Influence of flexible nailing in the later phase of fracture healing: strength and mineralization in rat femora

Abstract

In this experimental study, the influence of flexible nailing in the later phase of femoral fracture healing was investigated. Sixty rats were randomly assigned to three groups. In 20 rats no intervention was performed, and they served as a control group. Fracture and reamed nailing with a rigid steel nail was performed in the left femur in the other 40 rats. These rats were reoperated after 30 days, and the medullary nail was removed. In one group (20 rats) a flexible polyethylene nail was installed (flexibly nailed group), while the rats in the other group received a steel nail identical to the one that was removed (rigidly nailed group). At 60 and 90 days, the left femurs of 10 animals in each group were studied clinically, radiologically, and biomechanically, and bone mineralization was measured by dual-energy X-ray absorptiometry. Radiographs in two planes revealed a clearly visible fracture line in both intervention groups at 60 days. At 90 days, the fracture line was clearly visible in the flexibly nailed group, while bridging callus was apparent after the rigid nailing. At 60 and 90 days, the callus area in the flexibly nailed group was significantly larger than that in the rigidly nailed bones. Biomechanically, flexible nailing reduced maximum bending load and fracture energy at 60 and 90 days compared with findings in rigidly nailed bones, while bending rigidity was similar in the two groups. All values for biomechanical characteristics were reduced at 60 and 90 days in flexibly nailed bones compared with intact femurs, while in the rigid nailing group, bending load and fracture energy were similar to those in intact bones at 90 days. Bone mineral content in the callus segment and diaphysis was greater in the rigidly nailed bones than in the flexible nailing group at 60 days, while at 90 days, no differences were detected. In conclusion, this animal study indicates that: (1) flexible nailing in the later phase of fracture healing increases callus formation, while (2) the quality of bone healing is reduced.