The Classic: The Iliac Apophysis: An Invaluable Sign in the Management of Scoliosis

Growth and completion of growth of the body is best shown by development of the bone growth centers, epiphyses and apophyses. The ossification of the carpal bones have long been used to indicate the bone age of a child. In infancy the time of femoral head ossification is also used to determine age. A delay in development usually is associated with a delay in metabolism.

The last ossification centers to appear and develop are the iliac crest apophysis and, finally, the apophysis of the ischial tuberosity. The latter is smaller, more difficult to visualize in roentgenogram and thus is of little significance, whereas the iliac apophysis is plainly visible and has a rather long time element in its development.

An apophysis is a growing center which, as its name indicates, grows (physis) upon (apo) the mother bone. It differs from the epiphysis in that with the development of the ossification center all growth is completed.

Coincident with the development of the excursion of ossification of the iliac apophysis across the iliac crest, the vertebral growth plates are completed, and spinal growth is finished. It is difficult to visualize the vertebral body growth plates and determine growth completion. Because of an almost simultaneous development of the iliac apophysis and the vertebral growth plates, vertebral growth completion can be determined by observation of the development of the iliac apophysis.

In the anteroposterior roentgenographic view of the pelvis, the iliac apophysis appears laterally and anteriorly on the crest of the ilium as an ossification center. This is termed capping (Fig. 1). With continued growth it develops posteriorly in its excursion of ossification across the iliac crest to dip down to contact the ilium medially at its junction near the sacrum. This is considered to be attached or completed (Fig. 2). When this completed ossification occurs, vertebral growth can be considered to be complete. Closure of the line between the apophysis and the ilium has no vertebral growth significance. Two or 3 years may be required for its closure.

The average time for completion of the iliac apophysis to its medial and posterior attachment is about 1 year. The shortest lime was 7 months; the longest. 3 years (Fig. 3).

The iliac apophysis may develop in fragments. After the usual capping or the appearance of ossification anteriorly and laterally on the iliac crest, further development may occur posteriorly, leaving a space, or gap, to be filled in later.

Variations in development of the iliac apophysis may occur. Earlier development usually takes place on the iliac crest of the high side of a pelvis seen with leg-length difference. Posterior ossification of the apophysis has been seen in the occasional congenital spinal deformity and in the infantile pelvis of some polios.

The excursion of ossification of the apophysis may be short and appear to attach to the ilium at a distance one half to three quarters across the iliac crest. In these cases the initial ossification center is thicker than usual. These are termed short excursions (Fig. 4). Vertebral growth usually is completed with the short excursion of the apophysis.

The average chronologic age when the iliac apophysis is completed is 14 years in girls and 16 years in boys. It may occur as early as 10 or 11 years in girls and 13 or 14 in boys, and as late as 17 or 18 years in girls or 20 years in boys. Delayed development occurs in children in colder climates or in those whose metabolism is low. Early development of the apophysis occurs in warmer climates. These observations on the development of the iliac apophysis were begun in 1936 at the Los Angeles Orthopaedic Hospital and continued intensively for 10 years. The object of this study was to find some physiologic sign that would indicate the completion of vertebral growth.

From a review of 296 untreated scoliotic cases made at the New York Orthopaedic Hospital from 1926 to 1936,¹ it was learned that scoliotic deformity became static with completion of vertebral growth (Fig. 5). This was determined by comparison of vertical heights, standing and sitting, with measurement of the scoliotic deformity.²

In this study it was found that spinal growth was slow in the period of 5 to 10 years of age; the average increase in scoliotic deformity was 4° to 5° a year, and the increase in sitting height averaged less than ½ inch a year, whereas in the preadolescent age, 10 to 15 years, the average scoliotic increase was 10° and the average increase in sitting height was 1 inch. In cases of marked nutritional deficiency there may be a rapid increase in the scoliotic deformity, even in the slow vertebral growth years (8 to 10 years).

The relationship between vertebral growth and scoliotic deformity can be explained by Hueter-Volkmann’s epiphyseal pressure rule. This states that bone growth is retarded whenever pressure is increased, and is accelerated whenever pressure is diminished. Uneven pressure is possible when joint surfaces are not parallel, as seen in the convexity of the scoliotic spine.

The vertebral growth plates are not easily visible in a roentgenogram; therefore, they did not furnish reliable information of vertebral growth. The completion of the excursion of the ossification of the iliac apophysis generally was coincident with that of the vertebral growth plates. Therefore, the attachment of the iliac apophysis has proved to be an excellent physiologic sign (to indicate the completion of vertebral growth.

Two hundred untreated cases examined at the Los Angeles Orthopaedic Hospital were studied as to vertical heights standing, sitting and kneeling, measurement of the scoliotic deformity and development of the excursion of ossification of the iliac apophysis across the crest of the ilium. In general, the correlation was very favorable. The sitting height was not 100 per cent accurate. Variations were noted with fatigue of the patient and the addition to sitting height by the development of the ischial apophysis and increase in buttock size in fat girls.

Ten per cent of the cases showed no increase in scoliotic deformity, even though iliac apophysis was not complete and attached. This was especially difficult to determine in those cases with a short excursion of the iliac apophysis. During the past 20 years 3 cases have been reported which showed roentgenographs evidence of an increase in the scoliotic deformity following completion, and even posteromedial attachment of the iliac apophysis. This increase in deformity continued only 3 to 6 months after the development of the apophysis and averaged 10°. The coincidental development of the vertebral growth plates and the excursion of ossification of the iliac apophysis is not 100 per cent as seen in these 3 cases. This correlation was found in all cases, irrespective of etiology.

In the 2 years before the capping of the iliac apophysis. 75 per cent of the untreated cases increased from 10° to 35°. The deformity increases more slowly during the time when the iliac apophysis is completing its excursion. Two thirds of the untreated cases showed little appreciable increase (less than 10°) after the capping of the iliac apophysis. Any severe increase in the deformity during the excursion of the iliac apophysis was considered to be indicative of a nutritional deficiency.

It was important to use standing spinal roentgenograms for comparison. As the scoliotic grows older, flexibility decreases, even to ankylosis. Thus, the flexibility seen normally in the younger patient between standing and recumbent roentgenograms becomes less, and the recumbent deformity approaches the standing deformity. Therefore, there would be a gradual increase in the recumbent roentgenogram deformity with less and less flexibility until ankylosis was reached. At this time the recumbent deformity would have equaled the standing deformity.

Increase in the scoliotic deformity after completion of vertebral growth has been seen in very few cases. Superimposed pathology, such as marked osteoporosis, degenerative arthritis or disk degeneration, may allow an increase of lateral curvature. Compression fracture of an apical vertebra has caused an increase in the curvature of the spine.

Utilization of the development of the iliac apophysis as a guide to the progress of spinal growth and of the lateral curvature is of the greatest importance. In the management of scoliosis, no treatment to prevent an increase in the lateral curve is needed for the individual whose roentgenograms show an attached iliac apophysis. Conversely, the patient who has no visible iliac apophysis will require cast correction, surgical immobilization, or both, to prevent increasing deformity.

In a certain number of cases surgically treated, the fusion may not be solid, or it may not be long enough to cover the area of deformity (Figs. 6, 7). In these cases, if the individual has not completed vertebral growth, there will be an increase in the lateral curve, even beyond its original deformity. But if the patient is through growing, as shown by the attachment of the iliac apophysis, there will be the initial loss of part or all of the correction. But this loss will not cause the deformity to increase beyond its original curvature. Thus, during the growing years, repair of the pseudarthrosis or additional fusion as indicated is imperative to prevent an increasing deformity.

In the occasional use of the localizer cast without surgery to prevent an increase in the lateral curve, it is important to know when the cast can be safely discarded (Fig. 8). The attachment of the iliac apophysis is used as a criterion. If the growth center has completed its excursion of ossification, then it is safe to conclude that the cast treatment, for growth of the spine and of the lateral curve, can be stopped. But if the cast is removed before the iliac apophysis has attached, then we may expect a return of the deformity and an increase in the deformity in proportion to the anticipated spinal growth.

The significance of the iliac apophyses lies in its use as a more accurate criterion for the completion of vertebral growth and for the progress of the spinal curvature. Moreover, it is an invaluable aid that could be used widely in determining those patients whose deformity will remain static and, therefore, do not need preventative treatment. The patient could be told that the attachment of the iliac apophysis indicates the end of increase in his deformity. This information should save the patient needless worry and a considerable expenditure for unnecessary treatment.