FRANK J. MILNE STATE-OF-THE-ART LECTURE


and therefore the greater extension of the distal interphalangeal (DIP) joint, may make some foot- related lameness (eg, injuries of the deep digital flexor tendon [DDFT] or a collateral ligament of the DIP joint) more obvious at a walk than at a trot. In my opinion,a0to8 system applied independently for each situation under which the horse is exam- ined, supplemented by verbal qualifications, offers a far more flexible system than that of the AAEP grading scale and provides sufficient grades to cover a wide spectrum of gait abnormalities and facilitates grading of change in lameness after local analgesia. With both forelimb and hindlimb lameness, it is


useful to assess the horse walking in small circles, which often accentuates foot-related lameness but is not specific for foot pain. This also gives the oppor- tunity to assess the flexibility of the horse’s neck and back, the ease with which it crosses over its hindlimbs, and to detect any gait abnormalities sug- gestive of a component of ataxia, such as toe drag, hindlimb circumduction, leaving limbs in abnormal positions, irregularly sized steps, and interference between limbs. Evaluating the horse step back- ward can also give additional information about the presence of shivering and flexibility of the lumbosa- cral region. Whichever lameness grading system is used, it is important to recognize that for consistency of re- sults, the circumstances in which a horse is exam- ined must remain the same. The speed of trot may influence the degree of lameness; some horses may try to slow the speed to protect themselves. Lame- ness may be accentuated on a slight downward slope compared with a horizontal surface or on a deeper sand surface than on a firm, waxed rubber and sand arena. Detection of these variations under differ- ent conditions may give an indication of the likely source of pain causing lameness. For example, hindlimb lameness that is worse on a circle on a hard surface is most likely to reflect foot pain. Assigning a grade is not always straightforward because there are so many ways in which the gait may be modified. When a horse with unilateral hindlimb lameness is moving in straight lines, there is usually some degree of asymmetry of movement of the hindquarters. There may be reduced extension of the fetlock joint, reduced flexion of the hock, toe drag, or alteration in stride length; the horse may move on three tracks, usually drifting away from the lame limb; alternatively, the lame hindlimb may deviate axially during protraction or less commonly is swung outward during protraction. The rhythm may be altered both audibly and visually. Irrespec- tive of the degree of hindquarter asymmetry, there may be a head-nod mimicking ipsilateral forelimb lameness. Our ability to detect asymmetry of movement of


the hindquarters is limited. A computer model was devised to determine how capable we are of assess- ing hindlimb lameness, on the basis of evaluation of movement of the tubera coxae.3 The model had two


forms, one in which there was random asymmetry of movement between two objects and the other that simulated the patterns of movement seen in a lame horse. In the first model, no differences were seen in the skill of inexperienced assessors compared with experienced clinicians, suggesting that there are no innate differences in the ability to detect asymmetry. However, the experienced clinicians performed best with the real lameness-based data. Nonetheless, even with lameness-based data the ac- curacy of detecting asymmetry of movement simu- lating low-grade lameness was poor: asymmetries in movement of 25% could not be detected. In a more recent study of so-called normal horses, as- sessed by veterinarians with a range of experience, and also objectively with the use of inertial measure- ment units, an expert was able to detect lameness manifest as asymmetries of 10%.4 However, the expert was not confined to assessing asymmetry alone and could use any technique to determine whether the horse was lame or sound. I focus on both the tubera coxae and the tubera sacrale, although it may be impossible with a horse with a naturally high tail carriage, such as Arabi- ans, some Warmbloods, and gaited horses, when the tail conceals the tubera sacrale. A skewbald or pie- bald horse with one white hindquarter and one col- ored hindquarter, or a horse with unilateral gluteal muscle atrophy in either the lame or the non-lame limb, or a horse with asymmetry in height of the tubera sacrale, or an excitable horse that will not trot straight potentially confound our interpreta- tion. A bilaterally symmetrical hindlimb lameness may manifest merely as a short stride, stiffness, and lack of hindlimb impulsion. All of these factors potentially compromise our ability to detect the lame limb(s). Some can be solved—an excitable horse can either be worked or sedated, but you can- not change the markings of a colored horse or the positions of the tubera sacrale. The use of markers placed on the tubera coxae may facilitate assessment.5 With forelimb lameness, there is usually abnor-


mal movement of the head and neck, although in a horse with a naturally short-striding gait, with a tendency to roll from side to side, this may be diffi- cult to discern. Assessment of head and neck pos- ture is also important for detection of neck pain that can result in alterations in gait. I believe that it is important to assess the horse moving from behind, from the front, and from the side to assess all aspects of the gait and to both watch and listen to the horse. Irregularities of gait may be emphasized by listening to the limbs striking the ground or hearing a toe drag during protraction. An abnormally deliberate placement of hindlimbs to the ground may suggest a neurological component to the gait abnormality or a mechanical component such as stringhalt or fibrotic myopathy. Assess- ment of foot placement—toe first or flat-footed, lat- eral side first or flat, in line with the ipsilateral foot


AAEP PROCEEDINGS  Vol. 59  2013 93


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