STANCE-PHASE KINEMATICS AND KINETICS OF EMU LEVEL WALKING +*Brown, TD; **Derrick, TR; *Pedersen, DR; *Goetz, JE; **Robinson, DA; **Conzemius, MG +*University of Iowa, Iowa City, IA [email protected] INTRODUCTION: Quadrupedal animal models conventionally used for orthopaedic research have the limitation of potentially off-loading the study limb, a substantial confounding factor in situations where habitual mechanical stimulus affects pathogenesis or therapeutic response. Among plausible bipedal animals for musculoskeletal research, the emu (Dromaius novaehollandiae) is a little-explored alternative that holds attractions of large physical size (40-60 kg), high activity level (~2M steps/year), modest purchase expense (~$150), ease of maintenance, and reasonable homology with the human in many aspects of anatomy and physiology [1]. Another relevant consideration, however, is the emu’s level of homology with the human in terms of lower extremity functional biomechanics. Toward addressing that issue, we performed a study to collect kinematic and kinetic data for the stance phase of emu normal level walking. METHODS: Emus raised agriculturally are semi-domesticated animals that by temperament tend to be apprehensive/resistive to interaction with humans, thus posing difficulties for laboratory gait analysis. To overcome that problem, two emus were raised to maturity (one year) from hatchlings with daily habituation to a gait laboratory setting by (leashed) training walks, along with representative handler touching. For the actual experimental measurements, eight retro-reflective markers were attached to each emu: three on the pelvis, three on the femur and two on the tibiotarsus (Figure 1b-white). The hock, subtalar, and distal second interphalangeal joint centers were readily visible discrete anatomic locations digitizable without need for reflective markers Three video came (Figure 1b-green). of ff u ecorded, with p was rdinate of s. e with a distinctly smooth, almost “knifing-like” gait n t 0% and s showed r DISCUSSION: Owing to overlying soft tissue mass, especially that surrounding the g the respective contribution of hip joint versus knee ry e hip u - [1]Conzemius, MG, et al. J Orthop Res 20, 2002; 303-309. he Emu as a Model for Necrotic Femoral Head 2. **Iowa State University, Ames, IA NIH AR 49919 ras were used to image the emus as they walked down a walkway and across a force platform. The video and force platform were synchronized using an adjustable threshold sync box connected to the vertical force channel of the force platform. When approximately 10 N of force was sensed by the force platform, the sy box sent a signal to the analog to digital card and simultaneously stimulated two light emitting diodes that could be seen in the field view of the cameras. Video frames were split into fields to achieve a sampling rate of 60 Hz. Video data were low-pass filtered using a cut-o of 4 Hz. The force platform data were sampled at 600 Hz, low-pass filtered at 15 Hz, and downsampled to match the kinematic sampling rate. For this study five walking trials were analyzed for each emu. Em #1 (BW = 294 N) had a walking velocity of 1.01±0.16 m/s, and Emu 2 (BW = 361 N) had a walking velocity of 1.39±0.27 m/s. Prior to the walking trials, a normal standing trial was r nc joint angle excursions during walking being calculated relative to this standing datum. The hip axis of rotation was located by moving the hi surface marker medially 33.2% of the trochanter-to-trochanter distance plus ½ the surface marker diameter. For Emu # 1 this distance was 0.0651 m and for Emu # 2 it was 0.0753 m. The knee joint location obtained by averaging markers 5 and 6 in the vertical and anterioposterior directions, and using the medial lateral coo marker 8 during the standing trial. The knee joint location was then assumed to remain stationary relative to the markers on the tibiotarsu Cardan angles were calculated based on a flexion-adduction-internal rotation order. Ensemble averages (±1 s.d.) of the five trials were calculated for vertical ground reaction force, as well as hip and kne sagittal and frontal plane movement for each animal. RESULTS: Emus walk pattern seemingly evolved to minimize center-of-gravity acceleratio (See emuvid.avi). They conspicuously place the newly contacting foo in close sagittal-plane alignment with the stance foot, as if deliberately to minimize side-to-side sway. The vertical ground reaction force waveforms for study both animals were distinctly bimodal, with approximately equal peaks of nominally 2xBW occurring at 15-2 65-75% of stance phase (Figure 2). Both animals showed good trial-to- trial repeatability of GRF waveform morphology (± 1 s.d. shown for Emu 1), although the nuances of their respective individual waveform differed somewhat. Compared to the GRF waveforms, the two birds’ flex/extension waveforms were appreciably more idiosyncratic individually, and much less repeatable (Figure 3). Both animals very little ad/abduction of the hip joint (motion range ~ 7º), but had appreciable apparent ad/abduction at the knee (range ~ 45º), the latte accruing nominally linearly in time throughout stance. a b Figure 2. Ground reaction force (GRF) of both emus normalized to body weight. Dashed lines are +/-1 standard deviation. Figure 3. Flexion and extension angles for hip and knee of both emus. hip, distinguishin Figure 1. a.)Digitized markers during standing trial. b.)Marker location relative to emu osseous anatom joint motion to net tibio-tarsal angulation was presumably much more prone to marker motion artifact than is typically the case for gait analysis of human subjects. This probably accounts for much of the apparently idiosyncratic features of the individual flex/extension waveforms at the hip and knee joints, although the sums of those two angulations were much more consistent between animals. The ve small motion range for hip joint ad/abduction is well below that necessary to engage articular contact of the antitrochanter (~16º) [2], suggesting habitual mono-compartmental load transmission at th during normal level ambulation. The two stance-phase peaks in the GRF waveform were less pronounced that those typical of human motion, consistent with the noticeably smooth, twist-free nature of em motion. Plausibly, this is an adaptation to unavailability of counter balance by motion of the upper extremities, since the wings are vestigial in this flightless species. REFERENCES: y. [2]Reed, KL. “T Collapse.” PhD Thesis, University of Iowa, 2003; 124-13 AFFILIATED INSTITUTIONS FOR CO-AUTHORS: ACKNOWLEDGEMENTS: Paper No: 0420 52nd Annual Meeting of the Orthopaedic Research Society
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STANCE-PHASE KINEMATICS AND KINETICS OF EMU LEVEL WALKING
+*Brown, TD; **Derrick, TR; *Pedersen, DR; *Goetz, JE; **Robinson, DA; **Conzemius, MG +*University of Iowa, Iowa City, IA
[email protected] INTRODUCTION: Quadrupedal animal models conventionally used for orthopaedic research have the limitation of potentially off-loading the study limb, a substantial confounding factor in situations where habitual mechanical stimulus affects pathogenesis or therapeutic response. Among plausible bipedal animals for musculoskeletal research, the emu (Dromaius novaehollandiae) is a little-explored alternative that holds attractions of large physical size (40-60 kg), high activity level (~2M steps/year), modest purchase expense (~$150), ease of maintenance, and reasonable homology with the human in many aspects of anatomy and physiology [1]. Another relevant consideration, however, is the emu’s level of homology with the human in terms of lower extremity functional biomechanics. Toward addressing that issue, we performed a study to collect kinematic and kinetic data for the stance phase of emu normal level walking. METHODS: Emus raised agriculturally are semi-domesticated animals that by temperament tend to be apprehensive/resistive to interaction with humans, thus posing difficulties for laboratory gait analysis. To overcome that problem, two emus were raised to maturity (one year) from hatchlings with daily habituation to a gait laboratory setting by (leashed) training walks, along with representative handler touching. For the actual experimental measurements, eight retro-reflective markers were attached to each emu: three on the pelvis, three on the femur and two on the tibiotarsus (Figure 1b-white). The hock, subtalar, and distal second interphalangeal joint centers were readily visible discrete anatomic locations digitizable without need for reflective markers
Three video came
(Figure 1b-green).
of
ff
u
ecorded, with
p
was
rdinate of
s.
e
with a distinctly smooth, almost “knifing-like” gait n
t
0% and
s
showed
r
DISCUSSION: Owing to overlying soft tissue mass, especially that surrounding the
g the respective contribution of hip joint versus knee
ry
e hip
u -
[1]Conzemius, MG, et al. J Orthop Res 20, 2002; 303-309. he Emu as a Model for Necrotic Femoral Head
2.
**Iowa State University, Ames, IA
NIH AR 49919
ras were used to image the emus as they walked down a walkway and across a force platform. The video and force platform were synchronized using an adjustable threshold sync box connected to the vertical force channel of the force platform. When approximately 10 N of force was sensed by the force platform, the sybox sent a signal to the analog to digital card and simultaneously stimulated two light emitting diodes that could be seen in the field view of the cameras. Video frames were split into fields to achieve a sampling rate of 60 Hz. Video data were low-pass filtered using a cut-oof 4 Hz. The force platform data were sampled at 600 Hz, low-pass filtered at 15 Hz, and downsampled to match the kinematic samplingrate. For this study five walking trials were analyzed for each emu. Em#1 (BW = 294 N) had a walking velocity of 1.01±0.16 m/s, and Emu 2 (BW = 361 N) had a walking velocity of 1.39±0.27 m/s. Prior to the walking trials, a normal standing trial was r
nc
joint angle excursions during walking being calculated relative to this standing datum. The hip axis of rotation was located by moving the hisurface marker medially 33.2% of the trochanter-to-trochanter distance plus ½ the surface marker diameter. For Emu # 1 this distance was 0.0651 m and for Emu # 2 it was 0.0753 m. The knee joint location obtained by averaging markers 5 and 6 in the vertical and anterioposterior directions, and using the medial lateral coo
marker 8 during the standing trial. The knee joint location was then assumed to remain stationary relative to the markers on the tibiotarsuCardan angles were calculated based on a flexion-adduction-internal rotation order. Ensemble averages (±1 s.d.) of the five trials were calculated for vertical ground reaction force, as well as hip and knesagittal and frontal plane movement for each animal. RESULTS: Emus walkpattern seemingly evolved to minimize center-of-gravity acceleratio(See emuvid.avi). They conspicuously place the newly contacting fooin close sagittal-plane alignment with the stance foot, as if deliberately to minimize side-to-side sway. The vertical ground reaction force waveforms for study both animals were distinctly bimodal, with approximately equal peaks of nominally 2xBW occurring at 15-265-75% of stance phase (Figure 2). Both animals showed good trial-to-trial repeatability of GRF waveform morphology (± 1 s.d. shown for Emu 1), although the nuances of their respective individual waveformdiffered somewhat. Compared to the GRF waveforms, the two birds’ flex/extension waveforms were appreciably more idiosyncratic individually, and much less repeatable (Figure 3). Both animals very little ad/abduction of the hip joint (motion range ~ 7º), but had appreciable apparent ad/abduction at the knee (range ~ 45º), the latteaccruing nominally linearly in time throughout stance.
a b
Figure 2. Ground reaction force (GRF) of both emus normalized to body weight. Dashed lines are +/-1 standard deviation.
Figure 3. Flexion and extension angles for hip and knee of both emus.
hip, distinguishin
Figure 1. a.)Digitized markers during standing trial. b.)Marker location relative to emu osseous anatom
joint motion to net tibio-tarsal angulation was presumably much more prone to marker motion artifact than is typically the case for gait analysis of human subjects. This probably accounts for much of the apparently idiosyncratic features of the individual flex/extension waveforms at the hip and knee joints, although the sums of those two angulations were much more consistent between animals. The vesmall motion range for hip joint ad/abduction is well below that necessary to engage articular contact of the antitrochanter (~16º) [2], suggesting habitual mono-compartmental load transmission at thduring normal level ambulation. The two stance-phase peaks in the GRF waveform were less pronounced that those typical of human motion, consistent with the noticeably smooth, twist-free nature of emmotion. Plausibly, this is an adaptation to unavailability of counterbalance by motion of the upper extremities, since the wings are vestigial in this flightless species. REFERENCES:
y.
[2]Reed, KL. “T Collapse.” PhD Thesis, University of Iowa, 2003; 124-13 AFFILIATED INSTITUTIONS FOR CO-AUTHORS: ACKNOWLEDGEMENTS:
Paper No: 042052nd Annual Meeting of the Orthopaedic Research Society
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