Before a new foot prosthesis can be introduced to the public, gait testing must be performed to ensure that the gait patterns produced while wearing the foot are acceptable. At present there are no guidelines to determine what level of performance is acceptable. The most common method used to determine the suitability of a new foot prosthesis is to compare its gait pattern to the pattern of an existing prosthetic foot that has been deemed acceptable. Large deviations in the certain kinetic properties, such as the moments produced at the knee joint, can have detrimental affects on the individual wearing the foot.

A new prosthetic foot design, created by the Niagara Prosthetics and Orthotics company (NPO), was brought to Queen’s University, for the clinical testing. A comparison study with the Stationary Ankle Flexible Endoskeleton foot (SAFE) was used to determine if there were differences in the gait pattern while wearing the NPO foot and whether these differences would be problematic. Five below knee amputees volunteered to attend two testing sessions at the gait laboratory in Kingston General Hospital. Prior to the first session they were fitted with a SAFE prosthetic foot. Prior to the second visit they were fitted with the new NPO prosthetic foot. All fittings were performed by the same prosthetist. Subjects were allowed a minimum o f two days to accommodate to each prosthetic foot. Subjects walked at self-selected speeds across a six meter walkway that had an AMTI force plate mounted in the floor. An optoelectric motion tracking system was used to collect information on a series o f 12 markers placed at selected body landmarks. At the end of each testing session the subjects filled out a subjective questionnaire about the performance of the foot tested.

The two prosthetic feet were compared in four main categories:​ time distance parameters, gait curve patterns, gait curve parameters, and a subjective questionnaire. A two way ANOVA with repeated measures reveled that eight of the variables differed between the feet. The stance ratio was found to be smaller in the NPO. The maximum moment (AP) at the knee joint was lower in the NPO foot. The maximum moment (LM) occurred earlier in the gait cycle for the NPO foot. The NPO produced a larger degree of ankle dorsiflexion. The NPO foot generated a smaller braking impulse and a smaller propulsive impulse. The NPO had a higher vertical GRF peak and a lower vertical GRF slope suggesting that it absorbs less energy but does it over a longer period of time. Several of these differences were attributed to the lack of adequate cushioning, or shock absorptive properties in the heel of the NPO prosthetic foot. Although several variables were found to be significantly different between the prosthetic feet, no difference in NPO foot gait pattern were considered problematic and the foot was deemed acceptable.

The NPO foot was designed to meet the needs of individuals in developing countries. The high cost of modem foot components, short life expectancy, and lack of skilled prosthetists to fit and maintain complex prosthetics, combined with annual incomes far below those of North American countries, has created a serious need for an inexpensive, uncomplicated, and durable prosthetic foot able to produce adequate gait patterns. The NPO combines many of these attributes with its elegant one piece design produced from a polyethylene compound that is inexpensive, durable, flexible, and can be injection molded. The result is a prosthetic foot that can be produced at an estimated cost of S7-10 each.

Despite some small short comings in performance, when compared to the SAFE foot, the NPO foot produced an adequate gait pattern. The foot’s ability to meet the specific needs of a third world market in terms of cost, durability and simplicity, makes the NPO foot a potentially successful alternative to more costly components. Questions as to its acceptability in countries with cultural sensitivities and cultural-specific needs remain unanswered.