The Icelandic Horse is used as a pleasure riding horse as well as a high-performance athlete at special tournaments that focus on various gaits.a The tölt and flying pace put the horse's musculoskeletal system under exceptional stress. Injuries of tendons and ligaments are frequent reasons for the need of veterinary care.b Therefore, it is essential to study the locomotor apparatus of Icelandic Horses in detail, to determine standard values for this breed, and to determine whether there are morphological differences in comparison with other breeds.
For diagnosis of injuries to the tendinous and ligamentous structures of the limbs, imaging techniques are routinely used in addition to the basic clinical examination. Diagnostic ultrasonography is the tool of choice to evaluate damage to tendons or ligaments, which is characterized by a change in the echogenicity and the dimensions of the structure.1–4 In many cases, tendon and ligament disorders appear grossly only as a bulging of the structure.2,3,5,6 Before being able to give a statement concerning the damaged part of a structure, it is important for the veterinarian to acquire as much information as possible.7 For various breeds, such as Arabians, Andalusian Horses, Thoroughbreds, and Standardbreds, standard ultrasonographic values for the distal portions of the limbs have been reported.8,9,c
The purpose of the study reported here was to determine standard ultrasonographic values for tendons and ligaments of the palmar aspect of the metacarpal region in clinically normal Icelandic Horses.
Materials and Methods
Horses—The project was approved by the Animal Care and Welfare Committee in Germany. Included in this study were 50 nonlame (sound) Icelandic Horses (2 stallions, 30 geldings, and 18 mares, of which 2 were pregnant) with ages ranging from 4 to 20 years. The height at the withers was measured and ranged from 127 to 148 cm. Following assessment of the horses' body weight (range, 305.90 to 455.46 kg), the BMI was calculated by use of the following equation: BMI = BW/H2, where BW is the body weight (in kilograms) of the horse, and H is the height (in meters) of the horse at the withers. The BMI ranged from 149.41 to 250.11 kg/m2. The horses were clinically examined for general soundness (ie, lack of lameness) with a focus on the forelimbs, which were examined closely for any abnormalities in weight bearing or in a lifted position. Only horses that were clinically sound were included. Furthermore, the gait properties (4 or 5 gaited), use (pleasure, tournament, or breeding), training status, shoeing status, vaccination status, and deworming status were recorded after questioning the owner.
Ultrasonographic examination—The hair over the palmar region of both forelimbs was clipped from the distal aspect of the accessory carpal bone to the metacarpophalangeal (fetlock) region just above the ergot, on the palmar aspect as well as medial and lateral aspect, up to the most palmar aspect of the third metacarpal bone. The skin was washed with warm water and bandaged with pads soaked in warm water for 20 minutes. Five ROIs were determined: 4 cm (ROI 1), 8 cm (ROI 2), 12 cm (ROI 3), 16 cm (ROI 4), and 20 cm (ROI 5) distal to the distal margin of the accessory carpal bone (Figure 1). These ROIs were marked at the lateral aspect of the clipped area by use of a waterproof marker crayon.d Measurements were taken with the horse bearing full weight on all 4 limbs. The skin was then cleaned with alcohol, and ultrasonographic gel was applied to the prepared area for acoustic coupling.e,f
Illustration of the configuration of the distal portion of an equine forelimb and ultrasonographic measurement sites (ROIs) at the palmar aspect.
Citation: American Journal of Veterinary Research 71, 12; 10.2460/ajvr.71.12.1425
The ultrasonographic examination was performed with the mobile ultrasonographic device in combination with an 8- to 10-MHz linear probe and a standoff pad.g Transverse ultrasonographic scans were taken with the horse bearing full weight on all limbs. One operator took the images of the structures, obtaining 3 ultrasonograms of every structure for each ROI on both forelimbs of all horses.
The SDFT (from ROI 1 to ROI 5), DDFT (from ROI 1 to ROI 5), ALDDFM (from ROI 1 to ROI 3), and body of the SL (from ROI 1 to ROI 3) were measured by placing the probe on the palmar aspect of the examined area. The SL lat and SL med were imaged from the lateropalmar and mediopalmar aspect, respectively, at ROI 4 and ROI 5 (the point of attachment of the SL to each proximal sesamoid bone). The focus was adjusted in correspondence with the structure examined; it was set to one level for the imaging of the SDFT, DDFT, SL lat, and SL med and to another for the ALDDFM and SL at ROI 1 to ROI 3. All collected data were saved on the hard disk of the ultrasonographic device.g
Precision of measurements—A 12-year-old gelding was used to establish precision of measurements. The horse was clinically sound and was prepared following the described procedure. On the left forelimb, each structure was imaged 8 times for each ROI.
Acquisition of data—The ultrasonograms were analyzed by use of the ultrasonographic system.g For each structure at each ROI, 1 operator recorded the following variables: cross-sectional area (cm2), circumference (cm), dorsopalmar width (cm), and lateromedial width (cm). In ROIs 3, 4, and 5, the lateromedial width of the SDFT was measured not with a straight line as in the proximal ROIs but with a curved line through the middle of the tendon following its natural shape so as to measure the real width of the structure. All other dorsopalmar and lateromedial width measurements were obtained by use of a straight line connecting the 2 points on the circumference farthest apart from each other. The data for the ALDDFM were only collected at ROIs 1, 2, and 3 because the ALDDFM distally joins with the DDFT.
Statistical analysis—The data were analyzed on the basis of parametric statistics by use of software.h,i A symmetric distribution was assumed for the dependent variables circumference, dorsopalmar width, and lateromedial width. For the variable cross-sectional area, a skewed distribution was expected, so statistical tests were performed on the basis of the square root of the cross-sectional area. Because the histograms of the cross-sectional area and its square root values had similar distribution shapes, concerning the reference values, the untransformed measurements are provided. Repeatability of imaging (precision) was estimated by calculating the CV of 8 measurements for each structure and ROI of 1 limb. For further statistical analyses, mean values of the 3 images were used.
To determine reference values, the results of a descriptive statistical analysis of the data were examined for existence of groups with large differences in measurements that would require separate reference values. In relation to age, 3 groups were formed: group 1 (n = 11) included horses ≤ 6 years old, group 2 (28) included horses 7 to 14 years old, and group 3 (11) included horses > 14 years old. In relation to sex, 2 groups were formed: group 1 (n = 32) included stallions and geldings, and group 2 (18) included mares. In relation to the height at the withers, 2 groups were formed: group 1 (n = 20) included horses with heights ≤ 137 cm, and group 2 (30) included horses with heights > 137 cm. In relation to BMI, 2 groups were formed: group 1 (n = 21) included horses with a BMI ≤ 178 kg/m2, and group 2 (29) included horses with a BMI > 178 kg/m2. Descriptions of the differences in dimensions of each structure from ROI 1 through 5, dimensional relationships among the different structures, and comparisons among the different groups were made on the basis of the mean values collected from both limbs of each horse.
The mean difference between the 2 limbs for each structure was examined by use of a linear 3-factor mixed model. The model contained the random factor horse regarding the factors ROI and limb and their interaction as nested in the factor horse. Next, analysis was performed on the basis of mean values of measurements of scan, limb, ROI, and structure.
To describe differences among the ROIs, a mixed linear model was used with the random factor horse and the nested factor ROI. The same model was used to describe differences among structures at each ROI. By use of the Scheffé test, pairwise comparisons were made in case of rejection of the global null hypothesis.
Mean values for sex, age, height at the withers, and BMI were determined for the 3 scans and both limbs and grouped according to the described variables. The influence of the different variables on the tendon size was tested with a 1-way ANOVA (for age) or t test (for sex, height, and BMI) for each combination of ROI and structure. The differences among ROIs and the differences among structures were noted, but no substantial differences among the other subgroups were found. For this reason, the reference values are given as arithmetic mean ± SD as well as the 95% confidence interval for each combination of ROI and structure, on the basis of data from the right limb. For all tests, a value of P ≤ 0.05 was considered significant.
Results
Precision of measurements—Overall, the CVs for the different variables were < 5%. For cross-sectional area, CV ranged from 1.03% to 3.54%; for circumference, CV ranged from 0.72% to 4.66%; for dorsopalmar width, CV ranged from 0% to 1.33%; and for lateromedial width, CV ranged from 0.20% to 1.23%.
Differences in dimensions of the structures among the ROIs—The dimensions of the structures at the different ROIs were determined (Table 1). Significant differences among the ROIs for each structure were tabulated (Table 2).
Mean ± SD (95% confidence interval) values of ultrasonographic morphometric measurements at 5 ROIs of the digital flexor tendons and ligaments of the palmar metacarpal region in 50 Icelandic Horses.
| Structure | ROI | CSA (cm2) | C (cm) | DP (cm) | LM (cm) |
|---|---|---|---|---|---|
| SDFT | 1 | 0.539 ± 0.10 (0.511–0.567) | 2.925 ± 0.29 (2.845–3.005) | 0.596 ± 0.09 (0.571–0.621) | 1.047 ± 0.12 (1.014–1.080) |
| 2 | 0.493 ± 0.09 (0.485–0.518) | 2.945 ± 0.29 (2.865–3.025) | 0.517 ± 0.08 (0.495–0.539) | 1.078 ± 0.11 (1.047–1.109) | |
| 3 | 0.485 ± 0.09 (0.460–0.510) | 3.223 ± 0.38 (3.118–3.328) | 0.426 ± 0.07 (0.407–0.445) | 1.299 ± 0.17 (1.252–1.346) | |
| 4 | 0.511 ± 0.10 (0.483–0.539) | 3.640 ± 0.42 (3.524–3.756) | 0.361 ± 0.06 (0.344–0.378) | 1.554 ± 0.19 (1.501–1.607) | |
| 5 | 0.635 ± 0.15 (0.593–0.677) | 4.705 ± 0.65 (4.525–4.885) | 0.341 ± 0.07 (0.322–0.360) | 2.033 ± 0.27 (1.953–2.113) | |
| DDFT | 1 | 0.755 ± 0.12 (0.722–0.788) | 3.454 ± 0.36 (3.354–3.554) | 0.733 ± 0.06 (0.716–0.750) | 1.209 ± 0.15 (1.167–1.251) |
| 3 | 0.625 ± 0.11 (0.594–0.656) | 2.988 ± 0.26 (2.916–3.060) | 0.737 ± 0.11 (0.706–0.768) | 1.053 ± 0.09 (1.028–1.078) | |
| 4 | 0.821 ± 0.13 (0.785–0.857) | 3.418 ± 0.26 (3.346–3.490) | 0.854 ± 0.13 (0.818–0.890) | 1.200 ± 0.12 (1.167–1.233) | |
| 5 | 1.047 ± 0.16 (1.003–1.091) | 4.138 ± 0.47 (4.008–4.268) | 0.818 ± 0.13 (0.782–0.854) | 1.626 ± 0.27 (1.551–1.701) | |
| ALDDFM | 1 | 0.650 ± 0.21 (0.592–0.708) | 3.624 ± 0.65 (3.444–3.804) | 0.510 ± 0.10 (0.482–0.538) | 1.221 ± 0.26 (1.149–1.293) |
| 2 | 0.549 ± 0.16 (0.505–0.593) | 3.367 ± 0.53 (3.220–3.514) | 0.483 ± 0.09 (0.458–0.508) | 1.133 ± 0.18 (1.083–1.183) | |
| 3 | 0.496 ± 0.13 (0.460–0.532) | 3.350 ± 0.49 (3.214–3.486) | 0.450 ± 0.11 (0.419–0.481) | 1.082 ± 0.13 (1.046–1.118) | |
| SL | 1 | 0.841 ± 0.23 (0.777–0.905) | 3.713 ± 0.60 (3.547–3.879) | 0.746 ± 0.10 (0.718–0.774) | 1.219 ± 0.25 (1.150–1.288) |
| 3 | 0.846 ± 0.18 (0.796–0.896) | 3.663 ± 0.43 (3.544–3.782) | 0.819 ± 0.13 (0.783–0.855) | 1.117 ± 0.16 (1.073–1.161) | |
| SL lat | 4 | 0.613 ± 0.12 (0.580–0.646) | 3.431 ± 0.26 (3.359–3.503) | 0.580 ± 0.09 (0.555–0.605) | 1.409 ± 0.10 (1.381–1.437) |
| 5 | 0.663 ± 0.12 (0.630–0.696) | 3.329 ± 0.36 (3.229–3.429) | 0.871 ± 0.12 (0.838–0.904) | 1.145 ± 0.11 (1.114–1.176) | |
| SL med | 4 | 0.585 ± 0.14 (0.546–0.624) | 3.384 ± 0.35 (3.287–3.481) | 0.556 ± 0.11 (0.525–0.587) | 1.392 ± 0.17 (1.345–1.439) |
| 5 | 0.658 ± 0.12 (0.625–0.691) | 3.301 ± 0.37 (3.198–3.404) | 0.872 ± 0.13 (0.836–0.908) | 1.148 ± 0.15 (1.106–1.190) |
C = Circumference. CSA = Cross-sectional area. DP = Dorsopalmar width. LM = Lateromedial width.
Comparison (mean differences) of ultrasonographic morphometric measurements between ROIs of the digital flexor tendons and ligaments of the palmar metacarpal region in 50 Icelandic Horses.
| Structure | ROI | Compared ROI | √CSA (cm) | C (cm) | DP (cm) | LM (cm) |
|---|---|---|---|---|---|---|
| DFT | 1 | 2 | 0.066* | NS | 0.083* | NS |
| 3 | 0.076* | −0.351* | 0.175* | −0.266* | ||
| 4 | −0.050* | −0.789* | 0.230* | −0.532* | ||
| 5 | −0.151* | −1.806* | 0.257* | −1.006* | ||
| 2 | 3 | NS | −0.277* | 0.092* | −0.211* | |
| 4 | −0.116* | −0.716* | 0.147* | −0.477* | ||
| 5 | −0.217* | −1.733* | 0.174* | −0.952* | ||
| 3 | 4 | −0.126* | −0.438* | 0.055* | −0.266* | |
| 5 | −0.226* | −1.455* | 0.082* | −0.740* | ||
| 4 | 5 | −0.101* | −1.017* | NS | −0.474* | |
| DDFT | 1 | 2 | NS | 0.372* | NS | 0.120* |
| 3 | 0.032† | 0.449* | NS | 0.161* | ||
| 4 | NS | NS | −0.128* | NS | ||
| 5 | −0.059 | −0.673* | −0.070* | −0.397* | ||
| 2 | 3 | NS | NS | NS | NS | |
| 4 | NS | −0.392* | −0.142* | −0.117* | ||
| 5 | −0.085* | −1.044* | −0.084* | −0.517* | ||
| 3 | 4 | NS | −0.470* | −0.112* | −0.159* | |
| 5 | −0.091* | −1.122* | −0.055† | −0.558* | ||
| 4 | 5 | −0.066* | −0.652* | 0.057† | −0.400* | |
| ALDDFM | 1 | 2 | 0.058* | 0.248* | NS | 0.976* |
| 3 | 0.098* | 0.273* | 0.049* | 0.148* | ||
| 2 | 3 | 0.040* | NS | 0.035† | NS | |
| SL | 1 | 2 | NS | NS | −0.046† | 0.067† |
| 3 | NS | NS | −0.075* | 0.111* | ||
| 2 | 3 | NS | NS | −0.029† | NS |
ROIs are significantly (P ≤ 0.001) different.
ROIs are significantly (P ≤ 0.05) different.
√CSA = Square root of the cross-sectional area. NS = No significant (P ≤ 0.05) mean difference between ROIs.
See Table 1 for remainder of key.
Relationships among of the sizes of the structures—Significant differences among the structures at each ROI were determined (Table 3). At the first 3 ROIs, the body of the SL had the largest values for the cross-sectional area, followed by the DDFT and the ALDDFM; the SDFT had the lowest cross-sectional area values. Distally, the DDFT had the largest values for this variable; values of the branches of the SL were approximately 30% (ROI 4) and 40% (ROI 5) of the DDFT value. The smallest value for the cross-sectional area was found in the SDFT. At ROI 1, the values for circumference of all structures were less than those at ROI 2. At ROI 3, the DDFT had the smallest value and the SL had the highest. At ROIs 4 and 5, the SDFT had the highest circumference values, followed by the DDFT and the SL lat and SL med. For the dorsopalmar width, the SL had the largest values at ROIs 1, 2, and 3; at ROI 3, its value was almost twice that of the SDFT, which had the smallest value. The dorsopalmar value of the DDFT was more similar to that of the SL, whereas that of the ALDDFM was similar to that of the SDFT. At ROI 4, the DDFT had the highest value, whereas at ROI 5, the SL lat and SL med had the highest values. At the first 3 ROIs, the values for the lateromedial width of the DDFT, ALDDFM, and SL were similar; the SDFT values were smaller but increased over the ROIs, and the SDFT becomes the widest structure at ROI 5, followed by the DDFT and then the SL med and the SL lat. No significant differences among the 4 variables were associated with age group, sex, height at the withers, or BMI.
Comparison (mean differences) of ultrasonographic morphometric measurements between structures of the digital flexor tendons and ligaments of the palmar metacarpal region at 5 ROIs in 50 Icelandic Horses.
| ROI | Structure | Compared structure | √CSA (cm) | C (cm) | DP (cm) | LM (cm) |
|---|---|---|---|---|---|---|
| 1 | SDFT | DDFT | 0.139 | −0.533 | −0.140 | −0.170 |
| ALDDFM | 0.071 | −0.724 | 0.091 | −0.178 | ||
| SL | −0.049† | −0.809† | −0.161 | −0.177 | ||
| DDFT | ALDDFM | −0.068 | NS | 0.231 | NS | |
| SL | −0.188 | −0.276* | NS | NS | ||
| ALDDFM | SL | −0.120 | NS | −0.251 | NS | |
| 2 | SDFT | DDFT | 0.099 | NS | 0.209 | NS |
| ALDDFM | 0.063 | −0.402 | 0.231 | NS | ||
| SL | −0.114 | −0.635 | −0.080 | NS | ||
| DDFT | ALDDFM | −0.314 | NS | NS | ||
| SL | −0.213 | −0.548 | −0.289 | −0.060† | ||
| ALDDFM | SL | −0.176 | −0.233 | −0.311 | NS | |
| 3 | SDFT | DDFT | 0.095 | 0.268 | 0.331 | 0.257 |
| ALDDFM | 0.093 | NS | 0.295 | 0.237 | ||
| SL | −0.129 | −0.404 | −0.080 | 0.120 | ||
| DDFT | ALDDFM | NS | −0.367 | NS | NS | |
| SL | −0.224 | −0.671 | −0.411 | NS | ||
| ALDDFM | SL | −0.222 | −0.305 | −0.375 | NS | |
| 4 | SDFT | DDFT | 0.196 | 0.236 | −0.498 | 0.364 |
| SL lat | 0.140 | 0.282 | −0.235 | 0.194 | ||
| SL med | 0.153 | 0.310 | −0.207 | 0.193 | ||
| DDFT | SL lat | −0.056 | NS | 0.263 | −0.170 | |
| SL med | −0.043† | NS | 0.291 | −0.171 | ||
| SL lat | SL med | NS | NS | NS | NS | |
| 5 | SDFT | DDFT | 0.231 | 0.601 | −0.468 | 0.439 |
| SL lat | 0.206 | 1.406 | −0.552 | 0.920 | ||
| SL med | 0.210 | 1.425 | −0.543 | 0.919 | ||
| DDFT | SL lat | NS | 0.805 | −0.084 | 0.481 | |
| SL med | NS | 0.824 | −0.075 | 0.480 | ||
| SL lat | SL med | NS | NS | NS | NS |
See Tables 1 and 2 for key.
Discussion
The manner in which the different structures changed in size and shape from proximal to distal and in their dimensions relative to each other in Icelandic Horses was consistent with that of other breeds described in the literature.1,6,8 Only the branches of the SL appeared to be larger than in other breeds, which might be caused by different strains associated with the special gait patterns and conformational traits of the breed. It was stated that the cross-sectional area of the SDFT of Thoroughbreds decreased with age, but the findings of other authors1 were essentially the same as in the present study.
Because the BMI is a ratio of the weight of the animal to the square of its height at the withers, it can be compared among animals of different size, so the influence of height is excluded. Absence of significant differences between the 2 groups with different height at the withers and those with different BMI was similar to findings in other breeds reported in the literature.1,9,10 A linear relationship between conformational variables, body weight, and cross-sectional area of the SDFT and DDFT has been described, but other authors found no significant correlation between cross-sectional area of the SDFT and body weight.6,9,11
Ultrasonography is used as a standard diagnostic imaging technique for the assessment of musculoskeletal disorders in horses.2 Evaluation of the morphometric variables cross-sectional area, circumference, dorsopalmar width, and lateromedial width is important for detection of lesions in the tendons or ligaments.1–4,6 However, to use these values correctly, it is essential to know the standard values for the breed of horse examined7; there are considerable differences among breeds.1,6,8 Results of the present study appear to be consistent with this statement because the values found in the Icelandic Horses examined differed from those reported for other breeds. The SDFT of Thoroughbreds and Arabians appears to be larger than that of Icelandic Horses.8 The tendon seems to have a different shape in those 2 breeds, compared with Icelandic Horses, because the cross-sectional area and dorsopalmar width are larger at all ROIs, but the values for circumference and lateromedial width are almost the same in Thoroughbreds or are even smaller in Arabians at ROIs 4 and 5.8 A similar situation is found for the DDFT.8 In Thoroughbreds, the DDFT appears to be larger, whereas the values for Arabians are closer to those found in the present study. The values for the 2 most distal ROIs were similar for Thoroughbreds and Icelandic Horses, except for circumference, for which the values for the Icelandic Horses were approximately 0.5 cm greater. Arabians have the lowest values at these 2 ROIs concerning cross-sectional area and circumference. At ROI 1, values for the Icelandic Horses for cross-sectional area, circumference, and dorsopalmar width were almost the same as those reported for Thoroughbreds and were similar to or greater than those of Arabians. The finding that the DDFT was rather large at ROI 1 and at the distal ROIs might reflect the hourglass shape, which seems to be more pronounced in Icelandic Horses than in Thoroughbreds, Arabians, or Spanish Horses.1,8
The ALDDFM of the Icelandic Horses was about the same size as that reported for Thoroughbreds and Arabians, but the results differed at ROI 3, whereas in the other 2 breeds, all measurements of the ALDDFM were smaller than at the other ROIs.8 In Icelandic Horses, the ALDDFM values are almost the same for all 3 ROIs. The cross-sectional area, circumference, and lateromedial width values for the body of the SL are larger in Thoroughbreds and Arabians than in Icelandic Horses, but dorsopalmar width values are smaller than those of Icelandic Horses. The SL lat and SL med values in Thoroughbreds are greater than those for Icelandic Horses except for circumference, for which they are lower.8 The values for Arabians are generally lower; only the dorsopalmar width is approximately 0.15 cm larger at ROI 4.8
Another study9 dealing with the cross-sectional area of the SDFT and the DDFT of Thoroughbred racehorses found even higher values for the cross-sectional area of the DDFT, which were approximately 0.4 cm2 greater than those found in the Icelandic Horses. Standardbreds also had slightly higher values than Icelandic Horses.c Mean values of cross-sectional area of the SDFT and the DDFT of heavy Irish draft crossbreds, Thoroughbreds, and ponies were 2 to 3 times those of Icelandic Horses.6 The ponies had a mean height at the withers of 134.1 cm, mean age of 12.5 years, and mean body weight of 382 kg and were not saddle trained. The conformational type of the ponies was not specified by the authors but could be of interest because the mean values for height and body weight do not differ substantially from those of the horses examined in the present study. As defined by the breeding rules of the International Federation of Icelandic Horse Associations, the Icelandic Horse should have “firm, very strong tendons and good separations between the tendons and the bone.”12 Compared with the ponies, the morphometric values for the Icelandic Horses suggest that they have rather slim tendons.6 The fact that the ponies used in the previous study6 were not saddle trained is also a factor that has to be considered because training was found to have an effect on the cross-sectional area of the tendons of racing Thoroughbreds.6,13
Another report1 provides mean values for cross-sectional area of the tendons and ligaments in the palmar metacarpal region of purebred Spanish Horses that are similar to results of other studies,1,6,8,9,c although the values in the Spanish Horses are closer to those determined for Icelandic Horses. This could be attributable to the fact that the purebred Spanish Horses were taller than the Icelandic Horses but have a rather slim conformation of their metacarpal region.
The most obvious difference from results of other morphometric studies was the massive structure of the branches of the SL, which might be attributable to a response to strains caused by the special gait patterns of tölt and flying pace. In the present study, it was not possible to determine a difference between 4- and 5-gaited horses because the horses examined were mostly 5 gaited. Another study would be needed to draw conclusions about differences between the influence of the tölt and flying pace. In this regard, examination of other breeds with gaits similar to the tölt, such as the Tennessee Walking Horse, Paso Fino, and Paso Peruano, might be of interest to establish gait-specific modifcations in tendoligamentous structures. No data have been reported for Standardbred pacers, which might provide information on the influence of the pace on the variables.
Tension applied on tendons and ligaments can affect ultrasonographic results; for example, non–weight bearing of a limb can cause ultrasonographic images that might be misinterpreted as tendon lesions.14–17 To avoid such artifacts, ultrasonographic measurements were only performed with the horses bearing full weight on all 4 limbs.
The ultrasonographic measurements were performed at 5 equal zones starting 4 cm distal to the accessory carpal bone. On the basis of the length of the metacarpal region in Icelandic Horses, it was decided to divide the palmar metacarpal region into 5 zones and measure SL lat and SL med at the 2 most distal measurement sites (ROIs 4 and 5). These ROIs differed to some extent from those established in published studies, although those studies did not use a uniform system and the ROIs used for data collection vary among studies.1,2,8,18,c
Observations made during collection of the sonograms included certain characteristics of the skin of the Icelandic Horses. In combination with the subcutaneous connective tissue, it appeared to be comparatively thick, and if not prepared in the manner described, the tendoligamentous structures could not be imaged sufficiently. Because of ultrasonographic coupling difficulties, the appearance of the texture of the tendons in the ultrasonograms, mostly the SDFT, might be mistaken for lesions in this structure.19
Abbreviations
| ALDDFM | Accessory ligament of the deep digital flexor muscle |
| BMI | Body mass index |
| CV | Coefficient of variation |
| DDFT | Deep digital flexor tendon |
| ROI | Region of interest |
| SDFT | Superficial digital flexor tendon |
| SL | Suspensory ligament |
| SL lat | Lateral branch of the suspensory ligament |
| SL med | Medial branch of the suspensory ligament |
Albertsdóttir E. Genetic analysis of competition traits in Icelandic horses. Doctoral thesis, Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Uppsala, Sweden, 2007.
Sigurðsson H, DVM, Viðidalur, Iceland: Personal communication, 2009.
Herslow J, Uhlhorn M, Uhlhorn H. Cross-sectional area of the superficial and deep digital flexor tendon in Standardbred Trotters: an ultrasonographic field study (abstr), in Proceedings. 8th Annu Cong Eur Assoc Vet Diagn Imaging 2001;92.
Raidl Maxi, Raidex Germany, Otterbach, Germany.
Softasept, Braun Vetcare, Melsungen, Germany.
Ultraschallgel, Asid Bonz GmbH, Herrenberg, Germany.
GE Logiq e, General Electric Co, Munich, Germany.
PASW Statistics, release 17.0.2 for Windows, SPSS Inc, Chicago, Ill.
SPSS for Windows, version 17, SPSS Inc, Chicago, Ill.
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