| BUECHEL-PAPPAS™
ANKLE REPLACEMENT SYSTEM – PRIMARY* |
Total
Ankle
The
Buechel-Pappas™ Total Ankle Replacement is a time-tested
System which is the result of more than thirty years of development,
clinical investigation and use. The components have been available
in their current form since 1989. Tibial Component – 6 sizes
Talar Component – 6 sizes
Sliding Cylindrical Bearing – 6 sizes, 5 thicknesses
* Available
only under clinical investigation in the United States
Materials Used
- Ceramic
UltraCoat® coating reduces joint friction and both plastic
and metallic wear debris.
- BioCoat®
porous coating provides enhanced ingrowth fixation.
- Titanium
alloy provides superior compatibility
- Revision
Talar Unit allows for talar replacement in area where talar
bone stock is deficient.
Mobile
Bearing and Articular Surface Design
A mobile bearing is the key to a successful ankle replacement.
Loads in the ankle are similar to those in the knee. Yet the
ankle is much smaller. Thus the problem of excessive stress
in UHMWPe bearings that is common in fixed bearing knees is
even more difficult to deal with in the ankle. To date only
a mobile bearing has provided acceptable levels of contact
stress with needed ankle mobility.
In the
B-P Total Ankle this is achieved by a primary articulation
that is generated by the use of a compound curve. This curve
is identical for the talar and inferior bearing articular
surfaces. This provides congruent contact throughout the entire
range of flexion. These articulation surfaces not only allow
for full congruence in flexion/extension, but also in inversion/eversion
(I/E).
A secondary
articular surface is flat-on-flat. This articulation provides
the needed axial rotation and translations needed to avoid
unnecessary constraint without preventing congruent flexion.
Mobility
and Stability
The
B-P ankle provides natural mobility and stability. Normal
flexion/extension is provided. Medial-lateral stability is
provided by the mortise. Resistance to posterior shear present
during walking is provided by the 7° posterior tibial
inclination angle.
Normal inversion/eversion
stability is provided with the B-P ankle as opposed to abnormal
stability present in some other designs.
History
of Ankle Replacement
Introduction
Fixed bearing prosthesis do not work well and are plagued
with failure due to numerous problems exacerbated by high
load and small bone volume for fixation. In a survey of ankle
replacements, Buechel found that fixed bearing prostheses
displayed high contact stress, stability problems, and lack
of adequate prosthesis motion particularly due to constrained
axial rotation. He also found that the most common mechanical
complication was loosening followed by talar subsidence where
talar resection was necessary.
Other
publications on fixed bearing ankles show similar results.
In a study by Demottaz et al, 21 implants of various types
(Mayo, TPR, Smith, Oregon) showed only 2 of the 21 having
good results with the majority showing signs of loosening
and pain. Unger et al, reported the results of 22 Mayo implants
showed an 83% satisfactory result after 2 years; however,
deterioration of the results with time was noted.
or a
prosthesis to be successful, it must be able to accommodate
joint loading and motion. During a standard gait cycle, tibiotalar
forces have been estimated to exceed 4 times body weight.
Also, a prosthesis should allow normal ankle motion which
is approximately 30 degrees dorsi and plantarflexion, coupled
with internal and external rotation.
Mobile
bearing prosthesis have been successful due to their ability
to provide for complex ankle motion while maintaining low
contact stress by constant congruent contact throughout any
and all phases of motion. In a study by Keblish et al, 237
cementless ankle replacements of the original Buechel-Pappas
Meniscal Bearing design were examined. They show the device
worked well with an implant survivorship of 90.7% and less
than 4% showing radiolucencies at 18-72 month follow-up period.
Several
clinical studies outside the United States have shown that
mobile bearing prostheses provide the best results for ankle
replacements. Doets, displayed good results with both the
original and current meniscal bearing design. Tillman, compared
the current meniscal bearing design to fixed bearing designs
and showed the best mobility and pain relief came from the
mobile bearing design. Also, the original and current design
has shown near normal gait pattern duplication.
1974
- B-P CYLINDRICAL FIXED BEARING DESIGN
The first
design was a two piece component consisting of a metal tibial
and a plastic talar component. Failure of this design occurred
from three major reasons:
 |
- Lack
of axial rotation resulting in tibial loosening due
to torque.
- Talar
component subsidence secondary to talar dome resection.
- Wear
of polyethylene due to a metal edge of the tibial
component wiping over the bearing surface.
|
These
problems were common to all fixed bearing ankle devices of
the period, such as the Mayo and Oregon Ankles.2-3
1976
- TRUNION CYLINDRICAL DESIGN
 |
Due
to the problems identified after review of devices similar
to the 1974 design, the need to have congruent articulating
contact, without restriction to axial rotation was apparent.
This lead to the adaptation of the mobile bearing concept
(which was first used in the shoulder in 1974) to the
ankle. The rotating trunion device allowed axial rotation
with congruity. |
1978
- ORIGINAL MENISCAL BEARING DESIGN
 |
Although
the trunion ankle performed as expected initially, the
New Jersey Meniscal Bearing Knee replacement was developed
in 1977, and the benefits of lack of constraint were
apparent. These benefits included congruent articular
surfaces and the reduction of constraint forces.
This design worked except for three infrequent problems:
- Mechanical
bearing subluxation due to talar necrosis with component
subsidence and tilting. (15%)
- Fracture
of the tibial plate. (5%)
- Fracture
of the meniscal bearing. (2%)
|
1989
- CURRENT MENISCAL BEARING DESIGN
(B-P Low Contact Stress Total Ankle Replacement)
 |
 |
In
response to the infrequent problems discovered with the
original meniscal bearing design, and discoveries made
in wear reduction resulting from thin ceramic films, the
current design encompassing the following changes was
developed: |
- Titanium
alloy is used instead of Co-Cr due to its superior
•
Biocompatibility resulting from:
• Less toxic and fewer corrosion products.
• Improved ingrowth into porous coating.
• Avoidance of the nickel sensitivity condition (metal
allergy).
• Strength
• Material properties (elastic modulus) closer to
bone for better elastic compatibility.
• Reduced cost.
- UltraCoat®
TiN thin film ceramic coating
Although titanium alloy is superior to cobalt chromium in
almost all aspects, it is inferior in abrasion resistance.
Thin film ceramic coatings (TiN), allow for a durable, abrasive
resistant surface making titanium alloy viable for articulating
surfaces
This coating:
• Substantial decrease in polyethylene wear.
Improved
biocompatibility due to:
• Improved corrosion resistance.
• Greatly improved abrasion resistance eliminates
corrosion products.
- Dual
fin talar fixation to prevent tilting
In
the original meniscal bearing ankle device, a single, central
fin was used. This fin would invade the talar blood supply
on insertion, causing talar necrosis to occur, talar component
subsidence and subsequent bearing subluxation. The dual
fin design avoids transecting the blood supply, and prevents
talar tilting.
- Deep
sulcus of bearing/talar engagement to prevent subluxation
of bearing if tilting occurs.
- Tibial
plate thickness increase to prevent fracture.
- Bearing
is ETO sterilized to avoid the degradation resulting from
the gamma radiation of the original meniscal bearing which
experienced minor fracture due to oxidation resulting from
gamma irradiation sterilization.
Distribution
See:
section for international distribution outside the United
States |
Investigational
Trial*
The Buechel-Pappas
Ankle replacement system can not be generally sold in the United
States since all mobile bearing ankle and knee replacements
are classified as Class III by the FDA. Therefore Endotec has
conducted rigorous clinical trial that is completed and is preparing
to file a PMA for approval in the United States.
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