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BIOMECHANICS OF A TRANS-TIBIAL AMPUTEE RUNNING GAIT COMPARED TO NORMAL RUNNING BY ILSE VERMEULEN
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Biomechanics of a Trans-Tibial Amputee Running Gait Compared to Normal
I would like to kindly thank Ilse Vermeulen for donating the following literature review.
Her input while developing the Limbar(TM) machine was invaluable. Many thanks.
BIOMECHANICS OF A TRANS-TIBIAL AMPUTEE RUNNING GAIT COMPARED TO NORMAL RUNNING
ILSE VERMEULEN
Student Number: 99110283
POR31PGA
Pathological Gait Analysis
Subject coordinator: Tim Bach
SUMISSION DATE: 18 May 2001
WORD COUNT: ~ 2010
Biomechanics of trans-tibial amputee running gait compared to normal
running
Ilse Vermeulen
POR31PGA
2001
STATEMENT OF AUTHORSHIP
I certify that the attached material is my original work. No other persons' work has been used without due acknowledgment. Except where I have clearly stated that I have used some of this material elsewhere, I have not presented it for examination in any other course or subject at this or any other institution.
INTRODUCTION
The loss of part of a limb, as experienced by the trans-tibial amputee (TTA) would be expected to have a significant influence on the biomechanics of the person’s walking and running gait. The TTA seem to adapt for this and after a period of rehabilitation TTA’s appear to walk and run with improved temporal and kinematic symmetry (Hurley, Mckenney, Robinson, Zadravec, Pierrynowski, 1990). The aim of this assignment is a greater understanding of the biomechanical adaptations used by TTA runners. Knowledge in this field could aid in the development of rehabilitation strategies as well as enable us to objectively evaluate the influence of prosthetic componentry on the running gait of TTA’s.
The normal (non-amputee) runner show a uniform gain in the amplitude of hip, knee and ankle joint moments, as running speed is increases. In contrast to a non-uniform increase in joint moments for the sound and prosthetic sides in the TTA (Sanderson and Martin, 1996). Enoka, Miller, Burgess, (1982) reported that 60% of TTA runner’s temporal and kinematic patterns were similar to that of a normal runner. They also suggested that the differences in the remaining 40%, could be removed with prosthetic adjustments and training. A study by Smith (1990) indicated that with increasing TTA cadence, less variability in kinematic data was observed in contrast to a greater variability in the kinetics results.
Biomechanics of trans-tibial amputee running gait compared to normal
running
TEMPORAL CHARACTERISTICS
The trend in normal speed seems to favour an increase in step length at slower speeds and an increase in step frequency where higher speeds are demanded (Saito, Kobayashi, Miyashita and Hoshikawa, 1974 and Vaughan, 1985). This same trend seems to be followed in TTA running. Sanderson (1996) reported an increase in step length, with increased running speed. While Enoka et al. (1982) subjects’ were running at higher speeds, an increase in step frequency was noted. An increase in step frequency correlates with an increase in non-support phase for the prosthetic side, but not on the sound side. This period of non-support meets the criterion for running, which is to experience alternating periods of single support and complete non-support (Enoka et al., 1982). Buckley (1999) reported the average duration of TTA stance phase to be 31% of the running gait cycle.
Biomechanics of trans-tibial amputee running gait compared to normal
running
KINEMATICS AND KINETICS
HIP
The duration and magnitude for prosthetic side hip extensor moment is greater than that of the sound side during its corresponding stance phase (Miller, 1987; Miller et. al., 1979). In the normal running a brief concentric hip extensor moment is followed by an eccentric hip flexor moment which slows hip extension (Mann 1981, Winter 1983). The sound and prosthetic sides follow the same sequence, although the eccentric hip flexor moment is abbreviated on the prosthetic side. This extensor moment also provides some assistance to the quadriceps muscle in controlling the knee immediately following foot strike. It then helps with knee extension from mid stance, rotating the thigh backward in relation to the hip, causing either a slowing of knee flexion or promotion knee extension. A delayed transition from extension to flexion at the hip joint, occurred at around 26% of stride for the prosthetic side, whereas this change occurred at around the15% mark for both the normal and sound side hips. A study by Sanderson (1996) showed that the prosthetic side hip joint underwent less extension during stance phase than the sound side hip. Figure 1 shows the large amplitude of hip extensor moments.
Biomechanics of trans-tibial amputee running gait compared to normal
running
KNEE
The slow running gait of TTA’s is similar to that of the TTA walking gait, and is characterised by a restricted range of knee flexion of the sound side during swing phase. This causes the sound side foot to always be close to the floor (Enoka et al., 1982). As velocity increases the sound side more closely resembles the normal gait with the characteristic knee flexion and extension. (Buckley, 1999). During normal running the stance phase starts with an eccentric knee extensor moment to control knee flexion and is followed by a concentric knee extensor moment as the knee changes from flexion to extension (Mann, 1981 and Winter, 1983). The TTA gait differs from this kinematic pattern in that the knee on the prosthetic side begin stance phase slightly more extended and experience a smaller flexion and extension moment. Enoka et al. (1982) and Miller (1987) also remarked that some below-knee amputees maintain a straight or hyperextended knee on the prosthetic side throughout stance phase, with the sound side almost a mirror image. Generally a knee flexion moment is still present, evidenced by a concentric knee flexor power output immediately after heel contact (Winter and Sienko, 1988; Czerniecki, Gitter, Munro, 1991). Figure 2 demonstrates the knee flexor – extensor pattern for a TTA running at 2.8m/s.
Biomechanics of trans-tibial amputee running gait compared to normal
running
ANKLE
In normal running, heel contact commences with a dorsiflexion moment that continues through the first third of stance phase. The TTA runner’s ankle on the sound side acts similar to that of the normal runner, except for the earlier termination of plantarflexion during the late phase of swing, which is similar to that of the prosthetic side (Miller, 1987; Sanderson, 1996).
As expected the ankle joint on the prosthetic side has a smaller range of motion. Figure 3 demonstrates the lack of a plantarflexion moment, due to the absence of plantarflexion musculature and an ankle joint.
The TTA runner also lacks a talocalcaneal joint to help achieve plantigrade, like in normal running. As compensation the TTA can experience frontal plane rotation and translation of the leg or assume a position with the knee, ankle and foot directly underneath the hip. To accommodate for this increase Biomechanics of trans-tibial amputee running gait compared to normal
running
in angular momentum in the legs, a change of alignment is necessary in the upper body. These changes will obviously have a negative effect on running performance (Engsberg & Allinger, 1990). Further research in this direction is of paramount importance.
ENERGY MECHANISMS
In normal running the ankle plantarflexors are the major sources of energy generation, the knee extensors the major energy absorbers, while the hip musculature plays a minor role in energy absorption or generation
(Winter a+b; Czerniecki and Gitter, 1992). The amputee compensates by using the hip extensors as the major source of energy generation and interestingly enough becomes the predominant energy absorbers. Czerniecki (1996) suggested that energy transfer across the hip joint to the trunk during deceleration of the swing phase leg might be an important energy distribution mechanism to partially compensate for reduced power output during stance phase of the prosthetic side. A study done by Czerniecki and Gitter (1992) showed that the total muscle work on the prosthetic limb during stance phase is only 42 % of normal energy generation. In addition Czerniecki et al. (1991) showed in their study that the total amount of energy transferred into the trunk, during swing phase was 74% greater than that of normal running. These results support the importance of such an adaptive mechanism, to the TTA’s lower extremity energetics during swing phase. For energy generated in late stance phase is critical to the acceleration of the trunk.
Biomechanics of trans-tibial amputee running gait compared to normal
running
GROUND REACTION FORCE (GRF)
Peak forces for breaking, vertical and propulsion components are lower for the prosthetic limb in comparison with the sound and non-amputee limbs.
Miller (1987) measured an average vertical ground reaction force (VGRF) of 1.0 times body weight (BW) during stance phase for the prosthetic side, and 1.2 BW on the sound side, with the subject running at a speed of 2.6m/s. Sanderson (1996) measured 2.15 BW on the prosthetic side compared to 2.39 BW on the sound side, at a running speed of 3.5m/s. Brower, Allard, Labelle (1989) noted a VGRF of 2.44 BW for children running at an average running speed of 2.10m/s and a VGRF of 2.55 BW at 3.03m/s, for the sound side. For the prosthetic side he measured 2.0 BW at 2.10m/s and 2.25 BW at 3.03m/s. Increasing speed consequently increases peak forces for sound and non-amputee limbs. On the prosthetic side a substantial increase in propulsion force and a less marked increase in the breaking force was experienced (Sanderson, 1996).
Biomechanics of trans-tibial amputee running gait compared to normal
running
FLEXFOOT
The biomechanical analysis of a TTA’s running gait is valuable in many ways. One very important outcome is the development of improved prosthetic componentry. One such development field is that of dynamic elastic response (DER) or energy storing feet (Wing & Hittenberger, 1989).
The Flex-Foot (FF) is the most widely prescribed and clinically popular prosthetic foot at present for the TTA runner. Total work done by the lower extremity while running with a FF is 70% of normal comparing to the SACH foot’s 49.5% (Czerniecki et al., 1991). Czerniecki et al. (1991) also reported 84% energy return for the FF, which is significantly higher than other prosthetic feet tested.
The FF is a J-shaped carbon fibre leaf spring (CarbonX Active HeelTM)
that deforms during loading. This creates controlled dorsiflexion as the shank rotates forward over the planted foot and in turn allows flexion of the knee. Plantar and dorsiflexion similar to the sound limb is observed, leading to greater gait symmetry (Buckley, 1999). Unlike other DER feet which generally make use of an four inch keel and attach to the ankle by a rigid pylon, the FF has a graphite composite keel that extends to the prosthetic socket, and therefore increasing the working leaver arm (Edelstein, 1989). Not only does it result in a very responsive and resilient component, it also significantly improves the mass distribution of the prosthesis. Most of the weight is situated in the socket and attachment cone, with the rest uniformly distributed across the pylon. The inverted pendulum mechanism gives the patient a feel of a lighter prosthesis as it is propelled through space (Michael, 1987).
Biomechanics of trans-tibial amputee running gait compared to normal
running
The effectiveness of the FF can be demonstrated in its ability to propel the body forward in combination with reducing heel strike load on the sound side (Lehmann, 1993). Although the SACH foot shows more heel compliance, the FF shows more forefoot compliance, resulting in a greater ankle angle range (Torburn. Perry, Ayappa, Shanfield, 1990) and a shorter push off phase. Lehmann (1993), Hsu, Nielsen, Yack, Shurr, Lin (2000) and Torburn et al. (1990) didn’t find any significant increase in step length onto the sound limb, change in self-selected walking velocity or energy expenditure, as would be expected with the greater propulsion of the FF (Note: Tests done at walking speed). Lehmann (1993) suggested that this phenomenon could have been caused by the incorrect timing of the energy storage-release cycle of the FF, relative to the kinematic requirements of ambulation. In contrast Macfarlane, Nielsen, Shurr, Meier (1992) and Menard et al. (1992) did find an increase in step length of the sound limb as well as an increase in self-selected walking speed in their study on TTA walking. A more symmetrical gait was observed when walking with the Flexfoot, because larger more normal steps could be taken. Macfarlane et al. (1992) explained changes in step length due to the longer support in stance phase of the prosthetic side when using a Flexfoot, resulting in a shorter short push-off with a greater impulse force. Most subjects preferred to utilise this late ‘kick’ for sport activities rather than everyday living (Menard et al., 1992). Figure 4 shows the more normalised power output data obtained for the FF.
Biomechanics of trans-tibial amputee running gait compared to normal
running
FIG 4 Mean =1SD stance phase power outputs of the hip, knee and ankle in four amputee subjects wearing the FF (solid lines) and five normal subjects (dotted lines) running a 2.8m/s. (Concentric power output = positive; eccentric power output = negative.)
Although cosmetic finishing for the FF is difficult and time-consuming, it has the advantage of resulting in a very highly water-resistant structure. In Figure 5 and Figure 6 it can be seen that when using the FF energy generation return closer to normal, in both eccentric and concentric work.
FIG. 5 Distribution of total stance phase concentric muscle work between hip extensors, knee extensors and ankle plantarflexors in five normal and five amputee subjects running at 2.8m/s.
Biomechanics of trans-tibial amputee running gait compared to normal
running
FIG. 6 Distribution of total stance phase eccentric muscle work between hip extensors, knee extensors and ankle plantarflexors in five normal and five amputee subjects running at 2.8m/s.
A more advanced type of FF is the Re-Flex Vertical Shock Pylon (VCP). The Re-Flex VCP is the first prosthesis to successfully integrate a shock absorption system. It uses a carbon fibre compression spring, and telescoping tubes that provide up to an inch of vertical compression. Greater movement of the pylon occurs as speed increases, which results into greater energy storage and release (Miller & Childress, 1997). Energy storing-releasing properties were showed to be more pronounced in the Re-Flex VCP than in the FF (Hsu, Nielsen, Yack, Shurr, 1999). Hsu et al. (1999) also suggested that the Re-Flex VCP a positive effect on energy cost, gait efficiency, and relative exercise intensity comparing to other prosthetic foot types. Although limited testing has been performed on the Re-Flex VCP it has proven superior to the SACH and the FF.
Biomechanics of trans-tibial amputee running gait compared to normal
running
CONCLUSION
Below knee amputees seem to demonstrate different coping mechanics to the increase in speed demand. Although symmetry in stride frequency and support phase is demonstrated, asymmetry in ankle, knee and hip moments is marked. During the stance phase less ankle motion, a decrease in the flexion- extension at the knee and less extension at the hip joint.
Biomechanics of trans-tibial amputee running gait compared to normal
running
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Czerniecki, J.M., Gitter, A.J., Beck, J.C., (1996), Energy Transfer Mechanisms As A Compensatory Strategy In Below-Knee Amputee Runners.
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Czerniecki, J.M., Gitter, A.J., Munro, C., (1991), Joint Moment and Muscle Power Output Characteristics of Below-Knee Amputees During Running: The Influence of Energy Storing Prosthetic Feet. J. Biomechanics 24, 1: 63-75.
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Biomechanics of trans-tibial amputee running gait compared to normal
running
Ilse Vermeulen POR31PGA 2001
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