Vascular distribution of contrast medium during intraosseous regional perfusion of the distal portion of the equine forelimb

OBJECTIVE: To describe the vascular distribution pattern of contrast medium during intraosseous regional perfusion (IORP) of the distal portion of the equine forelimb. SAMPLE POPULATION: 13 cadaveric forelimbs from 12 horses without forelimb diseases. PROCEDURES: Serial lateromedial radiographic views were taken of the distal portion of 10 heparinized cadaveric forelimbs at 0, 1, 2, 6, 15, and 30 minutes during IORP of the third metacarpal bone (MCIII) by use of iodinated contrast medium and a tourniquet placed over the proximal portion of MCIII. Vascular regions of interest (ROI) were created for each radiograph. Reviewers identified the presence or absence of contrast medium-induced opacified vessels in all ROI on radiographs. This information was summarized to identify vessel-filling patterns over time. Vessel identification was verified by use of computed tomography angiography and latex perfusion studies on the distal portion of separate cadaveric forelimbs. RESULTS: During IORP, contrast medium filled the medullary cavity of the MCIII; exited via transcortical vessels; and diffused distally to the remaining arteries and veins of the forelimb, distal to the tourniquet. Maximum vessel and soft tissue opacification occurred in most specimens at 6 and 30 minutes, respectively. Serial radiography vessel patterns matched those of computed tomography images and dissected specimens. CONCLUSIONS AND CLINICAL RELEVANCE: IORP provides a repeatable pattern of vascular distribution in the distal portion of the equine forelimb. To our knowledge, our study provides the first documentation of arterial perfusion by use of IORP; results of previous reports indicate that IORP delivers medications to only the venous vessels of the perfused forelimb.     

Comparison of intraosseous or intravenous infusion for delivery of amikacin sulfate to the tibiotarsal joint of horses

OBJECTIVE: To establish the route of infusion (IV or intraosseous) that results in the highest concentration of amikacin in the synovial fluid of the tibiotarsal joint and determine the duration of peak concentrations. ANIMALS: 21 horses. PROCEDURE: Regional perfusion of a limb on 15 horses was performed. Amikacin sulfate was infused into the saphenous vein or via intraosseous infusion into the distal portion of the tibia (1 g in 56 ml of lactated Ringer's solution) or proximal portion of the metatarsus (1 g of amikacin in 26 ml of lactated Ringer's solution). Amikacin concentrations were measured in sequential samples from tibiotarsal joint synovial fluid and serum. Samples were obtained immediately prior to release of the tourniquet and 0.5, 1, 4, 8, 12, and 24 hours after the tourniquet was released. Radiographic contrast material was infused into the same locations as the antibiotic perfusate to evaluate distribution in 6 other horses. RESULTS: Infusion into the saphenous vein produced the highest concentration of amikacin in the tibiotarsal joint, compared with the distal portion of the tibia (mean +/- SE, 701.8 +/- 366.8 vs 203.8 +/- 64.5 microg/ml, respectively). Use of a lower volume of diluent in the proximal portion of the metatarsus produced a peak value of 72.2 +/- 23.4 microg/ml. CONCLUSIONS AND CLINICAL RELEVANCE: For regional perfusion of the tarsus, IV infusion is preferred to intraosseous infusion, because higher concentrations are achieved in the synovial fluid, and the procedure is easier to perform.     

Evaluation of safety and pharmacokinetics of vancomycin after intraosseous regional limb perfusion and comparison of results with those obtained after intravenous regional limb perfusion in horses

OBJECTIVE: To evaluate the clinical effects and pharmacokinetics of vancomycin in plasma and synovial fluid after intraosseous regional limb perfusion (IORLP) in horses and to compare results with those obtained after IV regional limb perfusion (IVRLP). ANIMALS: 6 horses. PROCEDURES: 1 forelimb of each horse received vancomycin hydrochloride (300 mg in 60 mL of saline [0.9% NaCl] solution) via IORLP; the contralateral limb received 60 mL of saline solution (control). Solutions were injected into the medullary cavity of the distal portion of the third metacarpal bone. Synovial fluid from the metacarpophalangeal (MTCP) and distal interphalangeal (DIP) joints and blood were collected prior to perfusion and 15, 30, 45, 65, and 90 minutes after beginning IORLP, and synovial fluid from the MTCP joint only and blood were collected 4, 8, 12, and 24 hours after beginning IORLP. Plasma urea and creatinine concentrations and clinical appearance of the MTCP joint region and infusion sites were determined daily for 7 days. Results were compared with those of a separate IVRLP study. RESULTS: Clinical complications were not observed after IORLP. Mean vancomycin concentration in the MTCP joint was 4 microg/mL for 24 hours after IORLP. Compared with IORLP, higher vancomycin concentrations were detected in the DIP joint after IVRLP. Compared with IVRLP, higher vancomycin concentrations were detected in the MTCP joint for a longer duration after IORLP. CONCLUSIONS AND CLINICAL RELEVANCE: IORLP with 300 mg of vancomycin in a 0.5% solution was safe and may be clinically useful in horses. Intravenous and intraosseous routes may be better indicated for infectious processes in the DIP and MTCP joints, respectively.     

Effects of immobilization followed by remobilization on mineral density, histomorphometric features, and formation of the bones of the metacarpophalangeal joint in horses

OBJECTIVE: To determine microradiographic appearance, bone histomorphometry, and mineral density of the long bones of the metacarpophalangeal joint in horses after immobilization followed by remobilization. ANIMALS: 5 healthy horses. PROCEDURE: One forelimb of each horse was immobilized in a fiberglass cast for 7 weeks, followed by 8 weeks of increasing exercise. Calcein and oxytetracycline were administered IV during the immobilization and exercise phases, respectively, for bone labeling and analysis after euthanasia. Sagittal sections of metacarpal bones and proximal phalanges were examined via radiography, dual energy x-ray absorptiometry, histomorphometry, and bone label analysis. RESULTS: Radiography revealed loss of bone mineral opacity in the subarticular regions of the immobilized metacarpal bones and phalanges and subchondral lesions in metacarpal bones in 2 horses. In phalanges, a significant decrease in subarticular volumetric bone mineral density was detected. There was significantly less bone volume and calcein-labeled bone surface and more vascular volume and oxytetracycline-labeled bone surface in immobilized phalanges, compared with contralateral phalanges. CONCLUSIONS AND CLINICAL RELEVANCE: Eight weeks of exercise after single-limb immobilization is insufficient for recovery of volumetric bone mineral density. During immobilization and remobilization, the subchondral and trabecular bone appear to be actively remodeling.     

Desmitis of the straight sesamoidean ligament in horses: 9 cases (1995-1997)

OBJECTIVE: To determine clinical signs, diagnostic findings, and outcome for horses with desmitis of the straight sesamoidean ligament (SSL) near its insertion on the middle phalanx. DESIGN: Retrospective study. ANIMALS: 9 horses. PROCEDURE: Medical records were reviewed, and information on signalment, history, clinical signs, diagnostic findings, and treatment was obtained. Follow-up information was obtained through telephone conversations with owners. RESULTS: In all horses, the diagnosis was made by use of high-resolution ultrasonography. Seven horses had moderate lameness on initial examination; lameness was exacerbated in 6 horses following flexion of the distal limb joints. The cause of lameness could not be determined on the basis of clinical signs, and diagnostic local anesthesia was necessary to localize the source of lameness to the distal portion of the limb. Five horses had forelimb involvement (1 bilateral), and 4 had hind limb involvement (1 bilateral). Treatment consisted primarily of a 6-month rest and rehabilitation program. Six of the 9 horses were able to return to their intended use. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that injury to the SSL proximal to its insertion on the middle phalanx should be considered as a possible cause of lameness in horses, particularly performance horses, with lameness localized to the distal portion of the forelimb or hind limb that do not have any radiographic abnormalities. High-resolution ultrasonography was necessary to make the diagnosis. Horses with an acute injury appeared to have a reasonable chance of responding to treatment and returning to their intended use.     

Use of magnetic resonance imaging identify suspensory desmitis and adhesions between exostoses of the second metacarpal bone and the suspensory ligament in four horses

Four horses were examined because of chronic forelimb lameness. In all horses, the cause of the lameness was localized to the metacarpus by means of physical examination and diagnostic anesthesia, and radiography of the affected limb revealed a small exostosis of the second metacarpal bone. Magnetic resonance imaging revealed suspensory desmitis in the region of this exostosis in all 4 horses. In addition, an abnormal area of low signal intensity, suggestive of an adhesion, was seen between the exostosis and the suspensory ligament. In all horses, an adhesion between the suspensory ligament and the exostosis on the second metacarpal bone was identified and transected at surgery, and the exostosis and distal portion of the second metacarpal bone were removed. All horses were able to return to their previous athletic use following a 6-month rest and rehabilitation program for treatment of the suspensory desmitis. Findings in these horses suggest that adhesions between the suspensory ligament and an exostosis of the second metacarpal bone may be a cause of chronic or recurrent forelimb lameness in horses.     

Scintigraphic evaluation of metacarpophalangeal and metatarsophalangeal joints in clinically sound horses.

The purpose of this study was to describe the pattern of radiopharmaceutical uptake in the metacarpophalangeal (MCP) and metatarsophalangeal (MTP) (fetlock) joints in clinically sound horses. Scintigraphic images from 29 clinically normal horses were evaluated. All the images were assessed subjectively. The lateral views were assessed quantitatively using vertical line profiles through the center of the joint, and mean ratios of radiopharmaceutical uptake were calculated from regions of interest around the third metacarpal or metatarsal bones, and the proximal phalanx and proximal sesamoid bones. From the vertical line profiles, in the majority of forelimbs (65%) the peak activity of radiopharmaceutical distribution was at the proximal region of the proximal phalanx, with a significantly lower activity within the condyles of the third metacarpal bone. However, in 84% of hindlimbs there was a broader profile peak incorporating the condyles of the third metatarsal bone and the proximal aspect of the proximal phalanx, indicating a more generalized even uptake of radiopharmaceutical across the MTP joint. When the regions of interest were compared between front and hindlimbs, there was no significant difference between proximal phalanx and proximal sesamoid bones, but the distal condyles of the third metacarpal bone of the forelimb had significantly lower radiopharmaceutical activity than hindlimbs (P < 0.04). In lateral images, the mean forelimb ratios tended to be higher in the left MCP joint compared with the right (P = 0.069). In hindlimbs, the mean ratios tended to be higher in the right MTP joint than the left (P = 0.052). There was no significant effect of age.     

Development of intraosseous infusion of the distal phalanx to access the foot lamellar circulation in the standing,conscious horse

Intraosseous (IO) infusion of the distal phalanx (IOIDP) as a delivery route targeting hoof lamellar tissue of standing, conscious horses was evaluated. Following sedation and regional nerve blockade in six Standardbred horses, a microdialysis (MD) probe was implanted into the hoof lamellar tissue of one forelimb. A purpose designed cannulated bone screw was introduced into the body of the distal phalanx, approximately 6 cm from the MD probe. Gentamicin solution (25 mg/mL) was infused at 20 μL/min through the bone screw for 2 h without the application of a tourniquet. MD and blood samples were collected at regular intervals and analysed for gentamicin concentrations.Gentamicin was present in lamellar tissue at much higher concentrations than peripheral serum. The mean concentration of gentamicin was 24.4, 20.5 and 4.4 μg/mL in extracellular fluid (ECF) and 0.28, 0.5 and 0.32 μg/mL in serum samples collected 60, 120 and 150 min after IOIDP was started, respectively. A clinically safe and efficacious IO drug delivery to the hoof lamellar tissue of standing, conscious horse was developed.     

FRACTURES OF THE DISTAL PHALANX AND ASSOCIATED SOFT TISSUE AND OSSEOUS ABNORMALITIES IN 22 HORSES WITH OSSIFIED SCLEROTIC UNGUAL CARTILAGES DIAGNOSED WITH MAGNETIC RESONANCE IMAGING

Ungual cartilage ossification in the forelimb is a common finding in horses. Subtle abnormalities associated with the ungual cartilages can be difficult to identify on radiographs. Magnetic resonance (MR) imaging findings of 22 horses (23 forelimbs) with a fracture of the distal phalanx and ossified ungual cartilage were characterized and graded. All horses had a forelimb fracture. Eleven involved a left forelimb (seven medial; four lateral), and 12 involved a right forelimb (five medial; seven lateral). All fractures were nonarticular, simple in configuration, and nondisplaced. The fractures were oriented in an axial proximal to abaxial distal and palmar to dorsal direction, and extended from the base of the ossified ungual cartilage into the distal phalanx. The fracture involved the fossa of the collateral ligament on the distal phalanx in 17 of 23 limbs. The palmar process and ossified ungual cartilage was abnormally mineralized in all horses. Ligaments and soft tissues adjacent to the ossified ungual cartilages were affected in all horses. The routine site of fracture in this study at the base of the ossified ungual cartilage extending into the distal phalanx suggests a biomechanical cause or focal stress point from cycling. The ligamentous structures associated with the ungual cartilages were often affected, showed altered signal intensity as well as enlargement and were thought to be contributing to the lameness. In conclusion, ossified ungual cartilages may lead to fracture of the palmar process of the distal phalanx and injury of the ungual cartilage ligaments.     

Evaluation of transfixation casting for treatment of third metacarpal, third metatarsal, and phalangeal fractures in horses: 37 cases (1994-2004)

OBJECTIVE: To evaluate clinical findings, complications, and outcome of horses and foals with third metacarpal, third metatarsal, or phalangeal fractures that were treated with transfixation casting. DESIGN: Retrospective case series. Animals-29 adult horses and 8 foals with fractures of the third metacarpal or metatarsal bone or the proximal or middle phalanx. PROCEDURES: Medical records were reviewed, and follow-up information was obtained. Data were analyzed by use of logistic regression models for survival, fracture healing, return to intended use, pin loosening, pin hole lysis, and complications associated with pins. RESULTS: In 27 of 35 (77%) horses, the fracture healed and the horse survived, including 10 of 15 third metacarpal or metatarsal bone fractures, 11 of 12 proximal phalanx fractures, and 6 of 8 middle phalanx fractures. Four adult horses sustained a fracture through a pin hole. One horse sustained a pathologic unicortical fracture secondary to a pin hole infec-tion. Increasing body weight, fracture involving 2 joints, nondiaphyseal fracture location, and increasing duration until radiographic union were associated with horses not returning to their intended use. After adjusting for body weight, pin loosening was associated with di-aphyseal pin location, pin hole lysis was associated with number of days with a transfixation cast, and pin complications were associated with hand insertion of pins. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that transfixation casting can be successful in managing fractures distal to the carpus or tarsus in horses. This technique is most suitable for comminuted fractures of the proximal phalanx but can be used for third metacarpal, third metatarsal, or middle phalanx fractures, with or without internal fixation.     

Nonsurgical management of type II fractures of the distal phalanx in 48 Standardbred horses

OBJECTIVE: To evaluate nonsurgical management of type II fractures of the distal phalanx in Standardbred horses. DESIGN: Retrospective study of 48 affected horses. RESULTS: Most fractures occurred on the lateral palmar process of the left forelimb or the medial palmar process of the right forelimb; 81% of horses were considered sound enough to return to training and 63% raced. Of those returning to racing, 41% competed in > 10 races, 37% in 2 to 10 races and 22% in only 1 race. There was no difference in performance before and after fracture. Twenty-four of 25 horses had a bar shoe fitted for > 50% of the treatment phase. Of those horses returning to training without a bar shoe, 89% refractured at the same site. Sixty percent of horses returning to training with a bar shoe raced successfully. The total convalescent time, the time rested in a box and the time spelled in a paddock were similar for horses returning to racing and those that did not. The age of the horse had no effect on the ability to return to racing. CONCLUSION: The prognosis for type II fractures of the distal phalanx is guarded. It is advisable to fit a bar shoe on the horse during convalescence. Horses returning to training and racing with a bar shoe appear less likely to refracture the distal phalanx. Those horses that return to racing can perform at a level similar to that prior to fracture.     

SCINTIGRAPHIC ASSESSMENT OF THE METACARPOPHALANGEAL AND METATARSOPHALANGEAL JOINTS OF HORSES WITH JOINT PAIN

Our aims were to evaluate the pattern of radiopharmaceutical uptake in horses with lameness related to the metacarpophalangeal and/or metatarsophalangeal joint and compare the results with similar information from sound horses. It was hypothesized that there would be a difference in radiopharmaceutical uptake between the lame and contralateral limb in unilaterally lame horses and that there would be a difference between lame and sound horses. Nuclear scintigraphic images of 43 horses with forelimb lameness and 30 horses with hindlimb lameness were evaluated. In all horses lameness was improved by intraarticular analgesia of the joint, or by perineural analgesia of the palmar/plantar (at the junction of the proximal 3/4 and the distal 1/4 of the metacarpal/metatarsal regions) and palmar/plantar metacarpal/metatarsal nerves. All images were assessed subjectively and a quantitative image analysis was performed by drawing a vertical line profile through the center of each joint in the lateral images and using region of interest analysis in both lateral and dorsal/plantar images. Ratios of radiopharmaceutical uptake were compared for each region between lame and contralateral limbs in unilaterally lame horses and between lame and control horses. There was a significant difference in the ratio of radiopharmaceutical uptake in the proximal aspect of the proximal phalanx between lame and nonlame forelimbs in unilaterally lame horses and in both lame and contralateral limbs of lame horses compared with control horses for the regions of the distal aspect of the third metacarpal/metatarsal bone and the proximal sesamoid bones. However, the profile analysis was of limited clinical value.     

Long‐Term Outcome after Arthroscopic Debridement of Distal Phalanx Extensor Process Fragmentation in 13 Horses

Objective— To report long-term outcome after arthroscopic removal of fragmentation of the extensor process of the distal phalanx in horses.
Study Design— Case series.
Animals— Adult horses (n=13).
Methods— Medical records (2003–2004) of horses that had arthroscopic debridement of fragmentation of the extensor process of the distal phalanx were reviewed. Inclusion criteria included: lameness localized to the foot, fragmentation of the extensor process of the distal phalanx debrided arthroscopically, and a follow-up period of ≥4 years.
Results— Of the 13 horses, lameness was resolved in 11 (85%) initially but distal interphalangeal joint pain recurred in 2 (15%) within 1 year of surgery. Three (23%) other horses were retired because of lameness at other sites during the follow-up period resulting in 46% (6/13) being not lame and in full work after 4 years. Substantial changes were identified at surgery in the contralateral joint of 7 horses, even when fragments were only present unilaterally.
Conclusions— Arthroscopic debridement of fragmentation of the extensor process of the forelimb distal phalanx has a good short-term prognosis for resolution of lameness and return to work but a more guarded prognosis for long-term soundness.
Clinical Relevance— These results allow for more accurate prognostication preoperatively and may support early debridement of fragmentation of the extensor process of the distal phalanx.     

RADIOGRAPHIC APPEARANCE OF THE FEET OF MAMMOTH DONKEYS AND THE FINDING OF SUBCLINICAL LAMINITIS

All feet of 10 clinically sound mammoth donkeys (Group I) were radiographed to determine the appearance of the distal phalanx. The distal phalanges had blunted to concave-shaped dorsal solar margins which varied in appearance from slight to pronounced. The distal phalanges of the forefeet were wider than those of the hindfeet, and also were positioned a greater distance from the dorsal aspect of the hoof wall. The greater distance between the dorsal aspect of the hoof wall and the distal phalanges seemed related to the presence of a periosteal-like bony proliferation on the dorsum of the distal phalanx. This bony proliferation occurred in those distal phalanges which also had radiographic findings consistent with pedal osteitis. Next, all feet of 5 additional mammoth donkeys (Group II) that were to be necropsied for various reasons, were examined similarly to Group I, necropsied and found to have laminitis. Only 2 of these 5 donkeys had been lame; only one had rotation of the distal phalanges (in the forefeet). Radiographic data from the 4 donkeys without rotation seemed most similar to that found in those Group I donkeys which had periosteal reactions on their distal phalanges. Conclusions from this study were that: 1) feet of mammoth donkeys have some anatomic differences from those of domestic horses, 2) subclinical laminitis and pedal osteitis can occur in mammoth donkeys, 3) rotation of the distal phalanx occurs in some, but not all laminitic donkeys, 4) laminitic changes may be more pronounced in their fore than in their hindfeet, and 5) additional studies of donkeys need to be done, examining both proven normal and confirmed laminitic feet.     

Segmental ostectomy of the second and fourth metacarpal and metatarsal bones in horses: 17 cases (1993-2002)

OBJECTIVE: To determine clinical findings in and outcome of horses with fractures of the second or fourth metacarpal or metatarsal bone that underwent segmental ostectomy, leaving the proximal and distal portions of the bone undisturbed. DESIGN: Retrospective case series. ANIMALS: 17 horses. PROCEDURES: Medical records were reviewed, and information on signalment, affected bone, lesion type, surgical procedure, amount of bone removed, and surgical and postsurgical complications was obtained. Follow-up information was obtained through telephone conversations with owners, trainers, and referring veterinarians. RESULTS: One horse had a fracture involving the distal third of the second metacarpal bone; 13 had fractures involving the middle third of the second metacarpal bone (n = 4), fourth metacarpal bone (5), or fourth metatarsal bone (4); and 3 had fractures involving the proximal third of the second (2) or fourth (1) metacarpal bone. Affected portions of the bones were surgically resected, leaving the proximal and distal portions undisturbed. All horses returned to previous performance levels without evidence of lameness. Cosmetic results were good to excellent. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that horses with a complicated injury of the proximal, middle, or distal portion of the second or fourth metacarpal or metatarsal bone may be successfully treated by means of segmental ostectomy of the abnormal portion of the bone.     

Evaluation of safety and pharmacokinetics of vancomycin after intravenous regional limb perfusion in horses

OBJECTIVE: To evaluate clinical variables, regional concentrations, and pharmacokinetics of vancomycin in the synovial fluid of distal forelimb joints of horses after IV regional limb perfusion. ANIMALS: 6 horses. PROCEDURE: Vancomycin was administered via IV regional limb perfusion to the distal portion of the forelimbs of anesthetized horses. Drug (300 mg of vancomycin hydrochloride in 60 mL of saline [0.9% NaCl] solution) was infused into 1 forelimb, whereas the contralateral limb served as a control and was perfused with 60 mL of saline solution. Solutions were injected into the lateral digital vein after digital exsanguination. Synovial fluid from the metacarpophalangeal (MTCP) and distal interphalangeal (DIP) joints and systemic blood were collected prior to perfusion and 15, 30, 45, 65, and 90 minutes after initiation of the infusion. Synovial fluid from the MTCP joint and blood were also obtained at 4, 8, 12, and 24 hours after infusion. Plasma urea and creatinine concentrations, degree of lameness, and certain clinical variables involving the MTCP joint and infusion site were assessed for 7 days. Results were compared between the vancomycin treatment and control groups. RESULTS: No complications or significant differences in renal function, lameness, or clinical variables were observed between groups. Vancomycin concentrations exceeded 4 microg/mL in MTCP joints for approximately 20 hours. Higher concentrations were reached in DIP joints than in MTCP joints. CONCLUSIONS AND CLINICAL RELEVANCE: IV regional limb perfusion with 300 mg of vancomycin as a 0.5% solution was safe and may be useful in horses as treatment for distal limb infections.     

Gamma scintigraphic analysis of the distribution of perfusion of blood in the equine foot during black walnut (Juglans nigra)-induced laminitis

Twelve horses, with acute laminitis (primarily in the forefeet) at 12 hours after intragastric dosing with an aqueous extract of black walnut (Juglans nigra) heart-wood, were studied. The distribution of perfusion of blood to the foot and to outlined regions within the foot was quantified, using gamma scintigraphy of regionally infused 99mTc-labeled macroaggregated albumin, before and 12 hours after extract administration. Horses 1 to 3 were not studied further. Perfusion was quantified again for horses 4 to 12 at 84 hours after extract administration. At the onset of acute laminitis, horses 7 to 12 were administered a single dose of prazosin (0.025 mg/kg of body weight, IV) immediately after scintigraphy of the right forelimb and before scintigraphy of the left forelimb. When compared with baseline images, perfusion to the forefoot of horses after the development of acute laminitis was quantitatively decreased vs perfusion to the entire distal portion of the forelimb. Also with the onset of laminitis, perfusion also decreased to the dorsal laminar and coronary corium regions vs the distal portion of the forelimb. The acute laminitis-associated deficit in perfusion to the dorsal laminitis-associated deficit in perfusion deficit in perfusion to either the coronary corium or the entire forefoot. Equivalent deficits in the distribution of perfusion were not detected in forelimbs from horses with acute laminitis and which had been treated with prazosin. When compared with baseline images, perfusion to the dorsal lamina was increased in relation to perfusion to the distal portion of the limb at postdosing hour 84. Prazosin treatment did not influence that increase in perfusion to the dorsal lamina.     

Intraosseous gentamicin perfusion of the distal metacarpus in standing horses

OBJECTIVE: To report tissue gentamicin concentrations after intraosseous (IO) perfusion in standing horses. STUDY DESIGN: In vivo study. ANIMALS OR SAMPLE POPULATION: Twelve horses. METHODS: Sedated horses had a cannulated cortical bone screw inserted into the dorsolateral aspect of the treated metacarpus and a tourniquet applied proximally. Gentamicin (2.2 mg/kg) diluted in sterile saline solution (0.1 mL/kg) was infused through the screw. Two horses were euthanatized at each time interval: 0, 2, 6, 12, 24, and 36 hours. Synovial fluid and bone samples were collected distal to the screw from both forelimbs. Gentamicin concentrations were measured using fluorescence polarization immunoassay. RESULTS: The highest synovial fluid gentamicin concentrations were 385+/-273 microg/mL (mean+/-SD) in the metacarpophalangeal joint, 225+/-205 microg/mL in the proximal interphalangeal joint, 215+/-205 microg/mL in the distal interphalangeal joint, 382+/-195 microg/mL in the digital flexor tendon sheath, and 206+/-161 microg/mL in the navicular bursa. The highest bone concentrations of gentamicin were 55+/-30 microg/g in the distal metacarpus, 34+/-27 microg/g in the proximal, 16+/-15 microg/g in the middle, and 16+/-2.2 microg/g in the distal phalanges, and 27+/-17 microg/g in the proximal and 24+/-11 microg/g in the distal sesamoid bones. CONCLUSION: Standing IO perfusion of gentamicin resulted in local antibiotic concentrations in the synovial structures and bones of the distal aspect of the limb that exceed the reported minimum inhibitory concentration of pathogens commonly implicated in equine orthopedic infections. CLINICAL RELEVANCE: Standing IO perfusion of gentamicin in the distal aspect of the limb should be considered for treatment of orthopedic infections of this region in horses.     

Subchondral bone cysts with fractures of the extensor processes in a horse.

Probable cause of fracture in a Paint gelding was a congenital bone defect involving the extensor process area of the right and left forelimb distal phalanges. Radiographically and histologically, subchondral bone cysts at the fracture lines were suspected. These cysts were thought to have developed in association with abnormal ossification centers at the extensor process areas of the third phalanx. Partial avulsion of weak extensor processes would then occur from natural forces exerted on these weakened bony prominences via the common digital extensor tendon. Support for osteochondrosis as a cause of this bone cyst formation was seen in histologic examination of fragments removed. Within the bony trabeculae, a dysplastic focus of cartilage with mineralized plaques and osseous tissues was observed. Findings supported a diagnosis of osteochondrosis, to the extent that the disease is presently understood in horses. Surgical correction by fragment removal was performed to circumvent progression of degenerative joint disease, which was evident as partial cartilage erosion of the distal dorsal articular surface of the second phalanx and fracture fragments. Recovery from surgery was rapid, and several months after surgery, the horse was sound for pleasure riding.