Experimental Study On Improved Femoral Intramedullary Nail’s Matched Target Device

Objective: To investigate the geometric feature of femoral medullary cavity through CT scanning,study it’s matching with femoral intramedullary nail, and analyis the reason for difficulties in implanting distal lock pin.To resolve the problem through the improvement of intramedullary nail’s matched target deviceMethods: Thirty dried femurs specimens were measured through CT scanning, and twenty images were taken evenly according to the total length of shaft of femur from each femur. In each image,the data of the central axis point and eight points around medullary cavity wall in X and Y axes were abtained, which were used to reconstruct the three-dimensional models of medullary cavity, central axis,intramedullary nail by computer software. And the models wre overlapped for comparison. Then the coronal and sagittal fold line charts for central axis of medullary cavity were drawn. The inserting progress of intramedullary nail were simulated to observe whether the nail would punch out of the medullary cavity wall.Results: The central axis of femoral medullary cavity and intramedullary nail were overlapped and compared. They matched well in the coronal plane, but the curves of femoral medullary cavity were larger than those of intramedullary nails in sagittal plane. While simulating the inserting progress of the intramedullary nail, 6 nails punched out of the medullary cavity wall in coronal plane(20%,6/30),so did13 nails in sagittal plane(43.3%,13/30). The improvement of intramedullary nail’s matched target device is to increase the width of the push rod.Conclusions: Intramedullary nails match well with most of the femoral medullary cavities.However, the anatomic structure of the femoral medullary cavity differs individually. Curves of some femoral medullary cavity are large,which can cause the intramedullary nail deformation of intramedullary nail, and this is the main reason for the failure of distal locking.The solution is to increase the width of the push rod of intramedullary nail’s matched target device.