Biomedical Engineering Reference
In-Depth Information
13.23
A dislocation of the head of the radius and a mid-shaft fracture
of the ulna, which required surgical treatment.
13.24
After reducing the head of the radius in place, appropriate
alignment and fixation of the ulna was obtained using an
intramedullary nail.
mechanics of a joint in a fashion different from that designed by nature,
like the inverted shoulder prosthesis, for example. In the past, even an
inverted hip-prosthesis was proposed (Fig. 13.25) but the vast majority of
joint prostheses nowadays reproduce the natural anatomy of a joint. in this
way they are 'resurfacing arthroplasty' prostheses, aimed at substituting the
worn component of the joint, namely, the articular cartilage. even with the
most sophisticated reproduction of natural geometry, the system does not
always work. Joints like the elbow or the metacarpo-phalangeal joint are still
far from having an effective artificial substitute able to provide a long-term
clinical survival.
The core problem seems to be the appropriate cyclic load transfer
between the prosthesis and the recipient bone. Loosening of the artificial
joint eventually follows any mismatch in mechanical coupling between the
prosthesis and bone. This may be partly circumvented by the best possible
biological interface between the prosthesis and the recipient bone but, in
the mid- or long-term, no biological integration can counteract the noxious
action of an inappropriate load transfer.
