The Journal of Bone and Joint Surgery 79:767-70 (1997)
© 1997 The Journal of Bone and Joint Surgery, Inc.
Premature Partial Closure of the Triradiate Cartilage Treated with Excision of a Physeal Osseous Bar. Case Report with a Fourteen-Year Follow-Up*
HAMLET A. PETERSON, M.S., M.D. and
R. CLIO ROBERTSON, M.D., ROCHESTER, MINNESOTA
Investigation performed at the Mayo Clinic, Rochester
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Introduction
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Traumatic disruption of the acetabular triradiate cartilage is an infrequent injury. When it occurs in young children, it may lead to premature physeal closure, even with little or no displacement of the innominate bones at the time of injury. Premature physeal closure results in a physeal osseous bar and progressive thickening of the wall of the acetabulum. This causes the acetabular cavity to become more shallow, resulting in gradual extrusion of the femoral head, subluxation, and eventually, hemipelvic hypoplasia and dysplasia of the hip1,2,10,13. Acetabular reconstruction is sometimes used to correct these abnormalities. Variable irregularities of growth at the proximal end of the femur, such as flattening of the medial side of the femoral capital epiphysis and coxa valga, also may occur.
In some patients, the physeal osseous bar may be small and located in a position that is amenable to excision. We are reporting the case of a patient who had what we believe to be the first successful excision of such a bar. The patient was followed for twelve years and four months postoperatively.
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Case Report
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A five-year-old boy sustained seven fractures, including two of the pelvis (Fig. 1), as well as a head injury, in an automobile accident. He was in a coma for twenty days. The pelvic fractures were treated with bed rest for three weeks. Premature partial closure of the right triradiate cartilage developed. At the age of seven years, radiographs showed that the right acetabular cavity, which was fourteen millimeters deep, was more shallow than the uninjured, left cavity, which was fifteen millimeters deep, and that the right femoral head was more laterally located (Fig. 2) than the left femoral head. A tomogram confirmed the presence of an osseous bar in the triradiate cartilage (Fig. 3). An incision was made over the anterior edge of the ilium to expose the inner wall of the acetabulum intrapelvically between the iliopsoas and the neurovascular bundle and extraperiosteally. The physeal osseous bar was excised, and the exposed osseous and physeal surfaces were covered with a thin layer of bone wax (Fig. 4). No other interpositional material was used. The patient was walking comfortably when he was discharged from the hospital five days postoperatively.
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Fig. 1 Initial anteroposterior radiograph of the pelvis, made at the age of five years, showing a fracture (large arrows) of the lateral portion of the superior ramus of the right pubic bone as it joins with the triradiate cartilage, as well as a fracture (small arrows) of the inferior part of the right ischium. Injury to the triradiate cartilage is less obvious.
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Fig. 2 Anteroposterior radiograph of the pelvis, made at the age of seven years (one year and nine months after the injury), showing widening of the wall of the acetabulum with an irregular and indistinct physis.
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Fig. 3 Anteroposterior tomogram, made at the age of seven years, showing an osseous bar (arrow) across the physis on the medial wall of the pelvis.
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Fig. 4 Intraoperative radiograph, made at the age of seven years, immediately after the osseous bar was excised. Metal markers that had been placed in the ilium and pubis at the time of the operation were measured to be twelve millimeters apart on this radiograph.
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At the age of ten, the triradiate cartilage remained open, and the acetabulum developed satisfactorily (Fig. 5).
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Fig. 5 Anteroposterior radiograph, made at the age of ten years (two years and ten months postoperatively), showing the wall of the right acetabulum to be no thicker than that of the left. The triradiate cartilage is open. The right acetabulum is as deep as or slightly deeper than the left. The metal markers are nineteen millimeters apart. The patient was normally active and asymptomatic.
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Between the ages of ten and nineteen years (Fig. 6), there was a slight increase in the width of the wall of the acetabulum and slight lateral displacement of the head of the right femur. This suggested that, despite additional growth after the age of ten years (the distance between the metal markers had increased from nineteen to twenty-eight millimeters), the right triradiate cartilage had closed prematurely near the time of maturity.
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Fig. 6 Anteroposterior radiograph, made at the age of nineteen years (twelve years and four months postoperatively), showing the wall of the right acetabulum to be slightly thicker than that of the left. All physes are closed. The right acetabulum is slightly more shallow than the left, and the head of the femur is situated slightly more laterally on the right than on the left. The metal markers are twenty-eight millimeters apart. The patient remained normally active and asymptomatic.
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Discussion
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The growth and development of the normal triradiate cartilage have been well documented2,9. Research on animals3-5,7,8,12 and case reports1,2,6,8,10,11,13,14 have documented that premature closure of the triradiate cartilage following trauma or infection has deleterious effects on the growth of the acetabulum, resulting in a shallow acetabulum, lateral extrusion of the femoral head, subluxation, and eventually dysplasia. Several types of corrective pelvic osteotomies have been performed in an attempt to correct these abnormalities1,2,11,13.
In 1982, Bucholz et al. stated: "Theoretically, if the osseous bridge were removed surgically, growth would resume and the normal shape of the acetabulum might be preserved. However, the rapid development of the osseous bridge and progression to closure of the triradiate cartilage certainly suggest that resection of the bridge and implantation of fat . . . may not have much success." Indeed, in 1980, Dias et al. reported a failure after excision of a triradiate osseous bridge that was filled with fat.
In the case reported here, after excision of the osseous bridge (in September 1982), the physis remained open and endochondral ossification proceeded normally, as evidenced by the increase in distance between the metal markers. Initially after the excision, the depth of the acetabulum and the width of its inner wall remained equal to those of the contralateral, normal acetabulum. After further growth and some time in adolescence, the acetabular triradiate cartilage on the right apparently closed earlier than that on the left, resulting in a very slight increase in the thickness of the acetabular wall and lateral displacement of the femoral head. This commonly occurs after excisions of the bars at other sites as well. Nevertheless, the result in our patient is superior to that reported for a patient who had a similar lesion but no treatment1. That patient had more severe thickening of the acetabular wall and more lateral displacement of the femoral head.
Small physeal bars of the triradiate cartilage may be amenable to excision. Early recognition and treatment before premature closure of the entire physis and before permanent osseous deformity are essential for a good outcome.
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Footnotes
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*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
Mayo Clinic, 200 First Street, S.W., Rochester, Minnesota, 55905. Please address requests for reprints to Dr. Peterson.
 6565 South Yale, Suite 1200, Tulsa, Oklahoma 74136.
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References
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Delgado Baeza, E.: Developmental displacement of hip joint. Experimental approach in the rat pelvis. Mapfre Med., 3 (Supplement 1): 7-9, 1992.
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Delgado Baeza, E.; Sanz-Laguna, A.; and Miralles-Flores, C.: Experimental trauma of the triradiate epiphysis of the acetabulum and hip dysplasia. Internat. Orthop., 15: 335-339, 1991.[Medline]
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Introduction
Case Report