Changes in tibial cortical dimensions and density associated with long-term locking plate fixation in goats.

PURPOSE: Cortical porosis, secondary to either vascular injury or stress-shielding, is a comorbidity of fracture fixation using compression bone plating. Locking plate constructs have unique mechanics of load transmission and lack of reliance on contact pressures for fixation stability, so secondary cortical porosis adjacent to the plate has not been widely investigated. Therefore, this study aimed to assess the effects of long-term locking plate fixation on cortical dimensions and density in a caprine tibial segmental ostectomy model. METHODS: Data was acquired from a population of goats enrolled in ongoing orthopedic research which utilized locking plate fixation of 2 cm tibial diaphyseal segmental defects to evaluate bone healing over periods of 3, 6, 9, and 12 months. Quantitative data included tibial cortical width measurements and three-dimensionally reconstructed slab density measurements, both assessed using computed tomographic examinations performed at the time of plate removal. Additional surgical and demographic variables were analyzed for effect on cortical widths and density, and all cis-cortex measurements were compared to both the trans-cortex and to the contralateral limbs. RESULTS: The tibial cis-cortex was significantly wider and more irregular than the trans-cortex at the same level. This width asymmetry differed in both magnitude and direction from the contralateral limb. The bone underlying the plate was significantly less dense than the trans-cortex, and this cortical density difference was significantly greater than that of the contralateral limb. These cortical changes were independent of both duration of fixation and degree of ostectomy bone healing. CONCLUSIONS: This study provides evidence that cortical bone loss consistent with cortical porosity is a comorbidity of locking plate fixation in a caprine tibial ostectomy model. Further research is necessary to identify risk factors for locking-plate-associated bone loss and to inform clinical decisions in cases necessitating long-term locking plate fixation.

In vitro analysis and in vivo assessment of fracture complications associated with use of locking plate constructs for stabilization of caprine tibial segmental defects.

PURPOSE: Locking plate fixation of caprine tibial segmental defects is widely utilized for translational modeling of human osteopathology, and it is a useful research model in tissue engineering and orthopedic biomaterials research due to its inherent stability while maintaining unobstructed visualization of the gap defect and associated healing. However, research regarding surgical technique and long-term complications associated with this fixation method are lacking. The goal of this study was to assess the effects of surgeon-selected factors including locking plate length, plate positioning, and relative extent of tibial coverage on fixation failure, in the form of postoperative fracture. METHODS: In vitro, the effect of plate length was evaluated using single cycle compressive load to failure mechanical testing of locking plate fixations of caprine tibial gap defects. In vivo, effects of plate length, positioning, and relative tibial coverage were evaluated using data from a population of goats enrolled in ongoing orthopedic research which utilized locking plate fixation of 2 cm tibial diaphyseal segmental defects to evaluate bone healing over 3, 6, 9, and 12 months. RESULTS: In vitro, no significant differences in maximum compressive load or total strain were noted between fixations using 14 cm locking plates and 18 cm locking plates. In vivo, both plate length and tibial coverage ratio were significantly associated with postoperative fixation failure. The incidence of any cortical fracture in goats stabilized with a 14 cm plate was 57%, as compared with 3% in goats stabilized with an 18 cm plate. Craniocaudal and mediolateral angular positioning variables were not significantly associated with fixation failure. Decreasing distance between the gap defect and the proximal screw of the distal bone segment was associated with increased incidence of fracture, suggesting an effect on proximodistal positioning on overall fixation stability. CONCLUSIONS: This study emphasizes the differences between in vitro modeling and in vivo application of surgical fixation methods, and, based on the in vivo results, maximization of plate-to-tibia coverage is recommended when using locking plate fixation of the goat tibial segmental defect as a model in orthopedic research.

Influence of a novel scaffold composed of polyurethane, hydroxyapatite, and decellularized bone particles on the healing of fourth metacarpal defects in mares.

OBJECTIVE: To determine the effect of a novel scaffold, designed for use in bone regeneration, on healing of splint bone segmental defects in mares. STUDY DESIGN: In vivo experimental study. SAMPLE POPULATION: Five adult mares (4-10 years old; mean weight, 437.7 kg ± 29 kg). METHODS: Bilateral 2-cm full-thickness defects were created in the fourth metacarpal bones (MCIV) of each horse. Each defect was randomly assigned to either a novel scaffold treatment (n = 5) or an untreated control (n = 5). The scaffold was composed of polyurethane, hydroxyapatite, and decellularized bone particles. Bone healing was assessed for a period of 60 days by thermography, ultrasonography, radiography, and computed tomography (CT). Biopsies of each defect were performed 60 days after surgery for histological evaluation. RESULTS: On the basis of radiographic analysis, scaffold-treated defects had greater filling (67.42% ± 26.7%) compared with untreated defects (35.88% ± 32.7%; P = .006). After 60 days, CT revealed that the density of the defects treated with the scaffolds (807.80 ± 129.6 Hounsfield units [HU]) was greater than density of the untreated defects (464.80 ± 81.3 HU; P = .004). Evaluation of histology slides provided evidence of bone formation within an average of 9.43% ± 3.7% of the cross-sectional area of scaffolds in contrast to unfilled defects in which connective tissue was predominant throughout the biopsy specimens. CONCLUSION: The novel scaffold was biocompatible and supported bone formation within the MCIV segmental defects. CLINICAL SIGNIFICANCE: This novel scaffold offers an effective option for filling bone voids in horses when support of bone healing is indicated.

Temporal Changes in Reverse Torque of Locking-Head Screws Used in the Locking Plate in Segmental Tibial Defect in Goat Model.

The objective of this study was to evaluate changes in peak reverse torque (PRT) of the locking head screws that occur over time. A locking plate construct, consisting of an 8-hole locking plate and 8 locking screws, was used to stabilize a tibia segmental bone defect in a goat model. PRT was measured after periods of 3, 6, 9, and 12 months of ambulation. PRT for each screw was determined during plate removal. Statistical analysis revealed that after 6 months of loading, locking screws placed in position no. 4 had significantly less PRT as compared with screws placed in position no. 5 (p < 0.05). There were no statistically significant differences in PRT between groups as a factor of time (p > 0.05). Intracortical fractures occurred during the placement of 151 out of 664 screws (22.7%) and were significantly more common in the screw positions closest to the osteotomy (positions 4 and 5, p < 0.05). Periosteal and endosteal bone reactions and locking screw backout occurred significantly more often in the proximal bone segments (p < 0.05). Screw backout significantly, negatively influenced the PRT of the screws placed in positions no. 3, 4, and 5 (p < 0.05). The locking plate-screw constructs provided stable fixation of 2.5-cm segmental tibia defects in a goat animal model for up to 12 months.

Effect of attentional focus levels on spontaneous eyeblink rate in horses.

OBJECTIVE: Spontaneous eyeblink rate (SEBR) is inversely proportional to the level of attentional focus in humans. The objective of this study was to evaluate the effects of attentional focus on SEBR in horses. PROCEDURES: Twenty client-owned horses (2.5-23 years of age, five mares, 15 geldings) were evaluated. A GoPro HERO5 Session™ video recorder was attached to the halter and directed toward the eyes. Horses were acclimated for two hours before study commencement. Horses were filmed in five scenarios requiring different levels of attention: alone in a stall ("stall"), stall with an observer ("person"), standing in an arena ("stand"), walking in an arena ("walk"), and trotting in arena ("trot"). Each of the five scenarios was filmed for ten minutes. Video recordings were reviewed, and SEBR (incomplete, complete, and total blinks) was measured for both eyes in each scenario. RESULTS: The median (25%,75%) total SEBRs (blinks/min) were as follows: STALL: OD-16.6 (12.4, 24.3), OS-18.8 (11.5, 26.9); PERSON: OD-17.7 (14.6, 24.2), OS-17.4 (13.9, 24.4); STAND: OD-18.7 (15.1, 24.4), OS-19.4 (16.2, 24.7); WALK: OD-40.1 (34.1, 44.8), OS-40.6 (33.8, 44.7); and TROT: OD-39.7 (30.3, 44.6), OS-39.4 (28.6, 45.0). The total SEBRs at walk and trot were significantly greater than SEBR in stationary scenarios. CONCLUSIONS: Despite requiring increased levels of attentional focus, activities involving motion caused increased SEBR in horses. We hypothesize the need for additional tear distribution due to tear evaporation (associated with air movement over the corneas) prevailed over the level of attentional focus to increase the SEBR.

Effects of 1-MHz Ultrasound on Epaxial Muscle Temperature in Horses.

Objective: The purpose of this study was to examine the tissue temperature changes that occur at various depths during 1.0-MHz ultrasound (US) treatments of the epaxial muscles in horses. Animals: Ten healthy adult mares with no lameness or orthopedic disease weighing between 465 and 576 kg were studied. Procedures: Two 1.0 MHz US treatments, one at an intensity of 1.0 W/cm2 and one at 2.0 W/cm2, were administered to the epaxial region. Needle thermistors were inserted in the epaxial muscles below the skin surface at depths of 1.0, 3.0, and 5.0 cm, directly under the US treatment area. Depths were verified with diagnostic ultrasound. Both intensities of US treatment were performed on each horse over a 20 cm2 area for 10 min using a sound head with an effective radiating area of 10 cm2. Treatments were administered in random order. Tissue temperature was measured before, during, and for an additional 10 min after the end of US treatment. Mean temperatures for each time point, location, and intensity was recorded at 30 s intervals. A mixed model analysis of variance (ANOVA) with repeated measures was used to test for differences in these means. Individual differences in the means was tested for by a Least Significant Difference (LSD) mean separation test. Results: At the completion of the 10 min US treatment, the temperature rise at an intensity of 1.0 W/cm2 was 1.55°C at the 1.0 cm depth, 1.18°C at 3.0 cm depth, and 1.29°C at 5.0 cm depth. At an intensity of 2.0 W/cm2, temperatures rose 2.48°C at the 1.0 cm depth, 1.24°C at 3.0 cm depth, and 1.95°C at 5.0 cm depth. Conclusion and Clinical Importance: The main findings of the study is that use of therapeutic ultrasound with a 1.0 MHz US for 10 min in horse's epaxial muscles when clipped creates the greatest heat at 1.0 cm. The heat in the tissues at 5 cm depth is more than at 3 cm depth.

Validity and repeatability of goniometry in normal horses.

PURPOSE: To assess validity and inter- and intra-tester reliability of equine goniometry and to establish values for carpal, metacarpophalangeal, tarsal, and metatarsophalangeal flexion and extension in horses. SUBJECTS: Seventeen healthy equine subjects of varied breeds were used. METHODS: Three investigators blindly and independently measured in triplicate the extension and flexion of carpal, metacarpophalangeal, tarsal, and metatarsophalangeal joints of 17 horses after sedation. Radiographs of these joints in flexion and extension were acquired while under sedation. Goniometric and radiographic measurements were compared statistically and were correlated. A Bland-Altman plot was constructed. Inter- and intra-tester repeatability of goniometry were evaluated by calculating intraclass correlation coefficients (ICC). Mean flexion and extension of carpal, metacarpophalangeal, tarsal, and metatarsophalangeal joints were calculated. RESULTS: Goniometric and radiographic measurements did not differ statistically and were significantly correlated (correlation coefficients ranged from 0.59 - 0.89). The mean difference between goniometric and radiographic measurements was 0.4°. Triplicate measurements collected by the three raters did not differ significantly within raters (ICC ranging from 0.950 - 0.995) and between raters (ICC ranging from 0.942 - 0.989). CONCLUSION: Goniometry is a valid and repeatable tool for evaluation of the range of motion of carpal, metacarpophalangeal, tarsal, and metatarsophalangeal joints in standing, sedated healthy horses.

Effects of hyperbaric oxygen treatment on horses with experimentally induced endotoxemia.

OBJECTIVE: To determine the effectiveness of preinduction hyperbaric oxygen treatment (HBOT) in ameliorating signs of experimentally induced endotoxemia in horses. ANIMALS: 18 healthy adult horses. PROCEDURES: Horses were randomly assigned to 1 of 3 equal-sized treatment groups to receive normobaric ambient air and lipopolysaccharide (LPS), HBOT and LPS, or HBOT and physiologic saline (0.9% NaCl) solution. Horses were physically examined, and blood was obtained for a CBC and to determine concentration or activity of plasma tissue necrosis factor-α, blood lactate, and blood glucose before the horses were treated with HBOT and then intermittently for 6 hours after administration of LPS or physiologic saline solution. RESULTS: All LPS-treated horses developed signs and biochemical and hematologic changes consistent with endotoxemia. Treatment with HBOT significantly ameliorated the effect of LPS on clinical endotoxemia score but did not significantly improve other abnormalities associated with endotoxemia. CONCLUSIONS AND CLINICAL RELEVANCE: The protective effect of HBOT was minimal, and results did not support its use as a treatment for horses prior to development of endotoxemia.

Effects of domperidone on digital laminar microvascular blood flow in clinically normal adult horses.

OBJECTIVE: To determine effects of domperidone and acepromazine maleate on microvascular blood flow in digital laminae of clinically normal adult horses. ANIMALS: 8 clinically normal adult horses (4 mares and 4 geldings). PROCEDURES: In a 4-period crossover study, domperidone was administered PO at 1.1 mg/ kg and 5.5 mg/kg and IV at 0.2 mg/kg; acepromazine was administered IV at 0.04 mg/kg. The washout period between treatments was 1 week. A 3-minute measurement of laminar microvascular blood flow (LMBF) was obtained with laser Doppler flowmetry. Baseline measurements were obtained at -2, -1, and 0 hours prior to administration of drugs. Post-treatment measurements were obtained at 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 10, and 12 hours. Percentage change from baseline values in LMBF for each treatment was subsequently calculated. RESULTS: Oral administration of domperidone at 1.1 mg/kg and 5.5 mg/kg significantly increased LMBF, compared with baseline values, beginning 4 hours after administration, and this effect persisted for at least 8 hours. Intravenous administration of domperidone at 0.2 mg/kg significantly increased LMBF, compared with baseline values, at 10 and 12 hours after administration. Administration of acepromazine (0.04 mg/kg, IV) significantly increased LMBF, compared with baseline values, at 3, 5, 8, and 10 hours after administration. No adverse effects of drugs were detected in any horse. CONCLUSIONS AND CLINICAL RELEVANCE: Domperidone may be useful for preventing vasoconstriction and reduction in LMBF believed to occur in horses with laminitis, but additional research of the drug's effects in horses with laminitis is required.