IN-DEPTH: SPORT HORSE LAMENESS Distal Limb Lameness in the Sport Horse: A Clinical Approach to Diagnosis Richard D. Mitchell, DVM, MRCVS Diagnosis of lameness caused by lesions of the distal limb requires a thorough clinical examination, including careful palpation, manipulative tests, hoof tester evaluation, examination of the horse in hand and under saddle, and regional anesthesia. Specific causative lesions may require technical imaging modalities to fully evaluate. Author’s address: Fairfield Equine Associates, PC, 32 Barna- bas Road, Newtown, CT 06470; e-mail: [email protected]. © 2013 AAEP. 1. Introduction proximal phalanx (P1, long pastern bone), the mid- Today’s high-level sport horse represents a signifi- dle phalanx (P2, short pastern bone), the distal pha- cant investment of time and money. High-level lanx (P3, coffin bone), and the distal sesamoid show jumpers, dressage horses, and Western perfor- (navicular bone). Each of the articulations is sup- mance horses often take several years to train to ported by collateral ligamentous structures and fi- their upper levels, and injuries or illness can sub- brous joint capsules. The distal sesamoidean stantially affect the time to produce a winning ligaments (as the extension of the suspensory appa- horse. Owners and trainers are concerned that ratus) and the flexor tendons attach along the pal- these horses receive the best possible care without mar aspect of the pastern and foot and provide excess expenses and down time. The veterinary support. The dorsal digital extensor attaches along care of such horses should take a more aggressive the dorsal aspect, ultimately inserting on the exten- approach to lameness diagnostics of the horse in sor process of the distal phalanx. training, not simply one of attending to lameness The distal limb plays a significant role in adap- after the horse is no longer able to train. Recogni- tation to footing and shock absorption during loco- tion of potentially serious distal limb lameness early motion. The corium parietis, composed of the on may prevent significant loss of training and com- epidermal and dermal lamellae, function as a liga- petition time as well as extending the horse’s career. ment suspending P3 within the hoof wall. There 2. Anatomy and Risk Factors is considerable movement of P3 within the hoof wall For the purposes of this discussion, the author will on landing and propulsion because of this function. address the anatomical region from the fetlock dis- The digital cushion also functions in shock ab- tally. The bony structures involve the three meta- sorption.1–3 Foot balance, both medial/lateral and carpals, (MC2, MC3, MC4 or medial splint bone, dorsal/palmar, can have a profound effect on the cannon bone, and lateral splint bone, respectively), excursion of joints and the stress on soft tissues of the proximal medial and lateral sesamoids, the the distal limb.1,4 Footing surfaces that are very NOTES 244 2013 ր Vol. 59 ր AAEP PROCEEDINGS IN-DEPTH: SPORT HORSE LAMENESS hard, excessively soft, or unstable can result in ab- with successfully managed orthopedic disease may errant motion and stress that may result in injury. need to be checked more often. The demands of high-level sports result in more A typical lameness examination should first in- concussion as well as greater extension and flexion volve a thorough visual exam of the horse, taking than casual exercise. Fatigue may not be as signif- notice of body symmetry and muscle structure. icant a factor in injuries of the sport horse compared Observing the horse in its stall may give the exam- with racing horses, but chronic repetitive trauma is iner some clues regarding the horse’s level of com- thought to be a factor. The types of injuries seen in fort. Watching the horse step out of its stall may the sport horse, racing horse, or pleasure horse may give big clues about chronic lameness issues. After vary considerably as to intensity and potential the visual inspection, a palpation examination chronicity.5,6 should be performed. The author uses a modifica- tion of an “acupuncture” examination that allows for 3. History and Clinical Signs complete palpation of the horse while eliciting re- sponses from potentially painful areas. Careful in- Distal limb lameness may present in a peracute spection of the feet for balance and symmetry should fashion with extreme discomfort such with a P3 be performed. Flexion manipulations can then be fracture or foot abscess, but more often, signs may performed in a “passive” sense (not asking the horse be more subtle with the horse having a subtle lame- to walk or jog away) while noting any resistance or ness that changes somewhat with work. “Gee doc, painful responses. It may be appropriate to use he feels tight in his shoulders,” is a frequent com- hoof testers at this point before starting any exer- ment for more insidious forms of early front distal cise. Next, the horse can be moved in hand at a limb lameness. Distal hind limb issues may mimic walk and trot, taking note of any obvious lameness more commonly thought-of conditions such as distal or unusual foot flight or limb motion. This is best tarsitis or proximal suspensory desmopathy in that performed on hard footing if available. It is useful the horse is “weak” behind and may “warm out” to see the horse walk in circles as well as on a of the lameness. Some heat or swelling may be straight line. Likewise, jogging the horse in circles perceived in the distal limb, but often this is not as well as in a straight line may provide much more the case. The current competitive environment insight related to the horse’s level of comfort. If in North America often allows for nonsteroidal the horse is too fractious to lunge in circles, jogging anti-inflammatory drug (NSAID) use in competing in hand on circles may provide an acceptable alter- horses; horses with mild distal limb pain are able native. The author frequently gives a small dose to compete comfortably. However, when Monday of sedative (detomidine hydrochloride, 1.5 mg total morning rolls around and the effects of the NSAIDS dose)a to evaluate lameness if the horse is not well- are gone, the horse is suddenly more uncomfortable behaved. Watching the horse move in straight than before the event. This presents a good oppor- lines and circles on both hard and soft footing can be tunity to investigate the case. immensely valuable in detecting lameness. Horses may present with a unilateral lameness of The next step is to perform flexion tests of all varying degrees (0–5/5) or appear bilaterally lame, limbs with the horse then walking or trotting away. especially if circled or ridden, which will be dis- These may give clues to soreness that is not other- cussed later. Some lameness may be very subtle wise evident. It may be worth pursuing some pos- and will require special efforts to make it more ap- itive flexion responses or readily apparent lameness parent for an objective diagnosis. Many horses at this point while simply recording some others for vary in their degree of lameness, improving pro- future reference. Keep in mind that a positive dis- foundly with a few days of rest. Such mild lame- tal limb flexion may indicate a problem in any num- ness issues may be best re-examined after a day or ber of places, from the distal interphalangeal joint two of exercise. (DIPJ) to even a suspensory ligament issue. It is a tool for regionalization and augmentation for obser- 4. Physical Examination vation purposes. This author is of the opinion that it is essential to “Wedge” tests are sometimes useful to aid in lo- have periodic veterinary inspections of the training calization of the source of lameness. A reverse sport horse to catch subtle lameness and perfor- wedge that stretches the deep digital flexor tendon mance problems before they become serious clinical (DDFT) may increase a lameness related to that issues. Although many trainers and owners are structure; a wedge placed laterally under the foot very adept at catching subtle soundness and health may stretch the medial collateral ligament of the related issues, many things may be overlooked by DIPJ and increase lameness if that structure is in- the individual who sees the horse every day. Peri- jured. The latter effect is because of compression odic veterinary inspection should include a general on the same side as the wedge and rotation of the health check and a thorough lameness evaluation. DIPJ on the contralateral side that stretches the The frequency of these exams will be somewhat de- collateral ligament on that side.1 pendent on the age and activity of the horse, but two Care should be taken to not overexert the very to four times yearly should be a minimum. Horses lame horse (Ͼ3/5) until a good sense of the nature of AAEP PROCEEDINGS ր Vol. 59 ր 2013 245 IN-DEPTH: SPORT HORSE LAMENESS the problem is recognized. A detailed record of ob- wise to pursue the lameness with diagnostic nerve servations should be maintained for each examina- blocks. Once localized, further physical examina- tion. After flexion tests, it is advisable to observe tion, radiographs, and diagnostic ultrasound may the horse work on a lunge line and under saddle. further elucidate the nature of the problem. In Some horses are difficult to lunge and may pose a some cases, physical examination and diagnostic im- hazard for injury to horse and handler. These aging may be sufficient to clearly define the diagno- horses should be lightly sedated or simply watched sis, and, in such cases, nerve blocks may not be under tack.