Ultrasonic surgical equipment was initially developed in the 1950s when it was mainly applied in dentistry and maxillofacial surgery [10]. The ultrasonic bone scalpel (UBS) is a relatively novel ultrasonic surgical device that cuts bone and spares soft tissues, and has been used for various spinal disorders [4, 5, 7, 8]. To date, although the advance of instruments and technique, thoracic spinal decompression surgery is still of great challenging. Unfavorable outcomes and high incidence of complications are frequently reported [11, 12]. To the best of our knowledge, few studies has described how to use UBS for thoracic spinal decompression, and no consistent surgical procedures have yet been established [13]. In view of UBS’S technical advantages in bone cutting, we believe that its standard use in decompression surgery will be conducive to achieved success of surgeons. Therefore, the purpose of this study is to present our experience and technique note of using UBS, and to put forward a standard surgical procedure for thoracic spinal decompression.
One of the primary advantages of UBS is that it cut bones with oscillation without rolling movement, thus allowing for precise bone cutting in a relatively narrowed surgical field. In the past, high-speed drills and Kerrison rongeurs have been extensively used in laminectomy. These instruments are commonly used when cutting bone; nevertheless, their use requires a relatively hard contact force with the bone, and the rotating bit increases the risk of grasping soft tissue structures such as dura matter and nerve roots[14, 15]. As a result, the risk of iatrogenic neurological complications is greatly increased. Taking advantage of the vertical micro-vibration characteristics of the UBS, bone cutting can be performed with more precision, while the possibility of instrument-related complications can be largely avoided.
Based on our experience, en block resection of the lamina and ossified ligamentum flavum along the midline of the facet joint using UBS is a safe and efficient surgical procedure. Using UBS, only minimal tip-bone surface pressure is required, which makes the equipment easier to handle and safer for manipulation in the vicinity of the neurovascular structures [8, 9]. Besides, the choice of the middle line of the articular process as a reference for grooving has technical advantages. Since some spinal cord compression occurs at the OLF site behind the facet joint, standard laminectomy does not completely remove the ossified lesions, which is why an extensive osteotomy is needed. Laminectomy combined with hemiarthrotomy is the best choice for complete decompression [16]. Furthermore, cutting bones at this site avoids the possibility of direct contact between the tip and the dura mater, and even if the blade accidentally penetrates the innermost cortex, the tip is inserted into the lateral side of the dura, reducing the risk of dura laceration.
En block resection of the lamina and OLF is strongly recommended [3]. When using this procedure, surgeons only need to cut through the four edges of the lamina and ossified lesions in a relatively safe area, instead of doing operations above the spinal cord like piecemeal resection does, thus significantly reducing the risk of accidental spinal cord injury. By gradually lifting the lamina, the surgeon can quickly assess the adhesion of the ossified lesions to the dura. With the careful operation, iatrogenic durotomy can be avoided in most cases and the ossified dura can be safely removed under direct vision. Otherwise, intraoperative blood loss is expected to be reduced due to reduced operating procedures and the clotting effect of UBS [7, 17]. Since the tip is not very thick, a precise length and narrow bone cutting can avoid extensive bone removal, therefore, the structural stability of the facet joint can be maintained to a certain extent.
UBS can significantly reduce operating time. Traditionally, high-speed drills have been widely used for thoracic spinal decompression. Yet, high mental concentration and experienced handle techniques were always required to prevent the slipping off drills [18, 19]. A time-consuming and tedious surgery can exhaust the surgeon. In our experience, it takes at least ten minutes for a single segment en block resection of the lamina and ossified lesions. Since 2014, we have been using UBS for thoracic decompression, which significantly shortened the operating time, with only 3.0 ± 1.4 min for single laminectomy. As surgeons become more familiar with the UBS, the operating time was shortened even further.
In circumferential decompression, bilateral facet joints can be precisely resected and the risks of grasping nerve root can be reduced because of the non-rotatory motion of UBS [4]. It utilizes vertical micro-vibration rather than rotatory-motion; the occurrence of spinal cord injury caused by the rebound of the rotating bit is theoretically avoided. By creating a buffer space beneath the ventral lesion, we can safely cut the OPLL base using our specially designed angled tip. OPLL can be entirely removed by carefully separating the adhesion between the dura and OPLL. Additionally, UBS is highly tissue-selective, allowing it to make brief contact with dura and thin shaving of OPLL. In this regard, the UBS may be more suitable for the removal of ventral lesions of the spinal cord over a high-speed drill.
Although UBS has demonstrated significant technical advantages over the high-speed drill, some pitfalls of using this device should be noted. In this research, two cases of device-related nerve root injury occurred. After screening the CT and MRI images, we found that in these two cases, the nerve roots were tightly pinched by OLF and vertebral body, thus, leaving no residual cushion space for it to elude. In such a case, when the blade penetrates the inner cortex of the ossified lesion, the vibratory force is directly transmitted to the dura mater of the nerve root, resulting in root injury. With this in mind, we chose to retain the last thin layer of ossification during future surgery, rather than penetrating it with UBS and using narrow bone osteotome to pry open and amputate the lamina. Since then, we have used this method to perform more than 300 cases of similar surgery, and no UBS related nerve root injuries occurred. The results indicate that this operation procedure is proved to be effective in the treatment of particularly stenotic spinal canal.