TECHNIQUE

Ewing Sarcoma of the Acetabulum in Children: A “Growth Plate–based” Surgical Strategy Je´roˆme Sales de Gauzy, MD, Vale´rie Lafontan, MD, Monica Urseı¨, MD, and Franck Accadbled, MD, PhD

Background: Surgical strategy for Ewing sarcoma (ES) of the pelvis relies on Enneking classification. In adults, in case the acetabulum is involved, excision of the entire acetabulum is needed and often leads to loss of function. In children, the surgeon may adopt a strategy, such as in metaphyseal tumors of long bones where an unaffected growth plate allows a transepiphyseal resection, therefore sparing the joint. Methods: We present a “triradiate cartilage strategy” for the excision of ES of the pubic component of the acetabulum, which allows a wide resection while preserving most of the socket. The approach is ilioinguinal. Osteotomies of the iliopubic and ischio pubicrami are performed, followed by hip arthrotomy and anterior dislocation. Transacetabular resection is achieved using osteotomes, under image intensifier guidance, with no further reconstruction. Cases are presented for 2 boys aged 6.5 and 9.5 years, treated with chemotherapy and transacetabular resection. Results: Resections were all rated R0. Patient #1 remained asymptomatic, including during sport activities, and had normal hip range of motion at 12-year follow-up. Radiograph demonstrated mild protrusio acetabuli. Patient #2 had no complain at 3-year follow-up with normal hip range of motion, although he presented with an equinus gait. Radiographs demonstrated a well-covered femoral head without medial shift. Conclusions: A “growth plate–based” surgical strategy can be adapted to malignant pelvic tumors in skeletally immature children. This technique leaves intact the ilio ischiatic component of the triradiate cartilage, which, according to Ponseti, contributes the most to the growth of the acetabulum. Joint sparing improves the functional result and decreases the risk of complication. Level of Evidence: IV. Key Words: children, bone tumor, pelvis, triradiate cartilage, conservative surgery

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wing sarcoma (ES) is, after osteosarcoma, the second most frequent malignant bone tumor in children. It occurs most commonly during the second decade of life. The median patient’s age is 15 years. It is located most frequently at the pelvis or the femur.1 Pelvic ES has a poor prognosis than those of long bones.2–4 The ilium is the most common location, followed by the pubis.5 Treatment includes neoadjuvant chemotherapy in association with surgery and/or radiation therapy. Surgery provides a better prognosis and a lower recurrence rate in patients with primary pelvic tumor.6,7 Pelvic resections are classified by region, according to Enneking and Dunham8: type I iliac, type II acetabular, and type III pubic. Treatment of type II is challenging, because resection of the whole acetabulum is recommended. Several reconstruction methods have been described, including autogenic strut fibula, massive allograft, and prosthetic replacement,9–11 but they all lead to high mechanical complication rates. For metaphyseal bone tumor of the long bones, surgical strategy in children is specific in relation to the presence of growth plates. MRI allows a clear delineation of tumor extension and the relationships between the tumor and the growth plate. When the tumor does not cross the physis, preservation of the epiphysis and the joint is possible, even if the tumor abuts the physis.12–14 Winkelmann15 reported a similar strategy by using the triradiate cartilage for the removal of iliac sarcoma. In this strategy it was proposed to cut the pelvic bone beyond the triradiate cartilage. We used a similar strategy for ES of the pubic ramus extended to the acetabulum (Enneking III+II) and performed a transacetabular resection close to the triradiate cartilage without reconstruction. We report here the oncological and functional results in 2 consecutive cases.

(J Pediatr Orthop 2014;34:326–330)

SURGICAL TECHNIQUE

From the Service de Chirurgie Orthope´dique et Traumatologique, Hoˆpital des Enfants, Toulouse, France. The authors declare no conflicts of interest. Reprints: Franck Accadbled, MD, PhD, Service de Chirurgie Orthope´dique et Traumatologique, Hoˆpital des Enfants, 330, Avenue de Grande Bretagne, 31059 Toulouse, Cedex 9, France. E-mail: faccadbled@ wanadoo.fr. Copyright r 2013 by Lippincott Williams & Wilkins

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The patient is positioned supine. The surgical approach is ilioinguinal. A wide dissection followed by bone section is performed at the level of the pubic ramus. Transacetabular section requires exposure of the acetabulum and the hip joint. Rectus femoris is divided distal to its insertion at the anterior inferior iliac spine. The iliopsoas muscle is transectioned at the level of the pubis. The hip joint capsule is dissected and opened at its cranial aspect. The hip is then anteriorly dislocated. Transacetabular section is performed J Pediatr Orthop



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cranial

anterior

resected section FIGURE 2. Case 1: T1 MRI, coronal view. Ewing sarcoma of the right pubic ramus extended to the triradiate cartilage without crossing it.

FIGURE 1. Latero medial view of the right acetabulum. Dashed lines represent the osteotomies.

with 2 osteotomes under image intensifier control. The section is situated just above the iliopubic and ischiopubic rami of the triradiate cartilage (Fig. 1). After removal of the tumor, the hip is relocated and the joint capsule is sutured to the remaining part of the acetabulum. The rectus femoris and iliopsoas tendons are sutured. A spica cast with 10-degree flexion and 20-degree abduction is maintained for 2 months.

weightbearing was allowed at 3 months postoperatively. The orthosis was removed at 4 months postoperatively. Running and bike riding were resumed at 9 months postoperatively. At 12-year follow-up, the patient was event-free and walked normally. He had no pain. The hip range of motion was normal and symmetrical. There was no leg length discrepancy. He practiced sports without restriction. According to the Musculoskeletal Tumor Society (MSTS) criteriae, the result was 100% (excellent).18 Radiographs showed that the femoral head was well centered and covered until 3 years postoperatively (Fig. 3) when it shifted medially, and then remained stable at 12-year followup (Fig. 4). Gait analysis at the latest follow-up showed prolonged hamstring activity at the middle stance phase.

CASE SERIES The surgical treatment was discussed in a multidisciplinary planning meeting. Both patients and their families were informed and their consent was obtained before any treatment.

Case 1 A 6.5-year-old boy with nonmetastatic ES of the pubic ramus (Enneking IIB) was first treated with 6 cycles of neoadjuvant chemotherapy composed of vincristine, etoposide, ifosfamide, and doxorubicine. On both prechemotherapy and postchemotherapy MRIs, the tumor was located at the pubic ramus with an extension to the acetabulum close to the triradiate cartilage (Enneking zone II+III). The tumor did not cross the triradiate cartilage (Fig. 2). Wide resection with transacetabular section above the triradiate cartilage was performed. Histology demonstrated wide margins, according to Enneking et al’s16 classification. Response to chemotherapy was good, according to Huvos criteriae.17 No radiotherapy was undertaken. Adjuvant chemotherapy was continued. A spica cast was applied for 2 months, and then it was replaced by an orthosis, allowing flexion and extension of the hip. Complete r

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FIGURE 3. Case 1: AP standing radiograph of the pelvis demonstrating a well-centered and well-covered femoral head at 3-year follow-up. www.pedorthopaedics.com |

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FIGURE 4. Case 1: Nonprogressive protrusio acetabuli at 12-year follow-up. A, AP standing radiograph of the pelvis. B, Lateral radiograph of the right hip. C, 3D-CT reconstruction.

Case 2 A 9.5-year-old boy with ES of the pubic ramus, nonmetastatic (Enneking IIB) was treated with 6 cycles of neoadjuvant chemotherapy composed of vincristine, etoposide, ifosfamide, and doxorubicine. According to both prechemotherapy and postchemotherapy MRIs, the tumor was located at the pubic ramus with an extension to the acetabulum and close contact to the triradiate cartilage (Enneking zone III+II)

without crossing it (Fig. 5). Wide resection with transacetabular section above the triradiate cartilage was performed. Histology demonstrated wide margins, according to Enneking et al’s16 classification. Response to chemotherapy was good, according to Huvos criteriae.17 No radiotherapy was undertaken. Adjuvant chemotherapy was continued. The patient was immobilized in a spica cast for 2 months, and then in an orthosis, allowing flexion and extension of the hip. Full weightbearing was allowed at

FIGURE 5. Case 2: Ewing sarcoma of the right pubic ramus extended to the triradiate cartilage without crossing it. A, T2 MRI, axial view. B, T2 MRI, coronal view.

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FIGURE 6. Case 2: Anteroposterior standing radiograph of the pelvis demonstrating a well-centered and well-covered femoral head at 3-year follow-up. 3 months postoperatively. The orthosis was removed at 4 months postoperatively. Sporting activities were resumed at 9 months postoperatively. At 3-year follow-up, the patient was event-free. He had a Trendelenburg limping gait with slight dynamic toe walking. He had no pain. The hip range of motion was normal and symmetrical. There was no leg length discrepancy. He had no limitations, but he did not want to practice sports. The result was excellent, according to MSTS classification (90%).18 Radiographs demonstrated that the femoral head was well centered (Fig. 6). Gait analysis showed loss of hip flexion, normal activity of the rectus femoris at the middle stance phase, and prolonged activity of both hamstrings and vastus medialis at the middle stance phase, with premature activity of the soleus and gastrocnemius at heel strike.

DISCUSSION Surgery improves the results of pelvic ES, but remains challenging particularly for type II in which reconstruction is needed. There are several methods for acetabular reconstruction including hip fusion, strut fibula, massive allograft, and prosthetic replacement.9–11 According to the MSTS score, the results of these procedures range from 45% to 70%.9 Reported complication rates range from 30% to 100%.9,10,19–22 On the contrary, in type I of Enneking and Dunham,8 the possibility of preserving the acetabulum allows better functional result and lower complication rates. Preserving at least a part of the acetabulum may avoid reconstruction, thus improving the functional outcome and decreasing the complication rate. In children, the presence of the triradiate cartilage may allow to perform a wide excision while preserving a part of the acetabulum.15 The growth plate has been considered to be capable of preventing the spread of the tumor, although this barrier is not impenetrable.13 Consequently, the prerequisite for this strategy is an open triradiate cartilage and the tumor not crossing it.14 MRI is the best technique for staging a bone tumor and assessing its physeal r

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involvement. It clearly shows the relationship between the tumor and the triradiate cartilage. Thus, it can determine whether a transacetabular section is a reasonable option or not. The triradiate cartilage strategy has been reported twice in the literature for ES of the ilium extended to the acetabulum (type I+II).15,23 The authors cut the pelvic bone beyond the triradiate cartilage. Reconstruction was achieved by sacroliac arthrodesis or hip transposition. They reported safe local control. In our 2 cases, the tumor was located on the pubic side of the triradiate cartilage. We used the same “growth plate–based” strategy. We cut above the triradiate cartilage, and therefore we removed the iliopubic and ischiopubic part of the triradiate cartilage, whereas the iliopubic component was left intact. In the literature, we found only 1 similar case.23 The authors performed the same surgical technique without any bone reconstruction. At 4-month follow-up, the patient could walk with full weightbearing. He then survived 15 months after the surgery before developing lung metastasis. Longer follow-up is not mentioned. In our 2 cases, the “growth plate–based” strategy led to a safe oncological result. At, respectively, 3 and 12 years postoperatively, both patients were free of events. For both the cases, the functional result was excellent. Gait analysis showed mild anomalies without obvious functional consequences. Furthermore, this technique does not cause limb length inequality. A very interesting point is the growth of the remaining acetabulum and its relationship with the femoral head. The triradiate cartilage is responsible for the growth of the acetabulum in width and depth. An early closure of the triradiate cartilage leads to acetabular dysplasia and poor coverage of the femoral head.24,25 Growth of the triradiate cartilage is faster and predominant at the ilio ischiatic ramus.24,25 As a result, sparing the ilio ischiatic ramus may preserve the acetabular development, thus avoiding the risk for acetabular dysplasia and lateral subluxation. The femoral head remained centered during the first 3 years and then we noticed a mild protrusion due to the loss of the medial part of the acetabulum. Nevertheless, the femoral head protrusion did not progress with time and did not cause any hip dysfunction at 12-year follow-up. Consequently, we think that it is not necessary to do any medial reconstruction. However, female patients may have issues related to protrusio acetabuli during pregnancy and childbirth. Additional techniques may improve the safety of this procedure. Ganz-type hip dislocation may diminish the risk for avascular necrosis of the femoral head,26 and computer-assisted surgery may increase the accuracy of tumor resection.27 Of course, both longer follow-up and larger series are needed to confirm these encouraging preliminary results, as local recurrence is a devastating outcome. With more experience and closer margins, radiotherapy might be necessary and could compromise the functional results. These 2 cases showed that the triradiate cartilage should be carefully considered for ES located at the acetabulum (type II) in children. Much alike long bone tumors, the presence of a disease-free growth plate can allow a less extensive resection and preserve most of the acetabulum. Advantages are multiple: no need for reconstruction, www.pedorthopaedics.com |

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less complications, no leg length discrepancy, and excellent functional outcome as far as 12-year follow-up.

of preoperative MRI and the pathologic examination. Pediatr Radiol. 1993;23:421–424. Canadell J, Forriol F, Cara JA. Removal of metaphyseal bone tumours with preservation of the epiphysis. Physeal distraction before excision. J Bone Joint Surg Br. 1994;76:127–132. Winkelmann W. A new surgical method in malignant tumors of the ilium. Z Orthop Ihre Grenzgeb. 1988;126:671–674. Enneking WF, Spanier SS, Goodman MA. A system for the surgical staging of musculoskeletal sarcoma. Clin Orthop Relat Res. 1980; 153:106–120. Huvos AG, Rosen G, Marcove RC. Primary osteogenic sarcoma: pathologic aspects in 20 patients after treatment with chemotherapy en bloc resection, and prosthetic bone replacement. Arch Pathol Lab Med. 1977;101:14–18. Enneking WF, Dunham W, Gebhardt MC, et al. A system for the functional evaluation of reconstructive procedures after surgical treatment of tumors of the musculoskeletal system. Clin Orthop Relat Res. 1993;286:241–246. Hillmann A, Hoffmann C, Gosheger G, et al. Tumors of the pelvis: complications after reconstruction. Arch Orthop Trauma Surg. 2003; 123:340–344. Delepine F, Delepine G, Sokolov T, et al. Hand on composite prosthesis after resection of peri-acetabular sarcoma. Rev Chir Orthop Reparatrice Appar Mot. 2000;86:265–277. Dominkus M, Darwish E, Funovics P. Reconstruction of the pelvis after resection of malignant bone tumours in children and adolescents. Recent Results Cancer Res. 2009;179:85–111. Campanacci M, Capanna R. Pelvic resections: the Rizzoli Institute experience. Orthop Clin North Am. 1991;22:65–86. Ozaki T, Hillmann A, Winkelmann W. Treatment outcome of pelvic sarcomas in young children: orthopaedic and oncologic analysis. J Pediatr Orthop. 1998;18:350–355. Ponseti IV. Growth and development of the acetabulum in the normal child. Anatomical, histological, and roentgenographic studies. J Bone Joint Surg Am. 1978;60:575–585. Scuderi G, Bronson MJ. Triradiate cartilage injury. Report of two cases and review of the literature. Clin Orthop Relat Res. 1987;217: 179–189. Shin SJ, Kwak HS, Cho TJ, et al. Application of Ganz surgical hip dislocation approach in pediatric hip diseases. Clin Orthop Surg. 2009;1:132–137. Hufner T, Geerling J, Gansslen A, et al. Computer-assisted surgery for pelvic injuries. Chirurg. 2004;75:961–966.

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Ewing sarcoma of the acetabulum in children: a "growth plate-based" surgical strategy.

Surgical strategy for Ewing sarcoma (ES) of the pelvis relies on Enneking classification. In adults, in case the acetabulum is involved, excision of t...
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