Extra- and intra-articular synovial chondromatosis and malignant transformation to chondrosarcoma.

Intra- and extra-articular primary synovial chondromatosis (SC) was observed in a five-year-old, entire male German Shepherd. Thousands of small cartilaginous nodules were removed from the stifle joint as well as from several adjacent muscles. Diagnosis of SC was established based on clinical, radiographic and biopsy results. The owner declined to have a new surgery performed for complete nodule removal and partial synovectomy. Nine months after the initial presentation, a proximal pathological intra- articular tibial fracture was observed and malignant transformation to chondrosarcoma was diagnosed after limb amputation. No metastasis was observed after 1.5 years of follow-up.