Mechanical Properties and Failure Mode of Proximal Screw Fixation Technique Using Locking Compression Plate for Proximal Interphalangeal Arthrodesis in Horses: An Ex Vivo Study.

OBJECTIVE: The aim of this study was to measure the mechanical properties and failure mode of an ex vivo model of proximal interphalangeal arthrodesis in horses with different methods of proximal screw fixation using a locking compression plate. STUDY DESIGN: Pastern joint arthrodesis with a 3-hole 4.5-mm narrow locking compression plate was performed on 20 forelimbs of equine cadavers, randomized into four groups based on the fixation method and type of proximal screw used: unicortical cortex, bicortical cortex, unicortical locking, bicortical locking. Single-cycle axial compression testing was conducted until failure. The frequency of implant plastic deformation was recorded. Bone failure analysis was performed through computed tomography examinations and fractal analysis. RESULTS: There were no differences in the analysed mechanical variables and fractal dimension among the groups. Transarticular screws showed a higher frequency of deformation (75%) regardless of the group. Both unicortical locking and bicortical locking groups deformed the plate more frequently. CONCLUSION: The type of screw used in the proximal hole of the locking compression plate and its method of anchoring in the proximal phalanx do not affect the mechanical properties of pastern arthrodesis in equine cadavers subjected to single-cycle axial compression tests until failure.

3-D technology used to accurately understand equine ileocolonic aganglionosis.

Ileocolonic aganglionosis (ICA) is the congenital and hereditary absence of neurons that constitute the enteric nervous system and has been described in various species including humans - Hirschsprung's disease - and horses - overo lethal white syndrome (OLWS). Hirschsprung's disease affects circa 1 in 5,000 live births. At best, this disease means an inability to absorb nutrients from food (humans). At worse, in horses, it always means death. Despite our general understanding of the functional mechanisms underlying ICA, there is a paucity of reliable quantitative information about the structure of myenteric and submucosal neurons in healthy horses and there are no studies on horses with ICA. In light of these uncertainties, we have used design-based stereology to describe the 3-D structure - total number and true size - of myenteric and submucosal neurons in the ileum of ICA horses. Our study has shown that ICA affects all submucosal neurons and 99% of myenteric neurons. The remaining myenteric neurons (0.56%) atrophy immensely, i.e. 63.8%. We believe this study forms the basis for further research, assessing which subpopulation of myenteric neurons are affected by ileocolonic aganglionosis, and we would like to propose a new nomenclature to distinguish between a complete absence of neurons - aganglionosis - and a weaker form of the disease which we suggest naming 'hypoganglionosis'. Our results are a step forward in understanding this disease structurally.

Effect of postoperative xylazine administration on cardiopulmonary function and recovery quality after isoflurane anesthesia in horses.

OBJECTIVE: To evaluate equine cardiopulmonary function and recovery quality after administration of 0.25 or 0.50 mg/kg xylazine intravenously (IV) during recovery. STUDY DESIGN: Randomized, blinded, prospective, clinical study. ANIMALS: Horses (n = 20). METHODS: During recovery after 3 hours of isoflurane anesthesia for arthroscopic surgery, horses were administered either 0.25 mg/kg (G25, n = 10) or 0.50 mg/kg (G50, n = 10) xylazine intravenously. Vital signs and arterial blood samples were obtained during recovery before sedation (baseline), 5, 10, 20, 30, and 45 minutes after xylazine and 30 minutes after standing. The quality of recovery scores ranged from 10 to 72 (10 = best, 72 = worst). RESULTS: G25 horses recovered faster (mean ± SD, 33 ± 5 min) than G50 horses (50 ± 7 min, P < .0001). Mean maximal decrease in arterial oxygen tension was 55 ± 11 mmHg in G25 (at 10 minutes; P < .05) and 54 ± 7 mmHg in G50 (at 20 minutes; P < .01). G25 group had a total recovery score (23 [range 18-29]) and number of attempts to stand (4 ± 2) greater than the G50 group (18 [10-23] and 1 ± 1, respectively; P < .001). CONCLUSIONS: Both doses of xylazine promoted a moderate and transient hypoxemia during recovery; however, the 0.5 mg/kg dose produced a longer and improved quality of recovery from anesthesia.

Effect of ephedrine and phenylephrine on cardiopulmonary parameters in horses undergoing elective surgery.

OBJECTIVE: To assess the cardiopulmonary effects of ephedrine and phenylephrine for management of isoflurane-induced hypotension in horses. STUDY DESIGN: Prospective randomized clinical study. ANIMALS: Fourteen isoflurane-anesthetized horses undergoing digital palmar neurectomy. METHODS: Ephedrine (EPH group; 0.02 mg kg(-1) minute(-1); n = 7) or phenylephrine (PHE group; 0.002 mg kg(-1) minute(-1); n = 7) was administered to all horses when mean arterial pressure (MAP) was <60 mmHg. The infusions were ended when the target MAP was achieved, corresponding to a 50% increase over the pre-infusion MAP (baseline). The horses were instrumented with an arterial catheter to measure blood pressure and allow the collection of blood for pH and blood-gas analysis and a Swan-Ganz catheter for measurement of cardiac output using thermodilution. Cardiopulmonary parameters were recorded at baseline and at 5, 30, 60 and 90 minutes after achieving the target MAP. RESULTS: In both groups, the MAP and systemic vascular resistance (SVR) increased significantly at 5, 30, 60 and 90 minutes post infusion compared to baseline (p < 0.05). The EPH group had a significant increase in cardiac index (CI) and systemic oxygen delivery index at 5, 30, 60 and 90 minutes post infusion compared to baseline (p < 0.05) and compared to the PHE group (p < 0.05). The PHE group had significantly higher SVR and no decrease in oxygen extraction compared with the EPH group at 30, 60 and 90 minutes post infusion (p < 0.05). No significant differences in ventilatory parameters were observed between groups after the infusion. CONCLUSIONS: Ephedrine increased the MAP by increasing CI and SVR. Phenylephrine increased MAP by increasing SVR but cardiac index decreased. Ephedrine resulted in better tissue oxygenation than phenylephrine. CLINICAL RELEVANCE: Ephedrine would be preferable to phenylephrine to treat isoflurane-induced hypotension in horses since it increases blood flow and pressure.

Effect of pressure support ventilation during weaning on ventilation and oxygenation indices in healthy horses recovering from general anesthesia.

OBJECTIVE: To determine if pressure support ventilation (PSV) weaning from general anesthesia affects ventilation or oxygenation in horses. STUDY DESIGN: Prospective randomized clinical study. ANIMALS: Twenty client-owned healthy horses aged 5 ± 2 years, weighing 456 ± 90 kg. METHODS: In the control group (CG; n = 10) weaning was performed by a gradual decrease in respiratory rate (fR ) and in the PSV group (PSVG; n = 10) by a gradual decrease in fR with PSV. The effect of weaning was considered suboptimal if PaCO2 > 50 mmHg, arterial pH < 7.35 plus PaCO2 > 50 mmHg or PaO2 < 60 mmHg were observed at any time after disconnection from the ventilator until 30 minutes after the horse stood. Threshold values for each index were established and the predictive power of these values was tested. RESULTS: Pressure support ventilation group (PSVG) had (mean ± SD) pH 7.36 ± 0.02 and PaCO2 41 ± 3 mmHg at weaning and the average lowest PaO2 69 ± 6 mmHg was observed 15 minutes post weaning. The CG had pH 7.32 ± 0.02 and PaCO2 57 ± 6 mmHg at weaning and the average lowest PaO2 48 ± 5 mmHg at 15 minutes post weaning. No accuracy in predicting weaning effect was observed for fR (p = 0.3474), minute volume (p = 0.1153), SaO2 (p = 0.1737) and PaO2 /PAO2 (p = 0.1529). A high accuracy in predicting an optimal effect of weaning was observed for VT > 10 L (p = 0.0001), fR /VT ratio ≤ 0.60 breaths minute(-1) L(-1) (p = 0.0001), VT /bodyweight > 18.5 mL kg(-1) (p = 0.0001) and PaO2 /FiO2 > 298 (p = 0.0002) at weaning. A high accuracy in predicting a suboptimal effect of weaning was observed for VT < 10 L (p = 0.0001), fR /VT ratio ≥ 0.60 breaths minute(-1) L(-1) (p = 0.0001) and Pe'CO2 ≥ 38 mmHg (p = 0.0001) at weaning. CONCLUSIONS AND CLINICAL RELEVANCE: Pressure support ventilation (PSV) weaning had a better respiratory outcome. A higher VT , VT /body weight, PaO2 /FiO2 ratio and a lower fR /VT ratio and Pe'CO2 were accurate in predicting the effect of weaning in healthy horses recovering from general anesthesia.

Arthrodesis of the equine proximal interphalangeal joint: a biomechanical comparison of 3-hole 4.5 mm locking compression plate and 3-hole 4.5 mm narrow dynamic compression plate, with two transarticular 5.5 mm cortex screws.

OBJECTIVES: To compare the biomechanical characteristics of 2 arthrodesis techniques for the equine proximal interphalangeal joint (PIP) using either a 3-hole 4.5 mm locking compression plate (LCP) or 3-hole 4.5 mm narrow dynamic compression plate (DCP), both with 2 transarticular 5.5 mm cortex screws. STUDY DESIGN: Experimental. SAMPLE POPULATION: Cadaveric adult equine forelimbs (*n=6 pairs). METHODS: For each forelimb pair, 1 limb was randomly assigned to 1 of 2 treatment groups and the contralateral limb by default to the other treatment group. Construct stiffness, gap formation across the PIP joint, and rotation about the PIP joint were determined for each construct before cyclic axial loading and after each of four, 5000 cycle loading regimens. After the 20,000 cycle axial loading regimen, each construct was loaded to failure. RESULTS: There were no significant differences in construct stiffness, gap formation, or sagittal plane rotation between the LCP and DCP treatment groups at any of the measured time points. CONCLUSION: Biomechanically, fixation of the equine PIP joint with a 3-hole 4.5 mm LCP is equivalent to fixation with a 3-hole 4.5 mm narrow DCP under the test conditions used.

Bilateral sinus cysts in a filly treated by endoscopic sinus surgery.

Bilateral cysts in the frontal and caudal maxillary sinuses in a filly treated by endoscopic sinus surgery (sinoscopy) and triangulation technique are described. Sinoscopy has the advantage of being a minimally invasive technique and permits a complete inspection of the frontal and maxillary sinuses, which is not possible through flap sinusotomy.

Histologic and immunohistochemical evaluation of biocompatibility of castor oil polyurethane polymer with calcium carbonate in equine bone tissue.

OBJECTIVE To evaluate the efficacy of castor oil polyurethane polymer with calcium carbonate for use in a unicortical ostectomy on the dorsal surface of the third metacarpal bone of horses. ANIMALS 6 adult horses. PROCEDURES A unicortical ostectomy was created on the dorsal surface of both third metacarpal bones of each horse. Castor bean (Ricinus communis) oil polyurethane polymer with calcium carbonate was implanted into the ostectomy on 1 limb, and the ostectomy of the contralateral limb was left unfilled and served as a control sample. Ostectomy sites were evaluated histologically 120 days later. Biopsy specimens were obtained from the interface of bone and polymer or the interface of bone and newly formed tissue; specimens were processed for histomorphometric evaluation by use of light microscopy, immunohistochemical analysis, histochemical analysis, and transmission electron microscopy. RESULTS Osteoconductive activity of the biomaterial was confirmed by the presence of osteoblasts in the biopsy specimens. Absence of a chronic inflammatory response or foreign body reaction indicated biocompatibility. Expression of osteoblast markers was detected in the newly formed tissue. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that castor oil polyurethane polymer with calcium carbonate could be an acceptable compound for use as a bone substitute in horses with fractures in which bone filling is necessary.

Avaliação histológica e histomorfométrica da regeneração óssea a partir da utilização de biomateriais em tíbias de ovinos / Histological and histomorphometric evaluation of bone regeneration with biomaterial in the tibia of sheep

Falhas ósseas são comumente encontradas na medicina veterinária em diferentes enfermidades, principalmente por traumas em grandes animais. Frequentemente faz-se necessário auxiliar este reparo tecidual para melhor correção desta falha. Os biomateriais foram desenvolvidos para cumprir esta função. A fim de avaliar o comportamento celular perante estes substitutos ósseos, a realização de testes in vivo é fundamental. A partir da observação da unidade morfofuncional do tecido é possível avaliar a quantidade e a qualidade do tecido neoformado. Atualmente, em estudos ortopédicos, os ovinos são considerados animais de escolha como modelo experimental. Falhas ósseas foram realizadas experimentalmente em ovinos, onde foram implantados biomateriais à base de quitosana, hidroxiapatita e colágeno. Após 60 dias foi realizada biopsia no local do reparo tecidual e por meio da histomorfometria da matriz orgânica, da análise descritiva da microscopia de luz e da microscopia eletrônica de transmissão, o tecido neoformado foi avaliado e comparado. Na histomorfometria, não houve diferença significativa quanto à quantidade de tecido neorformado do grupo controle e do grupo com biomaterial, porém quando comparado ao osso pré-existente, retirado no momento da confecção da falha, a área de matriz óssea foi menor. Na descrição da microscopia de luz e em maiores detalhes na análise ultra estrutural, observou-se o biomaterial em contato íntimo com o tecido neoformado, sugerindo boa biocompatibilidade. Foi possível observar o padrão da reparação tecidual, onde o membro controle e o membro com biomaterial não diferiram quanto à arquitetura tecidual, porém nas amostras com o implante do biomaterial foi identificada a presença do mesmo. Todas estas informações sugerem que o biomaterial não prejudicou a regeneração óssea, apresentou boa biocompatibilidade e denota potencial para auxiliar na rotina ortopédica de grandes animais.(AU)

Bone defects are commonly found in veterinary medicine through different disease such as trauma, especially in large animals. Frequently it is necessary to assist this tissue repair for better regeneration. Biomaterials in general are designed to this function. In order to understand the bone cells in the presence of bone substitutes, tests in vivo are essential for these studies. The quantity and quality of new tissue formation can be assessed by observation of tissue morphofunctional unit. Currently, in orthopedic studies sheep are considerated animals of choice for experimental development. Bone defects were performed experimentally in sheep and were implanted chitosan, hydroxyapatite and collagen biomaterials. After 60 days, biopsy was performed at the site of tissue repair and the new tissue formation was described, evaluated and compared by organic matrix bone histomorphometry and electronic transmission microscopy. After hystomorfometry analysis there was no difference between control group and biomaterial group, but when compare with pre-existent tissue, the values are smaller. In descriptive analysis was observed intimate contact with biomaterial and new tissue formation suggesting biocompatibility. It observed the pattern of tissue repair in control group and biomaterial group did not differ in the architecture tissue. However, in the biomaterial group was identified presence of the biomaterial in the specimen. All these data suggest that the biomaterial did not impair bone regeneration, had good biocompatibility and potential to assistant in orthopedic routine of large animals.(AU)

Characterization of equine adipose tissue-derived progenitor cells before and after cryopreservation.

In horses, stem cell therapies are a promising tool to the treatment of many injuries, which are common consequences of athletic endeavor, resulting in high morbidity and often compromising the performance. In spite of many advantages, the isolation of stem cells similar to human, from equine adipose tissue, occurred only recently. The aim of this study was to isolate equine adipose tissue-derived progenitor cells (eAT-PC), to characterize their proliferative potential, and to study their differentiation capacity before and after cryopreservation. The cells, isolated from horse adipose tissue, presented similar fibroblast-like cell morphology in vitro. Their proliferation rate was evaluated during 63 days (23 passages) before and after cryopreservation. After the induction of osteogenic differentiation, von Kossa staining and positive immunostaining studies revealed the formation of calcified extracellular matrix confirming the osteogenic potential of these cells. Adipogenic differentiation was induced using two protocols: routine and other one developed by us, while our protocol requires a shorter time (Oil Red O staining revealed significant accumulation of lipid droplets after 7 days). Chondrogenic differentiation was observed after 21 days of induced pellet culture, as evidenced by histological (toluidine blue) and immunohistochemistry studies. Our data demonstrate that eAT-PC can be easily isolated and successfully expanded in vitro while presenting significant proliferating rate. These cells can be maintained undifferentiated in vitro and can efficiently undergo differentiation at least into mesodermal derivates. These eAT-PC properties were preserved even after cryopreservation. Our findings classify eAT-PC as a promising type of progenitor cells that can be applied in different cell therapies in equines.