Choice of Surgical Procedures for Thoracic
Ossification of the Posterior Longitudinal Ligament
Atsushi Seichi, Katsushi Takeshita, and Kozo Nakamura
Introduction
Thoracic myelopathy caused by ossifi cation of the pos- terior longitudinal ligament (OPLL) is rare compared to cervical OPLL, even in the Japanese population.
However, once myelopathy appears in patients with thoracic OPLL, it is progressive and often leads to serious paraplegia. In such cases, surgical treatment is required because conservative treatment, such as immobilization by a brace, is not effective. The mechan- ical stability of the upper and middle thoracic spine is greater than that of the cervical spine. Therefore, with thoracic OPLL, the static factor—compression of the spinal cord from the anterior aspect—is a major factor for the progression of myelopathy rather than the dynamic factor. When myelopathy is mild, both sur- geons and patients sometimes hesitate to undertake surgery because of the potential risk of the neurological complications that might occur. As myelopathy pro- gresses, the risk of surgery increases, which presents a dilemma for both patients and surgeons.
Surgical Procedure for Thoracic OPLL
There have been a limited number of reports describing operative treatment for thoracic OPLL, although several surgical methods have been advocated (Fig. 1) [1–10].
Spinal cord damage during surgery has been described in almost all the reports, and a surgical strategy for this condition has not been established.
The investigative committee to study ossifi cation of the spinal ligament established by the Japanese Minis- try of Public Health and Welfare recently performed a multicenter study of the surgical results for thoracic OPLL and reported that neurological complications occurred in 35 of 198 cases (18%) between 1998 and 2002 (unpublished data). Most patients displayed recovery to some degree, but this high rate of neuro-
logical complications cannot be ignored. Operative management of thoracic OPLL has proved to be extremely diffi cult, especially with beak-type or sawtooth-type OPLL around the T4 level near the apex of thoracic kyphosis, where access is limited through both the sternum-splitting approach and the transtho- racic approach. Detailed descriptions of the surgical techniques and their results are discussed in the follow- ing chapters. Here we review the treatment options for thoracic OPLL and discuss the advantages and disad- vantages of each procedure.
The choice of surgical treatment can be divided into two categories based on the type of decompression. The fi rst is direct removal of the thoracic OPLL through an anterior or posterior approach (or both) [2,3,6,7,10].
The second is indirect posterior decompression of the spinal cord without directly touching the OPLL [1,8].
The choice of surgical decompression is still controver- sial because neurological complications may occur with any technique.
Direct Removal Surgery
Anterior Removal of Thoracic OPLL via an Anterior Approach
Posterior decompression by laminoplasty for OPLL has been reported to be effective in the cervical spine with lordosis. However, the effi cacy of posterior decompres- sion for thoracic OPLL is uncertain because the align- ment of the thoracic spine is kyphotic [1,9]. OPLL compresses the spinal cord anteriorly, and anterior decompression has been considered a reasonable treat- ment choice (Figs. 1b-1, 2). There have been a few reports describing anterior methods, and incomplete release or removal of thoracic OPLL (inadequate decompression) has been recognized as one of the caus- ative factors of a poor outcome [2–4]. Insuffi cient rec- ognition of the OPLL structure and poor handling of the air drill can also cause iatrogenic spinal cord injury [4]. The “trick” of this procedure is to approach the upper and midthoracic spine and to obtain a good sur- gical fi eld; the OPLL can then be removed completely.
Department of Orthopaedic Surgery, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan
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Tomita et al. described a circumspinal decompression technique for thoracic OPLL (Fig. 1b2) [7]. They drilled a deep gutter from the posterior aspect into the vertebral body. During the second-step anterior operation, the gutters served as landmarks to identify the location of the OPLL [7]. We have sometimes used a modifi cation of this method, “three-quarter decompression,” in which the surgeon makes a deep gutter at the left side of the OPLL through the posterior approach followed by the right-side anterior approach (Fig. 1b3).
Massive OPLL in the upper and midthoracic spine is quite diffi cult to access and remove because the operat- ing fi eld is extremely deep in relation to a surgeon’s hands. The OPLL is diffi cult to shave using an air drill.
Compared with disc disease, the location of thoracic OPLL is also diffi cult to identify. Concomitant ossifi ca- tion of the anterior longitudinal ligament also makes the shape of the vertebral body irregular and causes misdirection when trimming the vertebral body. Thus, a surgeon’s requirement for a surgical navigator is high.
To access the thoracic OPLL and precisely release it through the anterior approach, the authors have employed an image-guidance system (see the chapter by Seichi, this volume) [11].
In the authors’ experience, surgeons can access the anterior thoracic spine up to T2–T3. The lower part of the scapula is released; and after resecting the fourth rib, a transthoracic approach can be applied for the upper thoracic spine. For anterior surgery, the OPLL is thinned with a diamond burr, and the continuity of the ossifi ed ligament and the posterior cortices of vertebral bodies are released. If the dura mater is ossifi ed, the anterior fl oating technique is recommended to prevent massive bleeding from epidural vessels and leakage of cerebrospinal fl uid (CSF) into the pleural cavity.
Leakage of CSF into the pleural cavity after dural tears is one of the troublesome complications of anterior surgery, but it can usually be managed by placing a chest tube in the thoracic cavity; rarely, it requires additional surgery for closure of the fi stula [2,10].
Fig. 1. Various surgical methods for thoracic ossifi cation of the longitudinal ligament (T-OPLL). a Preoperative image.
b Direct removal surgery. b1 Anterior decompression and fusion. b2 Circumspinal decompression [7]. b3 Three-quarter decompression. b4 Anterior removal of T-OPLL through a
posterior approach [6]. c Indirect decompression by correct- ing thoracic kyphosis. d Extensive cervicothoracic lamino- plastic decompression. d1 Bilateral open door type. d2 Unilateral open door type
For patients with combined thoracic OPLL and ossi- fi cation of the ligamentum fl avum (OLF), resection of the OLF through a posterior approach is a fi rst step. For resection of the OLF, a surgeon can make a gutter at the lateral side of the OPLL by drilling down the inner part of the facets and pedicle into the vertebral body. This procedure makes the second step of anterior surgery easier.
Anterior Removal of Thoracic OPLL via a Posterior Approach
Ohtsuka et al. developed a method for removing tho- racic OPLL through a posterior approach (Fig. 1b4) [6].
With this method, after wide laminectomy the OPLL is resected from a posterior oblique direction. For ante- rior decompression using the anterior approach, the Fig. 2. Anterior decompression and fusion. Preoperative and
postoperative magnetic resonance imaging (MRI) and com- puted tomography (CT) of a 54 year-old man with OPLL between T12 and L2. a, b Axial and reconstructed CT revealing
a beak-type OPLL severely compressing the spinal cord between T12 and L2. c, d Postoperative CT shows successful removal of OPLL
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b
c
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number of spinal segments to be decompressed is limited to three or four. In contrast, anterior decom- pression through the posterior approach has no restric- tion on the number of decompressed spinal segments and can be applied from the upper thoracic spine down to the thoracolumbar junction. In addition, this method allows resection of the OLF at the same time [6].
However, manipulation of OPLL through the poste- rior approach is highly dangerous. In Japan, this method temporarily became popular among experienced spinal surgeons but lost its popularity because of the risk of spinal cord injury and incomplete descriptions of the details of the technique.
Problems of Direct Removal Surgery
With anterior decompression through either the ante- rior or posterior approach, it is diffi cult to create a fl at-fl oor reconstruction of the spinal canal without making a step at the junction between decompressed and nondecompressed portions to avoid the develop- ment of junctional impingement. Surgeons should be aware that a kink in the spinal cord at the nonremoved edge of OPLL may cause neurological deterioration [6,7]. Slight manipulation of the thoracic OPLL might cause damage to the spinal cord, which has already been debilitated by severe long-term compression.
Even slight pressure on the spinal cord during excision of the OPLL can result in spinal cord injury. The spinal cord in the midthoracic spine is a watershed for the blood supply from the cervical and thoracic regions, and the arteries in this area are small. Spinal cord blood fl ow in the upper thoracic region is therefore poor.
Sudden change in blood circulation of the spinal cord just after decompression may cause neurological dete- rioration owing to edematous swelling or reperfusion syndrome of the spinal cord [4,12].
Indirect Decompression Surgery
As mentioned above, direct removal of thoracic OPLL, whether through an anterior or a posterior approach, is still technically demanding. Because of the technical diffi culties involved, indirect decompression through posterior surgery has been advocated for this condition.
The results of localized laminectomy for thoracic OPLL have been miserable because the procedure cannot provide suffi cient decompression of the spinal cord and causes intra- and postoperative progression of kyphosis [5,13,14]. Matsuyama et al. reported sudden deterioration of spinal cord potentials immediately after laminectomy for isolated beak-like OPLL at the
upper thoracic level, and the patient exhibited postop- erative neurological deterioration [5]. They speculated that minimal progression of kyphosis immediately fol- lowing laminectomy might cause spinal cord injury.
Because of poor results, localized laminectomy has been abandoned.
Extensive Cervicothoracic Laminoplasty Decompression
Tsuzuki et al. reported that extensive posterior decom- pression, including the cervical lordotic portion (exten- sive cervicothoracic laminoplasty decompression), resulted in a good posterior shift of the thoracic spinal cord with few neurological complications [8] (Fig. 1d) (see the chapter by Yoshida, this volume), but the results of this method also included occasional unsat- isfactory recovery with residual OPLL impingement. To secure the safety of the spinal cord and obtain better results, they advocated staged spinal cord decom- pression through the posterior approach, but their preliminary results included postoperative transient neurological deterioration; thus, a good result is not guaranteed with this method [9]. Postoperative devel- opment of an arachnoid cyst around the decompressed spinal cord after a second surgery has been reported to result in neurological deterioration [9]. Extensive cer- vicothoracic laminoplasty decompression seems rela- tively safe, but its effect on extensive OPLL remains inconclusive.
Indirect Decompression by Correcting Thoracic Kyphosis
Recently a few Japanese spinal surgeons have employed indirect decompression by correcting thoracic kypho- sis for thoracic OPLL (Figs. 1c, 3) [15] (see the chapter by Matsuyama, this volume). The mechanical stability of the upper and middle thoracic spine is great, but in patients with thoracic OPLL even minimal motion of the spinal column has the possibility of affecting the spinal cord. The principles of this technique are as follows: (1) There is fi xation of the thoracic spine using a pedicle screw system to reduce the dynamic factor.
(2) Reduction of the kyphotic alignment of the thoracic spine provides a better decompression effect for the spinal cord. (3) There is no manipulation of the OPLL, reducing the potential risk of spinal cord injury. We have recently employed this method as the treatment of choice for thoracic OPLL with or without cervical OPLL. However, the history of the technique is rela- tively short, and its effi cacy must be proven in future studies.
Fig. 3. Indirect decompression is accomplished by correcting thoracic kyphosis. Preoperative and postoperative CT and MRI of a 58-year-old woman with OPLL between T4 and T7.
a Preoperative reconstructed CT. b Preoperative MRI. c, d Postoperative lateral radiography and MRI reveal mild correc- tion of thoracic kyphosis
Staged Spinal Cord Decompression via a Posterior and Anterior Approach
As mentioned in the previous section, indirect decom- pression by correcting thoracic kyphosis is now one of the treatment choices for thoracic OPLL in Japan. This method has been reported to be safe [13]. However, when thoracic OPLL is extensive, the surgical results of indirect decompression may not be very good. There- fore, when the fi rst surgery using indirect decompres- sion to correct thoracic kyphosis is not effective, a second surgery using the anterior approach becomes a viable option (see the chapter by N. Kawahara, this volume, Part 5).
Conclusions
In our opinion, for patients with both cervical and tho- racic OPLL, wide-ranging posterior decompression surgery with or without instrumentation is the treat- ment of choice [14]. For localized and exceedingly thick OPLL without cervical OPLL, either (1) posterior decompression and correction of thoracic kyphosis by instrumentation with or without a second anterior surgery or (2) anterior surgery may be the choice. The authors have not yet determined which of these two procedures is better. When the spinal cord is com- pressed by OLF together with thoracic OPLL, posterior surgery alone or posterior and anterior surgery is the choice.
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