Original Article

The Reliability of the Ultrasonic Bone Scalpel in Cervical Spondylotic Myelopathy: A Comparative Study of 46 Patients

Mehmet Resid Onen, Evren Yuvruk, Sinem Akay, Sait Naderi

- BACKGROUND: In patients with cervical spondylotic myelopathy (CSM), laminectomy is usually performed with a Kerrison rongeur or a high speed drill (HSD).The HSD, which is most often selected for laminectomy, may cause complications such as duratomy, thermal and mechanical neural injuries. With an ultrasonic bone scalpel (UBS), a less traumatic laminectomy can be performed in a shorter time. The aim of this study was to compare the results of laminectomies using HSD and UBS.

- METHODS: Evaluation was made in 46 patients who were operated on for CSM. Cervical laminectomy was performed on 23 patients using the UBS (group I) and to 23 using the HSD (group II). A comparison was made of the 2 groups in respect of demographic characteristics, lam- inectomy levels, mean laminectomy duration, bleeding rates, and surgical complications.

- RESULTS: In group I, the mean laminectomy time was 2.2 ! 0.4 min/level, mean blood loss was 180 mL, hospital- ization was 3.0 ! 0.0 days, and C5 radiculopathy was seen in 1 patient. In group II, the mean laminectomy time was 7.4 ! 2.6 min/level, mean blood loss was 380 mL, hospital- ization was 3.7 ! 1.3 days, C5 radiculopathy was seen in 1 patient and dura injuries in 3 patients. The recovery rate was determined as 47.6% in group I and 48.8% in group II.

- CONCLUSIONS: For patients with CSM, laminectomy using the UBS provides a safe, rapid, and effective decompression with a lesser blood loss. The low rate of complications lessens the postoperative morbidity rates and shortens hospital stay.

Key words

- Cervical spondylotic myelopathy - High speed drill
- Laminectomy
- Ultrasound bone scalpel

Abbreviations and Acronyms

CSM: Cervical spondylotic myelopathy HSD: High speed drill
JOA: Japanese Orthopedic Association UBS: Ultrasonic bone scalpel

INTRODUCTION

ervical myelopathy is the loss of motor and sensory functions associated with damage occurring in the spinal cord. It generally occurs as an acute or chronic process

associated with degenerative pathologies. Many surgical treat- ments can be performed with anterior or posterior approaches. One of the treatment choices in cervical spondylotic myelopathy (CSM) is posterior laminectomy. The most frequently used in- struments for laminectomy in the posterior approach are the high speed drill (HSD) and the Kerrison rongeur. One of the most commonly observed complications associated with these 2 in- struments is dura injury.1 In patients with more narrowing in the diameter of the spinal canal, dura injury from laminectomy may be inevitable. Effective and rapid decompression can be made with the use of HSD, although several complications may be seen such as dura injury, bleeding, thermal and neurological damage, and insufficient decompression.2,3 Dura injury may lead to serious complications such as cerebrospinal fluid fistula, menin- gitis, lengthy hospitalization stay, arachnoiditis, spinal epidural abscess, pseudomeningocele, subdural higroma, or pneumocephaly.1,4,5

These potential risks associated with HSD have led to the devel- opment of new systems for safe laminectomy. Ultrasonic bone scalpel (UBS) is an instrument for bone exposure, which has been developed in recent years.6 As soft tissue is not injured while cutting bone tissue with ultrasound, it is used in spinal surgery. The aim of this study was to compare the results of laminectomies performed with HSD or UBS in patients diagnosed with CSM.

METHODS

A retrospective evaluation was made of 46 patients who underwent surgery for CSM at a single center between 2010 and 2014. Approval for the study was granted by the Local Ethics Committee of the training hospital where the surgery was performed. All patients with

Department of Neurosurgery, Umraniye Teaching and Research, State Hospital, Istanbul, Turkey

To whom correspondence should be addressed: Mehmet Resid Onen, M.D. [E-mail: mresid@gmail.com]

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MEHMET RESID ONEN ET AL. THE ULTRASONIC BONE SCALPEL IN CERVICAL SPONDYLOTIC MYELOPATHY

Figure1. Laminectomytechniqueusingultrasoundbonescalpel(A)andhighspeeddrill(B).(CopyrightNurettinERKAN and Mehmet Resid ONEN.)

CSM were operated on consecutively. Of the 46 patients, lam- inectomy was performed using UBS on 23 (group I) and using HSD on 23 patients (group II). Posterior cervical stabilization was then applied to all patients with lateral mass screws. In addition to the demographic characteristics (age, gender) of the patients, statistical comparison of preoperative and postoperative Japanese Orthopedic Association (JOA) scores was made of the 2 groups, laminectomy levels, mean laminectomy times, blood loss, and complications.

Laminectomy times were calculated according to the data ob- tained from the neuromonitorization records at the beginning and end of the laminectomy. By dividing the total time spent on laminectomy by the number of laminectomies, the laminectomy time per level was obtained.

Clinical recovery of the patients was calculated according to the Hirabayashi formula.7

Recovery rate 1⁄4 f1⁄2Postop JOA $ Preop JOA=1⁄217 $ Preop JOAg & 100

All patients were evaluated with preoperative and postoperative cervical computed tomography and neutral and dynamic (flexion- extension) 1.5 Tesla cervical magnetic resonance imaging.

Surgical Technique

At the level to which laminectomy was to be performed, the attachment site with the lateral mass on both sides of the lamina

and the lateral cervical groove were first cut superficially then deeply with the UBS. The UBS cuts the bone with its own power without exerting any force on the bone and after passing through the internal cortex, the softness of the dura is felt and the cutting process is halted. After cutting both sides of the laminae, the most cranial and most caudal soft tissues were removed and all the laminae were removed singly or as a whole (Figure 1).

In the HSD group, marks were done on the lamina with a cauterizer before drilling. Then with a 2- or 3-mm round drill bit, the lamina was thinned. When the internal cortex was neared, a no. 2 diamond bit was used to thin the internal cortex. The thinned internal cortex was then raised with a fine hook. After opening the laminar grooves on both sides, the soft tissue was removed and then the laminae were removed.

All laminectomies were performed by surgeons with similar surgical ability.

Statistical Analysis

Data were expressed as mean ! standard deviation calculated with Microsoft Excel. Using SPSS 16.0 software the results of both groups were compared with the t-test. A value of P < 0.05 was accepted as statistically significant.

RESULTS

The UBS group of 23 patients (5 women and 18 men) had a mean age of 61 years (range, 41e78 years). The HSD group of 23 patients

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MEHMET RESID ONEN ET AL. THE ULTRASONIC BONE SCALPEL IN CERVICAL SPONDYLOTIC MYELOPATHY

Table 1. Demografic and Clinic Information of our 46 Patient

Parameters Group 1 (UBS group) Group 2 (HSD group)

Gender (M/F) 23 (5 F; 18 M) 23 (7 F; 16 M)

Mean age (years) 61 (range, 41e78) 62.4 (range, 49e74)

Preoperative JOA score* 12.8 ! 4.3 12.4 ! 2.8

Postoperative JOA score* 14.8 ! 2.6 14.5 ! 3.2

Recovery rate* 47.6% 48.8%

UBS, ultrasound bone scalpel; HSD, high speed drill; JOA, Japanese Orthopedic Association.

*P > 0.05.

Table 2. Perioperative and Postoperative Outcome of the Surgeries Using 2 Different Surgical Tools

Group 1 (UBS group)

Group 2 (HSD group)

No. of laminectomies 78 74

Duration of laminectomy* 2.2 ! 0.4 min/level 7.4 ! 2.6 min/level

Duration of hospitalization* 3.0 ! 0.0 days 3.7 ! 1.3 days

Dural tears* None 3 (13.0%)

Bleeding* 180 mL (range, 380 mL (range, 140e250 mL) 280e450 mL)

Temporary C5 palsy 1 1

UBS, ultrasound bone scalpel; HSD, high speed drill. *P < 0.05.

(7 women and 16 men) had a mean age of 62.4 years (range, 49e74 years). The mean preoperative JOA score was 12.8 ! 4.3 in the UBS group and 12.4 ! 2.8 in the HSD group (Table 1).

In group I, laminectomy was performed at 78 levels using the UBS and in group II, laminectomy was performed at 74 levels using the HSD. In group I, the mean laminectomy time was 2.2 ! 0.4 min/level, mean blood loss was 180 mL (range, 140e250 mL), hospitalization was 3.0 ! 0.0 days, and C5 radiculopathy was seen in 1 patient. In group II, the mean laminectomy time was 7.4 ! 2.6 min/level, mean blood loss was 380 mL (range, 280e450 mL), hospitalization was 3.7 ! 1.3 days, and C5 radiculopathy was seen in 1 patient and dura injuries in 3 patients (13.0%) (Table 2).

DISCUSSION

With CSM, sufficient decompression can be applied with anterior or posterior surgery. Several factors affect the choice of surgical approach. Posterior decompression is an approach selected pri- marily in multilevel cervical stenosis and ligamentum flavum hy- pertrophy.1,5,8,9 Laminectomy surgery can be performed with different techniques and instruments.10,11 Classic cervical lam- inectomy is performed with a Kerrison rongeur. It is known that with this method the spinal cord is sometimes traumatized, leading to spinal cord injury.4,8 Therefore, with the increased use of HSD in the past 2e3 decades, laminectomy has been mainly applied with HSD. Laminectomies made on both sides and along the lateral groove with HSD were more dominant and the risk of neural damage on the midline decreased. However, it has been reported that there could be thermal or indirect neural injury associated with HSD due to the vibrations or direct neural injury as a result of drill slippage or uncontrolled use.2,3 Due to the po- tential complications of HSD, UBS came into use.

UBS is an instrument that was developed to cut bone with sound waves. It was designed for use in oral and maxillofacial surgery, then with further development, it was able to be used in surgeries requiring the cutting of all bones.12 With ultrasonic blades (0.5- to 1.0-mm wide, 10- to 20-mm long), and L-shaped microdissection tips, bone can be cut without soft tissue damage and with minimal bone loss.13 Bone cutting is applied at a high frequency of 22,500 longitudinal vibration movements of the ultrasonic blade. As this process creates a serious thermal effect, the system is continuously cooled with water. The level of water

and ultrasonic vibration in the system can be adjusted. Although there is a cutting effect on bony structures, there is no direct cutting or splitting effect on soft tissue, such as the dura and ligamentum flavum, because the UBS tips are not sharp. Furthermore, when the UBS tips come into contact with osseous structures, they do not bend, deform, or deviate. As a result the target tissue absorbs a large portion of the instrument’s energy and is subsequently broken through, at the point of contact. In contrast, the soft tissue moves away, deforms and vibrates when in contact with the bone scalpel probes, yet maintaining its structural integrity and viability. Due to its elastic properties, the soft tissue can generally withstand exposure to the ultrasonic energy resulting from incidental, instrument-to-tissue contact, without any adverse effects.

The risk of damage to the dura or vascular structures may occur with mechanical pressure associated with its incorrect use rather than as a direct effect of vibration. There is no risk of slipping to the sides out of control with UBS as there is with HSD.

We currently use UBS for cervical laminectomy in all patients with CSM; cervical and thoracic hemi or total laminectomies in all patients with intradural tumor; and some patients with lumbar spinal stenosis.

The use of UBS can be extended to some parts of corpectomies, resection of osteophytes, and ossification of the posterior longi- tudinal ligament. The high temperature created on the surface where HSD is used may result in thermal damage. To reduce the heating effect, cooling is applied with an injector or similar sys- tem. In a study by Sasaki et al,14 the investigators concluded that injector or similar cooling systems were not very effective in reducing the thermal effect. It was reported that a spray system directly on to the drill tip as used in some drill systems, was more effective. In UBS, a water system is used that directly cools the ultrasonic blade. In the event of the ultrasonic blade overheating due to long periods of use or inadequate water level, the system issues a warning and the process is halted. Burns seen on the bone surface associated with the thermal effect in HSD. They are not seen with the UBS. In the current case series, no neurological deficit was seen to develop as a result of thermal injury during cutting. In both groups, only temporary C5 paraesthesia was seen, which was concluded to be

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MEHMET RESID ONEN ET AL. THE ULTRASONIC BONE SCALPEL IN CERVICAL SPONDYLOTIC MYELOPATHY

Figure 2. A 64-year old man with cervical spondylotic myelopathy underwent a four-levels laminectomy with an ultrasonic bone scalpel. (A) Preoperative T2-weighted sagittal magnetic resonance image. (B) Postoperative T2-weighted sagittal magnetic resonance image. (C, D) Postoperative computed tomography images.

Figure 3. A 68-year old man with cervical spondylotic myelopathy underwent a four-levels laminectomy with a high speed drill. (A) Preoperative T2-weighted sagittal magnetic resonance image. (B) Postoperative T2-weighted sagittal magnetic resonance image. (C, D) Postoperative computed tomography axial images.

a secondary effect of laminectomy rather than the result of thermal injury.

With the UBS, a straight-bordered incision line, thinner than 1 mm, is formed (Figure 1). Compared with HSD that there is less bone loss in UBS, thus providing a great advantage in surgeries that require remodeling, as in pediatric cases and in maxillofacial surgery.15,16 In cases of laminoplasty, greater ease is provided in the placement of the lamina. In patients where fusion is applied with laminectomy, as in our patients, sufficient bone can be provided for autogenous graft by reducing bone loss to a minimum. At the same time, the use of a cutting tip offers the possibility of cutting the bone to the desired shape.

In the present study, an evaluation was made of 46 patients operated on with a posteror approach for CSM. In half of these patients, laminectomy was performed using HSD and in the other half patients laminectomy was performed using UBS (Figures 2 and 3). A comparison was made of JOA levels, mean laminectomy times, blood loss, and complications in all the patients. In the evaluation of clinical recovery, no significant difference was determined between the groups in terms of the

preoperative and postoperative JOA levels (P > 0.05). However, a statistically significant difference was determined in laminectomy times, bleeding rates, complications, and postoperative hospitalization days. The mean laminectomy time was 2.2 ! 0.4 min/level in the UBS cases and 7.9 ! 2.6 min/ level in the HSD cases (P < 0.05). The duration of postoperative hospitalization was 3.0 ! 0.0 days for the UBS group and 3.7 ! 1.3 days for the HSD group (P < 0.05). These data show that UBS provided a significant time advantage in laminectomy and postoperative hospitalization.

In a study by Hu et al17 of UBS used on 128 cases of spinal pathology for different indications, UBS-related dura injury was reported in 2 patients. It was also reported in that study that the mean operating time and blood loss had been reduced with UBS, as was seen in our present study.

Dura injury has been reported at rates of 1.9%e6% in cases undergoing laminectomy or laminoplasty using HSD in posterior cervical approaches for CSM or other pathologies.6,11,18e22 Blood loss has been reported at 250e380 mL in cases of laminectomy performed for CSM. In a study by Bydon et al,23 pediatric cases of

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MEHMET RESID ONEN ET AL. THE ULTRASONIC BONE SCALPEL IN CERVICAL SPONDYLOTIC MYELOPATHY

achondroplasia operated on with UBS and HSD were compared and dura injury was reported in 9 patients (45%) where HSD had been used. The risk of dura injury with HSD is increased in cases of complex spinal stenosis. In another study, including posterior laminectomy cases in the same study group of 337 patients, duratomy was seen at 5.7% with HSD and at 3.6% with UBS.23

In the present study, comparing perioperative bleeding and complications, mean blood loss was measured at 180 mL (range, 140e250 mL) in the UBS group and at 380 mL (range, 280e450 mL) in the HSD group (P < 0.05). Dura injury was seen in 3 pa- tients (13.0%) of the HSD group and C5 paralysis developed in 1 patient from each group.

In both groups, the desired radiologic decompression and ex- pected clinical recovery was obtained. In the postoperative period, the findings of C5 radiculopathy completely recovered by the second month of follow-up. A second posterior cervical approach was not performed to any of the cases for insufficient decom- pression or for any other reason.

Another advantage of the UBS is its cost effectiveness,24,25 which is a consequence of reduced operative time, decreased blood loss, reduced incidental durotomy rate, and reduced overall operation room time.

The present study has some limitations. It compared diamond drill bit and USB. However, it is known that many different drill tips (diamond bit and regular fluted tip) are used for laminectomy. Each has their advantages and disadvantages. Although the

diamond bit seems to be safer, it greatly extends surgical time. Therefore, many surgeons prefer to use the fluted tip, which may shorten the surgical time, although there is a higher risk of dural injury. Both tips have risk of heat generation. A comparison of different drill tips and UBS will be the subject of another trial.

Another limitation is the lack of focus on the effect of these tools on spine fusion. In the present study, similar stabilization and fusion techniques were used in both groups. Nevertheless, because of the lack of long-term follow-up for assessment of spine fusion, the results of the fusion rates could not be reported.

CONCLUSION

A posterior cervical approach in cases of CSM is a frequently selected. To increase success rates, different forms of treatment have been attempted to maintain patient satisfaction at the highest level. UBS, which was developed for bone excision, is a rapid and safe instrument in many surgeries requiring bone excision, including laminectomy. Compared with the high-speed drill and Kerrison rongeur, this instrument shortens operating time by a significant degree, as well as reducing blood loss and the likeli- hood of dura and neural injury. Decreased complication rates not only increase patient satisfaction, but also shorten hospitalization. The most important obstruction to routine use of UBS is its high cost. If costs can be decreased, UBS could be a routine surgical instrument.

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ORIGINAL ARTICLE

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Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Received 4 June 2015; accepted 5 August 2015

Citation: World Neurosurg. (2015) 84, 6:1962-1967.

http://dx.doi.org/10.1016/j.wneu.2015.08.043

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WORLD NEUROSURGERY 84 [6]: 1962-1967, DECEMBER 2015