Surgical results and complications of anterior decompression and fusion as a revision surgery after initial posterior surgery for cervical myelopathy due to ossification of the posterior longitudinal ligament
Authors: Odate Seiichi , Shikata Jitsuhiko , Soeda Tsunemitsu , Yamamura Satoru , Kawaguchi Shinji 
Published: January 2017

OBJECTIVE
Ossification of the posterior longitudinal ligament (OPLL) is a progressive disease. An anterior cervical decompression and fusion (ACDF) procedure for cervical OPLL is theoretically feasible, as the lesion exists anteriorly; however, such a procedure is considered technically demanding and is associated with serious complications. Cervical laminoplasty is reportedly an effective alternative procedure with few complications; it is recognized as a comparatively safe procedure, and has been widely used as an initial surgery for cervical OPLL. After posterior surgery, some patients require revision surgery because of late neurological deterioration due to kyphotic changes in cervical alignment or OPLL progression. Here, the authors retrospectively investigated the surgical results and complications of revision ACDF after initial posterior surgery for OPLL.

METHODS
This was a single-center, retrospective study. Between 2006 and 2013, 19 consecutive patients with cervical OPLL who underwent revision ACDF at the authors' institution after initial posterior surgery were evaluated. The mean age at the time of revision ACDF was 66 ± 7 years (± SD; range 53–78 years). The mean interval between initial posterior surgery and revision ACDF was 63 ± 53 months (range 3–235 months).

RESULTS
The mean follow-up period after revision ACDF was 41 ± 26 months (range 24–108 months). Before revision ACDF, the mean maximum thickness of the ossified posterior longitudinal ligament was 7.2 ± 1.5 mm (range 5–10 mm), and the mean C2–7 angle was 1.3° ± 14° (range −40° to 24°). The K-line was plus (OPLL did not exceed the K-line) in 8 patients and minus in 11 (OPLL exceeded the K-line). The mean Japanese Orthopaedic Association score improved from 10 ± 3 (range 3–15) before revision ACDF to 11 ± 4 (range 4–15) at the last follow-up, and the mean improvement rate was 18% ± 18% (range 0%–60%). A total of 16 surgery-related complications developed in 12 patients (63%). The main complication was an intraoperative CSF leak in 8 patients (42%). Neurological function worsened in 5 patients (26%). The deterioration was due to spinal cord herniation through a defective dura mater in 1 patient, unidentified in 1 patient, and C-5 palsy that gradually recovered in 3 patients. Reintubation, delirium, and hoarseness were observed in 1 patient each (5%). No patient required reoperation for reconstruction failure, and all patients eventually had a solid bony fusion.

CONCLUSIONS
ACDF as revision surgery after initial posterior surgery for cervical myelopathy due to OPLL is associated with a high incidence of intraoperative CSF leakage and an extremely low improvement rate. The authors think that while the use of revision ACDF must be limited, it is indispensable in special cases, such as progressing myelopathy following posterior surgery due to a very large beak-type OPLL that exceeds the K-line. Postoperative OPLL progression and/or kyphotic changes can possibly cause later neurological deterioration. Fusion should be recommended at the initial surgery for many cases of cervical OPLL to prevent such a challenging revision surgery.