Introduction
Myelopathy caused by ossifi cation of the posterior lon- gitudinal ligament (OPLL) of the thoracic spine cannot be treated suffi ciently by conservative treatment and therefore demands surgical intervention. However, sur- gical outcomes reported to date have not been satisfac- tory, and surgical procedures for this disease remain to be established [1–12]. Thoracic OPLL is classifi ed into two types: the fl at type and the surgically challenging, sharply protruding type [1,2]. Recently, we have per- formed one-stage posterior decompression surgery—
expansive laminoplasty combined with correction of kyphosis with instrumentation—regardless of the type of ossifi cation. The purpose of this study was to assess the surgical outcomes of this posterior decompression with the corrective fusion procedure.
Materials and Methods
Altogether, 15 of 37 patients with thoracic OPLL who were subjected to surgical treatment at our hospital from March 1985 to October 2002 underwent posterior decompression with a corrective fusion procedure and were included in this study. The patients ages were 37–
67 years (mean 59 years). The mean follow-up period was 2 years 3 months. The operative results were rated using the Japanese Orthopaedic Association (JOA) scoring system (total 11 points) and Hirabayashi’s recovery rate as excellent (75%–100), good (50%–74%), fair (25%–49%), unchanged (0%–24%), or deteriorated (decrease in score, i.e., <0%). Also evaluated were the JOA score, recovery rate, extent of fusion, preoperative
and postoperative Cobb angles of the thoracic kyphosis, intraoperative and postoperative blood loss, operating time, and complications.
We obtained intraoperative recordings of compound muscle action potentials (CMAPs) using high-frequency transcranial electrical stimulation to monitor spinal motor tract function. Multichannel monitoring (16 channels) has been utilized since August 2002. This method allows intraoperative monitoring of spinal cord function as a whole as well as easy detection of surgical and mechanical technical failures.
Results
The mean JOA scores before and after the operation were 6.3 (range 3–9) and 8.9 (3–10), respectively. The recovery rate was excellent in six patients, good in four, fair in three, and unchanged in two; none of the patients deteriorated. The extent of fusion included T1–T6 in one patient, T2–T11 in four patients, T2–T10 in three patients, T3–T11 in four patients, and T4–T11 in three patients. Cervical laminoplasty was also performed in 12 of these patients. The mean pre- and postoperative angles of the thoracic kyphosis were 58 (48–72) degrees and 51 (43–65) degrees, respectively. The mean operat- ing time was 7 hours 30 minutes (ranging from 5 hours 50 minutes to 8 hours 45 minutes), and the mean blood loss was 1200 ml (670–1800 ml). Spinal fl uid leak was observed in seven patients.
Case 1
The patient was a 68-year-old woman with OPLL of the cervical and thoracic spine. Imaging studies demon- strated OPLL at the C7–T2 level, with maximal spinal stenosis at T1–T2 (Fig. 1). The patient exhibited gait disturbance, and her preoperative muscle strength was Department of Orthopaedic Surgery, Nagoya University
School of Medicine, 65 Tsuruma-cho, Showa-ku, Nagoya 466-8550, Japan
259
grade 4 by the manual muscle test (MMT). In October 2002, the patient underwent Kurokawa’s laminoplasty at C3–C7, laminectomy at T1–T2, and posterior fusion at T1–T3. The baseline waveforms recorded from all 16 channels before the surgical procedures were normal (Fig. 2a). Although CMAPs were stable during cervical laminoplasty, potentials from the lower extremities became weak during the T1–T2 laminectomy. There- fore, we suspended the procedure for 5 min. The CMAPs subsequently recovered to the baseline waveforms, and we quickly completed the rest of the procedure (Fig.
2b). Pedicle screws were placed bilaterally at T1 and T3, and the kyphosis in the cervicothoracic junction region was corrected; further decompression was subsequently performed. No reductions in the potentials were observed thereafter, nor did the muscle strength of the lower extremities decrease after the operation.
Case 2
Case 2 shows the importance of correcting spinal kyphosis. The patient experienced attenuation of CMAPs immediately after laminectomy. Intraoperative ultrasonography (IOSS) revealed posterior displace- ment of the spinal cord by OPLL. After kyphosis was corrected by spinal instrumentation, alleviation of the spinal cord compression was confi rmed by IOSS, and recovery of the CMAPs was observed.
This 53-year-old man presented with gait distur- bance. Muscle strength in the upper and lower extremi- ties was normal, except for slight weakness in the tibialis anterior muscles. Sensory disturbances below the navel, hyperrefl exia in the lower extremities, and ankle clonus were demonstrated. Contrast-enhanced computed Fig. 1. a Sagittal T2-weighted magnetic resonance imaging
(MRI), demonstrating spinal cord compression from C4 to T2.
b Computed tomography (CT) image with multiplanar recon-
struction (MPR), demonstrating ossifi cation of the longitudi- nal ligament (OPLL) at the C7–T2 level. c Axial MRI view, demonstrating severe spinal cord compression at T1–T2
tomography (CT) using Isovist and magnetic resonance imaging (MRI) revealed sharply protruding OPLL at T4–T5 and T5–T6 and severe spinal cord compression at T4–T5 due to the presence of both OPLL and ossifi ca- tion of the yellow ligament (OYL) (Fig. 3a). En bloc open-door laminoplasty was performed initially at the C3–T2 level, followed by laminectomy using a Kerrison punch and a diamond drill at the T3–T5 level. The OYL adhered partially to the dura mater at T3–T4 and T4–
T5, especially on the right side. IOSS demonstrated OPLL at T4–T5 and T5–T6 and severe anterior com- pression of the spinal cord at T4–T5, corresponding to the apex of thoracic kyphosis (Fig. 3b). After laminec- tomy, CMAPs began to decrease in amplitude (Fig. 3c), and slight progression of kyphosis was visualized by ultrasonography. We therefore stopped the laminec- tomy at the T6–T7 level, which had been planned pre- operatively, after confi rming the absence of spinal cord compression at this level. Pedicle screws were placed at T3, T4, T7, and T8; and kyphosis was corrected and fused with the aid of cantilever force (Fig. 3d).
Immediately after the correction procedure, CMAPs
recovered (Fig. 3c) and the reduction in kyphosis atten- uated the spinal cord compression by OPLL, as revealed by IOSS (Fig. 3b).
This case suggests that spinal cord compression sec- ondary to the progression of thoracic kyphosis during or after laminectomy is one of the primary causes of post- operative spinal paralysis. In practice, it is desirable to perform laminectomy after preventing kyphotic pro- gression by temporary rod fi xation by instrumentation.
Discussion
Expansive laminoplasty for cervical and thoracic spinal lesions is a relatively safe procedure [10,11]. This surgery generally provides good outcomes, which is comparable to that of anterior decompression [3–7].
However, some cases deteriorate after the operation [1,2]. One-stage posterior decompression and correc- tive fusion, achieved by expansive laminoplasty com- bined with correction of kyphosis with instrumentation, allowed both direct and indirect decompression of the resumed
TA
a
b
Fig. 3. a Contrast-enhanced CT using Isovist (center), plain MPR and axial view (right) and MRI (left), demonstrating sharply protruding OPLL at T4–T5 and T5–T6, and severe spinal cord compression at T4–T5 caused by both OPLL and ossifi cation of the yellow ligament (OYL). b Intraoperative ultrasonograms immediately after laminectomy (left) and after correction of kyphosis (right). Laminectomy enhanced spinal cord compression including decreased CMAP ampli- tude. Indirect decompression by correction of kyphosis
resulted in recovery of CMAPs. c CMAPs diminished 10 min after laminectomy. Progression of kyphosis and spinal cord compression by OPLL were confi rmed by ultrasonography.
Correction of kyphosis resulted in recovery of CMAPs. d MRI (left) and myelo-CT, sagittal reconstruction (center) and axial view (right) demonstrated suffi cient decompression of the spinal cord. Indirect decompression was achieved by correct- ing the kyphosis
5
6
4
5
4
6 5
4
a
b
Post laminectomy 10 min
Post laminectomy 11 min
1 min after correction of kyphosis
6 5
4
c
d Fig. 3. Continued
spinal cord. Spinal decompression as a result of correct- ing the kyphosis was confi rmed by IOSS. The two patients presented herein exhibited spinal dysfunction secondary to progression of kyphosis following decom- pression procedures. IOSS demonstrated that the spinal cord was compressed anteriorly as a result of increased kyphosis. The kyphosis, which led to indirect decompression of the spinal cord, was subsequently corrected by spinal instrumentation. The decline in CMAPs following spinal decompression also recovered following correction of kyphosis. Dysfunction of the vulnerable spinal cord as a result of mechanical com- pression or heat produced by the laminectomy proce- dure was detected early by the CMAP monitoring, which contributed signifi cantly to the prevention of spinal cord paralysis. This surgical procedure with CMAP monitoring provided good outcomes, regardless of the type of OPLL.
Conclusions
One-stage posterior decompression surgery by expan- sive laminoplasty combined with correction of kypho- sis with instrumentation was performed to treat OPLL of the thoracic spine, regardless of the type of ossifi ca- tion. The procedure allowed both direct and indirect decompression of the spinal cord. Spinal decompres- sion as a result of correcting kyphosis was confi rmed by IOSS. In some cases, both motor evoked potentials and CMAPs, which had initially diminished following the decompression procedure, recovered immediately after correcting the kyphosis. This surgical procedure provided good outcomes, regardless of the type of OPLL.
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