Biomedical subjects

Alon Wolf

Publications and source records attributed to Alon Wolf.

4 recordsLinked to original sources

PubMed2006

A potential function approach to surface coverage for a surgical robot.

This paper considers some implementation issues in a path planner for achieving uniform coverage of a non-Euclidean bony surface embedded in R3 space. The target application for this planner is bone removal in orthopaedic surgery, but the technique can also be applied to other general surface-coverage problems. Specifically, we use cellular decomposition and sweep lines to generate a set of meaningful way-points for the bone-burring robot to visit, then navigate between these way-points using potential functions.

Humans↗

PubMed2005

Cup alignment error model for total hip arthroplasty.

Almost all computer-assisted orthopaedic surgery systems that rely on the anterior pelvic plane definition, such as in computed tomography and magnetic resonance image-based, fluoroscopy-based, and nonimage total hip replacement approaches, are derived from identifying two pairs of pelvic bony landmarks: anterior superior iliac spines and the pubic tubercles. Although these systems strive to achieve cup alignment accuracy of approximately 1 degree, even a minor failure to correctly identify these anatomic landmarks can lead to higher inaccuracies in the final cup alignment. This study shows how to examine the effects of these inaccuracies on the final acetabular cup implant orientation during total hip replacement by generating a kinematic model, which then is simulated. Simulation results indicate that, for example, a total error of 4 mm in measuring the anterior superior iliac spine and the pubic tubercles would result in a final cup orientation of 47 degrees and 27 degrees in abduction and version respectively, resulting in a 2 degrees abduction error and 7 degrees error in version when targeting 45 degrees abduction and 20 degrees version results. These calculations can be repeated for any error values.

Acetabulum↗

PubMed2004

A kinematic model for calculating cup alignment error during total hip arthroplasty.

Reduced range of motion, prosthetic impingement, and joint dislocation can all result from misalignment of the acetabular component (i.e. cup alignment) in patients undergoing total hip arthroplasty. Most methods for acetabular component alignment are designed to provide 45-50 degrees abduction and 15-25 degrees of operative anteversion (also known as flexion) with respect to the anterior pelvic plane coordinate system. Yet in most cases, this coordinate system is not assigned properly, due to differences in patient anatomy and improper positioning in the operating room. This misalignment can result in an error in the cup alignment, which can cause the above-mentioned consequences. This work presents a complete mathematical formulation for the analysis of the inaccuracies related to the anterior pelvic plane axes (APPA) definition and their effect on final cup orientation. We do this by introducing a method taken from Kinematics of Mechanisms, and by representing the errors in the APPA as three concurrent axes of rotation, followed by the version and abduction rotations which are defined relative to the previous rotations. We also present a sensitivity analysis of the results by introducing differential changes between sequential coordinate frames, which simulates the errors in the APPA and their effect on cup orientation. Finally, we demonstrate a computational method which provides corrected version and abduction angles to achieve the desired cup orientation, given that the actual measurement errors are known.

Arthroplasty, Replacement, Hip↗

PubMed2004

Feasibility study of a mini, bone-attached, robotic system for spinal operations: analysis and experiments.

STUDY DESIGN: In this investigation, a new concept of a miniature, bone-attached, medical robotic system for spinal operations is presented. As part of the design parameters of the robot, the forces and moments applied by the physician during insertion of Kirschner wires to soft tissues and drilling in hard tissues were examined. A theoretical model for the expected error of the robotic system due to the applied force has been derived and verified experimentally. The results of a clinical experiment that was carried out on a cadaver support the theoretical model derived and the miniature, bone-attached, robotic concept. OBJECTIVES: 1) Examining the concept of attaching a miniature robotic system to the spinous process of the operated vertebra. 2) Measuring the forces applied by the physician during insertion of Kirschner wires to soft tissues and drilling in hard tissues. 3) Evaluating the expected error of the robot due to mechanical and anatomic deflection caused by the forces applied by the physician during operation. 4) Testing and verifying the theoretical background by a clinical experiment. SUMMARY OF BACKGROUND DATA: Spinal operations are reported in the literature to have a relatively low success rate (70%-90%). This low success rate is affected by misunderstanding of the disease and its indications, resulting in bad selection of patients. From the technical point of view, the low success rate is greatly affected by the physician's lack of experience and the complexity of the spinal anatomy. The development of a miniature bone-attached robotic system for spinal operations could improve the success rate of spinal operations, introduce new percutaneous procedures, and shorten recovery and hospitalization time. Moreover, it will reduce the use of fluoroscopic exposure during operation; consequently, it will decrease considerably exposure to radiation during spinal operations. METHODS: Forces and moments applied by the physician during operation were measured by a 6-DOF miniature sensor. The measurements were taken during K-wire insertion both to soft and to hard tissues of a sheep and a human cadaver. A theoretical model of the expected location error of a K-wire, inserted to selected vertebralanatomies by the robotic system, was derived and verified experimentally. RESULTS: The theoretical model agreed with the experimental results, meaning that the combination of the spinous process and the robotic structure is rigid enough to guide a K-wire accurately. The forces and moments were measured and analyzed, and the total expected error due to the forces and moments was calculated. The clinical experiments supported the theoretical model and proved the system's feasibility. CONCLUSIONS: The given results support the theoretical model developed. Moreover, a miniature robotic guiding system can be attached to the spinous process of a given vertebra. The deflection and system error resulting from the forces and moments acting during operation are within the allowable errors.

Animals↗