Precise Intra-operative Assessment of Rotation in Femoral Fracture Nailing

摘要

Background: A novel modification of an existing technique was developed to allow precise fluoroscopic assessment of rotational alignment of the fractured femur during intramedullary nailing. It is hypothesized that this will reduce the incidence of rotational malalignment which is reported to occur in 20-30 % of femoral fractures managed with intramedullary nails. The neck lateral technique has been described to assess the rotational alignment of the femur, however, observation error renders it increasingly inaccurate with C arm obliquity or hip flexion. Method: The neck lateral technique was modified with a calculation to correct for the observation error that occurs with obliquity of the C arm to the femur. This was tested on an adjustable radiopaque sawbone model in a blinded fashion. Results: When tested on the sawbone at random settings of anteversion between 0o and 60° the mean error was 2.1° (std error 1.8o). Conclusion: Femoral anteversion can be accurately assessed intra-operatively with fluoroscopy by measuring the femoral neck lateral with consideration of hip flexion and the obliquity of the X-ray tube. Corresponding Author Background Femoral shaft fractures are common injuries. [1] Closed reduction and locked intramedullary nailing is the gold standard treatment [1-5] and is associated with high rates of union and low rates of complications[2]. Intramedullary devices aid in coronal and sagittal plane reduction of diaphyseal fractures but reduction in the axial plane is determined operatively, and is much more difficult to assess accurately.Malrotation (when defined as > 15o of rotational malalignment) in nailed femoral fractures has been reported to occur in 20-30 % of cases [3]. Clinically, a large deformity may cause patient dissatisfaction, functional impairments [3, 4] and secondary osteoarthritis [5].Anteversion (AV) was defined by Dunn as the angle of the neck, if one were to look longitudinally up a stripped femur. [6]. The mean anteversion is reported as 10??to 15??with a large range of -4??to 36?. The standard deviation is 10??[7, 8]. There is typically a narrow side-to-side difference in any one person (1-4°) [8-10]. Rotational malalignment may be expressed as the side to side difference in anteversion after fracture fixation.Many techniques exist to measure rotational alignment during intramedullary nailing of the femur. These include the Tornetta neck lateral technique[11], the Braten floor neck angle[12], the Deshmukh mirror normal limb technique[13], the Jaarsma lesser trochanter estimation[14], the “patella to the sky technique,” the cortical width technique[15] and computer navigation[16].Computer navigation and the mirror normal technique are the most mathematically accurate methods. However, navigation clearly relies on resources and the mirror normal technique may be inflexible regarding intra-operative manipulation. The neck lateral technique and the floor neck angle technique have observation errors and the floor neck angle is also influenced by the neck shaft angle. The remaining techniques involve some element of estimationThe aim of our study was to demonstrate that a modification of the neck lateral technique corrects for an observation error and allows precise intra-operative assessment of the rotational alignment of the proximal femur with the C arm.The neck lateral technique is based on the angle required to take a lateral image of the proximal femur where the shaft and neck appear as a straight line with the image intensifier (II). The inclination required for this image describes the anteversion of the femur but errors are introduced if the observation is not made perpendicularly to the femoral shaft or if there is flexion or extension. This is significant because intraoperatively it is usually not possible to position the C arm square to the shaft of the femur for the lateral images.