Partial Median Vertebrectomy and Strut Grafting

To resect one or two vertebral bodies and even for extensive level of fusion a horizontal incision is used. The platysma is divided in line with the skin incision. The investing layer of deep fascia is divided along the anterior border of the sternocliedomastoid and the muscle is retracted laterally. The omohyoid muscle is identified in the lower half of the exposure: its borders are defined and the muscle is preserved. The facial, lingual and middle thyroid tributaries of the jugular vein rarely ligated and transected. The jugular vein is gently retracted laterally. exposing the carotid artery. It is traced cephalad to its bifurcation, and the superior thyroid branch of the external carotid artery is kept intact. For high cervical exposures, division of the lingual and facial arteries never be necessary. The rostral dissection is carried to the level of the hypoglossal nerve and the lower border of the digastric muscle. The trachea and pharynx are retracted medially, exposing the prevertebral space. The medial borders of the longus colli muscles are cauterized and retracted. The cranial and caudal limits of the proposed vertebrectomy are defined and confirmed by lateral roentgenograms after placing appropriate markers.

It is generally convenient to start the dissection at the caudal end and move cephalad. The anterior longitudinal ligament and the annulus are excised from the lowest disc space. Using a high-speed drill, the cortical plates of the adjacent vertebral bodies are removed, and the drilling is continued posteriorly until the posterior longitudinal ligament is reached. Discectomy and end plate removal are done similarly at the higher disc spaces. The intervening cancellous portions of the vertebral bodies are then removed using a combination of Leksell rongeurs and the high-speed drill. Using the high-speed drill, a trough is created in the vertebral bodies above and below to allow seating of the fibular strut graft. This technique is superior to notching the upper and lower ends of the fibular strut and trying to impact it against the anterior cortex of the vertebral bodies above and below, as is conventionally done. At this point, the cutting burr is changed to a diamond burr and the final remnants of the posterior cortical plates of the vertebral bodies are removed, exposing the posterior longitudinal ligament. The ligament is excised piecemeal.

A fibular graft is then fashioned to conform to the dimensions of the vertebral defect, and its ends are bevelled to fit the vertebral trough created above and below. Manual traction to the head through a Mayfield clamp is applied. The cranial end of the graft is inserted first, and with distraction the caudal end is gently tamped into place and the distraction released. This manoeuvre generally locks the graft in place. After that, the graft is removed and attached with the miniplate with one or tow 10 mm screws. The size of the miniplate must be at least 10 mm longer in the cephalic and caudal ends to have proper 18-20 mm length screw fixation with normal upper and lower intact vertebrae. The cancellous bone from the removed vertebral bodies is then divided into small pieces and impacted on either side of the fibular graft. Meticulous haemostasis is obtained.

Postoperative immobilization in a soft collar for approximately 3 weeks is adequate in most instances to decrease the pain.

Three types of bone graft are available for fusion: autogenous fibula, a fibular allograft, and autogenous iliac crest. An autogenous iliac crest graft should be used whenever possible: in contrast to the fibular graft, fusion occurs rapidly, usually within 3 months. The iliac crest graft may fracture under axial loading, but this complication can be eliminated with the use of a locking plate and screw stabilization system. As a general rule, it is preferable to use iliac crest graft to replace up to three cervical vertebral bodies; if more vertebral bodies have to be removed or if the iliac crest is not of satisfactory quality, then a fibular graft may be used.

The use of a fibular allograft has the advantage of reducing the operative time and the morbidity related to harvesting the patient's fibula. However, the fusion of an allograft is slower because the grafted bone remains indolent for a considerable time. On average, it takes about 1 year for a' fibular allograft to incorporate. in contrast to an autogenous fibula, which may incorporate in 8 to 10 months.

Partial median vertebrectomy with strut grafting seems to give the best results of all the surgical procedures currently available for cervical spondylotic myelopathy. The result is considered excellent in 39 percent, good in 39 percent. and fair in 11 percent. Eleven percent of patients showed no improvement.

Failure of improvement after surgery may be due to one of three factors: (1) inadequate decompression, (2) mistaken diagnosis (for example, a patient with early amyotrophic lateral sclerosis who may also have some degree of cervical spondylosis). or (3) irreversible myelomalacia from advanced disease. It may be possible to exclude patients with definite myelomalacia from having surgery by preoperative evaluation with magnetic resonance imaging.

Potential complications include a wound hematoma from extensive dissection; injury to the marginal mandibular branch of the facial nerve, superior laryngeal nerve, or recurrent laryngeal nerve; graft migration; failure of fusion; edema of the foot and ankle because of the interruption of the peroneal plexus of veins at the graft donor site: and wound infection. It is not known at this time whether accelerated degenerative changes may occur at the mobile segments above and below the grafted site. causing recurrent cord compression.