Biomedical Engineering Reference
In-Depth Information
Another more common pathological condition, which may end with the
complete destruction and disappearance of the articular cartilage and the
painful contact of underlying bone, is osteoarthrosis. This is a degenerative
chronic non-inflammatory (Dorland's Medical Dictionary, 2007) bone
disease (hence the suffix '-osis'), whose mechanism of action is not yet fully
understood but where there is a definitive role for excessive and repeated
mechanical overload on the joint. it affects all the joints but it is particularly
severe in the larger weight-bearing joints of the lower limb, like the hip and
the knee. The clinical disturbance in gait, for patients whose lower limb
joints are affected, is not different from that associated with inflammatory
conditions which were common in the 19th century and which were properly
called 'osteoarthritis'; so the names 'osteoarthrosis' and 'osteoarthritis' are
both found in broad use with a certain degree of overlap in the orthopaedic
literature (Stedman's Medical Dictionary, 2007).
13.2.3 Bone replacement
A bone loss which does not repair spontaneously will require a bone
replacement to diminish the risk of fracture in its bone segment. A permanent
replacement with an autograft or an artificial material is still commonly
applied (Urabe
et al
., 2007) but a lot of research is directed towards possible
replacement with bioactive materials, which could eventually give rise to
new bone in the patient until final full recovery of the integrity of the bone
segment is achieved.
13.3 Materials
13.3.1 Metals
Stainless steel and titanium alloys are widely used because of their mechanical
strength. They are key materials in devices needed for osteosynthesis, in which
they must guarantee a mechanical stability in the early phases of fracture
healing, prior to the completion of the healing process. They are, also, the main
constituents of heavy weight-bearing joint prostheses, like hip and knee.
Designing a metallic device generally achieves the goal of coping with
the mechanical performance which is required but problems may arise
from the biological response at the metal-bone interface. Several stainless
steel alloys promote a fibrous reaction that may end up with a multicellular
layer of fibroblasts interposed between the recipient bone and the implant,
eventually leading to implant loosening. Titanium alloys proved to be better
able to promote integration with bone (Fig. 13.2) and, sometimes, only a
tiny non-ossified rim remains between them and the recipient bone, so thin
that it can be only characterized by the higher magnification provided by
electron microscopy (Fig. 13.3).
