Hemiarthroplasty is when half of the hip joint is replaced. It is always the femoral rather than the acetabular half that is replaced. There are two versions: hemi resurfacing and endoprosthesis.

Hemi resurfacing was once used for stage 3 osteonecrosis. But now that total resurfacing is available, there is no longer any role for hemi resurfacing. Pain relief is incomplete in active people when only the femoral side is resurfaced, even when the acetabular cartilage is normal.

Endoprosthesis is still a useful option for elderly people who suffer a femoral neck (hip) fracture. If the patient is very active a stemmed total hip is superior, but if the patient is not very active, an endoprosthesis is a better solution.