Objective—To design and fabricate fiberglass-reinforced composite (FRC) replicas of a canine radius and compare their mechanical properties with those of radii from dog cadavers.
Sample—Replicas based on 3 FRC formulations with 33%, 50%, or 60% short-length discontinuous fiberglass by weight (7 replicas/group) and 5 radii from large (> 30-kg) dog cadavers.
Procedures—Bones and FRC replicas underwent nondestructive mechanical testing including 4-point bending, axial loading, and torsion and destructive testing to failure during 4-point bending. Axial, internal and external torsional, and bending stiffnesses were calculated. Axial pullout loads for bone screws placed in the replicas and cadaveric radii were also assessed.
Results—Axial, internal and external torsional, and 4-point bending stiffnesses of FRC replicas increased significantly with increasing fiberglass content. The 4-point bending stiffness of 33% and 50% FRC replicas and axial and internal torsional stiffnesses of 33% FRC replicas were equivalent to the cadaveric bone stiffnesses. Ultimate 4-point bending loads did not differ significantly between FRC replicas and bones. Ultimate screw pullout loads did not differ significantly between 33% or 50% FRC replicas and bones. Mechanical property variability (coefficient of variation) of cadaveric radii was approximately 2 to 19 times that of FRC replicas, depending on loading protocols.
Conclusions and Clinical Relevance—Within the range of properties tested, FRC replicas had mechanical properties equivalent to and mechanical property variability less than those of radii from dog cadavers. Results indicated that FRC replicas may be a useful alternative to cadaveric bones for biomechanical testing of canine bone constructs.
Objective—To compare temporospatial variables (TSVs) and kinetic variables (KVs) for fore-limbs and hind limbs of small and large dogs of various breeds during walking and to determine associations among body weight (BW), TSVs, and KVs in these groups.
Animals—12 adult dogs with no evidence of lameness.
Procedures—Dogs (grouped according to BW as small [< 10 kg; n = 6] or large [> 25 kg; 6]) were walked in a straight line at their preferred velocity on a wooden platform with an embedded pressure-sensing walkway. Five valid trials were analyzed for each dog; mean TSVs and KVs were determined for each group. The TSVs and KVs for forelimbs and hind limbs were compared between groups, and correlations among BW, TSVs, and KVs were determined.
Results—Small dogs had significantly smaller TSVs and KVs than did large dogs. Temporal variables of small dogs and absolute vertical force variables of small and large dogs increased as BW increased. However, normalized peak vertical force and weight distribution values among the 4 limbs were similar between groups.
Conclusions and Clinical Relevance—Substantial similarities and differences were detected in gait characteristics between small and large dogs. Results indicated TSVs and KVs can be used for comparison of the walking gait between dogs or for comparison of variables between limbs in an individual dog. Use of the pressure-sensing walkway is a simple method for acquisition of TSVs and KVs for large and small dogs.
Objective—To evaluate the ability of industrial polystyrene foam insulation pads to redistribute loads placed on clinically normal weight-bearing structures of the foot and shift the location of the center of pressure palmarly in horses.
Animals—25 nonlame mature horses.
Procedures—Both forefeet from each horse were evaluated. Center of pressure data and solar load distribution patterns were recorded during a 5-second trial by use of a commercial pressure measurement system prior to placement of foam sole support and at 0, 6, 12, 24, and 48 hours after placement. Total contact surface area, contact pressure, peak contact pressure, and center of pressure positions were compared by use of a linear mixed model with repeated measurements.
Results—Total contact surface area was increased significantly at all time points, whereas contact pressure and peak contact pressure were significantly decreased at all time points following application of foam sole supports. Immediately following application of sole support, the position of the center of pressure was significantly moved cranially. However, by 48 hours, the center of pressure was significantly positioned more palmarly than prior to application of the foam supports.
Conclusions and Clinical Relevance—Results indicated that the use of foam sole supports may be an effective, economical, and immediate treatment for acute laminitis.
Objective—To quantify changes in hoof wall strain distribution associated with exercise and time in Standardbreds.
Animals—18 young adult Standardbreds.
Procedures—9 horses were exercised 4 d/wk for 30 to 45 minutes at a medium trot for 4 months; 9 nonexercised horses served as the control group. Rosette strain gauges were used to measure the principal surface strains at the toe, lateral quarter of the hoof wall (LQ), and medial quarter of the hoof wall (MQ) of the right forefoot at the beginning and end of the experiment. Midstance maximal (msϵ1) and minimal (msϵ2) principal and peak minimal principal (pkϵ2) surface strains were measured; SDs of each of those variables were also calculated. Results were compared through ANOVA of time and exercise effects between and within the groups.
Results—Both the exercised and nonexercised groups had changes in strain distribution in their hooves over time. The msϵ1 did not change significantly with exercise; however, it changed significantly in both groups at both hoof quarters over time. At the beginning of the study, mean msϵ2 and pkϵ2 values were significantly higher in the exercised group than in the control group at the MQ and LQ but not at the toe. At the end of the study, these values were significantly higher in the control group than in the exercised group at the toe but not at the MQ or LQ.
Conclusions and Clinical Relevance—Detected changes in hoof wall surface strain may indicate the ability of hoof capsule material to respond to exercise. A better understanding of hoof adaptation to applied forces may allow implementation of proper trimming and shoeing techniques to promote adaptation to exercise loads in horses.
Objective—To determine the effect of differences in structural and mechanical tendon properties on functionality of the passive stay apparatus in horses.
Sample—5 forelimbs each from nondwarf Friesians, dwarf Friesians, and ponies.
Procedures—Harvested forelimbs were loaded to test the passive stay apparatus. Tendons that stabilize the distal portion of the limb (superficial digital flexor tendon, deep digital flexor tendon, and tendo interosseus [suspensory ligament]) were isolated, and force-elongation data were obtained. Bone lengths, initial tendon lengths, and initial tendon cross-sectional areas were measured, and Young moduli were calculated. A model was used to determine whether joint angles could be explained by these 4 factors only.
Results—Dwarf limbs were unable to stand passively under loading because tendons that prevent overextension of the distal limb joints were too long and compliant to prevent over-extension. Tendon properties of limbs of nondwarf Friesians appeared to be intermediate between those of ponies and dwarf Friesians.
Conclusions and Clinical Relevance—Dysfunction of the passive stay apparatus in dwarf Friesians could be related to differences in structural and material properties of the tendons that result in hyperextension of the joints under loading. Nondwarf Friesians had intermediate tendon properties, which might be a breed-specific variation. Results indicated that certain tendon properties were associated with load failure of the stay apparatus and provided additional information about the functionality and requirements of the passive stay apparatus.
Objective—To evaluate symmetry of the hind limbs in orthopedically normal trotting dogs.
Animals—19 orthopedically normal Labrador Retrievers with no history of lameness.
Procedures—Retroreflective markers were applied to the hind limb joints, and a 4-camera kinematic system captured positional data at 200 Hz in tandem with force platform data collection while the dogs trotted. Morphometric data were combined with kinematic and force data in an inverse dynamics method to calculate net joint moments and powers at the joints as well as total support moment for each limb. Dogs were identified as right or left dominant when their total support moment was > 10% asymmetric between sides.
Results—10 of the 19 dogs were mechanically dominant in the right hind limb as determined by their total support moments. One dog was left dominant, and the remaining 8 were symmetric. Right-dominant dogs had larger net joint moments at the right hip, tarsal, and metatarsophalangeal joints and a smaller moment at the right stifle joint, compared with values for the left hind limb. The 1 left-dominant dog had the exact opposite findings. Hip and stifle joint moments and powers varied between limbs of the right-dominant and left-dominant groups in the timing of their transition from negative to positive, and power amplitudes varied at the hip, tarsal, and metatarsophalangeal joints but not the stifle joint.
Conclusions and Clinical Relevance—Sound trotting dogs can have asymmetries in limb and joint mechanics. These natural mechanical asymmetries should be taken into account when considering models to evaluate stresses at joints and when considering surgery for cruciate ligament rupture.
Objective—To assess the impact of partial immersion in water on vertical ground reaction force (vGRF) and vGRF distribution in dogs.
Animals—10 healthy adult dogs.
Procedures—Weight placed on each limb of each dog was measured 3 times (1 scale/limb). Dogs were then immersed in water to the level of the tarsal, stifle, and hip joints, and vGRFs were measured. Coefficients of variation for triplicate measurements were calculated. Mixed-effects ANOVAs were used to compare the vGRF for thoracic versus pelvic limbs and the vGRF at various immersion levels as well as the vGRF distributions among limbs at various immersion levels.
Results—Mean ± SD vGRF before immersion was 249 ± 34 N. It was significantly decreased by 9% after immersion to the tarsal joints (227 ± 32 N), by 15% after immersion to the stifle joints (212 ± 21 N), and by 62% after immersion to the hip joints (96 ± 20 N). The vGRFs were significantly higher for the thoracic limbs than for the pelvic limbs before immersion and at all immersion levels. Dogs placed 64% of their weight on the thoracic limbs before immersion. That ratio did not differ significantly after immersion to the tarsus (64%) or stifle (63%) joints, but was significantly larger after immersion to the hip joints (71%).
Conclusions and Clinical Relevance—vGRF decreased as the depth of immersion increased. The thoracic limb-to-pelvic limb vGRF ratio was unchanged in dogs after immersion to the tarsal or stifle joints, but it increased after immersion to the hip joints.
Objective—To assess forelimbs and hind limb joint kinematics in dogs during walking on an inclined slope (uphill), on a declined slope (downhill), or over low obstacles (cavaletti) on a horizontal surface and compare findings with data acquired during unimpeded walking on a horizontal surface.
Procedures—By use of 10 high-speed cameras and 10 reflecting markers located on the left forelimbs and hind limbs, joint kinematics were recorded for each dog during uphill walking, downhill walking, and walking over low obstacles or unimpeded on a horizontal surface. Each exercise was recorded 6 times (10 s/cycle); joint angulations, angle velocities and accelerations, and range of motion for shoulder, elbow, carpal, hip, stifle, and tarsal joints were calculated for comparison.
Results—Compared with unimpeded walking, obstacle exercise significantly increased flexion of the elbow, carpal, stifle, and tarsal joints and extension in the carpal and stifle joints. Only uphill walking caused increased hip joint flexion and decreased stifle joint flexion; downhill walking caused less flexion of the hip joint. During obstacle exercise, forward angle velocities in the elbow and stifle joints and retrograde velocity in the tarsal joint changed significantly, compared with unimpeded walking. Joint angle acceleration of the elbow joint changed significantly during all 3 evaluated exercises.
Conclusions and Clinical Relevance—These evidence-based data indicated that each evaluated exercise, except for downhill walking, has a specific therapeutic value in physical therapy for dogs.
Objective—To assess the net mechanical load on the distal end of the third metacarpal bone in horses during walking and trotting.
Animals—3 Quarter Horses and 1 Thoroughbred.
Procedures—Surface strains measured on the left third metacarpal bone of the Thorough-bred were used with a subject-specific model to calculate loading (axial compression, bending, and torsion) of the structure during walking and trotting. Forelimb kinematics and ground reaction forces measured in the 3 Quarter Horses were used with a musculoskeletal model of the distal portion of the forelimb to determine loading of the distal end of the third metacarpal bone.
Results—Both methods yielded consistent data regarding mechanical loading of the distal end of the third metacarpal bone. During walking and trotting, the distal end of the third metacarpal bone was loaded primarily in axial compression as a result of the sum of forces exerted on the metacarpal condyles by the proximal phalanx and proximal sesamoid bones.
Conclusions and Clinical Relevance—Results of strain gauge and kinematic analyses indicated that the major structures of the distal portion of the forelimb in horses acted to load the distal end of the third metacarpal bone in axial compression throughout the stance phase of the stride.
Objective—To quantitate changes in hoof wall growth and hoof morphology induced by mild exercise in Standardbreds.
Procedures—Horses were exercised at approximately 6 m/s (4,200 to 5,600 m/d) on 4 d/wk for 17 weeks. Both exercise (n = 9) and nonexercise (control group; 9) groups were housed in a large paddock throughout the study. At the beginning and end of the study, right forelimb feet of all horses were digitally photographed and underwent magnetic resonance imaging. Hoof wall measurements were obtained from the images to evaluate hoof wall growth and morphometric variables. Data were compared between the groups and within each group via a quadratic model. Changes in each variable and pairwise correlations between variables were evaluated.
Results—Morphometric variables did not significantly differ between the control and exercise groups. However, differences within each group between the start and the end of the study were significant for several variables; overall, values for hoof wall variables increased and those for solar variables decreased. Between the beginning and the end of the study, the amount of variation in values of hoof capsule variables in the exercise group decreased to a greater extent, compared with control group findings. Patterns of pairwise correlations for variables differed between the groups.
Conclusions and Clinical Relevance—In Standardbreds, mild exercise for 17 weeks caused no significant changes in hoof wall growth or morphometric variables. Subtle changes may develop in equine hooves in response to loading, and mild exercise may not be a strong adaptive stimulus.