An externally fixed femoral fracture model for mice

Abstract

Transgenic and knockout mouse models can be used to help understand the molecular mechanisms of fracture repair. This study examines the feasibility of applying an external fixator to the mouse femur as one model for studying fracture repair. The external fixator consisted of two aluminum blocks connected by two rods. Four pins are used to connect the blocks to the bone. Mechanical characterization of the fixators was carried out prior to their use. Sixty-two wild type mice with bilateral femoral fractures were created using an open technique and fixed using the fixator. The progress of fracture healing was monitored radiologically before sacrifice and by mechanical testing and histology after sacrifice. Initially four mice died intraoperatively from excessive blood loss, the intraoperative mortality was subsequently reduced by subcutaneous saline infusion. The bone healed between 14 and 21 days after fracture and remodeled by 60 days. Both radiological and mechanical assessments showed a steady progression of bone healing. Histology demonstrated callus and endochondral bone formation. This study demonstrated that it is possible to create a mouse femoral fracture model stabilized by external fixation and will provide an additional model to the understanding of fracture healing in transgenic and knockout mice.

Can Normal Fracture Healing Be Achieved When the Implant Is Retained on the Basis of Infection? An Experimental Animal Model

“…Torque to failure and stiffness both were lower in the infection group than in the control group at 6 weeks, but with the numbers available for testing, they were not different at 3 weeks (p = 0.615 and p = 1, respectively; Table 2 [3][4][5][6][7][8][9][10][11][12][13][14][15][16]; p = 0.004) both were greater in the control group than in the group with infection. Maximum torque to failure was lower in the infection group than in the control group at all time points.…”

“…Rat osteosynthesis models have previously used open incisions and stabilization with plates or external fixator systems [4,8,9,17]. Although these systems are commonly associated with gap osteotomy models, a fracture model could be similarly achieved by making a single saw cut (rather than two needed for a gap osteotomy).…”

“…Radiographic analysis at 6 weeks demonstrated the fracture line was less distinct (Lane and Sandhu score of 2-3) in the infection group and complete union was observed (Lane and Sandhu score of [3][4] in the control group (p = 0.001). Semiquantitative histology scores were not different between the noninfected controls and the rats with infection (score 10 versus 9).…”

“…Results Infection decreased callus strength at 6 weeks. Torque to failure (299.07 ± 65.53 Nmm versus 107.20 ± 88.81, mean difference with 95% confidence interval, 192 ; p = 0.007) and stiffness at 6 weeks (11.28 ± 2.67 Nmm versus 2.03 ± 1.68, mean difference with 95% confidence interval, 9 [3][4][5][6][7][8][9][10][11][12][13][14][15][16]; p = 0.004) both were greater in the control group than in the group with infection.…”

Pause Insertions During Cyclic In Vivo Loading Affect Bone Healing

“…Concordantly, healing appeared at an accelerated stage in the cycleequivalent pause-inserted group as indicated by increased osteoid deposition. This time in the healing process may have been before substantial mineralization [4,21], accounting for the lack of differences in von Kossa staining or microCT-based bone mineral content and density. Considerably smaller mineralized callus size with applied loading was measured by microCT compared with controls.…”