Posterior three-column osteotomies for the treatment of rigid thoracic kyphosis - a case series

Introduction

he development of spinal surgery has led surgeons to face increasingly complex cases, aiming not only at spinal decompression and stabilization, but also at deformities correction and the spine biomechanical balance restoration.1

In the last decade, subtraction osteotomies have become popular in the management of spinal deformities2,3 and have begun to be used in a wide range of situations. The focuses of this study are pedicular subtraction osteotomy (PSO), bonedisk-bone osteotomy (BDB), and vertebral column resection (VCR), all ofwhich are posterior, middle, and anterior resection techniques through a single posterior access that can be used in very rigid deformities, with three-column arthrodesis or ankylosis, providing significant angular corrections in a single level without elongation of the anterior column of the spine (Fig. 1).

Material and methods

This was a retrospective study of15 cases ofpatients with rigid dorsal kyphotic or kyphoscoliotic deformities of several etiologies, surgically treated, whose postoperative follow-up ranged from 6 to 60 months (mean of 36 months). Data from charts and measurements of spine curves were collected by the four-line Cobb method. Lumbar lordosis and dorsal kyphosis were measured between the points of inversion of the curve, regardless of the level (Fig. 2). In cases where more than one surgery was performed, results considered measurements taken after the last approach. Surgical technique Patients were operated on a conventional surgical table, positioned in a manner that allowed transoperative maneuvers of hyperextension of the trunk or thighs, either through the controls of the table or through access to the positioning pads. Intraoperative neurophysiological monitoring was available in only eight cases (53%). The extent of the fixation was defined based on current principles of deformity correction; in all cases, it was sought to use a minimum of six anchorage points above and below the osteotomy. Wide laminectomy and disarticulation of the ribs were performed at the level to be osteotomized and at the levels above and below it. In more complex cases, secondary to tumors, infections, or associated with scoliosis, laminectomy and osteotomy were performed in a manner that was adapted to the pathology, comprising more levels or conducted asymmetrically. Nerve roots were sacrificed only when necessary to allow bone resection. An intersomatic cage was not used.

Results

Sample data Five men and ten women, aged between 13 and 66 years (mean: 38, SD = ±18.8), were operated. There were four cases of post-traumatic kyphosis (26.6%), four cases of kyphoscoliosis due to hemivertebrae (26.6%), two cases of Pott’s disease (13.3%), two cases of junctional kyphosis (13.3%), one case of deformity after pathological fracture due to multiple myeloma, one case of kyphoscoliosis due to neurofibromatosis, and one case of rigid Scheuermann’s kyphosis in an adult patient. Only the two patients with junctional kyphosis, in whom a long fixation of the lumbosacral spine was observed, presented significant sagittal imbalance. For all other cases, even in the presence of significant kyphosis, overall sagittal balance was maintained at the expense ofcompensatory lumbar hyperlordosis and pelvic anteversion. Nine of the 15 cases presented very significant spinal cord compression, but there were only two cases of neurological compressive deficits (case 1, Pott’s disease and case 8, post-neoplastic). In case 5, paraplegia was caused by acute trauma, not by late deformity.

The following procedures were performed: six PSOs (40%), one of which occurred in two adjacent vertebrae (case 6); two BDBs (13.3%); and seven VCRs (46.7%), two of which were conducted in two adjacent vertebrae (cases 1 and 2). One osteotomy was performed in the proximal thoracic segment (T2–T4), seven (46.7%) in the middle thoracic segment (T5–T9), and seven (46.7%) in the lower thoracic segment (T10–T12). Data are summarized in Table 1.

Surgical results

The mean angular kyphosis correction was 39.3? (SD = ±14.6?) and total kyphosis 33.9? (SD = ±17.7?). Considering the operated segment, angular kyphosis correction and full dorsal kyphosis were, respectively, 33? and 22? in upper dorsal lesions (T2–T4), 41.1? (SD = ±13?) and 35? (SD = ±21.3?) in medial dorsal lesions (T5–T9), and 38.3? (SD = ±17.7?) and 34.4? (SD = ±15.9?) in lower dorsal lesions (T10–T12). Considering the type of osteotomy used, the correction of angular kyphosis achieved by BDB was 28? (26? and 30?); by PSO, 41.5? (29–53?, SD = ±9.4?); and by PTV, 42? (10–63?, SD = ±19.5?). Complete neurological recovery was observed in the two cases that presented paraparesis due to deformity.

Complications

Eight complications occurred in six patients, as shown in Table 2. The clinical complications were a pulmonary thromboembolism and a thyroid storm in a young woman with hypothyroidism who discontinued the medication on her own. Both cases were resolved without major sequelae.

In the case of neurofibromatosis, there was a partial medullary lesion during vertebrectomy, which was performed via the transdural access, since the meningoceles embraced the entire contour of the vertebra. Patient presented left dorsal paresis in the postoperative period, compatible with gait, and with progressive improvement. However, seven months after surgery, patient returned with severe spastic paraparesis. Investigation showed significant spinal cord compression by an arachnoid cyst above the operated area, probably due to arachnoid adhesions after the transdural approach. Further surgery was performed, but patient remained paraparetic and spastic (case 9, Fig. 3). There were three early mechanical complications, one instrumentation failure (case 8, Fig. 4), and two junctional fractures at the most caudal instrumented level, with a small loss of correction in one and important loss in another, which led to the decompensation of the sagittal balance (case 11, Fig. 5). A significant loss of correction was not observed in any of the other cases during follow-up.

Discussion

Three-column osteotomies are aggressive surgeries, usually indicated in situations in which other techniques with lower potential morbidity are not applicable, either due to lack of flexibility of the spine or the presence of severe focal angular deformity.2 Its primary advantage is to allow the correction of rigid deformities without the need for anterior release. PSO is the best known technique; some publications have described a gain of 30 to 40 degrees of lordosis per level addressed.4–6 In the dorsal spine, its use has been much more limited and the potential for correction is not so clear.7 In 1994, Lehmer et al.8 reported four cases operated in the lower dorsal spine, with a mean correction of 29.5 degrees. Bridwell2 reported gains of approximately 25 degrees. With the use of the VCR in the dorsal spine, Rajasekaran et al.9 reported a mean of 36 degrees of correction in cases of tuberculosis, while Shimode et al.5 reported a mean correction of56 degrees in severe kyphoscoliosis. In the present series, the corrections were of approximately 40 degrees, with no significant difference between techniques.

Thoracic osteotomies differ greatly from those of the lumbar. First, to allow an effective closure of the osteotomy, the ribs that articulate with the superior and inferior disks must be released; second, because the surgery is done at levels where there is bone marrow, there is a limit to the bone mobilization that can be achieved with acceptable risk. O’Shaughnessy et al.7 reported that 20–25 mm of posterior laminar closure can be tolerated without neurological problems, but this value has not been validated experimentally. Tomita has shown that spinal cord shortening associated with the removal of a vertebral body is not a problem, and neither is the ligation of segmental vessels in up to three levels.10,11 Gertzbein and Harris12 postulated that distortion of the cord and clamping of the dural sac are potential risks associated with spinal cord shortening; these authors recommend avoiding corrections of more than 40?. In the present series, resections of up to two vertebral bodies and corrections of up to 63 degrees were made, without neurological complications. The care measures taken included very large decompressions and laminectomy of at least one level above and below the injury,13 which allows observing the dural sac during correction maneuvers and avoids distortions by subluxation, dural compression, or impingement. Perioperative neurophysiological monitoring is a desired standard, but it was used in only eight cases (53%), due to limitations of access in public healthcare patients. In the literature, the incidence of postoperative neurological deficits in dorsal osteotomy is quite small,5,7,14,15 probably due to the great care taken regarding spinal manipulation in all series, in addition to the fact that the nerve structures better resist shortening of the dural sac than its stretching.2 The potential for neurological complications is greater in VCR than in PSO, since there are more manipulations and the spine is left more unstable at the time of correction.2,13 Rajasekaran et al.9 reported 17 cases with irreversible neurological damage. Bakaloudis et al.16 reported complete loss ofmotor evoked potentials in one case, with immediate improvement after loosening of correction and without postoperative clinical deficit. Lenke et al.17 published a series of 40 TVPs of the thoracic spine without spinal cord injury. Seven patients, however, presented alterations in motor evoked potentials during surgery, five due to vertebral subluxation during correction maneuvers, and two due to exaggerated spinal cord shortening. In all cases, the potentials returned after correction of the subluxation or placement of larger cages.17 In another study, the same author reported a complete loss of motor potentials with normal somatosensory findings in 21.4% of cases. The recommended approach is to maintain a mean arterial pressure of at least 75 mHg, loosen the correction and, if the potentials do not restore, then remove the rods and undo the correction, attempting again with another strategy after signals are restored.15 Neurological deficit in the present series was not related to the correction of the deformity, but rather occurred during bone resection performed via transdural access in the case of neurofibromatosis, while the patient was being monitored. Mechanical complications are more common than neurological ones, since kyphotic deformities have a natural tendency to progression and instrumentation overload is not uncommon, especially when sagittal balance is not corrected. In some cases, the patient appears to be used to the anterior position of the trunk and the projection of the head, and assumes this type of posture even after correction of the deformity, which suggests the existence of some neurological or proprioceptive mechanism that influences the individual ability to maintain the body balance.6 The most described mechanical complications are pseudarthrosis, failure of instrumentation, and loss of correction over time. In the literature, the incidence of pseudarthrosis ranges from 0 to 5%5,18,19 and instrumentation failures occur in up to 8% of the cases, generally related to insufficient correction, osteoporosis, or lack of anterior support in VCR.7,9,19 In the present series, there were no cases of pseudarthrosis, and only one patient was followed-up for less than a year. Three early mechanical complications were observed: one case in which screws pulled out (case 8, Fig. 4) and two fractures of the instrumented lower vertebra, both related to osteoporosis. The first case was a fixation from T5 to T12, and fracture occurred due to insufficiency in T12. As loss of correction was small and clinical outcome was satisfactory, the authors decided not to perform a second surgical approach. After this case, the group’s conduct was modified and the definition of distal fixation levels was made including the first level in lordosis, as recommended in the treatment of Scheuermann’s kyphosis.20 In the second case, there was an L4 fracture with significant impact on sagittal balance and functional outcome, but patient was not reoperated due to clinical contraindication (case 11, Fig. 5). With the exception of these two cases of fracture, no significant loss of correction was observed during follow-up. This maintenance of the correction over time in uncomplicated cases was observed in most series.8,10,11,17,21 As there are no absolute values for defining normal kyphosis, the important parameters in the evaluation of corrections are reduced angular kyphosis and the restoration of sagittal balance.22 In this series, only two cases ofjunctional kyphosis, which had previous fixations of T10 to the sacrum, had significant sagittal decompensation. This is due to two factors: first, the most powerful spinopelvic sagittal compensation mechanism is the adjustment of lumbar lordosis,23,24 and injuries that do not compromise the lumbar mobility are more easily balanced; second, as a matter oftrigonometry, the higher the level of angular kyphosis, the lower its impact on the overall sagittal balance, because it is further away from the base.25 In both cases, an improvement on the sagittal vertical axis (SVA) without complete normalization was observed. In cases oflumbar osteotomies for sagittal imbalance correction, Rose et al.26 concluded that the combination ofPI + CD-LL ≤ 45? has a predictive value of 91% for maintaining sagittal balance up to two years after surgery. In the dorsal spine, this principle does not appear to be valid, since the loss of balance that occurs over time is mainly due to the progression of dorsal kyphosis; it is more noticeable in cases in which the superior instrumented level is below T5.26 In the present series, only 50% of patients met this criterion and yet there was no loss of correction. Final considerations Although these procedures are complex, aggressive, and subject to complications, osteotomies with three-column resection have proved to be quite effective and sufficiently safe for the correction of rigid sagittal deformities. Due to the severity of this type of deformity, the authors believe that the use of osteotomies in the treatment of this condition is highly justified.

Conflicts of interest

The authors declare no conflicts of interest.

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