A below knee amputation (BKA) is a transtibial amputation that involves removing the foot, ankle joint, distal tibia, and fibula with related soft tissue structures. TRANSTIBIAL SOCKET DESIGNS 1.Specific surface bearing (SSB )SOCKETS a)PTB b)PTB-SC PTB-SCSP PTK OR KBM 2.Total surface bearing (TSB)SOCKET 3.HYBRID SOCKET 5. Hydrostatic Socket design TRANSTIBIAL PROSTHETIC ALIGNMENT Alignment refers to spatial orientation of the prosthetic socket relative to the foot. Goals: • FacilitatingHSatIC • Provideadequatesinglelimbstability • Smoothrolloverduringthetransition • Adequatetoeclearance

1. BIOMECHANICS
OF
PROSTHETIC MANAGEMENT OF
TRANSTIBIALAMPUTATION
PRESENTED BY:
FIONA VERMA
MPO 1ST YEAR (6TH BATCH)
2023
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2. CONTENTS
• INTRODUCTION
• SUB-LEVELS OF TRANSTIBIAL AMPUTATION
• TRANSTIBIAL PROSTHETIC COMPONENTS
• TRANSTIBIAL SOCKET CLASSIFICATION
• PTB SOCKET
• TSB SOCKET
• PTB VS TSB
• HYBRID
• BIOMECHANICAL FORCES IN TT PROSTHESIS
• TRANSTIBIAL PROSTHETIC ALIGNMENT
• A-P FOOT POSITIONING
• M-L FOOT POSITIONING
• A-P SOCKET TILTING
• M-L SOCKET TILTING
• BENCH ALIGNMENT OF TT PROSTHESIS
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3. INTRODUCTION
A below knee amputation (BKA) is a transtibial
amputation that involves removing the foot, ankle
joint, distal tibia, and fibula with related soft tissue
structures.
Causes for amputation:
• Peripheral vascular disease (60% - 70%)
• Diabetes mellitus
• Trauma
• Infections
• Tumors
• Chronic non-healing ulcers
• Congenital deformities
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4. SUB-LEVELS OF TRANSTIBIAL AMPUTATION
1. Very short BK: function is highly
compromised, therefore consider
amputation at next higher level
2. Short BK: (upper leg amputation)
consider removing entire fibula
along with some muscle bulk.
3. Medium BK: (middle leg
amputation) considered ideal bone
length
4. Long BK : (lower leg amputation)
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5. TRANSTIBIAL PROSTHETIC COMPONENTS
• A transtibial prosthesis is typically has 5 major parts:-
Soft interface
Socket
Pylon
Prosthetic foot
Suspension
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6. TRANSTIBIAL SOCKET CLASSIFICATION
TRANSTIBIAL SOCKET DESIGNS
SSB SOCKETS
(Specific Surface Bearing)
TSB SOCKET
(Total Surface Bearing)
HYBRID SOCKET
PTB-SC PTB-SCSP PTK OR KBM
PTB
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7. PATELLAR-TENDON BEARING SOCKET
• Patellar-tendon bearing socket
originally developed after World War
II and was described in the 1950’s by
Radcliff.
• PTB designs are based on the
principle of specific surfaces being
tolerable and intolerable.
• Such socket designs are used with
sock interfaces or foam interface thus,
they are beneficial when gel liners are
not used.
a) Anterior view b) Posterior view
PTB socket- pressure-tolerant tissue (red) &
pressure intolerant tissues (green)
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8. SSB SOCKET OR PTB SOCKET BIOMECHANICS
WORKING PRINCIPLE:
• PTB socket relied on the concepts of socket
biomechanics as proposed by Radcliff.
• As the design of the socket takes advantage of
the pressure tolerant areas in the stump,
especially “patellar-tendon bar and
posterior aspect of stump or popliteal
fossa”.
• Weight is borne over anatomically pressure
tolerant areas and offloaded from pressure
intolerant areas.
PT BAR
POPLITEAL
FOSSA
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9. The patellar-tendon supracondylar socket (PTS or PTB-SC),PTB-SCSP, patellar-tendon kegel (PTK) or
kondylen-Bein-Muenster (KBM) socket designs each follow a similar principle to the PTB with extra
functional effect derived from extended proximal socket trimlines .
The PTB socket design is usually manufactured with a foam interface liner fitting however may have a
silicone or gel based liner within the rigid socket design.
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10. Socket PTB (Patellar
Tendon Bearing)
Socket PTB SC (patellar
tendon Bearing
Supracondylar)
Socket PTB SC SP (Patellar
Tendon bearing Supracondylar
Suprapatellar)
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11. Merits:
• The carved out areas and buildups on specific surfaces.
• Comfortable fit and weight-bearing.
• Easy accommodation of dynamic forces during gait cycle.
Demerits:
Patellar-tendon –bearing designs create regions of very high localized pressure that can induce adverse
limb changes such as callus formation and skin breakdown whereas other regions are subjected to
pressure levels far below their tolerances.
This creates large, unnecessary pressure differentials across the limb
In such socket designs, pressures have been reported as high as 220 to 400 kPa. Whereas, peak pressures
of less than 70 kPa was reported for total-surface bearing socket.
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12. TOTAL SURFACE BEARING SOCKET
• The next substantial advancement was made in socket
with Total Surface Bearing socket in 80s.
• It complement the ICEROSS system Ossur Kritinsson
in 1993 described the TSB socket concept; where the
weight was borne by the entire surface of the residual
stump.
• It rely on the principle of containing the entire mass of
the residuum in an equal volume of socket to keep the
socket in contact during the gait cycle.
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13. TOTAL SURFACE BEARING
SOCKET
Researchers stated that the TSB socket eliminates the piston
movement by providing a real Total Contact during walking.
Main feature:
• Reduction is global as per residual limb’s overall tissue
density.
• Reduces risk of edema and skin problems
• CAD/CAM technology usage can be beneficial as global
reduction is easy and accurate using the software.
• Its use has surpassed the PTB design because of decreased
pressure differentials and fewer negative changes to the
limb.
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14. TSB SOCKET BIOMECHANICS
WORKING PRINCIPLE:
• TSB, focuses on uniformly distributing the
weight over the entire residual limb in
order to deliver minimum amount of skin
pressure.
• This principle considered to lower peak
pressures due to larger area (P=F/A).
• Moreover, pressure within the socket is
reduced proximally and increased distally
to allow the above mention criteria to be
performed
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15. PTB SC SOCKET Vs TSB SOCKET
Transversal views show the difference between
internal shape of both socket designs
PTB SC SOCKET TSB SOCKET
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16. PTB SOCKET VS TSB SOCKET
In order to identify and evaluate the difference between both the socket designs, investigation was
made regarding the two socket types in walking and in other ambulation activities except sitting and
standing up from a chair.
Methods: prosthetic training on unilateral trans-tibial amputees with both PTB and TSB socket
respectively so the Difference was made regarding the below mentioned factors:-
• Temporal-distance characteristics of gait
• Weight-bearing characteristics/ Weight-acceptance on amputated side
• Socket volume of each type
• Time required to perform ambulatory activities.
• Balance evaluation
• the sufficiency of suspension of each socket type
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https://www.tandfonline.com/doi/abs/10.1080/030936402087
26649?journalCode=ipoi20

17. 1) Terminal-distance (TD) characteristics of gait:
Intact side step length, cadence during free and fast walking is increased and step width showed a
diminution in walking with TSB prosthetic socket than PTB.
There was also improvement in amputated side step length and stride length in the TSB prosthesis than
PTB.
2) Weight- acceptance on the amputated side:
It was determined that weight acceptance on the amputated side advanced to more normal value with
TSB prosthesis.
3) Balance evaluation:
The prosthesis with total –contact bearing socket produced more balanced stance than the prosthesis
with patellar-tendon bearing socket design.
4) Socket volume:
Socket volume was found to be smaller in TSB than PTB when two types of prosthetic fitting were
compared.
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18. 5) Time required to perform ambulatory activities:
Performing ambulatory activities, a statistically significant difference was obtained and it was found
that shorter time is required by the amputee to complete the ambulatory activities , except sitting and
standing up from a chair and crossing an obstacle, using TSB prosthetic socket.
6) Suspension system:
Another important result was found, there was no need to use suspension aids in the TSB sockets while
reversed Y strap was used in 90 percent of the patients during walking with PTB prosthesis.
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19. HYBRID SOCKET
• Hybrid designs use aspects of patellar-tendon-
bearing and total surface bearing sockets &
incorporate their collective advantages.
• It amalgamate the design concept of both PTB &
TSB to create sockets that combine global
reduction with modest localized reductions and
buildups in load-tolerant and load-intolerant regions
respectively.
• Merits: combined advantages.
• Demerits: not applicable to use with elevated
vacuum suspension system.
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20. HYDROSTATIC SOCKET DESIGN
• The first use of hydrostatic theory in socket
production was by Murdoch in 1965, which aim to
reduce some manual dexterity required to produce a
quality socket.
• It used fluid as a medium to apply uniform pressure
around the stump during casting.
• Hydrostatic theory is successful in eliminating
regions of high pressure, the total surface bearing
characteristics which used to result in
dermatological problems.
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21. WORKING PRINCIPLE
• CASTING TECHNIQUE:
• Casting is performed on the patient using an air
bladder system to produce socket shape based
on the hydrostatic principle for load transfer.
• The principle assumes soft tissue in the stump
behaves as a fluid and abides by Pascal’s Law
of Fluids (it states that a confined fluid will
transmit external pressure uniformly in all
directions perpendicular to the containers
surface.
• Pressure casting technique (PCAST) uses
similar theory using fluid pressure chamber-
wrapping plaster over stump before placing in
a sealed pressurized water chamber.
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Trans-tibial amputee in a normal standing posture unaided;
supported by the pressure cast system

22. 22
ADVANTAGES DISADVANTAGES

23. BIOMECHANICAL FORCES IN TT PROSTHESIS
In normal human locomotion, floor reaction forces produce moments at joints of LL. Similar forces
exist during ambulation with a prosthesis that need to be considered.
Major forces acting on prosthetic socket are:
• Shear
• Normal dynamic forces
• Antero-posterior forces
• Medio-lateral forces
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24. TRANSTIBIAL PROSTHETIC ALIGNMENT
Alignment refers to spatial orientation of the prosthetic socket relative to the foot.
Goals:
• Facilitating HS at IC
• Provide adequate single limb stability
• Smooth rollover during the transition
• Adequate toe clearance
These can be fulfilled by biomechanical adjustments:
• Antero-posterior foot positioning
• Medio-lateral foot positioning
• Antero-posterior socket tilting
• Medio-lateral socket tilting
• Height adjustment
• Foot rotation
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25. • A-P foot positioning:
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Typical alignment Typical alignment:
extensor moment
Heel lever too long Flexion moment

26. • M-L foot positioning:
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Typical alignment Varus moment is
created
Foot outset Valgus moment

27. • A-P and M-L socket tilting:
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28. BENCH ALIGHNMENT
Standard bench alignment has the socket in 5 degree of flexion and 5 degree of adduction.
• Sagittal plane view:
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29. • Frontal view:
Frontal view
Sagittal view 29

30. • Vertical alignment axis:
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31. REFERRENCES
• Orthotics and Prosthetics in Rehabilitation, Michelle M. Lusardi PhD PT (Author)
• (PDF) Sockets for Limb Prostheses: A Review of Existing Technologies and Open
Challenges (researchgate.net)
• https://www.tandfonline.com/doi/abs/10.1080/03093640208726649?journalCode=
ipoi20
• Atlas of Amputations & Limb Deficiencies, 4th edition: Print + Ebook (AAOS -
American Academy of Orthopaedic Surgeons)
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32. THANK
YOU
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