A tension system for angular correction of bent intramedullary nails: in vitro analysis.

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Although several techniques have been described for bent intramedullary nail removal, there is no universally accepted strategy. We hypothesized that a device based on the action principle of a three-point bend fixture could facilitate extraction of bent intramedullary nails; this paper describes its design and experimental testing. Five large synthetic left femurs and five steel intramedullary nails were used. The nails were bent in a manual hydraulic press and implanted into the model femurs, which had been previously sectioned as necessary. A device to correct the angular deformity imparted to the nails was designed, and a prototype fabricated from AISI 1045 steel. Specimens were secured in a vise and the device attached; manual tension was then applied to gradually correct the nail deformity. Plain radiographs were obtained, and the nails were removed. The model femurs and intramedullary nails were visually inspected for proper contact of the device tip, coronal and sagittal alignment, and points of failure. Before device application, the angles of the specimens averaged 40.2° (38.27°-41.32°) in the coronal plane and 7.22° (8.5°-10.2°) in the sagittal plane. After device application, these angles averaged 15.04° (2.5°-32.3°) and 4.16° (0°-9.8°), respectively. There were no implant fractures, but in two models, peri-implant fractures (one catastrophic) occurred close to the proximal and distal locking screws. The proposed device for bent intramedullary nail extraction was effective, but homogeneous behavior in terms of angle correction was not observed in the tested specimens. Further development is needed.