Symmetry matching of the medial acetabular surface - A quantitative analysis in view of patient specific implants

OBJECTIVE To quantify intrapelvic surface symmetry in reference to a pre-shaped suprapectineal acetabular implant. METHODS In this cross-sectional study, an anatomically pre-shaped acetabular fracture implant was fitted on 3D surface models of 516 pelvises from a pre-existing bone database using a software tool for automated implant fitting (SOMA, Stryker Orthopaedic Modeling and Analytics) of a CAD model of the implant. The distances between bone and the reference implant were measured at 2310 reference points for each hemipelvis. RESULTS The average distance between the left hemipelvis and the plate was 1.98 mm (median, 10% percentile: 1.45, 90% percentile: 2.78) and 2.0 mm (median, 10% percentile: 1.45, 90% percentile: 2.92) between the right hemipelvis and the plate. There was no significant difference between the two hemipelvises (medianabsolute pairwise delta: 0.25mm; 10% percentile: 0.04, 90% percentile: 0.82; Wilcoxon, p = 0.064). CONCLUSION With regard to the periacetabular surface of the inner pelvis, the pelvis can be considered sufficiently symmetric for using the mirrored contralateral hemipelvis as a template for patient-specific implants in acetabular fracture fixation

Haptic Rendering of Volumetric Anatomic Models at Sub-voxel Resolution

In this paper, a new approach for haptic rendering of high resolution voxel-based anatomic models is presented. For visualization the surface location is determined by a ray-casting algorithm at sub-voxel resolution. Since the same algorithm is used for the haptics as well, a very high level of detail is achieved for haptic feedback. Both graphical and haptic representation is congruent. The interaction forces are calculated based on a collision detection between an arbitrary sized sphere-shaped tool and an arbitrary complex anatomic model. Forces are calculated at an update rate of 6000 Hz and sent to a 3Degree -of-Freedom (3-DOF) Phantom device [7]. Compared to point-based haptic rendering, the unique combination of the sphere-based approach in combination with sub-voxel rendering provides more realistic and very detailed tactile sensations

Realistic Haptic Interaction in Volume Sculpting for Surgery Simulation

Realistic haptic interaction in volume sculpting is a decisive prerequisite for successful simulation of bone surgery. We present a haptic rendering algorithm, based on a multi-point collision detection approach which provides realistic tool interactions. Both haptics and graphics are rendered at sub-voxel resolution, which leads to a high level of detail and enables the exploration of the models at any scale. With a simulated drill bony structures can be removed interactively. The characteristics of the real drilling procedure like material distribution around the drill are considered to enable a realistic sensation. All forces are calculated at an extra high update rate of 6000 Hz which enables rendering of drilling vibrations and sti# surfaces. As a main application, a simulator for petrous bone surgery was developed. With the simulated drill, access paths to the middle ear can be studied. This allows a realistic training without the need for cadaveric material

A comparison between Asians and Caucasians in the dimensions of the femoral isthmus based on a 3D-CT analysis of 1189 adult femurs

Introduction!#!For successful intramedullary implant placement at the femur, such as nailing in unstable proximal femur fractures, the use of an implant that at least reaches or exceeds the femoral isthmus and yields sufficient thickness is recommended. A number of complications after intramedullary femoral nailing have been reported, particularly in Asians. To understand the anatomical features of the proximal femur and their ethnic differences, we aimed to accurately calculate the femoral isthmus dimensions and proximal distance of Asians and Caucasians.!##!Methods!#!In total, 1189 Asian and Caucasian segmented 3D CT data sets of femurs were analyzed. The individual femoral isthmus diameter was precisely computed to investigate whether gender, femur length, age, ethnicity or body mass index have an influence on isthmus diameters.!##!Results!#!The mean isthmus diameter of all femurs was 10.71 ± 2.2 mm. A significantly larger diameter was found in Asians when compared to Caucasians (p < 0.001). Age was a strong predictor of the isthmus diameter variability in females (p < 0.001, adjusted r!##!Conclusions!#!In absolute values, the proximal isthmus distance did not show much variation but is more proximal in Asians. The detailed data presented may be helpful in the development of future implant designs. The length and thickness of future standard implants may be considered based on the findings

Determination of Femoral Neck Angle and Torsion Angle Utilizing a Novel Three-Dimensional Modeling and Analytical Technology Based on CT Datasets.

INTRODUCTION:Exact knowledge of femoral neck inclination and torsion angles is important in recognizing, understanding and treating pathologic conditions in the hip joint. However, published results vary widely between different studies, which indicates that there are persistent difficulties in carrying out exact measurements. METHODS:A three dimensional modeling and analytical technology was used for the analysis of 1070 CT datasets of skeletally mature femurs. Individual femoral neck angles and torsion angles were precisely computed, in order to establish whether gender, age, body mass index and ethnicity influence femoral neck angles and torsion angles. RESULTS:The median femoral neck angle was 122.2° (range 100.1-146.2°, IQR 117.9-125.6°). There are significant gender (female 123.0° vs. male 121.5°; p = 0.007) and ethnic (Asian 123.2° vs. Caucasian 121.9°; p = 0.0009) differences. The median femoral torsion angle was 14.2° (-23.6-48.7°, IQR 7.4-20.4°). There are significant gender differences (female 16.4° vs. male 12.1°; p = 0.0001). Femoral retroversion was found in 7.8% of the subjects. CONCLUSION:Precise femoral neck and torsion angles were obtained in over one thousand cases. Systematic deviations in measurement due to human error were eliminated by using automated high accuracy morphometric analysis. Small but significant gender and ethnic differences were found in femoral neck and torsion angles

Femoral antecurvation-A 3D CT Analysis of 1232 adult femurs.

INTRODUCTION:For optimal treatment of femoral fractures, it is essential to understand the anatomical antecurvation of the human femur. Recent clinical studies have highlighted the problem of distal anterior encroachment or even perforation of the nail tip. The aim of this study was to accurately describe the femoral antecurvation in a large cohort. Another objective was to identify the most important influences on femoral antecurvation, such as age, femur length, gender and ethnicity. METHODS:A three dimensional modelling and analytical technology was applied for the analysis of 1,232 femurs. Individual femoral antecurvation was precisely computed to determine whether gender, femur length, age, ethnicity or body mass index influence the radius of curvature (ROC). RESULTS:The calculated mean ROC for all femurs was 943 mm. The lowest ROC of 826 mm was found in female Asian femurs. A regression analysis demonstrated that age and femur length could predict the variability of the curvature, with femoral length as most powerful predictor. A matched pair subgroup analysis between Asians and Caucasians could not show any significant differences of ROC values. CONCLUSIONS:The mean radius of the femoral antecurvation may be smaller than previously reported revealing a significant mismatch between the actual individual anatomy and existing implants. In opposite to existing literature, this study suggests, that antecurvation differences between various ethnicities may exclusively be attributed to differences in femoral length and age. The findings of this study may be found helpful in the development of novel designs for intra- and extramedullary implants