100% Positive Material Identification

Understanding Implants in Knee and Hip Replacement (continued)
the trend toward customizing
implants to achieve the best
results possible, in terms
of comfort, function, and
longevity,” says Dr. Windsor.
Prospective patients may
find that orthopedists in some
hospitals use only one or two
different implant systems,
whereas, orthopedists at HSS
have access to the systems
of all the major orthopaedic
implant manufacturers.
Types of Hip Replacement
Total hip replacement surgery
- in which the damaged joint
is replaced with an implant - is
associated with a high degree
of successful and predictable
outcomes.
Orthopedic surgeons may
approach the surgery in one of
three different ways:
• the direct anterior
approach in which the incision is
made on the front of the hip; this
approach may be less disruptive to the
muscles and soft tissues surrounding
the hip joint, however, surgeons who
employ this approach usually use a
custom operating table and fluoroscopy
(a type of x-ray) to guide placement
of the implant during surgery;
fluoroscopy is not routinely used with
the other two surgical approaches
• the anterolateral approach in which
the incision is made on the side of the
hip, toward the front of the body
• the posterolateral approach in which
the incision is made on the side of the
hip toward the back of the body
Each surgical approach calls
for slightly different post-operative
precautions related to position
restrictions to avoid possible early hip
joint dislocation. The posterolateral
surgical approach is most commonly
used in hip replacement surgery.
Although a minor improvement in
Figure 6: Anatomy of the hip joint
walking speed during the early phase
of recovery has been associated with
the direct anterior approach, there is no
data to suggest a significant advantage
of one approach over another explains
Douglas E. Padgett, MD, Chief, Adult
Reconstruction and Joint Replacement
division and Orthopaedic Surgeon at
HSS. “The decision to use a particular
approach is usually based on the
preference of the surgeon,” Dr. Padgett
adds.
Much of the important early work
in the development of successful hip
implants took place in the late 1960s
and early 1970s, including that of
British surgeon John Charnley, MD and
introduced at HSS by Philip D. Wilson,
Jr. MD.
Hip Implant Materials and Fixation
The majority of people who undergo hip
replacement receive a traditional hip
arthroplasty in which the surgeon uses
a stemmed device and prosthetic head
to replace the upper part of the femur
(the head and neck of the bone) and a
hemispherical shaped cup to
replace the acetabulum, the
socket of the pelvis in which
the femoral head fits. [Figure
6]
However, some patients
may be candidates for hip
resurfacing in which the head
and neck of the femur are not
removed. In this procedure,
the surgeon resurfaces or
sculpts the femoral head to
accept a metal cap with a
short stem. Hip resurfacing
is usually most successful in
male patients under the age of
55, who are larger in stature
There is little data to support
functional benefit of one type
of hip replacement over the
other, although if revision
surgery is needed, this may be
easier after hip resurfacing.
[Figure 7]
Hip implants come in two
primary types: the traditional singlepiece
implants and modular models, in
which the stem and head of the implant
portion that is placed in the femur can
be matched independently. Although
the single piece implants provide a
good fit for many patients, “modular
devices were developed to improve the
fit of the implant to the patient’s specific
anatomy,” explains Dr. Padgett. However,
he adds, some modular implants have
recently been found to be associated with
problems related to the linkage between
the various parts.
Some degree of corrosion and fretting
has been seen with these metal on metal
components, a process that can result
in the creation of metallic debris that is
destructive to the soft tissue surrounding
the joint. As a result, some of these
implants have been recalled.
Implants may be made of a variety
of materials including metal (usually
titanium), ceramic or polyethylene (a
type of hard plastic). Ongoing research
and enabling technology will determine
14 TITANIUMTODAY