3-D repositioning and differential images of volumetric CT measurements

Effect of improved navigation performance on the accuracy of implant placement in total hip arthroplasty with a CT-based navigation system

A computed tomography (CT)-based navigation system is one of the support tools to place implant with appropriate alignment and position in total hip arthroplasty (THA). To determine whether the higher performance of the navigation would further improve the accuracy of implant placement in the clinical setting, we retrospectively compared the navigation accuracy of two different versions of a navigation system. The newer version of the navigation system had an upgraded optical sensor with superior positional accuracy. Navigation accuracy, defined as differences between postoperative measurements on CT images and intraoperative records on the navigation system, of 49 THAs performed with the newer version of the navigation system was compared with that of 49 THAs performed with the older version. With the newer version, the mean absolute accuracy (95% limits of agreement) of implant alignment was 1.2° (± 3.3°) for cup inclination, 1.0° (± 2.4°) for cup anteversion, 2.0° (± 4.9°) for stem anteversion, and 1.1° (± 2.4°) for stem valgus angle. The accuracy of the implant position was 1.5 mm (± 3.1 mm), 1.3 mm (± 3.0 mm), and 1.5 mm (± 3.1 mm) for cup x-, y-, and z-axes, respectively, 1.6 mm (± 3.2 mm), 1.4 mm (± 2.9 mm), and 1.5 mm (± 2.7 mm) for stem x-, y-, and z-axes, respectively, and 2.4 mm (± 4.5 mm) for leg length discrepancy. The values for the newer version were significantly more accurate with less variation compared to those of the older version. With upgraded navigation performance, more accurate implant placement was demonstrated in the clinical setting.

Accuracy of Cup Positioning With the Computed Tomography-Based Two-dimensional to Three-Dimensional Matched Navigation System: A Prospective, Randomized Controlled Study

BACKGROUND

The accuracy of various navigation systems used for total hip arthroplasty has been described, but no publications reported the accuracy of cup orientation in computed tomography (CT)-based 2D-3D (two-dimensional to three-dimensional) matched navigation.

METHODS

In a prospective, randomized controlled study, 80 hips including 44 with developmental dysplasia of the hips were divided into a CT-based 2D-3D matched navigation group (2D-3D group) and a paired-point matched navigation group (PPM group). The accuracy of cup orientation (absolute difference between the intraoperative record and the postoperative measurement) was compared between groups. Additionally, multiple logistic regression analysis was performed to evaluate patient factors affecting the accuracy of cup orientation in each navigation.

RESULTS

The accuracy of cup inclination was 2.5° ± 2.2° in the 2D-3D group and 4.6° ± 3.3° in the PPM group (P = .0016). The accuracy of cup anteversion was 2.3° ± 1.7° in the 2D-3D group and 4.4° ± 3.3° in the PPM group (P = .0009). In the PPM group, the presence of roof osteophytes decreased the accuracy of cup inclination (odds ratio 8.27, P = .0140) and the absolute value of pelvic tilt had a negative influence on the accuracy of cup anteversion (odds ratio 1.27, P = .0222). In the 2D-3D group, patient factors had no effect on the accuracy of cup orientation.

CONCLUSION

The accuracy of cup positioning in CT-based 2D-3D matched navigation was better than in paired-point matched navigation, and was not affected by patient factors. It is a useful system for even severely deformed pelvises such as developmental dysplasia of the hips.

Isometric Scaling in Developing Long Bones Is Achieved by an Optimal Epiphyseal Growth Balance

One of the major challenges that developing organs face is scaling, that is, the adjustment of physical proportions during the massive increase in size. Although organ scaling is fundamental for development and function, little is known about the mechanisms that regulate it. Bone superstructures are projections that typically serve for tendon and ligament insertion or articulation and, therefore, their position along the bone is crucial for musculoskeletal functionality. As bones are rigid structures that elongate only from their ends, it is unclear how superstructure positions are regulated during growth to end up in the right locations. Here, we document the process of longitudinal scaling in developing mouse long bones and uncover the mechanism that regulates it. To that end, we performed a computational analysis of hundreds of three-dimensional micro-CT images, using a newly developed method for recovering the morphogenetic sequence of developing bones. Strikingly, analysis revealed that the relative position of all superstructures along the bone is highly preserved during more than a 5-fold increase in length, indicating isometric scaling. It has been suggested that during development, bone superstructures are continuously reconstructed and relocated along the shaft, a process known as drift. Surprisingly, our results showed that most superstructures did not drift at all. Instead, we identified a novel mechanism for bone scaling, whereby each bone exhibits a specific and unique balance between proximal and distal growth rates, which accurately maintains the relative position of its superstructures. Moreover, we show mathematically that this mechanism minimizes the cumulative drift of all superstructures, thereby optimizing the scaling process. Our study reveals a general mechanism for the scaling of developing bones. More broadly, these findings suggest an evolutionary mechanism that facilitates variability in bone morphology by controlling the activity of individual epiphyseal plates.

A novel computational approach for studying bone morphogenesis reveals that the longitudinal proportions of developing long bones are accurately maintained throughout elongation by the balance between proximal and distal growth rates.

One of the major challenges that developing organs face is scaling, that is, the adjustment of physical proportions during the massive increase in size. Bone superstructures are projections that typically serve for tendon and ligament insertion or articulation. Therefore, superstructure position along the bone is crucial for musculoskeletal functionality. As bones are rigid structures that elongate only from their ends, it is unclear how superstructure positions are regulated during growth to end up in the right locations.

Here, by analyzing a massive database of micro-CT images of developing mouse long bones, we show that all superstructures maintain their relative positions throughout development. It has been suggested that during development, superstructures are continuously reconstructed and relocated along the shaft, a process known as drift. However, our analysis reveals that most superstructures did not drift at all, implying the involvement of another mechanism. Indeed, we identify a novel mechanism for bone scaling, whereby each bone exhibits a specific and unique balance between the growth rates from its two ends, which accurately maintains the relative position of its superstructures. Moreover, we show mathematically that this mechanism minimizes the cumulative drift of all superstructures, thereby optimizing the scaling process.

Qualitative and quantitative assessment of bone fragility and fracture healing using conventional radiography and advanced imaging technologies--focus on wrist fracture

Fractures of the distal radius are one of the most common injuries presented to orthopaedic surgeons. A variety of treatment options are available for the vast array of fracture patterns. Research that explores bone fragility and fracture healing has led to new treatment modalities. As new products and methods are derived to aid in fracture healing it is essential to develop noninvasive and/or nondestructive techniques to assess structural information about bone. Quantitative assessment of macro-structural characteristics such as geometry, and microstructural features such as relative trabecular volume, trabecular spacing, and connectivity may improve our ability to estimate bone strength. Methods for quantitatively assessing macrostructure include (besides conventional radiographs) dual x-ray absorptiometry (DXA) and computed tomography (CT), particularly volumetric quantitative computed tomography (vQCT). Methods for assessing microstructure of trabecular bone include high resolution computed tomography (hrCT), micro computed tomography (microCT), high resolution magnetic resonance (hrMR), and micro magnetic resonance microMR. Volumetric QCT, hrCT and hrMR are generally applicable in vivo; microCT and microMR are principally applicable in vitro. Clinically, the challenges for bone imaging include balancing the advantages of simple bone densitometry versus the more complex architectural features of bone, or the deeper research requirements versus the broader clinical needs.

A survey of medical image registration

The purpose of this paper is to present a survey of recent (published in 1993 or later) publications concerning medical image registration techniques. These publications will be classified according to a model based on nine salient criteria, the main dichotomy of which is extrinsic versus intrinsic methods. The statistics of the classification show definite trends in the evolving registration techniques, which will be discussed. At this moment, the bulk of interesting intrinsic methods is based on either segmented points or surfaces, or on techniques endeavouring to use the full information content of the images involved.

Fast 3D registration of MR brain images using the projection correlation registration algorithm

Cross-correlation can be used to match 2D images in translation and in rotation. An extension to 3D mono-modality matching is presented. This process allows comparison of two sets of data along the same orientation. To decrease computation time, oblique projections of a 'wandering slice' are used. The precision is about +/- 0.2 degree in rotation and +/- 0.2 mm in translation. Some examples, applied to pre- and post-therapy comparison, are given.

In vivo reproducibility of three-dimensional structural properties of noninvasive bone biopsies using 3D-pQCT

Trabecular bone architecture is one of the main factors influencing the mechanical behavior of cancellous bone. To assess the three-dimensional trabecular microstructure of intact bones, we introduced the concept of noninvasive bone biopsy, a method to assess and analyze cancellous bone based upon three-dimensional peripheral quantitative computed tomography in vivo (3D-pQCT). The aim of this work was to demonstrate the potential of noninvasive bone biopsies as a basis for structural and mechanical analysis of trabecular bone in the process of rapid bone loss. A group of six healthy young male volunteers was measured to provide data on the reproducibility of structural parameters. Baseline and 1-month follow-up measurements were performed to provide data on short-term precision of the procedure, and three of the controls were reanalyzed within 3-6 months to estimate long-term precision. Prior to structural evaluation, the baseline and follow-up measurements were repositioned three-dimensionally to ensure matching volumes of interest (VOI). Trabecular bone density (TBD) as well as structural indices were analyzed for all measurements. The VOIs were analyzed morphometrically by evaluating bone volume (BV/TV) and trabecular number (Tb.N) based on a direct three-dimensional approach. Trabecular thickness (Tb.Th) and trabecular separation (Tb.Sp) were derived from these two indices. The data of the measurements at 1 month to determine the short-term precision was in excellent agreement with the baseline measurements. The results showed that structural parameters can be reproduced in vivo with a coefficient of variation of less than 0.5%. With a typical spread of 4% for the structural indices within the group of healthy volunteers, an intraclass correlation of better than 0.98 was reached. We conclude that high-resolution 3D-pQCT has the potential to detect structural changes in trabecular bone during therapeutic and diagnostic trials.