ± 2.4, and 32.4 ± 8.3 N/mm (p = 0.779). Interfragmentary strain (IFS) was calculated using the change in osteotomy gap displacement as measured using microstrain miniature differential reluctance transducer spanning the osteotomy gap. Increasing the gap size significantly reduced the IFS (p = 0.013). The mean ‘day 0’ IFS for the 1.0, 1.5 and 2.0 mm gaps were 11.2 ± 1.3, 8.4 ± 1.5 and 6.1 ± 1.2% respectively. A 1.5 mm gap resulted in a delayed fracture healing by 5 weeks and may represent a useful test environment for fracture healing therapy. Increasing gap size did not affect construct stiffness, but did reduce the ‘day 0’ IFS, with a doubling of non-union and halving of bone volume measured between 1.0 and 2.0 mm gaps.
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Affiliation(s)
- Richard Meeson
- Division of Surgery, University College London, Stanmore, UK; Royal Veterinary College, Hertfordshire, UK.
| | - Mehran Moazen
- Division of Surgery, University College London, Stanmore, UK; Mechanical Engineering, University College London, UK
| | | | | | - Melanie Coathup
- Division of Surgery, University College London, Stanmore, UK; University of Central Florida, USA
| | - Gordon Blunn
- Division of Surgery, University College London, Stanmore, UK; University of Portsmouth, Portsmouth, UK
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