Biomechanical Evaluation of a Microprocessor Controlled Prosthetic Knee Joint

Principal Investigator: Kenton R. Kaufman, Ph.D.
Project Coordinator: Barbara Iverson — iversonliterski.barbara@mayo.edu

Figure 1: Knee Moment

The purpose of this study was to quantify the functional characteristics of active transfemoral amputees using a microprocessor controlled knee compared to the most frequently prescribed mechanical knee joint, the Mauch SNS.

This study employed a crossover design whereby only the knee component was changed. Each subject was tested in the gait laboratory using a mechanical knee prosthesis (Mauch SNS or CaTech) and retested eight weeks after receiving a microprocessor controlled knee joint (OttoBock C-leg). The Prosthetic Evaluation Questionnaire (PEQ) was administered to each subject prior to each testing session. Subjects' balance was tested on the Equitest Posturography System. Energy consumption measurements were made using a commercially available automated system modified to interface to a respiratory mass spectrometer. Activity levels were quantified for 10 days using a Step Watch™. Total daily energy expenditure was quantified using doubly-labeled water.

Figure 2: Total Daily Energy Expenditure

Subjects demonstrated improved gait and balance characteristics after receiving the microprocessor controlled prosthetic knee joint. The knee moment demonstrated a significant shift from an internal flexion moment toward a more normal extension moment during midstance (Fig. 1). The subjects achieved greater gait symmetry. Their balance was improved when using the microprocessor controlled knee. The subjects demonstrated a 2% decrease in energy expenditure when using the microprocessor controlled knee compared to the mechanical prosthetic knee. The improvements in gait, balance and energy consumption when using the microprocessor controlled knee translated into increased activity levels. The subjects increased their steps per day and decreased the percentage of time with no activity. Most importantly, there was a significant increase in total daily energy expenditure of 600 Kcal/day (Fig. 2). When using the microprocessor controlled knee, the subjects indicated increased satisfaction in all aspects of their lives with the exception of a decline in residual stump health. This is not surprising since the subjects had such a significant increase in daily activity level, which would temporarily affect their residual stump health.

In summary, Individuals using a microprocessor-controlled knee demonstrate improvements in gait and balance with a concomitant decrease in energy consumption. These positive changes translate into increased activity in the users' daily life