For the Health of It
A significant number of pain-related gait ab-normalities in horses are evident only when the horse is ridden , and are not apparent when the horse is hand-walked or lunged . Even when these horses are ridden , the lameness may not be overt . While there have been many recent technical advancements in the objective assessment of gait , these are generally of limited value for detection of bilaterally symmetrical alterations in gait that result in reduced performance such as generalized stiffness , lack of willingness to work , alteration in quality of movements such as lack of hindlimb engagement and impulsion , and alteration in the rider ’ s feel of the contact via the reins and bit to the horse ’ s mouth .
A rider often assumes that these problems are attributable to thoracolumbar region pain , because the problems are only manifest when the horse is ridden . When observed on the lunge , such horses may lean into the circle — often more on one rein than the other — and show exaggerated contrac-tions of the epaxial muscles . However , studies have shown that experimentally induced forelimb or hindlimb lameness may reduce range of mo-tion of the thoracolumbosacral vertebral column . Radiographic examination may reveal impinging spinous processes , and this finding often results in an erroneous conclusion implicating thora-columbar pain as the primary problem . We have demonstrated that by using diagnostic analgesia to abolish overt or subclinical lameness , the rider often appreciates an increased range of motion of the horse ’ s back .
To investigate these clinical observations , we have studied normal horses subjectively free from lameness in hand , after flexion test , on the lunge on both soft and firm surfaces and when ridden . We objectively measured body lean on the lunge and range of movement of the thoracolumbar region using inertial measurement units placed at predefined locations on the thoracolumbar and pelvic regions . These studies established normal ranges of motion for the thoracolumbosacral spine and demonstrated that sound horses
12 • Walking On
Observation , Science , and Equine Lameness Diagnosis
Reprinted with permission from the January 2017 issue of Equine Disease Quarterly .
have a small degree of bilaterally symmetrical body lean on the lunge . We also measured body lean on the lunge in lame horses and demonstrated that there is frequently asymmetry between left and right reins , with greater lean compared with normal on at least one rein . Substantial improvement in lameness by performing diagnostic analgesia resulted in reduced body lean on both reins and reestablishment of symmetry between left and right reins . Likewise , when lameness was improved by diagnostic analgesia , range of motion of the thoracolumbosacral regions increased , especially in the caudal thoracic and lumbar regions .
We have observed that the tendency of a saddle to slip persistently to one side is most frequently associated with hindlimb lameness . Abolition of lameness by diagnostic analgesia results in resolu-tion of the saddle slip . The saddle most commonly slips to the side of the lame or more lame hindlimb , but less frequently slips toward the less lame limb . Presumably saddle slip is induced by altered range of motion of the thoracolumbosacral region , which may vary among horses . Saddle slip may actually be an indicator of the likely presence of hindlimb lameness .
Overt lameness may not be apparent when a horse is trotting , but musculoskeletal pain may be manifest at a canter by the horse ’ s tendency to become disunited or repeatedly change leading limbs behind or in front , crookedness , loss of a normal three time rhythm , placing the hindlimbs either abnormally close together spatially and tem-porally , or placing the limbs remarkably far apart . These observations may be apparent either on the lunge or when the horse is ridden . Abolition of baseline lameness seen in hand may paradoxically make the canter appear worse if sacroiliac pain is contributing to pain and poor performance .
These observations highlight the importance of evaluating horses with performance problems both in hand , on the lunge and ridden , preferably by the normal rider . Horses should be assessed in walk , trot , and canter , bearing in mind that while one aspect of the gait may improve with diagnostic analgesia , another may deteriorate . Horses should also be assessed performing the movements which they find most difficult , because in some horses this may be the only condition when the problem is manifest .
Contact : Sue Dyson , MA , VetMB , PhD , DEO , FRCVS sue . dyson @ aht . org . uk | + 44 ( 0 ) 1638 7519098
Centre for Equine Studies , Animal Health Trust Newmarket , Suffolk , UK