Computer assisted orthopaedic surgery. Image guided and robotic assistive technologies

Technologies are emerging that will influence the way in which orthopaedic surgery is planned, simulated, and performed. Recent advances in the fields of medical imaging, computer vision, and robotics have provided the enabling technologies to permit computer aided surgery to become an established area which can address clinical needs. Although these technologies have been applied in industry for more than 20 years, the field of computer assisted orthopaedic surgery is still in its infancy. Image guided and surgical navigation systems, robotic assistive devices, and surgical simulators have begun to emerge from the laboratory and hold the potential to improve current surgical practice and patients' outcomes. The goals of these new clinically focused technologies are to develop interactive, patient specific preoperative planners to optimize the performance of surgery and the postoperative biologic response, and develop more precise and less invasive interactive smart tools and sensors to assist in the accurate and precise performance of surgery. The medical community is beginning to see the benefit of these enabling technologies which can be realized only through the collaboration and combined expertise of engineers, roboticists, computer scientists, and surgeons.     

Computer-Assisted Orthopaedic Surgery

Over the last decade, orthopaedics has been one of the most active and diverse areas of development in computer-assisted surgery. Orthopaedics has been a specially challenging area of development as many orthopaedic surgeons consider the outcomes of conventional procedures generally successful. There is significant pressure to improve the efficiency and ergonomics, reduce cost and dependence on more expensive medical imaging modalities, and simplify the use and interfaces. Increasing emphasis on less invasive and minimally invasive procedures could give a significant boost to the adoption of computer-assisted surgery. In this paper, we present the overview of different approaches using a classification scheme that relies on two important criteria: 1) the autonomy of clinical action permitted to the system and 2) the imaging requirements     

Computer assisted measurement of cup placement in total hip replacement

The introduction of image guided systems in total hip replacement surgery provides the ability to plan precisely the alignment of the acetabular cup before surgery, and to perform the surgery according to the preoperative plan. Preoperative planners (interactive computer programs for surgical planning) based on three-dimensional medical images allow planning of optimal placement of implant components based on simulated implant performance. Exact measurement of the cup position during surgery allows precise placement of the cup and accurate measurement of the final position of the cup relative to the pelvis. This measurement is used to evaluate the radiographic techniques for postoperative measurement of cup alignment. Malposition of the acetabular component increases the occurrence of impingement, reduces the safe range of motion, and increases the risk of dislocation and wear. Dislocation of the implant after total hip replacement remains a significant clinical problem. Not fully understanding the interaction between pelvic orientation and final acetabular cup alignment may be one of the main contributing factors in the continued significant incidence of dislocations after total hip replacement. In this study an attempt was made to link the preoperative planning, intraoperative placement, and postoperative measurement of cup placement in total hip replacement using computer assisted techniques.     

The Otto Aufranc Award. Image guided navigation system to measure intraoperatively acetabular implant alignment

There has been little clinical research to examine the effects of patient positioning and pelvic motion on the alignment of the acetabular implant during total hip replacement surgery. Until now, no tools were capable of accurately measuring these variables during the actual procedure. As part of a broader program in medical robotics and computer assisted surgery, a clinical system has been developed that includes several enabling technologies. The hip navigation system (HipNav) continuously and precisely measures pelvic location and tracks relative implant alignment intraoperatively. HipNav technology is used to gauge current clinical practice and provide intraoperative feedback to surgeons with the goal of improving the precision and accuracy of acetabular alignment during total hip replacement. This system provides surgeons with a new class of image guided measurement tools and assist devices. These tools successfully were introduced into the clinical practice of surgery with results showing the following: (1) There exist unpredictable and large variations in the initial position of patients' pelves on the operating room table and significant pelvic movement during surgery and during intraoperative range of motion testing; (2) current mechanical acetabular alignment guides do not account for these variations, and result in variable and in the majority of cases unacceptable acetabular alignment; and (3) press fitting oversized acetabular components influences the final cup orientation.     

Flamespreading during Base Ignition of Propellant Charge: Theoretical and experimental studies

In the paper theoretical modeling of flamespreading through granular propellant charge during base ignition is given. The theoretical model includes the balance equations for the gas and solid phase, as well as necessary constitutive laws. The stable convergent numerical procedure for solution of the system of equations is developed. This procedure is included in computational program FSPC (Flame-spreading through Propellant Charge). The program FSPC enables investigations of influence of ignition material, physical and chemical characteristics of propellant and propellant charge loading density on the flamespreading process. The experimental investigations by an especially designed apparatus are performed. The verification of the theoretical-numerical access through the comparison with the experimental data (pressure vs. time and locations, flamespreading velocity, propellant grains displacements) is carried out. The entire access makes possible more successful solutions of many interior ballistics problems.     

A Model for Explosive Reactive Armor Interaction with Shaped Charge Jet

Study of interaction of explosive reactive armor (ERA) with shaped charge jet is the basis for evaluation of the effectiveness of ERA. The physically based theoretical model of this interaction is given. It is incorporated in the NERA computer code. The influences of backward moving plate and forward moving plate thickness, explosive layer thickness, jet attack angle, and distance between ERA and main armor are investigated. The comprehensive analysis of a longitudinal point of impact effect on ERA efficiency, based on NERA code calculations, is presented. Computational results of NERA code are compared with experimental data. The computational and experimental results of penetration in the steel armour target are in good agreement. The developed code enables optimization of explosive reactive armor characteristics.