Computational Radiology for Orthopaedic Interventions

Statistical shape models (SSM) describe the shape variability contained in a given population. They are able to describe large populations of complex shapes with few degrees of freedom. This makes them a useful tool for a variety of tasks that arise in computer-aided medicine. In this chapter we are going to explain the basic methodology of SSMs and present a variety of examples, where SSMs have been successfully applied.

This paper proposed an automated three-dimensional (3D) lumbar intervertebral disc (IVD) segmentation strategy from Magnetic Resonance Imaging (MRI) data. Starting from two user supplied landmarks, the geometrical parameters of all lumbar vertebral bodies and intervertebral discs are automatically extracted from a mid-sagittal slice using a graphical model based template matching approach. Based on the estimated two-dimensional (2D) geometrical parameters, a 3D variable-radius soft tube model of the lumbar spine column is built by model fitting to the 3D data volume. Taking the geometrical information from the 3D lumbar spine column as constraints and segmentation initialization, the disc segmentation is achieved by a multi-kernel diffeomorphic registration between a 3D template of the disc and the observed MRI data. Experiments on 15 patient data sets showed the robustness and the accuracy of the proposed algorithm.

Registration is the process of computing the transformation that relates the coordinates of corresponding points viewed in two different coordinate systems. It is one of the key components in orthopaedic navigation guidance and robotic systems. When assessing the appropriateness of a registration method for clinical use one must consider multiple factors. Among others these include, accuracy, robustness, speed, degree of automation, detrimental effects to the patient, effects on interventional workflow, and associated financial costs. In this chapter we give an overview of registration algorithms, both those available commercially and those that have only been evaluated in the laboratory setting. We introduce the models underlying the algorithms, describe the context in which they are used and assess them using the criteria described above. We show that academic research has primarily focused on improving all aspects of registration while ignoring workflow related issues. On the other hand, commercial systems have found ways of obviating the need for registration resulting in streamlined workflows that are clinically more acceptable, albeit at a cost of being sub-optimal on other criteria. While there is no optimal registration method for all settings, we do have a respectable arsenal from which to choose.

Augmented reality (AR) techniques, which can merge virtual computer-generated guidance information into real medical interventions, help surgeons obtain dynamic “see-through” scenes during orthopaedic interventions. Among various AR techniques, 3D integral videography (IV) image overlay is a promising solution because of its simplicity in implementation as well as the ability to produce a full parallax augmented natural view for multiple observers and improve surgeons’ hand-eye coordination. To obtain a precise fused result, patient-3D image registration is a vital technique in the IV overlay based orthopaedic interventions. Marker or marker-less based registration techniques are alternative depending on a particular clinical application. According to accurate AR information, minimally invasive therapy including cutting, drilling, implantation and other related operations, can be performed more easily and safely. This chapter reviews related augmented reality techniques for image-guided surgery and analyses several examples about clinical applications. Eventually, we discuss the future development of 3D AR based orthopaedic interventions.

Automatic segmentation of the hip joint with pelvis and proximal femur surfaces from CT images is essential for orthopedic diagnosis and surgery. It remains challenging due to the narrowness of hip joint space, where the adjacent surfaces of acetabulum and femoral head are hardly distinguished from each other. This chapter presents a fully automatic method to segment pelvic and proximal femoral surfaces from hip CT images. A coarse-to-fine strategy was proposed to combine multi-atlas segmentation with graph-based surface detection. The multi-atlas segmentation step seeks to coarsely extract the entire hip joint region. It uses automatically detected anatomical landmarks to initialize and select the atlas and accelerate the segmentation. The graph based surface detection is to refine the coarsely segmented hip joint region. It aims at completely and efficiently separate the adjacent surfaces of the acetabulum and the femoral head while preserving the hip joint structure. The proposed strategy was evaluated on 30 hip CT images and provided an average accuracy of 0.55, 0.54, and 0.50 mm for segmenting the pelvis, the left and right proximal femurs, respectively.

One of the most common methods to derive both qualitative and quantitative data to evaluate osseointegration of implants represents histomorphometry. However, this method is time-consuming, destructive, cost-intensive and the two-dimensional (2D) results are only based on one or a few sections of the bone-implant interface. In contrast, micro-computed tomography (µCT) imaging produces three-dimensional (3D) data sets in short time. The present work describes a new image reconstruction algorithm to calculate the effective bone-implant-interface area (eBIIA) by means of µCT. The reconstruction algorithm is based on a series of image processing steps followed by a voxel-boundary-conditioned surface reconstruction. The analysis of the implant-bone interface with µCT is suitable as a non-destructive and accurate method for 3D imaging of the entire bone-implant interface. Despite its limitations in metallic specimen (streak artefacts), μCT imaging is a valuable technique to evaluate the osseointegration of titanium implants.

Pelvic osteotomies improve containment of the femoral head in cases of developmental dysplasia of the hip or in femoroacetabular impingement due to acetabular retroversion. In the evolution of osteotomies, the Ganz Periacetabular Osteotomy (PAO) is among the complex reorientation osteotomies and allows for complete mobilization of the acetabulum without compromising the integrity of the pelvic ring. For the complex reorientation osteotomies, preoperative planning of the required acetabular correction is an important step, due to the need to comprehend the three-dimensional (3D) relationship between acetabulum and femur. Traditionally, planning was performed using conventional radiographs in different projections, reducing the 3D problem to a two-dimensional one. Known disturbance variables, mainly tilt and rotation of the pelvis make assessment by these means approximate at the most. The advent of modern enhanced computation skills and new imaging techniques gave room for more sophisticated means of preoperative planning. Apart from analysis of acetabular geometry on conventional x-rays by sophisticated software applications, more accurate assessment of coverage and congruency and thus amount of correction necessary can be performed on multiplanar CT images. With further evolution of computer-assisted orthopaedic surgery, especially the ability to generate 3D models from the CT data, examiners were enabled to simulate the in vivo situation in a virtual in vitro setting. Based on this ability, different techniques have been described. They basically all employ virtual definition of an acetabular fragment. Subsequently reorientation can be simulated using either 3D calculation of standard parameters of femoroacetabular morphology, or joint contact pressures, or a combination of both. Other techniques employ patient specific implants, templates or cutting guides to achieve the goal of safe periacetabular osteotomies. This chapter will give an overview of the available techniques for planning of periacetabular osteotomy.

Femoroacetabular impingement (FAI) is a dynamic conflict of the hip defined by a pathological, early abutment of the proximal femur onto the acetabulum or pelvis. In the past two decades, FAI has received increasing focus in both research and clinical practice as a cause of hip pain and prearthrotic deformity. Anatomical abnormalities such as an aspherical femoral head (cam-type FAI), a focal or general overgrowth of the acetabulum (pincer-type FAI), a high riding greater or lesser trochanter (extra-articular FAI), or abnormal torsion of the femur have been identified as underlying pathomorphologies. Open and arthroscopic treatment options are available to correct the deformity and to allow impingement-free range of motion. In routine practice, diagnosis and treatment planning of FAI is based on clinical examination and conventional imaging modalities such as standard radiography, magnetic resonance arthrography (MRA), and computed tomography (CT). Modern software tools allow three-dimensional analysis of the hip joint by extracting pelvic landmarks from two-dimensional antero-posterior pelvic radiographs. An object-oriented cross-platform program (Hip²Norm) has been developed and validated to standardize pelvic rotation and tilt on conventional AP pelvis radiographs. It has been shown that Hip²Norm is an accurate, consistent, reliable and reproducible tool for the correction of selected hip parameters on conventional radiographs. In contrast to conventional imaging modalities, which provide only static visualization, novel computer assisted tools have been developed to allow the dynamic analysis of FAI pathomechanics. In this context, a validated, CT-based software package (HipMotion) has been introduced. HipMotion is based on polygonal three-dimensional models of the patient’s pelvis and femur. The software includes simulation methods for range of motion, collision detection and accurate mapping of impingement areas. A preoperative treatment plan can be created by performing a virtual resection of any mapped impingement zones both on the femoral head-neck junction, as well as the acetabular rim using the same three-dimensional models. The following book chapter provides a summarized description of current computer-assisted tools for the diagnosis and treatment planning of FAI highlighting the possibility for both static and dynamic evaluation, reliability and reproducibility, and its applicability to routine clinical use.

This chapter proposed a personalized X-ray reconstruction-based planning and post-operative treatment evaluation framework called iJoint for advancing modern Total Hip Arthroplasty (THA). Based on a mobile X-ray image calibration phantom and a unique 2D-3D reconstruction technique, iJoint can generate patient-specific models of hip joint by non-rigidly matching statistical shape models to the X-ray radiographs. Such a reconstruction enables a true 3D planning and treatment evaluation of hip arthroplasty from just 2D X-ray radiographs whose acquisition is part of the standard diagnostic and treatment loop. As part of the system, a 3D model-based planning environment provides surgeons with hip arthroplasty related parameters such as implant type, size, position, offset and leg length equalization. With this newly developed system, we are able to provide true 3D solutions for computer assisted planning of THA using only 2D X-ray radiographs, which is not only innovative but also cost-effective.

Conventionally, orthopaedic tumor surgeons have to mentally integrate all preoperative images and formulate a surgical plan. This preoperative planning is particularly difficult in pelvic or sacral tumors due to complex anatomy and nearby vital neurovascular structures. At the surgery, the implementation of these bone resections are more demanding if the resections not only are clear of the tumor but also match with custom implants or allograft for bony reconstruction. CT and MRI are both essential preoperative imaging studies before complex bone tumor surgery. CT shows good bony anatomy, whereas MRI is better at indicating tumor extent and surrounding soft tissue details. Overlaying MRI over CT images with the same spatial coordinates generates fusion images and 3D models that provide the characteristics of each imaging modality and the new dimensions for planning of bone resections. This accurate planning may then be reproduced when it is executed with computer-assisted surgery. It may offer clinical benefits. Although current navigation systems can integrate all the preoperative images for resection planning, they do not support the advanced surgical planning that medical engineering CAD software can provide, such as virtual bone resections and assessment of the resection defects due to system incompatibility. Translating the virtual surgical planning to computer navigation by manual measurements may be prone to processing errors. Currently, the integration of CAD data into navigation system is made possible by converting the virtual plan in CAD format into navigation acceptable DICOM format. The fusion of the modified image datasets that contain the virtual planning with the original image datasets allow easy incorporation of virtual planning for navigation execution in bone tumor surgery. Image fusion technique has also been used in bone allograft selection from a 3D virtual bone bank for reconstruction of a massive bone defect. This facilitates and expedites in finding a suitable allograft that matches with the skeletal defect after bone tumor resection. The technique is also utilized in image-to-patient registration of preoperative CT/MR images. It takes the forms of 2D/3D or 3D/3D image registration. It eliminates the step of surface registration of the operated bones that normally require large surgical exposure. The registration method has great potential and has been applied for minimally invasive surgery in benign bone tumors. This article provides an up-to-date review of the recent developments and technical features in image fusion for computer-assisted tumor surgery (CATS), its current status in clinical practice, and future directions in its development.

Intraoperative 3D imaging offers benefits in the treatment of fractures in many anatomical regions. Using this procedure, inadequate reduction results and implant malpositions that were not identified by two-dimensional fluoroscopy can be detected in all the regions described. In addition, there is the possibility of connecting to a 3D navigation system. This allows a precise placement of the osteosynthesis material in anatomically narrow corridors. This chapter will provide an overview of intraoperative 3D imaging in fracture treatment with a mobile C-Arm.

During surgery, the surgeon’s view of the patient is complemented with imaging that provides an indirect visual feedback of the treated anatomy. For an advanced visualization, existing image-guided surgical systems employ tracking and registration methods to fuse medical images. Lately, medical augmented reality has enabled in situ visualization by registering three-dimensional preoperative data (e.g. CT, MRI, and PET) with two-dimensional intraoperative images (e.g. X-ray, Ultrasound, and Optics). Including the virtual locations of the surgical instruments within the visualization provides the most intuitive way to facilitate surgical navigation since the surgeon mental mapping between medical images, instruments, and patient is not necessary anymore. This book chapter investigates medical augmented reality solutions within orthopaedics and highlights the innovations that lead surgeons in surgical planning, navigation, and education in an efficient and timely manner.

The preferred modality for intraoperative imaging in orthopedic interventions is fluoroscopic imaging. But the exposure of the patient and the surgical team to high dose of x-ray radiation and the inappropriate handling of the fluoroscopic c-arm limit its application. In contrast to fluoroscopy, ultrasound imaging does not expose the patient to harmful ionizing radiation. Due to its excellent spatial resolution, B-mode ultrasound imaging is commonly used in the clinical routine to examine soft tissue such as muscles and organs. Thus, it is perfectly suited for preoperative diagnosis and is an essential tool in prenatal care. However, ultrasound images are subject to various types of artifacts, degrading the quality of the data and making the perception and interpretation rather difficult. Despite its known drawbacks, ultrasound imaging has the potential to become an efficient modality for intraoperative imaging. But the integration of ultrasound into the clinical workflow of a computer-assisted orthopedic surgery gives rise to new challenges. In this chapter the advantages and disadvantages of using ultrasound imaging in image-guided orthopedic interventions are pointed out. Moreover, an overview of the latest clinical applications and the current research is given. A special focus will be on the application of B-mode ultrasound imaging for intraoperative registration in image-guided interventions.

Bony structure has low shape deformity comparing to soft tissue. This fact has been made many trials of developing a robotic system for musculoskeletal surgery. ROBODOC was firstly used on human for total hip replacement in 1992 and was commercialized at 1994. It provides fully-automated surgery and has showed improved surgical precision. However, its usage was declined due to safety concerns. Trends have been changed to semi-automatic, a small size, and a bone-mountable robotic system. Nowadays, surgeons have some options on robotic surgery for total hip replacement, total knee replacement, unicompartmental knee replacement, and spine surgery. On the other hand there is not a commercialized robotic system for fracture surgery despite surgeon’s strong request. They want to increase precision in fracture-reduction and reduce a radiation exposure and fatigue with a robotic system. Several research groups including our group have developed robotic systems for this purpose. This chapter will introduce clinical facts and opinions about commercialized robotic systems, such as ROBODOC, RIO, and MAZOR. Robotic systems for fracture surgery under developing will be also introduced and some highlight data will be shared.

In this chapter a low-cost surgical navigation solution for periacetabular osteotomy (PAO) surgery is described. Two commercial inertial measurement units (IMU, Xsens Technologies, The Netherlands), are attached to a patient’s pelvis and to the acetabular fragment, respectively. Registration of the patient with a pre-operatively acquired computer model is done by recording the orientation of the patient’s anterior pelvic plane (APP) using one IMU. A custom-designed device is used to record the orientation of the APP in the reference coordinate system of the IMU. After registration, the two sensors are mounted to the patient’s pelvis and acetabular fragment, respectively. Once the initial position is recorded, the orientation is measured and displayed on a computer screen. A patient-specific computer model generated from a pre-operatively acquired computed tomography (CT) scan is used to visualize the updated orientation of the acetabular fragment. Experiments with plastic bones (7 hip joints) performed in an operating room comparing a previously developed optical navigation system with our inertial-based navigation system showed no statistical difference on the measurement of acetabular component reorientation (anteversion and inclination). In six out of seven hip joints the mean absolute difference was below five degrees for both anteversion and inclination.

Hip resurfacing is considered to be a viable alternative to total hip replacement in the treatment of osteoarthritis, especially for younger and more active patients. There are, however, several disadvantages reported in the literature, due to difficult surgical exposure and the technical challenges of the intraoperative procedure. Surgical errors, such as notching of the femoral neck, tilting of the femoral component in excess varus, or improper prosthesis seating, can result in early failure of the procedure. In this chapter we discuss the use of patient-specific instrument guides as an accurate and reliable image-guided method for the placement of the femoral and acetabulum components during hip resurfacing. The outcome of patient-specific guided procedures depends on many factors, starting with the accurate depiction of the anatomy in a preoperative image modality, the careful selection of registration surfaces for the guide, the accuracy of the guide creation, as well as the reliability of the guide registration intraoperatively. We will discuss in detail how current research is addressing these points in patient-specific instrument guided hip resurfacing applications.