Abstract
Background:The long-term pulmonary function of patients with
adolescent idiopathic scoliosis undergoing surgical correction is uncertain.
To our knowledge, no report has demonstrated the changes in pulmonary function
five years or more following spinal arthrodesis with use of modern segmental
spinal instrumentation techniques for the treatment of all types of adolescent
idiopathic scoliosis in a similar adolescent population.
Methods:One hundred and eighteen patients with adolescent idiopathic
scoliosis undergoing surgical treatment at a single institution were evaluated
with pulmonary function tests to assess the absolute and percent-predicted
value of forced vital capacity and forced expiratory volume in one second at
the preoperative examination and at regular intervals postoperatively. The
patients were divided into four groups depending upon the surgical procedure:
Group 1 comprised forty-nine patients who had posterior spinal arthrodesis
with iliac crest bone graft; Group 2, forty-one patients who had posterior
spinal arthrodesis with thoracoplasty; Group 3, sixteen patients who had open
anterior spinal arthrodesis with a rib resection thoracotomy; and Group 4,
twelve patients who had combined anterior and posterior spinal arthrodesis
with a rib resection thoracotomy and iliac crest bone graft, respectively.
Results:A comparison of absolute pulmonary function values from the
preoperative and final follow-up evaluations demonstrated a significant (p
< 0.0001) increase in both the forced vital capacity and the forced
expiratory volume in one second for Group 1, whereas no change was seen in
those values for Groups 2, 3, and 4. A comparison of the changes in the
percent-predicted pulmonary function values demonstrated significant (p <
0.05) decreases in forced vital capacity and forced expiratory volume in one
second for Groups 2, 3, and 4, except for the latter value for Group 4,
whereas Group 1 had no change.
Conclusions:Patients who have had any type of chest cage disruption
during the surgical treatment of adolescent idiopathic scoliosis demonstrate
no change in the absolute value and a significant decline in the
percent-predicted value of pulmonary functions at five years following
surgery. Chest cage preservation is recommended to maximize both absolute and
percent-predicted pulmonary function values after surgical treatment of
adolescent idiopathic scoliosis.
Level of Evidence:Therapeutic Level III. See Instructions
to Authors for a complete description of levels of evidence.
The scoliotic spinal deformity of lateral flexion and rotation of
the involved vertebrae around a vertical axis and the attached ribs causes
chest cage stiffness, reduced hemidiaphragmatic movement, and uneven
distribution of the inhaled air on the concave side resulting in a decrease in
pulmonary
function1-3.
The effect of surgical correction on the pulmonary function of patients with
adolescent idiopathic scoliosis is controversial. Although some investigators
have shown that surgical correction of scoliosis substantially improves
measured pulmonary functions such as vital
capacity4-11,
others have demonstrated no major improvement in pulmonary function after
operative
correction11-15
or have reported loss of pulmonary function
postoperatively15-19.
The controversies could perhaps be attributed to the fact that these studies
were done on nonhomogeneous populations with different treatment modalities,
age distribution, gender, curve patterns, curve severity, and etiology of the
scoliosis and with various measurement techniques and parameters of pulmonary
function evaluation such as the use of absolute versus percent-predicted
values. Only one study that we know of has described the long-term effect of
pulmonary function changes relative to the types of surgical procedure used
for spinal arthrodesis in patients with adolescent idiopathic
scoliosis10.
The purpose of the present study was to evaluate prospectively, at regular
intervals for a minimum of five years postoperatively, the changes in
pulmonary function after surgical correction of adolescent idiopathic
scoliosis.
Following institutional review board approval, we studied 118
patients with adolescent idiopathic scoliosis who were surgically treated by
two surgeons at our institution between 1985 and 1997. Both the data on
pulmonary function and radiographic changes at the preoperative and
postoperative examinations were obtained prospectively and then were
retrospectively evaluated. All patients had a minimum of five years of
follow-up (mean, six years; range, five to sixteen years). No patient had
prior spinal surgery.
Demographic Data
There were 110 girls and eight boys. The mean age (and standard deviation)
of the patients was 14.4 ± 1.9 years (range, 10.9 to eighteen
years).
The patients were classified according to the surgical classification
system of adolescent idiopathic scoliosis described by Lenke et
al.20. Sixty-three
patients (53%) had type-1 curves (main thoracic); eighteen (15%), type-2
curves (double thoracic); seven (6%), type-3 curves (double major); four (3%),
type-4 curves (triple major); fifteen (13%), type-5 curves (major
thoracolumbar/lumbar); and eleven (9%), type-6 curves (major
thoracolumbar/lumbar and minor thoracic structural). Forty patients had a
lumbar A modifier; twenty-two, a lumbar B modifier; and fifty-six, a lumbar C
modifier. The lumbar spine modifier was based on the relationship of the
center sacral vertical line, which should bisect the cephalad aspect of the
sacrum and be perpendicular to the true horizontal to the lumbar curve on the
coronal radiograph. The lumbar A modifier is used when the center sacral
vertical line runs between the lumbar pedicles at the apex of the lumbar
curve. The lumbar B modifier is used when the center sacral vertical line
touches the lumbar concave pedicle at the apex of the lumbar curve. The lumbar
C modifier is used when the center sacral vertical line falls completely
medial to the concave pedicle at the apex lumbar vertebra. The sagittal
thoracic modifier revealed normal kyphosis (T5 to T12 was +10° to
+40°) in eighty-five patients, hypokyphosis (T5 to T12 was less than
+10°; mean, 2.2°; range, -12° to 9°) in twenty-six patients,
and hyperkyphosis (T5 to T12 was greater than +40°; mean, +46.3°;
range, +42° to +53°) in seven patients.
For the purposes of evaluation, the patients were divided into four groups
depending upon the surgical procedure used for the spinal arthrodesis. The
surgical procedure was chosen on the basis of the curve type, magnitude,
flexibility, cosmetic appearance, and surgeon's preference. Indications for
anterior release included a major coronal Cobb angle of >80° with
lessened flexibility, thoracic hypokyphosis or hyperkyphosis, and skeletal
immaturity of the patient. Indications for anterior spinal arthrodesis and
instrumentation included a single thoracic or thoracolumbar curve with a
hypokyphotic thoracic spine and, preferably, instrumentation involving less
than seven vertebral bodies. Indications for a thoracoplasty included a
preoperative rib prominence of >15°, measured with use of a
scoliometer, and an expressed concern with the prominence of the rib hump
deformity by the patient and/or the caregiver. Without any of the specific
indications mentioned above, posterior spinal arthrodesis and segmental spinal
instrumentation with iliac crest bone graft was preferred. The patients were
divided into four groups depending upon the surgical approach: Group 1
included forty-nine patients who had posterior spinal arthrodesis with iliac
crest bone graft; Group 2, forty-one patients who had posterior spinal
arthrodesis with thoracoplasty; Group 3, sixteen patients who had open
anterior spinal arthrodesis with a rib resection thoracotomy; and Group 4,
twelve patients who had a combined anterior and posterior spinal arthrodesis
with a rib resection thoracotomy and iliac crest bone graft, respectively.
Pulmonary Function
All patients in this study had pulmonary function tests to evaluate
pulmonary volume and flow preoperatively and at three months, one year, two
years, and five years or more postoperatively. We excluded the patients who
were smokers and those with any comorbidities such as acute and chronic upper
respiratory infection or asthma. All pulmonary function tests were performed
on the same computerized spirometer (6200 Auto-box; SensorMedics, Yorba Linda,
California) that had an accuracy of ±3%, which met the criteria of the
American Thoracic
Society21. The
tests were performed with the patient standing, each measurement was repeated
three times, and the highest reading was selected. Pulmonary function test
results were expressed both as absolute values as well as percent-predicted
values with use of the arm span as representative of
height22,23.
The reason we used arm span rather than height was to make up for the loss of
trunk height caused by the scoliosis and the subsequent gain of trunk height
resulting from the spinal instrumentation. For the purposes of analysis and
comparison of pulmonary function of the four groups of patients, we chose the
forced vital capacity and forced expiratory volume in one second. The forced
expiratory volume in one second is a measurement both of volume and of mean
flow over the first second. The reductions in forced expiratory volume in one
second reflect the total effects of reduction in total lung capacity,
obstruction of the airways, loss of lung recoil, and relatively uncommon,
gross weakness of respiratory muscles. We chose these two parameters because
they provide an adequate assessment of the volume and flow functions as
measured by the pulmonary function
tests15. The
severity of the abnormality in forced expiratory volume in one second was
categorized as a mild, moderate, or severe impairment. Mild impairment was
defined as 65% to 80% of the normal value, moderate impairment was 50% to 64%
of the normal value, and severe was <50% of
normal24.
Radiographic Measurements
Coronal and lateral radiographs of the spine on 91-cm-long cassettes were
made with the patient standing. Preoperative and postoperative radiographic
measurements of the spinal curvature in the coronal plane were performed with
use of the Cobb
method25. Kyphosis
of the thoracic spine was measured, with use of the Cobb method, from the
superior end-plate of T5 to the inferior end-plate of T12. All radiographic
measurements were done by one of the authors (Y.J.K.), a senior spinal
surgeon, independent of the operative team.
Operative Procedure
All forty-nine patients in Group 1 had a posterior arthrodesis of the spine
with segmental Cotrel-Dubousset instrumentation with hooks, wires, and screws
(Medtronic Sofamor Danek, Memphis, Tennessee) and iliac crest bone-grafting.
Cotrel-Dubousset instrumentation was used in forty-three patients, and
Cotrel-Dubousset Horizon instrumentation (CDH; Medtronic Sofamor Danek) was
used in six patients.
All forty-one patients in Group 2 had a posterior arthrodesis of the spine
with use of Cotrel-Dubousset instrumentation (thirty-six had Cotrel-Dubousset
instrumentation, and five had CDH instrumentation) with a thoracoplasty as
described by Lenke et
al.16. A mean of
six ribs (range, five to eight ribs) were partially resected for the
thoracoplasty. After segmental excision, the ribs were not sutured tightly nor
approximated. The transverse processes were not excised.
In the sixteen patients in Group 3, an anterior arthrodesis of the spine
with a rib resection thoracotomy was performed. In thirteen patients, an
anterior arthrodesis of the spine by means of a rib resection thoracotomy as
well as a retroperitoneal approach (thoracolumbophrenotomy) was done. Fourteen
patients were managed with a flexible rod system; nine of them had Harms
instrumentation (DePuy AcroMed, Raynham, Massachusetts), and five had Zielke
instrumentation (Osteonics, Allendale, New Jersey). Solid Cotrel-Dubousset
instrumentation was used in the remaining two patients.
The twelve patients in Group 4 had an anterior arthrodesis of the spine by
means of a rib resection thoracotomy with or without a retroperitoneal
approach to the spine combined with a posterior arthrodesis and segmental
instrumentation of the spine as described above. Autogenous rib and posterior
iliac crest bone grafts were used for anterior and posterior arthrodesis,
respectively. Seven of the twelve patients in Group 4 also had anterior
instrumentation (Zielke anterior instrumentation in four patients, Harms
anterior instrumentation in two patients, and Texas Scottish Rite Hospital
anterior instrumentation in one patient) combined with a posterior
Cotrel-Dubousset implant (Cotrel-Dubousset instrumentation in eight and CDH
instrumentation in four patients). Noninstrumented anterior spinal arthrodesis
was performed in the remaining five patients.
Postoperatively, no patient in Groups 1, 2, or 4 was managed with
immobilization in an orthosis. The patients were initially engaged in a
supervised physical therapy program to encourage gentle mobilization of the
unfused segments of the spine. They were given a home exercise protocol to be
done for four to six months until they regained the preoperative level of
daily physical activities. Six patients in Group 3 were placed in a molded
thoracolumbosacral orthosis for four months. These patients were subsequently
given the same home exercise protocol as the patients in Groups 1, 2, and 4.
No patient had a video-assisted thoracoscopic surgery.
Statistical Analysis
The data were analyzed with use of the Statistical Analysis System (version
8.2, 1999; SAS Institute, Cary, North Carolina). The distributions of the
variables are given as the means, standard deviations, and ranges. Pearson
correlations were used to assess the association among radiographic
measurements and pulmonary function test results at the preoperative and final
time-points. Comparisons across the groups for measurements made at one
time-point were performed with use of analysis of variance. The Tukey honestly
significant difference test was used to determine which groups were
significantly different. For continuous variables measured at two time-points,
paired t tests were used for assessment of the change over time within a
group. For variables measured at more than two time-points, longitudinal
analyses were carried out with use of mixed-model repeated-measures analysis
of variance. The primary focus of analysis testing for change-over-time within
a group was on the significance of the time effect. When the time effect was
significant and within the frame-work of the mixed-model analysis, the
appropriate statistical contrasts were used in testing the null hypothesis
that no change occurred between two specific time-points. Of particular
interest were comparisons assessing the change between the values at the
preoperative evaluation and those at each follow-up examination and assessing
the change between the values at the two-year and final follow-up evaluations.
A p value of <0.05 was considered significant.
Radiographic Results
The mean Cobb angles at the preoperative and final follow-up
evaluations were 56° and 28° (a 50% correction), respectively, for
Group 1; 64° and 36° (a 44% correction) for Group 2; 56° and
24° (a 57% correction) for Group 3; and 66° and 35° (a 47%
correction) for Group 4. The mean thoracic kyphosis angles at the preoperative
and final follow-up examinations were 16° and 22°, respectively, for
Group 1; 27° and 27° for Group 2; 17° and 27° for Group 3; and
22° and 24° for Group 4 (Table
I). A negative correlation was detected between the preoperative
Cobb angle of the major curve and both the percent-predicted forced vital
capacity (r = -0.18, p = 0.04) and the forced expiratory volume in one second
(r = -0.26, p = 0.005). A negative correlation was found between the number of
involved vertebrae in the major curve and both the percent-predicted forced
vital capacity (r = -0.27, p = 0.003) and the forced expiratory volume in one
second (r = -0.23, p = 0.02) at the preoperative evaluation and between the
number of involved vertebrae in the major curve and the percent-predicted
forced vital capacity (r = -0.34, p = 0.0002) and forced expiratory volume in
one second (r = -0.32, p = 0.0005) at the final follow-up evaluation. We did
not measure the vertebral rotation because the Cobb angle difference and the
number of involved vertebrae in the major curve are closely related and
because of the known inaccuracy of measurements of vertebral body rotation.
However, no correlation was detected between the number of fused vertebral
bodies and the final pulmonary function tests.
Because there were too few patients with Lenke type-3, 4, and 6 curves and
as the curves had common characteristics, we grouped them together to reduce
the statistical bias in the comparison of Lenke curve types. Analysis of
variance indicated that there was a slightly significant difference between
Lenke groups (p = 0.045). We found that patients with a Lenke type-5 curve
(thoracolumbar/lumbar) had a significantly larger forced expiratory volume in
one second preoperatively than did those with a Lenke type-1 curve (main
thoracic) (p = 0.045). A comparison of the preoperative and postoperative
pulmonary function tests among the three different sagittal modifiers
demonstrated no significant differences, with the numbers available (p = 0.061
for preoperative forced vital capacity, p = 0.42 for final forced vital
capacity, p = 0.61 for preoperative forced expiratory volume in one second,
and p = 0.30 for final forced expiratory volume in one second).
Group 1: Posterior Spinal Arthrodesis with Autogenous Iliac Crest
Bone Graft
The mean age of the forty-nine patients in Group 1 was 14.3 ± 1.9
years (range, 10.9 to eighteen years), and the mean follow-up period was 6.9
years (range, five to sixteen years). Twenty-nine patients had type-1 curves;
six, type-2 curves; three, type-3 curves; five, type-5 curves; and six, type-6
curves. Eighteen patients had a lumbar A modifier; eight, a lumbar B modifier;
and twenty-three, a lumbar C modifier. Fifteen patients had a hypokyphotic
sagittal modifier, thirty-three had a normal sagittal modifier, and one had a
hyperkyphotic sagittal modifier. The mean Cobb angle was 56° ±
10° (range, 37° to 82°) preoperatively and 28° ±
11° (range, 9° to 48°) at the final evaluation. The mean thoracic
kyphosis was +16° ± 12° (range, -9° to 50°)
preoperatively and +22° ± 9° (range, 7° to 42°) at the
time of the final follow-up. A significant change was detected in the Cobb
angle and the thoracic kyphosis after surgery compared with the preoperative
values (p < 0.05) (Table
I).
Group 2: Posterior Spinal Arthrodesis with Concomitant
Thoracoplasty
The mean age of the forty-one patients in Group 2 was 14.4 ± 1.8
years (range, 11.5 to eighteen years), and the mean follow-up period was six
years (range, five to nine years). Twenty-one patients had type-1 curves; ten,
type-2 curves; three, type-3 curves; three, type-4 curves; one, a type-5
curve; and three, type-6 curves. Fourteen patients had a lumbar A modifier;
eight, a lumbar B modifier; and nineteen, a lumbar C modifier. Four patients
had a hypokyphotic sagittal modifier, thirty-two had a normal sagittal
modifier, and five had a hyperkyphotic sagittal modifier. The mean Cobb angle
was 64° ± 11° (range, 45° to 88°) preoperatively and
36° ± 10° (range, 17° to 54°) at the time of the last
follow-up. The mean thoracic kyphosis was +27° ± 13° (range,
-6° to 53°) preoperatively and +27° ± 11° (range,
6° to 60°) at the time of the final follow-up. A significant change
was detected in the Cobb angle compared with the preoperative values
(Table I). A total of 226 (90%)
of the 250 resected ribs regenerated three to six months after the operation.
The shape of the regenerated area assumed a lazy s-shape with deformed ribs in
the coronal plane. Some of them demonstrated synostosis around the resection
site.
Group 3: Anterior Spinal Arthrodesis with a Rib Resection
Thoracotomy
The mean age of the sixteen patients in Group 3 was 15.4 ± 1.5 years
(range, 13.7 to 17.8 years), and the mean follow-up period was 5 ± 0.7
years (range, five to 7.5 years). Ten patients had type-1 curves, one had a
type-2 curve, and five had type-5 curves. Four patients had a lumbar A
modifier; six, a lumbar B modifier; and six, a lumbar C modifier. Six patients
had a hypokyphotic sagittal modifier, and ten had a normal sagittal modifier.
The mean Cobb angle was 56° ± 8° (range, 43° to 74°)
preoperatively and 24° ± 12° (range, 4° to 43°) at the
time of the last follow-up. The mean thoracic kyphosis was 17° ±
15° (range, -12° to 34°) preoperatively and 27° ±
11° (range, 2° to 41°) at the time of the last follow-up. A
significant change was detected in the Cobb angle and the thoracic kyphosis
after surgery compared with the preoperative values (p < 0.05)
(Table I).
Group 4: Combined Anterior and Posterior Spinal Arthrodesis with
Autogenous Rib and Iliac Crest Bone Graft, Respectively
The mean age of the twelve patients in Group 4 was 13.7 ± 2.1 years
(range, eleven to 17.8 years), and the mean follow-up period was 5.3 ±
0.5 years (range, five to 6.2 years). Three patients had type-1 curves; one, a
type-2 curve; one each, a type-3 and a type-4 curve; four, type-5 curves; and
two, type-6 curves. Four patients had a lumbar A modifier, and eight had a
lumbar C modifier. One patient had a hypokyphotic sagittal modifier, ten had a
normal sagittal modifier, and one had a hyperkyphotic sagittal modifier. The
mean Cobb angle was 66° ± 22° (range, 35° to 110°)
preoperatively and 35° ± 16° (range, 7° to 55°) at the
final follow-up evaluation. The mean thoracic kyphosis was +22° ±
11° (range, 4° to 42°) preoperatively and 24° ± 12°
(range, 4° to 39°) at the time of the final follow-up. A significant
change was detected in the Cobb angle after surgery compared with the
preoperative values (p < 0.05) (Table
I).
Pulmonary Function Test
When the severity of the pulmonary impairment was analyzed preoperatively,
fifty-four (46%) of the 118 patients had normal findings. Forty-three patients
(36%) demonstrated mild impairment, and twenty-one (18%) had moderate
impairment. Forty-four patients (37%) had normal findings at the final
follow-up evaluation. Forty-nine patients (42%) demonstrated mild impairment,
and twenty-five (21%) had moderate impairment at the final follow-up
evaluation.
When all patients were evaluated, the mean absolute forced vital capacity
was 2.84 ± 0.72 L (range, 1.39 to 5.67 L) at the preoperative
examination and increased to 3.14 ± 0.66 L (range, 1.49 to 5.87 L) at
the final follow-up examination. The mean absolute forced expiratory volume in
one second was 2.41 ± 0.62 L (range, 0.98 to 4.98 L) at the
preoperative evaluation and increased to 2.56 ± 0.55 L (range, 1.40 to
4.96 L) at the final follow-up evaluation. The mean percent-predicted forced
vital capacity was 85% ± 16% (range, 50% to 134%) at the preoperative
examination and decreased to 78% ± 14% (range, 44% to 114%) at the
final follow-up examination. The mean percent-predicted forced expiratory
volume in one second was 80% ± 16% (range, 49% to 131%) at the
preoperative evaluation and decreased to 75% ± 13% (range, 44% to 105%)
at the time of the final follow-up.
Group 1: Posterior Spinal Arthrodesis with Autogenous Iliac Crest
Bone Graft
At a mean follow-up of 6.9 years, the absolute value of forced vital
capacity and forced expiratory volume in one second demonstrated continued
improvement compared with the preoperative values (the forced vital capacity
increased from 2.81 to 3.23 L [p < 0.0001] and forced expiratory volume in
one second increased from 2.41 to 2.71 L [p < 0.0001]) (see Appendix).
During the same time-period, the percent-predicted values of forced vital
capacity and forced expiratory volume in one second demonstrated no change
between the preoperative and final follow-up values (84% and 82%,
respectively, for forced vital capacity [p = 0.63] and 81% and 80% for forced
expiratory volume in one second [p = 0.52]) (see Appendix).
Group 2: Posterior Spinal Arthrodesis with Concomitant
Thoracoplasty
At a mean follow-up of six years, the absolute values of forced vital
capacity were unchanged from 2.92 to 3.0 L (p = 0.16) and those of forced
expiratory volume in one second were unchanged from 2.43 to 2.52 L (p = 0.36)
(see Appendix). During the same time-period, the percent-predicted values of
forced vital capacity decreased from 86% to 76% (p = 0.0005), and those of
forced expiratory volume in one second decreased from 80% to 72% (p = 0.009)
(see Appendix).
Group 3: Anterior Spinal Arthrodesis with a Rib Resection
Thoracotomy
At a mean follow-up of five years, the absolute values of forced vital
capacity were unchanged from 3.07 to 2.8 L (p = 0.06), and those of forced
expiratory volume in one second were unchanged from 2.6 to 2.4 L (p = 0.07)
(see Appendix). However, these data suggest a trend toward a decline in the
postoperative pulmonary function test values. At the same time-period, the
percent-predicted values of forced vital capacity decreased from 90% to 75% (p
< 0.0001), and those of forced expiratory volume in one second decreased
from 83% to 72% (p = 0.002) (see Appendix). This group can be subdivided into
the thoracotomy group (ten patients) and the thoracoabdominal approach group
(six patients). In the thoracotomy group, the absolute values of forced vital
capacity decreased from 2.9 to 2.6 L, and the percent-predicted values changed
from 86% to 69%. The values for forced expiratory volume in one second
decreased from 2.6 to 2.2 L, and the percent-predicted values changed from 79%
to 67%. In the thoracoabdominal approach group, the absolute values of forced
vital capacity decreased from 3.2 to 3.10 L, and the percent-predicted values
changed from 96% to 84%. The values for forced expiratory volume in one second
decreased from 2.76 to 2.65 L, and the percent-predicted values changed from
91% to 80%. This group was also subdivided into the hypokyphosis group (six
patients), which demonstrated a mean thoracic kyphosis increase from 1°
preoperatively to 22° at the time of the last follow-up, and the normal
kyphosis group (ten patients), which demonstrated a mean increase in the
thoracic kyphosis from 26° preoperatively to 30° at the time of the
last follow-up. In the hypokyphosis group, the absolute values of forced vital
capacity decreased from 2.92 to 2.62 L, and the percent-predicted values
changed from 83% to 66%. The values of forced expiratory volume in one second
decreased from 2.75 to 2.33 L, and the percent-predicted values changed from
79% to 67%. In the normal kyphosis group, the absolute values of forced vital
capacity decreased from 3.16 to 2.95 L, and the percent-predicted values
changed from 94% to 80%. The values of forced expiratory volume in one second
decreased from 2.63 to 2.48 L, and the percent-predicted values changed from
86% to 75%.
Group 4: Combined Anterior and Posterior Spinal Arthrodesis with
Autogenous Rib and Iliac Crest Bone Graft, Respectively
At a mean follow-up of five years, the forced vital capacity (absolute
value) showed no significant change from 2.38 to 2.55 L (p = 0.15). The forced
expiratory volume in one second (absolute value) showed a similar change from
2.00 to 2.14 L (p = 0.20) (see Appendix). At the same time-period, the
percent-predicted value of forced vital capacity demonstrated a significant
decrease from 81% to 70% (p = 0.02). The percent-predicted value of forced
expiratory volume in one second demonstrated no significant change from 73% to
67% (p = 0.16). Thus, the percent-predicted values at five years in this group
showed a significant decrease compared with preoperative values in the forced
vital capacity, but only a trend toward a decrease in the forced expiratory
volume in one second.
Although the rapid growth in the total number of pulmonary alveoli
ends around two years of age, the growth and development of the pulmonary
system is completed at about fifteen to sixteen years of age in girls and
eighteen to nineteen years of age in
boys26. After a
plateau period until the age of thirty-five years, there is a definite decline
in pulmonary function during the remainder of adult
life27. The growth
rate of the pulmonary function tests also varies with a child's stage of
growth23,28.
The point estimates of the somatic growth peak velocities precede all peak
pulmonary function tests in both males and
females29. Before
Wang et al.23
reported the pulmonary function data of children between six and eighteen
years old, which was based on 82,462 annual measurements from 11,630 white
children and 989 black children in 1993, reference pulmonary function test
data were subjective and were based on small population groups. Because
adolescence is a period of rapid growth and pulmonary function changes occur
independently of growth (by maturation ["age effect"]), sex, race,
body surface, smoking habit, and age at which peak velocity occurs, we need to
standardize the data to isolate the effect of the surgical technique itself on
pulmonary function tests as much as
possible23,27-31.
Our data did not include all of these compounding factors, and we have no
knowledge of their influence on these patients. Because there is a discrepancy
between arm span and height due to the changes that occur with thoracic
fusion, we elected to use both percent-predicted pulmonary function test
values as well as absolute values as objective and reliable parameters for
comparison on the basis of arm span, age, sex, race, and the published
reference values in the study by Wang et
al.23.
The current study demonstrated a significant negative correlation between
the preoperative Cobb angle and percent-predicted pulmonary function test
values and a significant negative correlation between the number of involved
vertebrae in the major curve and percent-predicted pulmonary function test
values. The smaller number of involved vertebrae in the major curve had a
strong correlation with higher pulmonary function test values preoperatively,
as in Lenke type-5 curves. However, the number of fused vertebrae did not
demonstrate any correlation with change in the pulmonary function test values.
Regarding the differences and changes in thoracic kyphosis, no correlations
were detected between the thoracic kyphosis and pulmonary function tests.
These results supported the finding that the larger Cobb angle and more
involved vertebrae in the major curve had a strong correlation with poor
pulmonary function tests, while the differences in the thoracic kyphotic angle
in adolescent idiopathic scoliosis did not affect the pulmonary function tests
because of small differences between patients with normal kyphosis and those
with hyperkyphosis or hypokyphosis.
The reported results of Harrington instrumentation and posterior spinal
arthrodesis with iliac crest bone graft on pulmonary function have varied from
an improvement in pulmonary function after
surgery4-7,9-11
to no
change12,14
or to a postoperative decline in pulmonary
function17-19.
After the introduction of modern segmental spinal instrumentation systems with
multiple hook and rod constructs aiming at three-dimensional correction, the
reported pulmonary function values have also varied, showing an improvement in
pulmonary function after
surgery8,32
to no change15 or
to a postoperative decline in pulmonary
function17-19.
In the current study, the patients in Group 1 (posterior spinal arthrodesis
with iliac crest bone-grafting) demonstrated a significant increase in
absolute pulmonary function; however, the change in percent-predicted
pulmonary function during the mean 6.9-year follow-up period was not found to
be significant. This suggests that the correction of the deformity and a
posterior spinal arthrodesis with use of iliac crest bone graft stabilizes
pulmonary function during the remainder of adolescent growth.
Several studies have focused on pulmonary function test changes after
thoracoplasty in patients with adolescent idiopathic
scoliosis15,16,33,34.
Pulmonary function test values after posterior spinal arthrodesis with
thoracoplasty have demonstrated initial substantial declines with a return to
normal
values16,33,34
or a decline at the time of the final follow-up after
surgery15,16.
In the current study, the patients in Group 2 (those who had posterior spinal
arthrodesis and thoracoplasty) demonstrated no significant change in absolute
pulmonary function; however, they had a significant decrease in the
percent-predicted pulmonary function at a mean of six years postoperatively.
This suggests that the regenerated ribs, which appeared between three and six
months postoperatively, did not allow proper function of the chest cage
because of a nonunion or a deformed shape of the regenerated rib or because of
a synostosis between the regenerated ribs created by the thoracoplasty
procedure.
Recently, thoracoscopic or open anterior spinal arthrodesis alone has
become a more accepted option in the treatment of thoracic adolescent
idiopathic scoliosis. Several studies have focused on pulmonary function test
changes after anterior spinal arthrodesis with a rib resection in patients
with adolescent idiopathic
scoliosis7,15,35,36.
The pulmonary function test values after anterior spinal arthrodesis with a
rib resection demonstrated no
change15 or a
decrease at the time of the final
follow-up7,35,36.
The current study showed that the patients in Group 3 (anterior spinal
arthrodesis) demonstrated a significant decrease in percent-predicted
pulmonary function at the mean five-year follow-up evaluation. This suggests
that an open anterior approach requiring resection of the rib, with
transection and scarring of the respiratory muscles and postoperative pleural
adhesions including the intercostal muscles and diaphragm (six patients), may
have a deleterious effect on pulmonary function for as long as five years
postoperatively. We had too few patients in this group to determine whether
there was a difference between the ten patients who had a thoracotomy for
correction of a thoracic curve and the six patients who were managed with a
thoracoabdominal approach for correction of a thoracolumbar or lumbar curve.
Although six patients with thoracic hypokyphosis (a sagittal Cobb angle
between T5 and T12 of <10°) demonstrated a decrease in pulmonary
function despite an increase in thoracic kyphosis (from 1° to 22° in
the sagittal Cobb angle), they are too few to determine whether increasing
kyphosis might enhance pulmonary function.
Several studies have focused on changes in the pulmonary function tests
after a combined anterior and posterior spinal arthrodesis in patients with
adolescent idiopathic scoliosis, demonstrating no change in
values15,37
or a decrease at the time of the final
follow-up6,34,35.
The current study showed that the patients in Group 4 (anterior and posterior
spinal arthrodesis) demonstrated no significant change in absolute pulmonary
function; however, a significant decrease in the percent-predicted forced
vital capacity and a tendency toward a decrease in the percent-predicted
forced expiratory volume in one second were detected at an average of five
years postoperatively.
The strengths of this study include a population of patients who were
similar in terms of age (all were between ten and eighteen years old),
diagnosis, severity of the Cobb angle (ninety-eight patients had between
45° and 75°), and thoracic kyphosis (eighty-five patients had normal
kyphosis); comparison with the standardized percent-predicted values based on
large population reference data corrected by arm span, age, sex, and race; and
the use of a senior spinal surgeon reviewer who was completely independent of
the surgical team. It is still unknown whether a 10% to 20% reduction in
pulmonary function at five years after thoracotomy or thoracoplasty has any
clinical importance and whether moderate restrictive pulmonary function has
any clinical or functional importance. However, preservation of possible
maximal pulmonary function is recommended, considering the natural
deterioration of pulmonary function as a result of aging, smoking, asthma, and
other pulmonary problems.
Tables presenting the forced vital capacity and forced expiratory volume in
one second for all four patient groups over time are available with the
electronic versions of this article, on our web site at
(go to
the article citation and click on "Supplementary Material") and on
our quarterly CD-ROM (call our subscription department, at 781-449-9780, to
order the CD-ROM). ?
The authors did not receive grants or outside funding in support of their
research or preparation of this manuscript. They did not receive payments or
other benefits or a commitment or agreement to provide such benefits from a
commercial entity. No commercial entity paid or directed, or agreed to pay or
direct, any benefits to any research fund, foundation, educational
institution, or other charitable or nonprofit organization with which the
authors are affiliated or associated.
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