REMODELING OF ARTICULAR STEP-OFFS - IS OSTEOARTHROSIS DEPENDENT ON DEFECT SIZE

One of the major unresolved questions in trauma repair concerns the de gree of step-off that can be accepted in a joint surface, In answer to this question, a new rabbit model of femoral step-off was developed.( 16) Osteoarthrotic changes in cartilage and bone and the failure of re pair responses were seen at 20 weeks in the presence of a 3-mm wide sa gittal defect displaced 5 mm from the joint surface and spanning the a nteroposterior extent of the medial femoral condyle.(16) This study ex amined the effects of a similar defect, displaced 2 mm from the joint surface, to determine whether the development of osteoarthrosis is dep endent on the size of the step-off. Defects were created in 18 New Zea land white rabbits, In a second group, the medial joint surface was os teotomized, but was not displaced. In contrast to the first study, car tilaginous and bony repair resulted in closure of the surgical defect and restoration of femoral congruity, Histologic and biochemical param eters did not differ significantly between groups, The results indicat e that cartilage and bone possess the ability to remodel small articul ar step-offs and to restore joint congruity, Furthermore, the combined data suggest that the development of osteoarthrosis requires signific ant articular incongruity.