Instrumentation for microsurgical osseous dissection Technical note L.
Section of Neurosurgery, University of Arizona Medical Center, Tucson, Arizona v The use of the operating microscope has revolutionized the surgical approach to many neurosurgical diseases. The microscope has provided magnification, binocular vision, and excellent lighting in the depths of neurosurgical wounds, allowing the performance of exceedingly delicate procedures that were previously impossible. Occasionally, an operative approach demands microscopic bone dissection. Instrumentation has been developed for working with soft tissue, but special instruments for osseous dissection have not been available. A set of newly developed punches and curettes with a bayonetted offset is described. These keep the surgeon's hand out of the operating field and allow unimpeded visualization through the operating microscope. These prototype instruments have been used successfully in over 100 microscopic neurosurgical procedures. KEY WORDS
microsurgery • bone dissection
operating microscope provides the neurosurgeon with excellent magnification and binocular vision in the depths of small wounds. A great deal of microsurgical instrumentation has been developed for work with soft tissue, tumor removal, and deep suturing; however, available instruments for osseous dissection have been quite limited. Because most bone dissection instruments are large and awkward for use in a microsurgical field, we have developed a set of punches and curettes with a bayonetted offset so that the surgeon's hands can be held out of the surgical field. These instruments were initially developed for microsurgical anterior cervical discectomy, but have proven quite useful in other procedures in small fields including thoracic disc excision with costotransversectomy, removal of the anterior clinoid process in craniotomies for aneurysms of the ophthalmic artery, and transoral odontoidectomy. They have been used in prototype form in well over 100 microsurgical procedures, and are effective in the microsurgical removal of bone. We frequently use a high-speed drill for thinning bone prior to its removal with these microsurgical instruments. HE
Description and Use of Instruments The bayonetted osseous punches have been constructed in standard sizes with special emphasis on the smaller sizes from I to 5 mm. These have a very thin small foot plate set at either a 90° or a 45° angle; the 156
• discectomy • instrumentation
bayonetted portion of the offset is approximately 3 cm in depth (Fig. I). The instrument can easily be slipped under the part of an anterior clinoid process protecting the carotid artery for biting off a portion of the clinoid process. In anterior cervical disc excision, lateral dissection near the nerve root is easily accomplished by grasping the posterior longitudinal ligament as well as the osteophytic spurs overlying the nerve root with the osseous punch. The bayonetted punch is also helpful in
FIG. 1. Bayonetted osseous punches are made in many sizes with either a 90· or a 45° angle. The offset allows the surgeon to keep his hand well back from the microscopic field.
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Instrumentation for microsurgical osseous dissection Discussion
FIG. 2. The curettes are made with either a 90' or 45" angle or straight with a cup. The bayonetted offset allows visualization under the operating microscope.
lumbar microdiscectomy. The larger punches can be used to remove the portion of the ligamentum flavum in the lateral recess overlying the nerve root as well as bone edges of the lateral recess. In some cases of transsphenoidal hypophysectomy, a longer extension of the distal portion of the instrument from the offset to the cutting surface is useful in removing the bone from the sphenoid sinus as well as from the anterior portion of the sella. The curettes vary in size from 1 to 5 mm. With the bayonetted offset, the surgeon's hand can be held away from the operating field (Fig. 2). The curettes are constructed either with a 90° or a 45° angle, or straight with a cup. The right-angled curettes are helpful in working back toward the surgeon in an anterior cervical discecto my with removal of osteophytes. The 45" -angled curette is probably the most useful instrument and is helpful in removing osteophytes and the posterior longitudinalligament in anterior cervical discectomies. We have found this instrument useful in the microsurgical costotransversectomy approach to a herniated thoracic disc and in removing the odontoid process in the transoral microsurgical odontoidectomy.
These instruments were initially designed for use in an anterior approach to the cervical spine. 3 Once the standard incision is made and self-retaining retractors are inserted, disc material is removed macroscopically until the posterior edge of the vertebra is approached. At this point, the operating microscope is brought into the field and further dissection of the posterior margin of the vertebral bodies, removal of the osteophytes, and removal of the posterior longitudinal ligament in the interspace is carried out with the aid of a high-speed air drill and the bayonetted microsurgical osseous instruments. The 45°-angled bayonetted punch is helpful in picking up the posterior longitudinal ligament and in trimming the bone edge leading away from the surgeon (Fig. 3 left). This can be accomplished over the nerve root with excellent visualization. As the surgeon works back toward himself, the 90°-angled instrument becomes more useful. The curettes serve both as dissectors and for removal of ligament and bone. The procedure continues until the pathological process has been removed and the dura is visualized in the region of interest. Although these instruments were developed for anterior cervical microdiscectomy, it became apparent that they had many other uses. They were found to be helpful for removal of the anterior clinoid process during dissection and clipping of ophthalmic artery aneurysms.] After coagulation and removal of the dura, the anterior clinoid process is thinned with a high-speed air drill, then the 45°-angled bayonetted punch is inserted under the clinoid process, which is removed to expose the carotid artery (Fig. 3 center). The 45°-angled bayonetted curettes are used to remove any thin bone that is still overlying the carotid artery. Dura edges are coagulated further so that they will shrink back and a significant amount of bone can be removed. In the approach to a thoracic disc, we have found that a costotransversectomy with microdissection has
FIG. 3. Drawings of the punches and a curette in use. Left: A punch is illustrated picking up the posterior longitudinal ligament in an anterior microsurgical cervical discectomy. Center: A punch is shown removing a portion of the anterior clinoid process in an approach to an ophthalmic artery aneurysm. Right: A curette is seen removing herniated disc in a microsurgical approach to the thoracic spine.
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L. P. Carter the advantage of avoiding retraction of the spinal cord and allowing excellent visualization of the disc, osteophytes, and dura across the anterior portion of the spine," Once the rib has been removed and the intercostal nerve root identified exiting from the neuroforamen, the pedicle of the bone can be thinned with a high-speed air drill and, under the operating microscope, a portion of the pedicle can be removed to identify the anterior dura margin. The herniated disc can be identified and, with bayonetted curettes and punches, osteophytes and disc are removed and broken away from the dural margin. Excellent visualization of approximately two-thirds of the interspace can be achieved in this fashion (Fig. 3 right), In both transoral microsurgical odontoidectomy and transsphenoidal approach to the pituitary, the surgeon works under magnification at significant depths. The bone edges can be grasped with the small osseous punches while the bayonetted curettes are used to free the odontoid from the underlying connective tissue, With bayonetted punches, the thinned walls of the sphenoid sinus and the anterior portion of the sella turcica can be removed, Larger versions of these offset punches and curettes have been found to facilitate routine lumbar microsurgical discectomy. Once the nerve root is identified, the lateral recess can be removed nicely with the offset punches,
Disclosure The instruments represented here were designed by L. Philip Carter, M,D" and were custom-manufactured by Codman and Shurtleff. Inc., Randolph, Massachusetts, Commercialization contracts are in force to co-develop these instruments for osseous dissection, References I, Crowell RM, Ojemann RG: Surgical treatment of carotidophthalmic aneurysms, in Schmidek HH, Sweet WH (eds): Operative Neurosurgical Techniques. Indications, Methods, and Results. New York: Grune & Stratton, 1982, Vol 1, pp 869-889 2, Simeone FA, Rashbaum R: Transthoracic disc excision, in Schmidek HH, Sweet WH (eds): Operative Neurosurgical Techniques. Indications, Methods, and Results. New York: Grune & Stratton, 1982, Vol I, pp 1259-1268 3, Wilson CB, Hoff JT: Clinical features and surgical treatment of cervical discogenic radiculopathy and myelopathy, in Ganant HK (ed): Spine Update: Perspectives for Radiologists, Orthopedists, and Neurosurgeons. Berkeley: University of California Press, 1984, pp 273-279 Manuscript received February 12, 1991, Accepted in final form May 30, 1991. Address reprint requests to: L. Philip Carter, M.D" Section of Neurosurgery, University of Arizona Medical Center, 150 I North Campbell, Tucson, Arizona 85724,
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