|Year : 2017 | Volume
| Issue : 2 | Page : 78-82
Nitinol piston versus conventional teflon piston in the management of otosclerosis: A comparative study
Poonam Raj1, Atul Gupta2, Ruchika Mittal1
1 Department of ENT-HNS, Army Hospital. (R and R), New Delhi, India
2 Department of ENT-HNS, Base Hospital, Delhi Cantt, New Delhi, India
|Date of Web Publication||14-Jun-2017|
Department of ENT-HNS, Army Hospital (R and R), New Delhi - 110 010
Source of Support: None, Conflict of Interest: None
Introduction: Otosclerosis is a primary metabolic localized disease characterized by conductive deafness. The mainstay of treatment of this condition remains surgical. Several techniques and approaches are commonly used with largely excellent results. A newly developed piston made of Nitinol has the property of crimping by heat activation rather than manually. This study, carried out at a tertiary care centre of the armed forces, proposed to evaluate the efficacy and complications of the Nitinol Smart piston in comparison to the conventional pistons currently being used. Methods and Materials: 50 patients of otosclerosis were evaluated with Pure tone audiometry and randomized into test and control groups of 25 each. The control group underwent stapedotomy by the conventional Teflon piston and in the test group Nitinol smart pistons were used. Pure tone Audiometry for hearing thresholds and AB gap was performed at 06 weeks after surgery and repeated at 06 months, 01 year and 02 years after surgery. Results: Results show an almost identical outcome in terms of improvement of hearing thresholds with the two kinds of prosthesis used with the 'Smart' piston showing marginally better results. There was no significant difference in the postoperative ABG (P < .23) or ABG closure (P < .09). Conclusion: The nitinol piston prosthesis represents the latest advancement in stapes prosthesis design in that incorporates heat-sensitive crimping to preclude the technically difficult step of manual crimping. It is at least as effective as a standard prosthesis in closing the ABG in patients with otosclerosis.
Keywords: Crimping, nitinol piston, otosclerosis, stapedotomy
|How to cite this article:|
Raj P, Gupta A, Mittal R. Nitinol piston versus conventional teflon piston in the management of otosclerosis: A comparative study. Indian J Otol 2017;23:78-82
|How to cite this URL:|
Raj P, Gupta A, Mittal R. Nitinol piston versus conventional teflon piston in the management of otosclerosis: A comparative study. Indian J Otol [serial online] 2017 [cited 2020 Aug 13];23:78-82. Available from: http://www.indianjotol.org/text.asp?2017/23/2/78/208016
| Introduction|| |
Otosclerosis is a primary metabolic localized disease of bone derived from the otic capsule, which is characterized by bony resorption alternating with new bone formation. In this process, lamellar bone is replaced with woven bone of increased thickness, cellularity, and vascularity by osteoclasis.
Otosclerosis primarily affects and has resultant effects on the functioning of the middle ear and inner ear. Otosclerosis may be asymptomatic if the foci are present in the areas of the middle ear other than the stapes footplate. However, if the footplate is involved, it may cause ankylosis and consequent conductive hearing loss. If the otosclerotic foci involve the labyrinth, sensorineural hearing loss and vestibular abnormalities may result.
The mainstay of treatment of this condition remains surgical. Several techniques and approaches are commonly used, with largely excellent results. The surgical technique and the prostheses available to the surgeon have continuously evolved since the Teflon piston, which was invented by Treace. Other than Teflon, other materials used are titanium, gold, platinum, or special steel. In all cases, stapes prosthesis used should have a good bio-tolerance with simple intraoperative handling and should result in good sound transmission leading to the improvement of hearing thresholds.
However, some operative steps, which have a critical impact on the hearing outcome, continue to pose a surgical challenge. The anchoring of the prosthesis on the long process of incus is one of the most important and difficult steps, which leads to acceptable and lasting postoperative hearing results.
A piston made of nitinol has the property of crimping by heat activation rather than manually. This is believed to reduce the instance of necrosis of long process of incus and piston slippage, which result from inaccurate crimping [Figure 1] and [Figure 2].
This study, carried out at a tertiary care center of the Armed Forces, aimed to evaluate the efficacy of the nitinol piston in terms of hearing outcomes and complications in comparison to the conventional pistons currently being used.
| Materials and Methods|| |
Fifty patients of conductive hearing loss with a probable diagnosis of otosclerosis were identified from the patients attending Ear-Nose-Throat (ENT) Outpatient Department. All patients underwent a thorough ENT examination including otomicroscopy. They were further subjected to a detailed audiological evaluation including pure tone audiometry, tympanometry, and stapedius reflex test to confirm the diagnosis. A high-resolution computed tomography temporal bone scan was also done for all patients.
All patients included in the study were adults with a history of insidious onset, progressive conductive hearing loss. Patients with infective middle ear pathology, tinnitus, and mixed/sensorineural hearing loss were excluded from the study. The selected patients were randomized into two groups, namely the control and the test groups. Informed consent for stapedotomy was obtained from all patients.
The control group underwent stapedotomy with a Teflon piston. The patient collected in this group consisted of 18 men and 7 women, with an age distribution of 18–37 years. In all cases, size 0.6 mm OD Teflon piston was used, 22 patients being operated on the right side and 3 on the left side.
The test group underwent stapedotomy with nitinol SMart piston. The test group consisted of 20 men and 5 women, with the age range of 19–36 years. Prosthesis with the size 0.5 OD was used in all cases. Stapedotomy was carried out in the right ear in 21 cases and in the left ear in 4 cases.
Surgery was carried out under local anesthesia in all cases. The steps followed were (1) postaural/permeatal approach, (2) raising of a posterior tympanomeatal flap, (3) posterosuperior bony overhang removal and access to the stapes footplate after identifying landmarks (stapes footplate, tympanic facial nerve, pyramidal eminence), (4) dislocation of the incudostapedial joint, (5) sectioning of the stapedius tendon and posterior crurotomy, (6) measuring the required piston length, (7) fashioning a stapedotomy with a perforator, (8) piston insertion and fixation by manual crimping or by a heater handle, (9) repositioning of the tympanomeatal flap, and (10) packing of external auditory canal (EAC).
EAC pack or tamponade was removed after 2 weeks in all cases. Pure tone audiometry for hearing thresholds and air-bone gap (ABG) was performed at 6 weeks after surgery and repeated at 6 months, 1 year, and 2 years after surgery.
The statistical evaluation of results was carried out using paired two-tailed t-test.
| Results|| |
In the control group, in all cases, the Teflon piston was successfully implanted and the average incision to closure time was 57.45 min. Intraoperatively, no complications occurred, neither were there any persistent complications such as infections, sensorineural hearing loss, or persistent vertigo.
The preoperative auditory diagnostic with a pure tone audiogram showed a four-tone average air conduction threshold, on an average reaching 41.5 dB. The average ABG in the four frequencies was about 28.5 dB.
Postoperatively, the average four-tone air conduction threshold reached 19.25 dB. The mean ABG for four tones was about 8.9 dB postoperatively. This ranged from 15 to 20 dB in 11% cases, 10 to 15 dB in 49% cases, and under 10 dB in 40% cases. A reduction in ABG down to <15 dB was thus achieved in 89% cases and reduction to <20% was achieved in 100% cases.
In the test group, the nitinol piston was successfully inserted and heat crimped [Figure 3] and [Figure 4]. In all cases, hearing improvement was noted on the operating table after repositioning the flap. The average incision to closure time was 51 min in this group. In two cases, a small tear of the tympanic membrane occurred intraoperatively which was repaired with a temporalis fascia graft. In one case, facial canal overlying the oval window was encountered during surgery. However, piston was successfully inserted. There were no postoperative complications in terms of infection, sensorineural hearing loss, or persistent vertigo. However, three patients reported deterioration of hearing thresholds at about 4 weeks postoperatively after an initial period of improvement. On re-exploration at 6-week postoperative, the nitinol piston was found dislodged from the incus. A revision was performed using a conventional Teflon piston.
|Figure 3: Nitinol piston placed in the stapedotomy and hooked onto the long process of incus|
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The preoperative pure tone audiogram showed a mean four-tone average air conduction threshold reaching 40 dB. The average ABG in the four frequencies was about 29.5 dB.
Postoperatively, the average four-tone air conduction threshold reached 17.5 dB. The mean ABG for four tones was about 8.7 dB postoperatively. This ranged from 15 to 20 dB in 7% cases, 10 to 15 dB in 15% cases, and under 10 dB in 78% cases. A reduction in ABG down to <10 dB was achieved in 78% cases and reduction to under 20% in 100% cases in this group also.
In both groups, the postoperative results were gathered with a pure tone audiometry at 6 weeks after surgery and repeated at 6 months, 1 year, and 2 years after surgery in the outpatient department. There was no deviation in hearing thresholds during the period of observation.
The results show an almost identical outcome in terms of improvement of hearing thresholds with the two kinds of prosthesis used, with the nitinol piston showing marginally better results [Figure 5] and [Figure 6]. The nitinol piston was crimped using a heater handle, and this resulted in a shorter surgical time and improved handling and ease of insertion for the surgeon. However, in three cases, the crimping with the heater was probably inadequate resulting in piston dislodgement.
|Figure 5: Average pre- and post-operative air-bone gap in different frequencies for both groups|
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|Figure 6: Average pre- and post-operative air conduction thresholds in both groups|
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Paired two-tailed t-test was used to compare the results in the two groups as the nitinol prosthesis could theoretically have either improved or worsened hearing results in comparison to the conventional Teflon prosthesis. A significant difference was defined as P< 0.05. There was no significant difference in the postoperative ABG (P < 0.23) or ABG closure (P < 0.09). There was also no significant difference in the occurrence of surgical complications in either group.
| Discussion|| |
A large number of different types of prostheses made of different materials are available for stapes surgery. Most prostheses are attached to the long process of incus with a loop by means of “crimping.” This is one of the most challenging steps during stapedotomy. Excessive crimping or inadequate anchoring of the prosthesis both result in poor hearing outcome for the patient. Excessively tight crimping on the long process of incus may even cause full-blown necrosis, which may occur as late as after 10 years of surgery.,,,
The method of fixing the prosthesis to the long process of incus is continually being simplified with newer, improved prostheses. Daniel Wengen, in 2000, for the first time, used a prosthesis which was fixed to the long process of incus. This was held in place by the tension of the prosthesis itself. With this so-called clip prosthesis, crimping was no longer necessary.,
In our study, we used a nitinol piston with minimal heat crimping properties. This prosthesis has a Teflon “vestibular” end and a wire shaft made by nitinol, with a heat activated self-crimping loop. Nitinol is an alloy of nickel and titanium, belonging to the class of “smart” materials, i.e., materials with shape memory and superelastic properties. Nitinol is lightweight and highly biocompatible because of a thin layer of titanium oxide (TiO2) covering the nickel surface. The special advantage of this piston is that the loop grips by itself uniformly and tightly around the incudal process when minimal heating (about 45°C–60°C) is applied using a disposable heater. The TiO2 layer formed at the surface of the nitinol implant prevents the release of nickel into the surrounding environment.
A preliminary trial Rajan et al. involved 16 patients of otosclerosis managed with stapedotomy using the nitinol stapes piston. Postoperatively, hearing results were tabulated at 3, 6, and 9 months and compared to matched reference patients who had been managed with conventional titanium piston stapedotomies. These preliminary results showed significantly smaller postoperative ABGs and individual variations compared to the control group which suggested that the nitinol stapes piston overcomes the limitations of manual crimping in stapedotomy.
In a study carried out by Harris and Gong, 54 patients of otosclerosis underwent stapedotomy using either SMart prosthesis or conventional prosthesis. Results demonstrated that comparable results may be achieved with either prostheses; however, the ease of crimping and the appropriate tightness of the crimp may prove to have long-term advantages.
Fayad et al. carried out a retrospective chart review of 416 ears. These included 306 stapedotomies with nitinol prosthesis and 110 conventional prostheses. Results showed no significant differences in audiometric outcomes, or complication rates were noted between groups.
Cho et al. studied the efficacy of the heat-activated nitinol SMart piston stapes prosthesis in stapedectomy surgery. Hearing results of 76 patients operated with nitinol piston prosthesis were compared to 21 patients who received the conventional manual crimp Fisch-type prosthesis. These results showed that the use of the SMart piston prosthesis results in ABG closure comparable to that of the traditional Fisch-type prosthesis but had the additional benefit of decreased operative time.
Histopathology of the incus after stapedectomy was studied by Gibbin, which showed that, in revision cases, incus erosion is due to the increased abrasive friction of the piston on the bare incus which led to resorptive osteitis and piston transmigration with tip loss. Incus erosion may also be caused by the postoperative chemical inflammation induced by the piston material.
In the best of “surgical hands” with vast experience and manual dexterity, manual crimping still has limitations due to its unequal pressure application and focal, noncircumferential nature. Problems may also result due to the limited space available for a crimping tool and nonvisualization of the incus undersurface.
Kasano and Morimitsu found that use of nitinol stapes prosthesis eliminated the need for piston manipulation and decreased the macroscopic damage to the mucoperiosteum of the incus.
Huber et al. concluded that tight fixation, as provided by nitinol prostheses, leads to improved functional results because of better sound transmission properties at the incus–prosthesis interface.
Our results in this study are consistent with those quoted in literature and no statistically significant difference in hearing results was elicited when comparing the use of nitinol stapes pistons with conventional stapes prosthesis. However, due to simple intraoperative handling, especially in placing the nitinol piston in position, the critical step of manual crimping was eliminated. The heat crimper design, however, was bulky and clumsy to use. Intraoperative complication rates were low.
| Conclusion|| |
The piston-style prosthesis has had a persistent disadvantage in terms of the relative difficulty in crimping and anchoring it to the long process of incus. This step is essential for obtaining an optimum hearing result. Tight crimping may result in trauma to the long process of the incus and/or may lead to avascular necrosis of the incus. On the other hand, loose crimping may lead to displacement/dislodgement of prosthesis.
Shape memory alloys, such as nitinol, conform to a preset shape on the application of heat. The prosthesis is provided in an open conformation, but on heat application at 45 degrees, it closes circumferentially around the long process of the incus. Hence, no manual crimping is necessary for this process. Although better postoperative outcomes achieved with a nitinol piston have been previously confirmed, the superiority of the nitinol piston over the conventional manual-crimping prostheses remains debatable.
Experienced surgeons may achieve comparable results with both prostheses. However, the ease of self-crimping and the optimal tightness of the crimp in nitinol prosthesis may have long-term benefits. Compared to conventional stapes prostheses, the nitinol-based SMart piston is a safe and reliable alternative that does away with manual crimping without altering the hearing outcome. Complications are rare, but a longer follow-up is needed before establishing long-term efficacy and acceptability.
The nitinol prosthesis may also potentially limit the increasing number of revision procedures being performed. Revision stapes surgery may result from manual malcrimping. Long-term follow-up will ultimately determine if the firm circumferential pressure provided by the nitinol prosthesis reduces the incidence of these complications.
In view of the above, the purpose of our study was to provide only an initial evaluation of hearing results in patients who received the nitinol prosthesis.
In conclusion, the nitinol piston prosthesis represents advancement in stapes prosthesis design, in that it incorporates heat-sensitive crimping to preclude the technically difficult step of manual crimping. It is at least as effective as the commonly used Teflon piston in closing the ABG in patients with otosclerosis. Long-term analyses of the performance of this prosthesis will ultimately demonstrate if the reproducible, firm crimp of the nitinol prosthesis results in fewer revision procedures in comparison to standard prostheses.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]