remnant.
The footwear, designed to minimise stress on vulnerable skin, has a rigid sole to compensate for the loss of toe lever and a rocker base to allow rollover at the metatarsal joints.
Alternatively, partial foot prostheses can be used, especially when higher levels of mobility are predicted.
Biomechanically, a full-length toe lever is restored.
This is connected to the anterior aspect of the leg, which counteracts the force generated by the toe lever during gait.
A higher anterior support will reduce the direct pressures and shear forces generated over the amputation site hence reducing the stress on the skin.
There is no need to enclose the posterior aspect of the leg, as this serves no mechanical purpose (Figure 27.1).
Syme’s Amputation/Ankle Amputation Syme’s amputation is classically performed just proximal to the ankle joint, using the strong heel pad to cover the distal end of the tibia.
The advantage is a very strong end-bearing stump, where the person may even take a few steps without the aid of a prosthesis (such as for walking from bed to the toilet at night).
The major disadvantage is the poor cosmesis caused through the bulbous distal end of the stump.
The Wagner modification17 where the malleoli are excised has improved the appearance.
An ankle amputation generally creates a good strong lever below the knee that can be utilised to power prosthetic ambulation.
The limb segment shortening caused by an ankle amputation is often less than 50 mm, which restricts the prosthetic hardware that can be used.
Consequently, only a small selection of commercially available prosthetic foot components can be fitted into the available space below the stump.
The circumference at the level of the malleoli is typically greater than the lower third of the shin.
Not only does this make it impossible to match the contralateral ankle dimensions for cosmetic purposes, but any prosthetic socket must allow this large distal circumference to enter through a narrower section of the socket.
This can be achieved in different ways.
An ‘access trap’ (a removable section of the socket that is repositioned once the residual limb is in situ) can be used (Figure 27.2).
Alternatively, an open cross section can be used where the posterior aspect is left open, since it serves no mechanical purpose.
The socket above the level of the malleoli effectively consists of an anterior support ending slightly below the patella.
This support resists the floor reaction force during terminal stance, hence providing forward propulsion.
Other variations exist and the choice of socket is dictated by individual factors.
Transtibial (Below-Knee) Amputation This is an important amputation where the knee joint is preserved. The ideal stump length should be approximately 15 cm as measured from the medial tibial plateau to the end of the tibia. Even very short stumps, barely 7 cm long, can be fitted with a prosthesis and produce a result functionally superior to the transfemoral (above-knee) amputation. The advantages of preserving the knee joint are