抄録
The air-cushion socket of below knee prosthesis was designed by Wilson in 1968. This socket is a modification of P. T. B. socket having three parts which are hard outer shell with no bottom, silicon rubber made inner elastic socket and a cap covering distal end of socket. In between the inner elastic socket and a cap, air-tight space is formed. This air-tight space acts like an air mat, supports a part of body weight at the stump end and aids suspension of prosthesis during swing phase. The fabrication of this socket, however, is too complicated.
The purpose of this study was to investigate the real function of air-cushion as well as to simplify fabricating method.
Methods:
1) The fabrication of socket was simplified making an inner socket with elastic silicon rubber made lower part and flexible resin made upper part, and rigid outer socket. Socket was designed for K. B. M. socket.
2) Pressure of air-cushion and strain of socket were recorded during walking with foot switches to show walking phase.
3) Two sockets were made. One was fabricated from the positive model from original K. B. M. socket, another was fabricated from the positive model according to Wilson's method. Former was called A-socket, latter was called B-socket. A piece of 2mm thickness of leather was attached to the patella tendon seat of B-socket later.
Results:
1) Dynamic change of pressure of A-socket was total 17.54mmHg±0.98, that of B-socket was 21.47mmHg±0.93, and that of B-socket with 2mm thickness leather attached to patella tendon seat was 20.37mmHg±0.96.
2) Pressure of air-cushion suddenly began to increase from heel contact and got into a peak at foot flat. From heel off, pressure began to decrease suddenly and got into a peak at just after toe off.
3) The strain of socket was maximum at later half of midstance.
Conclusion:
1) The air-cushion plays an important role for the weight bearing at the begining of stance phase.
2) Patella tendon seat supports weight mainly at the later half of stance phase.
3) Suspension at push off and early part of swing phase is important.
