Stapedotomy is a technically challenging operation.

Transcription

1 Task performance in stapedotomy: Comparison between surgeons of different experience levels DANIEL L. ROTHBAUM, MD, JAYDEEP ROY, PHD, GREGORY D. HAGER, PhD, RUSSELL H. TAYLOR, PhD, LOUIS L. WHITCOMB, PhD, HOWARD W. FRANCIS, MD, and JOHN K. NIPARKO, MD, Baltimore, Maryland OBJECTIVES: Two steps in stapedotomy are particularly challenging: (1) micropick fenestration of the stapes footplate (SF) and (2) crimping of the stapes prosthesis (SP) to the incus. We conducted trials to determine if experience correlates with differences in performance for these tasks. METHODS: In a surgical model of stapedotomy, performance was measured for 3 experienced and 3 novice surgeons. For fenestration, we measured ability to target the fenestration and force applied to the SF. For crimping, we measured crimp quality, movement of the SP during crimping, and force applied to the SF. RESULTS: Experienced surgeons demonstrated significantly better ability to target the fenestration and, during crimping, caused less SP movement and a significantly lower rate of SP dislodgment. CONCLUSIONS: Clear differences in task performance are measurable between more and less experienced surgeons during critical steps of stapedotomy. CLINICAL SIGNIFICANCE: The observed differences in task performance may contribute to an understanding of maneuvers that increase the risk of inadequate prosthesis placement and cochlear trauma factors likely responsible for variable hearing From the Departments of Otolaryngology Head and Neck Surgery (Drs Rothbaum, Francis, and Niparko) and Mechanical Engineering (Drs Roy and Whitcomb) and the Center for Computer Integrated Surgical Systems and Technology (Drs Hager and Taylor), Johns Hopkins University. This research was supported by an American Academy of Otolaryngology Foundation Resident Research Grant, an NIH Resident Training Grant, National Science Foundation grants IIS and EEC , The Dexter F. and Dorothy H. Baker Foundation, and The Sidgmore Family Foundation. Reprint requests: Daniel L. Rothbaum, MD, Department of Otolaryngology, JHOC 6252, Johns Hopkins Hospital, 601 N Caroline St, Baltimore, MD 21287; , rothbaum@robotics.me.jhu.edu. Copyright 2003 by the American Academy of Otolaryngology Head and Neck Surgery Foundation, Inc /2003/$ doi: /mhn results with strapedotomy. (Otolaryngol Head Neck Surg 2003;128:71-7.) Stapedotomy is a technically challenging operation. Mastery of the needed skills requires significant training. Successful stapedotomy is defined as closure of the air-bone gap to within 10 db. For experienced surgeons, reported success rates have traditionally been between 90% and 95%. 1,2 However, success rates can vary widely. Other authors have reported success rates closer to 80%. 3,4 More recently, using guidelines proposed by the Committee on Hearing and Equilibrium, success rates of approximately 70% for primary stapedotomy have been reported. 5 Complications associated with stapedotomy typically result from either cochlear or labyrinthine trauma. As manifested by elevated pure tone thresholds and reduced speech discrimination scores, cochlear trauma leads to sensorineural hearing loss in 5% to 15% of patients. Labyrinthine damage causing vertigo occurs in approximately 2% of patients. 4 Studies using care series design suggest that, inexperienced surgeons, particularly residents, demonstrate lower relative success rates. 6-8 In light of the decreasing number of stapes procedures for otosclerosis and the lower success rates of inexperienced surgeons, a number of requirements for performing stapedotomy have been suggested, including otology fellowship training and significant presurgical instruction in the temporal bone lab. 8,9 Some authors submit that surgeons with little experience in stapedotomy should not perform the operation. 8,10 Many authors have published recommendations on how better to prepare residents to perform stapedotomy. Mathews et al 11 described an incus and stapes footplate simulator designed to train residents in crimping the stapes prosthesis to the incus. Farrior 12 reported a method for simulating otosclerosis in temporal bones by fixing the footplate with cyanoacrylate (Super Glue gel). Leven- 71

2 72 ROTHBAUM et al January 2003 son 13 formulated a 6-week temporal bone course designed to teach stapedectomy to senior residents. He then compared the surgical outcomes of these residents with those of residents who had not taken the course. Interestingly, there was no statistically significant difference in outcome between the 2 groups. 13 Despite extensive research correlating surgical outcome with experience, relatively little data exist comparing the performance of specific tasks in the stapedotomy procedure between surgeons of different experience levels. Identifying knowledge of the tasks that are found to be most challenging and how performance of these tasks varies with surgeon experience would be useful in designing training programs to teach proper stapedotomy technique. Furthermore, a better understanding of experience-based differences in task performance might prompt the reengineering of instruments to optimize task performance by minimizing maneuvers that require significant experience to perform well. Fig 1. Stapedotomy surgical station. METHODS The goal of this investigation was to evaluate the effect of subspecialty expert versus novice differences in the comparative performance of two crucial steps in the stapedotomy procedure: (1) micropick fenestration of the stapes footplate and (2) crimping of the stapes prosthesis to the long process of the incus. These two steps have been identified as a particularly demanding part of the stapedotomy operation. 11,13 Expert surgeons are defined as full-time otologic surgeons (senior surgeons), and novice surgeons are defined as otology fellows at the beginning of their subspecialty training (junior surgeons). Expert surgeons have performed between 20 and 350 micropick fenestrations while novice surgeons have performed none. As a test bed, we developed a full-scale surgical model of the human ear 14 (Fig 1). A prepared human temporal bone is mounted on a ball-swivel joint (Newport Corporation, Irvine, CA), which allows the surgeon to position the temporal bone in a position amenable to transcanal surgery. The temporal bone has been modified to permit positioning beneath the oval window of an ELFS- T3M-L5 load cell (Entran, Fairfield, NJ) to measure forces. The load cell is mounted on 3-Axis Dovetail x-y-z stage (Newport Corporation, Irvine, CA). On the load cell, we place an artificial stapes footplate made of dense foam (Pacific Research Laboratories, Inc, Vashon, WA). The force required to fenestrate the stapes footplate varies with thickness. Because of the high variability in thickness of natural bony footplates, we use synthetic artificial stapes footplates of more uniform thickness with mechanical properties similar to natural footplates. For fenestration of the stapes footplate using a micropick, performance measures are (1) targeting of the fenestration to a desired point and (2) force both maximum and cumulative applied to the stapes footplate. Performance variables are measured for junior and senior operators. We measure performance as follows. MICROPICK FENESTRATION Targeting the Fenestration A target for fenestration is designated via a submillimeter dot on the artificial footplate. This is captured on a prefenestration image taken using a digital camera (Camedia E-10 Digital Camera, Olympus, Melville, NY). After fenestration, the footplate is again photographed. Displacement between the resulting images is calculated using a MATLAB (Version 6.0; The MathWorks, Inc, Natick, MA) image-processing program (Fig 2). Force Applied to the Stapes Footplate To measure force applied to the stapes footplate, we record forces on the load cell on which

3 Volume 128 Number 1 ROTHBAUM et al 73 Fig 2. Displacement. To measure fenestration targeting, prefenestration and postfenestration images are used to calculate the displacement between the desired and actual centers of fenestration (crossed lines). the stapes footplate is mounted. From these force measurements, we calculate both the maximum force and cumulative forces applied during fenestration (Fig 3). CRIMPING THE STAPES PROSTHESIS For crimping the prosthesis to the long process of the incus, we measure (1) crimp quality, defined as the extent of circumferential contact between the prosthesis wire and long process of the incus; (2) force applied to stapes footplate during crimping both maximum and cumulative; (3) movement of the prosthesis during crimping, ie, initial versus final position; and (4) dislodgment of the prosthesis from its position in the fenestrated stapes footplate. We quantify these performance variables. Circumferential Contact To measure the degree of circumferential contact between the prosthesis wire and incus, we use 6 circumferentially distributed electrodes embedded in an artificial incus (diameter, 660 m) and a sensitive high-impedance op-amp circuit to measure electrical continuity between the incus and each of the electrodes. Mechanical contact between prosthesis and incus results in a well-defined electrical continuity. The number of incus electrodes exhibiting continuity reveals the extent of mechanical contact between prosthesis wire and Fig 3. Forces. A load cell positioned beneath the stapes footplate measures forces during fenestration. incus. Incus electrode contacts are grouped into 1 of 3 ordinal categories: 2 contacts 0; 2 contacts 1; and 2 contacts 2 (Fig 4). Force Applied to the Stapes Footplate Force applied to the stapes footplate is measured as during fenestration trials (Fig 3). Prosthesis Movement To measure movement of the prosthesis during crimping, we image the crimping procedure with 2

4 74 ROTHBAUM et al January 2003 Fig 4. Electrodes measure contact between the wire of the stapes prosthesis and the incus. Results are grouped into 1 of 3 ordinal categories: 2 contacts 0; 2 contacts 1; and 2 contacts 2. endoscopic cameras (Karl Storz, Culver City, CA). Precrimping and postcrimping images are then used to calculate displacement using imagetracking software (Fig 5). Prosthesis Dislodgment To determine if the stapes prosthesis was dislodged from its position in the fenestrated footplate during crimping, video from the two endoscopic cameras is analyzed. Prosthesis dislodgment is defined as clear movement of the prosthesis from its precrimping seated position in the stapes footplate. To become familiar with both the surgical model of stapedotomy, subjects underwent a series of pretrial training drills. Three senior and three junior surgeons then performed five micropick fenestrations and five crimping procedures. For crimping data analysis, a t test for independent samples was used to compare results for both prosthesis displacement and force maximum and cumulative applied to the stapes footplate. The Mann-Whitney test and Fisher exact test were used to evaluate significance for incus electrode contacts and rate of prosthesis dislodgment, respectively. RESULTS Performance during micropick fenestration was compared using a t test for independent samples (Table 1). Senior surgeons demonstrated significantly better ability to target the fenestration as shown by lower displacements (P.01). The average displacement for senior surgeons was only 42% that of junior surgeons. There was no significant difference between the 2 groups in forces maximum or cumulative applied to the stapes footplate during free-hand fenestration. Performance for crimping of the stapes prosthesis to the long process of the incus was also compared (Table 2). Senior surgeons moved the prosthesis significantly less during crimping. This was seen in 2 ways. First, in comparing beginning versus ending position, senior surgeons moved the stapes prosthesis an average of 0.27 mm while junior surgeons moved it an average of 0.40 mm (P 0.08). Similarly, senior surgeons dislodged the prosthesis from its position in the stapes footplate at a rate of 6.7%. For junior surgeons, the rate was significantly higher: 46.7% (P 0.04). There were no significant differences in forces applied to the stapes footplate during crimping or in crimp quality as measured by the number of incus electrode contacts. DISCUSSION We present a novel approach to measure quantitatively surgeon performance for specific motor tasks that comprise the stapedotomy operation. Prior studies have documented the correlation between surgeon experience and surgical outcome for stapedotomy. 6-8,15,16 To explore the basis of experience-based outcome differences, we measured performance of specific tasks during steps in the stapedotomy operation identified as particularly challenging: (1) fenestration of the stapes footplate and (2) crimping of the stapes prosthesis to the incus In a surgical model of stapedotomy, we demonstrated significant quantitative performance differences between junior and senior surgeons during micropick fenestration and prosthesis crimping. To our knowledge, this is the first demonstration that quantifiable differences in task performance exist between surgeons of different experience levels during stapedotomy maneuvers.

5 Volume 128 Number 1 ROTHBAUM et al 75 Fig 5. Prosthesis displacement (mm) is calculated by comparing orthogonal images of the stapes prosthesis taken before and after crimping. *Final position of the prosthesis. Table 1. Micropick fenestration JR SR P value Displacement (mm) Maximum force (N) Cumulative force (Ns) The performance of full-time otologic surgeons (SR) and otology fellows at the beginning of their subspecialty training (JR) was compared during micropick fenestration of the stapes footplate. Mean and P values (t test for independent samples) for each performance variable are reported. Displacement denotes the distance between the actual and desired points of fenestration; Force, both maximum and cumulative, measures the force applied to the stapes footplate during fenestraton. Indirect evidence indicates that differences in performance during micropick fenestration we observed may relate to variations in surgical outcome for actual stapedotomy. The use of a laser for fenestration, instead of a micropick, significantly improves surgical outcomes for residentperformed stapes procedures. 17,18 For experienced surgeons, however, the use of a laser does not improve the functional outcome. 4 An advantage of the use of a laser is its precision, allowing for better targeting of the fenestration. 19 Therefore differences in surgical precision during fenestration that we measured between junior and senior surgeons may underlie differences in functional outcome based on a surgeon s experience. The most common cause of surgical failure in stapedotomy is prosthesis migration, which is responsible for 48.5% of failures. Prosthesis migration can result from inadequate crimp, poor placement of the prosthesis, or movement during crimping. Incus necrosis, from an overly tight crimp, causes 41% of failures. 20 In the present study, we found significant differences between junior and senior surgeons in movement of the prosthesis during crimping, in terms of both prosthesis dislodgment and beginning-versus-end position of the prosthesis. These differences seem to contribute to the poorer functional outcomes observed with inexperienced surgeons. In our trials, we found no difference in crimp quality (ie, how well the prosthesis is fastened to the incus) between junior and senior surgeons. We did not measure forces applied to the incus during crimping and therefore cannot speculate on experience-based differences in expected rates of incus necrosis. By illuminating specific skill differences based on experience, our results may be useful for training residents in stapedotomy. For example, both accuracy in targeting the fenestration and minimizing movement of the prosthesis during crimping require precise instrument control. Our observations suggest that in teaching techniques for

6 76 ROTHBAUM et al January 2003 Table 2. Crimping JR SR P value Test Incus contacts Mann-Whitney Displacement (mm) t test for independent samples Prosthesis dislodgement 46.7% 6.7% 0.04 Fisher s exact test Maximum force (N) t test for independent samples Cumulative force (Ns) t test for independent samples The performance of full-time otologic surgeons (SR) and otology fellows at the beginning of their subspecialty training (JR) was compared during crimping of the stapes prosthesis to the long process of the incus. Mean values, statistical test, and P values are reported for each performance variable. Incus contacts, Measures the number of postcrimping contacts between the wire of the stapes prosthesis and 6 electrodes circumferentially distributed around an artificial incus. Incus contacts are categorized into ordinal groups: 2 contacts 0, 2 contacts 1; or 2 contacts 2. Displacement describes the change in position of the stapes prosthesis after crimping (beginning versus ending position). Prosthesis dislodgement denotes the rate of dislodgement of the stapes prosthesis from its position seated in the fenestrated stapes footplate. Force, both maximum and cumulative, measures the force applied to the stapes footplate during fenestraton. enhancing precision, strategies for dampening natural tremor and optimal instrument trajectory should be emphasized. Understanding experience-based differences in task performance may also be useful when considering changes in surgical technique. Our results suggest that reducing reliance on precise maneuvers with hand-held instruments may improve performance for inexperienced surgeons. Data on laser stapedotomy performed by residents seem to support this hypothesis. With their greater precision, lasers seem to be better suited for inexperienced users than mechanical hand-held instruments like the micropick. Likewise, one might surmise that approaches to stapedotomy that reduce the reliance on precise maneuvers during crimping would improve success rates for residents. For instance, in comparison with the traditional crimped stapes prosthesis, the bucket-handle prosthesis may be easier to place. Therefore one might surmise that resident success rates would be higher using bucket-handle prostheses. One should be careful in generalizing conclusions derived in this model to actual surgical stapedotomy. Trials were carried out in a surgical model of stapedotomy. Three otology fellows and 3 full-time otologic surgeons participated in these trials. Performance differences observed in the model do not necessarily translate into similar differences during surgery. Conversely, lack of performance differences in the model does not automatically imply lack of difference during actual stapedotomy. These results expand our understanding of differences in surgical outcome for stapedotomy between experienced and inexperienced surgeons. They are also potentially useful for both developing training courses to teach stapedotomy and modifying the stapedotomy procedure so that it can be performed with greater facility and efficacy by less-experienced surgeons. We gratefully acknowledge the following individuals for their assistance: David Ryugo, Sam Lang, Peter Berkelman, Patrick Jensen, Eugene de Juan, Jr, Jack Lloyd, Terry Shelley, Jay Burns, Jason Wachs, Aaron Barnes, Robert Cammarata, Ingrid Shao, Han Seo Cho, and Matthew Hansen. We also thank the following companies for their support: Medtronic- Xomed, Storz Instruments, Smith and Nephew Instruments, Sawbones Corporation, Dentsply Caulk Corporation, Harwick Chemical, Jeneric/Pentron Corporation, Kerr Corporation, Stryker Leibinger, Dow Corning, and Ferro Corporation. REFERENCES 1. Shea JJ Jr. Forty years of stapes surgery. Am J Otol 1998;19: Kursten R, Schneider B, Zrunek M. Long-term results after stapedectomy versus stapedotomy. Am J Otol 1994; 15: Kos MI, Montandon PB, Guyot JP. Short- and long-term results of stapedotomy and stapedectomy with a Teflonwire piston prosthesis. Ann Otol Rhinol Laryngol 2001; 110: Sedwick JD, Louden CL, Shelton C. Stapedectomy vs stapedotomy. Do you really need a laser? Arch Otolaryngol Head Neck Surg 1997;123: de Bruijn AJ, Tange RA, Dreschler WA. Efficacy of evaluation of audiometric results after stapes surgery in otosclerosis. I. The effects of using different audiologic parameters and criteria on success rates. Otolaryngol Head Neck Surg 2001;124:76-83.

7 Volume 128 Number 1 ROTHBAUM et al Backous DD, Coker NJ, Jenkins HA. Prospective study of resident-performed stapedectomy. Am J Otol 1993;14: Sargent EW. The learning curve revisited: stapedotomy. Otolaryngol Head Neck Surg 2002;126: Hughes GB. The learning curve in stapes surgery. Laryngoscope 1991;101: Schuknecht HF. Training in otolaryngology. Arch Otolaryngol 1979;105: Bellucci RJ. Trends and profiles in stapes surgery. Ann Otol Rhinol Laryngol 1979;88: Mathews SB, Hetzler DG, Hilsinger RL Jr. Incus and stapes footplate simulator. Laryngoscope 1997;107: Farrior JB. Stapedectomy for the home temporal bone dissection laboratory. Otolaryngol Head Neck Surg 1986; 94: Levenson MJ. Methods of teaching stapedectomy. Laryngoscope 1999;109: Berkelman P, Rothbaum DL, Roy J, et al. Performance evaluation of a cooperative manipulation microsurgical assistant robot applied to stapedotomy. Lecture Notes in Computer Science: Medical Image Computing and Computer-Assisted Intervention MICCAI, The Fourth International Conference, Utrecht, the Netherlands, October 2001, Springer-Verlag. 15. Chandler JR, Rodriguez-Torro OE. Changing patterns of otosclerosis surgery in teaching institutions. Otolaryngol Head Neck Surg 1983;91: Coker NJ, Duncan NO 3rd, Wright GL, et al: Stapedectomy trends for the resident. Ann Otol Rhinol Laryngol 1988;97: Strunk CL Jr, Quinn FB Jr. Stapedectomy surgery in residency: KTP-532 laser versus argon laser. Am J Otol 1993;14: Strunk CL, Quinn FB Jr, Bailey BJ. Stapedectomy techniques in residency training. Laryngoscope 1992;102: Lundy LB. Otosclerosis update. Otolaryngol Clin North Am 1996;29: Langman AW, Lindeman RC. Revision stapedectomy. Laryngoscope 1993;103:954-8.