Page 531 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Distal Limb 497

forelimbs placed more anterior than normal and
hindlimbs placed more posterior than normal. Similarly,
VetBooks.ir animal with only forelimb involvement. Importantly,
their gait may be more normal in appearance than the
patients with distal displacement of the third phalanx in
all four limbs are usually intensely resistant to move-
ment and more commonly recumbent due to severe
pain. It is at times difficult to determine whether the
forelimbs or both forelimbs and hindlimbs are affected;
short‐lived anesthesia (using lidocaine) of the forefeet
with abaxial sesamoid nerve blocks helps determine
whether any lameness exists in the hindfeet or if any
abnormality noted in hindlimb gait is merely compensa-
tion for the painful forelimbs.
Increased hoof temperature and the strength of digi-
tal pulses must be interpreted in the context of the lame-
ness and other systemic symptoms, because it is not
unusual for an increase in hoof temperature to be tran-
sient, and the interpretation of digital pulses is highly
subjective. Application of hoof testers is useful to con-
firm the presence of pain around the dorsal margins of
the sole in cases with mild lameness in which laminitis is
suspected. The clinician can also use hoof testers to
detect unilateral (more accurately described as uniaxial) Figure 4.71. This foot from a horse with chronic laminitis
pain (medial vs. lateral pain) in unilateral distal displace- demonstrates abnormal hoof growth with wider growth rings at the
ment. Less commonly, hoof testers can be used to detect heel where there is more growth (small arrows) and converging to
heel pain in some chronically affected horses with sec- narrowly placed rings at the toe (large arrow) where minimal hoof
ondary heel contracture. The veterinarian must keep in growth is occurring. Source: Courtesy of Dr. Gary Baxter.
mind differential diagnoses such as sole bruising that, in
the early stages, can present similarly with digital pulses
and bilateral pain in response to hoof testers. Diagnosis
Horses with chronic laminitis have different degrees The diagnosis of laminitis may be obvious in acute
of hoof capsule deformation and lameness. Changes to severe cases due to the history, characteristic stance, and
the hoof capsule vary with the duration of the disease digital exam. The diagnosis may be much more difficult
and type of displacement and may be visible in both the in chronic mild cases, especially in older horses that may
wall and the sole. In the case of a patient with chronic have bilateral distal limb arthropathies contributing to
laminitis and rotation, the wall is unchanged in the the lameness. In the acute case with severe lameness of
immediate period after displacement of the distal pha- the forelimbs, one author (JKB) performs an abaxial
lanx, but commonly assumes a dorsally concave appear- sesamoid nerve block with lidocaine in order to:
ance as the disease progresses due to disparate growth
between the toes and the heels (slower growth in the toe 1. Enable the clinician to rapidly obtain good quality
region) and the presence of a lamellar wedge. This dispa- radiographs without undue stress to the horse
rate growth is also reflected in abnormal growth rings, 2. Enable thorough examination of the solar surface
which are more widely spaced in the heel than the toe 3. Assess for involvement of the hindlimbs (by limited
(Figure 4.71). The sole dorsal to the apex of the frog may walking of the horse around the stall in each
be soft and flattened (or convex) due to downward pres- direction)
sure on the sole from the dorsodistal aspect of the dis- 4. Enable the application of therapeutic shoes or pads
placed distal phalanx secondary to either rotation or to the affected limbs
distal displacement. The flat, soft character of the sole It is important to note that lidocaine is the local anes-
may lead to bruising around its dorsal margin. The white thetic of choice for this perineural anesthesia as its short
line may be wider than normal, frequently with elon- duration of action will ensure that the patient will not
gated keratinized lamellae, and show evidence of prior put excessive stress on already tenuous lamellar
bruising/hemorrhage. In cases of distal displacement of attachments.
the third phalanx, there may be a palpable (and some- In the chronic, mild case, it is best to initially block
times visible) groove at the junction of the skin of the the digit with a palmar digital (PD) nerve block, which
pastern and the coronary band. The lameness in the long‐ blocks solar pain due to a displaced distal phalanx, 65,66
standing chronic case is commonly only from excessive a common cause of pain in the chronic case of laminitis.
sole pressure by the displaced distal phalanx, with mini- Although it has recently been established that the PD
mal lamellar pain present due to healing of the lamellae nerve (not the dorsal branch) provides the majority of
(i.e. the lamellae are stable and therefore pain‐free even if the innervation to the lamellae in normal horses, the
58
abnormal morphologically). The most common excep- PD block does not appear to block a lameness due to
tion to this is the horse with recurrent laminitis due to dorsal lamellar pain in most laminitic horses. The rea-
either PPID or EMS, in which bouts of lamellar injury/ son for this disparity may be that lamellar pain in lami-
instability commonly recur. nitic horses is likely due to lamellar instability, which