A full 3D postoperative analysis, i.e. a quantitative comparison between planned and postoperative positions of bone(s) and implant(s) in 3D, is necessary for a thorough assessment of the outcome of the surgery, as well as to provide information that could be used to optimize similar procedures in the future. In this work, we present a method of postoperative analysis based on a pair of X-ray images only, which reaches a level of accuracy that is comparable with the results obtained with a 3D postoperative image. The method consists in using 3D models of bones, segmented from 3D preoperative image (e.g. CT or MRI scans), and 3D models of implant, and aligning them independently to X-rays by matching contours manually drawn on the X-rays and projected contours. The result gives the relative postoperative position of bone and implant. The method was tested on a phantom consisting of commonly available femoral knee implant on a physical model of a femur (Sawbones®). Result was compared to the optical scan, considered as ground truth, of the implanted saw bone. Two studies were performed: inter-operator (six operators), and intra-operator (5 tests). In addition, the inter-operator study was repeated while asking all the operators to use the same pre-drawn contours. The results are presented by calculating the distance (anterior/posterior, proximal/distal, medial/lateral) between the centers of gravity, and the angles (varus/valgus, flexion/extension, external/internal rotations) of the implants from the X-ray based method and the ground truth. Results were also compared with the relative position of bone and implant extracted from a 3D CT postoperative image. Saw bone and implant were first segmented from this image. In order to determine the position of the implant, despite the metal artefacts in the CT images, the 3D model of the implant was registered on the segmented implant. All processing, including segmentation, registration of X-rays, and measurements, was performed using Mimics Innovation Suite 17.0 ®.Introduction
Methods
The burden of Musculoskeletal (M-S) diseases and prosthetic revision operations is huge and increasing rapidly with the aging population. For patients that require a major surgical intervention, procedures are unsafe, uncertain in outcome and have a high complication rate. The goal of this project is to create an ICT-based patient-specific surgical navigation system that helps the surgeon safely reaching the optimal functional result for the patient and is a user friendly training facility for the surgeons. The purpose of this paper is to demonstrate the advancements in personalized musculoskeletal modeling for patients who require severe reconstructive surgery of the lower extremity. TLEMINTRODUCTION
METHODS
Computational models are the primary tools for efficient design-phase exploration of knee replacement concepts before in vitro testing. To improve design-phase efficiency, a subject-specific computational platform was developed that allows designers to assess devices in realistic conditions by directly integrating subject-specific experimental data in these models. Early in the design-phase of new implant design, numerous in vitro tests would be desirable to assess the influence of design parameters or component alignment on the performance of the device. However, cadaveric testing of knee replacement devices is a costly and time-consuming procedure, requiring manufacture of parts, preparation of cadaveric specimens, and personnel to carry of the experiments. Validated computational models are ideally suited for pre-clinical, high-volume design evaluation. Initial development of these models requires substantial time and expertise; once developed, however, computational simulations may be applied for comparative evaluation of devices in an extremely efficient manner [Baldwin et al. 2012]. Still, computational models are complementary of experimental testing and for this reason, computational models tuned with subject-specific experimental data, e.g. soft tissue parameters, could bring even more efficiency in the design phase. The objective of the current study was to develop a platform of tools that easily allows for subject-specific knee simulations. The system integrates with commercially available medical imaging and finite element software to allow for direct, efficient comparison of designs and surgical alignment under a host of different boundary conditions.Summary Statement
Introduction
With the increasing use of 3D medical imaging, it is possible to analyze 3D patient anatomy to extract features, trends and population specific shape information. This is applied to the development of ‘standard implants’ targeted to specific population groups. Human beings are diverse in their physical makeup while implants are often designed based on some key measurements taken from the literature or a limited sampling of patient data. The different implant sizes are often scaled versions of the ‘average’ implant, although in reality, the shape of anatomy changes as a function of the size of patient. The implant designs are often developed based on a certain demographic and ethnicity and then, simply applied to others, which can result in poor design fitment [1]. Today, with the increasing use of 3D medical imaging (e.g. CT or MRI), it is possible to analyze 3D patient anatomy to extract features, trends and population specific shape information. This can be applied to the development of new ‘standard implants’ targeted to a specific population group [2]. Our population analysis was performed by creating a Statistical Shape Model (SSM) [3] of the dataset. In this study, 40 full Chinese cadaver femurs and 100 full Caucasian cadaver femurs were segmented from CT scans using Mimics®. Two different SSMs, specific to each population, were built using in-house software tools. These SSMs were validated using leave-one-out experiments, and then analyzed and compared in order to enhance the two population shape differences.INTRODUCTION
PATIENTS & METHODS
The Bernese periacetabular osteotomy (PAO) described by Ganz, et al. is a commonly used surgical intervention in hip dysplasia. PAO is being performed more frequently and is a viable alternative to hip arthroplasty for younger and more physically active patients. The procedure is challenging because pelvic anatomy is prohibitive to visibility and open access and requires four X-ray guided Diagnosis and the decision for surgical intervention is currently based upon patient symptoms, use of two-dimensional (2D) radiographic measurements, and the intrinsic experience of the surgeon. With the advent of new technologies allowing three-dimensional reconstructions of hip anatomy, previous two-dimensional X-ray definitions have created much debate in standardizing numerical representations of hip dysplasia. Recent work done by groups such as Arminger et al. have combined and expanded two-dimensional measurements such as Center-Edge (CE) angle of Wiberg, Vertical-Center-Anterior margin (VCA) angle, Acetabular Anteversion (AcetAV) and applied them to three-dimensional CT rendering of hip anatomy. Further, variability in pelvic tilt is a confounding factor and has further impeded measurement translatability. Computer assisted surgery (CAS) and navigation also called image-guided surgery (IGS) has been used in clinical cases of PAO with mixed results. The first appearing study of CAS/IGS in PAO was conducted by Langlotz, et. al 1997 and reported no clinical benefit to using CAS/IGS. However, they did conclude that the use of CAS/IGS is undoubtedly useful for surgeons starting this technically demanding procedure. This is supported by a more recent study done by Hsieh, et. al 2006 who conducted a two year randomised study of CAS/IGS in PAO and concluded its feasibility to facilitate PAO, but there was not an additional benefit when conventional PAO is done by an experienced surgeon. A study done by Peters, et. Al 2006 studying the learning curve necessary to become proficient at PAO found that “The occurrence of complications demonstrates a substantial learning curve” and thus makes a compelling argument for the use of CAS/IGS. A major obstacle to navigation and CAS/IGS revolves around consistency, intra-operative time and ease of use. Custom made guides and implants may help circumvent these limitations. The use of CAS/CAM in developing custom made guides has been proven very successful in areas of oral maxillofacial surgery, hip arthroplasty, and knee replacement surgeries. Additionally, a significant study in the development of rapid prototyping guides in the treatment of dysplastic hip joints was done by Radermacher et. al 1998. They describe a process of using CAS/CAM within the operational theatre using a desktop planning station and a manufacturing unit to develop what they termed as “templates” to carry out a triple osteotomy. Our group is evaluating and developing strategies in PAO using CAS/IGS and more recently using CAS and computer aided modeling (CAM) to develop custom made guides for acetabular positioning. Our first study (Burch et al.) focused on CAS/IGS in PAO using cadavers and yielded small mean cut (1.97± 0.73mm) and CE angle (4.9± 6.0) errors. Our recent study used full sized high-resolution foam pelvis models (Sawbones The APG we developed was to demonstrate the concept of using a positioning guide to obtain accurate rotation of the acetabular fragment. For a clinical application a refined and sleeker design would be required. Further, because working space within the pelvis is extraordinary constrained, once fitted the APG would need to remain and serve as an implantable cage capable of holding bone graft. A potential material is polyetheretherketone (PEEK). Customised PEEK implants and cages have been established in the literature and is a potential option for PAO. The benefits of an implant not only serve to constrain the acetabular fragment in the Though CAS/IGS is a proven viable option, we envision a potentially simpler method for PAO, the use of a cut guide and an acetabular positioning implant. Using customized guides and implants could potentially circumvent the need for specialised intra-operative equipment and the associated learning curves, by providing guides that incorporate the pre-operational plan within the guide, constraining the surgeon to the desired outcome.
