J. Anim Sci. 2008. 86:992-998. doi:10.2527/jas.2007-0581
© 2008 American Society of Animal Science
OPEN ACCESS ARTICLE
Net joint kinetics in the limbs of pigs walking on concrete floor in dry and contaminated conditions1
V. M. Thorup*,
,2,
B. Laursen
and
B. R. Jensen
* Department of Animal Health, Welfare and Nutrition, Faculty of Agricultural Sciences, University of Aarhus, Dk-8830 Tjele, Denmark,
and
Department of Exercise and Sport Sciences, Faculty of Science, University of Copenhagen, Dk-2200 Copenhagen N, Denmark, and and
National Institute of Public Health, University of Southern Denmark, Dk-1399 Copenhagen K, Denmark
 |
Abstract
|
|---|
In pigs (Sus scrofa), joint disorders are frequent leg problems, and inappropriate pigpen floors and slippery floor conditions may contribute to these problems. Therefore, this study first aimed to quantify the net joint kinetics (net joint moments and net joint reaction forces) in the forelimbs and hindlimbs of healthy pigs walking on solid concrete floors. Second, this study aimed to examine the effect of floor condition on the net joint kinetics. Kinematic (50-Hz video recordings) and kinetic (1-kHz force plate measurements) data were collected from 30 pigs and combined with body segment parameters from a cadaver study. Net joint kinetics was calculated by using a 2-dimensional inverse dynamic solution. Inverse dynamics have, to our knowledge, not been applied in pigs before. Dry, greasy, and wet floor conditions were tested with 10 pigs each. In the forelimbs, peak joint moment was less (P < 0.01) on greasy (0.184 ± 0.012 Nm/kg, moment of force per kg of BW) than on dry (0.232 ± 0.012 Nm/kg) or wet (0.230 ± 0.012 Nm/kg) conditions. Additionally, the minimum forelimb joint moment was more negative (P < 0.05) on greasy (–0.119 ± 0.009 Nm/kg) than on dry or wet (both –0.091 ± 0.009 Nm/kg) conditions. The forelimb joint reaction forces and the hindlimb joint kinetics were unaffected by floor condition. The greatest (P < 0.001) joint moments occurred in the shoulder (–0.376 ± 0.007 Nm/kg), elbow (0.345 ± 0.009 Nm/kg), hip (0.252 ± 0.009 Nm/kg), and tarsal (0.329 ± 0.009 Nm/kg) joints, which may be related to the greater incidence of joint diseases in some of these joints. In conclusion, the forelimb joints of the pigs responded more markedly to floor condition than did their hindlimb joints, probably because the forelimbs carry more weight. In particular, between the dry and greasy floor conditions, the joint loading differed, most likely because the pigs adapted to a potentially slippery surface.
Key Words: floor condition • gait analysis • inverse dynamics • joint moment • pig
|
INTRODUCTION
|
|---|
In modern pig production, leg problems, including joint diseases and locomotor disorders, form a severe and frequent welfare issue often exacerbated by inappropriate floors (Jørgensen, 2003
). Many leg problems are related to the loading or internal forces acting on the involved structures; thus, joint degeneration has been associated with abnormal joint loading (Radin and Paul, 1971). Additionally, cartilage and bone overloading seem to trigger development of osteochondrosis and osteoarthrosis in the joints of sows (Grøndalen, 1974b).
Through inverse dynamics, joint moments and joint reaction forces (JRF) can be quantified. Net joint moments describe the net torque produced by muscles, tendons, and ligaments. Correspondingly, the net JRF describes the net force acting across a joint because of the reaction force from the floor. The joint moments and JRF are calculated by using an inverse dynamic model, taking kinematic and kinetic data from moving animals and body segment parameters as input. In quadrupeds, inverse dynamics has been applied to quantify the joint moments of walking horses (Colborne et al., 1998; Clayton et al., 2000, 2001). Furthermore, joint moments in the forelimbs of walking dogs (Nielsen et al., 2003) and in dogs with and without hip replacements (Dogan et al., 1991) have been calculated. In pigs however, neither joint moments nor JRF have been quantified.
Pigs adapt their gait to potentially slippery floors by lowering their walking speed and reducing their peak utilized coefficient of friction on greasy and wet (contaminated) floors compared with dry floors. Moreover, pigs shorten their progression length and prolong their stance phase duration on greasy floors compared with dry and wet floors (Thorup et al., 2007a). We hypothesized that floor condition also affects the net joint kinetics in pigs. This study aimed 1) to quantify net joint moments and JRF in healthy pigs walking on solid concrete floor, and 2) to examine the effect of floor condition on net joint kinetics.
|
MATERIALS AND METHODS
|
|---|
Animals and Procedures
The study complied with the guidelines for animal studies given by Sherwin et al. (2003). Further, it was noninvasive and did not subject any pigs to floor conditions more extreme than those occurring in normal intensive pig production.
The pigs and procedures have been described previously (Thorup et al., 2007a). In brief, 30 healthy Duroc x Yorkshire x Landrace crossbred pigs were used. Pigs weighed 75 ± 6 kg and showed no signs of lameness; that is, they walked without limping when allowed to walk on solid floors outside their home pen. Moreover, the behavior and gait of the pigs complied with the description of a lameness score of 0, as defined by Main et al. (2000). The pigs walked individually and at a self-selected, steady speed on a solid concrete floor (flag-stone, Perstrup Concrete Industry A/S, Kolind, Denmark) along a narrow aisle. Dry, wet (water), and greasy (rapeseed oil) floor conditions were tested with 3 different groups of 10 pigs each, because we wanted pigs to have no previous experience with the test floor. From the right limbs of each pig, 3 to 4 successful measurements were obtained, during which kinematic and kinetic data were collected simultaneously.
Recording Techniques
At 50 Hz, a digital video camera (Panasonic NV-DS30EG, Panasonic Denmark, Glostrup, Denmark) recorded the central 1.4 m of the aisle from the right side in the sagittal plane. Seven markers on each right limb, approximately 13 mm in diameter, were painted with white acrylic paint on the pigs (Figure 1). The locations of the joint axes of rotation of the shoulder, elbow, carpal complex, forefetlock, hip, stifle, tarsal, and hindfetlock joints were established in a previous study (Thorup et al., 2007b), which formed the basis of the marker placement.
View larger version (36K):
[in this window]
[in a new window]
|
Figure 1. Marker locations and joint names for the pigs. F = forelimb, H = hindlimb, F1 = spinous tuber of scapula, F2 = caudal part of major tubercle (shoulder), F3 = condyle of humerus (elbow), F4 = carpal bone IV (carpal complex), F5 = distal on metacarpal bone IV (fetlock), F6 = coronary band (coffin), F7 = distal on claw wall of the distal phalanx of fourth digit, H1 = tuber coxae; H2 = caudal part of major trochanter (hip), H3 = lateral condyle of femur (stifle), H4 = distal part of calcaneus (tarsal), H5 = distal on metatarsal bone IV (fetlock), H6 = coronary band (coffin), and H7 = distal on claw wall of the distal phalanx of fourth digit. Joint flexion is indicated by the arrows.
|
|
The kinetic protocol has been described in detail (Thorup et al., 2007a). Briefly, 3 perpendicular ground reaction forces (vertical, anteposterior horizontal, mediolateral horizontal) and their corresponding moments were sampled at 1 kHz from a 0.20 x 0.30-m2 force plate (MU2030, Bertec Corporation, Columbus, OH). The force plate was mounted in the central part of the aisle with the test floor on it and was invisible to the pigs. The resolution of the moment signal was 0.02 Nm/bit.
Inverse Dynamics
The kinematic and kinetic data were combined with the mass, length, relative center of mass location, and moment of inertia of the limb segments from a previous study (Thorup et al., 2007b). Joint kinetics (net joint moments and net joint reaction forces) were calculated by using a 2-dimensional (2D), inverse, dynamic, linked segment model. Thus far, inverse dynamics have not been applied in pigs. Each limb was modeled, and each consisted of 6 segments; thus, the forelimb consisted of the foot, pastern, metacarpus, radiusulna, and humerus; and the hindlimb consisted of the hindfoot, hind-pastern, metatarsus, tibia, and femur, thereby assuming that movement occurring in the pastern joint was negligible (Meershoek and van den Bogert, 2001). Assumptions to the model were that the segments were rigid, that the joints linking the segments were ideal hinge joints, and that movement was pure rotation around a fixed axis (Winter, 2004). Positive joint moments were defined such that counterclockwise moments acting on a segment distal to the joint were positive, whereas clockwise moments were negative. The extensor side was the cranial side for the elbow, hip, and tarsal joints and was the caudal side for the other joints (Figure 1
).
Data Processing
The video sequences were digitized by using Pinnacle Studio, version 8 (Pinnacle Systems, Inc., Mountain View, CA), and 2D coordinates were constructed and digitally low-pass filtered by a fourth-order Butterworth filter with a cutoff frequency of 8 Hz by using APAS (Ariel Dynamics Inc., Trabuco Canyon, CA). The filter cutoff frequency was determined based on a frequency analysis. Positional data were used to calculate 1) linear velocities (first derivative) and accelerations (second derivative) of segment end points; and 2) segment angles, defined as the angle between the segment and horizontal. Angular velocities and accelerations were then determined by the first and second derivates, respectively. Kinetic data were downsampled to 50 Hz and normalized in magnitude by BW. All data were normalized in time by interpolating data points to form 100 samples for each stance phase by fitting a cubic spline to the data. All calculations were made with MATLAB (2002, The MathWorks Inc., Natick, MA). The peak and minimum net joint moments (Nm/kg) and the peak vertical JRF (N/kg) were calculated for all joints.
Statistical Analysis
Comparisons between floor conditions and between joints were made in a 2-way ANOVA. The 3 response variables were tested separately in a repeated measurement model with PROC MIXED (SAS Inst. Inc., Cary, NC). Floor condition and joint were modeled as systematic effects, including the 2-way interaction between floor condition and joint. Random effects were the residual error term along with a repeated effect accounting for the correlations between joints for each pig. All random terms were considered independent. Residual analysis was used to verify the assumptions regarding normality of data and variance homogeneity. The means of 3 to 4 trials per limb per pig were calculated. Furthermore, differences between joints were compared within limbs only. The 3 floor conditions, 10 pigs per condition, and 5 joints per pig amounted to 150 observations per limb for each variable. Results are presented as least squares means with SE. A level of significance of 5% is used throughout unless otherwise mentioned.
|
RESULTS
|
|---|
The joint moment time-course patterns were similar across floor conditions (Figure 2). The shoulder moment had a small flexor-dominated peak around 16% stance phase, which then shifted to extensor domination with a large negative minimum around 76% stance. The elbow moment increased quickly toward an extensor-dominated peak around 26% stance, then declined to flexor domination having a negative minimum at 95% stance. The carpal joint was entirely flexor dominated. The flexor dominated fore- and hindfetlock joint moments had similar patterns, rising moderately toward the peaks around 73 and 62%, respectively. The flexor-dominated fore- and hindcoffin joint moment patterns were also alike, with slow increases until peaking at approximately 78% stance. The mainly extensor-dominated hip moment peaked around 38% stance, with only a short flexor-dominated period with a minimum at 90% stance. The stifle moment was initially small, with a flexor-dominated peak around 18% stance; it then shifted to extensor domination, with a negative minimum around 80% stance. The entirely extensor-dominated tarsal joint moment peaked around 37% stance.
View larger version (21K):
[in this window]
[in a new window]
|
Figure 2. Net joint moments (Nm/kg) of the hindlimb (left column) and forelimb (right column) for the 3 floor conditions; n = 10 pigs per condition. Asterisks indicate significant differences between the greasy (G) vs. the dry (D) or wet (W) floor conditions. The mean SD is indicated on each panel for each floor condition.
|
|
Floor condition affected the forelimb joint moment magnitudes (Figure 2). Thus, in the forelimbs, the greasy condition lowered (P < 0.01) the peak moment (by 21%) compared with the dry and wet conditions. Moreover, the minimum moment was more negative (P < 0.05) on the greasy condition (24%) compared with the dry and wet conditions. Because no interaction between floor condition and joint was found for any of the response variables (P > 0.05), for simplicity, all joints were pooled when looking at the effect of floor condition on each of the response variables (Table 1).
View this table:
[in this window]
[in a new window]
|
Table 1. Peak and minimum net joint moments (Nm/kg) and peak vertical joint reaction force (JRF, N/kg) of the fore- and hindlimbs of pigs for the 3 floor conditions1
|
|
The majority of the joints differed with regard to both peak and minimum moments. Because no interaction between floor condition and joint was found for any of the response variables (P > 0.05), for simplicity, all floor conditions were pooled when looking at the effect of joint on the response variables (Table 2). The greatest moment amplitudes (i.e., the range between the peak and minimum moments) in the forelimb were in the shoulder and elbow joints. In the shoulder, the large range was caused by a very negative moment, whereas in the elbow the range was due to a very high peak moment. In the hindlimbs, the greatest joint moment amplitudes were in the hip and tarsal joints, which both showed considerable peak and minimum moments.
View this table:
[in this window]
[in a new window]
|
Table 2. Peak and minimum net joint moments (Nm/kg) and peak vertical joint reaction force (JRF, N/kg) of the fore- and hindlimb joints of pigs1
|
|
Floor condition did not affect peak vertical JRF of the forelimb (P = 0.69) or the hindlimb (P = 0.42) (Table 1). Most joints differed within limb; thus, peak vertical JRF was greatest in the distal joints (P < 0.001) and decreased when moving proximally (Table 2).
|
DISCUSSION
|
|---|
The main findings of this study confirmed the hypothesis that floor condition affects the joint moments in walking pigs. Furthermore, the forelimbs responded more clearly to floor condition than did the hindlimbs.
The overall walking patterns of the pigs were similar on the 3 floor conditions with regard to joint moments. Nevertheless, the greasy, and potentially more slippery, floor displaced several dynamic features compared with the dry floor. Thus, the forelimb peak moment decreased and the minimum moment was more negative on the greasy condition than on the dry condition. The hindlimb net joint moments were unaffected by floor condition. The magnitude of decrease in the joint moments of the pigs as a response to the greasy floor agreed well with findings in humans. Thus, in walking humans, the anticipation of slippery floors lowered the peak ankle, knee, and hip moments by 24 to 30% (Cham and Redfern, 2002). Furthermore, as reported elsewhere (Thorup et al., 2007a), the walking speeds of pigs were 0.88 ± 0.03 m/s on dry floor, 0.79 ± 0.03 m/s on wet floor, and 0.74 ± 0.03 m/s on greasy floor. Thus, pigs reacted to contaminated conditions by walking slower than they did in the dry condition. Moreover, pigs walking on the greasy floor reduced their peak utilized coefficient of friction and took shorter steps compared with pigs walking on the dry floor (Thorup et al., 2007a). Hence, the displaced joint moments reported here were most likely consequences of the gait adaptations made by the pigs walking on the greasy floor.
Compared with other quadrupeds, the net joint moment patterns of pigs in this study were, to some extent, similar to those of horses (Colborne et al., 1998; Clayton et al., 2000, 2001), except that Colborne et al. (1998) defined the flexor side of the fetlock to be on the cranial joint side, thus resulting in the horses’ fetlock joint being dominated by an extensor moment. Further, the hip moment of the pigs was more extensor dominated than that of the horses. When the fetlock, carpal, and elbow joint moments of the pigs were compared with the corresponding joints of dogs, similarities were also evident (Nielsen et al., 2003). Although being normalized to BW, net joint moment magnitudes of pigs in the current study were smaller than those reported for horses (Colborne et al., 1998; Clayton et al., 2000, 2001), which may be caused by differences in body conformation and limb anatomy. The deviating magnitudes may, however, also be caused by different modeling approaches. In the current study, 2D data acquisition was used, in which some out-of-plane movement occurs, which would have been captured by the 3D approach used in the equine studies. Nevertheless, a comparison of 2D vs. 3D approaches in human walking showed that the joint moment patterns were identical, although differences in peak and minimum values occurred (Alkjær et al., 2001). Therefore, we were convinced that the simpler 2D solution was adequate for a biomechanical quantification of gait patterns in walking pigs.
In pigs, joint disorders occur in several joints (Nakano et al., 1987); however, the most frequent site of osteochondrotic lesions in the forelimbs is the elbow (Grøndalen, 1974a; Jørgensen, 2000; Jørgensen and Andersen, 2000). In the hindlimbs, the stifle and, to a lesser extent, the hip are frequent sites of osteochondrotic lesions (Grøndalen, 1974a; Jørgensen et al., 1995). This study found high net joint moment amplitudes in the shoulder, elbow, hip, and tarsal joints, which may help explain why joint diseases occur more frequently in the proximal than in the distal joints. However, because the net joint moments represent only a summation of all muscles acting across a joint, it is impossible to distinguish which muscle groups are creating the joint moment or to calculate the level of muscle activity (Winter, 1987). To make this distinction, a partitioning of the individual muscle forces is needed, for instance by measuring electromyography as done by Chambers and Cham (2007), who demonstrated in walking humans a more powerful muscular knee and ankle activity when the test person expected a slippery surface. Thus, it is possible that the muscle activity of the pigs walking on a greasy floor was high despite the lowered peak and minimum net joint moments observed in this study. Furthermore, humans suffering from moderate osteoarthritis in the knee have a reduced net knee joint flexion moment during the early stance phase compared with a control group without osteoarthritis (Landry et al., 2007). Therefore, it could be hypothesized that net joint moments in pigs suffering from joint disorders would be lowered as well.
Likewise, the net JRF, based on inverse dynamics, does not include forces caused by muscle co-contraction; therefore, the total JRF (bone-on-bone force) may be underestimated. The bone-on-bone force can be calculated by adding the muscle force to the net JRF. Muscle force can be obtained by dividing the joint moment by the moment arm of the dominating muscle group (Simonsen et al., 1995). To our knowledge, the moment arms of pigs’ muscles have not been examined. From a previous study on joint rotation axes (Thorup et al., 2007b), we roughly estimated the moment arm of the pigs’ elbow joint to be 0.05 m. Combined with the peak joint moment and peak JRF from the current study (Table 2), the estimate of the elbow moment arm allowed us to estimate the bone-on-bone force of the pig’s elbow in the following way: (0.345 Nm/kg x 0.05 m–1) + 5.52 N/kg = 12.42 N/kg. Thus, the contribution of the JRF to the bone-on-bone force is approximately 44% in the elbows of walking pigs. In the knees of humans, the contribution of the JRF is approximately 25% at peak bone-on-bone force during level walking (Kuster et al., 1997). Therefore, the JRF in pigs may contribute considerably more to the bone-on-bone forces compared with that in humans.
Pigs in the current study were more affected by floor property in their forelimbs than in their hindlimbs. This was in agreement with a study of younger pigs walking on differing wet concrete floors (Applegate et al., 1988), in which pigs’ forelimbs slipped more and longer and showed more changes in angular measurements compared with their hindlimbs. In addition, pigs carried 54% of the load on their forelimbs, as reported elsewhere (Thorup et al., 2007a). Thus, their larger load may explain why forelimbs responded kinetically more clearly to the floor condition than did the hindlimbs.
The kinematic part of this study was based on skin markers, which were subject to movement over the skeletal structures, movements that may potentially have introduced measurement errors. Skin displacements in the proximal (van Weeren et al., 1990) and distal limb parts (van Weeren et al., 1988) of walking horses have been quantified. Moreover, correction models for skin displacement in horses have been presented (van Weeren et al., 1992). These equine studies showed that skin displacement was larger in the more proximal joints than in the distal joints, was larger in the fore-than in the hindlimb, and took place mainly during the swing phase. In pigs, skin displacement has not been investigated, and the correction model for horses could not be used because the anatomy of the horse and pig differ to some extent; therefore, the effect of skin displacement on the findings of the current study remains unclear. Nevertheless, this study reported stance phase results only, during which errors arising from skin displacement presumably are minimal.
The current study provided a basic characterization of the physiological loading of the fore- and hindlimb joints in healthy pigs from a homogeneous population walking on different floor conditions. In horses, peak vertical ground reaction forces have been shown to differ between breeds (Back et al., 2007). Further, the forelimb bone lengths and muscle weights in Duroc pigs were affected by selection for leg weakness (Draper et al., 1988). Joint moments too may depend on breed, which should be taken into account in future biomechanical studies of pigs differing from the breed used here. Our study presented a normative benchmark to compare with data from lame pigs, thus enabling lameness diagnostics. Our data allow comparisons with pigs that have had operations or surgical implants, because pigs are increasingly used as model animals for humans.
In conclusion, this study showed that the greasy floor condition caused changes in gait biomechanics when compared with pigs walking on a dry floor, whereas the wet condition seemed more intermediate. As a consequence of adapting to a potentially slippery surface, the forelimb joint moments were displaced to a lower level on the greasy floor compared with the dry and wet floors. The forelimb joints of the pigs responded more obviously to the floor condition than their hindlimb joints, probably because the forelimbs carry more weight. Future studies should seek to quantify the level of muscle activity, which may be high on a greasy floor despite the lowered joint moments observed in this study.
|
Footnotes
|
|---|
1 This study was part of project no. 3412-04-00114 funded by The Danish Ministry of Food, Agriculture and Fisheries. We thank our colleagues at the University of Aarhus: B. Jørgensen for conceiving of the project, F. A. Tøgersen for statistical advice, and B. L. Nielsen for commenting on the manuscript. 
2 Corresponding author: vivim.thorup{at}agrsci.dk
Received for publication September 13, 2007.
Accepted for publication December 20, 2007.
|
LITERATURE CITED
|
|---|
Alkjær, T., E. B. Simonsen, and P. Dyhre-Poulsen. 2001. Comparison of inverse dynamics calculated by two- and three-dimensional models during walking. Gait Posture 13:73–77.[CrossRef][Medline]
Applegate, A. L., S. E. Curtis, J. L. Groppel, J. M. McFarlane, and T. M. Widowski. 1988. Footing and gait of pigs on different concrete surfaces. J. Anim. Sci. 66:334–341.[Abstract/Free Full Text]
Back, W., C. G. MacAllister, M. C. van Heel, M. Pollmeier, and P. D. Hanson. 2007. Vertical frontlimb ground reaction forces of sound and lame Warmbloods differ from those in Quarter Horses. J. Equine Vet. Sci. 27:123–129.[CrossRef]
Cham, R., and M. S. Redfern. 2002. Changes in gait when anticipating slippery floors. Gait Posture 15:159–171.[CrossRef][Medline]
Chambers, A. J., and R. Cham. 2007. Slip-related muscle activation patterns in the stance leg during walking. Gait Posture 25:565–572.[CrossRef][Medline]
Clayton, H. M., E. Hodson, and J. L. Lanovaz. 2000. The forelimb in walking horses: 2. Net joint moments and joint powers. Equine Vet. J. 32:295–299.[CrossRef][Medline]
Clayton, H. M., E. Hodson, J. L. Lanovaz, and G. R. Colborne. 2001. The hindlimb in walking horses: 2. Net joint moments and joint powers. Equine Vet. J. 33:44–48.[Medline]
Colborne, G. R., J. L. Lanovaz, E. J. Sprigings, H. C. Schamhardt, and H. M. Clayton. 1998. Forelimb joint moments and power during the walking stance phase of horses. Am. J. Vet. Res. 59:609–614.[Medline]
Dogan, S., P. A. Manley, R. Vanderby Jr., S. S. Kohles, L. M. Hartman, and A. A. McBeath. 1991. Canine intersegmental hip joint forces and moments before and after cemented total hip replacement. J. Biomech. 24:397–407.[CrossRef][Medline]
Draper, D. D., M. F. Rothschild, and L. L. Christian. 1988. Effects of divergent selection on muscle, tendon, and bone characteristics of three lines of Duroc swine with differing degrees of leg weakness. Anat. Histol. Embryol. 17:365. (Abstr.)
Grøndalen, T. 1974a. Leg weakness in pigs. I. Incidence and relationship to skeletal lesions, feed level, protein and mineral supply, exercise and exterior conformation. Acta Vet. Scand. 15:555–573.[Medline]
Grøndalen, T. 1974b. Osteochondrosis and arthrosis in pigs. IV. Effect of overloading on the distal epiphyseal plate of the ulna. Acta Vet. Scand. 15:53–60.[Medline]
Jørgensen, B. 2000. Osteochondrosis/osteoarthrosis and claw disorders in sows, associated with leg weakness. Acta Vet. Scand. 41:123–138.[Medline]
Jørgensen, B. 2003. Influence of floor type and stocking density on leg weakness, osteochondrosis and claw disorders in slaughter pigs. Anim. Sci. 77:439–449.
Jørgensen, B., and S. Andersen. 2000. Genetic parameters for osteochondrosis in Danish Landrace and Yorkshire boars and correlations with leg weakness and production traits. Anim. Sci. 71:427–434.
Jørgensen, B., J. Arnbjerg, and M. Aaslyng. 1995. Pathological and radiological investigations on osteochondrosis in pigs, associated with leg weakness. J. Vet. Med. A 42:489–504.
Kuster, M. S., G. A. Wood, G. W. Stachowiak, and A. Gächter. 1997. Joint load considerations in total knee replacement. J. Bone Joint Surg. 79-B:109–113.[CrossRef]
Landry, S. C., K. A. McKean, C. L. Hubley-Kozey, W. D. Stanish, and K. J. Deluzio. 2007. Knee biomechanics of moderate OA patients measured during gait at a self-selected and fast walking speed. J. Biomech. 40:1754–1761.[CrossRef][Medline]
Main, D. C. J., J. Clegg, A. Spatz, and L. E. Green. 2000. Repeatability of a lameness scoring system for finishing pigs. Vet. Rec. 147:574–576.[Free Full Text]
Meershoek, L. S., and A. J. van den Bogert. 2001. Mechanical analysis of locomotion. Pages 305–326 in Equine Locomotion. W. Back and H. M. Clayton, ed. W. B. Saunders, London, UK.
Nakano, T., J. J. Brennan, and F. X. Aherne. 1987. Leg weakness and osteochondrosis in swine: A review. Can. J. Anim. Sci. 67:883–901.
Nielsen, C., S. M. Stover, K. S. Schulz, M. Hubbard, and D. A. Hawkins. 2003. Two-dimensional link-segment model of the forelimb of dogs at a walk. Am. J. Vet. Res. 64:609–617.[CrossRef][Medline]
Radin, E. L., and I. L. Paul. 1971. Response of joints to impact loading. Arthritis Rheum. 14:356–362.[Medline]
Sherwin, C. M., S. B. Christiansen, I. J. Duncan, H. W. Erhard, D. C. Lay Jr., J. A. Mench, C. E. O’Connor, and J. C. Petherick. 2003. Guidelines for the ethical use of animals in applied ethology studies. Appl. Anim. Behav. Sci. 81:291–305.[CrossRef]
Simonsen, E. B., P. Dyhre-Poulsen, M. Voigt, P. Aagaard, G. Sjøgaard, and F. Boisen-Møller. 1995. Bone-on-bone forces during loaded and unloaded walking. Acta Anat. (Basel) 152:133–142.[Medline]
Thorup, V. M., F. A. Tøgersen, B. Jørgensen, and B. R. Jensen. 2007a. Biomechanical gait analysis of pigs walking on solid concrete floor. Animal 1:708–715.[CrossRef]
Thorup, V. M., F. A. Tøgersen, B. Jørgensen, and B. R. Jensen. 2007b. Joint rotation axes and body segment parameters of pig limbs. Acta Vet. Scand. 49:20.[CrossRef][Medline]
van Weeren, P. R., A. J. van den Bogert, and A. Barneveld. 1988. Quantification of skin displacement near the carpal, tarsal and fetlock joints of the walking horse. Equine Vet. J. 20:203–208.[Medline]
van Weeren, P. R., A. J. van den Bogert, and A. Barneveld. 1990. Quantification of skin displacement in the proximal parts of the limbs of the walking horse. Equine Vet. J. (Suppl. 9):110–118.
van Weeren, P. R., A. J. van den Bogert, and A. Barneveld. 1992. Correction models for skin displacement in equine kinematic gait analysis. J. Equine Vet. Sci. 12:178–192.[CrossRef]
Winter, D. A. 1987. Mechanical power in human movement: Generation, absorption and transfer. Med. Sport Sci. 25:34–45.
Winter, D. A. 2004. Biomechanics and Motor Control of Human Movement. John Wiley & Sons Inc., Hoboken, NJ.
Top
Abstract
INTRODUCTION
