214 • James C.C. Leisen, Howard Duncan, and J.M. Riddle 



Figure 4. Articular surface of a rheu- 

 matoid metacarpal head showing an 

 eroding front covered with continuous 

 resorption bays and an adjacent miner- 

 alized surface with prominent chondro- 

 cyte lacunae (volcanoes); x 560. 



SCANNING ELECTRON MICROSCOPIC 

 OBSERVATIONS 



The articular surface of the macerated 

 specimens (both control and rheu- 

 matoid specimens) was covered by nu- 

 merous volcanolike structures. These 

 were identified as mounds of mineral 

 enclosing lacunae which would have 

 originally contained a single or several 

 chondrocytes (Figure 4). 



At a higher magnification, many 

 small holes were seen perforating the 

 subchondral plate of both the medial 

 and lateral plateaus of the tibial tables 

 collected from the controls. These 

 holes were concentrated at a submenis- 

 cal location on the medial plateau and at 

 a central location on the lateral plateau. 

 In contrast, various-sized holes pene- 

 trated the subchondral plate covering 

 the medial and lateral plateaus of the 

 rheumatoid tibial tables. No distinct 

 distribution pattern of holes was ob- 

 served for the plateaus of the rheu- 

 matoid tibial table. Rather, the holes 

 frequently were present in both the sub- 

 meniscal and central locations of a 

 plateau. 



The articular surface of the rheu- 

 matoid specimens also showed focal 

 collections of continuous resorption 

 bays, an erosion with a morphology 

 characteristic of osteoclastic activity 

 (Figure 4). 



Discussion 



Our series included metacarpal heads 

 and tibial plateaus removed from con- 

 trol subjects and patients with chronic, 

 classic rheumatoid arthritis. The joints 

 of the rheumatoid patients were func- 

 tionally impaired and painful to the ex- 

 tent that the joint dysfunction necessi- 

 tated surgery and replacement with 

 prostheses. In this group, the rheu- 

 matoid erosion had characteristic fea- 

 tures which included; (I) partial or 

 complete resorption of the articular sur- 

 face, (2) obliteration of the chondro- 

 osseous junction, and (3) minimal para- 

 articular osteophytosis. The remaining 

 bony tissue, regardless of location, 

 contained holes or perforations through 

 the surface which often exposed epi- 

 physeal trabecular bone and marrow 

 space. Although histologic features 



were variable, the scanning electron 

 microscope consistently revealed pa- 

 tches of continuous resorption bays at 

 the eroded surfaces and lining the chan- 

 nels of many holes. 



A review of the literature contained 

 only four published papers (Table 3) in 

 which an erosive arthropathy was sug- 

 gested through the examination of dry 

 bone (Klepinger 1979: 1 19; Ortner and 

 Utermohle 1981:23; Rogers et al . 1 98 1 : 

 1668; Thould and Thould 1983:1909). 

 Seven skeletons were examined and six 

 were found to show evidence of appen- 

 dicular and axial (Ortner and Uter- 

 mohle 1981: 23) bony defects sugges- 

 tive of erosion. These defects were 

 studied by visual and radiographic ex- 

 amination. Although the authors sug- 

 gest a variety of disease entities, we 

 feel that the basic issue of "what is an 

 erosion" needs to be addressed using 

 radiographs and different microscopic 

 approaches including light microscopy 

 and scanning electron microscopy as il- 

 lustrated in our study. 



The peripheral joints of a number of 

 erosive arthropathies such as seronega- 

 tive rheumatoid arthritis and the spon- 



Zagreb Pulenpathnloiiy S\mp. 19HH 



