Dysplasia epiphysealis hemimelica, which is also known as Trevor disease, is a rare developmental lesion that is histologically identical to an osteochondroma. The more common solitary osteochondroma and multiple hereditary osteochondromatosis typically are located on the metaphysis of long bones, occasionally on the diaphysis of long bones, and on flat bones, but never on the epiphysis. The index lesion is intra-articular and characteristically involves only half of the joint (hemimelic). The osseous portions of the lesion distinguish it from synovial chondromatosis, which always consists of multiple lesions usually dispersed throughout the joint. The osteochondroma of dysplasia epiphysealis hemimelica, in addition to being hemimelic, is initially a solitary lesion, although portions may break off, producing multiple pieces17. It is typically found in the joints of the lower extremity, with a predisposition for the medial femoral condyle, the distal aspect of the tibia, and the talus1,2,4,5,7,12,15,21,25.
Mouchet and Belot16, in 1926, were the first to report this entity, and they called it tarsomégalie. Trevor25 described ten patients in 1950 and used the term tarso-epiphysial aclasis. In 1956, Fairbank5 reported on fourteen patients and renamed the condition dysplasia epiphysialis hemimelica.
We report the cases of two patients who had a subluxation of the hip that was found to be associated with an isolated intra-articular osteochondroma of the acetabulum. These two cases are presented because of the isolated and unique acetabular location of the lesion.
*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.
†Division of Orthopaedic Surgery, University of Southern California School of Medicine, Childrens Hospital Los Angeles, 4650 Sunset Boulevard, Mailstop 69, Los Angeles, California 90027. E-mail address for D. L. Skaggs: dskaggs@chla.usc.edu.
‡Department of Orthopaedic Surgery, University of Southern California Medical Center, 1200 North State Street, GH 3900, Los Angeles, California 90033.
§Mayo Clinic, 200 First Street S.W., Rochester, Minnesota 55905.
CASE 1. A five-year-old girl was referred to one of the authors (H. A. P.) because of a several-month history of bilateral discomfort of the lower limb. The patient's father had noted a change in the child's gait a few days before she was seen by us. The child did not complain of pain in the hip.
Examination revealed mild flexion and abduction contractures of the right hip with complete loss of rotation and a decreased abduction-adduction arc, a positive Allis sign, and an abnormal gait. The flexion contracture was 5 degrees, and the abduction contracture was 20 degrees. The gait was abnormal because of these contractures and the absence of internal and external rotation. The lower limbs were of equal length. Radiographs showed a space-occupying lesion located in the ischial and pubic portions of the right acetabulum (Fig. 1-A). A computerized tomography scan confirmed the location of the lesion (Fig. 1-B). There were no other palpable lesions, and none were visible on radiographs of the chest and pelvis. We did not perform a skeletal survey. There was irregular increased radiodensity involving the acetabulum, indicating that the lesion was osteocartilaginous. There were no patchy lytic lesions suggestive of malignancy.
An excisional biopsy was performed through an anterior approach. The hip was dislocated so that an excision of the ischial and pubic portions of the tumor could be performed and injury to the triradiate cartilage could be avoided. We believed that dislocating the hip for an hour would not result in any long-term sequelae. To the best of our knowledge, temporary intraoperative dislocation of the hip has not been reported to be associated with avascular necrosis or other hip disability. Furthermore, there was no other way to excise this lesion.
The histological findings were consistent with benign osteochondroma (Fig. 1-C), showing a preponderance of large but otherwise normal chondrocytes with an indiscrete border between the cartilage and osseous trabeculae. Postoperative radiographs and computerized tomography scans showed the lesion to have been excised completely. An above-the-knee cast was applied bilaterally, with a bar separating the legs (a simulated A-frame) to keep the hips in mild abduction.
Three months after the biopsy, the patient had no pain or limp. The hip lacked the last 25 degrees of internal rotation (measured with the patient in the prone position) in comparison with the contralateral side, and all other ranges of motion were symmetrical with the contralateral side. Three years after the procedure, when the child was nine years old, she was participating in normal activities for her age and was asymptomatic. The Allis and Trendelenburg signs were negative. The gait was normal, and the lower limbs were of equal length. Radiographs showed continued growth and development of both hips, with mild coxa magna and flattening of the medial side of the femoral head on the right (Fig. 1-D). The triradiate cartilage was indistinct, and the thickening of the outer wall of the acetabulum suggested a new lesion (Fig. 1-E). Computerized tomography scans confirmed a recurrent lesion in the depths of the acetabulum (Fig. 1-F). The patient subsequently had another excision performed through an anterior approach. The hip was again dislocated to facilitate the approach; the lesion was resected, and histological findings confirmed it to be osteochondroma.
Eight years after the second procedure, when the patient was seventeen years and nine months old, she was participating in sports with no pain or limp. Internal and external rotation of the right hip lacked 10 degrees compared with the left hip, but other motions were equal and symmetrical. Radiographs showed excellent remodeling of the acetabulum, with complete filling of the defect (Figs. 1-G and 1-H). There was some persistent, mild asymmetry of the femoral head.
CASE 2. A seven-year-old girl was first seen at another institution because of a two-month history of discomfort of the right hip that did not respond to nonsteroidal anti-inflammatory drugs. The initial radiographs showed only subluxation of the right hip, with no other pathological lesion noted. A bone scan demonstrated increased uptake in the right acetabulum. The differential diagnosis of an infection of the hip joint or transient synovitis was considered likely, with the effusion thought to be the cause of the hip subluxation. An aspiration of the hip was performed with fluoroscopic control, followed by open incision and drainage of the hip through a posterior approach. We believe that the findings were not sufficient to warrant the open drainage and would have proceeded with imaging studies to assess the lesion. The gram stain and the cultures were negative. There were no systemic symptoms, and the hip remained subluxated. Magnetic resonance imaging was then performed and interpreted as showing an excess of fluid displacing the hip laterally. In retrospect, an acetabular mass was noted on the imaging studies.
Two weeks after the incision and drainage of the hip, the patient was referred to one of the authors (D. L. S.) for treatment of subluxation of the right hip. She reported continued activity-related pain in the right hip. On physical examination, there was a positive Galeazzi sign. Internal rotation of the affected right hip, measured with the patient in the prone position, was 10 degrees, compared with 45 degrees on the left, with a 10-degree loss of extension of the right hip. The patient walked with a mild antalgic gait and had a positive Trendelenburg sign.
Plain radiographs confirmed hip subluxation and showed the right acetabulum to have an increased density suggestive of a space-occupying lesion. A preliminary diagnosis of Trevor disease was made. Computerized tomography scans with cuts made, at 1.5-millimeter intervals, through the acetabulum revealed an osseous growth from the acetabulum and subluxation of the hip. No other lesions were found clinically or on radiographs of the lower extremities.
The hip was opened through an anterior approach, and the femoral head was dislocated. The cartilaginous surface of the mass was inflamed with hypertrophic tissue consistent with the appearance of an inflammatory response. On palpation, the lesion was continuous with and fixed to the acetabulum. This lesion was removed with rongeurs and high-speed burrs, with care taken to avoid the triradiate cartilage. The diagnosis of dysplasia epiphysealis hemimelica was confirmed by analysis of frozen and permanent sections. The femoral head had evidence of mild, abnormal wear in the posterior-inferior portion.
Postoperatively, the patient wore an abduction orthosis for nine weeks, although full weight-bearing was permitted. At the time of the two-year follow-up evaluation, she had a full, painless range of motion of the hip and reported no problems. A follow-up computerized tomography scan showed evidence of acetabular remodeling with no evidence of recurrence. There was no sign of avascular necrosis of the femoral head.
Permanent histopathological sections were reviewed by the hospital staff and independently by pathologists with expertise in orthopaedic pathology at two outside facilities. The final histological diagnosis was dysplasia epiphysealis hemimelica.