The operative procedures for ossification of the posterior longitudinal ligament (OPLL) of the cervical spine are mainly divided into two types, i.e., the posterior approach and the anterior approach. We conducted surgical treatment on about fifty cases of OPLL by the posterior approach until 1977. The results were mostly satisfactory for the spinal cord signs, but sometimes we could not improve the radicular signs. In addition, since ossification of the ligament continued to progress, we could do nothing about aggravation arising several years later. Therefore, we have tried a new and radical method which is called anterior decompression since 1978. The central part of the vertebral body and the ossified area of the posterior longitudinal ligament are removed and the defect is filled with a bonegraft. Twelve cases of OPLL were operated on in our department in the last two years. Surgical techniques, operative results and indications are discussed.
A longitudinal groove of sufficient length and approximately 1.2-1.5 cm in width is made in the center of the vertebral bodies using a rongeur and an air-drill. When the posterior surface of the vertebral bodies is approached, the procedure should be performed with extra caution under a surgical microscope. The normal part of the dura must be exposed first, and the ossified ligament is carefully removed with a micro-rongeur. When the ossified ligament adheres tightly to the dura, the dura involved must be extirpated. The posterior part of the body should be cut widely so that the lateral part of the ossified ligament can be removed easily. A bone-graft taken from the iliac crest is made to fit the graft bed.
The operative results were excellent even though the lateral parts of the ossified ligament were not removed completely in three cases and fracture of the grafted bone occurred in two cases. Marked improvements of radicular and spinal cord signs were seen in all twelve cases. There were no cases in which signs of aggravation of the neurological symptoms appeared after the operation. Three bodies fused in one case, four bodies in nine cases, and five bodies in two cases. The highest level of the fusion was C₂ and the lowest level was T₁. When the percent narrowing of the cervical spinal canal was over fifty percent and remarkable cord signs were present, there was a tendency for the improvement of the cord signs to be delayed. When there is a gait disturbance, the operation should be performed without hesitation. Theoretically, it is considered that any ossification of the ligament can be removed by the anterior approach as long as the number of vertebral bodies involved does not exceed five (C₃ C₇). Spinal CT scans were valuable and essential to obtain more detailed information about the stenotic spinal canal and shape of the ossified ligament.