Augmentation of bone defect healing using a new biocomposite scaffold: an in vivo study in sheep.

Previous studies support resorbable biocomposites made of poly(L-lactic acid) (PLA) and beta-tricalcium phosphate (TCP) produced by supercritical gas foaming as a suitable scaffold for tissue engineering. The present study was undertaken to demonstrate the biocompatibility and osteoconductive properties of such a scaffold in a large animal cancellous bone model. The biocomposite (PLA/TCP) was compared with a currently used beta-TCP bone substitute (ChronOS, Dr. Robert Mathys Foundation), representing a positive control, and empty defects, representing a negative control. Ten defects were created in sheep cancellous bone, three in the distal femur and two in the proximal tibia of each hind limb, with diameters of 5 mm and depths of 15 mm. New bone in-growth (osteoconductivity) and biocompatibility were evaluated using microcomputed tomography and histology at 2, 4 and 12 months after surgery. The in vivo study was validated by the positive control (good bone formation with ChronOS) and the negative control (no healing with the empty defect). A major finding of this study was incorporation of the biocomposite in bone after 12 months. Bone in-growth was observed in the biocomposite scaffold, including its central part. Despite initial fibrous tissue formation observed at 2 and 4 months, but not at 12 months, this initial fibrous tissue does not preclude long-term application of the biocomposite, as demonstrated by its osteointegration after 12 months, as well as the absence of chronic or long-term inflammation at this time point.

Tissue reaction to implants of different metals: a study using guide wires in cannulated screws.

Cannulated screws, along with guide wires, are typically used for surgical fracture treatment in cancellous bone. Breakage or bending deformation of the guide wire is a clinical concern. Mechanically superior guide wires made of Co-Cr alloys such as MP35N and L605 may reduce the occurrence of mechanical failures when used in combination with conventional (316L stainless steel) cannulated screws. However the possibility of galvanic or crevice corrosion and adverse tissue reaction, exists when using dissimilar materials, particularly in the event that a guide wire breaks, and remains in situ. Therefore, we designed an experiment to determine the tissue reaction to such an in vivo environment. Implant devices were designed to replicate a clinical situation where dissimilar metals can form a galvanic couple. Histological and SEM analyses were used to evaluate tissue response and corrosion of the implants. In this experiment, no adverse in vivo effects were detected from the use of dissimilar materials in a model of a broken guide wire in a cannulated screw.

Behavioural and cardiorespiratory effects of a constant rate infusion of medetomidine and morphine for sedation during standing laparoscopy in horses.

REASONS FOR PERFORMING STUDY: Standing surgical procedures are performed commonly in horses under sedation. This approach minimises the morbidity/mortality risks associated with general anaesthesia. The use of a medetomidine and morphine combination has not been investigated in horses despite the usefulness of each drug individually. OBJECTIVE: To determine the efficacy of a medetomidine and morphine combination to produce standing sedation with minimal cardiorespiratory changes and adequate analgesia for exploratory laparascopy in mature horses. HYPOTHESIS: The combination of medetomidine and morphine will induce reliable sedation with minimal cardiorespiratory changes. METHODS: Medetomidine (5 microg/kg bwt i.v.) followed in 10 min by morphine (50 microg/kg bwt i.v.) and 10 min later by a constant rate infusion (CRI) of medetomidine and morphine (5 and 30 microg/kg bwt/h, respectively) was administered in 7 horses undergoing standing exploratory laparoscopy. Quality of sedation and cardiorespiratory function were assessed. RESULTS: Sedation was satisfactory after the medetomidine and morphine bolus. The CRI of both drugs enhanced sedation and ataxia. Mean visual analogue scores on a scale of 10 varied between 7.8 and 8.8 and were similar between anaesthesiologists and surgeons. Heart rate, respiratory rate and packed cell volume (PCV) decreased significantly after medetomidine and, at some periods, during the CRI. Blood pressure only increased significantly at 5 min and arterial O2 decreased significantly at 10 min post medetomidine. PCV remained significantly lower and total protein decreased post morphine and CRI administration. Arterial CO2 increased towards the end of the CRI. Cardiac output did not change significantly over time. CONCLUSION AND CLINICAL RELEVANCE: The combination of medetomidine and morphine results in reliable sedation and stable cardiorespiratory function in horses undergoing exploratory laparascopy.

Acute small intestinal obstruction associated with Parascaris equorum infection in young horses: 25 cases (1985-2004).

AIMS: To retrospectively evaluate the medical and surgical records of horses with acute small intestinal obstructions associated with Parascaris equorum infection; to describe the gastrointestinal lesions; and to determine the outcome of cases with such lesions. METHODS: Records of 25 horses with acute small intestinal obstruction associated with P. equorum between 1985 and 2004 were reviewed to determine signalment, history, physical examination, surgical or post-mortem findings, and outcome. RESULTS: All horses except one were less than 12 months old. Standardbreds were over-represented in the population studied. Sixteen horses (72%) had been administered anthelmintics, including pyrantel (n=8), ivermectin (n=7), and trichlorphon (n=1), within 24 h prior to the onset of colic. Of the 25 cases reviewed, 16 had simple obstructive ascarid impactions (SOAIs), and nine had complicated obstructive ascarid impaction (COAI) including volvulus (n=6) or intussusception (n=3), both concurrent with ascarid impaction of the small intestine. Short-term survival (discharge from hospital) occurred in 79% of horses treated for SOAI, and was 64% for all horses. Long-term survival (>1 year) occurred in 33% of horses with SOAI, and the overall long-term survival was 27% for all horses. Formation of adhesions was the most frequent finding associated with death for horses that did not survive long-term. CONCLUSIONS AND CLINICAL RELEVANCE: The incidence of anthelmintic treatment within 24 h of the onset of colic in this study population (72%) was higher than that previously reported. Resistance of P. equorum to ivermectin recently reported in Ontario may be associated with increased ascarid burdens, predisposing horses to ascarid impaction. The long-term survival of these horses was better than that reported previously.

Effect of heel elevation on forelimb conformation in horses.

OBJECTIVE: To determine the conformational changes in the distal forelimb of horses following heel elevation of 15 degrees and greater. An experimental study with repeated, within-horse measurements. PROCEDURE: Five clinically normal, mixed-breed horses were used to determine distal forelimb conformation following heel elevation from 0 to 45 degrees in 15 degree increments. Data were also compared to conformation of the limb in a Kimzey splint. Conformation was determined using lateral to medial radiographic projections. Conformation parameters assessed included measurement of apparent lengths of digital flexor tendons from the origin of their accessory ligaments to the points of insertion, and the joint angles of the distal limb. RESULTS: For angles of heel elevation from 15 to 45 degrees, the degree of joint angulation increased (increasing flexion) with heel elevation for the metacarpophalangeal, and proximal and distal interphalangeal joints. Conversely, the measured apparent lengths of the digital flexor tendons in the distal limb, decreased. CONCLUSION: The data supports the practice of elevating the heel (greater than 15 degrees) for conditions in which decreased fetlock extension may be desired such as with laceration or injury to the digital flexor tendons. Further study is required to determine whether heel elevation greater than 15 degrees reduces in vivo digital flexor tendon tension and also to ensure that the marked flexion of the distal interphalangeal joint with greater heel elevation is not detrimental over a prolonged period that may be required for the rehabilitation of flexor tendon injuries in the horse.

Treatment of a granuloma caused by Halicephalobus gingivalis in a horse.

A 12-year-old Arabian gelding with a granuloma caused by the nematode Halicephalobus gingivalis caudal and dorsal to the left orbit was examined. There was no evidence of dissemination of the nematode to the kidneys or the CNS, and the horse was treated with ivermectin (1.2 mg/kg [0.55 mg/lb] of body weight, p.o., every 2 weeks for 3 treatments). The granuloma was surgically debulked 2 days after the first dose of ivermectin. The granuloma resolved with no evidence of nematode infection after 18 months. Halicephalobus gingivalis is a ubiquitous saprophytic nematode that has been reported to infect humans and horses. The nematode may form granulomas in the integument or may disseminate to various organs with a tropism for the CNS and kidneys. Once clinical signs of CNS involvement develop, the disease is rapidly fatal.