The term 'Jack Russell' is also commonly misapplied to other small tan and white terriers. Breeders have protected the gene pool, and direct in-line breeding has been prevented. Jack Russells can live from 13 to 16 years given proper care. However, certain lines have been noted for having specific health concerns and, therefore, could occur in any line or generation because of recessive genes. Some are prone to dislocation of the kneecaps, inherited eye diseases, deafness and Legg Perthes—a disease of the hip joints of small dog breeds. Prone to mast cell tumors. Legg–Calvé–Perthes syndrome, also called Avascular Necrosis of the Femoral Head, is where the ball section of the femur in the hip joint deteriorates following interruption of the blood flow and is the same condition as in humans.