Children with EOS can experience progression of the spine and chest wall deformity as they grow. One goal of inserting the VEPTR and other devices is to halt the progressive thoracic and spine deformity to halt respiratory decline and perhaps improve respiratory function. Therefore, measuring lung functions in children with EOS before and after surgical therapy is an integral part of the overall evaluation process. However, when lacking pulmonary diagnostic services, structural features alone are used to make decisions about surgery. The key question is whether Cobb angle, as the most commonly used index of scoliosis severity, can suffice as a surrogate for respiratory function abnormalities as it has in patients with AIS [8
]. We describe (1) the preoperative relation between Cobb angle and FVC in infants with EOS using a validated lung function testing procedure for infants; (2) how the changes in Cobb angle before and after surgical correction of scoliosis relate to changes in distribution of lung ventilation and perfusion in the right and left lungs; and then (3) place these findings in the context of previously reported structure-respiratory function relations in children with EOS.
There are several limitations to the data presented in this report. First, most studies of structure and function, including ours, have been conducted on small numbers of patients and changes in both structure and function after surgery have been derived from only two time points. There are no published data on serial changes in structure and respiratory function over time during the preoperative period to determine how much change occurs in both domains as spine deformities worsen. This is important because halting progression of respiratory decline may be the primary outcome that is achieved with current surgical methods. Serial measurements both pre- and postoperatively are limited to small case series that do not describe both structure and functional features [6
]. The patient population is sufficiently small that multicenter studies are needed to address these knowledge gaps. Second, there are multiple ways to assess respiratory function. There are little data on the relationships among functional respiratory outcomes to one another. There is a need to standardize the ways that children with EOS are assessed using the most specific, sensitive, and predictive methods available for all age groups. This will require multidisciplinary collaboration among centers that care for this group of children.
With these limitations in mind, the data are consistent with previously published reports correlating structure and respiratory function in children with EOS. In a previous report of 24 children with congenital scoliosis studied preoperatively, their vital capacity values (ranging from 13% to 68% of predicted normal values) and their Cobb angles (range, 27º–150º) correlated poorly with an r value of 0.5 [9
]. More recently, Mayer and Redding reported a poor correlation between the preoperative vital capacities and the Cobb angles of 53 children 5 to 15 years of age with EOS identified from seven collaborating spine centers (r = 0.11) [4
] (Fig. A). Using lung scans, Redding et al. reported a poor correlation (r = −0.14) between lung function asymmetry (right versus left lung contributions to total ventilation and perfusion) and preoperative Cobb angles (range, 30°–112º) in 39 children with EOS, ages 20 to 186 months of age, with congenital or infantile scoliosis [10
] (Fig. B).
Fig. 2A–C Correlations are poor among (A) forced vital capacity (FVC), (B) lung function asymmetry based on lung perfusion scans, and (C) apnea-hypopnea index (AHI) during sleep with Cobb angle in children with early-onset scoliosis [4, 10, 11]. Reprinted with (more ...)
Lung function has also been assessed by evaluating breathing during sleep in children with EOS. The most common abnormality that was described in children with EOS during sleep is an elevated apnea-hypopnea index (AHI), which includes the number of apneas or hypopneas per hour that occur during sleep. Normally the AHI is higher in rapid eye movement (REM) sleep compared with other sleep stages [5
]. Among 13 children with EOS studied preoperatively, Cobb angles ranged from 30º to 105º; the overall AHI (normal less than one event/hour) was elevated to four/hour throughout the night but 17/hour specifically during REM sleep [11
]. The AHI did not correlate with Cobb angle (r = 0.16) (Fig. C).
The data from our second study are consistent with those in a previous report suggesting changes in lung function after surgery do not correlate with changes in Cobb angles postoperatively. In a series of 40 children who underwent VEPTR insertion for EOS, the mean Cobb angle was reduced from 58° ± 4.5° to 46° ± 4°, whereas FVC, expressed as a percent predicted, fell from 61% ± 4% to 54% ± 3% [4
]. The correlation coefficient between change in Cobb angle and postoperative change in FVC was poor (r = −0.11). Of interest, measures of lung volumes before and after VEPTR treatment demonstrated an increase in residual volume, ie, the volume residing in the chest after a vital capacity maneuver, but no increase in vital capacity [4
]. The pre- to postoperative comparisons were limited to older children who could perform spirometry and postoperative lung function measurements were conducted before the first VEPTR expansion and therefore represent short-term results.
Our observations demonstrate the Cobb angle, however convenient, does not correlate with respiratory functions awake or asleep in children with EOS [4
]. Although one study reported a relationship between vital capacity and Cobb angles in AIS [8
], the Cobb angle alone does not accurately reflect the three-dimensional deformities of the spine and chest wall in EOS and hence the respiratory consequences. It is therefore logical to measure respiratory functions in conjunction with structural assessments and use them as complementary data in clinical decision-making and assessment of new surgical approaches.
More importantly, the respiratory impact of VETPR treatment is not reflected by the improvements in Cobb angle postoperatively [4
]. FVC, for example, is dependent on both the size of the thorax and also its ability to move with respiration. An increase in intrathoracic volume and a straighter spine postoperatively do not necessarily lead to more chest wall mobility or excursion during inspiration. The increase in residual volume rather than FVC in older children undergoing VEPTR implantation suggests the lung may be initially stretched after surgery rather than immediately growing into the new intrathoracic space [4
]. Whether it promotes long-term postnatal lung growth remains to be determined.
There have been apparent recent advances in the treatment options available for children with severe or progressive EOS. The respiratory features of this high-risk patient population have been described, but the prognostic importance of these findings is unknown. However, there are now fewer opportunities to study the natural history of EOS because approved procedures are available for use. There is a pressing need to assess the relative short- and long-term impact of various growth modulation and growth guidance constructs from a respiratory perspective. Standardization of preoperative and postoperative assessments using both structural and functional measures would represent an important first step in addressing these issues.