Evaluation of the local analgesic effect of ketamine in the palmar digital nerve block at the base of the proximal sesamoid (abaxial sesamoid block) in horses

OBJECTIVE: To evaluate the local analgesic effect of ketamine in a palmar digital nerve block at the base of the proximal sesamoid (abaxial sesamoid block) in horses. ANIMALS: 36 mature healthy Andalusian horses. PROCEDURE: Horses were randomly assigned to 4 groups of 9 horses each and received an abaxial sesamoid block in a randomly chosen forelimb with 1 of the following: saline (0.9% NaCl) solution, 1% ketamine solution, 2% ketamine solution, or 3% ketamine solution. To determine analgesia, the radiant heat lamp-hoof withdrawal model was used as a noxious thermal stimulus. Before each nerve block, baseline hoof withdrawal reflex latency (HWRL, time between lamp illumination and withdrawal of the hoof) was determined; after the nerve block, local analgesic effects were determined by measuring HWRL at 2 and 5 minutes after injection and then every 5 minutes for a total period of 1 hour. RESULTS: Significant differences in HWRL were found between baseline values and values at 2 to 15 minutes following a nerve block with ketamine. Significant differences were found between HWRL values at every time point from 2 to 10 minutes following a nerve block with saline solution, compared with 1 or 2% ketamine solution. Similarly, significant differences were found between HWRL values at every time point from 2 to 15 minutes following a nerve block with saline solution, compared with 3% ketamine solution. CONCLUSIONS AND CLINICAL RELEVANCE: Abaxial sesamoid block with ketamine ensures adequate analgesia in horses with an onset of action of 2 minutes and a maximal duration of action of 15 minutes.     

Evaluation of the Local Analgesic Effects of a Commercial Aqueous Extract of Sarracenia purpurea and Ammonium Sulfate in the Equine Abaxial Sesamoid Block Model

Sarracenia purpurea is a carnivorous plant whose aqueous extracts have been proposed to exert analgesic effects by neurolytical action on peripheral nerves. The aim of this study was to determine the local analgesic effects of a commercially available aqueous extract solution of S. purpurea (P-Bloc, St. Joseph, Missouri) and a 1% ammonium sulfate solution, using the horse abaxial sesamoid block model. Twenty horses were randomly assigned to two groups. The first group (n = 10) was used to evaluate the effect of P-Bloc. The horses received a bilateral (medial and lateral) abaxial sesamoid block with 5 mL of P-Bloc in one random forelimb, while in the contralateral forelimb, they received either 5 mL of 2% lidocaine as a positive control (n = 5) or 5 mL of 0.9% NaCl as a negative control (n = 5). The second group (n = 10) was treated as the first but received 5 mL of 1% ammonium sulfate in NaCl (0.9% NaCl) solution instead of P-Bloc. The period of hoof withdrawal reflex latency (HWRL, in seconds) was measured using a custom-made heat projector lamp as a source of a noxious skin heating stimulus applied to the pastern. Lidocaine (2%) prolonged (P ≤ .05) the HWRL period, returning to the negative control basal values after 240 minutes. Neither the treatment with P-Bloc nor 1% ammonium sulfate modified the HWRL period. The lack of effect of these compounds in this model reinforces the results reported elsewhere and suggests a nonlocal anesthetic mechanism of action for the aqueous extract of S. purpurea in the horse.     

Plasma concentration and local anesthetic activity of procaine hydrochloride following subcutaneous administration to horses

OBJECTIVE: To determine the durations of the local anesthetic effect and plasma procaine concentrations associated with 5- and 10-mg doses of procaine hydrochloride (with or without 100 microg of epinephrine) administered SC over the lateral palmar digital nerves of horses. ANIMALS: 6 healthy adult horses. PROCEDURES: The hoof withdrawal reflex latency (HWRL) period was determined by use of a focused heat lamp before and after administration of procaine with and without epinephrine. Blood samples were collected immediately before determination of each HWRL period to assess plasma concentrations of procaine via liquid chromatography-mass spectrometry-mass spectrometry (LC-MS-MS). RESULTS: 10 but not 5 mg of procaine alone and 5 and 10 mg of procaine administered with epinephrine significantly prolonged the HWRL period (mean durations of effect, 5, 120 and 180 minutes, respectively), compared with baseline values. Plasma procaine concentrations did not correlate well with local anesthetic activity; for example, although the HWRL was prolonged to the maximum permitted duration of 20 seconds at 60 to 180 minutes following administration of the 5-mg dose of procaine with epinephrine in certain horses, plasma procaine concentrations were less than the limit of quantitation of the LC-MS-MS assay. CONCLUSIONS AND CLINICAL RELEVANCE: Small doses of procaine coadministered with epinephrine provided long-lasting local analgesia and resulted in plasma procaine concentrations that were not always detectable via LC-MS-MS. On the basis of these results, the use of regulatory limits or thresholds for procaine concentration in equine plasma samples obtained after racing should be seriously reconsidered.     

Lack of local anaesthetic efficacy of fentanyl in the abaxial sesamoid block model

Fentanyl and other opioid drugs have their effect in the central nervous system; however, activity at peripheral sites has also been demonstrated. Pain-suppression activity at peripheral sites raises the possibility of skilled individuals producing local anaesthetic effects with small doses of opioid drugs that would be difficult to detect forensically and could be used to affect the outcome of a race. Therefore, the local pain-suppression effect (peripheral nerve inhibition) of fentanyl was tested using an abaxial sesamoid block/hoof withdrawal model. With this model, fentanyl did not produce significant anaesthesia when tested in eight Thoroughbred horses. This suggests that fentanyl at this or lower doses is unlikely to reduce pain perception when applied directly to sensory neurons. However, the effect of fentanyl and other opioids on joint pain perception of horses, especially inflamed joints, is unknown.     

Effects of buprenorphine on nociception and spontaneous locomotor activity in horses

OBJECTIVE: To investigate spontaneous locomotor activity (SLA) and antinociceptive effects of buprenorphine in horses. ANIMALS: 6 healthy adult horses. PROCEDURES: Horses received each of 3 treatments (10 mL of saline [0.9% NaCl] solution, 5 microg of buprenorphine/kg, or 10 microg of buprenorphine/kg).Treatments were administered IV. Order of treatments was randomized, and there was a 10-day interval between subsequent treatments. Spontaneous locomotor activity was investigated in a behavioral box by use of infrared photoelectric sensors connected to a computer, which detected movement of each horse. Antinociceptive effect was investigated by hoof-withdrawal reflex latency (HWRL) and skin-twitching reflex latency (STRL) after painful stimulation with a heat lamp. RESULTS: Moderate excitement was observed in all horses from 5 to 10 minutes after the administration of both dosages of buprenorphine. The SLA increased significantly for 6 and 14 hours after IV administration of 5 and 10 microg of buprenorphine/kg, respectively. Values for HWRL increased significantly only at 30 minutes after injection of 5 microg of buprenorphine/kg, whereas STRL and HWRL each increased significantly from 1 to 6 hours (except at 2 and 4 hours) and 11 hours, respectively, after injection of 10 microg of buprenorphine/kg. CONCLUSIONS AND CLINICAL RELEVANCE: IV injection of buprenorphine caused a dose-dependent increase in SLA, but only the dose of 10 microg/kg induced analgesia on the basis of results for the experimental method used.     

Characterization of the antinociceptive and sedative effect of amitraz in horses

Amitraz, an acaricide used to control ectoparasites in animals has a complex pharmacological activity, including α₂-adrenergic agonist action. The purpose of this research was to investigate the possible antinociceptive and/or sedative effect of amitraz in horses. The sedative effect of the intravenous (i.v.) injection of dimethylformamide (DMF, 5 mL, control) or amitraz (0.05, 0.10, 0.15 mg/kg), was investigated on the head ptosis test. The participation of α₂-adrenergic receptors in the sedative effect provoked by amitraz was studied by dosing yohimbine (0.12 mg/kg, i.v.). To measure the antinociception, xylazine hydrochloride (1 mg/kg, i.v., positive control) and the same doses of amitraz and DMF were used. A focused radiant light/heat directed onto the fetlock and withers of a horse were used as a noxious stimulus to measure the hoof withdrawal reflex latency (HWRL) and the skin twitch reflex latency (STRL). The three doses of amitraz used (0.05, 0.10 and 0.15 mg/kg) provoked a dose-dependent relaxation of the cervical muscles. The experiments with amitraz and xylazine on the HWRL showed that after i.v. administration of all doses of amitraz there was a significant increase of HWRL up to 150 min after the injections. Additionally, there was a significant difference between control (DMF) and positive control (xylazine) values up to 30 min after drug injection. On the other hand, the experiments on the STRL show that after administration of amitraz at the dose of 0.15 mg/kg, a significant increase in STRL was observed when compared with the control group. This effect lasted up to 120 min after injection. However, no significant antinociceptive effect was observed with the 0.05 and 0.10 mg/kg doses of amitraz or at the 1.0 mg/kg dose of xylazine.     

Effect of gentamicin sulfate and sodium bicarbonate on the synovium of clinically normal equine antebrachiocarpal joints

The effect of gentamicin sulfate, unbuffered and buffered with sodium bicarbonate, on synovial fluid and membrane of clinically normal equine joints was evaluated. Thirty-six adult horses with clinically normal antebrachiocarpal joints were allotted to 6 treatment groups of 6 horses each. One antebrachiocarpal joint in each horse was chosen for treatment. Group-1 horses were given gentamicin (3 ml; 50 mg/ml); group-2 horses were given sodium bicarbonate (3 ml; 1 mEq/ml); group-3 horses were given gentamicin (3 ml; 50 mg/ml) and sodium bicarbonate (3 ml; 1 mEq/ml); group-4 horses were not treated; and horses of groups 5 and 6 were given polyionic physiologic solution (3 and 6 ml, respectively). Synovial fluid specimens were obtained from 5 horses of each group for cytologic analysis at postinjection hours (PIH) 0, 24, 72, and 192 and for pH determination at PIH 0, 0.25, 0.5, 1, 4, 8, 24, 72, and 192. The sixth horse of each group was euthanatized at PIH 24, and the synovial membrane of the treated and contralateral (nontreated) antebrachiocarpal joints was examined macroscopically and microscopically. After intra-articular gentamicin administration, the mean synovial fluid pH was lowest (5.98) at PIH 0.25, but by PIH 8, it was not significantly different from the control value (group-5 horses). When sodium bicarbonate was combined with gentamicin before intra-articular administration, the mean synovial fluid pH was lowest (7.07) at PIH 0.25, but by PIH 1, it was not significantly different from the control value (group-6 horses).(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of skin sensitivity after shock wave treatment in horses

OBJECTIVE: To evaluate the effects of shock wave treatment on cutaneous nerve function, compared with the effects of local nerve block and sedation. ANIMALS: 18 clinically sound Swiss Warmbloods. PROCEDURE: Horses were randomly allocated to 3 groups and received different amounts and types of shock waves (extracorporeal shock wave treatment [ESWT] or radial pressure wave treatment [RPWT]). Horses were sedated with xylazine and levomethadone. Shock waves were applied to the lateral palmar digital nerve at the level of the proximal sesamoid bones on 1 forelimb. Skin sensitivity was evaluated by means of an electrical stimulus at the coronary band before and 5 minutes after sedation and at 4, 24, and 48 hours after application of ESWT or RPWT. On the contralateral forelimb, skin sensitivity was tested before and 10 minutes after an abaxial sesamoid nerve block. RESULTS: No significant changes in skin sensitivity were detected, regardless of the shock wave protocol applied. Mean reaction thresholds after sedation were more than twice the baseline thresholds. After the abaxial sesamoid block, no reaction was recorded in any of the horses. CONCLUSIONS AND CLINICAL RELEVANCE: Application of ESWT or RPWT to the palmar digital nerve had no effect on cutaneous sensation distal to the treated region for at least 2 days after application. The analgesic effect of sedation on reaction to electrical stimuli was distinct but varied among horses.     

Sensory nerve conduction and nociception in the equine lower forelimb during perineural bupivacaine infusion along the palmar nerves

The purpose of this investigation was to study lateral palmar nerve (LPN) and medial palmar nerve (MPN) morphology and determine nociception and sensory nerve conduction velocity (SNCV) following placement of continuous peripheral nerve block (CPNB) catheters along LPN and MPN with subsequent bupivacaine (BUP) infusion. Myelinated nerve fiber distribution in LPN and MPN was examined after harvesting nerve specimens in 3 anesthetized horses and processing them for morphometric analysis. In 5 sedated horses, CPNB catheters were placed along each PN in both forelimbs. Horses then received in one forelimb 3 mL 0.125% BUP containing epinephrine 1:200 000 and 0.04% NaHCO(3) per catheter site followed by 2 mL/h infusion over a 6-day period, while in the other forelimb equal amounts of saline (SAL) solution were administered. The hoof withdrawal response (HWR) threshold during pressure loading of the area above the dorsal coronary band was determined daily in both forelimbs. On day 6 SNCV was measured under general anesthesia of horses in each limb's LPN and MPN to detect nerve injury, followed by CPNB catheter removal. The SNCV was also recorded in 2 anesthetized non-instrumented horses (sham controls). In both LPN and MPN myelinated fiber distributions were bimodal. The fraction of large fibers (>7 μm) was greater in the MPN than LPN (P < 0.05). Presence of CPNB catheters and SAL administration did neither affect measured HWR thresholds nor SNCVs, whereas BUP infusion suppressed HWRs. In conclusion, CPNB with 0.125% BUP provides pronounced analgesia by inhibiting sensory nerve conduction in the distal equine forelimb.     

Association between findings on palmarodorsal radiographic images and detection of a fracture in the proximal sesamoid bones of forelimbs obtained from cadavers of racing Thoroughbreds

OBJECTIVE: To determine the distribution for limbs and bones in horses with fractures of the proximal sesamoid bones and relationships with findings on palmarodorsal radiographic images. SAMPLE POPULATION: Proximal sesamoid bones obtained from both forelimbs of cadavers of 328 racing Thoroughbreds. PROCEDURE: Osteophytes; large vascular channels; and fracture location, orientation, configuration, and margin distinctness were categorized by use of high-detail contact palmarodorsal radiographs. Distributions of findings were determined. Relationships between radiographic findings and fracture characteristics were examined by use of chi2 and logistic regression techniques. RESULTS: Fractures were detected in 136 (41.5%) horses. Biaxial fractures were evident in 109 (80%) horses with a fracture. Osteophytes and large vascular channels were evident in 266 (81%) and 325 (99%) horses, respectively. Medial bones typically had complete transverse or split transverse simple fractures, indistinct fracture margins, > 1 vascular channel that was > 1 mm in width, and osteophytes in abaxial wing and basilar middle or basilar abaxial locations. Lateral bones typically had an oblique fracture and distinct fracture margins. Odds of proximal sesamoid bone fracture were approximately 2 to 5 times higher in bones without radiographic evidence of osteophytes or large vascular channels, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Biaxial fractures of proximal sesamoid bones were common in cadavers of racing Thoroughbreds. Differences between medial and lateral bones for characteristics associated with fracture may relate to differences in fracture pathogeneses for these bones. Osteophytes and vascular channels were common findings; however, fractures were less likely to occur in bones with these features.     

Use of Electrocautery Probes in Arthroscopic Removal of Apical Sesamoid Fracture Fragments in 18 Standardbred Horses

OBJECTIVE: To develop a technique for arthroscopic excision of apical sesamoid fracture fragments using electrocautery probes. ANIMALS OR SAMPLE POPULATION: A total of 18 Standardbred horses. METHODS: Arthroscopic removal of apical sesamoid fracture fragments using both hook and loop electrocautery probes was performed on 18 Standardbred horses. The fracture fragments were approached using either an ipsilateral (3) or contralateral (15) arthroscopic triangulation technique. Distension of the metacarpo- (metatarso)-phalangeal joints was achieved using a 1.5% glycine solution. Under arthroscopic guidance, both the suspensory and intersesamoidean ligament attachments to the abaxial and the axial margins of the apical fragment were transected using a hook electrocautery probe. Subsequently, the palmar (plantar) soft tissue attachments to the apical fragment were transected with a loop electrocautery probe. Once freed of soft tissue attachments, the apical fragment was removed with Ferris-Smith intervertebral disc rongeur. The arthroscopic portals were closed in a routine manner. RESULTS: Horse ages ranged from 2 to 8 years (median, 2.5 years). Eighteen apical sesamoid fracture fragments were removed from the left (8) and right (8) hind limbs and the left (1) and right (1) forelimbs. Apical fragments occured in 15 lateral and 3 medial proximal sesamoid bones. No major complications occurred during or after surgery. The electrocautery probes permitted an easy and precise dissection of all soft tissue attachments to the apical sesamoid fracture fragments in all horses. Follow-up time was 7 to 44 months (median, 26 months); 10 of 14 horses returned to racing. Seven of nine horses that raced before surgery raced again and three of five that had not raced before surgery, raced afterwards. CONCLUSION: Arthroscopic excision of apical sesamoid fracture fragments can be accomplished arthroscopically using electrocautery probes. CLINICAL RELEVANCE: Arthroscopic electrosurgery is an efficient and safe alternative for intra-articular dissection in horses.     

THE EFFECTS OF REGIONAL PERINEURAL ANESTHESIA ON SOFT TISSUE AND BONE PHASE SCINTIGRAPHY IN THE HORSE

Soft tissue phase scintigrams were acquired from 7 normal horses before and over a 17-day period after palmar digital, abaxial sesamoid, low palmar and high palmar nerve blocks. Bone phase scintigrams were acquired from 4 additional horses prior to performing similar regional anesthesia and over a 14-day period postanesthesia. Images were evaluated subjectively and quantitatively for increased activity in nerve block regions. On soft tissue phase scintigrams, palmar digital and abaxial sesamoid blocks resulted in increases in activity which were relatively mild, of short duration, and subjectively had little or no effect on image interpretation. Low palmar and high palmar blocks resulted in obvious focal accumulation of activity during the soft tissue phase. Such increases in activity were usually greatest at 1 day postanesthesia and persisted up to 17 days postanesthesia. On bone phase scintigrams, abnormal accumulation of activity was not evident.     

Digital blood flow and plasma endothelin concentration in clinically endotoxemic horses

OBJECTIVE: To measure plasma endothelin-1 (ET-1) concentrations and digital blood flow in clinically endotoxemic horses. ANIMALS: 36 adult horses that underwent emergency celiotomy for primary gastrointestinal tract disease. PROCEDURE: On days 2 and 5 following surgery, Doppler ultrasonographic digital arterial blood flow measurements were obtained. Hematologic and biochemical analyses were performed, and plasma concentrations of ET-1 and endotoxin (lipopolysaccharide) were determined. A scoring system based on 9 clinical variables was used to assign horses to group B (quartile with greatest cumulative score) or group A (remaining 3 quartiles). Follow-up at 2.5 years was obtained by telephone questionnaire. RESULTS: For all horses on day 2, median (interquartile values) plasma ET-1 concentrations were 1.4 (0.8, 1.7) pg/mL, whereas on day 5, plasma ET-1 concentrations were 1.0 (0.5, 1.6) pg/mL. On day 2, digital blood flow was 0.057 (0.02, 0.07) mL/min in group A horses and 0.035 (0.02, 0.03) mL/min in group B horses. On day 5, plasma ET-1 concentration was significantly (73%) higher in group B horses, compared with group A horses. Thirty of 36 horses were alive at 2.5 years; group A horses were more likely to have survived (odds ratio, 25; 95% confidence interval, 2.4 to 262). Significant associations were found between an increase in digital pulses, hoof wall temperatures, or both and increased digital blood flow (0.14 vs 0.04 mL/min) on day 2 and increased digital arterial diameter (0.32 vs 0.23 cm) on day 5. CONCLUSIONS AND CLINICAL RELEVANCE: Horses with more severe endotoxemia had decreased digital blood flow, increased plasma ET-1 concentrations, and decreased long-term survival.     

Effects of ketamine and magnesium on the minimum alveolar concentration of isoflurane in goats

OBJECTIVE: To evaluate the effects of ketamine, magnesium sulfate, and their combination on the minimum alveolar concentration (MAC) of isoflurane (ISO-MAC) in goats. ANIMALS: 8 adult goats. PROCEDURES: Anesthesia was induced with isoflurane delivered via face mask. Goats were intubated and ventilated to maintain normocapnia. After an appropriate equilibration period, baseline MAC (MAC(B)) was determined and the following 4 treatments were administered IV: saline (0.9% NaCl) solution (loading dose [LD], 30 mL/20 min; constant rate infusion [CRI], 60 mL/h), magnesium sulfate (LD, 50 mg/kg; CRI, 10 mg/kg/h), ketamine (LD, 1 mg/kg; CRI, 25 microg/kg/min), and magnesium sulfate (LD, 50 mg/kg; CRI, 10 mg/kg/h) combined with ketamine (LD, 1 mg/kg; CRI, 25 microg/kg/min); then MAC was redetermined. RESULTS: Ketamine significantly decreased ISOMAC by 28.7 +/- 3.7%, and ketamine combined with magnesium sulfate significantly decreased ISOMAC by 21.1 +/- 4.1%. Saline solution or magnesium sulfate alone did not significantly change ISOMAC. CONCLUSIONS AND CLINICAL RELEVANCE: Ketamine and ketamine combined with magnesium sulfate, at doses used in the study, decreased the end-tidal isoflurane concentration needed to maintain anesthesia, verifying the clinical impression that ketamine decreases the end-tidal isoflurane concentration needed to maintain surgical anesthesia. Magnesium, at doses used in the study, did not decrease ISOMAC or augment ketamine's effects on ISOMAC.     

Effects of an intravenous endotoxin challenge on glucose and insulin dynamics in horses

OBJECTIVE: To evaluate the effects of endotoxin administered IV on glucose and insulin dynamics in horses. ANIMALS: 16 healthy adult mares. PROCEDURES: Each week of a 2-week randomized crossover study, each horse received an IV injection (duration, 30 minutes) of Escherichia coli O55:B5 lipopolysaccharide (LPS) in 60 mL of sterile saline (0.9% NaCl) solution (20 ng/kg) or sterile saline solution alone (control treatment). Frequently sampled IV glucose tolerance test procedures were performed at 24 hours before (baseline) and 24 and 48 hours after injection; glucose and insulin dynamics were assessed via minimal model analysis. RESULTS: 13 of 16 horses had a clinical response to LPS, which was characterized by mild colic and leukopenia. Before treatment, mean +/- SD insulin sensitivity was 2.9 +/- 1.9 x 10(4) L x min(1) x mU(1); this significantly decreased to 0.9 +/- 0.9 x 10(4) L x min(1) x mU(1) 24 hours after treatment (69% reduction) and was 1.5 +/- 0.9 x 10(4) L x min(1) x mU(1) 48 hours after treatment. At baseline, mean +/- SD acute insulin response to glucose was 520 +/- 196 mU x min x L(1); this significantly increased to 938 +/- 620 mU x min x L(1) (80% increase) and 755 +/- 400 mU x min x L(1) (45% increase) at 24 and 48 hours after LPS treatment, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Compared with baseline values, insulin sensitivity was decreased for 24 hours after IV injection of LPS, and affected horses had a compensatory pancreatic response. These disturbances in glucose and insulin dynamics may contribute to development of laminitis in horses.     

Decreased expression of p63, a regulator of epidermal stem cells, in the chronic laminitic equine hoof

Reasons for performing study: Abnormal epidermal stem cell regulation may contribute to the pathogenesis of equine chronic laminitis. Objective: To analyse the involvement of p63, a regulator of epidermal stem cell proliferative potential, in chronic laminitis. Methods: Epidermal tissues from skin, coronet and lamellae of the dorsal foot were harvested from 5 horses with chronic laminitis and 5 control horses. Tissues were analysed using histopathology, immunofluorescence microscopy and quantitative immunoblotting Results: Hoof lamellae of laminitic horses had a lower frequency of p63 positive cells than control lamellae, particularly in the distal region. Quantitative immunoblotting confirmed reduced p63 expression in the laminitic distal lamellar region. The decreased p63 expression in laminitic epidermal lamellae was most apparent in the abaxial region adjacent to the hoof wall and highly associated with the formation of terminally differentiated, dysplastic and hyperkeratotic epidermis in this region, whereas lamellae from control horses maintained high p63 expression throughout the axial‐abaxial axis. Conclusions: Expression of p63 in equine skin resembles that reported in other species, including man and rodents, suggesting that p63 can serve as a marker for the proliferative potential of equine epidermal stem cells. p63 expression was significantly lower in the chronic laminitic hoof than in that of control horses, suggesting laminitic hoof epithelium has more limited proliferative potential with a shift towards differentiation. This may reflect reduced activity of epidermal stem cells in laminitic hoof. It is proposed that p63 contributes to the maintenance of hoof lamellae and that misregulation of p63 expression may lead to epidermal dysplasia during lamellar wedge formation. Potential relevance: This study suggests that loss of epidermal stem cells contributes to the pathogenesis of equine laminitis. Autologous transplantation of p63‐positive epidermal stem cells from unaffected regions may have regenerative therapeutic potential for laminitic horses.     

Fungal osteomyelitis of the axial border of the proximal sesamoid bones in a horse

CASE DESCRIPTION: A 12-year-old Standardbred gelding was referred for swelling of the right metacarpophalangeal joint. CLINICAL FINDINGS: Ultrasonography of the right metacarpal area revealed hypoechoic areas in the right digital sheath and metacarpophalangeal joint consistent with synovial effusion. Radiography of the right metacarpophalangeal joint revealed lysis of the axial border of the proximal sesamoid bones. Aspergillus fumigatus was detected on fungal culture of synovial fluid. TREATMENT AND OUTCOME: Regional limb perfusion (150 mg of amikacin in 60 mL of saline [0.9% NaCl] solution perfused for 30 minutes) was performed 2 and 4 days after admission. Itraconazole (5 mg/kg [2.27 mg/lb], PO, q 24 h) was administered for approximately 9 weeks. Joint lavage with amikacin (500 mg) in 1 L of saline solution was performed 4 times. Three months after discharge, the owner reported that the horse was mildly lame during trotting but was moving freely and comfortably during all gaits and had gained a considerable amount of weight. Because the osteoarthritis was not expected to improve and because it was recommended that the horse not return to purposeful exercise, the owner decided to retire the horse from racing. CLINICAL RELEVANCE: Various diagnostic imaging methods and fungal cultures are useful for diagnosing fungal osteomyelitis of the axial borders of the proximal sesamoid bones in horses. Fungal osteomyelitis of the sesamoid bones and erosive arthritis should be considered as a differential diagnosis for horses in which corticosteroids have been administered intra-articularly.     

Lack of local anaesthetic efficacy of Sarapin® in the abaxial sesamoid block model

Sarapin® is a distillate of the pitcher plant that has long been used in human and veterinary medicine for'regional analgesia'. The mechanism of the reported analgesic response is unknown; however, the agent is purported to provide more effective analgesia for slow, chronic pain than for sharp, acute pain. Reportedly, Sarapin® is also widely used as an analgesic agent in the horse, generally in combination with corticosteroids and other agents. To determine its local anaesthetic efficacy in the horse, we tested Sarapin® in a unilateral abaxial sesamoid block model at two dose levels, 2 mL and 10 mL per site, respectively. Cutaneous pain was induced with a light/heat lamp, and analgesia was assessed by measuring the hoof-withdrawal reflex latency period. Neither dose of Sarapin® altered hoof-withdrawal reflex latency in this experimental model tested over a two-week period. Based on the demonstrated efficacy of this local anaesthetic model, it seems clear that Sarapin® has no significant classical local anaesthetic actions in the horse, and probably not in other species either.     

Keratomas in horses: seven cases (1975-1986)

The diagnosis of keratoma in 7 horses and their treatment and outcome were evaluated. Horses were 2 to 20 years old, of various breeds, and were intact or castrated males. All were lame, and 6 horses had had previous injuries of the affected hoof that had not responded to prior treatments. Only 1 hoof was affected in each horse. Keratomas were beneath the hoof wall (6 horses) or sole (1 horse). Radiographically, a circular or semicircular defect with a discrete margin was present in the distal portion of the third phalanx in 3 horses. Grossly, keratomas were firm solitary masses (1.5 to 5 cm diameter); gray, tan, or yellow; and oval or conical. Keratomas were excised from beneath the hoof wall by removing a section of hoof wall (5 horses) or by undermining the wall beginning at its junction with the sole (1 horse). A keratoma beneath the sole in 1 horse was excised by excavating the sole to the level of the palmar surface of the third phalanx. Keratoma was verified microscopically by the presence of characteristic rings of squamous epithelial cells with abundant keratin. Purulent exudate and inflammatory infiltrate often were present concurrently, reflecting an associated localized infection. Aftercare included daily application of an antiseptic iodine solution and foot bandages, and shoeing with a treatment plate several weeks after surgery. Hoof and sole defects healed completely between 6 months and 1 year. By 1 year after surgery, 6 horses were sound, and keratoma had not recurred.     

Digit innervation of the thoracic limb of Criollo horses: Anatomical description and consequences to perineural blocks

Criollo horse breeding is an important economic activity in South America. Because of their athletic performance, these animals tend to show great incidence of musculoskeletal disorders, many of them diagnosed by means of perineural blocks. However, incorrect interpretation of these blocks may be due to anatomical differences in nerve distribution. The objective of this study was to describe the innervation of the digit region of thoracic limbs in Criollo horses, in order to improve the interpretation of tests for claudication diagnosis based on nerve block. Thirty thoracic limbs from Criollo horses were dissected. It could be observed that in 90% of the limbs, dorsal branches of the palmar nerve originated proximally to the proximal sesamoid bone. In 93% of the cases, the palmar digital nerve and the dorsal branches communicated; in 87% of the cases, communication between branches of the dorsal branch was observed; and in 27% (8/30) of the limbs, the palmar metacarpal nerve and the dorsal branch presented communications. None of the specimens showed complete symmetry in the distribution of nerves in contralateral limbs. The high frequency of communication between the nerves may be a particularity of the Criollo breed that may interfere with the interpretation of perineural blocks. Based on the anatomical position, it may be inferred that divergent results in Criollo horses may occur when abaxial sesamoid nerve block is used. Palmar digital nerve block may be less influenced by these variations, provided it is performed as distal as possible from the ungular cartilage.