Ultrasound-guided injection of the cranial tibial artery for stem cell administration in horses.

BACKGROUND: A technique for intra-arterial injection of mesenchymal stem cells (MSC) has been established for front limbs with the use of the median artery. This approach has been proposed for treatment of soft tissue injuries of the equine distal limb. A technique has not been validated yet for hindlimb injection. OBJECTIVES: To assess the feasibility of injection of the cranial tibial artery in horses, and to evaluate the distribution and persistence of MSC after injection. STUDY DESIGN: In vivo experiment. METHODS: In a first phase, the cranial tibial arteries of both hindlimbs of three research horses were catheterised with ultrasound guidance under general anaesthesia and injected with iodinated contrast. In the second phase, iodinated contrast was injected in three standing sedated horses with ultrasound guidance. In the final phase, 99m Technetium-HMPAO labelled allogenic bone marrow derived equine MSC were injected under standing sedation with the same technique in three other horses. Scintigraphy was used to assess MSC distribution and persistence for 24 h. Ultrasound was performed 24 h after injection to assess vessel impairment. RESULTS: Arterial injection was achieved in all 18 limbs without any significant complications. Mild partial periarterial injection was observed in four limbs. Scintigraphic images demonstrated diffuse MSC distribution from the tarsal area to the foot. Persistence decreased over time but signal was still present at 24 h. MAIN LIMITATIONS: Limited retention of the radiolabel in the MSC. CONCLUSIONS: Ultrasound-guided injection of the cranial tibial artery can be performed both under general anaesthesia and standing sedation in horses. This technique could be used for MSC treatment of equine proximal suspensory desmopathy or other injuries in the distal hindlimb.

18 F-sodium fluoride positron emission tomography of the racing Thoroughbred fetlock: Validation and comparison with other imaging modalities in nine horses.

BACKGROUND: Early and accurate detection of stress remodelling in racehorses is of utmost importance to prevent catastrophic injuries. Current imaging techniques have limitations in assessing early changes predisposing to catastrophic breakdowns. Positron emission tomography (PET) using 18 F-sodium fluoride (18 F-NaF) is a sensitive method for the detection of early bone turnover and may improve early recognition of subtle injuries. OBJECTIVES: To validate the clinical use of 18 F-NaF PET in Thoroughbred racehorses, to assess the value of PET in the detection of bone lesions and to compare PET results with findings of other advanced imaging modalities, clinical examination and pathology. STUDY DESIGN: Experimental exploratory study. METHODS: Twenty fetlocks from nine Thoroughbred racehorses were imaged using 18 F-NaF PET, computed tomography (CT) and scintigraphy. Five fetlocks were also imaged with magnetic resonance imaging and four fetlocks were also examined histologically. Imaging findings were independently reviewed by three board certified radiologists. Imaging, clinical and histopathological findings were correlated. RESULTS: PET imaging was well-tolerated by all horses. PET detected focal areas of 18 F-NaF uptake in instances where other imaging modalities did not identify abnormalities, in particular in the proximal sesamoid bones. Maximal standardised uptake values could be measured to quantify the activity of lesions. Areas of 18 F-NaF uptake corresponded to regions of increased vascularity and increased osteoblastic activity. MAIN LIMITATIONS: Limited number of cases. CONCLUSIONS: 18 F-NaF PET imaging of the Thoroughbred fetlock is feasible and compares favourably with other imaging modalities in detecting stress remodelling in Thoroughbred racehorses. PET appears to be a beneficial imaging modality when used for early detection of stress remodelling in an effort to prevent catastrophic musculoskeletal injuries in this population of horses.

18 F-sodium fluoride positron emission tomography of the equine distal limb: Exploratory study in three horses.

BACKGROUND: Positron emission tomography (PET) is a cross-sectional, functional imaging modality that has recently become available to the horse. The use of 18 F-sodium fluoride (18 F-NaF), a PET bone tracer, has not previously been reported in this species. OBJECTIVES: To assess the feasibility of 18 F-NaF PET in the equine distal limb and explore possible applications in the horse in comparison with other imaging modalities. STUDY DESIGN: Exploratory descriptive study involving three research horses. METHODS: Horses were placed under general anaesthesia prior to intravenous (i.v.) administration of 1.5 MBq/kg of 18 F-NaF. Positron emission tomography imaging of both front feet and fetlocks was performed using a portable scanner. Computed tomography (CT) of the distal limb was performed under a separate anaesthetic episode. Bone scintigraphy and magnetic resonance imaging (MRI) were subsequently performed under standing sedation. Images obtained from PET and other imaging modalities were independently assessed and the results correlated. RESULTS: Positron emission tomography images were obtained without complication. The radiation exposure rate was similar to equine bone scintigraphy. Positron emission tomography detected focal 18 F-NaF uptake in areas where other imaging modalities did not identify any abnormalities. This included sites of ligamentous attachment, subchondral compact bone plate and the flexor cortex of the navicular bone. 18 F-NaF uptake was identified in some, but not all, osseous fragments and areas of osseous formation, suggesting a distinction between active and inactive lesions. MAIN LIMITATIONS: A small number of horses were included and histopathology was not available. CONCLUSIONS: 18 F-NaF PET imaging of the equine distal limb provides useful additional information when compared with CT, MRI and scintigraphy and has the potential for both research and clinical applications in the horse. The Summary is available in Chinese - see Supporting information.

Evaluation of the Tekscan F-SCAN system for measurement of the kicking force in horses.

INTRODUCTION: The incidence of fractures after a kick, coupled with marked soft tissue trauma at the site of injury, suggests that the force of a kick from the hind limb of a horse is enormous. The goal of this study was to measure this force and to investigate whether the Tekscan F-SCAN in-shoe pressure measuring system is suitable for quantification of the impact strength of a kick from a horse. The system was tested in 6 horses that had undergone clinical examination and gait analysis. The sensor-shoe combination was attached to each hind foot and the horse was stimulated to kick against a wall. The F-SCAN system measured the maximum vertical and horizontal force (N), the main contact area (cm2) of the sole with the floor (stance phase limb) or wall (kicking limb) and the duration (sec) that the sole was in contact with the floor or wall. In addition, each kicking event was recorded with a video camera for subjective evaluation. The mean kicking force measured was lower than that recorded in horses trotting on a treadmill, where the forces exerted on one limb were similar to the horse's body weight. The results of this study indicate that the Tekscan F-SCAN system is not ideally suited to measure the force of a kick of a horse in vivo.

INTRODUCTION: La fréquence des fractures et les importants dégâts aux tissus mous consécutifs à des coups de pieds laissent à penser que la force de frappe transmise à cette occasion doit être très importante. Le but du présent travail était de mesurer cette force et de voir si le système F-Scan Tekscan est adapté pour quantifier la force de frappe d'un cheval. Après un examen clinique et orthopédique, le système a été utilisé sur 6 chevaux, en incluant le senseur dans une hipposandale et en stimulant ensuite le cheval pour qu'il rue contre une paroi. Le système F-Scan a mesuré lors de chaque coup de pied la force maximale verticale respectivement horizontale (N), la surface de contact (cm2) de la sole avec le sol (membre à l'appui) ou avec la paroi (membre donnant le coup) ainsi que la durée de contact avec le sol respectivement avec la paroi. Chaque coup de pied a simultanément été enregistré sur vidéo et le force du coup a été estimée subjectivement. Les forces mesurées étaient toutefois plus faibles que celles enregistrées chez des chevaux au trot sur un tapis roulant dans une étude précédente. Les forces exercées sur les membres étaient globalement égales au poids du cheval. Les résultats de notre étude laissent à penser que le système F-Scan Tekscan n'est pas idéal pour mesurer la force de frappe d'un cheval.

Ultrasonographic appearance of normal and injured lateral patellar ligaments in the equine stifle.

REASONS FOR PERFORMING STUDY: Ultrasound is widely used in horses with stifle lameness, yet limited information is available regarding the appearance of normal and injured lateral patellar ligaments (LPL). OBJECTIVES: To map the normal ultrasonographic appearance of the LPL. To describe the clinical and ultrasonographic features of LPL injuries. STUDY DESIGN: Descriptive study of healthy horses and retrospective case series. METHODS: Twelve horses without stifle lameness underwent ultrasonographic examination of bilateral LPLs and ultrasonographic features were recorded. Eighteen horses with LPL injury were identified from 1999 to 2011. RESULTS: The normal LPL changes in appearance from origin to insertion. It shows ill-defined margins at the patella, becomes flattened and bilobed over the lateral trochlear ridge, is oval-triangular shaped with variable echogenicity and fibre pattern distal to the LTR, and becomes tapered with striations at the tibial insertion. LPL injury was identified in 18 horses of multiple breeds and uses. All injuries were acute, and 12 had wounds. Eleven horses were severely lame (grade 4-5/5). Ultrasonographic lesions were severe in 78% of cases. The mid to insertional portion of the LPL was most often affected. Radiography showed fractures of the tibial tuberosity (n = 6), patella (n = 4) and lateral trochlear ridge (n = 1). Fractures involved LPL attachments in 9 horses. Five were treated for osteomyelitis and one for synovial sepsis. Recheck ultrasound in 4 horses showed minimal to no change in the appearance of LPL injuries. Nine horses returned to riding, one continued as a broodmare, 2 were retired, one became a broodmare, 2 were lost to follow-up and 3 were subjected to euthanasia owing to concurrent injuries. CONCLUSION: Normal variations in shape, echogenicity and fibre pattern of the LPL are important considerations to prevent false positive diagnoses during ultrasonography. LPL injuries were often severe and associated with craniolateral stifle trauma. Prognosis varied from good to guarded in horses without additional severe injuries.

Ultrasound-guided injection of the median artery in the standing sedated horse.

REASONS FOR PERFORMING STUDY: Injection of the median artery of horses leads to better distribution and persistence of mesenchymal stem cells than i.v. regional limb perfusion. Due to technical difficulties, intra-arterial injections thus far have only been performed under general anaesthesia. OBJECTIVES: To assess the feasibility of injection of the median artery in standing sedated horses. STUDY DESIGN: Experimental study. METHODS: Six horses were included in the study. After median and ulnar regional analgesia, radiographic contrast material was injected in the median artery of both front limbs, using a catheter in one limb and a direct needle injection in the other. Ultrasound guidance was used for catheter and needle placement. Radiographs were obtained for confirmation of successful injection. Post procedural ultrasound examination was performed to assess vascular compromise. RESULTS: Catheter placement was successful in all 6 limbs, but in one limb injection was not possible due to arterial spasm. Movement of the limbs after the initial injection resulted in loss of functionality of the catheter in 2 other horses. Direct needle injection was successful on all 6 limbs, with periarterial extravasation observed in 2 limbs. No clinical complications were observed. CONCLUSIONS: Injection of the median artery can be performed in standing horses under sedation. Direct needle injection is a more practical technique than catheterisation, as it is easier to perform and less likely to induce arterial spasm. Periarterial extravasation remains a possible limitation of the technique. Intra-arterial injections may be useful for administration of therapeutic agents such as mesenchymal stem cells on standing sedated horses.

Scintigraphic comparison of intra-arterial injection and distal intravenous regional limb perfusion for administration of mesenchymal stem cells to the equine foot.

REASONS FOR PERFORMING STUDY: Intra-arterial (i.a.) and intravenous (i.v.) regional limb perfusions (RLP) through the median artery and cephalic vein, respectively, have been previously investigated for administration of mesenchymal stem cells (MSCs) to the equine distal limb. Limitations due to thrombosis of the arteries after i.a. RLP and poor distribution of MSCs to the foot with i.v. RLP were observed. These techniques need to be modified for clinical use. OBJECTIVES: Evaluate the distribution, uptake and persistence of radiolabelled MSCs after i.a. injection through the median artery without a tourniquet and after i.v. RLP through the lateral palmar digital vein. STUDY DESIGN: In vivo experimental study. METHODS: (99m) Tc-HMPAO-labelled MSCs were injected through the median artery of one limb and the lateral palmar digital vein of the other limb of 6 horses under general anaesthesia. No tourniquet was used for the i.a. injection. A pneumatic tourniquet was placed on the metacarpus for i.v. injection. Scintigraphic images were obtained up to 24 h after injection. RESULTS: Intra-arterial injection resulted in MSCs retention within the limb despite the absence of a tourniquet and no thrombosis was observed. Both i.a. injection and i.v. RLP led to distribution of MSCs to the foot. The i.a. injection resulted in a more homogeneous distribution. The MSC uptake was higher with i.v. RLP at the initial timepoints, but no significant difference was present at 24 h. CONCLUSIONS: Both i.a. injection through the median artery without a tourniquet and i.v. RLP performed through the lateral palmar digital vein under general anaesthesia are safe and reliable methods for administration of MSCs to the equine foot. The i.a. technique is preferred owing to the better distribution, but is technically more challenging. The feasibility of performing these techniques on standing horses remains to be investigated.

Distribution and persistence of technetium-99 hexamethyl propylene amine oxime-labelled bone marrow-derived mesenchymal stem cells in experimentally induced tendon lesions after intratendinous injection and regional perfusion of the equine distal limb.

REASONS FOR PERFORMING STUDY: Intralesional (i.l.) injection is currently the most commonly used technique for stem cell therapy in equine tendon injury. A comparison of different techniques of injection of mesenchymal stem cells for the treatment of tendon lesions is required. OBJECTIVES: We hypothesised that vascular perfusion of the equine distal limb with mesenchymal stem cells (MSCs) would result in preferential distribution of MSCs to acute tendon injuries. STUDY DESIGN: In vivo experimental study. METHODS: Lesions were surgically induced in forelimb superficial digital flexor tendons of 8 horses. Three or 10 days after lesion induction, technetium-99 hexamethyl propylene amine oxime-labelled MSCs were injected via i.v. or intra-arterial (i.a.) regional limb perfusion (RLP) at the level of the distal antebrachium and compared to i.l. injection. Mesenchymal stem cell persistence and distribution within the forelimb and tendon lesions was assessed with scintigraphy for 24 h. RESULTS: Lesion uptake was higher with i.l. injection than with RLP, but MSC persistence decreased similarly over time in all 3 techniques. Intra-arterial RLP resulted in a better distribution of MSCs and a higher uptake at the lesion site than i.v. RLP. Limbs perfused i.a. on Day 10 showed greater accumulation of MSCs in the lesion than limbs perfused on Day 3. Arterial thrombosis occurred in 50% of the i.v. RLP limbs and in 100% of the i.a. RLP limbs, which led to clinical complications in one horse. CONCLUSIONS AND POTENTIAL RELEVANCE: Compared with i.l. injection, RLP results in lower uptake but similar persistence of MSCs at the site of tendon lesions. A time dependent accumulation of MSCs was identified with i.a. RLP. The i.a. RLP appears more advantageous than the i.v. RLP in terms of distribution and uptake. However, the described i.a. technique produced arterial thrombosis and thus cannot currently be recommended for clinical use.

The effects of therapeutic concentrations of gentamicin, amikacin and hyaluronic acid on cultured bone marrow-derived equine mesenchymal stem cells.

REASONS FOR PERFORMING STUDY: Joint inflammation and septic arthritis are both potential complications of intra-articular injections of bone marrow-derived mesenchymal stem cells (BM-MSCs). Clinicians may prophylactically co-inject BM-MSCs admixed with either antimicrobials or hyaluronic acid; however, the effect of these agents on cultured BM-MSCs is unknown. OBJECTIVE: To determine the effects of therapeutic levels of gentamicin, amikacin and hyaluronic acid on cultured equine BM-MSCs in vitro. STUDY DESIGN: In vitro experimental study. METHODS: Equine BM-MSCs from 4 healthy mature horses were isolated. Cultured BM-MSCs from each donor were incubated with gentamicin (150 mg), amikacin (250 mg), hyaluronic acid (22 mg) or 1% penicillin/streptomycin (control) under sterile conditions. Mesenchymal stem cells viability, proliferation, mediator secretion and culture media pH were measured. RESULTS: Incubation of BM-MSCs with gentamicin resulted in >95% MSC death after 45 min, and incubation of BM-MSCs with amikacin resulted in >95% MSC death after 2 h. Incubation of BM-MSCs with hyaluronic acid or penicillin/streptomycin (control) for up to 6 h resulted in sustained BM-MSC viability of 80% and >93%, respectively. All additives resulted in decreased media pH in the first minute; however, the pH then remained constant over the 6 h incubation period. No significant differences in BM-MSC proliferation or mediator secretion between the penicillin/streptomycin (control) and cells treated with hyaluronic acid were observed. CONCLUSION: Therapeutic concentrations of aminoglycoside antimicrobials are toxic to cultured equine BM-MSCs. The effects of hyaluronic acid on cultured MSC viability, proliferation and mediator secretion are minimal. POTENTIAL RELEVANCE: Based on these findings, the mixing of aminoglycoside antimicrobials and cultured equine BM-MSCs prior to therapeutic use is not recommended.

Autologous point-of-care cellular therapies variably induce equine mesenchymal stem cell migration, proliferation and cytokine expression.

REASONS FOR PERFORMING STUDY: Autologous cellular therapy products including adipose-derived stromal vascular fraction (SVF), bone marrow mononuclear cells (BMMNs), cord blood mononuclear cells (CBMNs) and platelet rich plasma are options for treatment of acute orthopaedic lesions while mesenchymal stem cells (MSCs) are culture expanded. These products may contribute to healing by secreting matrix proteins or growth factors, but they may also act on endogenous MSCs to facilitate healing. OBJECTIVES: To determine the effects of cell therapy products on MSCs function in vitro. The hypothesis was that cell therapy products promote MSCs functions including proliferation, migration and mediator release. METHODS: Fat, bone marrow (BM), cord blood and platelets were obtained from 6 Quarter Horses. The BM-MSCs and their autologous cell therapy products were co-incubated in transwells. Mesenchymal stem cells proliferation, migration, gene expression and cytokine concentrations were determined. RESULTS: All cell therapy products increased MSCs proliferation, but SVF induced significantly more proliferation than any other product. Also SVF elicited more MSCs chemotaxis and, along with BMMNs, significantly more MSCs chemoinvasion. Cord blood mononuclear cells stimulated MSCs to produce high concentrations of interleukin-6 (IL-6), transforming growth factor-ß1 (TGF-ß1), and prostaglandin E(2) (PGE(2)). Stromal vascular fraction and platelet lysate did not stimulate MSCs but SVF and platelet lysate themselves contained high concentrations of PGE(2) and IL-6 (SVF) and TGF-ß1 (platelet lysate). CONCLUSIONS: Autologous cell products variably stimulate MSCs functions with 2 primary patterns apparent. Products either contained preformed mediators that may have intrinsic healing function, or products stimulated MSCs to secrete mediators. POTENTIAL RELEVANCE: The specific clinical indications for these products may differ to include administration as a sole treatment modality prior to MSCs injection for intrinsic cell and cytokine activity (i.e. SVF) or administration concurrently with MSCs to activate MSCs for treatment of chronic lesions (i.e. CBMNs).

Scintigraphic evaluation of intra-arterial and intravenous regional limb perfusion of allogeneic bone marrow-derived mesenchymal stem cells in the normal equine distal limb using (99m) Tc-HMPAO.

REASONS FOR PERFORMING STUDY: Mesenchymal stem cells (MSCs) are commonly injected intralesionally for treatment of soft tissue injuries in the horse. Alternative routes of administration would be beneficial for treatment of lesions that cannot be accessed directly or to limit needle-induced iatrogenic damage to the surrounding tissue. OBJECTIVES: The purpose of our study was to evaluate MSC distribution after intra-arterial (IA) and intravenous (IV) regional limb perfusions (RLP) using scintigraphy. We hypothesised that MSCs would persist in the distal limb after tourniquet removal and that both techniques would lead to diffuse MSC distribution. METHODS: Six horses were used in the study. MSCs were labelled with hexamethyl propylene amine oxime (HMPAO) and technetium-99m. RLP was performed through the median artery of one forelimb and the cephalic vein of the opposite limb under general anaesthesia. The tourniquet was left in place for 45 min. Scintigraphic images were obtained at 0, 45, 75 min, 6 h and 24 h post injection. RESULTS: Distribution of labelled MSCs through the entire distal limb was achieved with all 6 IA RLP, but 3 out of 6 IV RLP showed poor or absent uptake distal to the metacarpus. Mesenchymal stem cell persistence was 39% (30-60%) and 28% (14-50%) (median [minimum-maximum]) at 6 h for IA and IV RLP, respectively. Severe arterial thrombosis occurred in one horse after IA RLP. CONCLUSIONS: Both IA and IV RLP of the distal limb result in MSC persistence in perfused tissues. The IA perfusion resulted in more reliable cell distribution to the pastern and foot area. POTENTIAL RELEVANCE: Regional limb perfusion of MSCs might be used in cases where intralesional injection is not possible or in order to avoid iatrogenic needle damage. Further work is needed to assess the safety of IA RLP before its clinical use.

Collection of equine cord blood and placental tissues in 40 thoroughbred mares.

REASONS FOR PERFORMING STUDY: Stem cells derived from umbilical cord tissue (UCT) and umbilical cord blood (UCB) in human subjects and horses can be obtained in a minimally invasive fashion with successful propagation of mesenchymal stem cells (MSCs). Currently there are no detailed protocols documenting a procedure to harvest UCB and UCT safely for equine stem cell propagation. HYPOTHESIS: UCB and UCT could be collected without harm to mare or foal. OBJECTIVES: To develop a standard and safe method for UCB and UCT collection, and prospectively to compare foal and mare health between groups of animals where tissue was and was not collected. METHODS: This study was conducted at a Thoroughbred breeding facility in central California in 2008. UCB and UCT were collected from 40 mare and foal pairs. Clinical parameters including time for foal to stand and nurse, time for mare to pass the placenta, and foal haematology data at age 24 h were documented and compared to a control group, consisting of the succeeding 40 mare and foal pairs. RESULTS: UCB was obtained successfully from 36 of 40 (90%) mares and UCT from 38 of 40 (95%) mares. Bacterial contamination was documented in 6 out of 36 (16.6%) UCB samples. There were no significant differences in time to stand or nurse for foals or time to pass the placenta for mares, between the experimental and control groups. There were no clinically relevant differences identified in haematological data obtained from foals with and without UCB collection. CONCLUSIONS: UCB and UCT can be harvested safely without harm to mares or foals. POTENTIAL RELEVANCE: UCB and UCT samples collected in an inherently contaminated environment can be successfully disinfected and transported with minimal bacterial overgrowth for use in cell culture to isolate MSCs.

An in vitro biomechanical investigation of an intramedullary nailing technique for repair of third metacarpal and metatarsal fractures in neonates and foals.

OBJECTIVE: To evaluate a dorsoproximal extra-articular approach for insertion of 8.25-mm, solid-titanium, intramedullary (IM) interlocking nails into ostectomized foal third metacarpal (MC3) and third metatarsal (MT3) bones; to compare the monotonic mechanical properties of IM nail constructs with paired intact bones; and to determine the effects of age, body weight, fore- or hindlimb, and left or right limb on the mechanical testing variables. ANIMAL OR SAMPLE POPULATION: Twenty bone pairs (10 MC3, 10 MT3) collected from 10 foals of various weights and ages. METHODS: One bone from each pair was randomly selected to be ostectomized and stabilized using an 8.25-mm, solid-titanium IM nail, and four 3.7-mm titanium interlocking screws (construct). Constructs and contralateral intact bone specimens were tested in axial compression and palmaro-/plantarodorsal (PD) 4-point bending. Monotonic mechanical properties were compared between intact specimens and constructs with an ANOVA; significance was set at P <.05. RESULTS: Nail insertion caused bone failure in 6 MC3 and 2 MT3. In general, mean mechanical testing values indicated that intact specimens were significantly stronger and stiffer than constructs for all age and weight ranges when tested in compression and PD 4-point bending (P <.05). Bone strength and stiffness of intact specimens tested in compression and bending tended to increase linearly with age and weight. CONCLUSION: IM interlocking nail fixation of gap-ostectomized MC3 and MT3 with 8.25-mm IM nails and 3.7-mm interlocking screws did not achieve sufficient strength or stiffness to be recommended as the sole means of repair for comminuted MC3 and MT3 fractures in young foals. CLINICAL RELEVANCE: IM interlocking nail fixation of foal cannon bone fractures may be useful to decrease soft-tissue disruption at the fracture site; however, there is a risk of bone failure associated with extra-articular insertion. This method should be combined with other forms of external coaptation for added stability in axial compression and PD bending.

A biomechanical comparison of headless tapered variable pitch and AO cortical bone screws for fixation of a simulated lateral condylar fracture in equine third metacarpal bones.

OBJECTIVE: To compare drilling, tapping, and screw-insertion torque, force, and time for the 4.5-mm AO and 6.5-mm Acutrak Plus (AP) bone screws, and to compare the mechanical shear strength and stiffness of a simulated complete lateral condylar fracture of the equine third metacarpal bone (MC3) stabilized with either an AO or AP screw. STUDY DESIGN: In vitro biomechanical assessment of screw-insertion variables, and shear failure tests of a bone-screw-stabilized simulated lateral condylar fracture. SAMPLE POPULATION: Eight pairs of cadaveric equine MC3s METHODS: Metacarpi were placed in a fixture and centered on a biaxial load cell in a materials-testing system to measure torque, compressive force, and time for drilling, tapping, and screw insertion. Standardized simulated lateral condylar fractures were stabilized by either an AO or AP screw and tested in shear until failure. A paired t test was used to assess differences between screws, with significance set at P < .05. RESULTS: Insertion and mechanical shear testing variables were comparable for AO and AP insertion equipment and screws. CONCLUSION: The 6.5-mm tapered AP screw can be inserted in equine third metacarpal condyles and is mechanically comparable with the 4.5-mm AO screw for fixation of a simulated lateral condylar fracture. CLINICAL RELEVANCE: Considering the comparable mechanical behavior, the potential for less-persistent soft-tissue irritation with the headless design, and the ability to achieve interfragmentary compression by inserting the screw in one hole drilled perpendicular to the fracture plane, the 6.5-mm tapered AP screw may be an attractive alternative for repair of incomplete lateral condylar fractures in horses.

Evaluation of an in-shoe pressure measurement system in horses.

OBJECTIVE: To develop an objective, accurate method for quantifying forelimb ground reaction forces in horses by adapting a human in-shoe pressure measurement system and determine the reliability of the system for shod and unshod horses. ANIMALS: 6 adult Thoroughbreds. PROCEDURE: Horses were instrumented with a human in-shoe pressure measurement system and evaluated at a trot (3 m/s) on a motorized treadmill. Maximum force, stance time, and peak contact area were evaluated for shod and unshod horses. Three trials were performed for shod and unshod horses, and differences in the measured values were examined with a mixed model ANOVA for repeated measures. Sensor accuracy was evaluated by correlating measured variables to clinically observed lameness and by a variance component analysis. RESULTS: 4 of 6 horses were determined to be lame in a forelimb on the basis of clinical examination and measured values from the system. No significant differences were observed between shod and unshod horses for maximum force and stance time. A significant decrease in peak contact area was observed for shod and unshod horses at each successive trial. Maximum force measurements provided the highest correlation for detecting lameness (r = 0.91, shod horses; r = 1.0, unshod horses). A variance component analysis revealed that 3 trials provided a variance of 35.35 kg for maximum force (+/- 5.78% accuracy), 0.007 seconds for stance time (+/- 2.5% accuracy), and 8.58 cm2 for peak contact area (+/- 11.95% accuracy). CONCLUSIONS AND CLINICAL RELEVANCE: The in-shoe pressure measurement system provides an accurate, objective, and effective method to evaluate lameness in horses.

Equine basal cell tumors: 6 cases (1985-1999).

Basal cell tumors are rare benign tumors in horses. Over a 15-year period, 6 horses were diagnosed with basal cell tumors. The tumors were well-circumscribed. freely moveable, firm, raised papules, nodules, or masses that ranged from 0.6 to 5 cm in diameter. Five of the 6 tumors were ulcerated. Based on gross appearance, the tumors were diagnosed as sarcoids, and 1 was diagnosed as a melanoma. The range of age of affected horses was 6-26 years. The tumors were identified clinically 1 week to 3 years before excision. In 4 horses for which information was available, complete surgical excision was curative with no recurrence 4 months to 2 years after removal.

Scintigraphic detection of equine orthopedic infection using Tc-HMPAO labeled leukocytes in 14 horses.

The aim of this study was to evaluate the diagnostic value of 99mTc-HMPAO leukocyte scintigraphy (LS) by means of a retrospective review of its use in 14 horses that were evaluated for orthopedic infection as a cause of lameness. A total of 17 LS exams were performed in 14 horses. LS studies were positive in 10 of 14 horses. A bacterial infection was confirmed with cytology or culture in 9 of 10 positive horses. Negative LS studies occurred in 4 of 14 horses. Necropsy confirmed the lack of infection in 2 of the 4 horses. Other clinical data and a favorable clinical outcome supported a negative study in the other 2 horses. No false negative or false positive studies were identified. It may be concluded that HMPAO-LS is an effective tool for the diagnosis of orthopedic infection in horses.

A biomechanical comparison of double-plate and Y-plate fixation for comminuted equine second phalangeal fractures.

OBJECTIVES: To compare the biomechanical properties, in full limb preparations, of intact second phalanx and a simulated comminuted second phalangeal fracture stabilized with either two bone plates or a custom Y-plate. STUDY DESIGN: In vitro biomechanical assessment of intact limbs and of paired limbs with a simulated second phalangeal fracture stabilized by one of two fixation methods. Animal Population-Thirteen pairs of equine cadaveric forelimbs. METHODS: A comminuted second phalangeal fracture was created in six paired cadaveric limbs. For each limb pair, the fracture was stabilized with two plates in one limb, and with a Y-plate in the contralateral limb. These limbs and seven pairs of intact limbs were subjected to axial compression in a single cycle until failure. Mechanical properties were compared with a mixed-model ANOVA and post hoc contrasts. Joint contact pressure, screw insertion torque, and final screw torque remaining after mechanical testing were also evaluated for constructs. RESULTS: No significant differences in mechanical testing variables were detected between construct types. However, the Y-Plate construct had significantly greater yield load, yield displacement and yield energy, and failure load and stiffness values than those for intact specimens, whereas the double-plate construct only had greater stiffness than intact specimens. There were no significant differences in joint contact pressures for both constructs. The final screw torque for proximal phalangeal screws was significantly greater for the Y-plate constructs than for double-plate constructs. CONCLUSIONS: The Y-plate was as effective as the double-plate technique for stabilization of simulated comminuted second phalangeal fractures in monotonically tested equine cadaveric forelimbs. CLINICAL RELEVANCE: This investigation supports evaluation of the Y-plate for repair of comminuted second phalangeal fractures in equine patients. Its specific design may facilitate repair of second phalangeal fractures, and may provide increased stability by allowing the proximal fragments of the second phalanx to be fixed with three screws placed through the plate.

Comparison of incisional bursting strength of simple continuous and inverted cruciate suture patterns in the equine linea alba.

OBJECTIVE: To determine the bursting strength of ventral median abdominal incisions closed by either simple continuous or inverted cruciate suture patterns. STUDY DESIGN: Experimental. ANIMAL OR SAMPLE POPULATION: Twelve equine cadavers. METHODS: A 25 cm ventral median incision was made through the linea alba and a 200 L polyurethane bladder was placed within the abdomen. Either a simple continuous or an inverted cruciate pattern using 3 polyglactin 910 with a bite size and suture interval of 1.5 cm was used to close linea incisions. Closure time was recorded for each pattern. The bladder was inflated with air at 40 L/min, and the pressure at body wall failure recorded. The length of suture used for wound closure and the wound failure modes were recorded. Deviation from the linea (cm), total suture length (cm), suture length to wound length ratio (SL:WL), closure time (min), bursting pressure (mm Hg), and failure modes were compared between groups using Welch-Aspin t-tests. The effects of independent subject variables were assessed for possible effects on bursting strength using analysis of covariance. RESULTS: Mean bursting pressure was significantly greater for the simple continuous pattern than for the inverted cruciate pattern (P = .01). Significantly less suture material (P = .0002) was required with the continuous pattern than with the inverted cruciate pattern. Mean closure time, SL:WL, deviation from the linea, and failure modes were not significantly different between groups. No significant effects were noted for independent variables in both groups on bursting strength. CONCLUSIONS: In this model, a simple continuous closure pattern for ventral median abdominal incisions was stronger than an inverted cruciate pattern. A simple continuous pattern leaves less foreign material in the wound, which may be of benefit in reducing incisional complications. CLINICAL RELEVANCE: Use of a continuous closure pattern for the linea alba may offer greater wound security during episodes of increased intra-abdominal pressure in horses.

Evaluation of iodophor skin preparation techniques and factors influencing drainage from ventral midline incisions in horses.

OBJECTIVE: To document natural bacterial flora on the ventral aspect of the equine abdomen, to compare 2 preparation techniques, and to identify potential risk factors that may contribute to incisional drainage. DESIGN: Prospective study. ANIMALS: 53 horses undergoing exploratory celiotomy. PROCEDURE: Group-1 horses (n = 26) were prepared with povidone-iodine and alcohol. Group-2 horses (27) were prepared with a film-forming iodophor complex. Numbers of bacterial colony-forming units (CFU) were measured before and after surgical scrub, following skin closure, and after recovery from general anesthesia. Swab specimens to identify normal skin bacterial flora and potential pathogens were obtained by swabbing a 4 x 4-cm area. Variables that might affect incisional drainage were also investigated. RESULTS: For both techniques, there was a significant reduction in bacterial numbers after skin preparation. Incisional drainage was observed in 14 (26%) horses (8 group-1 and 6 group-2 horses). Preexisting dermatitis, poor intraoperative drape adherence, high number of bacterial CFU obtained after recovery from anesthesia, and high number of CFU obtained from the surgery room environment were the main risk factors associated with subsequent incisional drainage. Bacillus spp, nonhemolytic Staphylococcus spp, Micrococcus spp, Corynebacterium spp, Streptomyces spp, other nonenteric genera, and nonhemolytic Streptococcus spp were the most common isolates obtained before surgical scrub. CONCLUSIONS AND CLINICAL RELEVANCE: Both skin preparation techniques were equally effective in reducing numbers of bacterial CFU by 99%, and a significant difference was not found in incisional drainage rate between groups. Protection of the wound during recovery from anesthesia and the immediate postoperative period may reduce incisional drainage after abdominal surgery in horses.