The Journal of Foot & Ankle Surgery xxx (2015) 1–5
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Case Reports and Series
Giant Solitary Synovial Osteochondroma of the Subtalar Joint Tun Hing Lui, MBBS (HK), FRCS (Edin), FHKAM, FHKCOS Consultant, Department of Orthopaedics and Traumatology, North District Hospital, Sheung Shui, New Territory, Hong Kong SAR, China
a r t i c l e i n f o
a b s t r a c t
Level of Clinical Evidence: 4
A rapidly progressing calcified mass was found in the left sinus tarsi in a 12-year-old female after a trivial ankle sprain. The lesion mimicked an aggressive lesion clinically and radiographically. Ultrasound-guided biopsy confirmed the diagnosis of a synovial chondroma. Excision of the tumor and partial synovectomy were performed. The histologic diagnosis was a solitary synovial osteochondroma. The condition had not recurred after a follow-up period of 12 months. Ó 2015 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: calcaneus malignant osteochondroma synovial chondroma talus
Milgram (1) classified the disease process of synovial (osteo) chondromatosis into 3 distinct phases. The first phase is characterized by metaplastic cartilaginous nodules within the synovial membrane of the articular joint without loose bodies. The second phase includes both active intrasynovial proliferation and free loose bodies, and the third phase demonstrates only multiple free loose bodies without intrasynovial disease. The lesions can have various degrees of calcification and ossification. Edeiken et al (2) have described a large solitary chondroma as a fourth phase of the disease process. It can originate from either the chondroma coalesces or a single enlarged chondroma (2). It is an intra- and/or extra-articular lesion measuring >1 cm in size, sometimes as large as 20 cm (2). It has been reported in the hip (2), knee (2–4), elbow (5), ankle (6), temporomandibular joint (7), and soft tissues of the feet (2,8,9). We report a case of a giant solitary osteochondroma of the subtalar joint that was mimicking a malignant lesion clinically and radiographically. Case Report A 12-year-old female had sustained an inversion injury to her left ankle during rope skipping and then noticed swelling at the lateral side of her left ankle. All along she had experienced only mild pain over the swelling. She was treated by a bonesetter (traditional Chinese medical practitioner of joint manipulation), but the swelling persisted. She was then referred to our clinic for subsequent management 7 months after the injury. Clinically, a mobile bony hard mass was present at her left sinus tarsi. Diffuse swelling was found over the medial, lateral, and Address correspondence to: Tun Hing Lui, MBBS (HK), FRCS (Edin), FHKAM, FHKCOS, Department of Orthopaedics and Traumatology, North District Hospital, 9 Po Kin Road, Sheung Shui, New Territory, Hong Kong SAR, China. E-mail address: [email protected]
posterior heel. The subtalar joint motion was limited, especially on eversion. The left heel was in a slightly varus position compared with the right heel (Fig. 1). Radiographs were taken and showed a calcified mass that had increased in size compared with the size found on the previous radiographs (Fig. 2). Computed tomography (Fig. 3) and magnetic resonance imaging (MRI) (Fig. 4) showed a soft tissue mass with calcification arising from the lateral side of the posterior subtalar joint. MRI also showed effusion of the posterior subtalar joint, with rim contrast enhancement suggesting diffuse synovitis. Ultrasoundguided biopsy was performed, and the histologic diagnosis was a soft tissue chondroma without evidence of malignancy. Excision of the mass was performed. The mass was found to be an intracapsular lobulated cartilage mass with a soft tissue stalk arising from the interosseous ligament of the posterior subtalar joint (Fig. 5). No bone or cartilage invasion had developed. The surrounding soft tissue was plicated to reinforce the deficient lateral capsuloligamentous restraints after the excisional biopsy. Postoperatively, a short leg cast was applied, and she was instructed in non-weightbearing walking. The cast was removed 3 weeks after the operation, and she was advised on weightbearing walking with an air cast for another 3 weeks. Histologic examination confirmed the diagnosis of chondroma (Fig. 6). The soft tissue swelling required 6 months to subside. The bony mass had not recurred at 12 months postoperatively. However, the subtalar motion was still limited. Discussion Synovial osteochondromatosis can be found equally in males and females, occurring most frequently in those aged 30 to 50 years (11). Giant solitary synovial chondroma is a rare disease entity and has been reported only in case reports or series. The epidemiologic features are not known. To our knowledge, giant solitary synovial chondroma of the subtalar joint has not been reported in English
1067-2516/$ - see front matter Ó 2015 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2015.02.003
2
T.H. Lui / The Journal of Foot & Ankle Surgery xxx (2015) 1–5
Fig. 1. (A to D) Clinical photographs showing different views of the lesion (arrow) at the sinus tarsi, with the left heel in a slight varus position in (A).
published studies. It could not be determined whether the synovial chondroma in our patient developed after the ankle sprain or was just an incidental finding, although it has been reported after trauma (6). The clinical symptoms of intracapsular tumors and tumor-like lesions, such as pain, swelling, effusion, and joint locking, are not specific (10). The differential diagnosis includes extraskeletal osteochondroma, synovial (osteo) chondroma, chondrosarcoma, parosteal osteochondroma, tophaceous pseudogout, extraosseous osteosarcoma, and myositis ossificans circumscripta.
Extraskeletal osteochondroma is histologically similar to conventional osteochondroma, but it will not be attached to a parent bone or joint (11). This diagnosis was excluded in the present patient, because the mass had arisen from the posterior subtalar joint. Tophaceous pseudogout is a disease entity of tumor calcium deposition in the soft tissues and can be a complication of trauma, with associated tissue necrosis (12). Radiographs will show calcified lesions with a granular or fluffy pattern. Chondroid metaplasia within the lesion and, rarely, cellular atypia of the chondrocyte can occur. This can be misdiagnosed
Fig. 2. Sequential radiographs showing the calcified lesion had progressively increased in size: (A) 2 months, (B) 6 months, and (C) 8 months after the injury.
T.H. Lui / The Journal of Foot & Ankle Surgery xxx (2015) 1–5
3
Fig. 3. (A to D) Different views of computed tomography images showing the sinus tarsi lesion.
as a benign or malignant chondral tumor. The young age of our patient made such a diagnosis unlikely. Extraskeletal osteosarcoma represents an unusual soft tissue sarcoma that occurs as a large, deep, and high-grade lesion of the extremities in older patients (13). The diagnosis cannot be confirmed radiographically, and histologic examination is needed for diagnosis. This was unlikely to be the diagnosis for our patient because of her young age. Myositis ossificans circumscripta is a proliferative mesenchymal response to an initiating injury to the soft tissue, not necessarily to the muscle, that leads to localized ossification (14). Radiologically, it is difficult to distinguish this condition from soft tissue and bone malignancy; thus, a biopsy is necessary to confirm the diagnosis (14). The clinical presentation of a rapidly growing mass in the present patient raised the suspicion of an aggressive lesion. From the radiographic and computed tomography findings, the calcification of the lesion was peripheral and rim-like in our patient, instead of the typical ring or arc or comma-shaped chondral matrix in the case of chondroma. Moreover, because synovial chondroma has not been previously reported, a chondroma could not be diagnosed on the basis of the findings from radiography and computed tomography. MRI is an important diagnostic tool for synovial chondroma, especially in noncalcified or nonossified lesions (6). The mass will typically be isointense or slightly hyperintense to muscle on T1weighted and hyperintense to muscle on T2-weighted images (6,15). It
can be misinterpreted as a large effusion because of the rich water content of the hyaline cartilage tissue of the lesion (6). MRI is sensitive to the features of synovial chondroma, but great variation in the imaging findings exists (7). Three distinct MRI patterns of synovial osteochondromatosis have been described. MRI pattern A shows the presence of multiple hypointense septa, which can represent either areas of fibrosis or synovium coverage (6,15). MRI pattern B is pattern A plus the foci of signal void of calcified nodule on all pulse sequences. Pattern C is patterns A and B plus the foci of a peripheral low-signal surrounding the central fat-like signal of an ossified nodule (15). The associated bone marrow edema in the talus and calcaneum on the MRI in our patient supported the diagnosis of a more aggressive tumor. It can be difficult to differentiate synovial chondroma from chondrosarcoma and parosteal osteosarcoma radiographically, although the young age of our patient would tend to rule out these diagnoses (2,16). Similarly, myositis ossificans circumscripta and extraskeletal osteosarcoma cannot be excluded radiographically. A preoperative biopsy was therefore indicated. Partial synovectomy will usually be sufficient, because the whole synovium will not be involved in synovial chondromatosis (10). However, recurrence has been reported after partial synovectomy (6,13). It could result from cartilaginous seeds embedded in the remaining synovium that were not detected intraoperatively (17).
4
T.H. Lui / The Journal of Foot & Ankle Surgery xxx (2015) 1–5
Fig. 4. Magnetic resonance imaging scans showing the calcified lesion and subtalar effusion, with rim contrast enhancement. (A to D) Plain films. (E to H) Contrast films.
Fig. 5. Intraoperative photographs showing (A) the mass covered by the capsular structure, (B) the mass exposed after reflection of the capsule, (C) the posterior subtalar joint exposed after excision of the mass, and (D) the chondroma.
T.H. Lui / The Journal of Foot & Ankle Surgery xxx (2015) 1–5
5
Fig. 6. (A) Gross appearance of a cross-section of the chondroma. (B) Histologic view of the lesion.
Complete synovectomy might be a more effective method of preventing recurrence. Complete synovectomy was not performed in our patient because of the technical difficulty in performing complete subtalar synovectomy, especially over the medial joint gutter. Recurrence was not observed in our patient, although the preoperative MRI findings showed diffuse synovitis. That no recurrence was found might have been because the follow-up duration was short. However, the gradual subsidence of the medial heel swelling after removal of the chondroma could imply that the medial subtalar synovitis was secondary to the mechanical irritation of the tumor rather than primary involvement of the synovium of the medial joint gutter in the disease process. Giant solitary synovial chondroma of the subtalar joint can mimic a malignant lesion. A preoperative biopsy is needed to confirm the diagnosis and facilitate preoperative planning. Removal of the mass and partial synovectomy is the treatment of choice, and periodic follow-up over an extended period of time is indicated thereafter. References 1. Milgram JW. Synovial osteochondromatosis. J Bone Joint Surg Am 59:792–801, 1977. 2. Edeiken J, Edeiken BS, Ayala AG, Raymond AK, Murray JA, Guo SQ. Giant solitary synovial chondromatosis. Skeletal Radiol 23:23–29, 1994. 3. Jiang M, Zhang WG, Zhu J. Treatment of giant synovial chondroma of knee joint: a case report. Zhongguo Gu Shang 23:786–787, 2010.
4. Gentles C, Perin J, Berrey H, Griffiths HJ. Radiologic case study: soft-tissue chondroma. Orthopedics 30:241–243, 2007. 5. Pan YW, Pei XQ, Wang XM, Zhao WF, Xie PJ. Treatment of giant synovial chondroma at elbow joint: a report of 1 case. Zhongguo Gu Shang 2:470, 2008. 6. Hsueh CJ, Huang GS, Juan CJ, Wang SG, Liou CH, Hsiao HS, Gao HW. Synovial chondroma of the ankle in a young child after recent trauma: CT and MR features. Clin Imaging 25:296–299, 2001. 7. Cai XY, Yang C, Chen MJ, Jiang B, Wang BL. Arthroscopically guided removal of large solitary synovial chondromatosis from the temporomandibular joint. Int J Oral Maxillofac Surg 39:1236–1239, 2010. 8. Oliva F, Venanzi R, Fratoni S, Maffulli N. Chondroma of the subcutaneous bursa of the Achilles tendon. Bull Hosp Joint Dis 63:24–26, 2005. 9. Yin Y, Gilula LA. A 35-year-old-man with pain in the metatarsophalangeal joints: soft-tissue chondroma. Orthop Rev 22:483–488, 1993. }i M, Deodhar A. Synovial neoformations and tumours. Baillieres Best Pract 10. Szendro Res Clin Rheumatol 14:363–383, 2000. 11. Sit YK, Lui TH. Extraskeletal osteochondroma of the medial arch of the foot. Foot Ankle Spec 5:397–400, 2012. 12. Ishida T, Dorfman HD, Bullough PG. Tophaceous pseudogout (tumoral calcium pyrophosphate dehydrate crystal deposition disease). Hum Pathol 26:587–593, 1995. 13. McCarter MD, Lewis JJ, Antonescu CR, Brennan MF. Extraskeletal osteosarcoma: analysis of outcome of a rare neoplasm. Sarcoma 4:119–123, 2000. 14. Aneiros-Fernandez J, Caba-Molina M, Arias-Santiago S, O’Valle F, HernandezCortes P, Aneiros-Cachaza J. Myositis ossificans circumscripta without history of trauma. J Clin Med Res 2:142–144, 2010. 15. Kramer J, Recht M, Deely DM, Schweitzer M, Pathria MN, Gentili A, Greenway G, Resnick D. MR appearance of idiopathic synovial osteochondromatosis. J Comput Assist Tomogr 17:772–776, 1993. 16. Bahnassy M, Abdul-Khalik H. Soft tissue chondroma: a case report and literature review. Oman Med J 24:296–299, 2009. 17. Urbach D, McGuigan FX, John M, Neumann W, Ender SA. Long-term results after arthroscopic treatment of synovial chondromatosis of the shoulder. Arthroscopy 24:318–323, 2008.
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Case Reports and Series
Giant Solitary Synovial Osteochondroma of the Subtalar Joint Tun Hing Lui, MBBS (HK), FRCS (Edin), FHKAM, FHKCOS Consultant, Department of Orthopaedics and Traumatology, North District Hospital, Sheung Shui, New Territory, Hong Kong SAR, China
a r t i c l e i n f o
a b s t r a c t
Level of Clinical Evidence: 4
A rapidly progressing calcified mass was found in the left sinus tarsi in a 12-year-old female after a trivial ankle sprain. The lesion mimicked an aggressive lesion clinically and radiographically. Ultrasound-guided biopsy confirmed the diagnosis of a synovial chondroma. Excision of the tumor and partial synovectomy were performed. The histologic diagnosis was a solitary synovial osteochondroma. The condition had not recurred after a follow-up period of 12 months. Ó 2015 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: calcaneus malignant osteochondroma synovial chondroma talus
Milgram (1) classified the disease process of synovial (osteo) chondromatosis into 3 distinct phases. The first phase is characterized by metaplastic cartilaginous nodules within the synovial membrane of the articular joint without loose bodies. The second phase includes both active intrasynovial proliferation and free loose bodies, and the third phase demonstrates only multiple free loose bodies without intrasynovial disease. The lesions can have various degrees of calcification and ossification. Edeiken et al (2) have described a large solitary chondroma as a fourth phase of the disease process. It can originate from either the chondroma coalesces or a single enlarged chondroma (2). It is an intra- and/or extra-articular lesion measuring >1 cm in size, sometimes as large as 20 cm (2). It has been reported in the hip (2), knee (2–4), elbow (5), ankle (6), temporomandibular joint (7), and soft tissues of the feet (2,8,9). We report a case of a giant solitary osteochondroma of the subtalar joint that was mimicking a malignant lesion clinically and radiographically. Case Report A 12-year-old female had sustained an inversion injury to her left ankle during rope skipping and then noticed swelling at the lateral side of her left ankle. All along she had experienced only mild pain over the swelling. She was treated by a bonesetter (traditional Chinese medical practitioner of joint manipulation), but the swelling persisted. She was then referred to our clinic for subsequent management 7 months after the injury. Clinically, a mobile bony hard mass was present at her left sinus tarsi. Diffuse swelling was found over the medial, lateral, and Address correspondence to: Tun Hing Lui, MBBS (HK), FRCS (Edin), FHKAM, FHKCOS, Department of Orthopaedics and Traumatology, North District Hospital, 9 Po Kin Road, Sheung Shui, New Territory, Hong Kong SAR, China. E-mail address: [email protected]
posterior heel. The subtalar joint motion was limited, especially on eversion. The left heel was in a slightly varus position compared with the right heel (Fig. 1). Radiographs were taken and showed a calcified mass that had increased in size compared with the size found on the previous radiographs (Fig. 2). Computed tomography (Fig. 3) and magnetic resonance imaging (MRI) (Fig. 4) showed a soft tissue mass with calcification arising from the lateral side of the posterior subtalar joint. MRI also showed effusion of the posterior subtalar joint, with rim contrast enhancement suggesting diffuse synovitis. Ultrasoundguided biopsy was performed, and the histologic diagnosis was a soft tissue chondroma without evidence of malignancy. Excision of the mass was performed. The mass was found to be an intracapsular lobulated cartilage mass with a soft tissue stalk arising from the interosseous ligament of the posterior subtalar joint (Fig. 5). No bone or cartilage invasion had developed. The surrounding soft tissue was plicated to reinforce the deficient lateral capsuloligamentous restraints after the excisional biopsy. Postoperatively, a short leg cast was applied, and she was instructed in non-weightbearing walking. The cast was removed 3 weeks after the operation, and she was advised on weightbearing walking with an air cast for another 3 weeks. Histologic examination confirmed the diagnosis of chondroma (Fig. 6). The soft tissue swelling required 6 months to subside. The bony mass had not recurred at 12 months postoperatively. However, the subtalar motion was still limited. Discussion Synovial osteochondromatosis can be found equally in males and females, occurring most frequently in those aged 30 to 50 years (11). Giant solitary synovial chondroma is a rare disease entity and has been reported only in case reports or series. The epidemiologic features are not known. To our knowledge, giant solitary synovial chondroma of the subtalar joint has not been reported in English
1067-2516/$ - see front matter Ó 2015 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2015.02.003
2
T.H. Lui / The Journal of Foot & Ankle Surgery xxx (2015) 1–5
Fig. 1. (A to D) Clinical photographs showing different views of the lesion (arrow) at the sinus tarsi, with the left heel in a slight varus position in (A).
published studies. It could not be determined whether the synovial chondroma in our patient developed after the ankle sprain or was just an incidental finding, although it has been reported after trauma (6). The clinical symptoms of intracapsular tumors and tumor-like lesions, such as pain, swelling, effusion, and joint locking, are not specific (10). The differential diagnosis includes extraskeletal osteochondroma, synovial (osteo) chondroma, chondrosarcoma, parosteal osteochondroma, tophaceous pseudogout, extraosseous osteosarcoma, and myositis ossificans circumscripta.
Extraskeletal osteochondroma is histologically similar to conventional osteochondroma, but it will not be attached to a parent bone or joint (11). This diagnosis was excluded in the present patient, because the mass had arisen from the posterior subtalar joint. Tophaceous pseudogout is a disease entity of tumor calcium deposition in the soft tissues and can be a complication of trauma, with associated tissue necrosis (12). Radiographs will show calcified lesions with a granular or fluffy pattern. Chondroid metaplasia within the lesion and, rarely, cellular atypia of the chondrocyte can occur. This can be misdiagnosed
Fig. 2. Sequential radiographs showing the calcified lesion had progressively increased in size: (A) 2 months, (B) 6 months, and (C) 8 months after the injury.
T.H. Lui / The Journal of Foot & Ankle Surgery xxx (2015) 1–5
3
Fig. 3. (A to D) Different views of computed tomography images showing the sinus tarsi lesion.
as a benign or malignant chondral tumor. The young age of our patient made such a diagnosis unlikely. Extraskeletal osteosarcoma represents an unusual soft tissue sarcoma that occurs as a large, deep, and high-grade lesion of the extremities in older patients (13). The diagnosis cannot be confirmed radiographically, and histologic examination is needed for diagnosis. This was unlikely to be the diagnosis for our patient because of her young age. Myositis ossificans circumscripta is a proliferative mesenchymal response to an initiating injury to the soft tissue, not necessarily to the muscle, that leads to localized ossification (14). Radiologically, it is difficult to distinguish this condition from soft tissue and bone malignancy; thus, a biopsy is necessary to confirm the diagnosis (14). The clinical presentation of a rapidly growing mass in the present patient raised the suspicion of an aggressive lesion. From the radiographic and computed tomography findings, the calcification of the lesion was peripheral and rim-like in our patient, instead of the typical ring or arc or comma-shaped chondral matrix in the case of chondroma. Moreover, because synovial chondroma has not been previously reported, a chondroma could not be diagnosed on the basis of the findings from radiography and computed tomography. MRI is an important diagnostic tool for synovial chondroma, especially in noncalcified or nonossified lesions (6). The mass will typically be isointense or slightly hyperintense to muscle on T1weighted and hyperintense to muscle on T2-weighted images (6,15). It
can be misinterpreted as a large effusion because of the rich water content of the hyaline cartilage tissue of the lesion (6). MRI is sensitive to the features of synovial chondroma, but great variation in the imaging findings exists (7). Three distinct MRI patterns of synovial osteochondromatosis have been described. MRI pattern A shows the presence of multiple hypointense septa, which can represent either areas of fibrosis or synovium coverage (6,15). MRI pattern B is pattern A plus the foci of signal void of calcified nodule on all pulse sequences. Pattern C is patterns A and B plus the foci of a peripheral low-signal surrounding the central fat-like signal of an ossified nodule (15). The associated bone marrow edema in the talus and calcaneum on the MRI in our patient supported the diagnosis of a more aggressive tumor. It can be difficult to differentiate synovial chondroma from chondrosarcoma and parosteal osteosarcoma radiographically, although the young age of our patient would tend to rule out these diagnoses (2,16). Similarly, myositis ossificans circumscripta and extraskeletal osteosarcoma cannot be excluded radiographically. A preoperative biopsy was therefore indicated. Partial synovectomy will usually be sufficient, because the whole synovium will not be involved in synovial chondromatosis (10). However, recurrence has been reported after partial synovectomy (6,13). It could result from cartilaginous seeds embedded in the remaining synovium that were not detected intraoperatively (17).
4
T.H. Lui / The Journal of Foot & Ankle Surgery xxx (2015) 1–5
Fig. 4. Magnetic resonance imaging scans showing the calcified lesion and subtalar effusion, with rim contrast enhancement. (A to D) Plain films. (E to H) Contrast films.
Fig. 5. Intraoperative photographs showing (A) the mass covered by the capsular structure, (B) the mass exposed after reflection of the capsule, (C) the posterior subtalar joint exposed after excision of the mass, and (D) the chondroma.
T.H. Lui / The Journal of Foot & Ankle Surgery xxx (2015) 1–5
5
Fig. 6. (A) Gross appearance of a cross-section of the chondroma. (B) Histologic view of the lesion.
Complete synovectomy might be a more effective method of preventing recurrence. Complete synovectomy was not performed in our patient because of the technical difficulty in performing complete subtalar synovectomy, especially over the medial joint gutter. Recurrence was not observed in our patient, although the preoperative MRI findings showed diffuse synovitis. That no recurrence was found might have been because the follow-up duration was short. However, the gradual subsidence of the medial heel swelling after removal of the chondroma could imply that the medial subtalar synovitis was secondary to the mechanical irritation of the tumor rather than primary involvement of the synovium of the medial joint gutter in the disease process. Giant solitary synovial chondroma of the subtalar joint can mimic a malignant lesion. A preoperative biopsy is needed to confirm the diagnosis and facilitate preoperative planning. Removal of the mass and partial synovectomy is the treatment of choice, and periodic follow-up over an extended period of time is indicated thereafter. References 1. Milgram JW. Synovial osteochondromatosis. J Bone Joint Surg Am 59:792–801, 1977. 2. Edeiken J, Edeiken BS, Ayala AG, Raymond AK, Murray JA, Guo SQ. Giant solitary synovial chondromatosis. Skeletal Radiol 23:23–29, 1994. 3. Jiang M, Zhang WG, Zhu J. Treatment of giant synovial chondroma of knee joint: a case report. Zhongguo Gu Shang 23:786–787, 2010.
4. Gentles C, Perin J, Berrey H, Griffiths HJ. Radiologic case study: soft-tissue chondroma. Orthopedics 30:241–243, 2007. 5. Pan YW, Pei XQ, Wang XM, Zhao WF, Xie PJ. Treatment of giant synovial chondroma at elbow joint: a report of 1 case. Zhongguo Gu Shang 2:470, 2008. 6. Hsueh CJ, Huang GS, Juan CJ, Wang SG, Liou CH, Hsiao HS, Gao HW. Synovial chondroma of the ankle in a young child after recent trauma: CT and MR features. Clin Imaging 25:296–299, 2001. 7. Cai XY, Yang C, Chen MJ, Jiang B, Wang BL. Arthroscopically guided removal of large solitary synovial chondromatosis from the temporomandibular joint. Int J Oral Maxillofac Surg 39:1236–1239, 2010. 8. Oliva F, Venanzi R, Fratoni S, Maffulli N. Chondroma of the subcutaneous bursa of the Achilles tendon. Bull Hosp Joint Dis 63:24–26, 2005. 9. Yin Y, Gilula LA. A 35-year-old-man with pain in the metatarsophalangeal joints: soft-tissue chondroma. Orthop Rev 22:483–488, 1993. }i M, Deodhar A. Synovial neoformations and tumours. Baillieres Best Pract 10. Szendro Res Clin Rheumatol 14:363–383, 2000. 11. Sit YK, Lui TH. Extraskeletal osteochondroma of the medial arch of the foot. Foot Ankle Spec 5:397–400, 2012. 12. Ishida T, Dorfman HD, Bullough PG. Tophaceous pseudogout (tumoral calcium pyrophosphate dehydrate crystal deposition disease). Hum Pathol 26:587–593, 1995. 13. McCarter MD, Lewis JJ, Antonescu CR, Brennan MF. Extraskeletal osteosarcoma: analysis of outcome of a rare neoplasm. Sarcoma 4:119–123, 2000. 14. Aneiros-Fernandez J, Caba-Molina M, Arias-Santiago S, O’Valle F, HernandezCortes P, Aneiros-Cachaza J. Myositis ossificans circumscripta without history of trauma. J Clin Med Res 2:142–144, 2010. 15. Kramer J, Recht M, Deely DM, Schweitzer M, Pathria MN, Gentili A, Greenway G, Resnick D. MR appearance of idiopathic synovial osteochondromatosis. J Comput Assist Tomogr 17:772–776, 1993. 16. Bahnassy M, Abdul-Khalik H. Soft tissue chondroma: a case report and literature review. Oman Med J 24:296–299, 2009. 17. Urbach D, McGuigan FX, John M, Neumann W, Ender SA. Long-term results after arthroscopic treatment of synovial chondromatosis of the shoulder. Arthroscopy 24:318–323, 2008.
