Surgical intervention is necessary when thoracic myelopathy occurs secondary to ossification of the posterior longitudinal ligament (OPLL) because this condition is progressive and intractable to conservative therapy. However, surgical outcomes reported to date have not been satisfactory.1–3 There have been reports of neurological deterioration after surgery for thoracic OPLL, all of which exhibited a sharply protruded segmental form of ossification.4–6 For beak-type and flat-type OPLL accompanied by ossification of the ligamentum flavum and facet destruction, we have been performing indirect spinal cord decompression with primary dekyphosis using instrumentation through a posterior approach.7 Furthermore, we incorporated Ponte osteotomies8,9 during surgery for thoracic OPLL to obtain more effective indirect spinal cord decompression. There are no previous reports on the use of this procedure to treat thoracic OPLL. This is the first report using Ponte osteotomies in the treatment of thoracic myelopathy due to OPLL.
MATERIALS AND METHODS
The subjects were 10 patients (5 men and 5 women) with an average age at surgery of 47 years (range, 18–63 y), who underwent indirect posterior decompression and corrective fusion with Ponte osteotomies at our institute from 2010 to 2012. This study was approved by the institutional review board of the School of Medicine, University of Nagoya, and informed consent was obtained from each patient before enrollment. We followed the patients for a minimum of 2 years and an average of 2 year 6 months (range, 24–36 mo).
We performed lateral whole-spine radiographs with standing and multislice computed tomography (CT) images of the cervical and thoracic spine on all patients. Measurements were standardized and recorded by 2 independent observers and recorded on a study group data sheet. Using sagittal CT images, we classified the ossification types as beak or flat according to the criteria proposed by Matsuyama et al.4 To calculate the kyphotic angle, we measured the sagittal Cobb angle between the upper endplate of the uppermost vertebra and the lower endplate of the lowest vertebra at the instrumented fusion levels.
We performed follow-up examinations 1 year after the surgery using the Japanese Orthopaedic Association Scoring System (JOA score). This has a total of 11 points, consisting of 4 points each for motor dysfunction of lower extremities; 2 points each for sensory dysfunction of lower extremities and trunk; and 3 points for bladder dysfunction. Postoperative recovery rate was determined by Hirabayashi’s method as follows: recovery rate=(postoperative JOA score−preoperative JOA score)×100/(full score−preoperative JOA score).
We investigated fusion range, osteotomy levels, preoperative and postoperative Cobb angles of fusion levels using radiographs and sagittal CT, intraoperative and postoperative blood loss, operative time, recovery rate, and intraoperative ultrasonography findings. Cases in which the spinal cord free from OPLL on intraoperative ultrasonography were defined as the floating (+) group, and those without as the floating (−) group according to Matsuyama et al.7
The basic fusion area was 3 vertebrae above and below the OPLL lesion with segmental screw. Axial and sagittal CT images were used to determine the osteotomy levels. Usually, there were some areas of ligamentum flavum ossification (OLF) adjacent to an OPLL level (Fig. 1A). Because of this nonmobile segment at the OPLL level, osteotomies were performed to OLF areas at the mobile level adjacent to the OPLL.
Surgical procedure was performed as described by Matsuyama et al.10
In short, Luer bone rongeur forceps, bone punch, and diamond bur are used to perform Ponte osteotomies followed by screwing, in situ rod placement, and decompression. This is continued to the foramen at each level. Rod placement on the other side, at the beginning of the proximal end, then follows as the in situ rod is detached from the screw at the same level of the other rod placement. The reduction is a combination of cantilever and compression at each osteotomy level. Posterior fusion is completed with decortication and local bone grafting. Rehabilitation with a brace is started 2 days after surgery.
The average preoperative and postoperative (at the 1 y follow-up) JOA scores were 3.5 (range, 0–10) and 7.5 (range, 6–11), respectively, and the recovery rate was 56%. The fusion areas were C7–T11 in 1 case, C7–T12 in 1 case, T1–T12 in 2 cases, T2–T10 in 2 cases, T2–L3 in 1 case, T5–T12 in 1 case, T7–T12 in 1 case, and T9–L2 in 1 case. The mean fusion area was 9.8 vertebraes, with average laminectomy of 7.3 laminas (range, 3–10). Four cases received cervical laminoplasty simultaneously with their fusions. We performed osteotomies both rostrally and caudally to the OPLL level in 7 cases (T1/T2 and T6/T7/T8/T9 in 1 case; T4/T5, T6/T7, and T8/T9 in 1 case; T8/T9 and T10/T11 in 1 case; T3/T4/T5 and T9/T10 in 1 case; T3/T4 and T10/T11/T12 in 1 case; T9/T10 and T11/T12 in 1 case; and T3/T4 and T5/T6 in 1 case). We performed osteotomies to just the caudal side in 2 case (T6/T7/T8 and T9/T10) and to only the rostral side in 1 case (T4/T5/T6/T7/T8). The average number of osteotomy levels was 3 (range, 1–4). Preoperative kyphosis at the fusion level averaged 35 degrees (range, 20–60 degrees) on radiograph and 29 degrees (range, 20–47 degrees) on CT with a correction to 21 degrees (range, 7–38 degrees) after surgery. The mean operative time was 9 hours and 50 minutes (range, 6 h 50 min–11 h 10 min), with average blood loss of 2328 mL (range, 251–11,731 mL) (Table 1).
On intraoperative ultrasonography, 7 cases were included in the floating (+) and 3 in the floating (−) groups, and the recovery rates were 66.0% and 33.4%, respectively. Those in the floating (+) group as determined by ultrasonography tended to have good results although there was no significant difference between the 2 groups (P=0.173) (Table 2).
No patient had a decrease of amplitude on intraoperative spinal cord monitoring during the Ponte osteotomies, cantilever, and compression procedures. Regarding intraoperative and postoperative complications, cerebrospinal fluid leakage and wound infection was noted in 1 case with adhesion between the dura and ossified ligamentum flavum, but it was treated with irrigation.
A 49-year-old woman with continuous-type OPLL from T1–T3 and T4–T10 and OLF at the T3/T4 and T10/T11/T12 regions had progressive myelopathy (Fig. 1A). MR images revealed severe canal stenosis at several of the OPLL and OLF locations (Fig. 1B). Laminoplasty from C3 to C7 was performed for cervical canal stenosis followed by screwing and in situ rod placement from T1 to T12. Intraoperative ultrasonography revealed compression of the spinal cord by the OPLL anteriorly after laminectomy of T1–T11 (Fig. 2A). We performed Ponte osteotomies at T3/T4 and T10/T11/T12, and the kyphosis was corrected and fixed with cantilever and compressive forces with instruments. The preoperative kyphotic angle of T1–T12 of 48 degrees was corrected to 37 degrees after surgery (Fig. 1B). Ultrasonography showed that spinal cord compression decreased (Fig. 2B). Neither neurological aggravation nor improvement occurred after the surgery.
Symptomatic OPLL for the thoracic vertebrae requires surgical treatment. Matsumoto and colleagues reported that the combined use of instrumentation with surgery was associated with significantly better outcomes in a multicenter study in Japan. This procedure stabilized the thoracic spine to prevent the progression of or even to correct thoracic kyphosis thereby enhancing spinal cord decompression.11 Kawahara et al12 reported the usefulness of the circumferential decompression of thoracic cord with dekyphosis stabilization for thoracic OPLL. An anterior approach using an extrapleural or transpleural approach has been recommended by several authors, as it allows for direct decompression of the spinal cord by excising or floating the OPLL.13 In the multicenter study, Matsumoto et al14 reported the recovery rate tended to be higher among patients undergoing anterior decompression and fusion through an anterior approach or circumferential decompression and fusion than among those undergoing posterior decompression and fusion or anterior decompression through a posterior approach and fusion. However, they reported that posterior decompression and fusion was the most common procedure because this technique is less technically demanding, is associated with a lower risk of neurological complications, and requires less-intensive patient care after surgery.14 We have been performing indirect spinal cord decompression combined laminectomy and dekyphosis using instruments through a posterior approach.10 This surgical procedure not only stabilizes the thoracic spine, but also facilitates indirect decompression to the vulnerable spinal cord by dekyphosis of the thoracic. Furthermore, we reported the OPLL morphology, as seen on sagittal CT images, was discontinuous across the disk space between the rostral and the caudal ossification regions. Postoperatively, this discontinuity disappeared with the connection of the OPLL segments in all patients without further thickening of the OPLL.15 Micromotion may lead to OPLL progression even within the essentially immobile thoracic spine segments. In contrast, the connection may provide the efficient spinal cord recovery.
Alberto Ponte has been advocating a posterior-only procedure consisting of posterior column shortening through multiple, wide, segmental osteotomies and posterior compression instrumentation and fusion.8,9 The Ponte procedure with segmental posterior shortening osteotomies and segmental pedicle screw fixation provides good correction of the deformity in Scheuermann kyphosis.16 We have corrected the kyphosis seen with thoracic OPLL using only the cantilever technique. However, this technique puts a significant load on the pedicle screws. Therefore, we incorporated the Ponte procedure to correct the kyphosis without causing significant screw loads. As a result, correction angle on radiograph with this procedure averaged 14 degrees, whereas past surgical methods without the Ponte procedure averaged 7 degrees.7
This correction angle may not be as large as some reports on the Ponte procedure for the deformity.16–18 However, the mean angle of the fusion level was 35 degrees preoperatively, and the main purpose of this surgery was indirect decompression to the vulnerable spinal cord by correcting the thoracic kyphosis. The difference between the Ponte procedure when used for thoracic OPLL and when used for deformity is the levels receiving osteotomies. Whereas, multiple Ponte osteotomies are usually performed with maximum width at the deformity apex, we performed the osteotomies for thoracic OPLL at the levels adjacent to the OPLL because of the nonmobile segment at the OPLL level. Usually, some OLFs are adjacent to an OPLL level, and Ponte osteotomies are less difficult and less technically demanding after removing the OLF. In addition, no patient had a decrease of amplitude on intraoperative spinal cord monitoring during the Ponte osteotomies, cantilever, and compression procedures.
Seventy percent in the present study acquired the floating (+) on intraoperative ultrasonography, in contrast to 60% in our past study.7 The recovery rate tended to be higher among patients in the floating (+) group than among those in the floating (−) group as determined on intraoperative ultrasonography. Although there may not be satisfactory outcomes in all cases using the Ponte procedure for indirect posterior decompression and corrective fusion, it seems to be a more effective method for dekyphosis and achieving indirect spinal cord decompression. Thirty percent in the present study with the floating (−) on intraoperative ultrasonography and poor recovery rate may be performed the removal of OPLL.
In conclusion, we performed the Ponte procedure to achieve indirect posterior decompression and fusion for thoracic OPLL. “The Ponte procedure for indirect spinal cord decompression” is a novel concept used for the first time with thoracic OPLL in our study, and we consider it a useful method to achieve more effectively dekyphosis and indirect spinal cord decompression if there is not the spinal cord free from OPLL on intraoperative ultrasonography after only laminectomies. We believe that a comparative study of surgical outcomes between the groups treated by posterior decompression and fusion with and without Ponte osteotomies is needed to clarify the efficacy of Ponte osteotomies in the surgical treatment of OPLL.
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