The Lenke type 1, primary main thoracic curve pattern, is the most common spinal deformity pattern in adolescent idiopathic scoliosis.1,2 The primary goals in surgical management of these deformities are to achieve a solid arthrodesis to prevent progression and 3-plane correction, while maintaining coronal, sagittal, and axial balance. Surgical treatment options include thoracoscopic anterior spinal fusion (TASF), open anterior spinal fusion (OASF), or posterior spinal fusion (PSF), and instrumentation procedures. Each approach has been shown to have both benefits and drawbacks.
Posterior spinal fusion with segmental instrumentation has been shown to achieve reliable deformity correction and solid arthrodesis with a low rate of complication.3,4 Although this approach is considered the “gold standard,” there is concern regarding the limited ability to correct hypokyphosis and the necessity for a longer fusion.5–9 On the contrary, the OASF approach has demonstrated improved thoracic kyphosis restoration and the possibility of reducing the number of fusion levels5,7–9 compared with PSF with instrumentation. The disadvantage of this approach includes impaired pulmonary function and more frequent rod breakage.5,10,11 TASF offers many of the advantages of an OASF but has been shown to have a reduced effect on pulmonary function and perioperative morbidity.12–14 However, there is a significant learning curve with the thoracoscopic technique, and there have been concerns regarding rod breakage and nonunion.15–18
The objective of this study was to compare the radiographic and clinical outcomes after PSF, OASF, or TASF for the treatment of Lenke type 1 curves, in a series of patients with idiopathic scoliosis. We hypothesized, for similar thoracic curves, that there would be differences in radiographical, functional, and health-related quality-of-life outcomes between the 3 approaches.
MATERIALS AND METHODS
A multicenter, prospective nonrandomized trial was conducted by enrolling patients with primary main thoracic curves (Lenke 1), who underwent surgery between 2001 and 2005. Seven centers participated, although not all initiated the trial at the same time. Variations in the timing of initiation of patient enrollment occurred because of contracting, institutional review board, and study group participation variation. Inclusion criteria were as follows: diagnosis of main thoracic idiopathic scoliosis (Lenke 1) for which surgical treatment was recommended to prevent progression of the curvature or to correct trunk deformity, thoracic curve magnitude between 40º and 70º with the upper end vertebral level measured at T4 or distal, and lower level measured at L1 or proximal, kyphosis less than 40º (measured between T5 and T12), less than 21 years of age at the time of surgery, and the ability to tolerate 1-lung ventilation during anesthesia. The ranges for coronal and sagittal deformity were set on the basis of previous studies and concern of the participating surgeons that larger and/or kyphotic curves were relative contraindications to the anterior approaches and that restricting the inclusion criteria would limit study bias. Patients underwent one of the following procedures for surgical correction of scoliosis: (1) TASF, (2) OASF, or (3) PSF procedures. The surgical approach chosen for each case was a collaborative decision between the patient, the patient's family, and the surgeon. Not all of the surgeons were willing to perform all of the surgical techniques, and similarly not all patients were open to all approach options.
Operative, clinical, pulmonary function and radiographical data were collected at set intervals (preoperative, 6 wk postoperatively, 6 mo postoperatively, 1 and ≥2 yr postoperatively). The recorded operative and perioperative data consisted of levels fused, surgical time, estimated blood loss, blood products transfused, duration of chest tube usage, and incision length. Clinical data collected included physical appearance and the Scoliosis Research Society (SRS) outcomes tool. Four measures of trunk shape included were shoulder height difference, trunk shift, thoracic rib prominence, and lumbar prominence on forward bending via scoliometer measurement. Trunk flexibility, as measured by fingertip-to-floor distance during right and left lateral bending, was collected. The SRS Outcomes tool (SRS-24 version) was completed pre- and postoperatively by each patient. Pulmonary function testing was performed including forced vital capacity, forced expiratory volume in 1 second, and total lung capacity. Radiographs were measured for thoracic and lumbar coronal Cobb angles, coronal balance (C7–CSVL distance, where CSVL is Central Sacral Vertical Line)), sagittal thoracic kyphosis (T5–T12), and lumbar lordosis (T12–S1). Radiographically evident complications were divided into major and minor, according to Flynn et al.19 Perioperative and delayed nonradiographical complications were collected. Implant failure, reoperation, wound, and pulmonary complications were specifically noted. Complications were defined as major if they resulted in reoperation, were considered life-threatening, or resulted in spinal cord or nerve root injury.
Statistical Package for the Social Sciences (SPSS, Inc., Chicago, IL) was utilized for data analysis. Only patients with a minimum of 2-year follow-up were included in the outcome analysis. Descriptive statistics were calculated for clinical and radiographical data. Analysis of variance was utilized to compare continuous data between the 3 surgical approaches. Repeated-measures analysis of variance was used to compare changes during time between the groups. Bonferroni post hoc comparisons were used to identify differences between the 3 groups. Chi-square analysis was used for categorical outcome variables. Alpha level was set at 0.05 to declare significance, which was adjusted (0.01) on the basis of the Bonferroni method to control for multiple statistical tests (protecting against Type I error). The study was powered to detect a 5% difference in thoracic correction rates.
In total, 149 patients meeting the inclusion criteria were enrolled from 7 centers with an average age of 14.5 ± 2 years (range: 10.5–19.9 yr) at the time of surgery. The distribution of the cases from the various centers is shown in Table 1. Centers differed greatly in the distribution of each approach; however, in those centers performing more than 1 approach, the cases were equally distributed temporally throughout the enrollment period. Of the 149 patients, 84% (125) were females and 16% (24) were males. There were 55 (37%) patients in the TASF group, 17 (11%) patients in the OASF group, and 77 (52%) patients in the PSF group. Of these patients, 136 (91%) had a minimum of 2-year follow-up and were included in the analysis of outcomes.
These 136 patients who returned for follow-up were demographically similar to the larger cohort of 149 patients who had initially enrolled. Of the 136 patients, 85% (115) were females (115) and 15% (21) were males. The average age was 14.4 ± 2 years (range: 10.5–18.7 yr). There were 55 (40%) patients in the TASF group, 17 (13%) patients in the OASF group, and 64 (47%) patients in the PSF group. The average follow-up was 3 ± 1 years (range: 2–7 yr). There was no significant difference between the 3 groups in preoperative coronal thoracic or the lumbar Cobb magnitude, curve flexibility, coronal balance (C7–CSVL), or sagittal balance (lateral C7-sacrum) (Table 3). The PSF group did, however, have a significantly greater preoperative T5–T12 kyphosis (21º) than the TASF group (14º) (P < 0.01).
The posterior constructs were a combination of hooks and screws in 33% of the patients, all hooks in 2%, all screws except 2 hooks at the upper instrumented vertebra in 27%, and all screws in 39%. The majority of the posterior constructs (67%) had 5.5-mm rods. Approximately half of the posterior cases utilized stainless steel rods and approximately half utilized titanium. The majority of the TASF group was instrumented with either 4.5-mm (22%) or 4.75-mm (38%) titanium rods. The implants of the majority of patients undergoing OASF were 4.0 mm (41%) or 4.75 mm (29%) rods, with titanium utilized in 47% of OASF cases.
Patients in the PSF group had significantly longer fusions (average of 10 levels) than those in the TASF (average 6 levels) and OASF (average 7 levels) groups (P ≤ 0.001; Table 2). Surgical time was significantly greater in the 2 anterior groups than that in the PSF group (P ≤ 0.001). Estimated blood loss was significantly lower in the TASF group (470 mL) than in the PSF group (807 mL) (P = 0.003); the TASF group also had significantly less noncell saver blood products transfused (P ≤ 0.001), and a similar nonstatistically significant trend with regard to cell saver recovered blood transfused (P = 0.05). Chest tube removal occurred later in the OASF group (6 d) than in the TASF group (3 d, P ≤ 0.001). The average period (days) until hospital discharge requirements were met was significantly longer in the OASF group (9 d) than in the TASF group (6 d, P < 0.01) and the PSF group (5 d, P ≤ 0.001; Table 2).
All 3 approaches resulted in a similar percentage of thoracic and the lumbar Cobb angle correction (Figures 1, 2). Postoperative coronal (C7–CSVL) or sagittal (lateral C7-sacrum) balance was not statistically different between the groups (P > 0.01). The PSF group, on average, lost significantly more thoracic kyphosis than the 2 anterior groups, which on average gained kyphosis after surgery (P < 0.001). At final follow-up, 44% of the PSF group had a T5–T12 kyphosis of less than 15º compared with 6% of OASF and 18% of TASF (P < 0.001; Figure 3). On the contrary, none of the patients undergoing PSF had final thoracic kyphosis more than 40º, whereas 4% of the TASF and 12% of the OASF groups did. The PSF group also, on average, lost lumbar lordosis that was significantly different from the average gain of lordosis in the anterior groups (P < 0.001; Table 4).
Clinically, all patients improved between the preoperative and final postoperative assessments of the 5 trunk shape measures (shoulder height difference, coronal decompensation, thoracic rib prominence, lumbar prominence, and trunk shift; P ≤ 0.001). However, there were no significant differences in the changes of these 5 measures between the 3 surgical groups (Table 5). Patients undergoing OASF had less lumbar prominence preoperatively than the other 2 groups (P = 0.01; Table 5).
All patients have reported significant improvements from preoperative to final postoperative time points on the SRS domains of pain, self-image, and general function (P < 0.01). The total score had significant improvement (P = 0.01), whereas the activity score showed no significant change (P > 0.10). Change in scores on the SRS-24 outcome tool did not differ between the 3 groups (Table 6). There were no significant differences in the 3 postoperative domains of the SRS between the surgical groups (P > 0.01).
Pulmonary function results showed very slight changes from preoperative to latest postoperative time points when evaluating absolute best value; however, the OASF group consistently decreased on average, whereas the TASF and PSF groups demonstrated modest increases (Table 7). This was significantly different for forced vital capacity between the OASF and PSF groups (P < 0.001). The total lung capacity values were not analyzed for statistical differences because only one-third of the cohort had pre- and postoperative values for this test.
We were unable to demonstrate a statistically significant difference between the 3 approaches for the rate of implant-related complications despite a nearly 4-fold difference in the rate (11% TASF, 6% OASF, 3% PSF; P > 0.10; Table 8). In the anterior groups, these represented rod breakage (3), setscrew dislodgement (2), and screw pullout (2), whereas in the posterior groups, the failures were rod breakage (1) and loss of connection between the implants (1). There were no significant differences in the rate of reoperation (2% TASF, 6% OASF, 2% PSF; P > 0.10). There were more surgical site complications in the OASF group (18%) than in the TASF (5%) and PSF (0%) groups; however, this did not reach significance (P = 0.01). The minor complications rate was greater in the 2 anterior groups (53% TASF, 65% OASF) than in the posterior group (28%) (P < 0.01). There was no significant difference between the 3 groups for major complications (P > 0.10). Detailed complication information is given in Table 9.
The choice regarding surgical approach for single curves in adolescent idiopathic scoliosis has been debated for many years. Advocates of posterior, open anterior, and endoscopic anterior methods have suggested the advantages of each method. The surgeons from the centers involved in the study at the time varied in their opinions regarding the ideal approach. We initially sought to enroll patients in a randomized trial of the 3 approaches. In a pilot feasibility study, we presented patients with a video describing the 3 approaches along with the pros/cons and risks/benefits of each technique. We asked patients whether they would be willing to have their treatment randomized. The patients and families were uniformly opposed to randomization. Given this finding, we began the nonrandomized prospective trial reported in this article. The potential bias with regard to enrollment is acknowledged, but we thought that this study design was the best possible, given the patients' desire to participate in the decision making regarding their surgical approach.
We attempted to include only patients who had curve features appropriate for each of the 3 approaches. Unfortunately, only 1 site enrolled patients undergoing OASF, making it unclear that the results obtained at this institution (Site 2; as indicated by Table 1) are generalizable. At centers where more than 1 type of procedure was performed, questions regarding how/why patients chose one technique instead of the others complicate the interpretation of the results. Every effort was made to give the patients/families as much information about each technique as possible and allow them to make an informed unbiased decision. A minority of PSF cases were treated at centers that did not offer anterior methods. We do not think it is possible or practical to collect data regarding the surgical approach in a manner to yield level I evidence.
Overall, each treatment approach was able to correct the spinal deformity effectively while generally maintaining coronal and sagittal balance. SRS outcome scores as well as radiographical correction parameters were similar to each other between the 3 groups. The percentage of thoracic curve correction averaged 57% for each approach. The study had 81% power to detect a difference of 5% or more in thoracic correction. Clinical deformity correction, based on trunk shape measures, was also comparable between the 3 approaches. Each option, however, did have specific advantages and drawbacks that may influence a surgeon's recommendation for a particular patient.
PSF is considered the “gold standard” in managing the Lenke type 1 curve by many. It was also the most commonly utilized approach in this study. As reported in earlier studies, this approach was able to attain substantial correction in the coronal Cobb angle.3,4,20 A perceived advantage of PSF was the decreased surgical time needed to perform the procedure compared with anterior procedures. Although not statistically different in the current multicenter trial, Lonner et al 3 also previously demonstrated in his experience a significant difference in surgical time between PSF and TASF (3.3 vs. 6.0 hr, respectively). The PSF group also tended to have a lower rate of implant failure. This is likely related to the benefits of having 2 rods posteriorly compared to a single anterior rod construct used in these thoracic cases.
A potential drawback of the posterior technique was the perceived necessity to fuse on average 3 to 4 more vertebral levels compared with the anterior approaches. Betz et al 5 also reported that an additional 2.5 vertebral levels of fusion after PSF compared with an OASF. Lonner et al 3,20 reported a similar finding when compared with TASF. The difference in the number of levels fused may also be related to the type of posterior fixation used. Potter et al 4 found only a 1.2-level difference when all pedicle screw constructs were used posteriorly. We did not evaluate for differences in instrument type, but the majority of the posterior constructs were largely screw-based constructs.
Another concern regarding the posterior correction techniques is the reduced ability to restore kyphosis in hypokyphotic thoracic cases.7 Our data would support the concern considering the slight average loss of 4º in thoracic kyphosis seen in the PSF group. This decrease may be influenced by the type of implant used, rod contour, and extent of soft tissue release.6,21,22 Unfortunately, because of the heterogeneity of the PSF group, we were unable to specifically assess the effects of these variables.
OASF was the least commonly performed procedure in our series. The main benefits previously reported with an OASF compared with that of posterior instrumentation include decreased fusion lengths and improved thoracic kyphosis restoration.7,8,23 Our data corroborate these findings; the OASF group did have fewer levels fused than the PSF group. Pseudoarthrosis with rod breakage has remained a problem particularly with single rod anterior constructs. Another concern regarding the OASF is the negative effect on pulmonary function. At 2 years, there was a decrease in all pulmonary function values tested compared with either PSF or TASF. The present study findings are similar to the data reported in the literature.24,25 Kim et al 24 found a significant decline in absolute pulmonary function at 2 years postoperative, whereas Newton et al 25 found an open thoracotomy to be one of the largest predictors of a reduction in postoperative pulmonary function. It is still not clear whether these modest reductions in pulmonary function are clinically relevant for the patient during the long term. Previous research has also shown OASF to have a greater initial detrimental effect on shoulder strength than the other 2 approaches and a slower return to normal shoulder function. However, by 1 year, shoulder strength did normalize in the OASF group.14
In the late 1990s, the use of TASF gained popularity in the management of thoracic scoliosis. The less-invasive technique reportedly has many of the advantages of an anterior procedure including decreased fusion length and correction by shortening the anterior column.3 By minimizing the chest wall disruption compared with a thoracotomy, it has been shown consistently to have less effect on pulmonary function.12,26 Additional benefits from this minimally invasive approach are the smaller incisions as well as decreased relative blood loss.3,20,27 These advantages were also demonstrated in the present series.
A major drawback to the TASF is the learning curve needed to master the technique. Newton et al 15 have reported that a significant decrease in the time for disc excision during the course of 65 consecutive patients. This was supported in subsequent studies by Son-Hing et al 17 and Lonner et al.28 All the authors stated that although the learning curve, while significant, was acceptable. Rod breakage and pseudoarthrosis have been problematic in thoracoscopic cases just as in open anterior thoracic cases.16 While not statistically significant, there was a higher implant failure rate (broken implants and setscrew dislodgement) in the TASF group (11%) than in the OASF (6%) and PSF (3%) groups. Because of this risk, some have advocated the use of a postoperative brace and/or the use of autologous bone graft instead of allograft. Improvements in the implants have also minimized some of the risk. Yoon et al 29 demonstrated a lower incidence of rod breakage and pseudoarthrosis with a 4.75-mm titanium rod (0%/8%) compared with a 4.0-mm stainless steel rod (13%/21%) for thoracoscopic instrumentation procedures.
Thus, a case can be made for each of these 3 approaches. Although the PSF is straightforward, it requires attention, especially to the sagittal plane with slightly greater bleeding that should be anticipated. The thoracoscopic approach, although the least invasive from the standpoint of the skin incisions and blood loss, is the most challenging technically. The open anterior approach is certainly more straightforward than the endoscopic method and precludes having to work through the thoracoscopic learning curve. Generally shorter fusions and a more complete restoration of kyphosis are features of the anterior approaches; however, implant fixation and breakage remain problematic.
Since the completion of the enrollment of the patients in this series, most of the cases presently performed by the involved surgeons are done via a posterior approach. There are a number of reasons for this evolution in treatment that include perceived improvements in posterior methods that the authors consider advantages compared with any of the methods studied in this series (e.g., great comfort with thoracic pedicle screws and improved instruments for 3-plane posterior deformity correction). Unfortunately, enrollment of patients was completed before widespread all-screw constructs with segmental derotation technique were utilized by the treating surgeons. Despite the limitation, this comprehensive prospective comparison of the 3 accepted surgical options for the treatment of thoracic idiopathic scoliosis highlights the advantages and disadvantages of each, while confirming that all 3 remain acceptable choices for this patient population. With an average follow-up of 3 years, this study provides comprehensive outcomes of the surgical treatment of thoracic idiopathic scoliosis to which current and future treatments may be compared.
This level II prospective study with 81% power for the primary outcome variable of thoracic percent correction suggests that Lenke type 1 curves can be effectively managed surgically with an open anterior, thoracoscopic anterior, or a posterior instrumented fusion. Each option, however, has specific advantages and challenges that the surgeon must acknowledge when treating a specific patient. The patients undergoing PSF had more levels fused, yet shorter operative times. The TASF group had the smallest incisions and the lowest requirement for transfusion, but a higher minor complication rate. The OASF group had the lowest postoperative pulmonary function, yet may not require the learning curve associated with the thoracoscopic approach. Ultimately, the “best” choice for the surgical approach is dependent on various factors of which the most important may be the surgeon's skill and experience.
- Thoracic adolescent idiopathic scoliosis (40º–70º) can be effectively managed with a posterior spinal instrumentation, an open anterior instrumentation, or a thoracoscopic anterior instrumentation.
- The posterior approach was utilized in 47% of the cases and associated on average with 10 levels of fusion, 807 mL of blood loss, and a 57% correction rate.
- The open anterior approach was performed in 13% of cases with an average 7 levels of fusion, 750 mL of blood loss, and 57% correction rate.
- The TASF approach made up 40% of the series. On average, 6 levels were fused, with 470 mL of blood loss and a correction rate of 57%.
The authors would like to thank the central study infrastructure of the Setting Scoliosis Straight Foundation (FKA Harms Study Group) and also the site coordinators at each participating Harms Study Group research site for their tireless efforts on this study.
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Keywords:© 2013 Lippincott Williams & Wilkins, Inc.
adolescent idiopathic scoliosis; surgical correction; comparison of approaches; posterior; anterior; thoracoscopic