Direct current stimulation of bone production in the pony: observations with a diaphyseal osteotomy model

Electrically induced osteogenesis exhibits a dose response curve and can induce bone formation in the absence of trauma and in nonunions. Electrically induced osteogenesis, using direct electric current (DC) in a third metacarpal diaphyseal osteotomy model, in conjunction with internal fixation and postoperative loading, was investigated. Twelve young adult ponies of mixed sex were divided into 2 treatment groups (A and B) of 3 stimulated and 3 controls each and evaluated, using a specifically designed procedure. Stimulated ponies in both groups were given 20 microA of DC via an implanted bone growth stimulator (BGS); group A ponies were stimulated for 60 days and group B ponies for 120 days. Biocompatibility of the BGS was excellent in all ponies. Radiographically, there was more advanced healing with better vascular development in the ponies stimulated for 60 days compared with controls, but no discernible difference was seen at 120 days. Nuclear medical bone imaging revealed a peak uptake at 4 weeks in stimulated groups and the uptake decreased after 8 weeks. Radiopharmaceutical uptake in stimulated ponies was consistently below control uptake throughout the study. Mean specific gravity (SG) of specimens prepared for testing materials properties for group A and B controls were 2.044 +/- 0.119 and 1.939 +/- 0.065, respectively. The SG for group A and group B stimulated were 1.992 +/- 0.049 and 1.876 +/- 0.031, respectively. The SG of specimens obtained from metacarpi of age-matched control ponies was 2.194 +/- 0.166. The ultimate bending strengths and the flexural moduli of elasticity in 60-day control ponies and stimulated ponies were 57 +/- 8.4, 59 +/- 23.9 MN/m2 and 89 +/- 3.5, 106 +/- 6.5 MN/m2 and in 120-day control ponies and stimulated ponies were 13 +/- 1.0, 13 +/- 3.2 GN/m2 and 13 +/- 2.89, 15 +/- 0.577 GN/m2, respectively. Sixty-day samples and 120-day samples had pending strengths (SU) of 25% and 50% that of unfractured cortex, respectively. These findings indicate that 20 microA of DC stimulation on a diaphyseal osteotomy model may not stimulate sufficient bone production to affect the mechanical properties of the bone. Therefore, based on our research, clinical use of BGS in fresh fracture management cannot be recommended.     

Electrical stimulation on skin wound healing in the horse: preliminary studies

The effect of low-level direct-current stimulation on skin wound healing in the horse was assessed. Self-sustaining electrical circuits with electrodes were implanted subcutaneously in or near the wound. Stimulation by direct current (10 or 20 microA) was used to determine the effect on equine skin healing. The efficacy of electrotherapy was evaluated by sequentially comparing the clinical appearance of the wound and measuring the size of the granulating wound bed. The histologic appearance of the healing stimulated wounds was compared with that in nonstimulated control wounds created on 9 horses. Seemingly, electrical stimulation had no discernible effect on experimentally created skin wounds. Clinical observation and histologic examination of the wounds indicated that severe tissue reaction from the implanted electrodes and concurrent local infection produced local detrimental effects to wound healing.     

Capacitively coupled electrical stimulation of bone healing in the horse: in vivo study with a Salter type IV osteotomy model with stainless steel surface electrodes

The use of capacitively coupled low-voltage signals for stimulation of osteogenesis has been reported in a variety of animal models. Electrically induced osteogenesis was investigated with a capacitively coupled electric field on a radius (distal-lateral orientation) osteotomy model, in conjunction with internal fixation and postoperative loading. Twelve adult horses of either sex were allotted to 2 groups of 6; 1 group was given electrical stimulation and the other served as controls. A low-voltage high-frequency capacitively coupled electrical signal was locally and continuously applied to the electrically stimulated group for 60 days through external, bare stainless steel surface electrodes which were placed on the skin in circuit with a small, portable power source. Harness compatibility and stimulator and battery durability were excellent. However, stainless steel electrodes required a rigid maintenance schedule to maintain consistent current levels. Synovial fluid evaluation demonstrated intra-articular inflammation (decreased viscosity, hyaluronic acid, and increased protein concentration) 1 week postoperatively that generally improved during subsequent weeks and no distinction between groups was observed at 60 days. Radiographically, there was no difference in the appearance of the healing process of control and that of stimulated horses during the 60 days. Angiography showed bridging blood vessels in both groups. Uptake of a bone seeking radiopharmaceutical peaked at 3 weeks in both groups and was 1.92 +/- 0.6 cps/pixel/mCi and 1.26 +/- 0.40 csp/pixel/mCi for control and stimulated horses, respectively. At any given observation period, uptake in the lesion area was greater in the control group. Ultimate strengths of trabecular bone in 60-day control radii and stimulated radii were 12.64 +/- 3.013 and 9.60 +/- 3.95 MN/m2, and the flexural moduli of elasticity were 698.0 +/- 423 and 402.0 +/- 523 MN/m2, respectively. Porosity index was similar for all specimens. Gross, histologic, and microradiographic evaluations indicated that controls healed more efficiently than stimulated horses. A capacitively coupled applied voltage of 2.2 V RMS (mean) producing a current of 17.32 mA (mean) did not stimulate sufficient bone production in a metaphyseal osteotomy model to affect the mechanical properties of the bone or accelerate the healing process.     

Intestinal decompression: preliminary study in the horse

A technique of nasoduodenal (N-D) intubation and intestinal decompression was developed and used in the horse to explore the prevention of gastric and intestinal distention after abdominal surgical operation. Three styles of tubes (2 single-lumen tubes and 1 double-lumen tube) were positioned in the duodenum of 12 mature horses (10 experimental and 2 clinical) during laparotomy (without enterotomy), and an iatrogenic occlusion at the small intestine was created and later released in the 10 experimental horses. The 2 clinical horses had an exploratory laparotomy to correct a natural obstruction of the small intestine. After each horse recovered from surgical manipulation, suction was used to keep fluids from accumulating in the cranial part of the gastrointestinal tract. In 5 of the 12 horses, the most simple N-D tube was positioned successfully and functioned properly. Three of the 5 horses which were fasted before surgical manipulation (to obtain an empty stomach) survived without postsurgical complications. Volume of reflux material was measured. Clinical data, such as periods of comfort during decompression without giving analgesics, were recorded. Necropsies were done on 10 of the 12 horses (9 experimental and 1 clinical). Although already tested in 2 clinical horses, use of the N-D tube remains experimental, and the N-D tube functioned only in horses which were fasted before surgical manipulation. Perfection of a safe and dependable means of emptying the equine stomach of its solid ingesta before gastrointestinal intubation is done, is the next step in affording greater clinical application of the N-D tube for gastrointestinal decompression.     

Fracture healing after stabilization with intramedullary xenograft cortical bone pins: a study in pigeons

OBJECTIVE: To investigate the effectiveness of intramedullary xenograft cortical bone pins compared with stainless steel Kirschner wire for the repair of a standardized avian humeral fracture. STUDY DESIGN: Prospective randomized study. SAMPLE POPULATION: Thirty mature pigeons (Columba livia). METHODS: Birds were randomly assigned to 3 groups. Transverse mid-diaphyseal humeral fractures were created in 1 humerus in each bird. Fractures were stabilized with intramedullary ostrich or canine xenograft cortical bone pins or Kirschner wire. Radiographic, histological, and biomechanical assessments were used to compare fracture healing 6 weeks after fracture stabilization. The contralateral humerus of each bird was used as a control. RESULTS: All fractures healed regardless of intramedullary pin type. There were no statistically significant biomechanical differences among groups or within groups. Xenograft cortical bone pins induced a mononuclear inflammatory reaction that did not impair bone healing. Bones stabilized with intramedullary cortical bone pins had more periosteal callus and inflammation at the fracture site than bones stabilized with stainless steel Kirschner wires. CONCLUSIONS: Intramedullary xenograft cortical bone pins, derived from mammalian or avian sources, appear to represent an alternative for the repair of avian humeral fractures. CLINICAL RELEVANCE: Intramedullary xenograft cortical bone pins are biodegradable and may reduce the need for additional surgery to remove implants after fracture healing.     

Renal cell carcinoma with bone metaplasia in a horse

A case of renal tubular carcinoma with bone metaplasia is reported in a 20-year-old male, mixed breed horse having a history of weight loss and hematuria. This report includes the clinical signs, macroscopic and microscopic lesions, and the immunohistochemical findings of this neoplasm.     

Comparable bone healing capacity of different bone graft matrices in a rabbit segmental defect model

We compared the bone healing capacity of three different demineralized bone matrix (DBM) products applied using different carrier molecules (hyaluronic acid [HA] vs. carboxymethylcellulose [CMC]) or bone compositions (cortical bone vs. cortical bone and cancellous bone) in a rabbit segmental defect model. Overall, 15-mm segmental defects in the left and right radiuses were created in 36 New Zealand White rabbits and filled with HA-based demineralized cortical bone matrix (DBX), CMC-based demineralized cortical bone matrix (DB) or CMC-based demineralized cortical bone with cancellous bone (NDDB), and the wound area was evaluated at 4, 8, and 12 weeks post-implantation. DBX showed significantly lower radiopacity, bone volume fraction, and bone mineral density than DB and NDDB before implantation. However, bone healing score, bone volume fraction, bone mineral density, and residual bone area at 4, 8, and 12 weeks post-implantation revealed no significant differences in bone healing capacity. Overall, three DBM products with different carrier molecules or bone compositions showed similar bone healing capacity.     

Dermatitis associated with "hypopodes" in a horse: the first case reported in Italy

The authors report, for the first time in Italy, a case of dermatitis of "hypopodes" origin in a horse. The hypopodes are a particular nymphal stage of mites of the suborder Astigmata. The "hypopus" is non-feeding, lacks a mouth and has a ventral suctorial plate with suckers and conoids for attaching itself to insects as a mode of dispersal. Some of these larval stages can enter into the hair follicles and into the subcutaneous layers causing lesions similar to mange. There are few reports of dermatitis in horses specifically associated with the presence of hypopodes and these have been attributed to an allergic response to the body fluid of crushed hypopial stage. It may be that infestations of these nymphal stages are widespread, but the nature of the condition is not yet clear; therefore, they may be underdiagnosed.     

Distal splint bone fractures in the horse: an experimental and clinical study

An experimental and clinical study to investigate the aetiology of distal splint bone fractures is described. In vitro, extension of the fetlock did not appear to alter the position of the distal ends of the splint bones, although tension in the interosseous tendons increased. Flexion of the fetlock resulted in slight outward displacement of the distal ends of the splint bones. It is suggested that concurrent desmitis of the suspensory ligament can cause movement of the ends of the splint bones thus predisposing to a fatigue fracture. In a clinical study of 87 horses, 114 splint bone fractures were identified. In at least 70 per cent of horses, suspensory desmitis was present. Follow up information was available in 24 horses in which more than 80 per cent of the fractures healed spontaneously. Non-union fractures were not painful and did not cause lameness.     

Keratoconjunctivitis sicca associated with fracture of the stylohyoid bone in a horse

Keratoconjunctivitis sicca developed in a mare with fracture of the stylohyoid bone. Treatment was directed at preserving the health of the globe while local inflammation at the fracture site was resolved.     

Cimetidine inhibits nitric oxide associated nitrate production in a soft-tissue inflammation model in the horse

Cimetidine (CIM) is an H2-receptor antagonist that has been used in racehorses in an attempt to reduce the occurrence of stress-related gastric ulceration. It has also been shown to produce several useful effects other than its gastric acid suppression properties. Further, it is a well documented antagonist of cytochrome P-450 (CYP) mediated oxygenation reactions. Nitric oxide (NO), a recently discovered mediator or modifier of numerous physiological functions, is generated by several forms of nitric oxide synthase (NOS), one of which is inducible (iNOS). Inducible NOS, expressed in neutrophils and macrophages as part of the inflammatory response to noxious stimuli, contains both a CYP and a CYP reductase domain. Because of the similarity of structure of iNOS and CYP, it was decided to determine whether CIM could reduce NO production, using a carrageenan inflammation model in the horse. Two experiments were conducted. In Trial 1, six female Thoroughbred horses each had three tissue chambers inserted subcutaneously on the sides of the neck. The study was divided into three treatments: 0.9% NaCl (NaCI), CIM (3 mg/kg), and aminoguanidine (AG; 25 mg/kg), an inhibitor of iNOS. Each mare received three i.v. injections 12 h apart prior to instillation of 1 mL of carrageenan into the test chamber. Blood and tissue chamber fluid (TCF) were collected serially. Concentrations of NO3- (the major metabolite of NO), albumin, total protein, CIM and AG were measured and complete cell counts and differentials were conducted. Trial 2 also used six female Thoroughbred horses implanted with at least two tissue chambers inserted subcutaneously on the sides of the neck. The study was divided into two treatments: NaCl (0.9%) and CIM (6 mg/kg). Each mare received seven i.v. injections of either NaCl or CIM 8 h apart prior to instillation of 1 mL of carrageenan into the test chamber. Blood and TCF were collected serially as before, and analysed for NO3- and CIM content. Areas under the curve (AUC) of the different parameters were calculated for the periods of -1-1, -1-3 and -1-7 days (Trial 1) and -2-1 for Trial 2. Absolute values were also compared at 4, 8 and 12 h postcarrageenan. Saline treatment did not reduce the elevated concentrations of NO3- in either plasma or TCF. Plasma, test chamber and control chamber NO3-concentrations rose from 0 to 12 h, and were very similar in all three sampled fluids. Cimetidine significantly (P< or =0.05) decreased NO3- production in plasma over the periods of -1-1, -1-3, and -1-7 days post inflammation when compared to NaCl treatment in Trial 1. Aminoguanidine and CIM decreased NO3-production in TCF for the periods -1-1, 1-3, and -1-7 days post inflammation in Trial 1 and -2-1 for Trial 2. Both CIM and AG also significantly reduced NO3-concentrations in plasma and TCF at 12 h postinitiation (Trials 1 and 2). Thus CIM, at the doses studied, was capable of reducing NO3- concentrations in this model as effectively as AG, a relatively specific inhibitor of iNOS activity.     

Feline model for the study of frozen osteoarticular hemijoint transplantation: qualitative and quantitative assessment of bone healing

Twenty-four outbred cats underwent massive osteoarticular allograft and control autograft transplantation, using the right distal femur with its articular cartilage, capsule, and medial collateral ligament intact. The cats were monitored clinically and radiographically for 1 year. Groups of cats (4 allografts and 2 control autografts) were euthanatized at 3-, 6-, 9-, and 12-month intervals. At necropsy, the grafts were photographed and assessed for bone healing and replacement by standard radiography, quantitative 99mTc bone scans, microradiography, and histologic examination of decalcified and nondecalcified specimens. The osteosynthesis site of the allografts usually healed by 5 months, compared with the autografts that healed by 3 months. As illustrated by quantitative bone scans, creeping appositional new bone slowly invaded and replaced the allograft bone. Seemingly, the cat can be used as an acceptable and clinically comparable model for the massive osteoarticular allografts currently being used for the reconstruction of joints damaged or destroyed by neoplasm surgery in limb-sparing procedures in human beings. This model may also be used to assess the rate and method of bone healing.     

Muscle disorders in the horse: a retrospective study

Case records of horses with muscle disorders presenting to the Veterinary Medical Teaching Hospital of the University of California, Davis, over a nine year period were evaluated. The objectives of the review were to identify the common myogenic muscle problems and their clinical features. Muscle disease of idiopathic aetiology following exercise was by far the most common condition noted. Other causes of myogenic muscle disorders included congenital, infectious, immune-mediated and nutritional factors.     

Assessment of a bone biopsy technique for measuring tiludronate in horses: a preliminary study

This study assessed the feasibility of measuring tiludronate in horses using a minimally invasive bone biopsy technique. Eight horses were treated with intravenous (IV) tiludronate [1 mg/kg bodyweight (BW)], either once (n = 4) or twice, 28 d apart (n = 4). The horses that were treated once were euthanized on days 1, 43, 57, or 92 and those that were treated twice, were euthanized on days 112, 154, 194, or 364. Bone samples were taken bilaterally from each horse at 4 sites: the third metacarpal bone (MCIII), the 13th rib (R13), the tuber coxae (TC), and the cuboid bone (CB). Test samples were taken with a 5-mm diameter dental drill, while larger reference samples were taken with an osteotome. The concentrations of tiludronate were measured by high performance liquid chromatography (HPLC) with ultraviolet (UV) detection. The TC was the easiest site to sample, and no technical difficulties were encountered for extraction and measurement. Drill sampling at the MCIII was difficult. Moreover, both the extraction and measurement caused technical problems and results were unreliable in most cases (93%). Drill samples obtained from the R13 were very small and access to the CB required considerable dissection, which would not be feasible in vivo. Forty-six percent and 36% of the tiludronate measurements performed on the R13 and CB samples, respectively, were unreliable. The ratio of tiludronate concentrations ranged from 73% to 185% (median: 118%) in the TC, 65% to 208% (median: 81%) in the R13, and 26% to 110% (median: 57%) in the CB. In all but 1 horse, the highest concentrations of tiludronate were found in the TC. It was concluded that bone biopsies performed at the TC were adequate for measuring tiludronate in horses and should be considered in future for repeated measurements over time in living animals.     

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.