ISSN 2319-8885
Vol.03,Issue.49
December-2014,
Pages:10012-10019
www.ijsetr.com
Design and Analysis of Artificial Ankle Joint
JOELSUNIL KUMAR PUTLA1, GITHENDHRA. B2
1
PG Scholar, Dept of Mechanical Engineering, Nova College of Engineering and Technology, Jangareddygudem , AP, India,
E-mail: [email protected].
2
Assoc Prof, Dept of Mechanical Engineering, Nova College of Engineering and Technology, Jangareddygudem , AP, India.
Abstract: CAD engineers are finding a fertile ground for exploitation in the process of design of customized to match to body
shape. In this process, while total joint replacement has been successful in the shoulder, the hip and the knee, there has not been
similar success with total ankle replacement in the past. In 1979, initial reports on total ankle replacement were promising.
However, long-term follow up studies painted a different picture due to many failures and poor survivorship of the implants. As
a result, it has been regarded as an inferior procedure to arthrodesis. Yet, with the introduction of new implants there has been a
recent resurgence (renewal) of interest in Total Ankle Replacement (TAR). The currently available implants are Agility, Salto,
ESKA, Buechel-pappas, HINTEGRA and STAR. Of all these designs, STAR system has found to be the reasonable alternative
to Ankle Replacement. It is the only three piece mobile bearing, non constrained, un cemented total ankle replacement. Also, it
is the first three part ankle prosthesis to receive FDA approval to replace painful arthritic ankle joint. The objective of this
thesis is to develop design approaches and models for ankle joints. The design advantages can be used in prosthetics. In this
study, the design approach for a 3-component mobile bearing artificial ankle joint using CATIA software has been developed.
Some design changes in talar component were made when compared to STAR (Scandinavian Total Ankle Replacement) ankle.
The design of an artificial ankle joint similar to STAR ankle has also been carried out. By introducing the contact pair in
between the components, non-linear static analysis of an artificial ankle joint has been done using ANSYS software. This will
clearly explain the working efficiency of the ankle joint. The analysis is carried out by the variation of load applied on the
ankle. It was found that at 15000 Newton’s of load, the Von Mises stresses induced in the member is 10.6 MPa, which is much
closed to the yield stress of UHMWPE material. From the results obtained it can be concluded that, the developed model can be
safely implanted into a human beings having body weight up to 110kg.
Keywords: Total Ankle Replacement (TAR), Scandinavian Total Ankle Replacement (STAR).
I. INTRODUCTION
The human body is a series of many bones, joints and
muscles. At birth the human body has about 350 bones, but
by the time adulthood rolls around, some of our bones have
fused together to give us a total of 206 bones in our body!
Here is the breakdown:
 The adult skeleton consists of 206 bones
 28 skull bones (8 cranial, 14 facial, and 6 ear bones);
 The horseshoe-shaped hyoid bone of the neck;
 26 vertebrae (7 cervical or neck, 12 thorax, 5 lumbar
or loins, the sacrum which is five fused vertebrae,
and the coccyx, our vestigial tail, which is four fused
vertebrae);
 24 ribs plus the sternum or breastbone; the shoulder
girdle (2 clavicles, the most frequently fractured bone
in the body, and 2 scapulae);
 The pelvic girdle (2 fused bones);
 30 bones in our arms and legs (a total of 120);
 There are also a few partial bones, ranging from 8-18
in numbers, which are related to joints.
A. Types of Joints in Human Body
The point where two or more bones meet is called a
joint. Joints are classified by their structure or the way they
move as shown in Fig.1.
Fig.1.Various joints in a human body.
Copyright @ 2014 IJSETR. All rights reserved.
JOELSUNIL KUMAR PUTLA, GITHENDHRA. B
Suture: The joints of the skull are known as sutures (top,
This section introduces mainly the biomechanical
left). Sutures do not have a wide range of movement.
literature on the human ankle. Specific subjects include:
Instead, they allow for growth and very limited flexibility.
anatomy of lower extremity, anatomy of the foot, its
Hinge joints: (top, right) allow for movement in one plane.
joints and movements, the gait cycle (walking cycle) and
The hinge joints of the elbow and knee, for example, bend
the biomechanics of an ankle.
up and down.
II. TOTAL ANKLE REPLACEMENT
Gliding Joint: Two flat-surfaced bones that slide over one
Ankle
replacement
or ankle
arthroplasty
is
another make up a gliding joint (bottom, right). Gliding
a surgical procedure to replace the damaged articular
joints, such as those in the wrist and the foot, provide for
surfaces of the human ankle joint with prosthetic
components. This procedure is becoming the treatment of
limited movement.
choice for patients, replacing the conventional use
Ball-And-Socket Joints: These joints allow the greatest
of arthrodesis, i.e. fusion of the bones. The restoration of
range of motion. The ball-and-socket joints of the shoulder
range of motion is the key feature in favor of ankle
and hip, for example, can rotate in a complete circle.
replacement with respect to arthrodesis.
Parts Of A Joint: parts of a joint as shown in Fig.2.
Fig.2. Parts of a joint.
Articular Cartilage (Purple): The end of each bone is
covered with articular cartilage. This is a tough material that
cushions and protects the ends of the bones. When it
degenerates, arthritis develops.
Synovial Membrane or Synovial Sac (Light Blue):
Around each joint is the synovial sac which protects the
joint and also secretes the synovial fluid. Synovial fluid
serves to protect the joint, lubricate the joint and provide
nourishment to the articular cartilage.
A. History of Total Ankle Replacement (TAR)
The history of total ankle arthroplasties date back to the
1970s with a rise in popularity of total hip and total knee
replacement a total ankle replacement was felt to be an easy
thing and several different designs were released. These
were cemented prostheses, in general two-part components
that were very non-anatomic. With short-term follow-up
some of these ankles did well but in intermediate follow-up
of even four or five years they began to fail. By the mid
1980s total ankle replacement in the United States was not
being done. Many of these ankles were later fused as a
salvage procedure. Thus over a fifteen to twenty year
period, ankle fusion was really the only choice for patients
with severe arthritis of the ankle.
B. Need for Total Ankle Replacement (TAR)
The ankle is a weight-bearing joint and carries the body's
full weight, so it is very important to treat a painful ankle.
Severe ankle pain can be debilitating and that's where ankle
replacement surgery comes in. Ankle replacement is an
alternative to arthrodesis in selected patients (Fig.3). It’s an
effective pain relief option and is taken up only when
conservative methods of relieving pain or deformities in the
ankle are unsuccessful. The advantage of replacing the ankle
is the preservation of movement and function.
Bursa (Dark Blue): A bursa is a small sac that is not part of
the joint but is near the joint. It contains a fluid that
lubricates the movement of muscles as the muscle moves
across muscle or as the muscle moves across bone. In some
ways it is similar to the synovial sac.
Muscle (Red): Muscles are elastic tissues that have the
ability to change length. By becoming shorter and longer,
muscles allow for motion at the joints.
Tendon (Red): Tendons are fibrous cords that attach
muscles to the bones. Unlike muscles which change length
(contract), the tendons are unable to change length.
However, as the muscle moves, the tendon to which it is
attached also moves. You can feel the tendons on the back
of your hand or in the back of your knee.
Fig.3. Right ankle arthrodesis and left
arthroplasty performed sequentially in a patient
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.49, December-2014, Pages: 10012-10019
ankle
Design and Analysis of Artificial Ankle Joint
This may also result in improvements in gait including
constrained or semi constrained with a majority of the
reduction of limp and protection of other joints. Multiple
current generation of implants being semi constrained.
techniques that are used for ankle replacement surgery to
Agility LP Total Ankle: The most widely-used fixed
allow relief from pain and regain stability are discussed the
bearing ankle in the U.S. is the Agility LP Total Ankle
following section.
manufactured by DePuy Orthopedics. It consists of a tibial
component with an UHMWPE insert that articulates against
C. Current Implants and Failures
The total number of Total Ankle Replacements (including
a CoCr talar component (Fig.5). The articulation is
revision) was approximately 7000 procedures in 2005 and is
cylindrical in the direction of plantar/dorsiflexion. This
estimated to increase to11, 000 in 2012 for an increase of 6device is considered semi-constrained as the tibial radius is
8% a year (Fig.4). Similarly, these procedures generated
larger than the talar radius. The Agility is a cemented
$285 million in revenue and are expected to increase to
implant. This was the only ankle approved for use in the
$476 million in 2012 industry wide.
United States until 2007 [11]. The clinical results for the
Agility ankle indicate survival rates between 80-95% at five
years and 63% at ten years [11], [5]. Some drawbacks of
this ankle are the large bone resections required and implant
stability [9].
Fig.4. Estimated procedure volume for total ankle
replacement through 2012.
Total ankle replacements were initially developed in the
1970s and have had varying degrees of success. The short
term results were promising but as the patients were
followed longer, the results became more disappointing. The
early designs of ankle replacements had problems with
loosening, instability and impingement that were primarily
attributed to excessive bone resection, poor instrumentation,
and poorly designed implants (overly constrained, too thick,
poor fixation methods). This led to a backlash against total
ankle replacements and the increase in use of fusion. As
total joint replacements improved for the hip and knee joints
in the last twenty years, ankle replacements have again
become an appealing alternative to fusion and its 5
complications. TARs can be classified into two major
groups: two and three component.
The two piece designs are also known as fixed bearing
while the three piece designs are referred to as mobile
bearing. The bearings currently on the market mostly use
Ultra High Molecular Weight Poly Ethylene (UHMWPE)
against a cobalt chrome alloy as the tribopair; but there is
one that uses titanium nitride (Buechal Pappas) and another
that uses ceramic in Japan. The ankles can then be further
classified as constrained/semi constrained and nonconstrained. Most fixed bearing ankles are either
Fig.5. Agility ankle by DePuy (from Agility website).
The Scandinavian Total Ankle Replacement (STAR):
The STAR is one of the most widely used ankle
replacement. The STAR Ankle is a non-constrained, total
ankle replacement, surgically implanted to replace an ankle
joint. It is non-constrained because the bearing can be free
to move in more than one plane along the tibial component.
Working of STAR: The STAR Ankle has three parts: a
metal tibial component, a metal talar component and a
plastic mobile bearing component. The upper flat surface of
the plastic component slides against the flat surface of the
tibial plate. The projecting cylinders of the tibial component
serve to fix the device to bone at the distal tibia. The lower
surface of the plastic mobile bearing component is concave,
fitting against the convex upper surface of the talar
component. The talar component is anchored into the
resurfaced native talus [7]. The STAR Ankle is intended for
use as a non-cemented implant to replace a painful arthritic
ankle joint due to osteoarthritis, post-traumatic arthritis or
rheumatoid arthritis.
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.49, December-2014, Pages: 10012-10019
JOELSUNIL KUMAR PUTLA, GITHENDHRA. B
However, the clinical performance of the STAR ankle has
been found to be 89% at 5 years and 76% at 10 years
according to the Norwegian Registry [4], and 78% at 5 years
in the Swedish ankle registry [12]. Other reports indicate 5
year survival rates between 70-98% [11]. As a result,
STAR has found to be the most effective solution for ankle
replacement. Also, the device is designed as an option to
allow the patient to regain and/or retain some of his/her
normal ankle mobility and function. Side effects may
include pain, nerve injury, wound healing problems, and
bone fracture.
Fig.6. STAR ankle.
The other leading mobile bearing ankle replacement is
Buechel Pappas (BP) ankle (Fig.7). The Scandinavian Total
Ankle Replacement (STAR) (Fig.6) manufactured by Small
Bones Innovations and the Buechel Pappas (BP) ankle
(Fig.7) manufactured by Endotec are the two leading mobile
bearing ankle replacements currently on the market. These
two ankles have both been used for approximately 20 years
in Europe. The BP is not currently approved for use in the
U.S. as it is currently in clinical trials, but the STAR was
approved for use in 2009 and is the only mobile bearing
device approved in the United States. Both of these designs
are unconstrained to anterior/posterior translation and
internal/external rotation at the tibial articular surface by
having a flat geometry. They are constrained at the talar
surface with a more conforming fit. The talar interface is
almost completely conforming which only allows the
flexion to occur while any joint rotations are intended to
occur at the tibial interface [9]. The conformity of the talar
surface also adds medial/lateral stability and prevents the
insert from disassociation.
Fig.7. BP ankle replacement.
III. RESULTS AND DISCUSSIONS
The artificial ankle joint that has been designed is
generated in the ANSYS software and the stresses at various
load conditions are obtained. The effect of yield stress of
polyethylene and total component Vonmises stresses are
taken into consideration. The non-linear static analyses are
mainly considered for the analysis of artificial ankle joint.
This will clearly explain the working efficiency of the ankle
joint. In this work, the analysis is carried out by the
variation of load applied on the ankle.
A. Application of Force On The Modeled Ankle
In normal day to day life, the force that acts on the ankle
joint of a human being varies from 5-10 times the body
weight. Hence, in this analysis the Force on the ankle joint
is varied from 3000-15000 N, which includes the persons
having body weight up to 120 kgs.
Therefore, the load on the ankle has been varied from
3000-15000N and the results obtained are shown in the
following Figs
Fig.8. VonMises stresses at 3000 Newton’s load.
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.49, December-2014, Pages: 10012-10019
Design and Analysis of Artificial Ankle Joint
Fig.9 VonMises stresses at 4000 Newton’s load.
Fig.12. VonMises stresses at 7000 Newton’s load.
Fig.10. VonMises stresses at 5000 Newton’s load.
Fig.13. VonMises stresses at 8000 Newton’s load.
Fig.11. VonMises stresses at 6000 Newton’s load.
Fig.14. VonMises stresses at 9000 Newton’s load.
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.49, December-2014, Pages: 10012-10019
JOELSUNIL KUMAR PUTLA, GITHENDHRA. B
Fig.15. VonMises stresses at 10000 Newton’s load.
Fig.18. VonMises stresses at 14000 Newton’s load.
Fig.16. VonMises stresses at 11000 Newton’s load.
Fig.19. VonMises stresses at 15000 Newton’s load.
TABLE I: The Results of Von Mises Stresses at
Different Body Eights
Fig.17. VonMises stresses at 12000 Newton’s load.
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.49, December-2014, Pages: 10012-10019
Design and Analysis of Artificial Ankle Joint
From the Fig.8 to Fig.19, it can be observed that at 15000
Plot between Von Mises stresses and loads shows that
Newton’s of load, the Von Mises stresses induced in the
during increasing the load on artificial ankle joint, von
artificial ankle joint is 10.6 MPa. This is almost approaching
mises stresses are increasing with respective to loads.
the yield strength of UHMWPE material. So, by these
results we can conclude that beyond these loads component
might fail. The results obtained are tabulated in the Table
No.1. From the Table No.1 we can conclude that, factor of
safety of an artificial ankle joint differs at different body
weights. For a 90 Kg weight person, 10 times of body
weight acting on the ankle joint then the factor of safety is
1.86. Hence, the designed artificial ankle can be safely
implanted into the humans having the body weight up to
110kgs. At which the factor of safety is 1.53.
TABLE II: Von Mises Stresses, Von Mises Strains and
Displacement Vector Sum to corresponding Loads
Fig.21. Plots between Displacement and Loads.
Plot between Displacements and loads shows that during
increasing the load on artificial ankle joint, displacements
are increasing with respective to loads
Fig.20. Plot between Von Mises stresses and Loads.
IV. CONCLUSION
Diligent study of normal ankle biomechanics and review
of previous implant failures has led to the development of a
new generation of implants. This improvement coupled with
improved cement less fixation, has led to prosthetic designs
with decreased failure rates. Increased awareness and
adequate surgeons training are probably the key factors to
transform TAR to a promising alternative to ankle
arthrodesis. However, appropriate selection of patients
remains a cornerstone for a successful ankle replacement. In
this study, the design approach for a 3-component mobile
bearing artificial ankle joint using CATIA software has been
developed. Some design changes in talar component were
made when compared to STAR (Scandinavian Total Ankle
Replacement) ankle. The design of an artificial ankle joint
similar to STAR ankle has also been carried out. By
introducing the contact pair in between the components,
non-linear static analysis of an artificial ankle joint has been
done using ANSYS software. Normally the load acting on
the ankle joint of human lower limb is 5–10 times of body
weight. The analysis is carried out by varying the load on
the ankle from 3000-15000 Newton’s. It was found that, at
15000 Newton’s of load, the Von Mises stresses are found
to be 10.6 MPa, which is almost equivalent to the yield
stress of UHMWPE material. Factor of safety of an artificial
ankle joint differs at different body weights. For a 90 Kg
weight person, 10 times of body weight acting on the ankle
joint then the factor of safety is 1.86. Hence, from Table 5.3
the designed artificial ankle can be safely implanted into the
humans having the body weight up to 110 Kg, at which the
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.49, December-2014, Pages: 10012-10019
JOELSUNIL KUMAR PUTLA, GITHENDHRA. B
factor of safety is 1.53. In conclusion, currently, selected
patients with painful ankle osteoarthritis can be offered a
total ankle replacement not only in U. S but also in INDIA.
Future Scope: There are several areas where further work
clearly needs to be done.
 Further designs should be directed toward reducing
ligament strain, restoring the normal axis of rotation
and maintaining mobile bearing stability.
 Further work can be carried out for dynamic analysis
from which wear rate and the life span of the implant
can be estimated.
V. REFERENCES
[1] Alexej Barg, Charles Saltzman, Beat Hintermann,
“Biomechanics of the Foot and
Ankle”, June 2011.
[2] Alvine, F.G., “Agility Total Ankle System, Surgical
Technique”, DePuy a Johnson & Johnson Company:
Warsaw, Indiana, 1999, p. 10.
[3] Barnett, C. and J. Napier, the Axis of Rotation at the
Ankle Joint in Man, its Influence upon the Form of the
Talus and Mobility of the Fibula”, Journal of Anatomy,
1952(86): p. 1-9.
[4] Bjorg-Tilde F, Lie SA, Havelin LI, Brun JG,
Skredderstuen A, Furnes O. “257 ankle arthroplasties
performed in Norway between 1994 and 2005”, Acta
Orthopaedica, Vol 78:5, pp575-583, 2007.
[5] Bonnin M, Judet T, Colombier JA, Buscayret F.
“Midterm results of the Salto Total Ankle Prosthesis”,
CORR, No 424, pp6-18, 2004.
[6] Calderale, P.M., et al., Biomechanical Design of the
Total Ankle Prosthesis. Engineering in Medicine, 1983.
12(2): p. 69-80.
[7] Craig Fryman J. “Wear of a Total Ankle Replacement”,
A Thesis Submitted to the Graduate School of the
University of Notre Dame, December 2010.
[8] Czerniecki, J. M., 1988, Foot and Ankle Biomechanics
in Walking and Running, American Journal of Physical
Medicine & Rehabilitation, 246-252.
[9] Easley ME, Vertullo CJ, Urban WC, Nunley JA. “Total
Ankle Arthroplasty”, J. Am Acad Ortho Surg, Vol 10, No
3, pp157, May/June 2002?
[10] Giannini, S., A. Leardini, and J.J. O’Connor, Total
Ankle Replacement: Review of the Designs and of Current
Status. Foot & Ankle Surgery, 2000. 6: p. 77-88.
[11] Gougoulias NE, Khanna A, Maffulli N. “History and
evolution in total ankle arthroplasty”, British Medical
Bulletin, Vol 89, pp111-151, 2009.
[12] Henricson A, Skoog A, Carlsson A. “The Swedish
ankle arthroplasty register: an analysis of 531 arthroplasties
between 1993 and 2005”, Acta Orthopaedica, Vol 78:5,
pp569-574, 2007.
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.49, December-2014, Pages: 10012-10019