A 3D-CT Analysis of Femoral Symmetry-Surgical Implications

Determination of intramedullary nail based on centerline adaptive registration

Objective: Internal fixation with intramedullary nails is a gold standard for the treatment of femoral shaft fractures. However, both the mismatch between intramedullary nails and the medullary cavity and inaccurate positioning of entry points will lead to deformation of intramedullary nails after implantation. The study aimed to determine a suitable intramedullary nail with an optimal entry point for a specific patient based on centerline adaptive registration.

Method: A homotopic thinning algorithm is employed to extract centerlines of the femoral medullary cavity and the intramedullary nail. The two centerlines are registered to obtain a transformation. The medullary cavity and the intramedullary nail are registered based on the transformation. Next, a plane projection method is employed to calculate the surface points of the intramedullary nail laid outside the medullary cavity. According to the distribution of compenetration points, an iterative adaptive registration strategy is designed to decide an optimal position of the intramedullary nail in medullary cavity. The isthmus centerline is extended to the femur surface, where the entry point of the intramedullary nail is located. The suitability of an intramedullary nail for a specific patient was calculated by measuring the geometric quantities reflecting the interference between the femur and nail, and the suitability values of all nails are compared and the most suitable one is determined.

Results: The growth experiment indicated that the bone to nail alignment is indeed affected by the extension of the isthmus centerline, including the extension direction and velocity. The geometrical experiment showed that this method could find the best registration position of intramedullary nails and select the optimal intramedullary nail for a specific patient. In the model experiments, the determined intramedullary nail could be successfully placed into the medullary cavity through the optimal entry point. A pre-screening tool to determine nails which can be successfully used has been given. In addition, the distal hole was accurately located within 14.28 s.

Conclusion: These results suggest that the proposed method can select a suitable intramedullary nail with an optimal entry point. The position of the intramedullary nail can be determined in the medullary cavity, while deformation is avoided. The proposed method can determine the largest diameter intramedullary nail with as little damage to the intramedullary tissue as possible. The proposed method provides preparation aid for internal fixation with intramedullary nails guided by navigation systems or extracorporeal aimers.

Optimizing femur symmetry judgment using three-dimensional data correction scheme in fractures of the proximal femur

BACKGROUND

The application of the 3D printing mirror image model is based on the symmetry of the limbs. Different from image fusion to judge the similarity, based on the commonality of the limb morphology of the same organism and the isotropic of the long bone cross-section, the symmetry of the femur has been determined by calculating the dimension difference of the corresponding cross-section of the non-fractured area. However, the previous version used equidistant cross-sections for measurement and two-dimensional data correction, and there were problems with insufficient reliability and data failure. The purpose of this study is to achieve a more accurate and universal symmetry verification scheme for bilateral tubular bones through an improved method.

METHODS

Forty-five imaging data of proximal femoral fracture and osteopathy were selected from October 2015 to September 2017. 10%, 30%, and 50% of the full-length of the bilateral femur is sliced to judge the similarity between paired femurs. Long and short axes of the bilateral femoral cross-sections on the two-dimensional slices were measured and compared. A stylized trigonometric were used to correct the measured axes lengths such that they more closely match with measurements taken from slices perpendicular to femoral shaft axis.

RESULTS

540 valid data items from the long axis and short axis of the bilateral side of the distal femur were obtained, and 192 of these were corrected. There were no significant differences between the left and right of the long and short axis of each cross-section in paired cases (P>0.05).

CONCLUSIONS

This study have demonstrated symmetricity of the left and right femurs. The availability of CT data at any position of the patient's lower limbs is realized through replacing the previous "two-dimensional data correction" with "three-dimensional data correction".

Morphometric Evaluation of Detailed Asymmetry for the Proximal Humerus in Korean Population

Computer-assisted orthopedic surgery and patient-specific instruments are widely used in orthopedic fields that utilize contralateral side bone data as a template to restore the affected side bone. The essential precondition for these techniques is that the left and right bone features are similar. Although proximal humerus fracture accounts for 4% to 8% of all fractures, the bilateral asymmetry of the proximal humerus is not fully understood. The aim of this study is to investigate anthropometric differences of the bilateral proximal humerus. One hundred one pairs of Korean humerus CT data from 51 females and 50 males were selected for this research. To investigate bilateral shape differences, we divided the proximal humerus into three regions and the proximal humerus further into five sections in each region. The distance from the centroid to the cortical outline at every 10 degrees was measured in each section. Differences were detected in all regions of the left and right proximal humerus; however, males had a larger number of significant differences than females. Large bilateral differences were measured in the greater tubercle. Nevertheless, using contralateral data as a template for repairing an affected proximal humerus might be possible.

Autoclave sterilization of an in-house 3D-printed polylactic acid piece: biological safety and heat-induced deformation

AIMS

Fused filament fabrication 3D printing with polylactic acid filaments is the most widely used method to generate biomodels at hospitals throughout the world. The main limitation of this manufacturing system is related to the biomodels' temperature sensitivity, which all but prevents them to be sterilized using conventional methods. The purpose of this study is to define an autoclave temperature-resistant FFF-PLA 3D printing protocol to print 3D fractures biomodels during preoperative planning.

METHODS AND RESULTS

Six different printing protocols were established, each with a different infill percentage. Ten distal radius biomodels were printed with each protocol and each biomodel was subject to 3D scanning. The biomodels were subsequently autoclave-sterilized at 134 °C and subjected to a new scanning process, which was followed by a calculation of changes in area, volume and deformity using the Hausdorff-Besicovitch method. Finally, 192 polylactic acid models were produced using the printing protocol offering the greatest resistance and were contaminated with 31 common nosocomial pathogens to evaluate the effectiveness of sterilizing the model printed using the said protocol. Sterilization resulted in a mean deformation of the biomodel of 0.14 mm, a maximum deformity of 0.75 mm, and a 1% area and a 3.6% volume reduction. Sterilization of the pieces printed using the analyzed protocol was 100% effective.

CONCLUSIONS

The analyzed 3D printing protocol may be applied with any FFF-PLA 3D printer, it is safe and does not significantly alter the morphology of biomodels. These results indicate that 3D printing is associated with significant advantages for health centers as it increases their autonomy, allowing them to easily produce 3D biomodels that can be used for the treatment of fractures.

Locating the Origin of Femoral Maltorsion Using 3D Volumetric Technology-The Hockey Stick Theory

BACKGROUND

The origin of femoral maltorsion is often unknown. However, defining the origin of the rotation of the femoral maltorsion can be useful for establishing the most suitable point to do an external derotational osteotomy. Previous studies have not considered the femoral diaphysis in their investigations of the origin of the deformity. The study of the whole morphology of the femur with 3D volumetric tools, including the femoral diaphysis can contribute to a better understanding of the behavior of femoral maltorsion.

METHODS

An atypical case of unilateral femoral anteversion was selected. Both femurs were used to obtain 3D bio-models. The mirror image of the asymptomatic side was obtained and overlapped with the symptomatic femur. The Hausdorff-Besicovitch method was used to evaluate the morphologic discrepancies (in mm) between the two femurs in three zones: (1) the femoral neck, (2) the proximal diaphysis, and (3) the distal diaphysis. The differences between the two femurs were analyzed and its correlation was statistically defined using a lineal regression model.

RESULTS

The deformity in the distal diaphysis increased from the supracondylar area until the apex of the antecurvatum angle (R² = 0.91) and then decreased until the base of the femoral neck (R² = (-0.83)), to finally increase significantly in the femoral neck area (R² = 0.87). All of the correlations were statistically significant (p-value ˂ 0.001).

CONCLUSION

The femoral maltorsion originates in the supracondylar area and its rotational axis is the longitudinal axis of the femoral diaphysis. Even though the deformity affects the femoral diaphysis, its clinical relevance is much higher in the femoral neck since the rotational axis passes through its base. Thus, the osteotomy can be conducted along all of the femoral diaphysis as long as it is done perpendicular to it.