Ossification of the posterior longitudinal ligament is a common cervical disease that can cause stenotic changes in the spinal canal and contribute to the development of quadriparesis [9, 25, 8]. Conservative treatment may be effective for some patients. However, for most of the patients, surgical decompression of the spinal cord to prevent the progression of neurological deterioration as rapidly as possible is the most effective measure [25, 26]. In general, anterior decompressions by cervical corpectomy and resection of OPLL seem to be an ideal surgical option, and posterior decompression is an alternative choice for severe OPLL when the anterior approach threatens iatrogenic deterioration of the neurological status [9, 27, 26, 8, 23]. The results of this study demonstrated the anterior corpectomy and some advantages on the complication of C5 palsy than posterior laminoplasty for OPLL. Although C5 palsy were two in ACCF and three in PCDL, the recovered cases were better in ACCF than PCDL.
It is commonly believed that the spinal cord drift and subsequent stretching of the C5 nerve root, which is more vulnerable than the other roots because of the C5 level, are typically at the apex of the cervical lordosis [27, 17, 20]. Because OPLL affects chiefly the cervical spine form C3 to C5, the extent of posterior shifting of the cord is greatest at the C5 level [28, 26, 21]. The cervical spinal cord is compressed and flattened by OPLL, and reduction of the blood supply in the grey matter in the ventral portion of the dorsal columns for small bold vessels was compressed. There may be compression of the spina roots when ossification extends to one of the lateral recesses of the spinal canal [25, 26, 21]. The degrees of spinal cord drift were more in PCDL than in ACCF, and five complication of C5 palsy were two in ACCF and three in PCDL in this series cases. For this reason, the spinal cord drift may not the reason for complication of C5 palsy in surgery.
Spinal cord movement is limited because the organ is tethered to nerve roots after common laminectomy [25, 17, 21]. The complication of C5 palsy were not only in anterior corpectomy, but also in posterior laminoplasty. Previous study shown the complication of C5 palsy is associated with the extent of decompression [29, 24, 20]. CSM can result in regional cord ischemia from the sural sac an spinal cord flattened by OPLL, and long term ischemia leads to an imbalance between spinal cord metabolic demand and oxygen supply [30, 26, 31, 32]. After surgery of ACCF and PCDL, the dural sac and flattened spinal cord were all expansion in this series cases. As previous study shown, the dural sac and spinal cord expansion can lead to spinal cord ischemia-reperfusion injury [33, 20, 31, 34]. In this series, the compression of spinal and expansion of dural sac and flattened spinal cord were similar between two groups. The five C5 palsy cases were the most compressed degrees of dural sac and flattened spinal cord more than 50%, and all had totally expansion after operation. For this reason, the complication may be related to the compression and expansion of spinal cord.
Long term of OPLL compression spinal cord in CSM patients lead the nerve tissue is starved of vital nutrients such as oxygen and glucose [35, 33, 26, 34]. Multiple mechanisms of cell damage are activated following spinal ischemia and reperfusion which can be a function of location in the spine as well as the time elapsed since the onset of ischemia [30, 3, 27, 36, 32]. Inflammatory responses are known as a major component of secondary injury of initial ischemic insult and play an important role in modulating the pathogenesis of C5 palsy [37, 8, 24, 20]. Effects of reperfusion, also known as reperfusion injury, are the causative factors for spinal edema [38, 25, 8, 18]. The results of this study shown the complication of C5 palsy in PCDL were serve than ACCF may be related the spinal ischemia and reperfusion injury. The spinal cord drift in ACCF patients were less than PCDL patients, this maybe causes the more serious of spinal ischemia and reperfusion injury. Despite of ACCF and PCDL can get good clinical results in OPLL patients, the tenets of C5 palsy prevention by evaluated the risk factors are important in clinical practice.