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Pathology of the Dorsal Triangular FIbrocartilage in Rheumatoid Arthritis Affecting the Metacarpophalangeal Joints II-V- Structure, Function and Imaging Criteria in Joint Instability
Michael W. Findlay, MBBS, PhD, FRACS1; Sandip Biswal, MD2; Sarah Hunter-Smith, BBiomedSci1; Bao Do, MD2; Rory Maher, MBBS3; Sian Fairbank, MBBS, FRACS4; Phillip Slattery, MBBS, FRACS5; James Chang, MD, FACS2; David Hunter-Smith, MBBS, FRACS, MPH6
1University of Melbourne, Australia; 2Stanford University, Stanford, CA; 3Peninsula Community Health Service; 4The Peter MacCallum Cancer Centre, Australia; 5Glenferrie Private Hospital, Australia; 6Monash University, Australia

Introduction: Joint subluxation with ulnar-deviation of the extensor tendons over metacarpophalangeal joints 2 through 5 is a common clinical constellation in advanced rheumatoid arthritis. Disease-modifying anti-rheumatoid drugs (DMARD's) are effective in limiting disease progression, but their side effect profiles and the lack of objective diagnostic criteria to indicate impending subluxation, make titration of therapy problematic. We sought to determine whether pathological changes in the dorsal triangular fibrocartilage (DTF), a poorly characterized meniscus- like structure between the joint and the extensor tendon(s), could contribute to this clinical picture with relevance for early diagnosis and the development of targeted treatment strategies before joint replacement is considered necessary.
Materials and Methods: Normal DTF structure and attachments were determined through cadaveric dissection of 100 MCPJ's (80 fingers, 20 thumbs for comparison). Six MCPJ's were decalcified for histological examination by a specialist histopathologist to confirm the composition of the DTF. T1 STIR and T2 fat saturated MRI sequences were used to characterize pathological changes. Putative criteria for the severity of DTF pathology were developed based on a review of healthy and diseased clinical cases (n=3 each) before the images from 9 individuals (34 joints including normal, RA with no subluxation or varying degrees of subluxation graded on a 1-5 severity scale) were randomized and assessed by two independent blinded specialist radiologists to grade the presence of the criteria and the degree of associated deformity with correlation to the patient's clinical profile.
Results: The DTF is crescent shaped fibrocartilage, triangular in cross-section, which deepens the fossa for the metacarpal head, forms part of the joint capsule with attachments over 120 degrees of the joint circumference and has intimate attachment to the overlying extensor tendon. 29 imaged joints met the inclusion criteria to assess the diagnostic criteria. Loss of DTF-tendon attachment, irregular DTF margins and marked signal heterogeneity within the DTF were all strongly associated with the presence of joint subluxation with marked loss of DTF-tendon attachment being the most significant (Spearman r=0.6882, p<0.0001), present in every RA joint with subluxation (n=9), one third of non-subluxed RA joints (n=6) and no normal joints (n=9).
Conclusions: Destruction of the DTF in RA is associated with joint instability and decentralization of the long extensor tendons during their passage over the joint. Improved understanding of the DTF and identification of relevant imaging criteria should permit refinements in the classification, staging and ultimate care of the MCP joints of RA patients.


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