Effects of analgesia of the distal interphalangeal joint or palmar digital nerves on lameness caused by solar pain in horses

OBJECTIVE: To determine if pain of the dorsal margin of the sole in horses can be attenuated by anesthesia of either the distal interphalangeal (DIP) joint or the palmar digital (PD) nerves. STUDY DESIGN: A unilateral forelimb lameness was induced by creating solar pain. Response to administration of local anesthetic or saline solution into the DIP joint and to administration of local anesthetic around the PD nerves was evaluated. Animals: Six horses. METHODS: Lameness was induced by creating pressure on the dorsal margin of the sole by screwing set-screws into a nut welded to the inside of each branch of a shoe. Gaits were evaluated before and after application of set-screws and after a local anesthetic or saline solution was administered into the DIP joint and, in a second trial, after a local anesthetic was injected around the PD nerves. Gaits recorded on videotape were evaluated, and lameness scores were assigned to each gait. RESULTS: Lameness scores were high after application of set-screws and remained high after saline solution was administered into the DIP joint. Scores decreased significantly (P < or = .05) after a local anesthetic was administered into the DIP joint or around the PD nerves. CONCLUSIONS: Analgesia of the DIP joint or the PD nerves desensitizes at least a portion of the sole. CLINICAL RELEVANCE: Pain arising from the sole should not be excluded as a cause of lameness when lameness is attenuated by analgesia of the DIP joint or PD nerves.     

The effects of local anaesthetic solution in the navicular bursa of horses with lameness caused by distal interphalangeal joint pain

REASONS FOR PERFORMING STUDY: Analgesia of the palmar digital (PD) nerves has been demonstrated to cause analgesia of the distal interphalangeal (DIP) joint as well as the sole. Because the PD nerves lie in close proximity to the navicular bursa, we suspected that that analgesia of the navicular bursa would anaesthetise the PD nerves, which would result in analgesia of the DIP joint. OBJECTIVES: To determine the response of horses with pain in the DIP joint to instillation of local anaesthetic solution into the navicular bursa. METHODS: Lameness was induced in 6 horses by creating painful synovitis in the DIP joint of one forefoot by administering endotoxin into the joint. Horses were videorecorded while trotting, before and after induction of lameness, at three 10 min intervals after instilling 3.5 ml local anaesthetic solution into the navicular bursa and, finally, after instilling 6 ml solution into the DIP joint. Lameness scores were assigned by grading the videorecorded gaits subjectively. RESULTS: At the 10 and -20 min observations, median lameness scores were not significantly different from those before administration of local anaesthetic solution into the navicular bursa (P > or = 0.05), although lameness scores of 3 of 6 horses improved during this period, and the 20 min observation scores tended toward significance (P = 0.07). At the 30 min observation, and after analgesia of the DIP joint, median lameness scores were significantly improved (P < or = 0.05). CONCLUSIONS: These results indicate that pain arising from the DIP joint can probably be excluded as a cause of lameness, when lameness is attenuated within 10 mins by analgesia of the navicular bursa. POTENTIAL RELEVANCE: Pain arising from the DIP joint cannot be excluded as a cause of lameness when lameness is attenuated after 20 mins after analgesia of the navicular bursa.     

A comparison of the effects of local analgesic solution in the navicular bursa of horses with lameness caused by solar toe or solar heel pain

We hypothesised that analgesia of the navicular bursa is not selective for the navicular apparatus; and that solar pain in some horses can be temporarily abolished or attenuated by analgesia of the navicular bursa. To test this hypothesis, we caused lameness in horses by inducing pain in the dorsal margin or the angles of the sole and then evaluated the ability of a local analgesic solution administered into the navicular bursa to attenuate lameness. The response of horses with solar pain in the dorsal or palmar aspect of the foot to 3.5 ml local analgesic solution administered into the navicular bursa was examined. Lameness was induced in 6 horses by creating solar pain in the dorsal aspect of one forefoot and, at another time, the palmar aspect of the other forefoot, with set-screws inserted into a custom-made shoe. Horses were videotaped trotting before and after application of set-screws and after administering 3.5 ml local analgesic solution into the navicular bursa. Lameness scores were assigned by examining videotaped gaits. Scores were significantly lower (P<0.05) for all horses with set-screws applied to the dorsal margin of the sole after administration of local analgesic solution into the navicular bursa. In conclusion, analgesia of the navicular bursa was less effective in desensitising the angles of the sole than in desensitising the dorsal margin of the sole. Pain arising from the sole should not be excluded as a cause of lameness when lameness is attenuated by analgesia of the navicular bursa.     

Effects of analgesia of the digital flexor tendon sheath on pain originating in the sole, distal interphalangeal joint or navicular bursa of horses

REASON FOR PERFORMING STUDY: Specific analgesic techniques are required in diagnosis of lameness to isolate the exact origin of pain to the many structures of the foot that may be involved. OBJECTIVE: To determine if analgesia of the digital flexor tendon sheath (DFTS) results in anaesthesia of other portions of the foot, such as the sole, distal interphalangeal joint (DIPJ), or navicular bursa (NB). METHODS: Lameness caused by pain in the dorsal margin or heel region of the sole of the foot was induced in 18 horses by: using set-screws to create solar pressure (Trial 1: n = 5); or administering endotoxin intrasynovially into the DIPJ (Trial 2: n = 6) and NB (Trial 3: n = 7). The gait of each horse was evaluated by examining videotape recorded before and after creation of lameness and after administration of mepivacaine hydrochloride into the DFTS. RESULTS: Median lameness scores in Trial 1 at 10 min post injection of the DFTS were not significantly different from those before administration of local anaesthetic solution into the DFTS (P> or =0.05), but median lameness scores were reduced significantly at 20 min (P< or =0.05). In Trials 2 and 3, median lameness scores were not significantly different at observations made at 10 and 20 min post injection of the DFTS. CONCLUSIONS: Analgesia of the DFTS has little effect on lameness caused by pain originating in the sole, DIPJ or NB. POTENTIAL RELEVANCE: Improvement of lameness in horses after intrasynovial analgesia of the DFTS is probably caused by attenuation of pain within the structures contained in the DFTS.     

Diagnostic analgesia of the equine digit

Analgesia usually occurs within 5 min after administration of local anaesthetic solution into joints or around nerves in the distal portion of the limb. Gait should be assessed within 10 min after diagnostic regional analgesia of the distal portion of the limb because rapid diffusion of anaesthetic solution can result in anaesthesia of other nerve branches, thus confusing results of the examination. A palmar digital nerve block (PDNB) anaesthetises most of the foot, including the distal interphalangeal (DIP) joint (coffin joint), rather than just the palmar half of the foot, as was once commonly believed. To avoid partially anaesthetising the proximal interphalangeal joint (pastern joint), the palmar digital nerves should be anaesthetised near or distal to the proximal margin of the collateral cartilages. Clinicians should be aware that an abaxial sesamoid nerve block (ASNB) may ameliorate or abolish pain within the metacarpo/metatarso‐phalangeal joint (fetlock joint). Mepivacaine administered into the DIP joint desensitises the DIP joint and probably the palmar digital nerves to also cause anaesthesia of the navicular bursa, the navicular bone, the toe region of the sole, the digital portion of the deep digital flexor tendon (DDFT) and the distal portions of the collateral ligaments of the DIP joint. When a large volume of mepivacaine HCl (e.g. 10 ml) is administered, the heel region of the sole may also be desensitised. Only a small percentage of horses with disease of the collateral ligament(s) of the DIP joint show a significant improvement in lameness after intra‐articular analgesia of the DIP joint, and no horse is likely to improve after intrabursal analgesia of the navicular bursa. A PDNB, however, improves lameness substantially in most horses that are lame because of disease of the collateral ligament(s) of the DIP joint, and all affected horses are likely to become sound after an abaxial sesamoid nerve block. The degree of improvement in lameness associated with injury to one or both collateral ligaments of the DIP joint after PDNB is determined by the extent of the injury and the level at which the palmar digital nerves are anaesthetised. The further proximal the level of the injury within the collateral ligament, the less likely that lameness is ameliorated by analgesia of the DIP joint or a PDNB. Verschooten's technique appears to be the most accurate technique for centesis of the navicular bursa. Even though analgesia of the DIP joint results in analgesia of the navicular bursa, analgesia of the navicular bursa does not result in analgesia of the DIP joint. Pain arising from the DIP joint can probably be excluded as a cause of lameness when lameness is attenuated by analgesia of the navicular bursa. Analgesia of the digital flexor tendon sheath (DFTS) is likely to desensitise only structures that are contained within or border on the sheath itself (i.e. the superficial and deep digital flexor tendons, the straight and oblique distal sesamoidean ligaments, the annular ligaments of the fetlock and pastern, and the portion of the DDFT that lies within the foot). Because lameness caused by disease of the DDFT within the foot may fail to improve appreciably after analgesia of the palmar digital nerves, the DIP joint, or the navicular bursa, a portion of the DDFT within the foot and distal to the DFTS probably receives its sensory supply from more proximal deep branches of the medial and lateral palmar digital nerves that enter the DFTS. Performing intrathecal analgesia of the DFTS on horses with lameness that is unchanged after anaesthesia of the palmar digital nerves but resolves after an ASNB, may be useful in localising lameness to that portion of the DDFT that lies within the foot. Resolution of lameness after intrathecal analgesia of the DFTS justifies suspicion of a lesion within the digital portion of the DDFT or within structures contained within the DFTS. The belief that concurrent or sequential intra‐articular administration of medication substantially increases the risk of joint infection or that inflammation caused by the local anaesthetic solution may dampen the therapeutic response to intra‐articular medication appears to be unfounded.     

A comparison of the effects of two volumes of local analgesic solution in the distal interphalangeal joint of horses with lameness caused by solar toe or solar heel pain

The response of horses, with solar pain in the dorsal or palmar aspect of the foot, to 6 or 10 ml local analgesic solution administered into the distal interphalangeal (DIP) joint was examined. Lameness was induced in 7 horses by creating solar pain in the dorsal aspect of one forefoot and, at another time, the palmar aspect of the other forefoot with set-screws inserted into a custom-made shoe. Horses were videotaped trotting before and after application of set-screws and, in separate trials, after 6 or 10 ml local analgesic solution was administered into the DIP joint. Lameness scores were assigned by examining videotaped gaits. Scores were significantly lower (P < 0.05) for horses with set-screws applied to the angles of the sole and receiving 10 ml, but not 6 ml, local analgesic solution into the DIP joint. Scores were significantly lower (P < 0.05) for all horses with set-screws in the dorsal margin of the sole receiving either volume of local analgesic solution. Analgesia of the DIP joint was less effective in desensitising the angles of the sole than in desensitising the dorsal margin of the sole, and 10 ml local analgesic solution was more effective than 6 ml in desensitising these regions. The response of horses with solar pain to local analgesic solution in the DIP joint was influenced by the volume administered and the region of sole affected.     

Use of Body-Mounted Inertial Sensors to Objectively Evaluate the Response to Perineural Analgesia of the Distal Limb and Intra-articular Analgesia of the Distal Interphalangeal Joint in Horses With Forelimb Lameness

Diagnostic analgesia of the distal interphalangeal (DIP) joint is theoretically helpful to localize the source of pain in the foot to the joint and/or navicular bursa. However, it has been suggested that potential diffusion of local anesthetic agent to nearby distal limb nerves may anesthetize other areas of the foot. The objective of this study was to compare the results of palmar digital (PD) and abaxial sesamoid (AS) nerve blocks to intra-articular anesthesia of the DIP joint in horses with distal forelimb lameness. Palmar digital nerve block (group 1) or PD and AS nerve blocks (group 2) were used to abolish digital pain in 22 horses. The following day lameness was again evaluated in all horses before and 2, 5, and 10 minutes after DIP joint anesthesia. All lameness evaluations were performed objectively with a body-mounted inertial sensor system (Lameness locator; Equinosis LLC, Columbia, MO). In group 1 horses, overall improvement in group lameness was the same after DIP joint block, but only six showed positive response after DIP joint analgesia, five after 2 minutes, and one after 5 minutes. In group 2 horses, overall improvement in lameness was less after DIP joint block, with seven showing a positive response after DIP joint analgesia, one after 2 minutes, four after 5 minutes, and two after 10 minutes. Intra-articular analgesia of the DIP joint and perineural analgesia of the digit result in overlapping but unequal areas of analgesia. In addition, a time-dependent response was observed after DIP joint block with full effect requiring 5–10 minutes.     

Lameness in 46 horses associated with deep digital flexor tendonitis in the digit: diagnosis confirmed with magnetic resonance imaging

REASONS FOR PERFORMING STUDY: The differential diagnosis of foot pain has long proved difficult and the use of magnetic resonance imaging (MRI) offers the opportunity to further the clinical understanding of the subject. OBJECTIVES: To determine the incidence of deep digital flexor tendon (DDFT) injuries in a series of 75 horses with lameness associated with pain localised to the digit, with no significant detectable radiographic or ultrasonographic abnormalities, using MRI; and to describe a variety of lesion types and relate DDF tendonitis with anamnesis, clinical features, response to local analgesic techniques and nuclear scintigraphic and ultrasonographic findings. METHODS: All horses undergoing MRI of the front feet between January 2001 and October 2002 were reviewed and those with DDFT injuries categorised according to lesion type; horses with primary tendonitis (Group I) and those with concurrent abnormalities of the navicular bone considered to be an important component of the lameness (Group II). The response to perineural analgesia of the palmar digital nerves and palmar (abaxial sesamoid) nerves, intra-articular analgesia of the distal interphalangeal (DIP) joint and analgesia of the navicular bursa were reviewed. The result of ultrasonography of the pastern and foot was recorded. Lateral, dorsal and solar pool and bone phase nuclear scintigraphic images were assessed subjectively and objectively using region of interest (ROI) analysis. RESULTS: Forty-six (61%) of 75 horses examined using MRI had lesions of the DDFT considered to be a major contributor to lameness. Thirty-two horses (43%) had primary DDFT injuries and 14 (19%) a combination of DDF tendonitis and navicular bone pathology. Lesions involved the insertional region of the tendon alone (n = 3), were proximal to the navicular bone (n = 23) or were at a combination of sites (n = 20). Lesion types included core lesions, focal and diffuse dorsal border lesions, sagittal plane splits, insertional injuries and lesions combined with other soft tissue injuries. Many horses had a combination of lesion types. Lameness was abolished by palmar digital analgesia in only 11 of 46 horses (24%). Twenty-one of 31 horses (68%) in Group I showed > 50% improvement in lameness after intra-articular analgesia of the DIP joint, whereas 11 of 12 horses (92%) in Group II had a positive response. Twelve of 18 horses (67%) in Group I had a positive response to analgesia of the navicular bursa. Nineteen horses had lesions of the DDFT extending proximal to the proximal interphalangeal joint seen using MRI, but these were identified ultrasonographically in only 2 horses. Scintigraphic abnormalities suggestive of DDFT injury were seen in 16 of 41 horses (41%), 8 in pool phase images and 8 in bone phase images. CONCLUSIONS AND POTENTIAL RELEVANCE: DDFT injuries are an important cause of lameness associated with pain arising from the digit in horses without detectable radiographic abnormalities. Lameness is not reliably improved by palmar digital analgesia, but may be improved by intra-articular analgesia of the DIP joint in at least 68% of horses. Ultrasonography is not sensitive in detecting lesions of the DDFT in the distal pastern region, but a combination of pool and bone phase scintigraphic images of the digit is helpful in some horses. Further follow-up information is required to determine the prognosis for horses with lesions of the DDFT in the digit and to establish whether this is related to lesion severity and/or location.     

Efficacy of an Epidural Combination of Morphine and Detomidine in Alleviating Experimentally Induced Hindlimb Lameness in Horses

Amphotericin B-induced synovitis of the left tarsocrural joint was used to create a grade 3 of 4 lameness in 11 horses. Caudal epidural catheters were placed and advanced to the lumbosacral region. Baseline heart and respiratory rates were recorded and horses were videotaped at a walk and trot. Morphine sulphate (0.2 mg/kg) and detomidine hydrochloride (30 μg/kg) were administered to treated horses (n = 8) through the epidural catheter; an equivalent volume of physiologic saline solution was administered to control horses (n = 3) through the catheter. At hourly intervals after epidural injection for a total of 6 hours, heart and respiratory rates were recorded, and horses were videotaped walking and trotting. At the end of the observation period, video recordings were scrambled onto a master videotape. Lamenesses were scored by three investigators unaware of group assignment or treatment time. Lameness scores, heart rates, and respiratory rates were compared between groups using repeated measures analysis of variance. There was a significant decrease in lameness score after treatment with epidural morphine and detomidine ( P =.0003); average lameness scores of treated horses were less than grade 1 at each hourly observation for 6 hours after drug administration. Early in the observation period, heart rates significantly increased in control horses and decreased in treated horses ( P =.03). A similar trend occurred for respiratory rates ( P =.07). Results of this study demonstrate that epidural administration of a combination of morphine and detomidine is capable of providing profound hindlimb analgesia in horses.     

Lameness due to pain associated with the distal interphalangeal joint: 45 cases

This paper describes the clinical and radiographic features, and response to treatment, of 45 horses which showed lameness that was improved by intra-articular anaesthesia of the distal interphalangeal (DIP) joint. Although many horses had poor conformation of the foot of the lame limb, the majority showed no localising clinical signs suggestive of involvement of the DIP joint. Lameness was usually unilateral. No horse with bilateral lameness responded to treatment. Palmar digital nerve blocks frequently improved or alleviated lameness, although in some horses palmar (abaxial sesamoid) nerve blocks were required to eliminate lameness. This difference in response did not affect response to treatment. Intra-articular anaesthesia of the DIP joint usually resulted in resolution of lameness within 5 mins; a partial improvement in lameness or a slow response were poor prognostic indicators. None of the horses had radiographic abnormalities compatible with navicular disease. Radiographic changes of the distal interphalangeal joint per se were generally detectable only in lateromedial views and were identified in less than one third of the horses. Success rates were low following treatment of cases with radiographic abnormalities. In those with no radiographic abnormalities the response to corrective trimming and shoeing and intra-articular administration of sodium hyaluronate, once or repeatedly, was variable and no parameters could be used to predict the likely outcome. Treatment was successful in approximately 30 per cent of cases. Subsequent treatment of horses which remained lame, by intra-articular administration of polysulphated glycosaminoglycans, was not helpful; only a small proportion became sound following prolonged (nine months) rest.(ABSTRACT TRUNCATED AT 250 WORDS)     

Epidural morphine and detomidine decreases postoperative hindlimb lameness in horses after bilateral stifle arthroscopy

OBJECTIVE: To determine whether preoperative epidural administration of morphine and detomidine would decrease postoperative lameness after bilateral stifle arthroscopy in horses. STUDY DESIGN: Prospective clinical controlled study. ANIMALS: Eight adult horses that had bilateral arthroscopic procedures, including drilling of cartilage and subchondral bone within the femoropatellar joints. METHODS: Horses were randomly separated into 2 groups. Preoperatively, 4 horses were administered a combination of epidural morphine (0.2 mg/kg) and detomidine (30 microg/kg), and 4 horses were administered an equivalent volume of epidural saline (0.9% NaCl) solution. Postoperative pain was assessed using 6 video recordings made at hourly intervals of each horse at a walk. Assessments began 1 hour after recovery from anesthesia. The recordings were scrambled out of sequence and evaluated by 3 observers, unaware of treatment groups, who scored lameness from 0 to 4. Lameness scores of the 2 groups of horses were compared using a Wilcoxon's rank sum test. Heart and respiratory rates were also measured at each hourly interval and compared between groups using a repeated-measures ANOVA; statistical significance was set at P <.05. RESULTS: Preoperative administration of epidural morphine and detomidine significantly decreased lameness and heart rates after bilateral stifle arthroscopy. The greatest decrease was detected at hours 1 and 2 after recovery from anesthesia. CONCLUSION: We conclude that horses undergoing a painful arthroscopic procedure of the stifle joint benefit from the administration of preoperative epidural morphine and detomidine. CLINICAL RELEVANCE: Preoperative epidural administration of detomidine and morphine may be useful in decreasing postoperative pain after stifle arthroscopy as well as pain associated with other painful disorders involving the stifle joint, such as septic arthritis and trauma.     

Collateral desmitis of the distal interphalangeal joint in 18 horses (2001-2002)

REASONS FOR PERFORMING STUDY: There have been no previously published case series of horses examined using either scintigraphy or MRI to diagnose collateral ligament injuries not detectable using ultrasonography or radiography, nor have other concurrent soft tissue lesions been described. OBJECTIVES: To describe the clinical features of horses with desmitis of the collateral ligaments of the distal interphalangeal (DIP) joint and to evaluate the results of radiographic, ultrasonographic, scintigraphic and magnetic resonance imaging (MRI) examinations. METHODS: Horses were examined between January 2001 and January 2003 and were selected for inclusion in the study if there was unequivocal evidence of collateral desmitis of the DIP joint based on ultrasonography or MRI. Subject details, case history, results of clinical examination and responses to local analgesic techniques were reviewed. The results of radiographic, ultrasonographic, scintigraphic and MRI examinations were assessed. RESULTS: Eighteen horses were identified with desmitis of a collateral ligament of the DIP joint, 3 horses (Group 1) based on ultrasonography alone, 7 (Group II) with positive ultrasonographic and magnetic resonance images and 8 (Group III) with no lesion detectable using ultrasonography, but lesions identified using MRI. Seventeen horses had forelimb injuries and one a hindlimb injury. The medial collateral ligament was injured most frequently (13 horses). In the majority of horses, no localising clinical signs were seen. Lameness was invariably worse in circles compared with straight lines. Lameness was improved by palmar digital analgesia in 16 horses (87%), but only 6 were nonlame. Intra-articular analgesia of the DIP joint produced improvement in lameness in 6/15 horses (40%). In 16 horses, no radiographic abnormality related to the DIP joint or collateral ligament attachments was identified. Eight of 14 horses (57%) had focal, moderately or intensely increased radiopharmaceutical uptake (IRU) at the site of insertion of the injured collateral ligament on the distal phalanx. Alteration in size and signal in the injured collateral ligament was identified using MRI. In addition, 5 horses had abnormal mineralisation and fluid in the distal phalanx at the insertion of the ligament. Eleven horses had concurrent soft tissue injuries involving the deep digital flexor tendon, distal sesamoidean impar ligament, navicular bursa or collateral ligament of the navicular bone. CONCLUSIONS AND POTENTIAL RELEVANCE: Collateral desmitis of the DIP joint should be considered as a cause of foot lameness. Although some injuries are detectable ultrasonographically, false negative results occur. Focal IRU at the ligament insertion on the distal phalanx may be indicative of injury in some horses. MRI is useful for both characterisation of the injury and identification of any concurrent injuries. Further follow-up information is required to determine factors influencing prognosis.     

Function of the ramus communicans of the medial and lateral palmar nerves of the horse

Reasons for performing study: The role of the communicating branch between the medial and lateral palmar nerves of horses (i.e. the ramus communicans) in conveying sensory impulses proximally should be determined to avoid errors in interpreting diagnostic anaesthesia of the palmar nerves. Hypothesis: Sensory nerve fibres in the ramus communicans of horses pass proximally from the lateral palmar nerve to merge with the medial palmar nerve, but not vice versa. Objective: To determine the direction of sensory impulses through the ramus communicans between lateral and medial palmar nerves. Methods: Pain in a thoracic foot was created with set‐screw pressure applied to either the medial or lateral aspect of the sole of each forelimb of 6 horses. The palmar nerve on the side of the sole in which pain was created was anaesthetised proximal to the ramus communicans with local anaesthetic. Lameness was evaluated objectively by using a wireless, inertial, sensor‐based, motion analysis system (Lameness Locator). Lameness was also evaluated subjectively by using a graded scoring system. Local anaesthetic was then administered adjacent to the ramus communicans to determine the effect of anaesthesia of the ramus communicans on residual lameness. Results: When pain originated from the medial or the lateral aspect of the sole, anaesthesia of the ipsilateral palmar nerve proximal to the ramus communicans did not entirely resolve lameness. Anaesthesia of the ramus communicans further attenuated or resolved lameness. Conclusions: Sensory fibres pass in both directions in the ramus communicans to connect the medial and lateral palmar nerves. Potential relevance: When administering a low palmar nerve block, both palmar nerves should be anaesthetised distal to the ramus communicans to avoid leaving nondesensitised sensory nerve fibres passing through this neural connection. Alternatively, local anaesthetic could also be deposited adjacent to the ramus communicans when anaesthetising the palmar nerves.     

Arthroscopically assisted arthrodesis of the distal interphalangeal joint with transarticular screws inserted through a dorsal hoof wall approach in a horse

CASE DESCRIPTION: A 16-year-old Thoroughbred gelding was examined because of chronic right forelimb lameness. CLINICAL FINDINGS: On radiographs of the right front foot, the distal interphalangeal (DIP) joint space was narrow, and osteophytes and periarticular bony proliferation indicative of severe osteoarthritis were seen. Arthrodesis of the right DIP joint was recommended to improve the horse's comfort on the limb. TREATMENT AND OUTCOME: The horse was anesthetized, and palmar and dorsal arthroscopic approaches were used to remove as much of the articular cartilage as was accessible. Holes were then drilled through the dorsal aspect of the hoof wall, and 3 transarticular, 5.5-mm cortical screws were placed in lag fashion through these holes across the distal phalanx and into the middle phalanx. Defects in the hoof wall were filled with gentamicin-impregnated polymethyl methacrylate plugs and sealed with cyanoacrylate. Eight months after surgery, fusion of the DIP joint was evident radiographically and the horse was sound at a walk. CLINICAL RELEVANCE: Transarticular placement of cortical screws through a dorsal hoof wall approach combined with arthroscopically guided cartilage removal can result in fusion of the DIP joint in horses.     

Histopathology in horses with chronic palmar foot pain and age-matched controls. Part 1: Navicular bone and related structures

REASONS FOR PERFORMING STUDY: Causes of palmar foot pain and the aetiopathogenesis of navicular disease remain poorly understood, despite the high incidence of foot-related lameness. HYPOTHESES: Abnormalities of the collateral sesamoidean ligaments (CSLs), distal sesamoidean impar ligament (DSIL), deep digital flexor tendon (DDFT), navicular bone, navicular bursa, distal interphalangeal (DIP) joint or collateral ligaments (CLs) of the DIP joint may contribute to palmar foot pain. METHODS: Feet were selected from horses with a history of unilateral or bilateral forelimb lameness of at least 2 months' duration that was improved by perineural analgesia of the palmar digital nerves, immediately proximal to the cartilages of the foot (Group 1, n = 32); or from age-matched control horses (Group 2, n = 19) that were humanely destroyed for other reasons and had no history of forelimb foot pain. Eight units of tissue were collected for histology: the palmar half of the articular surface of the distal phalanx, including the insertions of the DDFT and DSIL; navicular bone and insertion of the CSLs; DDFT from the level of the proximal interphalangeal (PIP) joint to 5 mm proximal to its insertion; synovial membrane from the palmar pouch of the DIP joint and the navicular bursa; CLs of the DIP joint and DSIL. The severity of histological lesions for each site were graded. Results were compared between Groups 1 and 2. RESULTS: There was no relationship between age and grade of histological abnormality. There were significant histological differences between groups for lesions of the flexor aspect, proximal and distal borders, and medulla of the navicular bone; the DSIL and its insertion and the navicular bursa; but not for lesions of the CSLs, the dorsal aspect of the navicular bone, distal phalanx and articular cartilage, synovium or CLs of the DIP joint. CONCLUSIONS: Pathological abnormalities in lame horses often involved not only the navicular bone, but also the DSIL and navicular bursa. Abnormalities of the navicular bone medulla were generally only seen dorsal to lesions of the FFC. POTENTIAL RELEVANCE: Adaptive and reactive change may be occurring in the navicular apparatus in all horses to variable degrees and determination of the pathogenesis of lesions that lead to pain and biomechanical dysfunction should assist specific preventative or treatment protocols.     

The range and prevalence of pathological abnormalities associated with lameness in working horses from developing countries

Reasons for performing study: Lameness is highly prevalent in working horses, but published reports on the associated pathological abnormalities are lacking. With over 42 million horses in developing countries and the majority used for work, lameness has major welfare implications. Objectives: To describe the range and prevalence of pathological abnormalities associated with lameness in working horses. Methods: A standard lameness assessment was adapted for field use in working equids. Data on pathological abnormalities and pain responses in the feet, limbs and spine were collected through observation, palpation, manipulations and gait assessment in working horses from India (n = 110) and Pakistan (n = 117). Lameness at the walk was scored on a scale of 0–4 (sound‐nonweightbearing). Results: All horses examined were lame. Overall, 98% showed a gait abnormality in all 4 limbs and 87% had at least one limb scoring 3 or 4 on the lameness scale. Multiple pathological abnormalities within each limb were associated with lameness, with similar results in both countries. Chronic foot pathology was seen in every horse; 94% horses showed signs of chronic joint disease; 83% had digital flexor tendonitis in at least one limb. Lameness and pathological abnormalities were associated with specific pain responses in the feet, limbs and spine. Conclusions: The extremely high prevalence of multilimb lameness and its association with pain is of great concern. The multiple pathological abnormalities present in working horses makes lameness complex to address. Potential relevance: The results of this detailed study of lameness should facilitate the identification of risk factors and the implementation of interventions to reduce the prevalence of lameness in working equids.     

Effect of anaesthesia of the palmar digital nerves on proximal interphalangeal joint pain in the horse

REASONS FOR PERFORMING STUDY: Anaesthesia of the palmar digital nerves is claimed to attenuate lameness in some horses that are lame because of pain in the proximal interphalangeal (PIP) joint. OBJECTIVE: To determine the response of horses with pain in the PIP joint to anaesthesia of the palmar digital nerves. METHODS: Horses were video recorded trotting before and after induction of pain in the PIP joint and 10 mins after anaesthesia of the palmar digital nerves. The palmar digital nerves were anaesthetised 3 times at different sites, and the video recorded gaits were scored subjectively. RESULTS: The median lameness score of gaits after administration of 2% mepivacaine 1 cm proximal to the cartilages of the foot was not significantly different from the median lameness score before anaesthesia of the palmar digital nerves (P > or = 0.05), although that of 1 of 6 horses improved markedly. The median lameness score was significantly (P < or = 0.05) improved after mepivacaine was administered 2 and 3 cm proximal to the cartilages of the foot. CONCLUSIONS: The PIP joint is unlikely to be anaesthetised when the palmar digital nerves are anaesthetised at the proximal margin of the cartilages of the foot. POTENTIAL RELEVANCE: Pain within the PIP joint cannot be excluded as a cause of lameness when lameness is attenuated by anaesthesia of the palmar digital nerves at any site proximal to the proximal margin of the cartilages of the foot.     

Histopathology in horses with chronic palmar foot pain and age-matched controls. Part 2: The deep digital flexor tendon

REASONS FOR PERFORMING STUDY: Causes of palmar foot pain and the aetiopathogenesis of navicular disease remain poorly understood, despite the high incidence of foot-related lameness. HYPOTHESES: Abnormalities of the deep digital flexor tendon (DDFT) may contribute to palmar foot pain; ageing degenerative changes may be seen in horses free from lameness; and horses with lameness are likely to have a greater severity of abnormalities than age-matched horses with no history of foot pain. METHODS: Feet were selected from horses with a history of uni- or bilateral forelimb lameness of at least 2 months' duration. Histology of the DDFT from the level of the proximal interphalangeal joint to its insertion were examined and the severity of lesions for each site graded. Associations between lesions of the navicular bone, collateral sesamoidean ligaments (CSL), distal sesamoidean impar ligament, navicular bursa, distal interphalangeal (DIP) joint synovium and collateral ligaments of the DIP joint and DDFT were assessed. RESULTS: There was no relationship between age and grade of histological abnormality of the DDFT. There were significant histological differences between groups for lesions of the dorsal layers of the DDFT, but not for lesions of the palmar aspect. There were significant associations between histological grades for the superficial dorsal layer of the DDFT and flexor aspect of the navicular bone; and between the deep dorsal layer of the DDFT and the proximal border and medulla of the navicular bone. The navicular bursa grade was correlated with grades for the superficial dorsal, deep dorsal and deep palmar layers of the DDFT. The histological grades for the CSL and the superficial dorsal layer of the DDFT were also associated. CONCLUSIONS: Pathological abnormalities in lame horses often involved the DDFT in addition to the navicular bone. Vascular and matrix changes may precede changes in the fibrocartilage of the navicular bone. POTENTIAL RELEVANCE: Identification of factors leading to vascular changes within the interstitium of the DDFT and changes in matrix composition, may help in future management of palmar foot pain.     

Retrospective analysis of distal limb conformation and lameness in mature horses after desmotomy of the accessory ligament of the deep digital flexor tendon for management of a flexural deformity

Mature horses that present with flexural deformity of the distal interphalangeal joint and lameness isolated to the foot may obtain long‐term benefits from desmotomy of the accessory ligament of the deep digital flexor tendon (ALDDFT). This retrospective analysis of medical records and radiographs included 13 horses, aged ≥2 years, presented for lameness isolated to the hoof region and diagnosed with flexural deformity of the distal interphalangeal joint. Radiographic angles of the hoof and distal interphalangeal joint and lameness scores were compared before and after desmotomy of the ALDDFT. Follow‐up data including the ability to perform the intended use were obtained at least one year after surgery. There was improvement in the angle between the dorsal aspect of the third phalanx and the weightbearing surface of the hoof, improved alignment between the dorsal hoof wall and dorsal aspect of the third phalanx, and improved alignment of the distal interphalangeal joint. Lameness was decreased in 9/13 horses and 10/13 horses were performing at their level of intended use. Evidence of improved hoof conformation and lameness following desmotomy of the ALDDFT in lame horses with flexural deformity of the distal interphalangeal joint would indicate this procedure should be considered in mature horses.     

Idiopathic hopping‐like forelimb lameness syndrome in ridden horses: 46 horses (2002–2014)

There has been no analysis of a hopping‐type forelimb lameness syndrome seen in ridden horses. The objectives of this retrospective study were to describe the clinical features of this syndrome, response to diagnostic analgesia and imaging findings and to document post mortem findings. Clinical records from 2002 to 2014 were reviewed and data concerning signalment, history, lame limb(s), lameness characteristics, response to diagnostic analgesia and diagnostic imaging were recorded. There were 46 horses from 4 to 13 years of age, 6 of which had a history of known or suspected trauma immediately before the onset of reduced performance or lameness. Lameness seen when ridden was characterised by an intermittent shortened cranial phase of the step of the lame forelimb at the trot and marked elevation of the head as the affected limb was protracted, with the horse appearing to ‘hop’ (on the contralateral limb) as if trying to break to canter. When lameness was at its worst horses were unwilling to trot. Three horses showed sporadic severe stumbling. Local analgesia of the affected limb did not improve the lameness and in 16 horses lameness deteriorated. Three of 5 horses showed some improvement (≥2/8 grades) in the hopping‐type lameness after intra‐articular analgesia of the articular process joints of the sixth and seventh cervical vertebrae, ipsilateral to the lame forelimb. Radiographic, ultrasonographic and nuclear scintigraphic examinations were inconclusive. Two of 4 horses responded to treatment with gabapentin. In 3 horses post mortem examination revealed mild lymphocytic inflammation within or around the dorsal root ganglia of the fifth and sixth cervical nerve roots, sixth cervical nerve root or second thoracic nerve root ipsilateral to the lame limb. Idiopathic hopping‐type lameness syndrome in ridden horses may be a pain‐related condition ± a neurological component and currently has a guarded prognosis.