Development and evaluation of economical trans-tibial prosthesis for rural area

Abstract

The mainstream of prosthetic research develops prostheses with cutting-edge technologies. However, only few people can afford luxurious products and most of amputees especially in rural area do not even receive foundational prosthetic service. Some researchers persist in developing economical prosthetic solution. Previous studies suggested the sand casting method (SCM) originated from dilatancy casting principle. It provided an effective casting method without conventional plaster. By combining thermoplastic vacuum forming technique, it was claimed that tans-tibial monolithic prosthesis (monolimb) could be custom-made for individuals in a single-day visit. However, previous clinical trial found that the monolimb made by SCM were loose. The method was further discouraged since monolimb is non-adjustable after fabrication. Previous studies tried to determine the height and alignment of monolimb for individual during the sand casting procedures. Nevertheless, the outcome was not desirable as dynamic alignment could not be determined during the casting process. Our pilot study found air leakage problem of SCM and the auxiliary belt-suspension system of monolimb were other disadvantages. The objective of present study is to deliver a clinically practical, reliable and economical method to facilitate trans-tibial prosthetic service in rural countries by improving previous technology. Latex membrane was used instead of original plastic bag to enhance endurance and reliability. Latex balloon donned on residual limb was then wrapped by bandage to reduce its girth end hence increased socket fit. It was evaluated by comparing girths of residual limbs and models made with plastic bag coating (condition 1) as well as latex balloon coating wrapping with bandage (condition 2) in six cases, the girths of models made in condition 1 were significantly larger than that of residual limbs, whereas there was no significant dimensional difference between residual limbs and models made in condition 2. The succeeding monolimbs also reflected that the bandage wrapping technique solved the loose socket problem. A pair of pads was introduced to SCM in order to make indentations over femoral supracondylar regions. The resultant temporary socket was suspended by self suspension mechanism rather than depending on auxiliary suspension system. Traditional prosthetic components were incorporated with SCM to form a temporary prosthesis for length and alignment assessments. Finally, the thermoplastic vacuum forming process was modified to cooperate with the improved SCM. Field test was conducted in a prosthesis center in Shaoguan. Six monolimbs were fabricated for daily use over a year. The casting model was modified to deal with long residual limbs experienced in the test. The system was subsequently introduced to a prosthesis research center in Beijing to collect comment from professionals. The thermoplastic vacuum forming process was modified to adopt conventional prosthetic ankle joint so that the ankle joint of succeeding monolimb was adjustable. In summary, the present study provides a reliable and economical method of monolimb fabrication within few working hours. Further studies include mechanical test of monolimb with conventional adaptor and performance comparisons between monolimb and conventional prosthesis.