Commentary & Perspective

Commentary & Perspective on
"The Characteristics of Thoracic Insufficiency Syndrome Associated with Fused Ribs and Congenital Scoliosis"
by Robert M. Campbell Jr., MD, et al.
and on
"Growth of the Thoracic Spine in Congenital Scoliosis After Expansion Thoracoplasty"
by Robert M. Campbell Jr., MD, et al.

Commentary & Perspective by
Stuart L. Weinstein, MD, and Sergio A. Mendoza, MD*,
University of Iowa Hospitals and Clinics, Iowa City, IA

The treatment of congenital spinal deformities is one of the more challenging areas in pediatric orthopaedics. The variability of the anomalies and of their growth potentials may lead to a host of three-dimensional deformities. Deformities affecting the growth and development of the thoracic spine also affect thoracic volume and the kinematics of thoracic function. Furthermore, early-onset scoliosis of any etiology may profoundly affect the development of the pulmonary parenchyma and lead to compromised pulmonary function¹.

In this issue of The Journal, Campbell et al. address these deformities and their treatment in two separate reports. In the first, a review article, the authors define "thoracic insufficiency syndrome" in patients with fused ribs and congenital scoliosis, and, in the second, they report the results of growth of the thoracic spine after expansion thoracoplasty in twenty-one children with congenital scoliosis.

In the first article, the authors' definition of thoracic insufficiency syndrome as the inability of the thorax to support normal respiration or lung growth is based on their observations of more than 500 children with severe malformations of both the spine and the ribcage, treated and untreated, who were referred to them for treatment. They also classified and characterized this subset of patients with congenital scoliosis and rib-cage deformity and suggested a methodology for the quantitative analysis of thoracic function.

In their review, the authors also discussed extensively the effects of chest-wall deformity on lung development in early life. Evaluation of pulmonary function and exercise tolerance in children is very difficult, and the findings are inconsistent. Also, restrictive lung disease may be manifested by a decrease in chest volume as well as altered chest-wall kinematics with an increased cost of breathing. Campbell et al. also discussed in detail the possible effects of fused ribs and of absent ribs and the effects of anatomical abnormalities in the sagittal plane of the thorax on thoracic volume and respiratory function. The authors outlined their assessment techniques, including the use of sophisticated computer imaging, such as computed tomography scanning, and noted the difficulties of defining some of the parameters of thoracic function in infants and children under the age of five years.

In their second article in this issue, the authors reported on twenty-one patients with congenital scoliosis and fused ribs who were treated with expansion thoracoplasty. Longitudinal growth of the thoracic spine was found to be increased on both the concave side and the convex side, suggestive of growth across the end plates of the vertebral bodies and/or growth of the unilateral unsegmented bar. Previously published data on growth patterns in children with congenital vertebral anomalies² suggest a proportionately decreased growth potential in comparison with national standards. Those patients with a prior spinal fusion showed the least increase in growth of the thoracic spine. The origins of these anomalies may occur in early somatogenesis through a disruption of the genetic control program (hox), resulting in vertebral malformation, dysmorphology of the torso, and growth disturbance³. The role of surgical intervention in correcting the shape and size of the chest is still unclear⁴. Finally, the authors speculated that increased growth of the thoracic spine may increase chest volume, and subsequently, the growth of the underlying lungs.

The authors are to be commended on their novel approach to an extremely difficult and complex subject. As with all stimulating and difficult subjects, many questions arise from their exploration, and these two articles have raised questions which await answers.

As the authors rightly pointed out, no controls who could provide natural history data were available. In light of the complexity of congenital spinal deformities, even a group in which all patients have fused ribs and a unilateral unsegmented bar adjacent to a convex hemivertebra may still constitute a heterogeneous group with a wide array of spinal deformities.

Many other key questions remain unanswered. Is the change in growth that the authors demonstrated a result of treatment or of normal growth potential in these variable segments? Does changing the length of the spine by several centimeters affect the ultimate outcome? Does this increase in longitudinal length of the thoracic spine allow increased development of pulmonary parenchyma? What are the mechanisms by which growth is stimulated? Will multiple procedures be required, and will the results provide a total growth of only several centimeters over the course of treatment? Will the patient achieve spinal stability, improved pulmonary function, and an increased rate of survival?

What is the validity of the methods used to assess the longitudinal growth of the spine? The standard measurements were established with use of an artificially arched adult cadaver specimen. Are they truly comparable to measurements made in the immature spine where the amount of ossification varies considerably depending on the age of the patient as well as according to the varying deformities that occur as a result of congenital spinal anomalies?

While expansion thoracoplasty was originally developed to treat flail chest, most of the patients in this series had rigid chest wall deformities. The effect of other widely used treatments, such as in situ fusion or placement of subcutaneous "growing rods," on changes in pulmonary function and parenchymal development are also not known. Although these treatments are considered today the "standard of care," their effectiveness has not been able to be objectively assessed.

While these studies have some shortcomings, Campbell et al. are to be congratulated on addressing and treating a very difficult clinical problem in patients who, in many cases, would otherwise have an unfavorable outcome. As with all new procedures, the authors must clearly define the indications and the patient selection criteria, define a treatment protocol, and develop objective measures for follow-up evaluation in this group of patients until they reach skeletal maturity. Only in this way can the authors demonstrate the efficacy of this treatment.

*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.

References

1. Davies G, Ried L. Effect of scoliosis on growth of alveoli and pulmonary arteries and on right ventricle. Arch Dis Child. 1971;46:623-32.
2. Goldberg CJ, Fallon MC, Moore DP, Fogarty EE, Dowling FE. Growth patterns in children with congenital vertebral anomaly. Spine. 2002;27:1191-201.
3. Kessel M, Balling R, Gruss P. Variation of cervical vertebrae after expression of a Hox-1.1 transgene in mice. Cell. 1990;61:301-8.
4. Goldberg CJ, Moore DP, Fogarty EE, Dowling FE. Long-term results from in situ fusion for congenital vertebral deformity. Spine. 2002;27:619-28.