Northwestern University Feinberg School of Medicine

Northwestern University Prosthetics-Orthotics Center

A Comparison of Computer-Controlled and Passive Prosthetic Knee Joints

Steven A. Gard, PhD and Dudley S. Childress, PhD, Principal Investigators

Margrit R. Meier, PhD, Project Director

Funded by: Department of Veterans Affairs (DVA)

Status: Completed


The purpose of this study is to evaluate walking performance (level ground, obstacle course, stairs) of persons with unilateral transfemoral amputations when fitted with three different prosthetic knee joints: Otto Bock C-leg®, Otto Bock 3R60 and CaTech SNS.

Objective evidence is needed to determine if significant benefit is derived when prescribing expensive microprocessor-controlled knee mechanisms over the high-performance passive knee units that cost significantly less. Most previous studies have analyzed microprocessor-controlled knee joints primarily during walking on level, smooth surfaces, although the appeal of these knee mechanisms seems to be in their excellent stance stability and enhanced swing phase responsiveness on uneven surfaces. Gauthier-Gagnon et al. (1999) found that the activities most often reported by their amputee population as ones that could not be performed using conventional knee units were ascending and descending stairs without handrails, and walking outdoors on uneven grounds and in inclement weather. We therefore tested the C-leg® in those specific areas where the manufacturers claim that it provides unique benefit to the prosthetic user: Ease of walking over uneven ground due to stumble control, ascent and descent of stairs and reduction of mental loading. Testing of the C-leg® on the basis of an obstacle course with different surfaces in combination with a mental loading test should demonstrate the benefits of the C-leg's® new design. The results of our study will contribute to a better understanding of microprocessor-controlled prosthetic knee joint systems and may ultimately lead to better prescription criteria.


The testing session consists of (1) a gait analysis on level ground at three different walking speeds (normal, as slow as possible and as fast as possible) without and with a mental loading task, (2) completing an obstacle course (see figure 2), without and with a mental loading task, and (3) stair ascent and descent, again without and with a mental loading task. The mental loading task consisted of a counting task in which the participants are requested to count vocally backwards in three-step increments (e.g., 100, 97, 94 etc.). At each of the different speeds, on the obstacle course and for the stairs, different starting numbers were given to avoid repetition. During the entire testing session heart rate is monitored to estimate the energy expenditure by using the Total Heart Beat Index (Hood et al., 2002).

The study is near completion and data are being processed and analyzed. The publications to date are based on preliminary results and their conclusion may therefore change once the entire data analysis is completed.


Gauthier-Gagnon C, Grise MC, Potvin D. Enabling factors related to prosthetic use by people with transtibial and transfemoral amputation. Archives of Physical Medicine & Rehabilitation 1999;80:706 –713.

Hood VL, Granat MH, Maxwell DJ and Hasler JP. A new method of using heart rate to represent energy expenditure: the Total Heart Beat Index. Archives of Physical Medicine & Rehabilitation 2002; 83(9):1266-73.

Related Publications

Meier M, Hansen A, Gard S. Does mental loading change the energy expenditure during level walking? A comparison between C-leg, SNS and 3R60. Paper presented at: Annual Meeting and Scientific Symposium of the American Academy of Orthotists and Prosthetists; March 1-4, 2006; Chicago, IL.

Meier M, Hansen A, Gard S, Childress D. Obstacle Course Performance: Comparison of the C-Leg to Two Conventional Knees. Paper presented at: 20th Congress of the International Society of Biomechanics and 29th Annual Meeting of the American Society of Biomechanics 2005; Cleveland, OH.

Meier, Margrit R., "Performance on an obstacle course: Otto Bock C-leg vs. Otto Bock 3R60 vs. CaTech SNS," ** American Academy of Orthotists and Prosthetists AAOP 2005 Annual Meeting and Scientific Symposium, Orlando, Florida, USA, March 16-19, 2005.

Meier, Margrit R., "A comparison of C-leg and 3R60 prosthetic knee joint performance," ** 27th Annual Meeting of the American Society of Biomechanics (ASB), Toledo, Ohio, USA, September 25-27, 2003.

Meier, Margrit R., "A comparison of the C-leg and the 3R60 prosthetic knee joint," ** Biomechanics of the lower limb in health, disease and rehabilitation, Salford-Manchester, UK, September 1-3rd, 2003.

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