A Simple Method to Improve Detection of Femoral Nail Abutment in the Distal Femur: A Computer Modeling Study.

BACKGROUND: Proximal femur fractures are more frequently treated with long femoral nails. Lateral radiographs are used to assess the nail position in the distal femur. However, because of the asymmetric shape of the distal femur, standard lateral radiographs alone are suboptimal for assessing anteriorly positioned nails in the distal femur. Consequently, instances of nail abutment or even perforation might be missed intraoperatively. QUESTION/PURPOSE: Using a three-dimensional (3D) modelling approach, we asked: When the nail is in the anterior fifth of the canal, will rotating the femur to align the simulated x-ray beam with the anterior femoral condyles instead of the posterior femoral condyles increase the diagnostic accuracy of detecting nail perforation of the anterior cortex? METHODS: 3D models of 42 unilateral femora from a population sample representative of patients with hip fractures (mean age of 76 ± 7 years, 10 males and 32 females, and 16 left and 26 right femora) were used. The patients had a mean height of 158 ± 9 cm; 27 femora were from Asians and 15 were from Caucasians. Clinically appropriately sized nails had already been virtually implanted previously as part of a quantitative nail fit assessment study. In a preliminary step, the mean angles of inclination of the distal anterior supracondylar region were quantified using four axial sections of the distal femur. For the femora with the nail tip in the anterior fifth of the canal, projections representing a lateral radiograph were generated along with rotated projections at mean angle (5°, 8°) rotations, with the anterior femoral condyles aligned, and anterior femoral condyle alignment followed by internal and external rotation to detect maximum nail perforation. The distance from the nail to the distal anterior cortex was measured for each rotational projection and used to detect anterior nail perforation. The accuracy of detection was assessed using the area under the curve (AUC) of the receiver operating characteristic (ROC) analysis. RESULTS: Rotating the 3D models by aligning the x-ray beam with the anterior femoral condyles improves the diagnostic ability of detecting anterior nail perforation compared with standard lateral radiographs. The AUC increased with rotation from 0.50 (95% confidence interval 0.50 to 0.50) on the lateral projection to 0.73 (95% CI 0.57 to 0.88, difference = -0.23; p = 0.004) at 5° of rotation, 0.77 (95% CI 0.62 to 0.93, difference = -0.27; p = 0.001) at both 8° of rotation and with the anterior femoral condyles aligned, and to 0.82 (95% CI 0.67 to 0.97, difference = -0.32; p < 0.001) with internal/external rotations past the anterior femoral condyles. There were no differences in accuracy between the four methods of rotation. CONCLUSION: This study shows that rotating the femur to align the anterior femoral condyles on a lateral radiograph and then internally/externally rotating it, improves the accuracy assessed via the AUC of detecting anterior perforation when long nails are positioned in the anterior fifth of the distal femur. CLINICAL RELEVANCE: This approach can easily be used in a clinical setting. Intraoperatively, the image intensifier can be rotated around the leg to produce an image with the anterior femoral condyle aligned, providing surgeons with an opportunity to identify and improve the nail's position or exchange the nail while the patient is still under anesthesia.

Potential pitfalls of lateral radiographic assessment of the nail position in the distal femur.

INTRODUCTION: Antegrade nailing of proximal femur fractures is a widely accepted treatment that relies on lateral radiographs to assess distal nail positioning. However, the distal femur is trapezoidal in cross section, consequently standard lateral radiographs may be insufficient. This study aimed to utilise 3D modelling to virtually assess the accuracy of lateral radiographs in defining the position of a femoral nail in the distal femur, specifically considering distal cortical encroachment. MATERIALS AND METHODS: Three-dimensional models of a commonly used nail, were positioned in 3D models of 63 femora, generated from CT scans. Lateral projections, representative of lateral radiographs, were generated and measurements of the closest point distance between the distal nail and anterior inner cortex were recorded. Axial slices through the model at the same distal position were produced for any nails located in the canal's anterior 1/5th and used to quantify the shortest nail to anterior cortex distance. RESULTS: A significant (p = 0.000) difference exists between the positions of the nail in the lateral projection (- 1.7 ± 1.24 mm) compared with axial position (- 0.23 ± 1.41 mm) with reference to the inner cortical surface. In the lateral projection, 30 nails were located in the canal's anterior 1/5th, of these, 14 nails were identified in the axial position as perforating the inner cortex, with four also perforating the outer cortex surface. CONCLUSION: Femoral nails are often anteriorly located in the distal femur and reviewed using lateral radiographs. However, this research demonstrates that owing to the geometry of the distal femur, a lateral radiograph may be inadequate for determining the true position of a femoral nail within the distal femur. Accurately assessing the position of femoral nails may help to address and prevent thigh pain, and iatrogenic fracture or perforation which have been associated with anterior positioning.

Effects of ethnicity on proximal femoral intramedullary nail protrusion-a 3D computer graphical analysis.

INTRODUCTION: Antegrade nailing of proximal femur or femoral shaft fractures is a proven treatment with good to excellent results. Nonetheless, clinical evidence from Asia indicates that proximal femur nails can be too proud at the greater trochanter (GT) causing irritation for some Asian patients. This study aimed to identify any significant differences in proximal nail misfit for a set of Asian and Caucasian femora. MATERIALS AND METHODS: Two nails (Gamma3, TFNA) were virtually inserted into 63 femoral 3D models (28 Japanese, 4 Thai, 31 Caucasian). In AP, the entry point was 4° lateral for Gamma3 and 5° for TFNA; laterally the same location was used for both. Insertion depth was controlled by aligning the lag screw centre head. The distance of the nail end from the GT was measured at five (medial, lateral, anterior, posterior and centre) reference points (RPs). The correlation between GT height, CCD angle and proximal nail distance to GT was analysed. RESULTS: There was no significant difference between either nail (p = 1.0). The TFNA was overall less prominent than the Gamma3, and significantly less prominent at all RPs except lateral. The Asian femora were 3.76 (p = 0.016) times more likely to have the nail protruding proximally. The Asian subjects were shorter (p < 0.05) than the Caucasians. Their GT height was slightly shorter and CCD angles larger compared to Caucasian (Asian: 41.1 mm, 128.1°, Caucasian: 42.2 mm, 126.4°), but the differences were not significant (p = 0.36). Stature, GT height and CCD angle significantly correlated with nail distance to GT. CONCLUSIONS: This study illustrated a significantly increased incidence of proximal nail protrusion in Asian compared to Caucasian femora, corroborating clinical findings. The combination of shorter stature and GT height and a larger CCD angle in Asians likely contributes to this difference.

Distal Clavicle Physeal Separation Mimicking an Acromioclavicular Joint Separation: A Case Report.

CASE: A 9-year-old boy sustained a right distal clavicle physeal separation with superior and posterior displacement through the periosteum. He was treated surgically with open reduction, Kirschner wire fixation, and periosteal repair and had an excellent outcome. CONCLUSION: Distal clavicle fractures are rare in children, and acromioclavicular joint (ACJ) separations are exceedingly rare. Differentiating between the 2 is often difficult radiographically and clinically. Our case represents a Type IV distal clavicle fracture but could be confused with an ACJ separation. Surgical treatment was successful.