Computer-Aided Orthopedic Surgery with Near-Real-Time Biomechanical Feedback
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M. ARMAND ET AL. Computer-Aided Orthopedic Surgery with Near-Real-Time Biomechanical Feedback Mehran Armand, Jyri V. S. Lepistö, Andrew C. Merkle, Kaj Tallroth, Xiaofeng Liu, Russell H. Taylor, and James Wenz This article describes our ongoing efforts in computer-aided surgery. We are develop- ing and testing a biomechanical guidance system that will interact with the surgeon and report the biomechanical state of the joint during hip surgery. The system uses informa- tion from the imagery of a computer-assisted navigation system and displays the contact pressure distribution in the hip joint as the joint realignment is modifi ed intraoperatively. We describe the use of the presented technique for preoperative planning, assessment of surgical outcome, and validation of results as well as intraoperative applications. Although the focus of this work is on periacetabular hip osteotomy, applications of this research can be extended to other types of hip osteotomies, joint osteotomies, and total joint replace- ment techniques. INTRODUCTION Computer-aided surgery (CAS) systems provide • Patient-specifi c preoperative planning through cre- a broad range of technologies to surgeons before and ation of three-dimensional (3D) virtual environ- during surgical procedures. Examples of these tech- ments using medical imagery nologies include navigation systems, computer models, • Intraoperative registration of the virtual environ- robotic assisted tools, and visualization devices. CAS ment (which includes the patient model and the systems can be used as both training and research tools surgical plan) to the actual patient and the interven- and in routine clinical practice. CAS enables the sur- tional system geon to develop new, more accurate, and less invasive • Computer-assisted execution of the plan using a vari- surgical techniques. In orthopedic surgery, CAS sys- ety of technologies tems combining preoperative modeling and planning with navigational or robotic intraoperative assistance This paradigm—combining preoperative planning, are becoming increasingly accepted among surgeons. registration, and execution—has been discussed exten- The individual applications may differ, but the funda- sively by various authors,1–4 including a co-author of mental paradigm of these systems is as follows: this article.5–8 242 JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 25, NUMBER 3 (2004) COMPUTER-AIDED ORTHOPEDIC SURGERY Patient-Specifi c Planning known as shallow hip socket, is a condition in which Computer-aided preoperative planning for orthope- the acetabulum of the patient is not adequately devel- dic surgery aims at creating virtual environments using oped; rather, the acetabulum is shallow and its roof is 3D reconstructed computed tomography (CT) images obliquely rotated outward. Therefore, the superior and and radiographs. In orthopedic applications for the hip, anterior part of the femoral head is not covered (Fig. 1). preoperative planning is commonly developed for oste- This results in abnormally high stresses on the lateral otomies9–12 and total hip replacements.13–17 Many stud- edge of the acetabular rim. Patients with hip dysplasia ies have demonstrated the importance of biomechanical cannot walk long distances, have chronic pain, and usu- 29,30 analyses for preoperative planning environments.18–22 ally limp. Hip dysplasia may result in osteoarthritis, Few preoperative environments, however, include fracture of the acetabular rim, and/or breakdown of the 31 detailed biomechanical planning. Rather, they are com- cartilage of the acetabular rim. monly based on the kinematics and geometrical analysis A variety of techniques can be used to treat hip dyspla- of the patient’s anatomy. One reason is that the devel- sia, including arthroscopic procedures, total hip replace- 32–37 opment of high-quality patient-specifi c biomechanical ment, and hip osteotomy surgeries. Total hip replace- models, such as fi nite element models (FEMs), obtained ment surgery is the preferred choice for elderly patients. from 3D images is not an automated process, and simu- However, because the effective life of current hip prosthe- lations take a considerable amount of time. These tech- ses is less than 15 years, it is not suitable for young patients. niques are less desirable for the structural optimization Patients younger than 45 years may need two to four addi- scheme usually required for surgical planning. tional hip revision surgeries during their lifetime. Periace- tabular hip osteotomy is the technique of choice for young Computer-Assisted Registration and Execution adults. In this procedure, the surgeon completely detaches the acetabular cup from the rest of the pelvis. The sur- of the Plan geon then realigns the acetabular cup in order to restore The most common systems for CAS execution use predefi ned anatomical angles in three orthogonal planes, some sort of 3D tracking device to sense the relative similar to the alignment of a normal joint (Fig. 2). Periac- positions of the surgical instruments in the surgical etabular osteotomy usually requires preoperative planning fi eld. The coordinate system of the tracking device is to determine the amount of necessary acetabular rotation. registered to the patient and to the preoperative images. Preplanning is usually performed using radiographs or CT Interactive displays are often used to provide informa- scans. As mentioned, while the goal of surgery is to reduce tion that helps the surgeon perform the surgery. These abnormally high stresses, few surgeons use biomechanical types of systems have been applied extensively in ortho- analysis for preoperative planning. pedics,23–28 neurosurgery, and craniofacial and maxil- lofacial surgery. To our knowledge, the available systems do not provide intraoperative biomechanical informa- Image-Guided Intervention in Periacetabular tion to the surgeon. Therefore, any modifi cation to the Osteotomy surgical plan during the surgery would deal only with Bernese periacetabular osteotomy, fi rst performed by geometrical constraints. Ganz et al. in 1988,35 is the most common osteotomy. PERIACETABULAR OSTEOTOMY: AN APPLICATION OF CAS In this article, we describe our previous and ongoing work on the development and validation of the CAS system with pre- and intraop- erative biomechanical guidance for planning and execution of the sur- gery. In one application, we apply the system to image-guided periacetabu- lar hip osteotomy surgery. Periacetabular hip osteotomy is performed on patients with hip dysplasia to reduce abnormally high Figure 1. Views of a dysplastic hip (also known as shallow hip socket) using volume- contact stresses within the acetabu- rendered CT data: (a) preoperative frontal, (b) postoperative frontal, (c) preoperative lat- lum (hip socket). Hip dysplasia, also eral, and (d) postoperative lateral. JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 25, NUMBER 3 (2004) 243 M. ARMAND ET AL. navigation, remain attractive. Currently a co-author of this article, Dr. Lepistö, is one of the few surgeons who perform image-guided periacetabular osteotomies. Intraoperative Revision of the Preoperative Plan The current state of research has shown the advan- tages and importance of using biomechanics and joint contact pressure calculations in planning the periac- 9,19,21 Figure 2. Reconstructed CT-slices in the (a) frontal plane, (b) etabular osteotomy. For the following reasons a horizontal plane, and (c) lateral (sagittal) plane. The realignment signifi cant improvement can be obtained if the surgeon angles shown in their respective views are F-AC, the articular car- can intraoperatively access and visualize the biome- tilage angle in the frontal plane; F-CE, the center edge angle in the frontal plane; H-AT, the anteversion angle in the horizontal plane; chanical state of the surgery: and S-AC, the articular cartilage angle in the sagittal plane. F-AC is the angle between the horizontal line and a line connecting the • There is a degree of unpredictability in the fi nal medial edge of the sourcil line and the most lateral point on the fi xation of the bone fragment because of variations in acetabulum (points 4 and 5 in Fig. 7) measured clockwise. F-CE is quality, the thickness of cortical structures, and the the angle between a vertical line passing through the center of the femoral head and a line between the center of the femoral head fi nal shape of the cut of the bone fragment. Because of and the most lateral edge of the acetabulum measured counter- concerns regarding secure fi xation and bone healing, clockwise. H-AT is the angle of a line parallel to the opening of the trade-offs in alignment are often necessary. The acetabulum and a line perpendicular to the line drawn through the centers of the femoral heads. S-AC is the angle between a interactive biomechanical guidance system (BGS), horizontal line and a line passing through the anterior edge of the therefore, can help the surgeon to revise the plan in contact surface and the uppermost point of the acetabular contact real time and fi nd the new optimal fi xation. surface. • Bone or soft tissue impingement may become evi- This technically challenging technique consists of a dent during surgery, requiring the surgeon to revise sequence of cuts through the ischium, pubis, and ilium the plan and consider an alternative alignment. using various surgical instruments. The procedure com- • If the realignment strategy is modifi ed as a result of pletely detaches the acetabular cup from the rest of the either of the above conditions, the joint