Lower limb ProsthesisAdib Mursyidi Iskandar MirzaOrthopedics

Outline

• Definition• Aim of prosthesis• Level of amputations of lower limbs• Components of prosthesis• General issues

Definition

• Prosthesis• Device to replace part of the limb or missing limb

“substitute”• Orthosis• Externally applied mechanical devices • Support weakened injured, paralyzed, diseased part

as supplementation• Prosthetist• Person skilled in prosthetics and its application

Aim of prosthesis

• To substitute for a lost part• To restore lost function• Comfortable ambulation • Minimal/reduce of expenditure of energy• Minimizing the shift of the center of gravity of the body during gait

Level of amputation• There are several

levels of lower limb amputation

• Most common are transtibial and transfemoral

Component of prosthesis of Lower Limbs

Parts of prosthesis1. Socket

2. Suspension system

3. Knee Joint

4. Shank/pylon

5. Foot/Terminal device

Suction& Mechl close fitting

Socket

• Most important part• Is the connection between the stump

and the prosthesis• Protects the stump and transmits

forces• Uncomfortable rejected• Contoured sockets fit closer to bone,

muscle, soft tissue• Provide support and relief

Suspension systems• For attaching socket

to body• Types of suspension• Sleeve, belt, straps,

or cuff • Suction prosthesis • Mechanical close

fitting or silicon sock helps to maintain airtight seal

Suspension systems materials• Sleeve – made from

latex• Cuff – used to hold

prosthesis in residual limb• Belt/straps – use a

waist belt with elastic strap to suspend prosthesis

• Suction method – consist of silicon sleeve with short pin at the end will fit into residual limb and locks into socket

Knee joint1. Axis system2. Friction 3. Stabilizer

Axis system

• Single axis• Axis of prosthetic knee is same as that of weighty

bearing axis• Flexion easier, but stance phase control difficult

• Polycentric• Permits momentary axis of knee flexion to change

through the arc of motion increase knee stability

Medium friction

(hydraulic) friction

Constant friction

Friction mechanism• Changes knee swing by modifying the speed of knee motion• Adjust knee swing accordingly

• Constant friction• Applies uniform resistance throughout swing phase

• Variable friction-cadence control• Greater friction is applied at early and late swing

• Medium friction• Oil (hydraulic) friction• Air (pneumatic)friction• Allows best gait pattern best for active patients, but expensive

StabilizersManual locking

Stabilizer

Most unit do not have special device to increase stabilityPatient control knee actions through hip motions by• Manual locking : prevent knee

flexion• Friction brake : resist knee flexion

during early stance

Shank/pylon

• Use to connect the socket to the ankle-foot assembly• Allow axial rotation and absorb, store, and release

energyConsist of two types• Exoskeleton• soft foam contoured to match other limb with hard

outer shell• Endoskeleton• internal metal frame with cosmetic soft covering

Ankle-Foot Assembly

Ankle Foot Assembly

• Designed to provide support during standing/walking and shock absorption as well• Consist of 3 categories• Single axis foot• Solid ankle cushioned heel (SACH) foot• Dynamic response• Articulating• Non articulating

• Ankle hinge allow dorsiflexion and plantar flexion• Disadvantages• Poor durability• Poor cosmesis

Single Axis Foot

Solid ankle cushion heel (SACH)

• Most widely prescribed foot• Due to simple, low

cost and durability• Uses in patient with

low activity• Disadvantages – may

overload the non amputated foot

Dynamic response energy storing foot

• General use for most normal activities• Consist of • Articulating• Non articulating

Articulating

• Allow motion at the level of human ankle• Indications• Patients walking on uneven surfaces

• Advantages• Absorbs loads and decreases shear forces• Flexible keels• acts as a spring to decrease contralateral loading, allow

dorsiflexion, and provide a spring-like push-off

Non articulating

• Have short or long keels• shorter keels are not as responsive and are indicated

for moderate-activity patients• longer keels are indicated for high-demand patients

• Different feet for running and lower-demand activities available

Prescription of prosthesis• Type of prosthesis required• Level of amputation• Material of socket• Suspension mechanism• Type of cosmesis required

General Issues

• Choke syndrome• caused by obstructed venous outflow due to a socket

that is too snug• acute phase• red, indurated skin with orange-peel appearance

• chronic phase• hemosiderin deposits and venous stasis ulcers

• Skin problems• Contact dermatitis• most commonly caused by liner, socks, and suspension

mechanism• treatment• remove the offending item with symptomatic treatment

• Cysts and excess sweating• signs of excess shear forces and improperly fitted components

• Scar• Post operative scar

• Painful residual limb• possible causes include bony prominences, poorly

fitting prostheses, neuroma formation, and insufficient soft tissue coverage

• Ineffective suspension system• Poor socket fit• Stump volume changes• Foot alignment abnormalities