Synovial osteochondromatosis is characterized by the formation of multiple osteochondral nodules arising from metaplasia of the synovial tissue. The most prevalent sites are the knee, elbow, and hip3,9,11,18,19. The disorder rarely occurs in the ankle or the foot2,17,22,27. Trauma has been implicated but has never been confirmed as a precipitating factor in the development of this condition4,6,10,18,24.
We report the rare case of a patient who had previous trauma and in whom synovial osteochondromatosis developed in the retrocalcaneal bursa in association with intraosseous lesions of the calcaneus. Magnetic resonance imaging and computed tomography scanning were useful in guiding the decisions regarding the operative approach in this patient who had atypical synovial osteochondromatosis.
*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.
†Department of Orthopaedic Surgery, Osaka University Medical School, 2-2 Yamada-oka, Suita 565, Japan.
‡Okada Orthopaedic Hospital, 3—22 Dougo-Kitashiro, Matsuyama Ehime 790, Japan.
A twenty-year-old male sailor sprained the left ankle in a fall down stairs in May 1989. The whole foot with the exception of the toes was swollen and severely painful, especially on weight-bearing. The patient had less discomfort when he was not standing. Pain was caused by light touch to the region, but it was not localized. He did not have treatment at that time because the injury occurred during a long voyage at sea.
One month later, the entire hindfoot was still painful and swollen and the patient consulted a physician. The findings on standard radiographs were normal, and therefore he was managed with decreased activity and analgesics. After one month, the swelling had disappeared and the pain was localized around the insertion of the Achilles tendon. The patient reported that the pain was severe after he had been running and caused him to limp for a few days. He did not need medication for pain continually, but he used analgesics after walking a long distance or after running.
In April 1990, the patient noticed a mass lateral to the Achilles tendon. The mass gradually enlarged, and he had mild pain intermittently. In May 1992, he reported that the pain over the mass became worse when he was playing baseball. He was managed with analgesics for a week, but the discomfort was not relieved.
On June 2, 1992, when he was first seen at Kure National Hospital, a tumorous mass that measured three by two centimeters was found. The patient reported that he had pain over the mass while he was standing or walking. At the time of admission, physical examination revealed a trilobed mass with a smooth, hard surface and a clear margin. The color and turgor of the skin were normal. There was marked tenderness over the mass, and the patient reported pain on dorsiflexion of the ankle. The passive range of motion of the ankle was normal, although it was painful. Laboratory tests showed that the leukocyte count was 7900 cells per cubic millimeter (7.9 x 109 per liter), the erythrocyte sedimentation rate was fourteen millimeters per hour, and the C-reactive protein level was 0.01 milligram per liter. The serum calcium level was 4.7 milliequivalents (2.35 millimoles) per liter (normal, 4.2 to 5.4 milliequivalents [2.10 to 2.70 millimoles] per liter), and the alkaline phosphatase level was 6.8 King-Armstrong units per deciliter (forty-eight units per liter) (normal, 2.8 to 13.0 King-Armstrong units per deciliter [twenty to ninety-two units per liter]).
Standard radiographs of the left foot, made on June 6, 1989, one month after the trauma, showed no abnormalities (Fig. 1-A). Radiographs made on April 3, 1990, showed multiple radiopaque nodules posterosuperior to the calcaneus, close to the area of the retrocalcaneal bursa (Fig. 1-B). Radiographs made when the patient was admitted on June 2, 1992, revealed that the mass, which contained granular shadows, had enlarged further and that the radiodensity of the mass had increased (Fig. 1-C). The radiographic findings suggested that the mass was not connected with the ankle joint. The differential diagnosis was calcifying tendinitis, atypical osteochondromatosis in the retrocalcaneal bursa, or chondrosarcoma. Technetium-99m scintigraphy showed non-specific uptake of the radionucleotide in the foot. A computed tomography scan revealed a soft-tissue mass with multiple granular shadows at the anterior aspect of the Achilles tendon (Fig. 2-A) that was contiguous with the intraosseous lesion in the calcaneus (Fig. 2-B). No connection was seen between the mass and the ankle on magnetic resonance imaging (Fig. 3). Angiography showed no abnormal vessels or tumor.
The mass was excised on June 22, 1992. Beneath the skin, there was an elastic, hard, trilobed mass with an irregular thin capsule situated at the lateral border of the left Achilles tendon. The three lobes of the mass were connected by fibrous tissues. Many hard whitish fragments, which were osteochondral nodules, were seen. There was no connection between the mass and the ankle joint or between the mass and the talocalcaneal joint. Intra-articular involvement was ruled out by exploring the ankle joint through a posterior incision in the capsule. There were no abnormal findings inside the joint. Erosion of the bone was evident at the posterosuperior aspect of the calcaneus. We believed that the erosion was caused by compression from the mass, as we did not suspect that synovial osteochondromatosis could involve bone. Because the intraosseous lesion within the calcaneus was thought to be osseous erosion caused by the mass, the lesion was not treated.
Histological examination showed proliferative chondrocytes with some ossification in the hypertrophied synovial bursa (Figs. 4-A and 4-B). The diagnosis of synovial osteochondromatosis was confirmed. After wearing a below-the-knee cast for two weeks, the patient was permitted to bear weight on the foot with the aid of a single cane. He was allowed to walk without a cane one month after the operation.
The pain and tenderness were relieved for two months, but when the patient was seen on September 22, 1992, he reported that he had pain when walking. Physical examination revealed tenderness over the operative area with radiating pain along the lateral border of the hindfoot extending to the heel. Because this was the area where the counter of the shoe pressed the foot, the patient had pain when he walked. Hypoesthesia was present posterior and distal to the lateral malleolus, and paresthesia was present in the area of the heel. However, motion of the ankle joint was not painful. Standard radiographs showed no recurrent radiopaque nodules or soft-tissue masses. We believed that the sural nerve was entrapped by scar tissue and that the nerve possibly was being compressed by the residual mass from the intraosseous lesion.
On October 8, 1992, an operation was performed for the purpose of neurolysis and for confirmation of the nature of the intraosseous lesion. A number of nodules, which were covered with a smooth, lustrous white surface, were seen in close contact with the sural nerve and seemed to be compressing it. The nodules were in the area that had been tender to palpation preoperatively. Additional exploration showed that the nodules extended on the superior aspect of the calcaneus to the retrocalcaneal bursa. The nodules were removed, the nerve was freed from the surrounding tissues, and the superoposterior prominence of the calcaneus was excised. The ostectomy that was done was as small as possible, allowing for complete excision of the intraosseous lesion, including the sclerotic margin and the bursa. As had been seen on the preoperative computed tomography scan, numerous osteochondral nodules were present within the calcaneus. Histological examination of the fragments within the calcaneus also showed synovial osteochondromatosis similar to that in the extraosseous mass.
The patient returned to his original work three weeks after the reoperation with only slight discomfort. Fourteen months after the second operation, he was still free of symptoms and radiographs showed no evidence of recurrence.
The cases of only ten patients who had synovial osteochondromatosis of the ankle have been reported in the literature2,4,8,11,12,16,22-24. Synovial osteochondromatosis develops in the synovial tissue in the joint capsule, the tendon sheath, or the bursal sac9,26. When it is present in the joint capsule, standard radiographs can easily delineate the locality of the lesion and help to establish the diagnosis. However, when it is extra-articular or in association with intraosseous lesions as seen in our patient, computed tomography scanning and magnetic resonance imaging studies are needed. These studies reveal either the origin of the soft-tissue mass with calcified nodules or the connection between the mass and the joint.
Our patient had both an extra-articular soft-tissue mass and intraosseous lesions, which had revealed the same histological features. Therefore, the origin was considered to have arisen from the retrocalcaneal bursa. To our knowledge, this is the first report of synovial osteochondromatosis originating from the retrocalcaneal bursa.
Recent pathological studies of osteochondromatosis have demonstrated an increase of type-II collagen20,21 and conversion of fibroblasts to chondrocytes1,13,14, resulting in metaplasia of the synovial tissue with the proliferation of cartilaginous nodules. However, the etiology is still unclear.
Trauma has been reported as a possible precipitating factor in the development of synovial osteochondromatosis4,18,22,24. Of the ten patients who reportedly had a lesion in the ankle, five had had previous trauma to the ankle (four had had a sprain and one had had a bruise). Our patient also had trauma to the ankle; the mass gradually enlarged in the hindfoot. The clinical course of these patients suggests that trauma could play a part in the development of synovial osteochondromatosis, although the association of trauma with the lesion may be coincidental.
When the diagnosis of synovial osteochondromatosis is made at phase III of the classification of Milgram16 and the patient is asymptomatic, the nodules may be resorbed7,15,16,25. Therefore, operative treatment is not indicated6,11,15,28. However, in a patient who has symptoms, operative removal of the loose bodies and simultaneous synovectomy may be necessary5,29.
Synovectomy usually is not performed for a bursal lesion. Instead, total bursectomy is recommended. Moreover, a diagnosis of a phase-III lesion16 cannot be determined in most bursae because the bursae are too small. Therefore, treatment is indicated if the lesion is symptomatic.
Synovial osteochondromatosis usually is an intra-articular condition. Thus, extra-articular involvement may present a diagnostic problem. When a soft-tissue mass is seen to have spotty shadows on plain radiographs, especially with osseous involvement as in our patient, it may be mistaken for chondrosarcoma. For an accurate diagnosis of such masses, it is important to rule out osseous involvement by this condition.
NOTE: The authors thank Atsumasa Uchida, M.D., Ph.D., for his valuable comments and suggestions, and Youichi Shigeno, M.D., Ph.D., for his assistance with the present study.