Journal of Investigative Surgery, 28, 103–108, 2015 C 2015 Informa Healthcare USA, Inc. Copyright ISSN: 0894-1939 print / 1521-0553 online DOI: 10.3109/08941939.2014.981323
SURGICAL TECHNIQUE
Piezoelectric Surgery – A Novel Technique for Laminectomy Felix M. Duerr, DVM, MS, Diplomate ACVS-SA, Diplomate ECVS, Diplomate ˜ an,1 Ross H. Palmer, ACVSMR,1 Howard B. Seim, III, DVM, Diplomate ACVS,2 Ana L. Bascun´ DVM, MS, Diplomate ACVS,2 Jeremiah Easley, DVM, Diplomate ACVS 2 1
Department of Clinical Sciences, Colorado State University Veterinary Teaching Hospital, 300 West Drake Road, Fort Collins, Colorado, USA 2 Preclinical Surgical Research Laboratory, Department of Clinical Sciences, Colorado State University, 300 W Drake Road, Fort Collins, Colorado, USA
ABSTRACT Objective: Piezoelectric surgery is a novel technology that allows for the osteotomy of mineralized tissue with less risk of damaging underlying soft tissue structures. This selective cutting increases the safety of osteotomies performed in close vicinity to delicate structures such as dura mater, blood vessels, and neural tissue. This study aimed to develop and describe the technique of piezoelectric surgery for dorsal laminectomy and to assess its clinical safety in normal sheep. Methods: A piezoelectric, dorsal laminectomy technique was developed using ovine cadavers. Following technique development, six live sheep underwent a piezoelectric (n = 6) two-level dorsal laminectomy at L2 -L3 and L4 -L5 (PiezoL2-3,4-5 ), and another 30 live sheep underwent a three-level laminectomy at L1 , L3 , and L5 (PiezoL1,3,5 ) for a total of 102 laminectomy sites. Surgery time and postoperative complications were recorded. Results: Dorsal laminectomy was safely and accurately performed in 35/36 study sheep using a Piezoelectric surgical instrument. No dural tears were noted in any animal. Non-ambulatory paraparesis in one study sheep (PiezoL1,3,5 ) led to euthanasia at 48 hr and only mild epidural hematoma was noted on necropsy. No other major postoperative complications were observed in any of the animals. Subjectively, PiezoL was easy to perform and with a rapid learning curve. Mean surgery time was 105 min (range: 75–165 min; median: 97.5) for PiezoL2-3,4-5 and 93 minutes (range 55–100 min; median: 67.5) for PiezoL1,3,5 . Conclusions: Based on our study, PiezoL is considered a safe and viable technique for performing ovine dorsal laminectomy in the preclinical research setting. R ; osteotomy; ovine; neurosurgery Keywords: laminectomy; Piezosurgery
ric (60–210 μm), linear, and of variable frequencies (approximately 25–30 kHz) [4, 5, 7, 8]. Nerves and blood vessels are spared because these structures can oscillate at the same frequency as the piezoelectric device [8, 9]. In spinal surgery, osteotomies and drilling of bone are frequently performed in close vicinity of neural tissues and blood vessels. Rotary cutting instruments are disadvantageous for this purpose because of the associated heat production and the possibility to severely injure underlying soft tissue structures. Since piezoelectric surgery reduces heat production and does not require a rotary high speed movement in
INTRODUCTION Piezoelectric surgery utilizes microvibrations of ultrasonic frequency to selectively cut bone without significant damage to underlying soft tissue structures [1–4]. These vibrations are generated by the deformation of piezoelectric crystals or ceramics exposed to an electric field (called “indirect piezo effect”) [5]. Deformation of piezoelectric materials results in the oscillations of ultrasonic frequencies, which are then amplified and transferred onto the instrument tip [6]. Application of this tip to mineralized tissue produces a mechanical cutting effect. Vibrations are micrometReceived 9 June 2014; accepted 23 October 2014.
Address correspondence to Jeremiah Easley, DVM, Diplomate ACVS , Preclinical Surgical Research Laboratory, Department of Clinical Sciences, Colorado State University, 300 W Drake Road, Fort Collins, CO 80523, USA. E-mail: [email protected]
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close vicinity of the spinal cord, it provides a safer alternative for such procedures [7, 9]. This novel technology is frequently used in dental/oral surgery in human medicine, and has been shown to be beneficial by multiple investigators [2–4, 7, 9–11]. Piezoelectric surgery resulted in less pain and swelling in people undergoing molar extraction compared with conventional surgery performed with a rotary handpiece device [3]. Duration of hospital stay was significantly decreased in patients undergoing mastoidectomy when piezoelectric surgery was used [12]. In patients undergoing various orthognathic procedures, piezoelectric surgery was associated with reduced blood loss and nerve injury compared with conventional techniques [13]. The effects of piezoelectric surgery on nervous tissue have been investigated in an experimental study in rats undergoing craniotomy with either piezoelectric surgery or a conventional drill. Brain tissue damage (based on MRI and histopathologic evaluation) was significantly decreased on the side on which piezoelectric surgery was performed [14]. Schaeren et al. [7] showed that even sudden contact with a force of 3 N (to simulate accidental “slipping” during surgery) does not transect the sciatic nerve when piezoelectric surgery is performed. In spite of obvious benefits, reports of piezoelectric surgery for spinal surgery are rare, even in the human field where piezoelectric surgery is well established [11, 14]. The aim of this study is to develop and describe the technique for piezoelectric laminectomy and to report the outcome of dorsal piezoelectric laminectomies in normal sheep.
MATERIALS AND METHODS Prior to in vivo evaluation of PiezoL, the piezoelectrical surgical device was tested and procedural details developed utilizing ovine cadavers. Cadavers utilized for this development phase were euthanized for reasons unrelated to the study. The spinal muscles were removed to provide access to the lumbar vertebrae.
Technique Description of the PiezoL Ovine Model The dorsal spinous processes were removed from L2 , L3 , L4 , and L5 with bone cutting forceps for twolevel, non-contiguous dorsal laminectomy at L2 -L3 and L4 -L5 (PiezoL2-3,4-5 ). A compressed air drill and bur were used to remove the dorsal (outer) cortex, cancellous bone, and a thin portion of the inner cortical R blade tip EX1 layer of the lamina. The Piezosurgery R (Piezosurgery , Piezosurgery Incorporated, Columbus, Ohio, USA; Figure 1) was then used to gently penetrate the thin inner cortical layer at a single corner (Figure 2). The penetration site was created by gently sliding the blade tip back and forth ∼1–2 mm across the bony surface until a distinct penetration of the inner cortical layer was felt. After penetrating R blade tip, the spinal canal with the Piezosurgery R the edge of the Piezosurgery blade was used to cut the lamina on all four sides by pulling the blade tip through the full thickness of the thin inner cortical layer. The ligamentum flavum was preserved. When inner periosteum was spared during osteotomy, it was
R FIGURE 1 (a) Piezosurgery device, (b) blade tip EX1 used for the laminectomies.
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R technique for PiezoL2-3,4-5 (ovine). (a) Removal of the FIGURE 2 Cadaveric demonstration of the Piezosurgery dorsal spinous processes with right-angled bone forceps and rongeurs, (b) outer cortical layer and cancellous bone are removed with conventional high speed bur, (c) laminectomy site exposed to the inner cortical layer, (d) use of the R Piezosurgery blade tip to penetrate the inner cortical layer, (e) creating a laminectomy “window” by drawing blade tip from the inner cortical penetration site across the margins of laminectomy site, (f) and (g) elevation of the inner R cortical layer with the Piezosurgery blade tip, (h) partially completed elevation, and (i) completed PiezoL2-3,4-5 .
subsequently penetrated with a dural hook and elevated. Kerrison rongeurs were used to remove the ligamentum flavum to complete the laminectomy. The resulting laminectomy was approximately 5 cm in length and 1 cm in width.
Procedural Details – Live Sheep After the development of the technique in cadavers, a group of six skeletally mature, female, RambouilletColumbian cross sheep underwent PiezoL2-3,4-5 (n = 12 laminectomy sites). A second group of 30 sheep underwent a three-level, non-contiguous dorsal laminectomy at L1 , L3 , and L5 (PiezoL1,3,5 ) (n = 90 laminectomy sites). All procedures performed were approved by the Institutional Animal Care and Use Committee (IACUC) – Colorado State University. Animals underwent laminectomy procedures as participants in an unrelated preclinical study evaluating anti-adhesion properties in selected biomaterials. All animals were musculoskeletally and neurologically normal prior to surgery. Procedures were performed by three boardcertified veterinary surgeons. Procaine penicillin G (22,000 units/kg, subcutaneous [SQ]) and two fentanyl patches (100 and 50 C
2015 Informa Healthcare USA, Inc.
mcg) were applied to all sheep 24 hr prior to surgery and maintained for three days. The auricular vein and artery were catheterized and anesthesia was induced using a combination of ketamine (3.3 mg/kg, intravenous [IV]) and diazepam (0.1 mg/kg, IV). Following anesthetic induction, the sheep were intubated with a cuffed endotracheal tube, placed in dorsal recumbency, and maintained on isoflurane (1.5%–3%) with 100% oxygen using positive pressure ventilation (20 cm H2 O) for the duration of the procedure. Atracurium (15 mg/kg) was administered IV intraoperatively to facilitate muscle dissection and retraction. The dorsal (posterior) surgical site was clipped and aseptically prepared from T11 to L6 . A midline incision was made into the skin and subcutaneous tissue from T13 -L6 using the cutting mode on a bipolar electrocautery unit. Periosteal elevators and electrocautery were used to elevate the fascia, thoracolumbalis and semispinalis, multifidi, and longissimus lumborum muscles from the dorsal spinous processes, and laminae and pedicles from the dorsal (posterior) aspect of L2 , L3 , L4 , and L5 for the PiezoL2-3,4-5 . The dorsal spinous processes were removed from L2 , L3 , L4 , and L5 using right-angled Liston–Key bone cutting forceps. An en bloc dorsal laminectomy was performed at L2 -L3 and a similar procedure at L4 -L5 extending between adjacent
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FIGURE 3 (a) En bloc removal of inner cortical shell at L4 of L4 -L5 PiezoL2-3,4-5 , preserving the ligamentum flavum. A similar cortical shell was subsequently removed at L5 . (b) Appearance of completed ovine PiezoL2-3,4-5 at L4 -L5 after removal of both cortical shells and ligamentum flavum. A similar non-contiguous PiezoL2-3,4-5 was performed at L2 -L3 . (c) Appearance of completed ovine PiezoL1,3,5 at L5 after removal of cortical shell and preservation of ligamentum flavum. A similar non-contiguous PiezoL2-3,4-5 was performed at L1 and L3 .
interarcuate spaces cranially and caudally and just axial to the articular facet joints bilaterally for the PiezoL2-3,4-5 (Figure 3). Similar procedures were performed for the PiezoL1,3,5 at L1 , L3 , and L5 (Figure 3); however, the ligamentum flavum was left intact cranially and caudally since each laminectomy site was restricted to a single vertebral lamina. The resulting PiezoL1,3,5 measured approximately 2 cm in length and 1 cm in width. Following dorsal PiezoL, the periosteum, dura mater, and nerves were visually inspected for injuries. If cerebrospinal fluid was noted following removal of the lamina, a tear in the dura mater was assumed. The thoracolumbar fascia, subcutaneous tissue, and skin were closed in a routine manner. Penetration of the periosteum and dura mater, if any, and operative time were recorded. Operative time was defined as the time from initiating surgery to discontinuation of gas anesthesia and recorded in 5-min intervals. All animals were administered procaine penicillin G (22,000 units/kg SQ) and phenylbutazone (4.4 mg/kg, postoperative) for three days following surgery, and fentanyl patches (100 and 50 mcg) remained in place during this time. Animals were monitored daily for two weeks following surgery for any signs of neurologic or musculoskeletal abnormalities.
RESULTS The cadaveric technique development of the ovine PiezoL was subjectively beneficial in the live sheep procedures. All surgeons found the PiezoL to be technically simple and intuitive with a rapid learning curve. R blade tip provided a clean, square The Piezosurgery cut that was easily repeatable in all sheep. The inner periosteal layer and the dura mater remained intact in all 12 PiezoL2-3,4-5 sites and all 90 sites undergoing PiezoL1,3,5 . Mean surgery time was 105 min (range: 75–165 min; median: 97.5) for PiezoL2-3,4-5 and 93 min (range 55–100 min; median: 67.5) for PiezoL1,3,5 .
Of the 36 animals, 35 had normal neurologic status throughout the two-week postoperative monitoring period (n = 99 laminectomies). One PiezoL1,3,5 animal was non-ambulatory paraparetic with voluntary and purposeful motor movement and intact deep pain perception in the pelvic limbs following surgery. This animal was euthanized with an overdose of pentobarbital sodium (88mg/kg) 48 hr after surgery according to the IACUC protocol due to the absence of response to medical treatment. On necropsy, the only noted finding was a mild spinal epidural hematoma (SEH) that may have contributed to paraparesis via compression of the spinal cord. The dura mater was intact and no blood was noted in the subarachnoid space.
DISCUSSION This report demonstrates that piezoelectric surgery is a feasible, safe, simple, and intuitive technique for performing an ovine dorsal laminectomy that can be used in the research setting. Subjectively, each of the operating surgeons found this technique to be much less demanding than conventional laminectomies and have since performed all experimental ovine laminectomies utilizing this method. As experience has been gained with this method, operative time has continued to improve progressively. The mean surgical time for the original two-level laminectomies (PiezoL2-3,4-5 ) was 105 min (range: 75–165 min; median: 97.5), but the surgical time for the first animal was twice as long as the surgical time for the final animal. The median surgical time of subsequent three-level laminectomies (PiezoL1,3,5 ) was 30 min less than the two-level laminectomies, which is reflective of growing surgeon experience with the technique. Some studies report increased operative time with piezoelectric surgery, while others saw no difference as compared with conventional methods [3, 13, 15]. In our laboratory, operative time in our first six PiezoL2-3,4-5 procedures was equivalent to that of previous conventional two-level dorsal laminectomies (n = 6) performed in sheep (mean surgical time Journal of Investigative Surgery
Piezoelectric Surgery – A Novel Technique for Laminectomy = 105 min [range: 90–135 min; median: 97.5] – unpublished data) in spite of our extensive experience with the conventional technique. No previous surgical time data are available within our laboratory for conventional three-level, non-contiguous laminectomy at L1 , L3 , and L5 for comparison with the PiezoL1,3,5 operative time. One of the 36 sheep was euthanized due to postoperative non-ambulatory paraparesis. Voluntary and purposeful motor movement of the limbs combined with intact deep pain perception suggests the likely recovery of ambulation. Nonetheless, in a research setting, humane euthanasia was the appropriate course of action from a standpoint of humane and research integrity. Upon necropsy, a small SEH was the only abnormality detected, and it can only be speculated that this was related to postoperative neurologic deficits. Spinal epidural hematoma is a well-known complication of spinal surgery in humans that is often asymptomatic. Studies have shown magnetic resonance imaging and computed tomography to have identified asymptomatic SEH in 33% to 100% of patients following lumbar disc or decompression surgery [16–19]. In contrast, clinically significant hematomas resulting in neurologic deficits are rare (0.1%–0.2%) [19]. Assuming that the SEH noted in our one sheep was responsible for the postoperative neurologic deficits, it remains unclear whether the SEH was directly related to the use of piezoelectric instrumentation in this animal. The source of hemorrhage could not be identified and there was no direct evidence to suggest that it was related to the use of the piezoelectric instrument. Benefits pertaining to neurologic surgery include the soft tissue sparing osteotomy and decreased heat production [9, 12, 14]. Another advantage of piezoelectric osseous surgery may be the improved bone healing, as piezoelectric surgery has been shown to cause less bone loss during the healing period in a canine model compared with conventional bur devices [20]. This may be of particular benefit in procedures where replacement of an osseous flap is desired. However, since the osteotomized bone is generally not replaced when performing a laminectomy, this benefit may not be applicable to this particular indication. Unfortunately, ex vivo data was not available in this study. Histopathological analysis may provide further understanding of potential advantages of piezoelectric osseous surgery in the dorsal laminectomy procedure described in this paper. Subjectively, the authors found that the PiezoL technique was intuitive and required less mental concentration than conventional laminectomy because the power burring was restricted to the outer cortex, cancellous bone, and only the superficial surface of the inner cortex. Conventional laminectomy technique requires power burring down to an almost “paper-thin” shell of inner cortex in order to utilize Kerrison rongeurs to expose the dura mater and spinal cord. The PiezoL technique does not require a “shell-like” inner cortex, C
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thus reducing the risk or exposing or damaging of the spinal cord when using the high speed air drill and bur. The authors do not recommend performing the laminectomy entirely with the PiezoL to avoid prolonged surgical time. Eggers et al. [2] reported that Piezoelectric cutting speed was slow when bone was more than 3 mm in thickness. Thus, if the entire procedure were to be performed utilizing piezoelectric technology, surgery time certainly would be much longer and less controlled. The PiezoL technique descibed here in normal animals is likely to be less challenging than laminectomy performed on animals or humans with spinal disease; however, a new surgical technique that allows consistent results in normal animals and subjectively decreases surgeon mental fatigue certainly warrants evaluation for clinical application. A prospective study evaluating clinically diseased patients comparing both PiezoL and conventional laminectomy techniques would be beneficial in further understanding the true benefits of the PiezoL in a clinical setting. Based on the authors’ experience from this study utilizing normal sheep, further evaluation of piezoelectric surgery in clinical patients is strongly recommended because of the potential benefits associated with this technology. Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.
REFERENCES [1] Vercellotti T, Pollack AS. A new bone surgery device: sinus grafting and periodontal surgery. Comp Cont Educ Dent. 2006;27(5):319–325. [2] Eggers G, Klein J, Blank J, et al.. Piezosurgery: an ultrasound device for cutting bone and its use and limitations in maxillofacial surgery. Brit J Oral Maxil Surg. 2004;42(5):451–453. [3] Goyal M, Marya K, Jhamb A, et al. Comparative evaluation of surgical outcome after removal of impacted mandibular third molars using a Piezotome or a conventional handpiece: a prospective study. Brit J Oral Maxil Surg. 2012;50:556–561. [4] Salami A, Mora R, Mora F, et al. Learning curve for Piezosurgery in well-trained otological surgeons. Otolaryngol Head Neck Surg. 2010;142(1):120–125. [5] Stubinger S, Kuttenberger J, Filippi A, et al. Intraoral piezosurgery: preliminary results of a new technique. J Oral Maxil Surg. 2005;63(9):1283–1287. [6] Crosetti E, Battiston B, Succo G. Piezosurgery in head and neck oncological and reconstructive surgery: personal experience on 127 cases. Acta Otorhinolaryngol Italica 2009;29(1):1–9. [7] Schaeren S, Jaquiery C, Heberer M, et al. Assessment of nerve damage using a novel ultrasonic device for bone cutting. J Oral Maxil Surg. 2008;66(3):593–596. [8] Vercellotti T, De Paoli S, Nevins M. The piezoelectric bony window osteotomy and sinus membrane elevation: introduction of a new technique for simplification of the sinus augmentation procedure. Int J Periodont Rest Dent. 2001;21(6):561–567.
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[9] Harder S, Wolfart S, Mehl C, et al. Performance of ultrasonic devices for bone surgery and associated intraosseous temperature development. Int J Oral Maxil Implants 2009;24(3):484–490. [10] Blus C, Szmukler-Moncler S. Atraumatic tooth extraction and immediate implant placement with Piezosurgery: evaluation of 40 sites after at least 1 year of loading. Int J Periodont Rest Dent. 2010;30(4):355–363. [11] Schaller BJ, Gruber R, Merten HA, et al. Piezoelectric bone surgery: a revolutionary technique for minimally invasive surgery in cranial base and spinal surgery? Tech Note Neurosurg. 2005;57(4 Suppl):E410; Discussion E. [12] Salami A, Mora R, Dellepiane M, et al. Piezosurgery versus microdrill in intact canal wall mastoidectomy. Eur Arch Otorhinolaryngol. 2010;267(11):1705–1711. [13] Landes CA, Stubinger S, Rieger J, et al. Critical evaluation of piezoelectric osteotomy in orthognathic surgery: operative technique, blood loss, time requirement, nerve and vessel integrity. J Oral Maxil Surg. 2008;66(4):657–674. [14] Pavlikova G, Foltan R, Burian M, et al. Piezosurgery prevents brain tissue damage: an experimental study on a new rat model. Int J Oral Maxil Surg. 2011;40(8):840–844.
[15] Barone A, Santini S, Marconcini S, et al. Osteotomy and membrane elevation during the maxillary sinus augmentation procedure. A comparative study: piezoelectric device vs. conventional rotative instruments. Clin Oral Impl Res. 2008;19(5):511–515. [16] Awad JN, Kebaish KM, Donigan J, et al. Analysis of the risk factors for the development of post-operative spinal epidural hematoma. J Bone Joint Surg BR. 2005;87:1248– 1252. [17] Kabaish KM, Awad JN. Spinal epidural hematoma causing acute cauda equina syndrome. Neurosurg Focus 2004; 16:e1 [18] U HS, Wilson CB. Postoperative epidural hematoma as a complication of anterior cervical discectomy. Report of three cases. J Neurosurg. 1978;49:288–291. [19] Kaner T, Sasani M, Okenoglu T, et al. Postoperative spinal epidural hematoma resutling in cauda equina syndrome: a case report and review of the literature. CASES J. 2009;2:8584 [20] Vercellotti T, Nevins ML, Kim DM, et al. Osseous response following resective therapy with piezosurgery. Int J Periodont Rest Dent. 2005;25(6):543–549.
Journal of Investigative Surgery
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SURGICAL TECHNIQUE
Piezoelectric Surgery – A Novel Technique for Laminectomy Felix M. Duerr, DVM, MS, Diplomate ACVS-SA, Diplomate ECVS, Diplomate ˜ an,1 Ross H. Palmer, ACVSMR,1 Howard B. Seim, III, DVM, Diplomate ACVS,2 Ana L. Bascun´ DVM, MS, Diplomate ACVS,2 Jeremiah Easley, DVM, Diplomate ACVS 2 1
Department of Clinical Sciences, Colorado State University Veterinary Teaching Hospital, 300 West Drake Road, Fort Collins, Colorado, USA 2 Preclinical Surgical Research Laboratory, Department of Clinical Sciences, Colorado State University, 300 W Drake Road, Fort Collins, Colorado, USA
ABSTRACT Objective: Piezoelectric surgery is a novel technology that allows for the osteotomy of mineralized tissue with less risk of damaging underlying soft tissue structures. This selective cutting increases the safety of osteotomies performed in close vicinity to delicate structures such as dura mater, blood vessels, and neural tissue. This study aimed to develop and describe the technique of piezoelectric surgery for dorsal laminectomy and to assess its clinical safety in normal sheep. Methods: A piezoelectric, dorsal laminectomy technique was developed using ovine cadavers. Following technique development, six live sheep underwent a piezoelectric (n = 6) two-level dorsal laminectomy at L2 -L3 and L4 -L5 (PiezoL2-3,4-5 ), and another 30 live sheep underwent a three-level laminectomy at L1 , L3 , and L5 (PiezoL1,3,5 ) for a total of 102 laminectomy sites. Surgery time and postoperative complications were recorded. Results: Dorsal laminectomy was safely and accurately performed in 35/36 study sheep using a Piezoelectric surgical instrument. No dural tears were noted in any animal. Non-ambulatory paraparesis in one study sheep (PiezoL1,3,5 ) led to euthanasia at 48 hr and only mild epidural hematoma was noted on necropsy. No other major postoperative complications were observed in any of the animals. Subjectively, PiezoL was easy to perform and with a rapid learning curve. Mean surgery time was 105 min (range: 75–165 min; median: 97.5) for PiezoL2-3,4-5 and 93 minutes (range 55–100 min; median: 67.5) for PiezoL1,3,5 . Conclusions: Based on our study, PiezoL is considered a safe and viable technique for performing ovine dorsal laminectomy in the preclinical research setting. R ; osteotomy; ovine; neurosurgery Keywords: laminectomy; Piezosurgery
ric (60–210 μm), linear, and of variable frequencies (approximately 25–30 kHz) [4, 5, 7, 8]. Nerves and blood vessels are spared because these structures can oscillate at the same frequency as the piezoelectric device [8, 9]. In spinal surgery, osteotomies and drilling of bone are frequently performed in close vicinity of neural tissues and blood vessels. Rotary cutting instruments are disadvantageous for this purpose because of the associated heat production and the possibility to severely injure underlying soft tissue structures. Since piezoelectric surgery reduces heat production and does not require a rotary high speed movement in
INTRODUCTION Piezoelectric surgery utilizes microvibrations of ultrasonic frequency to selectively cut bone without significant damage to underlying soft tissue structures [1–4]. These vibrations are generated by the deformation of piezoelectric crystals or ceramics exposed to an electric field (called “indirect piezo effect”) [5]. Deformation of piezoelectric materials results in the oscillations of ultrasonic frequencies, which are then amplified and transferred onto the instrument tip [6]. Application of this tip to mineralized tissue produces a mechanical cutting effect. Vibrations are micrometReceived 9 June 2014; accepted 23 October 2014.
Address correspondence to Jeremiah Easley, DVM, Diplomate ACVS , Preclinical Surgical Research Laboratory, Department of Clinical Sciences, Colorado State University, 300 W Drake Road, Fort Collins, CO 80523, USA. E-mail: [email protected]
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close vicinity of the spinal cord, it provides a safer alternative for such procedures [7, 9]. This novel technology is frequently used in dental/oral surgery in human medicine, and has been shown to be beneficial by multiple investigators [2–4, 7, 9–11]. Piezoelectric surgery resulted in less pain and swelling in people undergoing molar extraction compared with conventional surgery performed with a rotary handpiece device [3]. Duration of hospital stay was significantly decreased in patients undergoing mastoidectomy when piezoelectric surgery was used [12]. In patients undergoing various orthognathic procedures, piezoelectric surgery was associated with reduced blood loss and nerve injury compared with conventional techniques [13]. The effects of piezoelectric surgery on nervous tissue have been investigated in an experimental study in rats undergoing craniotomy with either piezoelectric surgery or a conventional drill. Brain tissue damage (based on MRI and histopathologic evaluation) was significantly decreased on the side on which piezoelectric surgery was performed [14]. Schaeren et al. [7] showed that even sudden contact with a force of 3 N (to simulate accidental “slipping” during surgery) does not transect the sciatic nerve when piezoelectric surgery is performed. In spite of obvious benefits, reports of piezoelectric surgery for spinal surgery are rare, even in the human field where piezoelectric surgery is well established [11, 14]. The aim of this study is to develop and describe the technique for piezoelectric laminectomy and to report the outcome of dorsal piezoelectric laminectomies in normal sheep.
MATERIALS AND METHODS Prior to in vivo evaluation of PiezoL, the piezoelectrical surgical device was tested and procedural details developed utilizing ovine cadavers. Cadavers utilized for this development phase were euthanized for reasons unrelated to the study. The spinal muscles were removed to provide access to the lumbar vertebrae.
Technique Description of the PiezoL Ovine Model The dorsal spinous processes were removed from L2 , L3 , L4 , and L5 with bone cutting forceps for twolevel, non-contiguous dorsal laminectomy at L2 -L3 and L4 -L5 (PiezoL2-3,4-5 ). A compressed air drill and bur were used to remove the dorsal (outer) cortex, cancellous bone, and a thin portion of the inner cortical R blade tip EX1 layer of the lamina. The Piezosurgery R (Piezosurgery , Piezosurgery Incorporated, Columbus, Ohio, USA; Figure 1) was then used to gently penetrate the thin inner cortical layer at a single corner (Figure 2). The penetration site was created by gently sliding the blade tip back and forth ∼1–2 mm across the bony surface until a distinct penetration of the inner cortical layer was felt. After penetrating R blade tip, the spinal canal with the Piezosurgery R the edge of the Piezosurgery blade was used to cut the lamina on all four sides by pulling the blade tip through the full thickness of the thin inner cortical layer. The ligamentum flavum was preserved. When inner periosteum was spared during osteotomy, it was
R FIGURE 1 (a) Piezosurgery device, (b) blade tip EX1 used for the laminectomies.
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R technique for PiezoL2-3,4-5 (ovine). (a) Removal of the FIGURE 2 Cadaveric demonstration of the Piezosurgery dorsal spinous processes with right-angled bone forceps and rongeurs, (b) outer cortical layer and cancellous bone are removed with conventional high speed bur, (c) laminectomy site exposed to the inner cortical layer, (d) use of the R Piezosurgery blade tip to penetrate the inner cortical layer, (e) creating a laminectomy “window” by drawing blade tip from the inner cortical penetration site across the margins of laminectomy site, (f) and (g) elevation of the inner R cortical layer with the Piezosurgery blade tip, (h) partially completed elevation, and (i) completed PiezoL2-3,4-5 .
subsequently penetrated with a dural hook and elevated. Kerrison rongeurs were used to remove the ligamentum flavum to complete the laminectomy. The resulting laminectomy was approximately 5 cm in length and 1 cm in width.
Procedural Details – Live Sheep After the development of the technique in cadavers, a group of six skeletally mature, female, RambouilletColumbian cross sheep underwent PiezoL2-3,4-5 (n = 12 laminectomy sites). A second group of 30 sheep underwent a three-level, non-contiguous dorsal laminectomy at L1 , L3 , and L5 (PiezoL1,3,5 ) (n = 90 laminectomy sites). All procedures performed were approved by the Institutional Animal Care and Use Committee (IACUC) – Colorado State University. Animals underwent laminectomy procedures as participants in an unrelated preclinical study evaluating anti-adhesion properties in selected biomaterials. All animals were musculoskeletally and neurologically normal prior to surgery. Procedures were performed by three boardcertified veterinary surgeons. Procaine penicillin G (22,000 units/kg, subcutaneous [SQ]) and two fentanyl patches (100 and 50 C
2015 Informa Healthcare USA, Inc.
mcg) were applied to all sheep 24 hr prior to surgery and maintained for three days. The auricular vein and artery were catheterized and anesthesia was induced using a combination of ketamine (3.3 mg/kg, intravenous [IV]) and diazepam (0.1 mg/kg, IV). Following anesthetic induction, the sheep were intubated with a cuffed endotracheal tube, placed in dorsal recumbency, and maintained on isoflurane (1.5%–3%) with 100% oxygen using positive pressure ventilation (20 cm H2 O) for the duration of the procedure. Atracurium (15 mg/kg) was administered IV intraoperatively to facilitate muscle dissection and retraction. The dorsal (posterior) surgical site was clipped and aseptically prepared from T11 to L6 . A midline incision was made into the skin and subcutaneous tissue from T13 -L6 using the cutting mode on a bipolar electrocautery unit. Periosteal elevators and electrocautery were used to elevate the fascia, thoracolumbalis and semispinalis, multifidi, and longissimus lumborum muscles from the dorsal spinous processes, and laminae and pedicles from the dorsal (posterior) aspect of L2 , L3 , L4 , and L5 for the PiezoL2-3,4-5 . The dorsal spinous processes were removed from L2 , L3 , L4 , and L5 using right-angled Liston–Key bone cutting forceps. An en bloc dorsal laminectomy was performed at L2 -L3 and a similar procedure at L4 -L5 extending between adjacent
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FIGURE 3 (a) En bloc removal of inner cortical shell at L4 of L4 -L5 PiezoL2-3,4-5 , preserving the ligamentum flavum. A similar cortical shell was subsequently removed at L5 . (b) Appearance of completed ovine PiezoL2-3,4-5 at L4 -L5 after removal of both cortical shells and ligamentum flavum. A similar non-contiguous PiezoL2-3,4-5 was performed at L2 -L3 . (c) Appearance of completed ovine PiezoL1,3,5 at L5 after removal of cortical shell and preservation of ligamentum flavum. A similar non-contiguous PiezoL2-3,4-5 was performed at L1 and L3 .
interarcuate spaces cranially and caudally and just axial to the articular facet joints bilaterally for the PiezoL2-3,4-5 (Figure 3). Similar procedures were performed for the PiezoL1,3,5 at L1 , L3 , and L5 (Figure 3); however, the ligamentum flavum was left intact cranially and caudally since each laminectomy site was restricted to a single vertebral lamina. The resulting PiezoL1,3,5 measured approximately 2 cm in length and 1 cm in width. Following dorsal PiezoL, the periosteum, dura mater, and nerves were visually inspected for injuries. If cerebrospinal fluid was noted following removal of the lamina, a tear in the dura mater was assumed. The thoracolumbar fascia, subcutaneous tissue, and skin were closed in a routine manner. Penetration of the periosteum and dura mater, if any, and operative time were recorded. Operative time was defined as the time from initiating surgery to discontinuation of gas anesthesia and recorded in 5-min intervals. All animals were administered procaine penicillin G (22,000 units/kg SQ) and phenylbutazone (4.4 mg/kg, postoperative) for three days following surgery, and fentanyl patches (100 and 50 mcg) remained in place during this time. Animals were monitored daily for two weeks following surgery for any signs of neurologic or musculoskeletal abnormalities.
RESULTS The cadaveric technique development of the ovine PiezoL was subjectively beneficial in the live sheep procedures. All surgeons found the PiezoL to be technically simple and intuitive with a rapid learning curve. R blade tip provided a clean, square The Piezosurgery cut that was easily repeatable in all sheep. The inner periosteal layer and the dura mater remained intact in all 12 PiezoL2-3,4-5 sites and all 90 sites undergoing PiezoL1,3,5 . Mean surgery time was 105 min (range: 75–165 min; median: 97.5) for PiezoL2-3,4-5 and 93 min (range 55–100 min; median: 67.5) for PiezoL1,3,5 .
Of the 36 animals, 35 had normal neurologic status throughout the two-week postoperative monitoring period (n = 99 laminectomies). One PiezoL1,3,5 animal was non-ambulatory paraparetic with voluntary and purposeful motor movement and intact deep pain perception in the pelvic limbs following surgery. This animal was euthanized with an overdose of pentobarbital sodium (88mg/kg) 48 hr after surgery according to the IACUC protocol due to the absence of response to medical treatment. On necropsy, the only noted finding was a mild spinal epidural hematoma (SEH) that may have contributed to paraparesis via compression of the spinal cord. The dura mater was intact and no blood was noted in the subarachnoid space.
DISCUSSION This report demonstrates that piezoelectric surgery is a feasible, safe, simple, and intuitive technique for performing an ovine dorsal laminectomy that can be used in the research setting. Subjectively, each of the operating surgeons found this technique to be much less demanding than conventional laminectomies and have since performed all experimental ovine laminectomies utilizing this method. As experience has been gained with this method, operative time has continued to improve progressively. The mean surgical time for the original two-level laminectomies (PiezoL2-3,4-5 ) was 105 min (range: 75–165 min; median: 97.5), but the surgical time for the first animal was twice as long as the surgical time for the final animal. The median surgical time of subsequent three-level laminectomies (PiezoL1,3,5 ) was 30 min less than the two-level laminectomies, which is reflective of growing surgeon experience with the technique. Some studies report increased operative time with piezoelectric surgery, while others saw no difference as compared with conventional methods [3, 13, 15]. In our laboratory, operative time in our first six PiezoL2-3,4-5 procedures was equivalent to that of previous conventional two-level dorsal laminectomies (n = 6) performed in sheep (mean surgical time Journal of Investigative Surgery
Piezoelectric Surgery – A Novel Technique for Laminectomy = 105 min [range: 90–135 min; median: 97.5] – unpublished data) in spite of our extensive experience with the conventional technique. No previous surgical time data are available within our laboratory for conventional three-level, non-contiguous laminectomy at L1 , L3 , and L5 for comparison with the PiezoL1,3,5 operative time. One of the 36 sheep was euthanized due to postoperative non-ambulatory paraparesis. Voluntary and purposeful motor movement of the limbs combined with intact deep pain perception suggests the likely recovery of ambulation. Nonetheless, in a research setting, humane euthanasia was the appropriate course of action from a standpoint of humane and research integrity. Upon necropsy, a small SEH was the only abnormality detected, and it can only be speculated that this was related to postoperative neurologic deficits. Spinal epidural hematoma is a well-known complication of spinal surgery in humans that is often asymptomatic. Studies have shown magnetic resonance imaging and computed tomography to have identified asymptomatic SEH in 33% to 100% of patients following lumbar disc or decompression surgery [16–19]. In contrast, clinically significant hematomas resulting in neurologic deficits are rare (0.1%–0.2%) [19]. Assuming that the SEH noted in our one sheep was responsible for the postoperative neurologic deficits, it remains unclear whether the SEH was directly related to the use of piezoelectric instrumentation in this animal. The source of hemorrhage could not be identified and there was no direct evidence to suggest that it was related to the use of the piezoelectric instrument. Benefits pertaining to neurologic surgery include the soft tissue sparing osteotomy and decreased heat production [9, 12, 14]. Another advantage of piezoelectric osseous surgery may be the improved bone healing, as piezoelectric surgery has been shown to cause less bone loss during the healing period in a canine model compared with conventional bur devices [20]. This may be of particular benefit in procedures where replacement of an osseous flap is desired. However, since the osteotomized bone is generally not replaced when performing a laminectomy, this benefit may not be applicable to this particular indication. Unfortunately, ex vivo data was not available in this study. Histopathological analysis may provide further understanding of potential advantages of piezoelectric osseous surgery in the dorsal laminectomy procedure described in this paper. Subjectively, the authors found that the PiezoL technique was intuitive and required less mental concentration than conventional laminectomy because the power burring was restricted to the outer cortex, cancellous bone, and only the superficial surface of the inner cortex. Conventional laminectomy technique requires power burring down to an almost “paper-thin” shell of inner cortex in order to utilize Kerrison rongeurs to expose the dura mater and spinal cord. The PiezoL technique does not require a “shell-like” inner cortex, C
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thus reducing the risk or exposing or damaging of the spinal cord when using the high speed air drill and bur. The authors do not recommend performing the laminectomy entirely with the PiezoL to avoid prolonged surgical time. Eggers et al. [2] reported that Piezoelectric cutting speed was slow when bone was more than 3 mm in thickness. Thus, if the entire procedure were to be performed utilizing piezoelectric technology, surgery time certainly would be much longer and less controlled. The PiezoL technique descibed here in normal animals is likely to be less challenging than laminectomy performed on animals or humans with spinal disease; however, a new surgical technique that allows consistent results in normal animals and subjectively decreases surgeon mental fatigue certainly warrants evaluation for clinical application. A prospective study evaluating clinically diseased patients comparing both PiezoL and conventional laminectomy techniques would be beneficial in further understanding the true benefits of the PiezoL in a clinical setting. Based on the authors’ experience from this study utilizing normal sheep, further evaluation of piezoelectric surgery in clinical patients is strongly recommended because of the potential benefits associated with this technology. Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.
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