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Concept of fitting P.T.B, s

HISTORY
BASIC DESIGN – PROSTHESIS WITH NO THIGH CORSET:-

P.T.B (PATELLA TENDON BEARING)

CONCEPT OF FITTING P.T.B’S –

The P.T.B requires high skills in the taking and rectifying of the cast if the limb is to be worn successfully over long periods. Complications of below knee amputations are neuromas, phantom pain, adherent scars, infections, bursars, and at times, vascular problems. Whilst poor limb fitting can result in exasperation of these complications, they can be for the most part be avoided if sufficient care is taken and skill used when taking and rectifying the cast.

Over the years the P.T.B has been modified and changed in a number of ways to suit or fit silicone or polyurethane liners, and in some cases away from the concept of the P.T.B fit, relying on the silicone liner to displace areas for relief and pressure, or in other cases of total contact including contact in distal end of stump and bony areas. Theories of fitting the P.T.B were a deliberate change in shape and variation of unit pressure between the socket and the stump. Pressure areas are reduced on the male cast and areas of relief have plaster added. Allowances must be for return circulation and changes during normal gait flexing and extending, sitting and standing. The patella tendon is a strong tendon and suited for high pressure and used for weight bearing. The back of the socket and the popliteal area is also an area of acceptance to take pressure and is a counter pressure for the patella tendon. The surface of the condyles known as the medial flare can also take weight and helps control of the socket from rotation. The paratibials are also an area to take moderate pressure and help with the transfer of the limb from toe-off and heel-strike, with the points of relief being the tibial shaft, distal cut end of tibia, head of fibula, lateral and medial tendons, thus giving a shape to the socket which is basically triangular. Other sensitive areas which may need relief ie cut end of fibula nerve ends, arthritic joints should be relieved on the final cast.


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