Introduction: The aim of the study was to analyse selected densitometric and geometric parameters in the third metacarpal bone along the long axis in horses. The densitometric parameters included the cortical and trabecular bone mineral density, while the geometric parameters included the cortical, trabecular, and total areas, strength strain index X, strength strain index Y, and the polar strength strain index. Material and Methods: The parameters were analysed using eight sections from 10% to 80% of the length of the bone. Peripheral quantitative computed tomography was used in the study. Statistical analysis was carried out using the Friedman analysis of variance and post-hoc tests. Results: The proximal metaphyseal region showed the highest predicted resistance to bone fractures in the transverse (back-front) plane, the distal metaphyseal region had the highest predicted resistance to transverse and torsional fractures in the transverse (side-side) plane. The cross-sectional area and the shape of the cross-section of the cortical bone of the MCIII had the highest coefficient of variation. The density of the cortical bone was least variable. Conclusions: The cortical area and cortical bone mineral density assumed the highest values in the diaphyseal region, while the highest total area, trabecular area and trabecular bone mineral density values were obtained in the metaphyseal proximal and distal region.

OBJECTIVE To compare results obtained with a handheld reference point indentation instrument for bone material strength index (BMSi) measurements in the equine third metacarpal bone for various testing conditions. SAMPLE 24 third metacarpal bones. PROCEDURES Third metacarpal bones from both forelimbs of 12 horses were obtained. The dorsal surface of each bone was divided into 6 testing regions. In vivo and ex vivo measurements of BMSi were obtained through the skin and on exposed bone, respectively, to determine effects of each testing condition. Difference plots were used to assess agreement between BMSi obtained for various conditions. Linear regression analysis was used to assess effects of age, sex, and body weight on BMSi. A mixed-model ANOVA was used to assess effects of age, sex, limb, bone region, and testing condition on BMSi values. RESULTS Indentation measurements were performed on standing sedated and recumbent anesthetized horses and on cadaveric bone. Regional differences in BMSi values were detected in adult horses. A significant linear relationship (r2 = 0.71) was found between body weight and BMSi values. There was no difference between in vivo and ex vivo BMSi values. A small constant bias was detected between BMSi obtained through the skin, compared with values obtained directly on bone. CONCLUSIONS AND CLINICAL RELEVANCE Reference point indentation can be used for in vivo assessment of the resistance of bone tissue to microfracture in horses. Testing through the skin should account for a small constant bias, compared with results for testing directly on exposed bone.

Objective-To evaluate whether additive genetic correlations existed between certain aspects of the radiographic appearance of the distal sesamoid (navicular) bones (RNB) or between RNB and other types of radiographic changes in the limbs of Hanoverian Warmblood horses. Animals-5,157 horses. Procedures-Quasi-linear and binary traits were defined by the appearance of canales sesamoidales (CSs) and the structure and contour of the forelimb navicular bones (NBs). Prevalences of osseous fragments in the metacarphophalangeal and metatarsophalangeal (fetlock) and tarsocrural joints and deforming arthropathy in tarsal joints were analyzed as binary traits. Genetic parameters were estimated by use of multivariate linear models. Results-Heritability estimates for the RNB traits ranged from 0.10 to 0.34. Additive genetic correlations among those traits were usually close to unity. Extensive radiographic changes in the NBs, including changes in CSs and alterations in structure and contour, had correlations with less distinct radiographic changes. Negative additive genetic correlations were observed between small numbers of short and conical CSs in the central portion of the distal border of the NB and osseous fragments and arthropathy, and between most types of radiographic findings in the NBs and osseous fragments in tarsal joints. Conclusions and Clinical Relevance-The genetic bases for different types of RNB were not identical. The detection of correlations between normal RNB and findings of short and conical CSs versus deformed CSs and structural and contour changes warrants further study. Genetically justified distinction between physiologic and pathologic NB changes will increase the efficiency of selecting against NBs with radiographically apparent alterations.

Objective-To determine significant molecular and cellular factors responsible for differences in secondintention healing in thoracic and metacarpal wounds of horses. Animals-6 adult mixed-breed horses. Procedure-A full-thickness skin wound on the metacarpus and another such wound on the pectoral region were created, photographed, and measured, and tissue was harvested from these sites weekly for 4 weeks. Gene expression of type-I collagen, transforming growth factor (TGF)-β1, matrix metalloproteinase (MMP)-1, and tissue inhibitor of metalloproteinase (TIMP)-1 were determined by quantitative in situ hybridization. Myofibroblasts were detected by immunohistochemical labeling with α-smooth muscle actin (α-SMA). Collagen accumulation was detected by use of picrosirius red staining. Tissue morphology was examined by use of H&E staining. Results-Unlike thoracic wounds, forelimb wounds enlarged during the first 2 weeks. Myofibroblasts, detected by week 1, remained abundant with superior organization in thoracic wounds. Type-I collagen mRNA accumulated progressively in both wounds. More type-I collagen and TGF-β1 mRNA were seen in forelimb wounds. Volume of MMP-1 mRNA decreased from day 0 in both wounds. By week 3, TIMP-1 mRNA concentration was greater in thoracic wounds. Conclusions and Clinical Relevance-Greater collagen synthesis in metacarpal than thoracic wounds was documented by increased concentrations of myofibroblasts, type-I collagen mRNA, TGF-β1 mRNA, and decreased collagen degradation (ie, MMP-1). Imbalanced collagen synthesis and degradation likely correlate with development of exuberant granulation tissue, delaying healing in wounds of the distal portions of the limbs. Factors that inhibit collagen synthesis or stimulate collagenase may provide treatment options for horses with exuberant granulation tissue.

Paired metacarpi obtained at necropsy from 100 horses ranging in age from term fetus to 35 years were examined to estimate the prevalence and sites of metacarpal fusion. Metacarpal fusion was seen in 192 of 200 metacarpi, and 78% of all horses 2 years or older had 2 or more fusions. Fusion of the second metacarpal bone to the third metacarpal bone was significantly (P < 0.001) more common than was fusion of the fourth to the third metacarpal bone. Fusions appeared for the most part in pairs and were bilaterally symmetric. Rooney-Prickett type-A carpometacarpal joint configurations (in which there is no measurable articulation between the third carpal and second metacarpal bones) were rare in this population, and Rooney-Prickett type-B configurations (in which there is a measurable articulation between the third carpal and second metacarpal bones) were observed in 98.5% of metacarpi. Medial metacarpal fusion was positively correlated with age, occupation, and proportion of the proximal projection of the carpometacarpal distal joint surface that was taken by the second metacarpal bone. Lateral metacarpal fusion was positively correlated with age and the proportion of the proximal projection of the carpometacarpal distal joint surface taken by the fourth metacarpal bone. Horses in performance careers (racing, race training, or show ring occupations) had an earlier development of the first 2 fusions than did horses in other or unknown occupations; development of the third and fourth fusions were not significantly different between occupation groups. The rate of metacarpal fusion per horse-year appeared to be at least 10 times higher than a clinically evident rate.

Breaking strength (torque at failure) of equine third metacarpal bones, with transfixation pins placed parallel in the frontal plane and 30 degrees divergent from the frontal plane, was determined in vitro. Two transfixation pins were placed through the distal metaphysis, using a jig designed to drill the holes in the assigned configuration. Paired metacarpal bones II through IV from 12 horses were tested in torsion. The torsional moment of the force applied through the transfixation pins at failure was compared for each limb. Metacarpal bones with divergent pins were significantly (P = 0.030) stronger, compared with those with parallel pins. Metacarpal bones with parallel pins failed with longitudinal oblique fractures through a proxidmal bone-pin interface, whereas those with divergent pins failed with more comminuted fractures through multiple bone-pin interfaces.

Sonographic observations were made of the image mean gray scale (MGS) of the flexor tendons and ligaments in the left and right metacarpal regions of each of 10 clinically normal horses. In images made in the dorsal and sagittal planes, the MGS was measured at multiple sites in the superficial digital flexor tendon (SDFT), deep digital flexor tendon (DDFT), accessory ligament (AL), and suspensory ligament (SL), and at single sites in the medial and lateral limbs of the SL, and the palmar ligament. Relative sonographic brightness of each tendon and ligament was calculated by dividing the value of its MGS by the mean value for the MGS of images of 3 soft tissue equivalent phantoms. When a multivariate repeated-measures of ANOVA of the relative brightness values was statistically significant (P < 0.05), Tukey's method of multiple comparisons was used to determine which values were significantly different from each other. In the dorsal plane, the SL was significantly brighter than the DDFT, SDFT, and AL; relative brightnesses of the DDFT and SDFT were similar, as were those of the SDFT and AL. In the sagittal plane, the SL again was the significantly brightest structure, followed by the Al, and similar brightnesses of the DDFT and SDFT. In dorsal images made 25 cm distal to the accessory carpal bone, relative brightnesses of the SDFT, DDFT, and the medial and lateral limbs of the SL were similar. In images made 30 cm distal to the accessory carpal bone, relative brightness of the palmar ligament was significantly (P < 0.05) less than that of the SDFT and DDFT in the dorsal plane, but not in the sagittal plane, where it was significantly greater. Relative brightness values represented a unique sonographic characteristic of each structure and, in the future, may provide further insights into tendon and ligament structure and function.

Bilateral, midshaft metacarpal osteotomies were performed in 11 sheep and bilateral, midshaft radial osteotomies were performed in 7 sheep. The lesions were repaired with bone plates. One of each pair of plates was luted with polymethylmethacrylate and all screws were tightened uniformly with a torque screwdriver. Sheep were allowed unrestricted exercise after surgery. At 8 weeks, 10 of 11 sheep with metacarpal osteotomies were sound and both osteotomies were healing. Seven were lame on the limb with the unluted plate during the first 3 weeks; 4 were never lame on either limb. The screws of the unluted plates were significantly (P < 0.01) looser at 8 weeks than those in the luted plates. All of the sheep with radial osteotomies were lame in the limb with the unluted plate. Four of 7 sheep had overt loosening of the unluted plates. One sheep only had mild screw loosening with continued alignment of the osteotomy. Two of 7 sheep fractured the radius with the luted plate; these 2 sheep were lame in the limb with the unluted plate and were using the limb with the luted plate vigorously. Excluding the 2 sheep with fractures, all had substantially more screw loosening in the unluted plate. Histologically, there were no discernible differences in the vascularity or porosity of the bone under the luted vs the unluted plates. The only adverse consequence of the luting technique was introduction of a small amount of polymethylmethacrylate into the osteotomy gap in 5 bones.

The breaking strength (stress at failure) of equine third metacarpal bones, with and without clustered drill holes, was determined in vitro. Paired ossa metacarpalia II-IV of 39 horses (n = 39) between 2 and 7 years old were tested in palmarodorsal 3-point bending. Four treatments were compared. Clustered 2.7- or 3.5-mm drill holes, in a 4- or 7-hole pattern, were made in the dorsal cortex of the distal diaphysis of the left third metacarpal bone. Undrilled right third metacarpi were used as controls. Bones with clustered drill holes failed by an oblique fracture through 1 or more drill holes, whereas undrilled bones failed with a middiaphyseal transverse fracture. Clustered drill holes acted as a stress concentrator and significantly (P < 0.05) decreased the stress required for failure. However, differences in breaking strength between treatment groups were not significant (P > 0.05).

To study communications and boundaries of the middle carpal and carpometacarpal joints of the horse, 50 forelimbs were obtained from fresh cadaver specimens. Blue latex solution (20 +/- 2.5 ml) was injected into the middle carpal joint, and the specimens were frozen in extension. Frozen specimens were cut into 1-cm sagittal sections from the middle of the radius to the middle of the metacarpus. The communications between the middle carpal and carpometacarpal joints and the presence, length, and position of the distopalmar outpouchings of the carpometacarpal joint were recorded. The middle carpal and carpometacarpal joints always communicated between os carpale III (C3) and os carpale IV (C4). An additional communication between the joints existed in 17 (34%) of the specimens, 10 on the palmar aspect of C4, and 3 on the palmar aspect of os carpale II (C2). When os carpale 1 (C1) was present (n = 5), communication between C1 and C2 was observed in 4 of the 5 specimens. In all specimens, medial and lateral distopalmar outpouchings of the carpometacarpal joint were observed and were located between the axial surface of os metacarpale II (MC2) and os metacarpale IV (MC4) and the abaxial surface of the suspensory ligament. There was no significant difference between the lengths of the lateral (2.3 +/- 0.54 cm) or medial (2.6 +/- 0.75 cm) distopalmar outpouchings. Small extensions from the distopalmar outpouchings were seen and extended axially into the fibers of the suspensory ligament or between the suspensory ligament and the distal accessory ligament of the deep digital flexor tendon. In one carpus, the middle carpal joint communicated with the antebrachiocarpal joint between the articulation of the os carpi intermedium (Ci) and the os carpi ulnare (Cu).