Estimation of tibial shaft defect volume using standard radiographs: development and validation of a novel technique

No simple clinical technique with which to measure the volume of bone gaps in the treatment of open fractures or nonunions of the tibia is currently available. It is difficult to compare the three-dimensional magnitude of bone defects in research studies on bone grafting without such a tool, and clinicians have no way of determining the magnitude of defects in clinical practice. The purposes of this study were to develop and to validate a technique with which to accurately measure bone gap volumes of the tibial shaft by using only simple measurements on already available clinical radiographs and a simple equation. We hypothesized that a technique could be developed using anteroposterior- and lateral-view radiographs of the tibia to accurately determine the volume of a tibial shaft fracture.

We created standardized fracture gap models using 45 synthetic tibiae cut in different locations and orientations, rendering 135 gaps. We developed and validated a hydrostatic suspension technique to determine the volume of each bone, which underwent anteroposterior- and lateral-view radiography after each cut. Radiographic measurements were used to calculate defect volumes based on a simple equation. Predicted volumes were compared with measured volumes.

The triangular prism equation matched well with the actual volumes. Linear regression analysis showed a slope of 0.92 and R(2) of 0.97.

The equation provides a simple technique with which to calculate three-dimensional gap volumes based on standard radiographs. The simplicity of the equation and availability of standard radiographs make this a practical research and perhaps clinical tool that might be useful in quantifying volumes of the tibial shaft defect.