Para-articular Osteochondroma of the Knee

Case Report

Para-articular Osteochondroma of the Knee Giacomo Rizzello, M.D., Francesco Franceschi, M.D., Maria Chiara Meloni, M.D., Emanuela Cristi, M.D., Simona Angela Barnaba, M.D., Carla Rabitti, M.D., and Vincenzo Denaro, M.D.

Abstract: We report a case of para-articular chondroma located in the infrapatellar fat pad of the knee of a 42-year-old woman with a history of anterior knee pain and restricted range of motion. On clinical examination, a solid palpable mass in the infrapatellar region was detected. Radiography and computed tomography of the knee revealed the presence of 3 different “popcorn”-like gross calcifications within Hoffa’s fat pad. Magnetic resonance imaging showed areas of signal intensity in Hoffa’s fat pad that were consistent with calcific nodules surrounded by chondral tissue. During arthroscopy, a dense extrasynovial mass was discerned within Hoffa’s fat pad. The mass was entirely removed through an open approach medial to the patellar tendon. Resection specimens consisted of 3 well-circumscribed nodules of 5 ⫻ 2.5 ⫻ 1.5, 2 ⫻ 2 ⫻ 1, and 1.5 ⫻ 2 ⫻ 1 cm, respectively. Grossly, these nodules were surrounded by adipose tissue and presented a thin fibrous membrane. Histologic examination showed that the nodules were composed of cartilaginous tissue surrounded by fibrous connective and adipose tissue with multifocal endochondral ossification. The precise pathogenetic mechanism of these tumors remains unknown, but cartilaginous metaplasia of articular and para-articular connective tissue seems to be the primary cause. Patients with these lesions are currently treated with the use of marginal resection or excision. Key Words: Para-articular osteochondromas—Synovial chondromatosis—Osteochondromas—Mass within Hoffa’s fat pad—Cartilaginous metaplasia.

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hree types of extraskeletal chondromas have been identified: synovial chondromatosis, soft tissue chondroma, and para-articular chondroma. Para-articular chondromas are solitary lesions that are associated with a joint.1 These tumors arise in the capsule of

From the Department of Orthopaedics (G.R., F.F., M.C.M., S.A.B., V.D.), and Department of Surgical Pathology (E.C., C.R.), University Campus Bio-Medico, Rome, Italy. The authors report no conflict of interest. Address correspondence and reprint requests to Giacomo Rizzello, M.D., Department of Orthopaedics, University Campus BioMedico, Via E. Longoni 83, 00155 Rome, Italy. E-mail: g.rizzello@ unicampus.it © 2007 by the Arthroscopy Association of North America Cite this article as: Rizzello G, Franceschi F, Meloni MC, Cristi E, Baranaba SA, Rabitti C, Denaro V. Para-articular osteochondroma of the knee. Arthroscopy 2007;23:910.e1-910.e4 [doi: 10.1016/j.arthro.2006.05.030]. 0749-8063/07/2308-5407$32.00/0 doi:10.1016/j.arthro.2006.05.030

a joint or from the connective tissue close to the capsule and are caused by cartilaginous metaplasia.2,3 Many of the difficulties associated with diagnosing osteochondral lesions are caused by inconsistencies and confusion in the nomenclature. Given that marginal excision is the treatment of choice exclusively for paraarticular osteochondroma,4,5 it is important for the clinician to distinguish para-articular osteochondroma from chondrosarcoma and synovial chondromatosis. This report describes a case of para-articular osteochondroma and provides helpful criteria for use in distinguishing these lesions from similar entities.

CASE REPORT A 42-year-old woman presented with a 3-year history of right knee pain. Two years earlier, computed tomography (CT) showed a round neoformation with

Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 23, No 8 (August), 2007: pp 910.e1-910.e4

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FIGURE 1. Radiographs and computed tomography axial scans of the knee. (A) Lateral radiograph shows the presence of 3 different “popcorn”like gross calcifications in Hoffa’s fat pad. (B) Axial radiographic view shows a single calcification in the medial compartment of the joint. (C,D) Computed tomography axial scan shows a soft tissue density mass in Hoffa’s fat pad with “popcorn”-like calcification within.

noninfiltrative borders and large calcifications inside the medial region of Hoffa’s fat pad (Fig 1). Before visiting our clinic, the patient had undergone arthroscopic medial meniscectomy and lateral release but continued to have anterior knee pain with restricted range of motion. On physical examination, a solid palpable mass was detected in the infrapatellar region close to the medial edge of the patellar tendon. A knee lateral view radiograph revealed the presence of 3 different “popcorn”-like gross calcifications in Hoffa’s fat pad. The axial view showed a single calcification in the medial knee compartment (Fig 1). A sagittal magnetic resonance imaging (MRI) T1-weighted sequence showed a mass in Hoffa’s fat pad with an intermediate signal intensity and an inhomogeneous signal in the T2-weighted sequence. Areas of low signal intensity in all sequences interspersed within the mass had similar consistency to calcific nodules. Areas of high signal intensity on T2-weighted images suggested the presence of chondral tissue; this was confirmed by the absence of fat in fat-saturated (FAT-SAT) sequences (Fig 2). During arthroscopy, no loose bodies were discerned. However, a dense extrasynovial mass was noted within Hoffa’s fat pad. We continued surgery through an open approach medial to the patellar tendon, and the mass was entirely removed. Resection specimens consisted of 3 well-circumscribed nodules of 5 ⫻ 2.5 ⫻ 1.5, 2 ⫻ 2 ⫻ 1, and 1.5 ⫻ 2 ⫻ 1 cm, respectively. Grossly, these nodules were surrounded by adipose tissue and presented a thin fibrous membrane with a yellowish white lobular appearance on the cut surface (Fig 3). Histologic examination of the 3 nodules revealed that they were of multilobated shape, were composed of cartilaginous tissue, and were surrounded by fibrous connective and adipose tissue. Multifocal endochondral ossification was evident, and no atypical cells or mitotic figures were seen (Fig 4A). Masson trichrome staining revealed prominent fibrocollag-

enous bundles within the fibrous-adipose-cartilaginous matrix (Fig 4B). The absence of intra-articular calcifications was noted on postoperative radiographs. Preoperative symptoms disappeared, pain in the anterior knee was eliminated, and full range of motion was regained. The patient returned to work 3 weeks after undergoing surgery. DISCUSSION Several different types of lesions composed of bone and cartilage may arise around joints; the most fre-

FIGURE 2. Magnetic resonance imaging (MRI) of the knee. (A) Median sagittal MRI T1-weighted sequence shows a mass of intermediate signal intensity in Hoffa’s fat pad; (B) an inhomogeneous signal is exhibited in the T2-weighted sequence. Areas of low signal in all sequences interspersed in the mass are consistent with calcific nodules. Areas of high signal intensity on (B) T2weighted images suggest the presence of chondral tissue, given the absence of fat in the lesion as demonstrated by (C) the fat suppression sequence.

PARA-ARTICULAR OSTEOCHONDROMA OF THE KNEE

FIGURE 3. Gross appearance after formalin fixation and decalcification: The cut surface of the lesions demonstrates a lobular pattern surrounded by fibrous connective tissue. At surgery, a well-formed pseudocapsule was observed to surround the nodule, and no evidence suggested association with the joint capsule.

quent of these is the conventional osteochondroma, which usually originates from a developmental defect in the growth plate that results in surrounding of bone tissue by a cartilaginous cup that grows away from the joint.6,7 Synovial chondromatosis is characterized by multiple cartilaginous or osteocartilaginous nodules within the synovium that may gain access to the joint space, resulting in numerous loose bodies. Histologic examination reveals small hyaline nodules that are arranged in characteristic chondrocyte clusters with slight atypia and focal endochondral

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ossification.8 The largest osteochondromas rarely arise inside the articular capsule or within soft para-articular tissue. These were described for the first time by Jaffe9 in 1958 (para-articular chondroma or intracapsular chondroma) as lesions that occur in the fibrous joint capsule or within soft tissue adjacent to a joint. Subsequently, the term para-articular osteochondroma was used to differentiate this lesion from synovial chondromatosis.10-12 In most cases described in the literature,8 tumors are composed of a single mass of multiple osteochondral nodules. Histologically, each nodule shows a peripheral hyaline cartilage and a central portion that contains lamellar and trabecular bone. Endochondral ossification is evident in the interface between bone and cartilage. The cartilaginous component shows evidence of continued proliferation; however, no other histologic features, such as infiltrative borders or nodules of isolated cartilage nodules within adjacent adipose tissue, suggest that the lesion should be considered malignant. Conventional radiograph shows a large soft tissue mass with a wide central radiodensity caused by central ossification. Magnetic resonance imaging scan shows areas of low signal intensity on T1-weighted images and regions of high signal intensity on T2weighted images with contrast enhancement; these correspond to hyaline cartilaginous tumor tissue with high water content.

CONCLUSIONS The precise pathogenetic mechanism of these tumors remains unknown. Cartilaginous metaplasia of articular and para-articular connective tissue seems

FIGURE 4. (A) H&E stain (original magnification ⫻4): Low-power view shows a well-circumscribed nodular lesion with a proliferative cartilage cap overlying trabecular bone with enchondral ossification at the interface between the cartilage and the bone. (Inset, original magnification ⫻10): Detail of enchondral ossification. (B) Masson trichrome staining (original magnification ⫻4). Masson staining revealed prominent fibrocollagenous bundles that exhibit a lobular pattern within the fibrous-adipose-cartilaginous matrix.

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to be the main cause.3,9,13 Radiologically, intracapsular and para-articular chondromas, including old hematomas, calcifying bursitis, tumoral calcinosis, periosteal chondromas, calcified synovial sarcoma, primary synovial chondromatosis, and synovial chondrosarcoma, must be considered in the differential diagnosis. The treatment of choice for patients with these lesions is marginal resection or excision. Local recurrence has been reported in only 1 case14; malignant transformation has never been reported. For accurate diagnosis, as with all bone lesions, clinical, radiologic, and histologic features must be integrated. REFERENCES 1. Resnick D, Niwayama G. Diagnosis of bone and joint disorders. Philadelphia: WB Saunders, 1988;3602-4010. 2. Marcial-Seoane RA, Marcial-Seoane MA, Ramos E, MarcialRojas RA. Extraskeletal chondromas. Bol Assoc Med P R 1990;82:394-402. 3. Fechner RE, Mills SE. Atlas of tumor pathology: Tumors of the bones and joints. Series 3, Fascicle 8. Washington, DC: Armed Forces Institute of Pathology, 1993;79-128,279-291.

4. Milgram JW, Dunn E. Para-articular chondromas and osteochondromas: A report of three cases. Clin Orthop Relat Res 1980;148:147-151. 5. Enneking WF. Musculoskeletal tumor surgery. New York: Churchill Livingstone, 1983;99. 6. Li C, Arger PH, Dalinka MK. Soft tissue osteochondroma: A report of three cases. Skeletal Radiol 1989;18:435-437. 7. Reith JD, Bauer TW, Joyce MJ. Paraarticular osteochondroma of the knee: Report of 2 cases and review of the literature. Clin Orthop Relat Res 1997;334:225-232. 8. Mosher JF, Kettelkamp DB, Campbell CJ. Intracapsular or para-articular chondroma: A report of three cases. J Bone Joint Surg Am 1966;48:1561-1569. 9. Jaffe H. Tumors and tumorous conditions of the bones and joints. Philadelphia: Lea and Febiger, 1958;558-567. 10. Gonzalez-Lois C, Garcia-de-la-Torre P, SantosBriz-Terron A, Vila J, Manrique-Chico J, Martinez-Tello J. Intracapsular and para-articular chondroma adjacent to large joints: Report of three cases and review of the literature. Skeletal Radiol 2001; 30:672-676. 11. Milgram JW, Jasty M. Case report 238: Para-articular osteochondroma of the knee. Skeletal Radiol 1983;10:121-125. 12. Steiner GC, Meushar N, Norman A, Present D. Intracapsular and paraarticular chondromas. Clin Orthop Relat Res 1994; 303:231-236. 13. Rodriguez-Peralto JL, Lopez-Barea F, Gonzalez-Lopez J. Intracapsular chondroma of the knee: An unusual neoplasm. Int J Surg Pathol 1997;5:49-54. 14. Chung EB, Enzinger FM. Chondroma of soft parts. Cancer 1978;41:1414-1424.