3D bone models to study the complex physical and cellular interactions between tumor and the bone microenvironment.

As the complexity of interactions between tumor and its microenvironment has become more evident, a critical need to engineer in vitro models that veritably recapitulate the 3D microenvironment and relevant cell populations has arisen. This need has caused many groups to move away from the traditional 2D, tissue culture plastic paradigms in favor of 3D models with materials that more closely replicate the in vivo milieu. Creating these 3D models remains a difficult endeavor for hard and soft tissues alike as the selection of materials, fabrication processes, and optimal conditions for supporting multiple cell populations makes model development a nontrivial task. Bone tissue in particular is uniquely difficult to model in part because of the limited availability of materials that can accurately capture bone rigidity and architecture, and also due to the dependence of both bone and tumor cell behavior on mechanical signaling. Additionally, the bone is a complex cellular microenvironment with multiple cell types present, including relatively immature, pluripotent cells in the bone marrow. This prospect will focus on the current 3D models in development to more accurately replicate the bone microenvironment, which will help facilitate improved understanding of bone turnover, tumor-bone interactions, and drug response. These studies have demonstrated the importance of accurately modelling the bone microenvironment in order to fully understand signaling and drug response, and the significant effects that model properties such as architecture, rigidity, and dynamic mechanical factors have on tumor and bone cell response.

Three-Dimensional Quantification of Cam Resection Using MRI Bone Models: A Comparison of 2 Techniques.

Background: The current clinical standard for the evaluation of cam deformity in femoroacetabular impingement syndrome is based on radiographic measurements, which limit the ability to quantify the complex 3-dimensional (3D) morphology of the proximal femur. Purpose: To compare magnetic resonance imaging (MRI)-based metrics for the quantification of cam resection as derived using a best-fit sphere alpha angle (BFS-AA) method and using 3D preoperative-postoperative surface model subtraction (PP-SMS). Study Design: Descriptive laboratory study. Methods: Seven cadaveric hemipelvises underwent 1.5-T MRI before and after arthroscopic femoral osteochondroplasty, and 3D bone models of the proximal femur were reconstructed from the MRI scans. The alpha angles were measured radially along clockfaces using a BFS-AA method from the literature and plotted as continuous curves for the pre- and postoperative models. The difference between the areas under the curve for the pre- and postoperative models was then introduced in the current study as the BFS-AA-based metric to quantify the cam resection. The cam resection was also quantified using a 3D PP-SMS method, previously described in the literature using the metrics of surface area (FSA), volume (FV), and height (maximum [FHmax] and mean [FHmean]). Bivariate correlation analyses were performed to compare the metrics quantifying the cam resection as derived from the BFS-AA and PP-SMS methods. Results: The mean ± standard deviation maximum pre- and postoperative alpha angle measurements were 59.73° ± 15.38° and 48.02° ± 13.14°, respectively. The mean for each metric quantifying the cam resection with the PP-SMS method was as follows: FSA, 540.9 ± 150.7 mm2; FV, 1019.2 ± 486.2 mm3; FHmax , 3.6 ± 1.0 mm; and FHmean, 1.8 ± 0.5 mm. Bivariate correlations between the BFS-AA-based and PP-SMS-based metrics were strong: FSA (r = 0.817, P = .012), FV (r = 0.888, P = .004), FHmax (r = 0.786, P = .018), and FHmean (r = 0.679, P = .047). Conclusion: Strong positive correlations were appreciated between the BFS-AA and PP-SMS methods quantifying the cam resection. Clinical Relevance: The utility of the BFS-AA technique is primarily during preoperative planning. The utility of the PP-SMS technique is in the postoperative setting when evaluating the adequacy of resection or in patients with persistent hip pain with suspected residual impingement. In combination, the techniques allow surgeons to develop a planned resection while providing a means to evaluate the depth of resection postoperatively.

Comparative accuracy of lower limb bone geometry determined using MRI, CT, and direct bone 3D models.

Advancements in imaging and segmentation techniques mean that three dimensional (3D) modeling of bones is now increasingly used for preoperative planning and registration purposes. Computer tomography (CT) scans are commonly used due to their high bone-soft tissue contrast, however they expose subjects to radiation. Alternatively, magnetic resonance imaging (MRI) is radiation-free: however, geometric field distortion and poor bone contrast have been reported to degrade bone model validity compared to CT. The present study assessed the accuracy of 3D femur and tibia models created from "Black Bone" 3T MRI and high resolution CT scans taken from 12 intact cadaveric lower limbs by comparing them with scans of the de-fleshed and cleaned bones carried out using a high-resolution portable compact desktop 3D scanner (Model HDI COMPACT C210; Polyga). This scanner used structured light (SL) to capture 3D scans with an accuracy of up to 35 µm. Image segmentation created 3D models and for each bone the corresponding CT and MRI models were aligned with the SL model using the iterative closest point (ICP) algorithm and the differences between models calculated. Hausdorff distance was also determined. Compared to SL scans, the CT models had an ICP error of 0.82 ± 0.2 and 0.85 ± 0.2 mm for the tibia and femur respectively, whilst the MRI models had an error of 0.97 ± 0.2 and 0.98 ± 0.18 mm. A one-way analysis of variance found no significant difference in the Hausdorff distances or ICP values between the three scanning methods (p > .05). The black bone MRI method can provide accurate geometric measures of the femur and tibia that are comparable to those achieved with CT. Given the lack of ionizing radiation this has significant benefits for clinical populations and also potential for application in research settings.