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Medicine Meets Virtual Reality 15 J.D. Westwood et al. (Eds.) IOS Press, 2007 © 2007 The authors. All rights reserved.
A New Force-Based Objective Assessment of Technical Skills in Endoscopic Sinus Surgery Toru Kumagai a,1, Juli Yamashita a, Osamu Morikawa a and Kazunori Yokoyama b a National Institute of Advanced Industrial Science and Technology, Japan b Hana Clinic @ South Avenue, Japan
Abstract. We propose objectively assessing endoscopic sinus surgery (ESS) skills by measuring the force applied to a patient model. We collected data on 16 subjects performing gauze packing task using a precise human nasal model with a sixdegree-of-freedom force/torque sensor. Mann-Whitney’s U test was used to analyze their performance. Intermediates (ESS: 10-50 cases) used significantly greater force than students or experts (ESS: over 150 cases) at the 5 % level. Maximum force improved only among experts. These results imply that young surgeons pay too little attention to force applied to patients or tissues. Keywords. Objective assessment, technical skill, endoscopic sinus sugery
Introduction Objective assessment is one key to effective surgical technical skills training. Recent attempts to assess surgical skills have involved measuring the forces exerted during procedures using virtual reality [1] or by employing instrument-installed force sensors [2]. We are developing a training system for endoscopic sinus surgery (ESS). In this study we selected, as objective measures, maximum force (Fm) and average force (Fa) generated during instrument-to-patient contact, which we measured and evaluated during gauze packing (GP) into the ethmoidal sinus using a nasal model equipped with a force sensor (Figures 1 and 2). GP is the packing of gauze via the nasal cavity to ensure hemostasis or surface anesthesia, using forceps under endoscopic guidance. Appropriate packing pressure (PP) between the packed gauze and the lesion is necessary. The nasal mucosa
Figure 1. Bone unit of Nasal model. 1
Figure 2. Experiment system.
Corresponding Author: Senior Research Scientist, Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan; E-mail:
[email protected].
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en route to the lesion must be protected from abrasion by the instrument.
1. Tools and Methods Fm and Fa applied during GP to the ethmoidal sinus were experimentally measured and compared among four groups of subjects. The subjects were 16 volunteers (13 otolaryngologists and 3 medical students), classified according to experience: 3 Experts (Group E: ESS experience > 100 cases; PGY > 9 years), 6 Intermediates (Group I: ESS experience 10–50 cases; PGY, 3–10 years), 4 Beginners (Group B: ESS experience 0–2 cases; PGY, 0–10 years), and 3 students (Group S). A nasal model with an open ethmoidal sinus (Figures 1 and 2), precisely reconstructed from CT images, was employed. A questionnaire survey had confirmed this model to be as useful as a cadaver for intranasal observation training [3]. The bone unit was separate from the head shell and supported by only a six-degree-of-freedom force sensor (Model IFS-67M25A 25-140, Nitta Corp., Japan). The force sensor detected the force and torque on the bone unit. Forces (Fx2 + Fy2 + Fz2)1/2 were recorded at 10Hz on a PC. The surgical instruments were a ø 4mm 0˚ rigid nasal endoscope (Shinko Optical Co., Ltd., Japan), a monitor (14 inch color CRT, Sony, Japan), forceps (Lucae, 17cm), and gauze (3cm x 40cm) moistened with 2ml water. The subjects watched an instruction video on ethmoidal sinus anatomy, use of the instruments, and GP, and then performed GP on the right ethmoidal sinus of the nasal model. The force applied, completion time (T), endoscopic images, and images of the subjects were recorded.
2. Results Mann-Whitney’s U test was performed between Group E and the other groups for T, Fm, and Fa (Figure 3). The results of GP were evaluated by video observation. Good results (good) were obtained by Groups B, I, and E. In Group S, gauze projected from the ethmoidal sinus (poor). 3. Discussion Origin of Fm was evaluated by video observation. In Group E, Fm of ~1.5–3N developed while confirming appropriate packing by pushing the packed gauze in the ethmoidal sinus. In Groups S, I and B (excluding two subjects with Fm of ~1.5–3N), the subjects frequently generated Fm of ~3–8N by instrument-to-model contact: a) Hitting due to interference between instruments or lack of tactical feedback for depth, b) Unnecessary pressure against the intraFigure 3. Results.
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nasal walls, and c) Movement of forceps outside the endoscope’s visual field, causing abrasion of the mucosa. Inexperienced physicians tended to be unaware of intranasal damage being caused by instrument-mucosal contact; Group I was particularly inept, corroborating a survey on laparoscopic cholecystectomy[4] revealing that 90% of injuries occur in a surgeon's first 30 cases. The low Fa in Group S matched that in Group E, but Group S produced poor results. Thus, it was determined that low Fm and Fa are not predictors of good GP. Subjective assessment by experts combined with feedback of Fm and Fa has the potential to increase patient safety.
4. Conclusions We confirmed that Fa and Fm applied to the patient model are effective and objective measures of surgical skill assessment in ESS through the analysis of GP. Force has a clinical implication not provided by T. More experienced subjects naturally required shorter T. In contrast, Fa increased and Fm did not improve with experience, except among experts. These results imply that young surgeons pay less attention to force applied to patients or tissues, potentially leading to unexpected bleeding during surgery and poor prognosis caused by unnecessary pressure on tissues. Force is not predictable from video records and must be measured for proper assessment. The small deviations in T, Fa, and Fm among experts suggest that an optimal task technique exists. Analysis of expert techniques and development of training that enables trainees to acquire this expertise is essential for safe and swift introduction of newly developed surgical procedures such as minimally invasive surgery. Future work should include analysis of torque data, the study of learning curve in consecutive GP tasks, and assessment of ethmoidectomy.
Acknowledgements This study was supported in part by the 2005 Industrial Technology Research Grant Program of the New Energy and Industrial Technology Development Organization (NEDO) of Japan.
References [1] [2] [3] [4]
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