We studied the prognostic value of MRI in 32 radiographically normal, asymptomatic hips in 25 patients at risk of osteonecrosis from glucocorticoids or alcoholism. The early findings were band-like hypointense zones on spin-echo images. No operations were performed. Life-table survival curves showed that femoral heads in which the hypointense zone traversed the middle portion of the head were most at risk of subsequent segmental collapse.

We prepared a prosthesis for the replacement of the lumbar vertebrae of sheep, using apatite- and wollastonite-containing glass-ceramic. The material is stronger than human cortical bone and has the special feature of chemical bonding to bone. Ten sheep underwent replacement of L3 and L4 vertebrae, without bone grafting. The animals were killed at intervals from three months to 27 months after operation, and the interface between the prosthesis and bone was examined radiologically, histologically and crystallographically. Bone bonding with the prosthesis had occurred in half the implants. It took at least one year for bonding to be complete, but an apatite layer on the surface of the prosthesis was observed as early as three months after the operation, suggesting the possibility of much earlier bone bonding if more rigid fixation of the prosthesis had been provided.