The causes of cracking in degenerating cartilage are examined using analytical models of layered elastic spheres in normal and tangential contact. Vertical surface and deep radial cracks as well as interfacial separation between cartilage and bone are observed in osteoarthritic joints. Blunt trauma experiments show vertical cracking in the underlying bone and calcified cartilage, and at the cartilage surface for higher loads. The single layer model shows that normal loading induces tensile stresses at the surface for small contact radius to layer thickness (a/h) values. Significant shear stress is predicted at the cartilage-bone interface.