Foot

The importance of the foot cannot be overemphasized, and it is for this reason that palpation of the forelimb begins here. The feet are included in evaluation of conformation, symmetry, and posture. Detailed static examination (examination at rest) of the foot must always be supplemented with, and correlated to, dynamic observations of foot flight and foot striking patterns. Some horses continually attempt to pick up the limb as the clinician tries to evaluate it with the horse in the standing position; it may be necessary to stroke the contralateral limb to divert attention. A hoof pick, wire brush, hoof knife, shoe-removing equipment, and hoof testers are required (Figure 6-1). The sole and frog and wall of the foot should be cleaned thoroughly. Removal of the shoe at this stage in the examination usually is indicated only if a subsolar abscess is suspected. The veterinarian should take care to preserve the hoof wall, and if it is cracked, protect it with tape.

Fig. 6-1 Instruments needed to examine the hoof, remove a shoe without tearing the hoof wall, and prepare the hoof for radiographic examination. Shown are apron, rasp, shoe pullers, nail pullers, clinch tool, hoof knife, hammer and hoof pick, and wire brush.

Foot and hoof balance are assessed by evaluating toe and heel length, hoof capsule conformation, condition and integrity, type of shoe and shoe position relative to the hoof capsule, hoof and pastern angle (axis), medial-to-lateral hoof balance, coronary band conformation, and distal interphalangeal (coffin) joint capsule distention and response to hoof testers. The coronary band should normally be parallel to the ground surface. Deviation from parallel often indicates mediolateral foot imbalance (Figure 6-2). Medial and lateral wall lengths should be assessed while the horse is standing and again with the limb off the ground, with the foot viewed from palmar to dorsal along the solar aspect. The limb is lifted and held in neutral position so the solar surface is perpendicular to the ground. Sheared and underrun heels are commonly associated with lameness (Figure 6-3). Deformation of the hoof capsule is not necessarily a cause of lameness. Many horses with proximal displacement of the medial heel bulb have level foot strikes and otherwise balanced feet. Toe and heel length should be assessed, and the hoof-pastern axis should be determined. The angle of the hoof and pastern should be equal to allow equal loading of all portions of the foot. Forelimb hoof-pastern angles normally range from 48 to 55 degrees, but the absolute angle should not be overemphasized. A straight (parallel) pastern-foot axis is more important. A long-toe, underrun-heel foot conformation causes a broken foot axis and predisposes to palmar foot pain (Figure 6-4).

Fig. 6-2 The coronary band is uneven compared with the ground in this trotter’s unbalanced left forelimb hoof. The medial wall (right) appears to be shorter than the lateral wall. A toe weight and bariun point are also shown.

Fig. 6-3 Elevated foot viewed from the palmar aspects shows that the hairline at the medial bulb of heel (on the right) is displaced proximally compared with the lateral heel bulb. The medial wall is longer. Note also the prominent cleft between the heel bulbs. These features are typical of a sheared heel.

Fig. 6-4 This trotter has long toe, underrun heel hoof conformation, and broken hoof-pastern axis.

The conformation, condition, and integrity of the hoof capsule should be assessed. It is easy to miss hoof wall defects on the medial aspect. Small quarter or heel cracks and defects at the coronary band should not be overlooked. The clinician should evaluate the solar surface, bars, and frog. Thrush, although a reflection of poor management, rarely causes lameness.

The shoe type, shoe wear patterns, and the shoe size relative to the foot need to be assessed. The clinician should note the presence of pads or additions to the shoe, such as toe grabs, borium, and heel caulks. There is an association between toe grabs and suspensory apparatus failure in TB racehorses.³ Low heel angle also has been associated with injury.⁴ Shoe wear is important, because it reflects how the horse has been moving over the last several weeks. The clinician should note the breakover point and whether one branch of the shoe is worn more than the other. Shoe size should be assessed relative to foot size and the fit of the shoe. A shoe that is too small or set too close to the frog may predispose to lameness.

Careful palpation of the coronary band in the standing and non–weight-bearing position is critical in detecting foot soreness (Figure 6-5). In horses with sore feet, heat and pain often are detected on the sore side of the foot, and a prominent digital pulse usually is present. Effusion of the distal interphalangeal joint capsule accompanies many abnormalities of the foot, from early synovitis to chronic osteoarthritis of the distal interphalangeal joint, and those with non-specific foot soreness. The clinician places one finger lateral to, and another medial to, the common digital extensor tendon and gently pushes in on the joint capsule, first laterally and then medially. Ballottement is a useful technique to detect effusion in many synovial structures: with effusion, pushing in on the capsule on one side of the tendon causes elevation of the capsule on the other side. The region of the collateral ligaments of the distal interphalangeal joint should be assessed carefully; focal heat or mild swelling may signify acute injury.

Fig. 6-5 Palpation of the coronary band should include assessing the dorsal joint pouch of the distal interphalangeal joint. In this horse, distal interphalangeal effusion and fibrosis appear as a bulge just proximal to the coronary band, dorsally.

The clinician should palpate the cartilages of the foot, either with the horse standing or with the limb elevated. Sidebone, mineralization of the cartilages of the foot, rarely causes lameness. The cartilages of the foot normally are pliable and readily compressed axially. Fracture at the attachment of the cartilage of the foot to the distal phalanx is an occasional cause of lameness, and compression of the heel with hoof testers may elicit pain in some horses. Horses with sidebone often have medial-to-lateral hoof imbalance.

Hoof Tester Examination

“… I feel naked going into a stall without my hoof testers!”⁵ Hoof testers are essential for evaluation of the foot and are a basic requirement for all lameness examinations. Many types of hoof testers are available (Figure 6-6), but I favor one that is adjustable and can be applied with one hand. A proper evaluation of the foot with hoof testers cannot be done with a pad in place, although useful information can be acquired. The instrument can be applied with or without a shoe in place. The amount of force to apply varies from horse to horse and by region of the hoof, and both false-positive and false-negative responses occur. More force is required when the instrument is used across the heel than when used from sole to quarter. The foot should be held between the clinician’s legs in a relaxed manner. The clinician must be able to feel the horse react to subtle pressure, and if the limb is held too tightly or the horse is not calm during the examination, it is difficult to feel a response. The veterinarian should be careful not to place the outside jaw of the instrument too close to the coronary band, because this may cause a false-positive result. Sole sensitivity is assessed by applying the instrument to three to five sites from heel to toe, on both the medial and lateral aspects of the foot, starting from the angle of the sole (seat of the corn) and proceeding dorsally (Figure 6-7). The responses should be compared. If the sole is readily compressible, pain from bruising, a subsolar abscess, laminitis, fracture of the distal phalanx, and other injuries may be elicited, but in horses with hard horn the response may be negative. To evaluate sensitivity of the frog and underlying deeper structures, the hoof testers should be applied from the lateral aspect of the frog to the medial wall, and from the medial aspect of the frog to the lateral wall, each in the palmar, midportion, and dorsal aspects of the frog (Figure 6-8). Pain over the middle third of the frog has been attributed to navicular disease or navicular syndrome, but the specificity of this association is questionable and there are many false-negative responses. Horses with generalized foot soreness or any other cause of palmar foot pain may respond positively or not at all. Only 19 of 42 horses with navicular region pain responded positively to hoof tester examination in the middle third of the frog, with 50% specificity, 50% positive predictive value, and 48% accuracy.⁶ Horses with palmar foot pain caused by other conditions were as likely to respond to the test, a finding that obviously prompts questioning of the value of hoof tester examination.⁶ It is difficult if not impossible to create adequate pressure to cause pain in large breed horses or if the horn is hard. Application of a poultice or soaking the foot may be necessary to soften a hard foot, and reexamination after several days may be rewarding. Hoof tester application to the small feet of foals or ponies may elicit a false-positive response, and hoof tester size or amount of compression may require adjustment.

Fig. 6-6 A variety of hoof testers are available for lameness examinations. I prefer hoof testers that are easily adjusted and used in one hand (two pairs on the right). Large hoof testers (left) can be applied only with two hands, and small hoof testers (bottom) are inappropriate for medium to large hooves.

Fig. 6-7 Hoof testers should be applied from the sole to the wall, from heel to toe, and to both sides of the hoof.

Fig. 6-8 Hoof testers applied from the middle of the frog to the contralateral hoof wall put pressure on the navicular region. Horses with many abnormal conditions of the hoof may manifest a positive response.

Application of hoof testers across the heel may cause pain in horses with palmar foot pain but is not specific (Figure 6-9). Application of the hoof tester to the area of the sole adjacent to each nail, nail hole, or defect in the sole or white line is useful to detect a subsolar abscess or a close nail (Figure 6-10). Areas of pain can be gently explored with a hoof knife, but unless clearly indicated, the veterinarian should refrain from digging too deeply. The hoof tester can then be used as a hammer to percuss each nail in the shoe and the frog and toe regions.

Fig. 6-9 Adjustable hoof testers are easily placed across the heel. I prefer to apply hoof testers in this manner to assess horses for palmar foot pain during static examination and as a provocative test for lameness.

Fig. 6-10 Acute, severe lameness causing increase in digital pulse and profound hoof tester sensitivity in the toe region resulted from this hoof abscess. Exudate drains from the pared region at the toe.

(Courtesy Greg Staller, Pottersville, New Jersey.)

After completing the hoof tester examination, the clinician should reassess the digital pulses. In horses with foot pain the digital pulse may now be bounding. Horses that have recently been shod or trimmed or have raced or performed recently, especially on hard surfaces, may have mild elevations in digital pulse amplitude and may show hoof tester sensitivity normally. Pain causing lameness may not be in the foot.

Wedge Test and Other Forms of Static Manipulation

The wedge test is used most commonly as a dynamic procedure to induce lameness during the movement phase of the examination, but can be used to assess the static response of a horse to dramatic changes in dorsal-to-palmar or medial-to-lateral hoof angles (see Chapter 8, Figure 8-12). A digital extension device, with which the author gauged static painful responses to changes in hoof angle to make shoeing recommendations, was recently described.⁷

Pastern

The proximal interphalangeal (pastern) joint capsule is assessed by ballottement, although severe effusion must be present for fluid distention to be perceived. Bony swelling associated with this joint, proximal or high ringbone, is a classic cause of lameness yet an unusual clinical finding. Osteoarthritis of the proximal interphalangeal joint is a common diagnosis, but one made by a combination of clinical findings, diagnostic analgesia, radiography, and sometimes scintigraphy. The distal extent of the digital flexor tendon sheath (DFTS), deep digital flexor tendon (DDFT), and distal sesamoidean ligaments are palpated. Deep pain associated with the origin and insertion of the distal sesamoidean ligaments is assessed by palpation with the limb in flexion (Figure 6-11). In some horses with lesions of the DDFT within the hoof capsule a positive response to compression of the palmar pastern region is present, but this finding is inconsistent and many false-negative responses occur. The oblique sesamoidean ligaments are difficult to differentiate from the branches of the SDFT, but injury of the SDFT is more common. Distal sesamoidean desmitis or chronic suspensory desmitis may result in subluxation of the proximal interphalangeal joint (Figure 6-12). Swelling should prompt ultrasonographic examination if relevance has been confirmed using diagnostic analgesia. The proximal interphalangeal joint is manipulated in a medial-to-lateral direction to assess pain and collateral ligament integrity and is flexed independently of the fetlock joint. The proximal, dorsal aspect of the proximal phalanx is palpated (Figure 6-13). Horses with short, midsagittal fractures or dorsal frontal fractures of the proximal phalanx or proliferation at the attachment of the common digital extensor tendon may show pain. Enthesophyte formation at the common digital extensor tendon attachment, seen most commonly in older ex-racehorses with chronic osteoarthritis of the fetlock joint, results in prominent bony and soft tissue swelling and pain on palpation.

Fig. 6-11 Palpation of oblique distal sesamoidean ligaments.

Fig. 6-12 Subluxation and osteoarthritis of the left front proximal interphalangeal joint resulted from primary suspensory desmitis.

Fig. 6-13 Proliferative changes at the common digital extensor attachment or pain from midsagittal fracture of the proximal phalanx should be palpated along the dorsal, proximal aspect of the proximal phalanx.

Fetlock

The clinician palpates the joint capsule of the metacarpophalangeal (fetlock) joint with the limb bearing weight, keeping in mind that pain associated with the joint can be present without localizing clinical signs. The dorsal aspect is palpated using ballottement on either side of the common digital extensor tendon. The clinician should determine whether localized heat is present. Osselets is a North American term used to describe early osteoarthritis of the metacarpophalangeal joint in young racehorses, with firm bony and soft tissue swelling on the dorsal, medial aspect of the proximal phalanx, and the distal aspect of the McIII, caused by traumatic capsulitis and early enthesophyte formation. Occasionally in horses with prominent effusion of the metacarpophalangeal joint, a soft tissue swelling can be palpated in the proximal, dorsal aspect of the joint from excessive proliferation of the dorsal synovial pads, called proliferative or villonodular synovitis. The palmar pouch of the metacarpophalangeal joint is palpated dorsal to the SL branches, both medially and laterally. Mild effusion may be present without associated lameness, especially in older performance horses. The PSBs are palpated and assessed for mild swelling and heat, clinical signs of sesamoiditis, or SL avulsion injury. The digital pulse amplitude is reassessed by placing fingers both medially and laterally, abaxial to both PSBs (Figure 6-14).

Fig. 6-14 Digital pulse quality can be assessed easily at the level of the proximal sesamoid bones.

The DFTS extends from the distal metacarpal region to the distal palmar aspect of the pastern. Usually no palpable fluid is found. Effusion of the DFTS (tenosynovitis) causes swelling in the palmar fetlock region that must be differentiated from effusion of the metacarpophalangeal joint. Tenosynovitis causes swelling palmar to the branches of the SL, medially and laterally. Fluid can be compressed from medial to lateral. With severe effusion, distention is found in the palmar aspect of the pastern, but there may be distention proximal to the palmar annular ligament without obvious distention distally. Wind puffs or windgalls describe incidental fluid distention of the DFTS, commonly seen in older performance horses unassociated with lameness. Tenosynovitis can cause lameness, but additional diagnostic techniques are required to confirm the diagnosis.

The limb is elevated to assess range of joint motion and the horse’s response to flexion. Normally the fetlock can be flexed to 90 degrees (the angle between the proximal phalanx and the McIII) or slightly more. A reduction in fetlock flexion range is indicative of chronic fibrosis but is not necessarily a cause for concern. A pronounced response to static flexion is noteworthy, although many horses resent static flexion but do not show a positive response to dynamic flexion (lower limb or fetlock flexion tests; see Chapter 8). Horses with clinically relevant tenosynovitis usually strongly resent fetlock flexion. With the limb in flexion, the clinician palpates the PSBs and the branches of the SL, avoiding compression of the palmar digital nerves.

Metacarpal Region

The clinician should assess the dorsal aspect of the McIII for heat and swelling. This is a common area for traumatic injury (barked shins) or stress-related bone injury (bucked shin syndrome). Many ex-racehorses have incidental, prominent, chronic, and nonpainful swelling of the McIII caused by extensive modeling and remodeling of the dorsal cortex while in race training. Racehorses currently in training may have heat and pain on deep palpation (performed with the limb elevated), but prominent swelling may be lacking. Any combination of palpation findings is possible in horses with stress-related bone injury of the McIII. It is difficult to apply deep pressure to the dorsal aspect of the McIII without concomitant pressure to the palmar soft tissue structures or PSBs, so the responses should be assessed carefully.

The entire length (abaxial surface) of the second and fourth metacarpal bones (McII/IV) should be palpated with the horse in the standing position to detect exostoses, callus, or fractures. Swelling of the SL branches or body may make this difficult. Palpation of the McII and the McIV should be repeated with the limb elevated, because the axial aspect of these bones is impossible to assess in the weight-bearing position. Splint exostoses are common, particularly in young horses. Therefore the presence of even large bony swellings is not unusual. Exostoses detected axially, possibly impinging on the SL or causing adhesions to the SL (or so-called “blind splints”) should be carefully noted. Both false-positive and false-negative results can occur when palpating a splint exostosis and results of palpation and compression should be confirmed using perineural analgesia. Pain from even small exostoses of the McII and the McIV usually is more accurately assessed immediately after training or racing, because pain and lameness resulting from these swellings can be subtle and transient. The clinician should carefully palpate the SL branches. Differentiation of branch or SL body injuries is important: the latter injuries usually are more serious and have a worse prognosis.

The medial and lateral palmar digital vein, artery, and nerve, in dorsal-to-palmar orientation, respectively, are located between the SL and DDFT. The accessory ligament (distal or inferior check ligament) of the DDFT (ALDDFT) normally is difficult to palpate and even when enlarged cannot easily be differentiated from the DDFT, but injuries of the ALDDFT are more common. All soft tissue structures should be palpated carefully, using digital compression, with the limb elevated (Figure 6-15