Transfemoral Prosthetic Design
• Amputation b/w femoral epicondyles and greater
trochanter are fitted with transfemoral
prosthesis.
• Consist of
• (1) foot-ankle assembly
• (2) shank
• (3)knee unit
• (4)socket
• (5)Suspension device
(1) foot-ankle assembly
• SACH Foot is most commonly used
• Single-axis foot is somewhat more frequently
prescribed . Nevertheless, any foot, including
the energy storing/releasing designs can be
incorporated in a transfemoral prosthesis.
Shank
• Either the sturdy exoskeletal or endoskeletal
shank may be used.
• Endoskeletal shank creates a more pleasing
appearance , particularly in the knee area and
adjustable , and lighter than exo…
Knee unit
• Prosthetic knee enables the user to bend the
knee when sitting or kneeling.
• Commercial knee units may be described
according to four features.
• 1)axis
• 2) friction mechanism
• 3) extension aid
• 4) mechanical stabilizer
• Many combinations of features are available; not
every knee unit has all four components.
(a)
Axis system
• The thigh piece can be connected to the shank
either by a simple single-axis hinge or by
polycentric linkage.
• Polycentric systems have four or more
pivoting bars and provide greater stability to
the knee. This style is less common b/c of its
greater complexity.
(b)Friction Mechanism
• If the knee does not have sufficient friction to
retard its natural pendular action
• Friction mechanisms change the knee swing
by modifying the speed of the knee motion
during various parts of the swing phase and by
affecting knee swing according to walking
speed.
• Constant and variable:-
• The most popular knee unit has constant friction
• Variable friction:-
• In which the amount of friction changes during a
given swing phase
• At early swing:-high friction…..retard excessive
knee flexion
• During mid swing:- friction diminishes to permit
the knee swing easily
• Late swing:- friction increases to dampen impact
(c) Extension aid
• Assist knee extension
• Simplest type…. External aid consisting of
elastic webbing in front of knee axis.
• Int ext aid ….. Elastic strap or coiled ring
within the knee unit…. Functions identically to
the ext aid during walking
d) Stabilizers
• Most knee units donot have a special device to
increase stability. The patient controls knee action by
hip motion, aided by the alignment of the knee in
relation to other components of the prosthesis.
• Elderly or debilitating pt may benefit from stabilizing
mechanism
• a) manual lock ….. Simplest mechanical stabilizer
• b)friction brake…… more elaborate stbilizing system,
provides very high friction mechanism during early
stance, resisting any tendency of the knee to flex.
socket
• As with all prosthetic sockets, the
transfemoral one should be a total contact
receptacle to distribute load over the
maximum area, thereby reducing pressure.
• Two types
• 1) quadrilateral socket (traditional type)
• 2) ischial containment socket ( its wall cover
the ischial tuberosity & part of the ischiopubic
ramus to augment socket stability
Quadrilateral flexible socket in rigid
frame viewed from above
Suction suspension
• Suction refers to the pressure difference
inside and outside the socket.
• with suction suspension, internal socket
pressure < external socket pressure
• Ap…… causes the socket to remain on the
thigh.
suspension
• Three means are used to suspend the
transfemoral prosthesis
• Total suction
• Partial suction
• No suction
• Total suction:-
• Max control of the prosthesis, without any
encumbering auxiliary suspension, can be
achieved only if the socks fits very snugly to give
total suction.
Partial suction
• Socket that is slightly loose may enable patial
suction susp.
• Pt wears one or more socks or a liner made of
silicone or other synthetic material.
• Auxiliary suspension aid is needed either a
fabric silesian bandage or a rigid plastic or
metal hip joint and pelvic band.
No suction
• If socket has distal hole but no valve, then there is
no pressure difference between inside and
outside the socket.
• The client wears one or more socks and require a
pelvic band.
• Loose socket makes prosthesis donning easy, but
hinders control of prosthesis and sitting comfort.
• Another alternative is the addition of a
transfemoral suspension sleeve.
