Posterior fusion and instrumentation is the gold standard in the surgical management of adolescent idiopathic scoliosis undergoing selective thoracic fusion.1
Minimally invasive surgery of the spine has been evolving rapidly in the past few years. With the introduction of video-assisted thoracoscopic surgery, it is now possible to access the anterior spinal column without the risk of thoracotomy and the disruption of the local biology.2,3 4 5 5 6,7
The early results of thoracoscopic techniques for the treatment of scoliosis are promising.2,3,8 versus thoracoscopic fusion and instrumentation. The objective of the present study is to compare the safety and efficacy of these two techniques in the surgical management of adolescent idiopathic scoliosis undergoing selective thoracic fusion.9
Materials and Methods
All consecutive female patients with adolescent idiopathic scoliosis who had undergone undergoing selective thoracic fusion between 1994 and 2000 were retrospectively analyzed by an independent physician not involved with the direct care of these patients. Thirty-one consecutive patients fit the criteria for the present study. The average age of these patients at surgery was 14.3 years (range, 9–17). The average follow-up period was 44 months (range, 25–97).
The patients were divided into two groups. Nineteen patients who underwent conventional posterior fusion and instrumentation (Moss-Miami, Depuy-Motech, Raynham, MA) were assigned to group 1. Twelve patients who had thoracoscopic fusion and instrumentation (Eclipse, Medtronic Sofamor-Danek, Memphis, TN) were assigned to group 2. Before the introduction of thoracoscopic instrumentation in 2000, all of the patients who had selective thoracic fusion for adolescent idiopathic scoliosis received posterior instrumentation. From 2000 onward, all potential surgical candidates were offered thoracoscopic instrumentation. Twelve of fourteen patients agreed to have their spinal deformities corrected via thoracoscopic approach. The biodata of these patients were summarized in Tables 1 and 2 . There were no patients who required combined anterior-posterior surgery. All of the patients had documented curve progression before surgery, and none had symptoms of back pain or symptoms suggestive of neurologic compromise.
Table 1: Patient Data
Table 2: Patient Data
Fusion Levels.
Preoperative erect, prone, and bending films were performed on all of the patients. Selection of fusion levels was based on erect and bending films of the whole spine. The fusion was usually performed from the end vertebra to the stable vertebra in group 1 patients. For group 2 patients, the fusion was typically from the end vertebra to the end vertebra using the Cobb measurement technique. In some patients, the fusion was shortened by one level if there was horizontalization of the end vertebra on bending films or if the disc above the end vertebra opened with bending towards the concavity.
Surgical Technique.
All of the patients were operated on by the senior surgeon (WHK). In those patients undergoing posterior fusion and instrumentation (group 1), the surgical approach used was a standard posterior midline incision. Facet decortication was performed using a high-speed burr, and facet fusion was performed with autogenous bone graft harvested from the posterior iliac crest in 15 patients and resected rib grafts (through a concomitant thoracoplasty) in 4 patients. Instrumentation was achieved via a double rod-hook construct in every case. No pedicle screws were used in the present study population. A claw construct (transverse process hook and pedicle hook) was always placed at the cephalad part of the convexity of the curve. Rod rotation and distraction was applied to the concavity first, and this was followed by application of compression to the convexity. This order was reversed if the sagittal profile of the patient revealed significant thoracic kyphosis. No brace or external orthosis was prescribed for patients after surgery.
In group 2 patients who had anterior fusion and instrumentation (Figure 1 ) done entirely via a thoracoscopic approach, the patients were positioned in a lateral position with the convexity facing upwards. One-lung ventilation was used in all cases. Typically, four or five small (2–3 cm) incisions were made on the midaxillary line over the 3rd , 5th , 7th , and 9th ribs or 4th , 6th , 8th , and 10th ribs, depending on the slope of the ribs and the projected trajectory to the vertebrae to be instrumented. Access to the chest cavity was made above and below the ribs. Under endoscopic visualization, the disc-anulus complexes were completely excised back to the posterior longitudinal ligament. Part of the anterior longitudinal ligament was also excised. Preparation of the endplates was achieved with long curettes through the working channels. All the intervertebral spacers were filled with morcellized rib autograft. Part of the width of the rib under each skin incision was removed to provide the autogenous rib grafts. Cannulated Eclipse screws were placed bicortically under fluoroscopic and endoscopic guidance. No rod contouring was done, as the rod was slightly flexible. Compression was subsequently applied either in a caudal-cephalad or cephalad-caudal direction using the rack-and-pinion device. One patient (patient number 30) had instrumentation from T6 to L2. A small retroperitoneal incision was made to allow discectomies and fusion of T12/L1 and L1/L2 as well as placement of cannulated Eclipse screws into the L1 and L2 vertebral bodies. The rod was passed under the diaphragm after detaching its attachment to the vertebra to reach the upper two lumbar screws. No formal detachment of the diaphragm was needed. After surgery, a thoracolumbosacral orthosis custom made for the body dimensions of each patient was prescribed. The patients wore the orthosis for three months or until evidence of radiographic fusion was apparent on follow-up radiographs.
Figure 1: Anterior fusion and instrumentation was performed thoracoscopically in this patient. Four portals through the right lateral chest wall were used. Bone grafts were taken from the ribs at the access ports.
Follow-Up Observation.
Evaluation included clinical and radiographic examination. Radiographs would include standing PA and lateral radiographs of the spine. The coronal alignment was assessed using the standard Cobb measurement technique. The measurement of spinal deformity after surgery was based on the maximum deformity independent of the levels instrumented or the original preoperative Cobb levels. The lateral films were evaluated for thoracic kyphosis (T2–T12) and lumbar lordosis (T12–S1) using the Cobb method of measurement. All measurements were taken before surgery, 1 week after surgery, 6 months after surgery, and on most recent follow-up review. For the purpose of the present study, the authors described normal ranges of thoracic kyphosis (20–50°) and lumbar lordosis (20–60°) in accordance with the study by Bernhardt et al 10
Data Analysis.
The percentage change in Cobb angle measurement in the coronal and sagittal planes at various time intervals after surgery was analyzed between the two surgical groups using repeated measurement analysis. The analysis included time trend measures (i.e. , whether the value changes over time), differences between the two groups (i.e. , whether the two groups are significantly different over the change in trend), and interaction between time and surgical group (i.e. , whether the two groups behave similarly. No interaction between the groups implies similar behavior (i.e. , if there is a time trend, it is present in both groups). The sagittal profiles in the thoracic and lumbar spines were also analyzed separately using independent samples tests. This was performed by comparing the absolute change in thoracic kyphosis and lumbar lordosis after surgery with the preoperative baseline values.
Other data gathered included the number of levels fused, operative time, length of intensive care unit (ICU) and hospital stay, duration of parenteral analgesia, estimated blood loss during surgery, and complications. All statistical analyses were performed with StatView software (SAS Institute, Cary, NC). P < 0.05 was considered statistically significant.
Results
The results of the study were summarized in Tables 1 and 2 . Thirty-one female patients were available for the study. Nineteen patients underwent posterior fusion and instrumentation (group 1). Their average age at surgery was 14.4 ± 1.4 years. Twelve patients had thoracoscopic fusion and instrumentation (group 2). Their average age at surgery was 14.3 ± 2.5 years. No patient was lost to follow-up review. There was no statistical difference between the two groups in terms of age at menarche (P = 0.89) and surgery (P = 0.87) using Student’s t test. The average Risser score was 2.6 ± 1.5 in group 1 and 2.7 ± 2.0 in group 2. The difference was not significant (P = 0.89).
Blood Loss.
Estimated blood loss at surgery averaged 368 ± 285 cc in group 1 and 313 ± 363 cc in group 2. The difference was significant using Student’s t test (P = 0.006).
Operative Time and Hospital Stay.
Operative time averaged 252 ± 35 minutes for group 1 and 415 ± 72 minutes for group 2. The difference was statistically significant using Student’s t test (P < 0.001). The mean ICU stay was 1.5 ± 0.8 days in group 1 and 2.6 ± 1.3 days in group 2. This difference was statistically significant (P = 0.01). Total hospital stay averaged 7.5 ± 0.9 days in group 1 and 8.3 ± 1.2 days in group 2. The difference revealed a trend towards statistical significance (P = 0.053). Group 1 patients required an average of 2.9 ± 0.9 days of parenteral analgesia compared with 3.3 ± 0.9 days in group 2. The difference was not significant (P = 0.24).
Complications.
There were no postoperative complications in group 1. Complications in group 2 included one lobar collapse and one scapula winging. The lobar collapse was managed with pain medications, aggressive chest physiotherapy, and increasing the underwater suction pressure of the chest tube. The winged scapula was treated conservatively, and partial recovery of the long thoracic nerve was observed on follow-up observation.
Scoliosis Improvement.
The average preoperative primary curve in the coronal plane was 50 ± 9° in group 1 and 52 ± 11° in group 2 (Table 3 ). The difference was not statistically significant (P = 0.56) using Student’s t test. The magnitude of the curve on right bending was 28 ± 11° in group 1 and 33 ± 12° in group 2 (P = 0.25). The magnitude of the curve in prone position was 37 ± 10° in group 1 and 41 ± 11° in group 2 (P = 0.29). The authors compared the erect Cobb angle with the bending Cobb angle in every patient to assess the spinal flexibility and found 44 ± 14% correction (percentage change from erect to bending Cobb angles) in group 1 and 37 ± 15% correction in group 2. Using both Levene’s test for equality of variances (P = 0.68) and Student’s t test for equality of means (P = 0.18), the authors found no statistically significant difference between the two groups in terms of spinal flexibility.
Table 3: Coronal and Sagittal Profiles After Surgery Compared to Preoperative Baseline
The scoliosis in group 1 improved from an average of 50° preoperative to 12° (1 week postoperative), 14° (6 months postoperative), and 16° (most recent follow-up review). Improvement in scoliosis among group 1 patients averaged 77 ± 12% (1 week), 72 ± 11% (6 months), and 67 ± 15% (most recent follow-up review). The scoliosis in group 2 improved from an average of 52° preoperative to 18° (1 week postoperative), 20° (6 months postoperative), and 20° (most recent follow-up review). In group 2 patients, the mean improvement in scoliosis was 66 ± 13% (1 week), 62 ± 14% (6 months), and 62 ± 16% (most recent follow-up review). The power analysis was found to be 63 (1 week postoperative), 55 (6 months postoperative), and 12% (most recent follow-up review). Repeated measurement analysis was performed using the percentage change from preoperative Cobb angle. There was no statistical difference between the two groups (P = 0.08). There was significant time trend for both groups (P = 0.001). There was no interaction between time and the category of surgical groups (P = 0.15).
In summary, there was no significant difference between the two groups in terms of scoliosis correction. However, both groups similarly exhibited loss of percentage correction of scoliosis on follow-up observation, with a significant time trend.
Sagittal Alignment.
Thoracic kyphosis (T2–T12) measured an average of 18 ± 13° in group 1 patients and 19 ± 12° in group 2 patients (Table 3 ). The difference was not significant according to Student’s t test (P = 0.86). In calculating the percentage change from preoperative kyphosis using repeated measurement analysis, the authors found no differences between the surgical groups (P = 0.13). There was no time trend (P = 0.09) and interaction between the groups (P = 0.23). The kyphogenic effects (Table 4 ) were not significantly different between the two groups at 1 week after surgery (P = 0.44), 6 months after surgery (P = 0.30), and on most recent follow-up review (P = 0.61). The total number of patients with hypokyphosis (<20°) decreased from 16 before surgery (group 1 = 11; group 2 = 5) to 10 after surgery (group 1 = 7; group 2 = 3) on most recent follow-up review. Eight patients in group 1 had normal thoracic kyphosis (20–50°) before surgery. At the most recent review, 12 patients achieved normal thoracic kyphosis in group 1. Seven patients in group 2 had normal thoracic kyphosis before surgery. At the most recent review, nine patients had normal thoracic kyphosis. No patients in either group had hyperkyphosis.
Table 4: Change in Thoracic Kyphosis and Lumbar Lordosis Compared to Preoperative Baseline
Lumbar lordosis (T12–S1) measured an average of 39 ± 12° in group 1 patients and 47 ± 13° in group 2 patients (Table 3 ). The difference was not significant according to Student’s t test (P = 0.11). In calculating the percentage change from preoperative lordosis using repeated measurement analysis, the authors found no differences between the surgical groups (P = 0.60). There was significant time trend in both groups (P = 0.004). There was no interaction between the groups (P = 0.83). There was no significant change in lumbar lordosis (Table 4 ) between the 2 groups at 1 week after surgery (P = 0.65), 6 months after surgery (P = 0.53), and on most recent follow-up review (P = 0.43). The total number of patients with normal lumbar lordosis (20–60°) increased from 29 before surgery (group 1 = 18; group 2 = 11) to 31 after surgery (group 1 = 19; group 2 = 12) on most recent follow-up review. The total number of patients with hyperlordosis decreased from two before surgery (group 1 = 1; group 2 = 1) to none on most recent follow-up review. None of the patients in the study had hypolordosis.
Number of Segments Fused.
The average number of spinal segments or levels of the primary thoracic curve was assessed before surgery (Table 2 ). In group 1, the average preoperative Cobb level was 7.4 ± 1.1, and this increased to 9.8 ± 1.5 after surgery (P = 0.001 using Wilcoxon signed rank test). In group 2, the average Cobb level before surgery was 6.6 ± 0.8, and this changed to 6.3 ± 0.7 after surgery (P = 0.26 using Wilcoxon signed rank test). The difference in the number of segments fused in group 1 versus group 2 was statistically significant using the Mann-Whitney U test (P < 0.001). Anterior instrumentation saved an average 3.5 segments compared with conventional posterior instrumented fusion. At the most recent review, all patients had radiographic evidence of fusion as assessed by the presence of trabeculated bone across the fused segments.
Discussion
To the best of the authors’ knowledge, this is the first report on the comparison of posterior and thoracoscopic approaches to manage adolescent idiopathic scoliosis undergoing selective thoracic fusion. The advantages of posterior segmental spinal instrumentation include stable fusion levels, good sagittal control, probable beneficial effects on pulmonary function, and low pseudarthrosis rates.11 12
On the other hand, there is some suggestion that the current rigid instrumentation may render the vertebral body segments of the spine osteoporotic.13
There are several advantages of anterior fusion for idiopathic scoliosis. The anterior approach offers a mechanical advantage, because the corrective force is applied at the greatest distance from the center of the curve in both lateral displacement and rotation.14 14 15,16 17–19 19
On the other hand, the efficacy of anterior instrumented fusion was questioned by the authors of a recent study, who reported unacceptably higher rates of loss of correction, pseudarthrosis, and rod breakage in the anterior group.6 14
With the advent of minimally invasive surgery, there has been tremendous interest in the field of thoracoscopic spine surgery. Traditionally, anterior approaches required a long posterolateral thoracotomy incision to access the vertebral bodies or intervertebral disc spaces.20,21 2,22,23
One prospective study concluded that the learning curve for thoracoscopy is substantial but not prohibitive.24 24,25 in vitro testing to increase the flexibility of the spine to a similar extent.26
One study attempted to address the issues of kyphosis, pseudarthrosis, or inadequate correction in instrumented anterior scoliosis surgery.7 6,16,27,28 et al 3 et al ,8
In the present study, thoracic kyphosis (T2–T12) did not increase significantly with thoracoscopic instrumentation versus posterior instrumentation. No significant change in lumbar lordosis (T12–S1) was noted with either thoracoscopic or posterior procedures. This finding differs from another report29 14
Both the posterior instrumented and thoracoscopic instrumented groups achieved 100% fusion rate. In the authors’ experience, the ability to perform anterior fusion thoracoscopically was excellent. Under good endoscopic visualization, discectomies and preparation of the endplates for fusion could be performed without difficulty.
The authors have shown that the efficacy of thoracoscopic surgery in terms of coronal and sagittal correction is similar to standard posterior procedures. One of the advantages of thoracoscopic instrumented fusion included lower blood loss. The average blood loss in patients after thoracoscopic surgery in the present study was 313 cc, comparable with recent studies on endoscopic scoliosis instrumentation.3,8 6,27 6,14,27
The disadvantages of thoracoscopic surgery were the significantly longer operative time and ICU stay. A recent study showed that the thoracoscopic approach took longer to perform than the open anterior approach.8 3,8
The authors believe that this technique would benefit most patients with single thoracic idiopathic curves. However, drawing on what is known regarding single-rod anterior systems, it might not be appropriate for patients who are too heavy (more than 70 kg), as the risk of pseudarthrosis is high.30 thoracoscopic instrumented fusion .8
An unusual complication noted in the patients in the present study who were undergoing thoracoscopic instrumented fusion was one patient who had scapula winging, which the authors attributed to long thoracic nerve palsy. On follow-up observation, there was partial recovery of the long thoracic nerve. One cadaveric study31 thoracoscopic instrumented fusion will certainly be helpful if this technique is to become widespread and iatrogenic long thoracic nerve injury is to be minimized. The complications reported by other authors included 10 cases of nonunion (attributed to the use of demineralized bone matrix), cephalad screw backing out in one patient, chest wall numbness in three patients, airway obstruction in five patients, plug separation from the screws in two patients, and rod fractures in two patients.3
One drawback of the present study is the relatively small number of patients in the series, where achieving statistical power for differences between the two groups could be more difficult. In the future, larger equivalence studies may be able to verify the authors’ findings. However, it is important to not merely focus on the statistical significance or nonsignificance (P values) but also on the clinical aspects of the study. In the present study, the authors have shown that both techniques worked well for idiopathic scoliotic curves undergoing selective thoracic fusion.
Conclusion
The results of the use of thoracoscopic instrumented fusion in the correction of scoliosis are comparable with those obtained with the use of more standard open approaches. A prospective randomized controlled trial will be required to validate the authors’ findings. Furthermore, a longer follow-up period will be needed to determine the durability of the thoracoscopic fixation and arthrodesis.
Despite the retrospective design of the present study, potential benefits for the patient with the use of thoracoscopic instrumentation cannot be overlooked. These techniques of spinal deformity correction are evolving, and the results will improve as surgical tools and approaches are streamlined and surgeons gain more skill and experience with these specialized techniques. However, careful consideration is required to select appropriate operative candidates for a good surgical outcome.
Key Points:
Thoracoscopic instrumented fusion allows scoliosis correction to a similar degree as posterior instrumented fusion.Sagittal profiles did not differ significantly between both procedures after surgical correction of scoliosis.
Advantages of thoracoscopic surgery include lower blood loss.
Disadvantages of thoracoscopic surgery include longer operative time and ICU stay.
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