CHAPTER 44 SUBCI_IONDRAL

Stepben J. Miller, D.P.M,

Cysts found in the sub-articular bone adjacent to macroscopic and microscopic characteristics. The joints afflicted by or rheumatoid cysts are usually solitary, but may be multilocular. arthritis were identified and described by Plewes in They commonly develop in the epiphyseal or meta- 1940, Coliins in 7949, and Landells in 1953 (Fig. 1). physeal areas of bone adjacent to joints. Generally, they have a whitish or bluish lining consisting of parallel bundles of collagen. The fibrocyes lying along the inner wall of the cavity sometimes form an incomplete lining of flattened, synovial-like cells. This makes for a smooth wall within which the contains a thick gelatinous mucoid fluid. Still, there are those who distinguish the subchondral bone cysts seen in conjunction with osteoarthritis or other joint damage, from intra- osseous ganglia or synovial cysts of bone. The former are more likely to communicate with the joint through the articular surface in up to 400/o of the cases, and therefore may be filled with synovial fluid; whereas the latter communicate with the joint cases the Figure 1. Sub-articular bone cyst in the metatarsal head of patient with in less than 3o/o of the documented and rheumatoid arthritis. fluid is more commonly a viscous mucoid material. In fact, the Armed Forces Institute of , as However, related subchondral bone cysts with a late as 1977, separated as distinct entities the sub- synovial-like lining were subsequently described by chondral bone cysts and the synovial cyst of bone. Fisk in 7949 and Hicks h 7955. Over the years, var- Other similar cystic lesions are found in con- ious synonyms for these lesions have appeared in junction with silastic joint implants (Fig. 2), and as the literature: synovial cysts, juxta-articular bone a consequence of the degenerative changes caused cysts, intra-osseous ganglia, ganglion cysts of bone, by osteochondral fractures such as those seen in and geodes. the ankle joint. According to the \X/orld Health Organization classification of bone tumors and tumor-like lesions, the term juxta-afiicular bone cyst (intra- osseous ganglion) is defined as "a benign cystic and often multi-loculated lesion made up of fibrous tissue, with extensive mucoid changes, located in the subchondral bone adjacent to a joint. Radiologically, it appears as a well-defined oste- olyic lesion with a surrounding area of sclerosis. It has been described as a synovial cyst, but it lacks a synovial lining." As such, the definition excludes the cystic juxta-articular bone lesions seen in con- junction with pigmented villonodular synovitis, as well as other osteolyic bone lesions. In spite of the great number of descriptive Figure 2. Silastic implant clegeneration resulting in periarticular names, these lesions share virtually the same multilocular r:vst frrrmation. 232 CHAPTER 44

PATHOGENESIS In the recent literature, a sunrey by Murff and Ashry of intraosseous ganglia identified of 273 Many theories have been proposed to describe the lesions: 430/o were found in women and 57o/o in genesis of these lesions. The early theories of "syn- men, with an averaple age of 4J years. The most ovial fluid intrusion," either as a primary event from common site was in the lower extremity, especially increased intra-articular pressure, or as a secondary the distal tibia (Table 1). event during the healing process when necrotic subchondral bone is removed, is more applicable Table 1 to the subchondral bone cyst associated with LOCATIONS OF arthritic disease. In contrast, it is believed that the intra-osseous INTRAOSSEOUS GANGLIA ganglion is caused by a primary intramedullary metaplasia of the mesenchymal cells into synovial- Upper Extremity 68 like cells and/or fibroblasts. This transformation is Lower Extremity 745 accompanied by clegenerative changes creating the Above Knee 41 mucin-like substance which is rich in hyaluronic Below Knee 101 acid. The role of trauma and compressive forces has Prox. Tibia 30 been postulated, but the association remains unclear. Mid Tibia 1 Medial Malleolus 39 DIAGNOSIS Prox. Fibula 8 Lateral Malleolus 5 Subchondral bone cysts associated with arthritis Talus 7 7 (especially rheumatoid arthritis) occur in the sub- Tarsus afiicular bone adjacent to joints. In the lower 1st Metatarsal 2 Great Toe 1 extremity, they are most commonly found in the (n: 213) metatarsal heads. Intra-osseous ganglia occur near Murff and Ashry 199,i joinls, and in the lower exlremity they more com- JFAS, monly occur in the medial malleolus, proximal fibula, Although cystic bone lesions may be asymp- proximal tibia, as well as the tarsus area and talus. tomatic, they commonly cause intermittent pain Subchondral bone cysts are well known to aggravated by increased activity. Joint movement occur in the first metatarsal head, particulady near the by itself does not necessarily calise pain. The dis- medial eminence in association with hallux valgus. comfort is thought to be caused by an increased This is commonly true even when there are no radi- intra-lesional pressure from the accumulation of ographically identifiable changes in the joint (Fig. 3). fluid. However, on rare occasions, pain may result from fracture through the subchondral bone. These lesions tend to weaken the surrounding bone. If there is communication between the cyst and the joint, then the synovial fluid may move back and forth between the twc-r. Occasionally, pain precedes the radiographic appearance of the lesion. Moreover, sr,rbchondral bone cysts have been repofied to occur preceding the subsequent diagnosis of inflammatory or degenerative afihdtis. On the radiograph, the lesion usually appears as a well-demarcated circular to oval radiolucent defect outlined by a thin margin of sclerotic bone, usually rreaf a joint. It may be multilocular, but is Figurc 3. Subchondral bone cysts associated with hallux more commonly unilocular with varying dimen- abductovalgus defonnity. sions, ranging from a few millimeters up to several CHAPTER 44 233 centimeters in diameter. There is no cortical expan- TABLE 2 sion or periosteal proliferation that occurs due to the presence of these lesions. DIFFERENTIAT DIAGNOSIS Computed tomography (CT) can better delin- SI.]BCHONDRAL BONE CYSTS eate the extent of the lesion within the bone, and may help determine if it communicates with the Arthritic Cysts ioint (Fig. 4). However, to better determine the soft Unicameral Bone Cysts tissue components, as well as the nature of the Other Epiphyseal, Osteolyic Bone Lesions: fluid within the cyst, magnetic resonance imaging (MRI) is a more precise diagnostic test. The T2- Chrondroma weighted images, in particular, clearly depict the Dermoid Fibrorrra synovial fluid demonstrated lry a high signal Osteoid Osteoma intensity, and differentiate it from the cartilage Brodie's Abscess which is of lower signal intensity. On T1-weighted Tuberculosis images, the cyst is usually of low to intermediate Pigmented Villonodular Synovitis signal intensity, and is surrounded by a very 1ow signal intensity rim. On T2-weighted and short T1 Unicameral bone cysts are predominantly inversion recovery images, the cyst is well-defined found in the central shafts of long or bodies and is of a very high signal intensity, due to the of short bones (Fig. 5) other considerations presence of fluid. include Rrodie's abscess associated with

Figr,u-e 4. CT scan iilustratin€i bone cysts in thc flrst mctatarsal heacl Figure 5. L1nicameral bone cyst in calcaneus. Unlike most intraosseous and adjacent sesamoid bones, cornmunicating with the joint. g:rnglia, it is not near a joint.

Differential Diagnosis , ancl pigmented villonodular synovi- tis, which generally shows erosive lesions on each Since these intra-osseous cysts are similar to other side of the joint. Occasionally, a systemic disease lesions of bone, a differential diagnosis must be such as tuberculosis can procluce osteolotic lesions developed (Table 2). The , of bone that resemble subchondral bone rysts (Fig. 6). giant cell tllmor, ancl chondromloroid fibroma usu- ally cause some expansion of the cortex or a . Cartilage tumors generally demonstrate intralesional calcification; a finding that is rarely present in intra-osseous ganglia. 234 CHAPTER 44

the fibrous tissue must be completely curetted, along with the adjacent intra-osseous lesions, so that bleeding cancellous bone is available for any further arthrodesis or grafting techniques that are necessary. If arthrodesis of a joint in close proximity to a large cystic lesion is being considered, it is recom- mended to curette and pack the site as described above, and allow it to heal before performing the arthrodesis. This treatment regime is usually successful in relieving the patient's symptoms. However, it is important to inform the patient that reoccurrence is possible, and that the same type of cystic lesion may exist near other joints. Figure 6. Cystic lesion caused by tuberculosis. Subchondral bone cysts that result from osteo- chondral fraclures, such as those seen in the ankle TREATMENT joint, require special consideration (Fig. 7). These defects are drfficult to pack with bone, since once Subchondral bone cysts associated with arthritis or they are opened into the joint, there is no method of afihrosis can improve with intra-afiicular steroid providing coverage with adequate cartilage. The best injection. The increased pressure can be relieved approach when such a lesion causes considerable by aspirations of the cyst, with or wlthout the sub- pain is to curette the cyst in a open method, or with sequent injection of corticosteroid preparations. an afihroscope. This tends to stop the high-pressure For the true intra-osseous ganglia, the lesion can be pistoning that is thought to be the source of the pain. aspirated and injected quite similar to soft tissue ganglia. However, the incidence of recurrence of symptoms is relatively high. \X/hen symptoms persist in spite of conserwa- tive treatment, the usual surgical approach consists of excision of the bone cyst. Curettage is utilized Cystic Changes ,==_ to remove any remaining components of the soft tissue lesion along with the surrounding zone of sclerosis. This is followed by packing of the defect with suitable material, usually in the form of allogenic cancellous bone chips. If this material is not available, then a bone substitute ,1i"3cf"m;G1: Cartilage may be considered. The cortical bone covering the subchondral bone cyst should be removed as a plate, so that it can be replaced after the lesion is excised and Figure 7. Subchondral bone cyst of the talus secondary to an packed with bone. The success rate of curettage osteochondral fracture. and packing is very high, with only a 7o/o recur- rence rate reported for intra-osseous ganglia. Vhen various joint procedures are being con- sidered, in the presence of subchondral bone cysts or intra-osseous ganglia, some special considera- tions are warranted. For example, if an implant is being planned, the bone cyst must be excised and packed, followed by allowing the defect to fiil-in before inserting the implant. Conversely, when an implant is removed in the presence of a bone cyst, CHAPTER 44 235

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