Prosthetics ::: Lower Limb Components

Lower limb prosthetic components
These will be described under the following headings:

Feet and ankles
Knees
Hips
[Click on any topic to jump directly to that specific topic.]

Feet and ankles
Most of these can be categorised as follows:

SACH
Uniaxial
Multi axial
Leaf spring
Silicone
[Click on any topic to go directly to that specific topic.]

SACH (Solid Ankle Cushion Heel)
[Click here to go back the Feet and Ankles section.]
A molded compressible foot with no moving components. A central keel provides resistance to bending in the forefoot, and a compressible heel section mimics plantarflexion at heel strike. Suitable for a wide range of activity levels depending upon the overall situation.

Examples of two types of SACH feet from the Otto Bock range. The components above the feet are adaptors for connecting them to lightweight endoskeletal systems. They can also be used for exoskeletal prostheses.

Uniaxial [Click here to go back the Feet and Ankles section.]
A foot with an ankle joint which allows movement in only one plane, i.e. plantar/dorsiflexion. Resistance to this movement is provided by compressible bumpers. Suitable for low to moderate activity levels.

An Otto Bock uniaxial ankle joint. The upper part attaches to the shin and the lower bolts attach the foot. This design is for an exoskeletal structure.

Even uniaxial feet are available in several different designs.This photo shows feet without toes, intended for use with two different heel heights.

Multi axial [Click here to go back the Feet and Ankles section.]

A foot with an ankle joint which allows movement in more than one plane. A common design is in effect a rubber universal joint, the range of which is limited by the shape of the housing. Suitable for all but the highest activity levels.

Leaf spring [Click here to go back the Feet and Ankles section.]
Generally a laminated carbon fibre construction with a cosmetic cover. Very high energy return makes this type very popular for sporting applications, but can also be specified for lower activity levels.

An Otto Bock SpringLite foot with endoskeletal adaptor. The foot is normally worn with a cosmetic cover.

A SpringLite foot which is designed for use where there is very little distal clearance as with an ankle disarticulation. See section on amputation levels. Normally used with a cosmetic cover.

Silicone feet [Click here to go back the Feet and Ankles section.]

Homogenous silicone structures with no moving parts. Only used for partial foot amputations, they slip on like shoes. Can be specified for very high cosmetic definition. The forefoot bends under load like a SACH foot. [Click here to see the Silicone Gallery, which opens in a new page.]

Prosthetic knee joints [Click to go to: Feet and Ankles : Hips]
Can be categorised as follows:

locking
free
Mechanically enhanced stability
Geometrically enhanced stability
Hydraulically enhanced stability
Cadence control
N.B. some knees will have combinations of these features.

Locking knee joints

These enable the user to lock the knee in full extension and unlock it to allow flexion for sitting. Some are designed to lock automatically when the knee is extended. These are referred to as semi-automatic knee joints (SAKL) Others require the user to lock and unlock the joint, which allows the option of walking with a free knee and are referred to as hand operated knee locks (HOKL)

The Otto Bock exoskeletal SAKL or HOKL components

Free joints
“Free” describes a joint which can be flexed or extended within limits without a lock. Very few have a basic uncontrolled hinge mechanism. Almost all will feature one or more mechanisms to enhance the control by the amputee.

Mechanically enhanced stability
These knees incorporate mechanical devices which increase the resistance to flexion in the stance phase, while remaining more free in the swing phase. These are appropriate for moderate activity levels.

Otto Bock endoskeletal knee units in steel and titanium

Geometrically enhanced stability
These are of a multi-link design which creates an effective knee centre which is posterior to the load line of the prosthesis with the knee extended. Until a certain point of knee flexion is reached, the knee will remain stable. These are appropriate for a wide range of activity levels and often have the advantage of folding under the socket in flexion, which can be beneficial.

Otto Bock endoskeletal 4 bar knee units in steel and titanium.

Otto Bock endoskeletal multi-link knee joint. This knee also features hydraulic stability and cadence control.

Otto Bock endoskeletal knee joint designed for use in knee disarticulation prostheses. Available in steel or titanium this also features hydraulic cadence control.

Hydraulically enhanced stability.
These knees incorporate a hydraulic unit which is designed to resist very rapid flexion, which makes the knee more stable. Often used for moderate to very high activity levels, an example is the Otto Bock

Otto Bock "C Leg" knee module

Otto Bock "C Leg" knee module as components.

Cadence control
These knees incorporate a device which is designed to provide independent adjustable resistance to flexion and extension. The resistance can be mechanical, hydraulic, pneumatic or electronic and the adjustment can often provide very fine control. Often used for a wide range of activity levels depending upon specification,

an example is the Otto Bock knee component

Various lower limb components

Lower limb components

Lower limb components

Lower limb components

Lower limb components

Prosthetic hip joints [Click to go to: Feet and Ankles : Knee ]
Because of the relatively low numbers of hip disarticulation or hemi-pelvectomy amputees, only a small number of designs exist. Some are lockable in stance but most provide geometrically enhanced stability with extension assisted by some type of spring.

Hip components

Hip components

The range of appropriate componentry.

There is a wide range of alternative components available when they are frequently required. There are literally dozens of types of prosthetic feet from many different manufacturers because many amputees require them. However, the choice is very limited with regard to hip or shoulder joints.

Alternative components

The complete hip prosthesis without its cosmetic cover.