Kevin K. Haussler

Forelimb muscle activity during equine locomotion

SUMMARY Few quantitative data exist to describe the activity of the distal muscles of the equine forelimb during locomotion, and there is an incomplete understanding of the functional roles of the majority of the forelimb muscles. Based on morphology alone it would appear that the larger proximal muscles perform the majority of work in the forelimb, whereas the smaller distal muscles fulfil supplementary roles such as stabilizing the joints and positioning the limb for impact with the ground. We measured the timing and amplitude of the electromyographic activity of the intrinsic muscles of the forelimb in relation to the phase of gait (stance versus swing) and the torque demand placed on each joint during walking, trotting and cantering. We found that all forelimb muscles, except the extensor carpi radialis (ECR), were activated just prior to hoof-strike and deactivated during stance. Only the ECR was activated during swing. The amplitudes of muscle activation typically increased as gait speed increased. However, the amplitudes of muscle activation were not proportional to the net joint torques, indicating that passive structures may also contribute significantly to torque generation. Our results suggest that the smaller distal muscles help to stabilize the forelimb in early stance, in preparation for the passive structures (tendons and ligaments) to be stretched. The distal forelimb muscles remain active throughout stance only during canter, when the net torques acting about the distal forelimb joints are highest. The larger proximal muscles activate in a complex coordination to position and stabilize the shoulder and elbow joints during ground contact.

Kinematic and kinetic analysis of dogs during trotting after amputation of a thoracic limb

OBJECTIVE To evaluate biomechanical gait adaptations in dogs after amputation of a pelvic limb. ANIMALS Client-owned dogs (12 pelvic limb-amputee and 24 quadruped [control] dogs). PROCEDURES Dogs were trotted across 3 in-series force platforms. Spatial kinematic and kinetic data were recorded for each limb during the stance phase. RESULTS Pelvic limb amputees had increased peak braking forces in the contralateral thoracic limb and increased propulsive forces and impulses in both the ipsilateral thoracic limb and remaining pelvic limb. Time to peak braking force was significantly decreased, and time to peak propulsive force was significantly increased in all remaining limbs in amputees. Amputees had an increase in range of motion at the tarsal joint of the remaining pelvic limb, compared with results for the control dogs. Amputees had increased vertebral range of motion at T1 and T13 and increased vertebral extension at L7 within the sagittal plane. In the horizontal plane, amputees had increased lateral bending toward the remaining pelvic limb, which resulted in a laterally deviated gait pattern. CONCLUSIONS AND CLINICAL RELEVANCE Pelvic limb amputees adjusted to loss of a limb through increased range of motion at the tarsal joint, increased range of motion in the cervicothoracic and thoracolumbar vertebral regions, and extension of the lumbosacral vertebral region, compared with results for the control dogs. Amputees alternated between a laterally deviated gait when the pelvic limb was in propulsion and a regular cranially oriented gait pattern when either forelimb was in propulsion with horizontal rotation around L7.

Gastrocnemius tendon strain in a dog treated with autologous mesenchymal stem cells and a custom orthosis.

OBJECTIVE To report clinical findings and outcome in a dog with gastrocnemius tendon strain treated with autologous mesenchymal stem cells and a custom orthosis. STUDY DESIGN Clinical report. ANIMAL A 4-year-old spayed female Border Collie. METHODS Bone-marrow derived, autologous mesenchymal stem cells were transplanted into the tendon core lesion. A custom, progressive, dynamic orthosis was fit to the tarsus. Serial orthopedic examinations and ultrasonography as well as long-term force-plate gait analysis were utilized for follow up. RESULTS Lameness subjectively resolved and peak vertical force increased from 43% to 92% of the contralateral pelvic limb. Serial ultrasonographic examinations revealed improved but incomplete restoration of normal linear fiber pattern of the gastrocnemius tendon. CONCLUSIONS Findings suggest that autologous mesenchymal stem cell transplantation with custom, progressive, dynamic orthosis may be a viable, minimally invasive technique for treatment of calcaneal tendon injuries in dogs.Objective To report clinical findings and outcome in a dog with gastrocnemius tendon strain treated with autologous mesenchymal stem cells and a custom orthosis. Study Design Clinical report. Animal A 4-year-old spayed female Border Collie. Methods Bone-marrow derived, autologous mesenchymal stem cells were transplanted into the tendon core lesion. A custom, progressive, dynamic orthosis was fit to the tarsus. Serial orthopedic examinations and ultrasonography as well as long-term force-plate gait analysis were utilized for follow up. Results Lameness subjectively resolved and peak vertical force increased from 43% to 92% of the contralateral pelvic limb. Serial ultrasonographic examinations revealed improved but incomplete restoration of normal linear fiber pattern of the gastrocnemius tendon. Conclusions Findings suggest that autologous mesenchymal stem cell transplantation with custom, progressive, dynamic orthosis may be a viable, minimally invasive technique for treatment of calcaneal tendon injuries in dogs.

Deformation of the equine pelvis in response to in vitro 3D sacroiliac joint loading.

REASONS FOR PERFORMING STUDY Sacroiliac joint injuries can cause poor performance; however, the interaction between pelvic mechanics and the sacroiliac joint is poorly understood. OBJECTIVE To measure pelvic displacement during 3D sacroiliac joint loading. METHODS Nine reflective triads were attached rigidly to bony prominences in sacropelvic specimens harvested from 14 horses for stereophotogrammetric analysis of triad displacements and joint kinematics. The sacrum was coupled to a load cell and mounted vertically within a material testing system (MTS). A pneumatic actuator was used to apply 90 Nm moments to the ischial arch to simulate nutation-counternutation and left and right lateral bending of the sacroiliac joints. Axial rotation of the sacrum was induced by torsion of the upper MTS fixture. Vectors of marker displacement within orthogonal planes of motion were measured during loading of the sacropelvic specimens. Comparisons in the magnitude and direction of triad displacements were made between paired left-right markers and paired loading conditions. RESULTS Nutation-counternutation of the sacroiliac joint caused vertical displacement of the ischial tuberosities and cranial-caudal displacement of the wings of the ilium. Lateral bending induced rotational displacement within the horizontal plane of all pelvic landmarks, relative to the sacrum. Axial rotation of the sacrum caused elevation of the wing of the ilium ipsilateral to the direction of sacral rotation and depression of the contralateral ilial wing. Significant paired left-right differences occurred during most sacroiliac joint loading conditions. Comparable magnitudes of pelvic displacement were measured during nutation-counternutation, left and right lateral bending, and left and right axial rotation. CONCLUSIONS The equine pelvis is not a rigid structure and asymmetric pelvic deformation occurs during most sacroiliac joint movements. CLINICAL RELEVANCE Bony pelvic deformation should be considered a normal response to any sacroiliac joint movement.

The Role of Manual Therapies in Equine Pain Management

Manual therapy includes a diverse array of techniques, such as touch therapies, massage, physical therapy, osteopathy, and chiropractic, that were originally developed for use in humans and have been gradually applied to horses. All forms of manual therapy have variable reported levels of effectiveness for treating musculoskeletal issues in humans, but mostly only anecdotal evidence exists in horses. This article explores the scientific literature for evidence of efficacy, safety, and common mechanisms of action of the different forms of manual therapies for potential use in managing acute or chronic pain syndromes in horses. Currently, there is limited evidence supporting the effectiveness of spinal mobilization and manipulation in reducing pain and muscle hypertonicity. Further research is needed to assess the efficacy of specific manual therapy techniques and their contribution to multimodal protocols for managing specific somatic pain conditions in horses.

The role of muscle activation in cruciate disease

Traditional investigations into the etiopathogenesis of canine cranial cruciate ligament (CCL) disease have focused primarily on the biological and mechanical insults to the CCL as a passive stabilizing structure of the stifle. However, with recent collaboration between veterinarians and physical therapists, an increased focus on the role of muscle activity and aberrant motor control mechanisms associated with anterior cruciate ligament (ACL) injuries and rehabilitation in people has been transferred and applied to dogs with CCL disease. Motor control mechanisms in both intact and cruciate-deficient human knees may have direct translation to canine patients, because the sensory and motor components are similar, despite moderate anatomic and biomechanical differences. Components of motor control, such as muscle recruitment and the coordination and amplitudes of activation are strongly influenced by afferent proprioceptive signaling from peri- and intra-articular structures, including the cruciate ligaments. In people, alterations in the timing or amplitude of muscle contractions contribute to uncoordinated movement, which can play a critical role in ACL injury, joint instability and the progression of osteoarthritis (OA). A better understanding of motor control mechanisms as they relate to canine CCL disease is vitally important in identifying modifiable risk factors and applying preventative measures, for development of improved surgical and rehabilitative treatment strategies. The purpose of this review article is to analyze the influence of altered motor control, specifically pelvic limb muscle activation, in dogs with CCL disease as evidenced by mechanisms of ACL injury and rehabilitation in people.Traditional investigations into the etiopathogenesis of canine cranial cruciate ligament (CCL) disease have focused primarily on the biological and mechanical insults to the CCL as a passive stabilizing structure of the stifle. However, with recent collaboration between veterinarians and physical therapists, an increased focus on the role of muscle activity and aberrant motor control mechanisms associated with anterior cruciate ligament (ACL) injuries and rehabilitation in people has been transferred and applied to dogs with CCL disease. Motor control mechanisms in both intact and cruciate-deficient human knees may have direct translation to canine patients, because the sensory and motor components are similar, despite moderate anatomic and biomechanical differences. Components of motor control, such as muscle recruitment and the coordination and amplitudes of activation are strongly influenced by afferent proprioceptive signaling from peri- and intra-articular structures, including the cruciate ligaments. In people, alterations in the timing or amplitude of muscle contractions contribute to uncoordinated movement, which can play a critical role in ACL injury, joint instability and the progression of osteoarthritis (OA). A better understanding of motor control mechanisms as they relate to canine CCL disease is vitally important in identifying modifiable risk factors and applying preventative measures, for development of improved surgical and rehabilitative treatment strategies. The purpose of this review article is to analyze the influence of altered motor control, specifically pelvic limb muscle activation, in dogs with CCL disease as evidenced by mechanisms of ACL injury and rehabilitation in people.

Comparison of subjective lameness evaluation, force platforms and an inertial-sensor system to identify mild lameness in an equine osteoarthritis model.

When mild lameness exists, agreement between clinicians is often controversial due to its subjective nature. The goal of the study was to compare subjective and objective methods to identify the presence of mild lameness using an established model of osteoarthritis (OA) in which OA was induced by creating a unilateral carpal osteochondral fragment (OCF) in the middle carpal joint of 16 horses. Subjective lameness evaluations (blinded and unblinded), force platforms (FP), and an inertial-sensor system (ISS) were used to detect forelimb lameness at four time points. Limbs identified as lame by each method were compared as well as compared with the OCF limb at each time point. Spearman correlations were calculated between all outcome parameters. Independent of time, blinded subjective evaluation (54%) and the ISS (60%) identified a higher percentage of horses as lame in the OCF limb compared to FP (40%). Blinded subjective evaluation and the ISS agreed which forelimb was lame more often (50%) compared with blinded subjective evaluation and the FP (38%). Induction of mild lameness within the OCF limb was supported by an increase in the frequency of horses considered lame by both subjective evaluations the ISS and a decrease (3.6%) in mean (among all horses) peak vertical force from baseline to post OCF induction. The percentage of horses identified as lame in the OCF limb, independent of time, was highest with the ISS (60%) followed by blinded subjective evaluation (51%) and the FP (42%). It was concluded that the best agreement was between subjective evaluation and the inertial-sensor system.

Modulating tibiofemoral contact force in the sheep hind limb via treadmill walking: Predictions from an opensim musculoskeletal model

Sheep are a predominant animal model used to study a variety of orthopedic conditions. Understanding and controlling the in‐vivo loading environment in the sheep hind limb is often necessary for investigations relating to bone and joint mechanics. The purpose of this study was to develop a musculoskeletal model of an adult sheep hind limb and investigate the effects of treadmill walking speed on muscle and joint contact forces. We constructed the skeletal geometry of the model from computed topography images. Dual‐energy x‐ray absorptiometry was utilized to establish the inertial properties of each model segment. Detailed dissection and tendon excursion experiments established the requisite muscle lines of actions. We used OpenSim and experimentally‐collected marker trajectories and ground reaction forces to quantify muscle and joint contact forces during treadmill walking at 0.25 m• s−1 and 0.75 m• s−1. Peak compressive and anterior–posterior tibiofemoral contact forces were 20% (0.38 BW, p = 0.008) and 37% (0.17 BW, p = 0.040) larger, respectively, at the moderate gait speed relative to the slower speed. Medial–lateral tibiofemoral contact forces were not significantly different. Adjusting treadmill speed appears to be a viable method to modulate compressive and anterior–posterior tibiofemoral contact forces in the sheep hind limb. The musculoskeletal model is freely‐available at www.SimTK.org.

Biomechanical and histologic evaluation of the effects of underwater treadmill exercise on horses with experimentally induced osteoarthritis of the middle carpal joint

OBJECTIVE To evaluate the effects of exercise in an underwater treadmill (UWT) on forelimb biomechanics and articular histologic outcomes in horses with experimentally induced osteoarthritis of the middle carpal joint. ANIMALS 16 horses. PROCEDURES An osteochondral fragment was induced arthroscopically (day 0) in 1 middle carpal joint of each horse. Beginning on day 15, horses were assigned to exercise in a UWT or in the UWT without water (simulating controlled hand walking) at the same speed, frequency, and duration. Thoracic and pelvic limb ground reaction forces, thoracic limb kinematics, and electromyographic results for select thoracic limb muscles acting on the carpi were collected on days -7 (baseline), 14, 42, and 70. Weekly evaluations included clinical assessments of lameness, response to carpal joint flexion, and goniometric measurements of thoracic limb articulations. At study conclusion, articular cartilage and synovial membrane from the middle carpal joints was histologically examined. RESULTS Exercise in a UWT significantly reduced synovial membrane inflammation and resulted in significant clinical improvements with regard to symmetric thoracic limb loading, uniform activation patterns of select thoracic limb muscles, and return to baseline values for carpal joint flexion, compared with results for horses with simulated hand walking. CONCLUSIONS AND CLINICAL RELEVANCE Overall improvements in thoracic limb function, joint range of motion, and synovial membrane integrity indicated that exercise in a UWT was a potentially viable therapeutic option for the management of carpal joint osteoarthritis in horses.

An In Vivo Ovine Model of Bone Tissue Alterations in Simulated Microgravity Conditions

Microgravity and its inherent reduction in body-weight associated mechanical loading encountered during spaceflight have been shown to produce deleterious effects on important human physiological processes. Rodent hindlimb unloading is the most widely-used ground-based microgravity model. Unfortunately, results from these studies are difficult to translate to the human condition due to major anatomic and physiologic differences between the two species such as bone microarchitecture and healing rates. The use of translatable ovine models to investigate orthopedic-related conditions has become increasingly popular due to similarities in size and skeletal architecture of the two species. Thus, a new translational model of simulated microgravity was developed using common external fixation techniques to shield the metatarsal bone of the ovine hindlimb during normal daily activity over an 8 week period. Bone mineral density, quantified via dual-energy X-ray absorptiometry, decreased 29.0% (p < 0.001) in the treated metatarsi. Post-sacrifice biomechanical evaluation revealed reduced bending modulus (-25.8%, p < 0.05) and failure load (-27.8%, p < 0.001) following the microgravity treatment. Microcomputed tomography and histology revealed reduced bone volume (-35.9%, p < 0.01), trabecular thickness (-30.9%, p < 0.01), trabecular number (-22.5%, p < 0.05), bone formation rate (-57.7%, p < 0.01), and osteoblast number (-52.5%, p < 0.001), as well as increased osteoclast number (269.1%, p < 0.001) in the treated metatarsi of the microgravity group. No significant alterations occurred for any outcome parameter in the Sham Surgery Group. These data indicate that the external fixation technique utilized in this model was able to effectively unload the metatarsus and induce significant radiographic, biomechanical, and histomorphometric alterations that are known to be induced by spaceflight. Further, these findings demonstrate that the physiologic mechanisms driving bone remodeling in sheep and humans during prolonged periods of unloading (specifically increased osteoclast activity) are more similar than previously utilized models, allowing more comprehensive investigations of microgravity-related bone remodeling as it relates to human spaceflight.