| BUECHEL-PAPPAS™
INTEGRATED HIP REPLACEMENT SYSTEM |
Acetabular
Component Design Rationale
Description
UltraCoat® is an inert, highly adherent, near diamond
hard titanium nitride (TiN) ceramic coating about 10 microns
thick. This coating reduces wear by more than two thirds and
friction by about one-half to Co-Cr alloy heads when articulated
against an UHMWPe bearing surface. The extreme hardness of
the TiN ceramic coating is attested to by its wide use on
tools for cutting steel and other metals. The use of TiN coatings
is now also becoming widespread to protect the cutting edges
of hardened steel surgical instruments. UltraCoat® is
produced by a series of proprietary processes that carefully
monitor and control pre-coating surface preparation, the coating
process, and the post-coating polishing. These procedures
guarantee the film adherence and the reductions in wear and
friction observed in our extensive testing program.
The coatings
are extremely adherent on a properly prepared, contaminant
free, substrate. Such adhesion results from an ionic (atomic)
bond between the film and the substrate. When a TiN ceramic
film is applied to titanium alloy, the film to substrate interface
is not susceptible to corrosion, and thus, corrosion delamination.
In fact, a titanium coating is applied to steel parts to be
coated with TiN for applications requiring corrosion resistance.
The substantial
reductions in wear and friction against UHMWPe result from
the extreme hardness of the TiN ceramic film. This film is
substantially harder than the alumina ceramic used for femoral
heads. To obtain these improvements, however, the TiN film
must be polished. Coating a polished femoral head with a TiN
film will produce a slightly roughened surface and can increase
polyethylene wear. The extreme hardness of the film, however,
through the proprietary post-coat polishing process allows
for the production of a substantially smoother surface than
can be obtained on softer materials. It is this substantial
increase in smoothness that results in a substantial decrease
in friction and wear. Further, the extreme hardness of TiN
ceramic results in a decrease in the rate of degradation of
the polished articular surface, thus reducing the rate of
increase in wear with time observed in testing. TiN ceramic
films are currently in use in Europe on articulating surfaces
and are approved by the FDA for use in the United States.
Enhanced
Biocompatibility
Titanium alloy is used for the Fixed Acetabular Cup since
it is more biocompatible than Co-Cr alloy whose major components
can be carcinogenic. Biocompatibility can be further enhanced
by the application of UltraCoat® film on titanium. TiN
ceramic is inert invivo. It shields the surface of the implant,
particularly the porous coated region with its high surface
area, against metallic ion release. As a result, titanium
acetabular cups with UltraCoat® represent the most biologically
compatible metal cups available.
Reduced
Acetabular Erosion and Metallic Debris
Endotec also employs UltraCoat® on its Universal Self-Aligning
Acetabular Metal Component because its smoothness, and resulting
low friction, should reduce erosion of the articular cartilage.
Further, its hardness and biocompatibility should minimize
the release of potentially harmful metallic debris which may
result from the metal cup to acetabular articulation.
Ease
of Assembly
The Buechel - Pappas acetabular components are designed to
assemble easily with digital pressure or simple impaction
without the need for special instrumentation.
Reliability
of Assembly
Clinically
Proven Fixed Bearing
The
Buechel - Pappas Fixed Acetabular Cup and Bearing Insert have
evolved from over 20 years of development and clinical use.
Large, flexible, locking tabs on the bearing insert engage
a deep groove in the metal cup providing a deep engagement
fit resisting separation of the bearing insert. Precision
machining of the cup and insert on computer controlled equipment
produces a locking fit resisting micromotion of the bearing
relative to the metal cup. Such micromotion can produce wear
debris at the bearing insert to metal cup interface. The UltraCoat®
film on the inside of the metal cup further reduces debris
associated with micromotion. An optional Acetabular Cup Plug
can be inserted into the central impaction hole producing
a fully sealed interface. Locking tabs are designed such that
they experience no load increases during the walking cycle
eliminating tab fracture and bearing dissociation.
Fixed
Bearing Stability
Frictional
torque between the femoral head and the fixed bearing insert
is resisted by a greater friction between the interior wall
of the fixed cup and the outer spherical surface of the bearing
insert. To prevent migration of the fixed bearing insert (such
migration does occur in the Self-Aligning insert), three anti-rotation
keys are used to resist the rotation of the bearing insert
relative to the metal cup. Further, these keys help resist
micromotion, since they are pressed into the metal cup wall.
The keys, particularly the superior key, help align the bearing
insert with the metal cup during its installation.
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