Materials retrieval and analysis - Orthopaedic Biomaterials in Research and Practice - page 397

some may view the medical device field as a vast experiment, involv-
ing millions of subjects and lasting far beyond the lifetimes of those
who started it. But while it is also widely accepted that there are risks
with any surgery and the use of any device, it is the implicit expectation
of the medical professional, the patient, and the design team that the
benefits of the device will outweigh its risks, even if such considerations
are not explicit. In the normal course of such a widespread application
of technology, we would expect a continual feedback from the user to
the developer and the manufacturer that would lead to an evolutionary
improvement and convergence of design and practice.
There has been some convergence, in the sense meant here, but in
most device applications in orthopaedics, there appears to be an increas-
ing divergence of design and materials with no real extension in the
length of the design change cycle, which still seems to be less than 3-5
years, even for permanent implants such as total joint replacements. This
is probably the case since the vast majority of evidence of device per-
formance is neither obtained nor studied publically. This situation has
arisen from two conditions.
First, devices only attract attention when they fail to fulfill their
intended function. Such failure, of either the device or treatment plan,
or both, is relatively rare, with clinical “success” rates generally exceed-
ing 90% for periods of as much as 10 years. The most common, easily
observable failure is the removal of a permanent device, such as a total
hip replacement (THR). Even if defects in the device are suspected or
recognized before or during revision, they are not generally studied in
depth. Frankly broken or damaged devices often excite fears of legal
action against surgeons, hospital, or manufacturers. Such devices may
simply “disappear.” Some devices are returned to the manufacturers for
analysis. The knowledge gained from such study is often limited by a
lack of access to clinical records and a resulting failure to understand the
clinical aspects of the origin of the problem. Some devices are given to
patients, either as a gift or on demand by the patient's lawyer. And many
devices end up, unlabeled and unprotected, in a drawer in the surgical
scrub area, or disposed of by the hospital.
Second, there is little or no effort made to study successful devices.
Clinical studies that are performed focus on improvement in overall
function and reduction in pain, along with temporal measures of reten-
tion of improvement. These studies are isolated; in fact, when a device
gains a degree of clinical acceptance, it apparently rapidly ceases to
be a suitable subject for study. Few clinical studies have included any
strategies for examination of implant function and condition, other than
by radiography, independent of the clinical condition of the patient.
Furthermore, a device that is performing successfully provides no rea-
son for it to be removed, providing no opportunity for investigation,
except postmortem.
In some ways, the failure to study this other 90%-99% of devices
is even more tragic. We know remarkably little about the normal host-
implant interactions, either local or systemic, in patients. Autopsy samples
are rarely available, with the declining rate of autopsy in the United States