Surgical correction of thoracic scoliosis often generates substantial debate regarding the best surgical approach and instrumentation construct.1,2 The anterior approach to scoliosis instrumentation has had proponents that suggest the primary advantages are shorter fusion and more normalized sagittal alignment.3–6 This may, however, come at the expense of approach-related morbidity, particularly with the double thoracotomy often required for anterior thoracic instrumentation.7–11
The effects of the thoracotomy on chest and shoulder girdle muscle function have been evaluated and found to be at least temporarily reduced after a standard thoracotomy.11 The effects on pulmonary function, however, may be more permanent.8 Early reductions in pulmonary function testing (PFT) values after thoracotomy are seen in the first year after surgery,7 and several studies have documented the effects as far as 2 to 5 years later.8–10 It has also been shown that disruption of the chest wall by thoracoplasty (with a posterior instrumentation approach) has a lasting detrimental effect on pulmonary function.12,13
The thoracoscopic approach was reintroduced into spinal surgery in the 1990s with the intent of reducing the morbidity associated with anterior thoracic surgery.14–16 Advantages in this technology eventually led to a means of performing a minimally invasive thoracoscopic correction of thoracic scoliosis with anterior instrumentation. The instrumentation and essential aspects of the open procedure were duplicated, allowing the surgery to be performed via much smaller skin incisions.17–20 Although the thoracoscopic approach has been claimed to be less invasive than the thoracotomy, there are few reports that compare the functional outcomes of these 2 techniques to support this claim.7,21,22 The purpose of this manuscript was to compare the pulmonary function of patients who underwent both open and thoracoscopic anterior thoracic scoliosis instrumentation.
This was part of an institutional review board-approved multicenter prospective study of the surgical treatment of adolescent idiopathic scoliosis. Pulmonary function data were prospectively collected in patients with structural thoracic scoliosis who met indications for anterior instrumented fusion. Posteroanterior and lateral radiographs of the spine in the standing position were obtained and classified according to the Lenke system.23
Inclusion criteria were all patients who had undergone isolated thoracic anterior instrumented spinal fusion by either an open or thoracoscopic approach. A minimum 2-year follow up was required. Patients requiring division of the diaphragm (thoracoabdominal approach) were excluded. The patients treated with a thoracotomy were subdivided based on whether an internal thoracoplasty was performed. Some surgeons in the group routinely osteotomized or removed a segment of the ribs adjacent to the spine as part of the procedure. Others surgeons, however, did not excise the rib heads or osteotomize the ribs for mobilization. Given the effect on pulmonary function of thoracoplasty performed posteriorly, a subgrouping of the open cases was performed to allow analysis of this variable. None of the thoracoscopic cases had rib osteotomy or rib head excision, so no subgrouping for these cases was possible. Thus, patients were divided into 3 groups: TSCOPIC included those instrumented thoracoscopically, OPEN−TP included patients with an open approach but not additional violation of the chest cage by thoracoplasty, and OPEN+TP involved thoracotomy approaches with an internal thoracoplasty included.
All patients underwent standard pulmonary function testing before surgery and at the 2-year post surgery time point. Plethysmography and spirometry testing were used to measure total lung capacity (TLC), forced vital capacity (FVC), and forced expiratory volume in 1 second (FEV1). Each test was repeated 3 times and the single best effort was used for the analysis. Age-, gender-, and height-matched standards published by the American Thoracic Society were used to generate percent predicted values for each pulmonary parameter.24
Repeated-measure analyses of variance were performed within surgical groups for the 3 PFT measures to identify any statistically significant changes from the preoperative to the 2-year postoperative measures. In order to evaluate the preoperative to postoperative changes between surgical groups, the difference in the PFT values from before surgery to 2 years after surgery was calculated for each patient and the results averaged for each group. Comparison among the 3 groups was done using analyses of variance with post hoc Bonferroni comparisons. Because of the multiple statistical analyses required, the level of significance of the overall P value of the study was set at 0.05 and adjusted using the Bonferroni method. This required a P value of less than 0.008 for each comparison in order to declare significance.
There were 107 patients that met the inclusion criteria for the study. This included 36 in the TSCOPIC group, 28 in the OPEN−TP group, and 43 in the OPEN+TP group. As expected, the vast majority of the patients (99 of 107) had a single thoracic curve pattern (Lenke 1). Additionally, there were 5 patients with Lenke 2 curves, 2 patients with Lenke 3 curves, and 1 patient with a Lenke 4 curve.
The 3 treatment groups were similar with regards to age and initial thoracic curve magnitude. This was also true for the postoperative correction and number of levels fused in each group. There were no statistical differences in these parameters between the 3 surgical groups (Table 1).
The baseline preoperative PFT values for the 3 groups were similar for all parameters measured. The TSCOPIC, OPEN−TP, and OPEN+TP groups had preoperative FVC values of 2.9 ± .7 L, 2.9 ± .6 L, and 3.0 ± .8 L, respectively (P = 0.70). This corresponded to percentage predicted values of 87% ± 19%, 83% ± 16%, and 91% ± 17%, respectively (P = 0.24) (Figure 1).
The FEV1 volumes were also comparable between the 3 surgical groups. The TSCOPIC, OPEN−TP, and OPEN+TP groups had preoperative FEV1 values of 2.5 ± .6 L, 2.5 ± .5 L and 2.5 ± 0.6 L, respectively (P = 0.77). This corresponded to percentage predicted values of 82% ± 16%, 79% ± 17%, and 87% ± 15%, respectively (P = 0.16) (Figure 2).
The TLC volumes were statistically similar with values of 3.4 ± .6 L, 3.3 ± 1.5 L, and 3.8 ± .9 L for the TSCOPIC, OPEN−TP, and OPEN+TP groups, respectively (P = 0.28). The corresponding percentage predicted values of 86% ± 13%, 84% ± 17%, and 87% ± 14% confirmed similar preoperative TLC for the 3 groups (P = 0.48) (Figure 3).
Change in Postoperative Pulmonary Function
Forced Vital Capacity.
The 2-year postoperative PFT values were compared with preoperative values and for FVC a significant change from the preoperative status was only noted in the OPEN+TP group (P < 0.001). In this group, the FVC declined 0.3 ± 0.5 L to a postoperative value at 2 years of 2.7 ± 0.7 L. The TSCOPIC and OPEN−TP groups had changes of 0.1 ± 0.5 L and −0.1 ± 0.3 L, respectively (P = 0.25; P = 0.10). There was a statistically significant difference in these changes between the 3 groups with individual comparisons confirming a significant (P = 0.003) difference in the FVC changes between the TSCOPIC and the OPEN+TP groups (Figures 1 and 4).
The changes after surgery in the percentage predicted FVC values showed similar trends, with the greatest decline seen in the patients treated with an open thoracotomy and a thoracoplasty (OPEN+TP). On average, all groups had a decline in the percent predicted FVC values. In the TSCOPIC group the change from 87% ± 19% to 86% ± 18% was not significant (P = 0.53). The OPEN−TP group dropped 8% ± 10% to 75% ± 17% (P = 0.003), while the OPEN+TP group declined even greater, 15% ± 11% (P < 0.001). The difference in these postoperative reductions was significant between the 3 groups. Among the individual comparisons only the difference between the TSCOPIC and OPEN+TP groups was significant (P < 0.001) (Figure 5).
Forced Expiratory Volume in 1 Second.
The FEV changed very little after surgery; however, there was a significant decline for the OPEN+TP group. The TSCOPIC average FEV1 gained 0.1 ± 0.4 L, while the OPEN−TP group was unchanged (0.0 ± 0.3) (P > 0.05 in both cases). The drop in the OPEN+TP group of 0.2 ± 0.3 L was significant (P = 0.002) (Figure 2). The changes in the percentage predicted values of FEV1 were −2% ± 9% in the TSCOPIC group and −5% ± 10% in the OPEN−TP group (TSCOPIC: P = 0.25; OPEN−TP: P = 0.02) were not statistically significant. Again, the greatest drop after surgery occurred in the OPEN+TP group with a decline in the percentage predicted FEV1 of 14% ± 12% (P = 0.002) (Figure 5). This drop in FEV1 percent predicted in the OPEN+TP group was significantly different from the changes in both the TSCOPIC (P < 0.001) and OPEN−TP (P = 0.002) groups. The differences between the TSCOPIC and the OPEN−TP group were not significant. With regards to the change in FEV1 volume values, only TSCOPIC and OPEN+TP groups were significantly different (P = 0.003) (Figure 4).
Total Lung Capacity.
The TLC in the TSCOPIC group improved 0.5 ± 0.5 L to a value of 4.0 ± .7 L after surgery; this increase was statistically significant (P < 0.001). The 2 open groups had insignificant changes in TLC after surgery; OPEN−TP increased 0.1 ± 1.3 L, while the OPEN+TP group dropped 0.3 ± 0.1 L. There was no significant difference in the postoperative changes between the 3 groups (P > 0.2) (Figures 3 and 4).
The normalized percent predicted TLC values improved 6% ± 10% for the TSCOPIC group, whereas the OPEN−TP group on average was unchanged (0% ± 6%). The OPEN+TP group, however, experienced a statistically nonsignificant decline in the percent predicted TLC of 8% ± 14% (P = 0.02). As with the TLC volumes, there was no difference between the 3 groups with regards to the changes in the percent predicted TLC values (P > 0.05) (Figures 3 and 5).
The results of this analysis suggest a clear benefit of thoracoscopic anterior instrumentation for thoracic scoliosis with regards to pulmonary function compared with open thoracotomy procedures where multiple rib heads are excised as part of the open approach. The chest cage and pulmonary function recovery 2 years after anterior scoliosis correction was complete in the thoracoscopic patients. All 3 of the PFT variables measured (FVC, FEV1, TLC) as a percentage of predicted were back to baseline without a significant difference from preoperative levels. This was not the case for the open procedures, where the OPEN−TP group had a significant drop in the percent predicted FVC and the OPEN+TP group had significant reductions in both FVC and FEV1. These data support the concept that increasing surgical dissection/disruption of the chest cage is associated with increasing loss of pulmonary function 2 years after surgery.
The thoracoscopic approach to the spine has been suggested to be “less invasive” because of the smaller skin incisions, yet the size of the incision on the skin certainly does not tell the entire story. Multiple intercostals portals (each which disrupt the intercostals muscles and to some degree the serratus anterior and/or latissimus dorsi muscles) are used to achieve thoracoscopic spinal instrumentation. The question of whether the sum effect of all of these portal dissections equals that of a thoracotomy with or without rib osteotomies prompted this investigation. The open approach has been previously shown to have long-term detrimental effects on pulmonary function, and the present data support these prior studies.9
The open approach for anterior thoracic instrumentation can be accomplished in a variety of manners. Depending on the number of vertebra to be instrumented, surgeon preference, and curve flexibility, the approach may be by single or double thoracotomy. Rib head excision is routine for some surgeons and not for others. Advocates of rib head excision note greater mobilization of the spine, access to the posterior aspect of the disc, and posterior longitudinal ligament for removal and more secure screws with greater purchase in the posterior half of the vertebral body. This also affords a thoracoplasty effect, allowing the rib hump to collapse anteriorly. It was a standard component of the procedure as described by Harms et al25 and Betz et al.26 Not all the members of our study group have felt this was required and some of the patients were treated by the thoracotomy approach without excision or osteotomy of multiple ribs. Although the statistical analysis comparing the effect on PFTs of the 2 open approaches only demonstrated a statistical difference in the change in FEV1, the power to do so was low (P = 0.5). The trends certainly suggest a greater detrimental effect on pulmonary function in the group with disruption of multiple ribs.
The effect of open anterior instrumentation approaches has been evaluated in the literature, with the most recent report by Kim et al suggesting a reduction in pulmonary function that remains 5 years after surgery.9 Early time points from the same group suggested less impairment at 2 years after surgery, particularly in the absolute volume measures.8 Data comparing the open and endoscopic approach effects on PFT are sparse. Lenke et al compared open endoscopic anterior release (without anterior instrumentation) in combination with posterior instrumentation and found no significant pulmonary function benefit to the minimally invasive approach for this procedure combination 2 years after surgery.22 On the other hand, comparing the open and thoracoscopic anterior instrumentation, Faro et al did find less effect on early postoperative pulmonary function with the minimally invasive approach.7 That study suggested a greater reduction at 3 months in the open group with an incomplete recovery in both the percentage predicted and absolute values for FVC and FEV1 1 year after surgery for the open approach.
Review of these studies emphasizes the importance of the percentage predicted values (compared with the absolute volumes) for comparisons over time, particularly in immature patients who can be expected to increase their PFT absolute values based purely on growth. Normalizing these values for age and size should largely correct for the increase in lung volumes that relates to growth, allowing the effect of the intervention (surgery in this case) to be measured. Caution is thus required in interpreting the changes in PFT absolute volumes. It is however valid to compare the relative change in PFT volumes between the 3 surgical groups. Absolute volumes in the thoracoscopic group generally increased while OPEN+TP group volumes generally decreased. However, the percentage predicted values are most appropriate to compare the preoperative to postoperative values for a given approach.
Although the percentage predicted values are best for comparing data at 2 points in time for a single patient and normalizing different size patients within a population, it does introduce another source of error and variation into the data. For this study, PFTs were performed at multiple sites with similar but not identical equipment and technicians. PFT results are without question dependent on patient effort and cooperation, a variable that is difficult to control. The statistical analysis of an appropriately sized study population should address many of these issues, especially if a significant effect is found, as in the comparison of the effect on PFT over time between the TSCOPIC and OPEN+TP groups. The number of patients, however, resulted in a relatively low overall power (P = 0.5), which makes conclusions about a lack of demonstrable effect difficult. Despite these challenges, this report represents one of the largest comparisons of open and thoracoscopic anterior scoliosis procedures, particularly with regard to pulmonary function.
The 3 surgical groups were comparable with regard to curve magnitude, age, and preoperative pulmonary function. Two years following anterior thoracic scoliosis correction, the thoracoscopic group was superior with regards to both absolute PFT volumes and percent predicted values compared with the open thoracotomy group that included a thoracoplasty. With regards to pulmonary function, the thoracoscopic instrumentation approach is truly minimally invasive with no lasting effect on pulmonary function at 2 years after surgery. This is unfortunately not the case for the open approach, particularly when performed with rib head excision and an internal thoracoplasty.
- At 2 years postoperative, patients who underwent thoracoscopic anterior instrumented fusion for scoliosis returned to baseline pulmonary function or better.
- Two years after surgery, patients who underwent open thoracotomy without a thoracoplasty had percent predicted forced vital capacity values that were significantly reduced compared with preoperative.
- The addition of thoracoplasty to an open thoracotomy caused an even greater decrease in pulmonary function at 2 years postoperative, and this difference was statistically significant compared with the thoracoscopic group.
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