Congenital Anomalies of the Ribs and Chest Wall Associated with Congenital Deformities of the Spine

Tsirikos, Athanasios I. MD, FRCS; McMaster, Michael J. MD, FRCS

Journal of Bone & Joint Surgery - American Volume: November 2005 - Volume 87 - Issue 11 - p 2523–2536
doi: 10.2106/JBJS.D.02654
Scientific Articles

Background: Congenital anomalies of the ribs and chest wall as well as Sprengel deformity of the shoulder are often associated with congenital deformities of the spine. It has been suggested that rib anomalies may adversely affect the progression of the spinal deformity.

Methods: We conducted a retrospective study of the medical records and spine radiographs of 620 consecutive patients with congenital deformities of the spine; 497 patients (80%) had scoliosis; eighty-eight patients (14%), kyphoscoliosis; and thirty-five patients (6%), kyphosis. The rib anomalies were classified into simple and complex, and the presence of a Sprengel deformity of the shoulder was recorded. The rate of scoliosis deterioration without treatment before the age of eleven years, as well as the patient age and curve size at the time of surgery, was compared for different types of vertebral abnormalities in patients with and without rib anomalies.

Results: A total of 119 patients (19.2%) had rib anomalies, which were most commonly associated with congenital scoliosis (111 patients; 93%) and were much less frequently associated with congenital kyphoscoliosis or kyphosis (eight patients). The rib anomalies were simple in ninety-five patients and complex in twenty-four. Eighty-five patients (71%) with rib abnormalities had a scoliosis due to a unilateral failure of vertebral segmentation, and seven patients had mixed or unclassifiable vertebral anomalies. In contrast, only sixteen of 203 patients with a scoliosis due to a hemivertebra alone had rib anomalies. The rib anomalies were most frequently associated with a thoracic or thoracolumbar scoliosis (102 patients; 92%) and occurred on the concavity in eighty-two patients (74%), the convexity in twenty-two patients (20%), and were bilateral in seven patients. The Sprengel deformity occurred in forty-five patients and most frequently in association with a thoracic scoliosis due to a unilateral failure of vertebral segmentation (twenty-seven patients). No significant difference was detected in the rate of curve progression without treatment in patients with and without rib anomalies. The only exception was the mean age at the time of surgery, which was higher for patients with a unilateral unsegmented bar without rib anomalies (p = 0.005). In addition, no significant difference was found with regard to any tethering effect due to the site of the rib fusions on the concavity of the scoliosis, i.e., whether they were in close approximation to the spine or were more lateral (p > 0.05).

Conclusions: Congenital rib anomalies occur most commonly on the concavity of a thoracic or thoracolumbar congenital scoliosis that is due to a unilateral failure of vertebral segmentation, and they do not appear to have an adverse effect on curve size or rate of progression.

Level of Evidence: Prognostic Level II. See Instructions to Authors for a complete description of levels of evidence.

1 Scottish National Spine Deformity Center, Royal Hospital for Sick Children (Level 5), Sciennes Road, Edinburgh EH9 1LF, United Kingdom. E-mail address for M.J. McMaster: m.mcmaster1@btinternet.com

Article Outline

Congenital malformations of the ribs and chest wall, as well as anomalies of the scapulae, are often found in association with congenital deformities of the spine. These developmental chest wall abnormalities, which may be simple or complex, are due to either a failure of segmentation or formation of the ribs.

Campbell et al. stated that extensive rib fusions affecting the hemithorax on the concavity of a congenital scoliosis in growing children can act as a powerful lateral tether to further unbalance the growth of the spine, which is already being deformed by asymmetrical vertebral growth1. In addition, an extensive thoracic congenital scoliosis associated with fused ribs may affect thoracic function and the growth of the lungs in young children and lead to a thoracic insufficiency syndrome. An imbalance in the mechanical thrust of the ribs may also adversely affect spinal growth as well as the function of trunk muscles and the pressure within the thorax2,3. Shahcheraghi and Hobbi, in a study of sixty patients with congenital scoliosis, reported that sixteen had fusion of the ribs4. They found that fused ribs on the concave side of a lower thoracic curve increased the rate of curve progression4.

In order to overcome the problem of a congenital scoliosis associated with chest wall anomalies producing thoracic insufficiency, Campbell and Hell-Vocke developed the surgical technique of expansion thoracoplasty, in which the concave hemithorax is lengthened and stabilized by serial rib distractions with use of a vertical expandable prosthetic titanium rib5.

To the best of our knowledge, no large study has been done on the prevalence of rib and chest wall anomalies associated with congenital deformities of the spine and the effect that these may have on curve progression. The purpose of our study was twofold: first, to document the prevalence and describe the different types of congenital rib and chest wall abnormalities as well as Sprengel deformity of the shoulder occurring in association with all types of congenital spine deformities, and, second, to assess the effect of congenital rib anomalies on the rate of progression of the spinal deformity.

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Embryological Development of the Ribs, Spine, and Scapulae

The embryological development of the ribs and spine are very closely associated, and the complete anatomical pattern is formed in mesenchyme during the first six weeks of intrauterine life. Developmental abnormalities of the ribs and spine may occur during this period, and, once the mesenchymal mold is established, the cartilaginous and osseous stages follow that pattern.

Vertebral anomalies occurring during the mesenchymal stage may be due to either a unilateral defect of formation or segmentation of the primitive vertebrae and can result in a unilateral imbalance in the longitudinal growth of the spine producing a congenital scoliosis6,7. Vertebral anomalies may also occur during the subsequent chondrification stage and are thought to be due to a localized failure of vascularization of the developing cartilaginous centrum. This results in varying degrees of failure of formation of the vertebral body producing a congenital kyphosis or kyphoscoliosis6,7. In the late chondrification and ossification stages, osseous metaplasia may occur in the anterior part of the anulus fibrosis and ring apophysis, producing an anterior or anterolateral unsegmented bar, which can also result in a congenital kyphosis or kyphoscoliosis8.

The ribs form from costal processes, which are small lateral mesenchymal condensations of the developing thoracic somites and contribute cells to all parts of the developing ribs9-13. The distal tips of the costal processes elongate to form ribs only in the thoracic region of the spine. Rib anomalies probably occur during the process of segmentation and resegmentation of the developing somites, after which the ribs come to articulate between the definitive thoracic vertebrae. The ribs develop into cartilaginous precursors that ossify during the fetal period.

The scapula develops embryologically along with the arm. The arm bud appears in the third week of embryonic life as a small swelling opposite the vertebral segments from the fifth cervical to the first thoracic vertebra. The scapula appears in mesenchyme during the fifth week and gradually migrates caudally. By the end of the third fetal month, the scapula reaches its final anatomical position located lateral to the spine and extending from the second to the seventh or eighth thoracic vertebra. Occasionally, the scapula may fail to fully descend to its normal location and remains in a permanently elevated position commonly known as a Sprengel deformity.

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Materials and Methods

We reviewed the medical records and spine radiographs of 620 consecutive patients with a congenital spine deformity who were seen at our institution between 1960 and 2003. All patients were followed and treated by the senior author (M.J.M.), who has reported previously on the natural history and surgical management of these patients14,15. There were 400 female and 220 male patients. Four hundred and ninety-seven patients (80%) had a scoliosis, eighty-eight (14%) had a kyphoscoliosis, and thirty-five (6%) had a kyphosis. Patients who had myelomeningocele, Scheuermann disease, neurofibromatosis, skeletal dysplasia, infection, or trauma were excluded.

The vertebral anomalies causing the spine deformity as well as the presence of rib anomalies or a Sprengel deformity of the shoulder were detected on anteroposterior and lateral spine and chest radiographs. We were unable to assess the prevalence of Klippel-Feil deformity because not all of our patients had cervical radiographs. The vertebral anomalies and the type of spine deformity were categorized according to the classification proposed by Winter et al.16,17 and McMaster et al.14,15 into failures of vertebral segmentation, failures of vertebral formation, and mixed anomalies producing a congenital scoliosis, kyphoscoliosis, or kyphosis (Tables I and II).

The site of the curvature was defined according to the classification proposed by the Scoliosis Research Society18: cervicothoracic (apex at C7 or T1), thoracic (apex between T2 and T11), thoracolumbar (apex at T12 or L1), lumbar (apex between L2 and L4), and lumbosacral (apex at L5 or caudad). There is a recognized difficulty in accurately measuring spine radiographs of patients with congenital scoliosis19. However, all of the serial spine radiographs for each patient in this study were measured by the senior author in both the coronal and sagittal planes with use of the Cobb method20 with the aim of eliminating interobserver measurement error. All spine radiographs were made with the patient standing, except for patients in early infancy for whom radiographs were made in the supine position. Care was taken to measure all curves with use of the same anatomical land-marks on the serial spine radiographs.

We classified the rib anomalies seen in our patients as simple or complex. A patient with a simple rib anomaly had only one of the following: a localized fusion of two or three ribs (Fig. 1) or a small chest wall defect that was due to a deviation of one or two ribs or an absence of a rib. Two patients had a bifid rib, which is a single rib separating into two ribs more distally, and one patient had a duplication of two ribs arising from the same vertebral segment. A patient with complex rib anomalies had multiple extensive rib fusions, usually without a set pattern, combined with an adjacent large chest wall defect that was due to an absence or deviation of ribs (Figs. 2, 3, and 4). Two patients had a bifid rib combined with either a large chest wall defect (Fig. 5) or multiple fused ribs. The location of the rib anomalies in relation to the convexity or concavity, as well as the apex of the spine deformity, was recorded. The radiographs in Figures 1, 2, 3, 4, 5 were reproduced with use of photographic contrast imaging in order to show the rib and shoulder anomalies.

The presence of an abnormal number of normally formed ribs was not considered to be an anomaly for the purpose of this study. Sixty-three (10%) of the 620 patients had an abnormal number of ribs, ranging from seven to fifteen, either unilaterally or bilaterally. An abnormal number of ribs was seen most often in patients who had a scoliosis due to a unilateral failure of vertebral segmentation (forty-five patients; 71%) (p < 0.01).

In order to assess the possible effect of the rib anomalies, either simple or complex, on the congenital scoliosis, we estimated the rate of progression of the untreated curves before the age of eleven years, as well as the patient age and size of the scoliosis before spine surgery and compared these findings with those in patients with similar spine deformities but without rib anomalies. We also evaluated the possible tethering effect due to the site of the rib anomalies on the concavity of the scoliosis, i.e., whether the rib anomalies were in close association to the spine or were more lateral.

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Statistical Methods

The prevalences of congenital rib anomalies among patients with different types of vertebral anomalies causing a scoliosis, kyphoscoliosis, or kyphosis were compared with use of the chi-square test (with continuity correction). Due to the low prevalence of rib anomalies in patients with congenital kyphosis, the analysis was performed with use of the Fisher exact test.

Analysis of variance was used to compare the yearly rate of scoliosis progression without treatment, as well as the age and curve size at the time of spine surgery, among patients with or without rib anomalies, either simple or complex. When significant differences were found, the t test was used to examine this association in more detail by grouping the three rib abnormality groups into two (those with or without rib anomalies). The t test was also used to compare the tethering effect produced by concave rib fusions either in close proximity to or more lateral and separate to a unilateral failure of vertebral segmentation. P values of <0.05 were considered to be of significance for all statistical tests.

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Results

The type and distribution of the rib anomalies (simple and complex) and the Sprengel deformity of the shoulder in patients with congenital scoliosis, kyphoscoliosis, and kyphosis due to different types of vertebral abnormalities, as well as the type and location of the spinal curves, are shown in Tables I and II.

Rib anomalies occurred in 119 (19.2%) of the 620 patients with congenital deformities of the spine. The female-tomale ratio was 2.5:1 for the patients with rib anomalies compared with 1.7:1 for the patients without rib anomalies.

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Type of Spine Deformity

Congenital Scoliosis

Rib anomalies occurred in 111 (22.3%) of the 497 patients with congenital scoliosis (Table I). These rib anomalies were most frequently associated with a unilateral failure of vertebral segmentation (p < 0.001). Of the 160 patients with a unilateral unsegmented bar alone, fifty-one (32%) had rib anomalies. Of the sixty-six patients with a unilateral unsegmented bar combined with contralateral hemivertebrae at the same level, thirty-four (52%) had rib anomalies. In contrast, patients with a unilateral failure of vertebral formation had a low prevalence of rib anomalies. Of the 203 patients with hemivertebrae alone, only sixteen had rib anomalies.

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Congenital Kyphoscoliosis and Kyphosis

Rib anomalies occurred in only eight of the 123 patients with a congenital kyphoscoliosis or kyphosis (Table II). No significant difference was detected in the distribution of rib anomalies between patients with a unilateral failure of vertebral formation and those with a failure of segmentation (p = 0.897).

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Site of Spine Deformity

Rib anomalies were most frequently associated with thoracic or thoracolumbar curves.

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Congenital Scoliosis

Of the 300 patients with a thoracic scoliosis, eighty-eight (29%) had rib anomalies. Of the fifty-four patients with a thoracolumbar scoliosis, fourteen had rib anomalies. In contrast, rib anomalies occurred in only two of the eighty patients with a lumbar or lumbosacral scoliosis (p < 0.001) (Table I).

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Congenital Kyphoscoliosis and Kyphosis

Rib anomalies were infrequent in this group. Of the sixty-five patients with a thoracic curve, only two had rib anomalies. Of the forty-eight patients with a thoracolumbar curve, six had rib anomalies. None of the ten patients with a lumbar curve had rib anomalies (p < 0.001) (Table II).

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Type of Rib Anomalies

Of the 119 patients with rib anomalies, ninety-five (80%) had simple anomalies and twenty-four (20%) had complex anomalies. The most common simple rib anomaly, occurring in seventy-two patients (76%), was a localized fusion of two or three ribs (Fig. 1). The most common complex rib anomaly, occurring in twenty-one patients (88%), was an extensive fusion of multiple ribs associated with a large adjacent chest wall defect (Fig. 3).

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Congenital Scoliosis

Simple rib anomalies occurred in eighty-nine (18%) of the 497 patients with congenital scoliosis, and sixty-eight (76%) of the eighty-nine patients had a localized fusion of two or three ribs (Fig. 1). Complex rib anomalies occurred in twenty-two patients (4.4%), and all had a combination of fused ribs with chest wall defects (Figs. 2, 3, and 4).

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Congenital Kyphoscoliosis and Kyphosis

Simple rib anomalies occurred in only six patients with congenital kyphoscoliosis or kyphosis; four patients had a fusion of ribs. Complex rib anomalies occurred in only two patients. One patient with a complex rib anomaly had a chest wall defect with an ipsilateral bifid rib, and another had a combination of fused ribs with a contralateral bifid rib. Complex rib anomalies also occurred in a patient with a thoracolumbar kyphosis.

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Side and Site of Rib Anomalies in Relation to the Scoliosis

Simple rib anomalies occurred most frequently on the concavity of the scoliosis (seventy [79%] of eighty-nine patients) and were less common on the convexity (thirteen patients). Six patients had simple rib anomalies bilaterally. Complex rib anomalies occurred on the concavity of the scoliosis in twelve patients and on the convexity in nine patients. One patient had complex rib anomalies bilaterally.

Rib anomalies, both simple and complex, occurring on the concavity of the scoliosis were most frequent in patients with a unilateral failure of vertebral segmentation (sixty-nine patients; p < 0.001). These anomalies were present in thirty-seven (23%) of the 160 patients with a unilateral unsegmented bar alone and in thirty-two (48%) of the sixty-six patients with a unilateral unsegmented bar with a contralateral hemivertebra at the same level. Twenty-three of the patients with a unilateral failure of vertebral segmentation had rib fusions on the concavity of the scoliosis, which were in close association with the unsegmented bar. Twenty of them had simple rib anomalies, and three had complex rib anomalies. An additional thirty-eight patients had concave rib fusions, but these lay more lateral and separate from the spine. Thirty of them had simple rib anomalies, and eight had complex rib anomalies.

Rib anomalies on the convexity of the scoliosis also occurred most frequently in patients with a unilateral failure of vertebral segmentation (fourteen patients) and all anomalies were separate from the spine.

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Rate of Scoliosis Progression in Untreated Patients with and without Rib and Chest Wall Anomalies

Of the 119 patients who had simple or complex rib abnormalities, the majority (eighty-five patients; 71%) had anomalies that occurred on the concavity of a thoracic or thoracolumbar scoliosis due to either a unilateral unsegmented bar or a unilateral unsegmented bar with contralateral hemivertebrae at the same level. We compared the rate of curve progression per year before the age of eleven years in the untreated patients with and without rib anomalies who had been followed for more than two years (mean, six years; range, two to 10.4 years) (Table III).

For the patients with other types of spine deformities, the number of those with rib anomalies was insufficient to make a meaningful comparison.

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Patients with a Unilateral Unsegmented Bar and Contralateral Hemivertebrae at the Same Level

Twenty-two patients with simple rib anomalies were followed for a mean of five years (range, two to 10.2 years) and had a mean rate of curve progression of 6.2° per year. Six patients with complex rib abnormalities were followed for a mean of 5.6 years (range, two to nine years) and had a mean rate of scoliosis deterioration of 5.7° per year. Thirteen patients without rib anomalies were followed for a mean of seven years (range, 2.4 to 10.4 years) and had a mean rate of curvature progression of 5.6° per year.

No significant difference was detected in the rate of scoliosis progression per year for patients with simple rib anomalies, with complex rib anomalies, or without rib anomalies (p = 0.85) (Table III).

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Patients with a Unilateral Unsegmented Bar Alone

Twenty-one patients with simple rib anomalies were followed for a mean of 4.8 years (range, two to 9.9 years) and had a mean rate of curve progression of 2.8° per year. Five patients with complex rib anomalies were followed for a mean of 5.4 years (range, two to 9.1 years) and had a mean rate of scoliosis progression of 4.4° per year. Twenty-eight patients without rib anomalies were followed for a mean of six years (range, two to 10.4 years) and had a mean rate of curvature progression of 3.9° per year.

No significant difference was detected in the rate of scoliosis progression per year among patients with simple rib anomalies, with complex rib anomalies, or without rib anomalies (p = 0.29) (Table III).

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Age and Severity of Scoliosis Before Spinal Arthrodesis in Patients with and without Rib and Chest Wall Anomalies

We estimated the age and the size of the scoliotic curve at the time of spinal arthrodesis in the patients with and without concave rib abnormalities who had a thoracic or thoracolumbar scoliosis due to a unilateral unsegmented bar with or without contralateral hemivertebrae at the same level (Table IV).

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Patients with a Unilateral Unsegmented Bar and Contralateral Hemivertebrae at the Same Level

In the twenty-three patients with simple rib anomalies, the mean age at the time of spinal arthrodesis was 8.5 years (range, 1.1 to eighteen years) and the mean curvature was 76° (range, 36° to 120°). The five patients with complex rib abnormalities underwent spinal arthrodesis at a mean age of seven years (range, 0.6 to thirteen years) and had a mean scoliosis of 62° (range, 37° to 88°). In the twenty-one patients without rib anomalies, spinal arthrodesis was performed at a mean age of nine years (range, 1.6 to sixteen years) and the mean curvature was 79° (range, 33° to 142°).

No significant difference was detected among patients with simple rib anomalies, with complex rib anomalies, or without rib anomalies with respect to the age or the curve at the time of surgery (p = 0.64 and 0.44, respectively) (Table IV).

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Patients with a Unilateral Unsegmented Bar Alone

In the twenty-two patients with simple rib anomalies, the mean age at the time of spinal arthrodesis was ten years (range, 1.5 to nineteen years) and the mean scoliosis was 61° (range, 33° to 100°). The ten patients with complex rib anomalies underwent spinal arthrodesis at a mean age of 11.5 years (range, 5.7 to 15.5 years) and the mean curvature was 68° (range, 54° to 95°). In the fifty-seven patients without rib anomalies, spinal arthrodesis was performed at a mean age of thirteen years (range, 5.9 to thirty-seven years) and the mean curvature was 61° (range, 37° to 115°).

No significant difference was detected in the curve size at the time of surgery in patients with simple rib anomalies, with complex rib anomalies, or without rib anomalies (p = 0.58) (Table IV). However, the age at the time of surgery was significantly different among the three rib anomaly groups (p = 0.005). When grouping the patients into those with and those without rib anomalies, we found that the mean age at the time of surgery was higher for those without rib anomalies (mean difference, 2.84 years; 95% confidence interval, 1.03 to 4.65 years) (p = 0.002).

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Effect of the Site of Concave Rib Fusions on the Rate of Curve Progression, Age, and Curve Size at the Time of Spinal Arthrodesis

We compared the rate of curve progression per year before the age of eleven years in patients with a thoracic or thoracolumbar scoliosis due to a unilateral failure of segmentation (with or without contralateral hemivertebrae at the same level) who had concave rib fusions located either in close association with or more lateral and separate from the unilateral unsegmented bar and were followed without treatment for more than two years (mean, 4.7 years; range, two to 9.2 years) (Table V). We also compared the two groups with respect to the age and curve size at the time of surgery.

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Patients with Rib Fusions in Close Association to the Unilateral Unsegmented Bar

The eight patients in this group were followed for a mean of 4.8 years (range, two to 9.2 years) and had a mean rate of curve progression of 4.6° per year. The mean age at the time of spinal surgery for this group of patients was 11.2 years (range, 1.1 to nineteen years) and the mean curvature was 68.2° (range, 33° to 105°). Seven patients had simple rib anomalies, and one patient had complex rib anomalies. The patient with complex rib anomalies had a combination of fused ribs with an adjacent chest wall defect.

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Patients with Rib Fusions Lying Lateral and Separate from the Unilateral Unsegmented Bar

The twenty-four patients in this group were followed for a mean of 4.7 years (range, two to nine years) and had a mean rate of curve progression of 5.4° per year. The mean age at the time of spinal arthrodesis for this group was 8.4 years (range, 0.6 to 14.4 years), and the mean curvature was 73.7° (range, 33° to 120°). Eighteen patients had simple rib anomalies, and six patients had complex rib anomalies. All of the patients with complex rib anomalies had a combination of fused ribs with an adjacent chest wall defect.

With the numbers available, no significant difference was detected among patients with rib fusions in continuity with or lateral and separate to a unilateral failure of vertebral segmentation with respect to the rate of scoliosis progression per year (p = 0.54), the age of the patient at the time of surgery (p = 0.07), and the curve size at the time of surgery (p = 0.54) (Table V).

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Sprengel Deformity

A congenital elevation of the scapula was present in forty-five (7%) of the 620 patients with congenital spine deformities. It occurred most frequently in association with a cervicothoracic or thoracic scoliosis (forty-three patients; 96%) (p < 0.001). Of the remaining two patients, one had a congenital kyphoscoliosis and the other had a kyphosis.

The associated scoliosis in forty-three patients was due to a unilateral unsegmented bar (with or without contralateral hemivertebrae at the same level) in twenty-seven patients (63%) and to mixed or unclassifiable vertebral anomalies in nine patients. The site of the elevated shoulder was on the concavity of the scoliosis in twenty-six patients (60%) and on the convexity in seventeen patients (40%). None of the patients included in this study had bilateral Sprengel deformity.

Rib anomalies (fourteen simple and ten complex) were also present on the same side of the elevated scapula in twenty-four (53%) of forty-five patients. In sixteen of those patients, the scoliosis was due to a unilateral unsegmented bar alone (p < 0.001).

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Discussion

Congenital deformities of the spine are a gradually blending spectrum of deformities, ranging from a congenital scoliosis through kyphoscoliosis to a pure kyphosis. These deformities are due to an asymmetrical failure of development of one or more vertebrae resulting in a localized imbalance in the longitudinal growth of the spine and an increasing spinal curvature, which continues to progress until skeletal maturity14-17. The ribs are formed in close association with the vertebrae, and it is, therefore, not surprising to have a combination of developmental abnormalities affecting both the ribs and the vertebrae9-13.

Shahcheraghi and Hobbi reported the curve patterns and progression seen in sixty patients with congenital scoliosis4. Sixteen of their patients had fusion of the ribs: eight had fusion on the concavity; three, on the convexity; and five, bilaterally. No distinction was made between simple rib anomalies, complex rib anomalies, and chest wall anomalies. The spine deformity in seven of these patients was due to multiple unclassifiable vertebral abnormalities. They found that the presence of fused ribs was associated with higher curve progression for all types of congenital vertebral anomalies except unilateral unsegmented bars with contralateral hemivertebrae4. However, this finding was not significant. The fusion of ribs on the concavity of a lower thoracic curvature was also associated with increased curve size and rate of progression4.

Other studies have been confined to two rare hereditary conditions affecting the thoracic cage and associated with congenital spinal anomalies, in which most of the vertebrae in the thoracic and thoracolumbar regions are malformed21-25. Spondylothoracic dysplasia (Jarcho-Levin syndrome) is transmitted with both autosomal and recessive inheritance and consists of multiple failures of vertebral segmentation, multiple posterior rib fusions, and frequent absence of segments. Constriction of the chest and consequent respiratory failure often results in premature death in early infancy21-24. Normal life expectancy is anticipated for patients with spondylocostal dysostosis, which is due to a lesser degree of rib deformation. However, marked stunting of the trunk occurs in these patients and is the result of the multiple vertebral anomalies24,25. In our series, we identified only one patient with a Jarcho-Levin syndrome who died shortly after birth from respiratory failure and one patient with spondylocostal dysostosis whose spine was stunted but not otherwise deformed.

To the best of our knowledge, there has been no large study of the association between congenital spine deformities and congenital anomalies of the ribs and chest wall and the effect that these might have on curve progression. Knowledge of the natural history of congenital spine deformities with and without rib abnormalities is essential in planning prophylactic treatment for these patients at an early stage.

In our study of 620 consecutive patients with congenital spine deformities due to developmental vertebral anomalies, we classified the associated rib and chest wall anomalies according to whether they were simple or complex and investigated their potential effect on curve progression. A total of 497 patients (80%) had congenital scoliosis, eighty-eight (14%) had kyphoscoliosis, and thirty-five (6%) had kyphosis. The overall prevalence of rib anomalies was 19.2% (119 patients). However, the prevalence of rib abnormalities was the highest for patients with congenital scoliosis (111 patients; 22.3%) (p < 0.001) and was rare in patients with kyphoscoliosis (four patients) and kyphosis (four patients). A congenital elevation of the scapula (a Sprengel deformity) also occurred in forty-five patients and was most commonly associated with congenital scoliosis.

A possible explanation for this variation in the prevalence of rib and chest wall anomalies among the different types of congenital spine deformities is that the vertebral anomalies responsible for the development of a scoliosis appear during the mesenchymal period (the first six weeks of intrauterine life), when the ribs and scapulae are also developing. However, the vertebral anomalies responsible for a congenital kyphoscoliosis or kyphosis are believed to occur at a later stage during the chondrification and ossification periods, when the basic anatomy of the osseous structures forming the ribs and scapulae has already been established6,7,17.

Simple rib anomalies occurred in ninety-five patients (80%), and complex rib anomalies occurred in twenty-four patients (20%). The most common type of simple rib deformity was a localized fusion of two or three consecutive ribs (seventy-two patients; 76%) (Fig. 1), and the most frequent type of complex rib abnormality was a combination of fused ribs with a large adjacent thoracic wall defect (twenty-one patients; 88%) (Figs. 2, 3, and 4).

In this series, rib anomalies were most frequently found in patients with a congenital thoracic or thoracolumbar scoliosis due to a unilateral failure of vertebral segmentation (eighty-four [40%] of 210 patients), and they occurred most commonly on the concavity of the scoliosis (sixty-nine patients; 82%). A likely explanation for this close association between the side of the rib abnormalities and this type of congenital scoliosis is a localized unilateral embryological error resulting in a failure of segmentation of both the primitive ribs and vertebrae on the same side occurring at the same time.

Ninety-five patients with a thoracic or thoracolumbar congenital scoliosis due to a unilateral failure of vertebral segmentation with and without rib anomalies were followed without treatment for more than two years before the age of eleven years (Tables III and IV). Seventy-six (80%) of them subsequently underwent surgical treatment to control the rapidly progressive spine deformity (Table III). We found no significant difference in the rate of curve progression without treatment or the Cobb angle at the time of surgery for these patients with or without rib anomalies, either simple or complex (p > 0.05) (Tables III and IV). The only difference was that patients with rib anomalies associated with a unilateral unsegmented bar alone had surgical treatment at a younger age compared with those without rib anomalies (p = 0.005) (Table IV). We have no good explanation for this finding. A limitation of the study was the relatively small number of patients after they were subcategorized into the three rib anomaly groups (those with simple, complex, or no rib anomalies).

Theoretically, it is possible that rib fusions lying on the concavity of a scoliosis in close association with the spine may have a different tethering effect compared with similar anomalies located more laterally. In order to assess this effect, we reviewed the cases of thirty-two patients with concave rib fusions associated with a thoracic or thoracolumbar scoliosis due to a unilateral failure of vertebral segmentation who were followed without treatment for more than two years (Table V). Eight of these patients had rib fusions in close association with the unsegmented bar, and twenty-four patients had fused ribs lying more laterally. All of these patients subsequently required surgical treatment to control the rapidly progressive scoliotic deformity. We found no significant difference in the rate of curve progression without treatment or the age and Cobb angle at the time of spine surgery for these patients regardless of the location of the concave rib fusions (p > 0.05). A limitation of this study is the small number of patients for comparison in the two rib-fusion groups.

In our opinion, it is likely that rib fusions on the concavity of a scoliosis can cause a lateral tether and contribute to the development of the curvature. However, these rib anomalies usually occur in association with a unilateral failure of vertebral segmentation, which is recognized to produce a severe unilateral imbalance in the longitudinal growth of the spine and a rapidly progressive scoliosis. We believe that the main driving force for the development of the scoliosis in these patients is the unilateral failure of vertebral segmentation, and this greatly exceeds any adverse effect from the rib anomaly. In these circumstances, our finding that there is no apparent difference in the rate of curve progression or the size of the curve at the time of spinal arthrodesis in the patients with or without concave rib fusions regardless of their location is understandable.

Congenital elevation of the scapula (Sprengel deformity of the shoulder) occurred most commonly in association with a cervicothoracic or thoracic scoliotic deformity due to a unilateral failure of vertebral segmentation (twenty-seven [60%] of forty-five patients). The site of the elevated scapula was on the concavity of the scoliotic curvature in twenty-six (60%) of forty-three patients with scoliosis and on the convexity in seventeen. The combination of a congenitally elevated scapula and its occurrence on the convexity of an upper thoracic congenital scoliosis causes a substantial deformity because of an elevation of the shoulder line and impairment of shoulder function. These deformities usually require surgical treatment to correct the scoliosis and also to perform a distal displacement of the scapula in relation to the vertebral column. However, when the Sprengel deformity is on the concavity of the scoliosis, it often partially compensates for the cosmetic deformity caused by the elevation of the contralateral shoulder on the convexity of the scoliotic curve. This minimizes shoulder asymmetry and usually does not require reduction of the congenitally elevated scapula.

In conclusion, this study showed that congenital rib and chest wall anomalies occur most frequently on the concavity of a thoracic or thoracolumbar congenital scoliosis that is due to a unilateral failure of vertebral segmentation. These rib abnormalities, either simple or complex, do not appear to have an adverse effect on the size or the rate of progression of the curve. ▪

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.

Investigation performed at the Scottish National Spine Deformity Center, Royal Hospital for Sick Children, Edinburgh, United Kingdom

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