Fibro-osseous (FOL) and degenerative joint lesions in female outbred NIH Black Swiss mice.

A review of spontaneous bone and joint lesions in female aging NIH Black Swiss mice (Cr:NIH BL[S]) revealed a high incidence of fibro-osseous lesions (FOL; 89%) and degenerative joint lesions (90%). FOL was characterized by the replacement of bone marrow by fibrovascular tissue and was first seen at 59 weeks of age, most commonly in the nasal bone, femur, and tibia. FOL in female Black Swiss was often accompanied by reproductive-tract lesions, including ovarian atrophy and uterine cervical dysplasia with hydrometra. Mild degenerative femorotibial joint lesions developed by 59 weeks and progressed to full-thickness articular cartilage ulceration and osteophyte development by 75 weeks; joint inflammation was minimal. Although the underlying etiology of FOL remains unknown, an accurate assessment of FOL and degenerative joint disease as background lesions in this stock is necessary to interpret lesions in genetically engineered mice produced from this outbred line.