An endoprosthesis utilizes a biomechanical structure based on the new inventive lever model of first degree. Contrary to the widespread practice, the inventive structure has a stem placed inside the femur bone, which is not rigidly attached to this bone. Accordingly, the bone, following its known tendency to slightly pivot away from the medial plane of the body in response to the loads, does not directly contact the stem. The neck portion experiences even greater loads then the stem. The supporting anchor has a region extending laterally from the stem and pressing against a supporting surface of the housing, which also extends laterally from the body of the housing. Since the stem, supporting anchor and neck are typically constitute a one-piece component, the lateral surfaces of the supporting anchor and housing are in continuous frictional contact during displacement of the stem and housing relative to one another.