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Biomedical subjects

D A Simon

Publications and source records attributed to D A Simon.

12 recordsLinked to original sources
PubMed2001

Virtual fluoroscopy: computer-assisted fluoroscopic navigation.

STUDY DESIGN: In vitro accuracy assessment of a novel virtual fluoroscopy system. OBJECTIVES: To investigate a new technology combining image-guided surgery with C-arm fluoroscopy. SUMMARY OF BACKGROUND DATA: Fluoroscopy is a useful and familiar technology to all musculoskeletal surgeons. Its limitations include radiation exposure to the patient and operating team and the need to reposition the fluoroscope repeatedly to obtain surgical guidance in multiple planes. METHODS: Fluoroscopic images of the lumbar spine of an intact, unembalmed cadaver were obtained, calibrated, and saved to an ). A was used for the sequential insertion of a light-emitting diode-fitted probe into the pedicles of L1-S1 bilaterally. The trajectory of a "virtual tool" corresponding to the tracked tool was overlaid onto the saved fluoroscopic views in real time. Live fluoroscopic images of the inserted pedicle probe were then obtained. Distances between the tips of the virtual and fluoroscopically displayed probes were quantified using the image-guided computer's measurement tool. Trajectory angle differences were measured using a standard goniometer and printed copies of the workstation computer display. The surgeon's radiation exposure was measured using thermolucent dosimeter rings. RESULTS: Excellent correlation between the virtual fluoroscopic images and live fluoroscopy was observed. Mean probe tip error was 0.97 +/- 0.40 mm. Mean trajectory angle difference between the virtual and fluoroscopically displayed probes was 2.7 degrees +/- 0.6 degrees. The thermolucent dosimeter rings measured no detectable radiation exposure for the surgeon. CONCLUSIONS: Virtual fluoroscopy offers several advantages over conventional fluoroscopy while providing acceptable targeting accuracy. It enables a single C-arm to provide real-time, multiplanar procedural guidance. It also dramatically reduces radiation exposure to the patient and surgical team by eliminating the need for repetitive fluoroscopic imaging for tool placement.

Fluoroscopy↗
PubMed2001

Accuracy requirements for image-guided spinal pedicle screw placement.

STUDY DESIGN: Accuracy requirement analysis for image-guided pedicle screw placement. OBJECTIVES: To derive theoretical accuracy requirements for image-guided spinal pedicle screw placement. SUMMARY OF BACKGROUND DATA: Underlying causes of inaccuracy in image-guided surgical systems and methods for quantifying this inaccuracy have been studied. However, accuracy requirements for specific spinal surgical procedures have not been delineated. In particular, the accuracy requirements for image-guided spinal pedicle screw placement have not been previously reported. METHODS: A geometric model was developed relating spinal pedicle anatomy to accuracy requirements for image-guided surgery. This model was used to derive error tolerances for pedicle screw placement when using clinically relevant screw diameters in the cervical (3.5 mm), thoracic (5.0 mm), and thoracolumbar spine (6.5 mm). The error tolerances were represented as the permissible rotational and translational deviations from the ideal screw trajectory that would avoid pedicle wall perforation. The relevant dimensions of the pedicle model were extracted from existing morphometric data. RESULTS: As anticipated, accuracy requirements were greatest at spinal levels where the relevant screw diameter approximated the dimensions of the pedicle. These requirements were highest for T5, followed in descending order by T4, T7, T6, T3, T12, L1, T8, T11, C4, L2, C3, T10, C5, T2, T9, C6, L3, C2, T1, C7, L4, and L5. Maximum permissible translational/rotational error tolerances ranged from 0.0 mm/0.0 degrees at T5 to 3.8 mm/12.7 degrees at L5. CONCLUSIONS: These results, obtained by mathematical analysis, demonstrate that extremely high accuracy is necessary to place pedicle screws at certain levels of the spine without perforating the pedicle wall. These accuracy requirements exceed the accuracy of current image-guided surgical systems, based on clinical utility errors reported in the literature. In actual use, however, these systems have been shown to improve the accuracy of pedicle screw placement. This dichotomy indicates that other factors, such as the surgeon's visual and tactile feedback, may be operative.

Biomechanical Phenomena↗
PubMed2001

Metacognition in motor learning.

Research on judgments of verbal learning has demonstrated that participants' judgments are unreliable and often overconfident. The authors studied judgments of perceptual-motor learning. Participants learned 3 keystroke patterns on the number pad of a computer, each requiring that a different sequence of keys be struck in a different total movement time. Practice trials on each pattern were either blocked or randomly interleaved with trials on the other patterns, and each participant was asked, periodically, to predict his or her performance on a 24-hr test. Consistent with earlier findings, blocked practice enhanced acquisition but harmed retention. Participants, though, predicted better performance given blocked practice. These results augment research on judgments of verbal learning and suggest that humans, at their peril, interpret current ease of access to a perceptual-motor skill as a valid index of learning.

Adult↗
PubMed1998

Medical imaging and registration in computer assisted surgery.

Imaging, sensing, and computing technologies that are being introduced to aid in the planning and execution of surgical procedures are providing orthopaedic surgeons with a powerful new set of tools for improving clinical accuracy, reliability, and patient outcomes while reducing costs and operating times. Current computer assisted surgery systems typically include a measurement process for collecting patient specific medical data, a decision making process for generating a surgical plan, a registration process for aligning the surgical plan to the patient, and an action process for accurately achieving the goals specified in the plan. Some of the key concepts in computer assisted surgery applied to orthopaedics with a focus on the basic framework and underlying technologies is outlined. In addition, technical challenges and future trends in the field are discussed.

Bone and Bones↗
PubMed1998

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.

Anthropometry↗
PubMed1996

Community leg ulcer clinics: a comparative study in two health authorities.

OBJECTIVE: To compare the outcome and cost of care for leg ulcers in community leg ulcer clinics in Stockport District Health authority with Trafford District Health Authority as a control. DESIGN: Detailed cost and efficacy studies conducted prospectively over a three month period in both districts both before and one year after the introduction of five leg ulcer clinics in Stockport. SETTING: Two large district health authorities of broad socioeconomic mix and total population of 540,000. PATIENTS: All patients receiving treatment for an active leg ulcer, irrespective of the profession or location of their carer. MAIN OUTCOME MEASURES: The proportion of ulcerated limbs completely healed within three months and total cost of leg ulcer care. RESULTS: The introduction of community clinics in Stockport improved healing of leg ulcers from 66/252 (26%) in 1993 to 99/233 (42%) in 1994 (P < 0.001) compared with in Trafford, where 47/203 (23%) healed in 1993 and only 43/213 (20%) in 1994. This improved result in Stockport was achieved while the annual expenditure on care of leg ulcers was reduced from 409,991 pounds to only 253,371 pounds. In the same year the cost of leg ulcer care in Trafford increased from 556,039 pounds to 673,318 pounds. CONCLUSION: In the first year after the introduction of community clinics, before most patients in Stockport had access to these clinics, healing of leg ulcers was already improved whereas costs were reduced.

Community Health Centers↗
PubMed1996

Approaches to venous leg ulcer care within the community: compression, pinch skin grafts and simple venous surgery.

The traditional approach to leg ulcer care is both expensive and achieves poor outcomes. The outcome of treatment for patients with venous ulceration has been improved using a more scientific and research-based approach to patient assessment, adequate compression bandaging, use of other procedures such as pinch skin grafting and simple venous surgery, and the delivery of these innovations in patient care to the community as a whole. Multi-layer compression bandaging is superior to standard (one-layer) bandaging because it can easily be adapted to a wide range of ankle circumferences and leg sizes to provide sustained, graduated compression. Pinch skin grafting is cost-effective, accelerates healing, and, following adequate training, may be performed by specialist nurses in the community. Simple venous surgery may be offered under local anaesthesia when only the superficial veins are incompetent; however, deep venous surgery has yet to prove itself in clinical practice. Implementation of dedicated community leg ulcer clinics using these research-based findings will result in a substantially reduced prevalence of venous leg ulceration.

Ambulatory Care↗
PubMed1995

Techniques for fast and accurate intrasurgical registration.

The goal of intrasurgical registration is to establish a common reference frame between presurgical and intrasurgical three-dimensional data sets that correspond to the same anatomy. This paper presents two novel techniques that have application to this problem, high-speed pose tracking and intrasurgical data selection. In the first part of this paper, we describe an approach for tracking the pose of arbitrarily shaped rigid objects at rates up to 10 Hz. Static accuracies on the order of 1 mm in translation and 1 degree in rotation have been achieved. We have demonstrated the technique on a human face using a high-speed VLSI range sensor; however, the technique is independent of the sensor used or the anatomy tracked. In the second part of this paper, we describe a general purpose approach for selecting near-optimal intrasurgical registration data. Because of the high costs of acquisition of intrasurgical data, our goal is to minimize the amount of data acquired while ensuring registration accuracy. We synthesize near-optimal intrasurgical data sets, based on an analysis of differential surface properties of presurgical data. We demonstrate, using data from a human femur, that discrete-point data sets selected using our method are superior to those selected by human experts in terms of the resulting pose-refinement accuracy.

Algorithms↗
PubMed1988

Effect of rioprostil on aspirin-induced gastrointestinal mucosal changes in normal volunteers.

Rioprostil, a 15-deoxy-16-methyl prostaglandin E1, was evaluated for its effect on aspirin-induced gastrointestinal mucosal changes in normal volunteers. Fifty-six normal male volunteers were evaluated by endoscopy in a double-blind, placebo-controlled study. Aspirin was given at a dose of 975 mg four times per day. Rioprostil was given at doses of 60, 120, and 300 micrograms four times per day. Rioprostil, at both antisecretory and subantisecretory doses, prevented or reduced aspirin-induced injury. Increased stool frequency was the most common side effect and appeared to be a dose-related effect of rioprostil occurring at only antisecretory doses.

Adolescent↗