C4/5 foraminal stenosis predicts C5 palsy after expansive open-door laminoplasty.

INTRODUCTION: Laminoplasty is frequently performed in cervical myelopathy patients, but can lead to unexpected postoperative C5 palsy. Although several studies have examined the pathogenesis and prevention of postoperative C5 palsy, many controversies remain and some radiological findings identified as risk factors were not correlated with our outcomes.
PURPOSE: This study sought reliable radiological findings that predict C5 palsy after laminoplasty and examined why the predictors of C5 palsy did not apply in our series.
METHODS: This study reviewed 116 patients who underwent open-door laminoplasty for cervical spondylotic myelopathy between January 2014 and April 2016, retrospectively. C5 palsy was defined as weakness of the deltoid muscle. We evaluated the incidence of C5 palsy, the preoperative C2-7 Cobb's angle, and Pavlov ratio at the C4/C5 level using simple cervical lateral radiographs. We also evaluated the existence of an ossified posterior longitudinal ligament, the transverse diameter of the C4/5 foramen, and increases in the anteroposterior diameter of the spinal canal at the C4/5 levels after surgery. Furthermore, a high signal intensity on T2-weighted images of the cervical spinal cord preoperatively was noted.
RESULTS: Of the 116 patients, 16 cases were excluded and 100 cases were analyzed; postoperative C5 palsy occurred in 8 patients (8%). There were no significant differences between the two groups except the average diameter of the C4/5 foramen. A diameter of the C4/5 foramen of less than 2 mm was significantly related to C5 palsy in the binary logistic regression test.
CONCLUSIONS: A smaller diameter of the C4/5 foramen was the only factor significantly correlated with C5 palsy after laminoplasty. The results suggest that C4/5 foraminal stenosis is one of the best predictors of C5 palsy, which might be related to ischemic/reperfusion injury of the C5 root nerve after laminoplasty.