|
June 2007 • Vol. 3, No. 3
|
Advancing Orthotic and Prosthetic
Care Through Knowledge
|
T. Schmalz, PhD
Introduction
Advances in modern modular prosthetic techniques have made it possible for prosthetists to better meet the individual needs of amputees. But even higher demands are made on the prosthetic joint when the amputee has to move over uneven ground, on sloped surfaces, or on stairs—all of which are common daily activities. Special systems with stance-phase resistance are well suited for these situations.
With the aid of the Otto Bock C-Leg® microprocessor-controlled knee, the demands placed on the amputee to control the knee joint have been substantially reduced. Sensors in this joint provide information concerning the immediate movement status. Indeed, the safety and comfort for an overwhelming majority of fittings has so clearly increased for patients with both lower and higher functional demands, that its importance is clearly relevant.
There currently exist several studies that compare the characteristics of the C-Leg with non-electronically controlled hydraulic knee systems while walking on even ground. These studies report improved swing-phase characteristics6 as well as a decrease in the metabolic rate7 while using the C-Leg. Prior to this study, there had been no known studies that considered whether the concept of electronic control is also advantageous when applied to common situations that require higher demands on the movement apparatus as opposed to normal walking. With this in mind, the goals of this study were to provide biomechanical analysis of stair descent by transfemoral amputees and to compare the C-Leg with non-electronically controlled hydraulic knee joints.
Methods
In order to analyze step-over-step stair descent, test stairs made with two steps (DIN-Norm 17.5cm) were installed in a gait laboratory. The first step was solidly anchored to a force measurement plate (Kistler, Kistler AG, Winterthur, Switzerland, 400hz) so that ground-reaction force could be measured.
Twelve transfemoral amputees took part in the study. The C-Leg, as well as two single-axis hydraulic systems, the 3C1 (Otto Bock, Mauch hydraulic) and the 3R80 (Otto Bock, rotary hydraulic), all make stair descent possible. A Dynamic-plus foot (1D25, Otto Bock) was used in all tests. As a control group, 21 healthy people, with no known orthopedic or neurological diseases, were tested.
In the first round of testing, the prosthetic leg came in contact with the middle step mounted on the pressure measurement plate. In the second round of testing, the test began with the alternating foot starting so that the contralateral leg could be measured when it came in contact with the step. From these measurements, the vertical and horizontal components of the ground reaction force as well as the sagittal knee angle were then evaluated.
Results
Subjective Ranking
After the tests were completed, the patients were asked to rank each of the three joints while descending stairs with a simple ranking system. For descending stairs, the C-Leg was judged to be most comfortable by all 12 amputees. For the 3R80, nine of the patients chose it as second best, and three chose it as third best, while ranking the 3C1 inversely to the 3R80.
Ground Reaction Force
The vertical force showed two prominent peaks in contrast to the interim unloading phase. The norm of the peaks when compared to those from walking on even ground, however, were lower, and were barely over 100 percent of body weight. The horizontal force showed a typical gait transition from a braking to an acceleration phase. Here the braking as well as the accelerating peaks were significantly reduced when compared to the peaks shown during walking on even ground.
The data for transfemoral amputees descending stairs, however, exhibited typical differences. Vertical forces measured on the prosthetic side were significantly reduced compared to those of a normal gait. Significant here was the quick unloading of the limb in the second part of the stance phase. When the joints were compared alongside each other, it was clear that this effect was considerably lessened with the C-Leg and that the unloading phase of the prosthesis that followed was more physiological than it was with the conventional hydraulic system. Another picture presented itself, however, when the contralateral leg was considered. Here the vertical force for both loading phases was measured for the amputees with an increase of up to 60 percent. It became apparent that the unphysiological increase of forces generated when the C-Leg was used was substantially less than when the 3C1 or 3R80 were used.
Biomechanical Characteristics of the Knee Joints
During stair descent, the prosthetic knee joint showed knee movement, which was qualitatively similar to natural movement. In doing this, the prosthetic knee joint stayed extended somewhat longer after the beginning of stance phase. In the second part of the support phase, the natural knee bent about ten degrees more than a prosthetic knee joint. The torque moments exhibited exceptions as well. After the support phase began, a longer extension moment was measured with the 3R80 than with the 3C1 or the C-Leg. In the second half of the support phase, the 3C1 and 3R80 reached about 0.7Nm/Kg—only about half of the flexion moment of a healthy subject. The knee joint of the C-Leg, on the other hand, was loaded with about 1Nm/Kg, a markedly closer approximation to that of the loading characteristics of a healthy subject. The knee angle characteristics of the contralateral leg of an amputee showed typical differences from the characteristics of a healthy subject. Immediately after the support phase began, a noticeable flexion angle was initiated, which continued into the middle of the support phase and then transitioned into the direction of extension. From this we saw a strong flexion moment with a distinct localized extreme value even in the early part of the support phase. By comparing the joints, it became clear that the abnormal initial knee flexion during testing with the C-Leg was markedly less than those tested with the 3R80 and 3C1.
Biomechanical Characteristics of the Hip Joint
The loading of the hip joint in healthy individuals in the first half of the stance phase was distinguished by an external flexion moment. After about half of the contact time with the step, this effect reversed itself and registered an extension moment. Substantially higher flexion moments were measured at the beginning of stair contact during stair descents by amputees than by the control group. In this situation, the 3R80 had a 100 percent increase, as opposed to the C-Leg and 3C1, where the increase was substantially less.
In the second half of the support phase, the results of the 3C1 and 3R80 became more similar. With both joints, after they had reached 85 percent of the stair contact period, the effect of the torque moment reversed itself. During use with the C-Leg, however, a structure was registered in the second half of the stance phase, which most closely approximated the structure of a healthy person.
Discussion
The measurement results of the control group showed qualitative agreement of biomechanical characteristics when compared with previous tests of healthy individuals in which the measurement step was positioned in the middle of several steps.1,3 Thus one can assume that the characteristics of step-over-step stair descent for transfemoral amputees that have been investigated here have been well described both qualitatively and quantitatively. The measured joint angle and moments reflect not only the functional principles but also the effectiveness of the tested knee/joint systems.
The 3R80 differentiated itself from the 3C1 and C-Leg during activation of the hydraulic stance phase yielding. The fluid-controlled stance phase yielding of the 3R80 was only effective when the joint was loaded beyond its individual stance sensitivity engagement setting.2 The amputee caused this to happen during step-over-step stair descent with an increased activity of the hip extensors immediately after initiating stair contact. Further testing during the stance phase has shown the special capabilities of the C-Leg's electronically controlled stance-phase dampening. Compared with the 3R80 and 3C1, the C-Leg hydraulics can compensate for significantly stronger external flexion moments at the knee joint and more closely approximate the physiological loading situation of a sound knee. The characteristics of the knee and hip joints related to the prosthetic side have consequences for the next stair contact by the contralateral side. Deviating from approximately symmetrical stair descent by non-amputees, the transfemoral amputee "falls" onto the sound leg, where the considerably increased initial peaks of vertical force are markedly apparent.
This unphysiological loading had a striking effect on the biomechanical characteristics of the anatomical knee joint. The initially large flexion moment could only be compensated for by an increased activation of the knee joint extensor muscles and an increased strain on the capsule and ligament structures. Further clues concerning these compensatory effects may be revealed in further studies. Overloading of the contralateral extremity was measurable with all three tested joints but was proven to be noticeably less with use of the C-Leg. It can be derived from these results that for amputees, the secure functional properties5 and joint characteristics of the C-Leg contribute to the protection of the sound limb.
For more information, contact T. Schmalz, PhD, Otto Bock Research and Development, Biomechanics Laboratory, Hermann-Rein Str. 2a, 37075 Göttingen, Germany.
References
Andriacchi, T., G. Andersson, R. Fermier, D. Stern, O. Galante: A study of lower-limb mechanics during stair climbing, Journal of Bone and Joint Surgery 62-A, 5 (1980), 749-757. Blumentritt, S., H. Scherer, T. Schmalz: Ganganalyse von Oberschenkelamputierten mit einem Kniegelenk mit Rotationshydraulik, Med.Orth.Tech. 118 (1998), 51-61. McFadyen, B., D. Winter: An integrated biomechanical analysis of normal stair ascent and descent. J. Biomechanics, 21 9 (1988), 733-744. Dietl, H., R. Kaitan, R. Pawlik, P. Ferrara: C-Leg—ein neues System zur Versorgung von Oberschenkelamputationen, Orthopädie-Technik 49 (1998), 197-211. Köcher, L.: Das Kniegelenksystem C-Leg—Klinische Versorgungsstatistik. Med.Orth.Tech. 121 4 (2001), 129-134. Kastner, J., R. Nimmervoll, P. Wagner: Was kann das C-Leg? Ganganalytischer Vergleich von C-Leg, 3R45 und 3R80, Med.Orth. Tech. 119 (1999), 131-137. Schmalz, T., S. Blumentritt, K. Tsukishiro, L. Köcher, H. Dietl: Energy efficiency of trans-femoral amputees walking on computer-controlled prosthetic knee joint "C-Leg." Kongressband 9. Weltkongress der International Society for Prosthetics and Orthotics (1998), 455-460.
Take the quiz at the Academy's Online Learning Center.
|
|
