Biomedical Engineering Reference
In-Depth Information
degradability of the polymer while employing the bioceramic component
to try to avoid any excessive inflammatory reaction towards its breakdown
products. This should also help in the early stages of interaction with
bone.
The same principle applies to the HA-PE composite. These materials have
already been applied in fields like inner-ear surgery, dental and maxilofacial
surgery. Application in orthopaedic surgery is envisaged for small implants,
like those required in hand surgery, for example.
13.4 Devices
Many different devices are used in orthopaedic surgery (Chapman, 1993).
From earlier times when devices where often made from a single material,
like stainless steel plates to fix long-bone fractures or PE cups for acetabular
replacement, it is now possible to assemble different components made of
different materials. Examples are HA coated-metallic prosthetic stems or
Pe-polished metal cups for metal-on-metal joint surfaces. in the near future
it has been envisaged that a new 'material' component will be added to the
artifact, in the form of cell-loading.
For decription purposes we will present orthopaedic surgery devices
according to the main categories of operative techniques addressed in Section
2, namely osteosynthesis, joint replacement and bone replacement.
13.4.1 Devices for osteosynthesis
Screws
Screws are extremely common in the orthopaedic surgery inventory and they
are applied as primary internal fixation devices in several instances. Joining
two bone fragments by a screw may be a quite straightforward technique.
Historically, it has evolved from the 19th century nail transfixtion (where
a nail joined the two segments and was 'press-fitted' in place without the
help of the screw thread), to the contemporary double-threaded canulated
screws. The latter complex devices are screws that have a hollow canal; the
two bone segments may be held in place by a tiny nail, termed pin or wire,
even without open surgery but percutaneously with the help of intraoperative
radioscopy; then the screw is driven through the nail and guided into place
with high accuracy (Fig. 13.16). Double-threaded compression screws have a
defined pitch in their apex, to grasp the distal segment, and a different pitch
in their head, so that while giving the final twists, a further compression
between the two bone segments is obtained. A typical application for these
screws is the percutaneous osteosynthesis of a carpal scaphoid fracture (Fig.
13.17 and Fig. 13.18), a severe lesion which affects the crucial bone which
