Proximal phalanx fractures are one of the most common injuries that occur in the equine forelimb [1
]. Based on four-year observations of 850 two-year old Thoroughbreds that underwent training, changes were found in as many as 19 out of 47 of all the limb bone fractures. Pastern bone fractures comprised 39.6% of all the fractures that were recorded in the 4-year-long observation period. Fractures of proximal navicular bone were slightly less frequent - 11 cases (22.9%) Fractures of other bones were rare [1
]. Proximal phalanges are most often subject to longitudinal fractures. Such fractures are probably facilitated by the characteristic shape of the proximal bone end. On the articular surface of their proximal end, there is an the sagittal groove of the proximal phalanx with the sagittal ridge of the third metacarpal bone. The sagittal ridge acts as a wedge by “squeezing into” the cup-shaped depression, which can facilitate this type of fractures. It is also suggested that the decrease in the bone tissue parameters in the vicinity of proximal metaphysic of the proximal phalanx can be conducive to this type of fractures. Bone fractures are more likely to occur in the context of low bone tissue parameters such as decrease in the number of bone trabeculae, their volume, density and width [2
]. Unfortunately, there are few reports on the bone tissue parameters of the proximal phalanges. The analysis comprises only densitometric parameters of the proximal phalanges [5
]. However, the mechanic strength of the bone tissue, which affects its supporting functions, is affected not only by the mineral composition but also its spatial architecture [6
]. Unfortunately, the evaluation of bone tissue quality is most often based on densitometric methods. The reason for the imperfections of these methods is the inability to evaluate the spatial structure of the bone trabeculae. The mineralization level is not the only factor affecting bone durability as the bone trabeculae architecture is also very important [8
]. Computed Tomography (CT) allows for studying the geometry of the examined bone, providing important information regarding the bone microarchitecture [10
The asymmetry of long bones has been examined in humans. The studies on this subject explicitly showed that there is a statistically significant difference between the bilateral thoracic limbs in humans. It was proved that the densitometric parameters in the studied bones are tightly related to hand preference [11
]. Importantly, it was also shown that densitometric parameters of the bilateral femoral bones in humans are linked to handedness [14
Particular feature of highly developed animals is the fact that they do not move in straight position, but tend to twist their body into one side. It can be said that they have a left-side or right-side tendency [15
]. The right-sided have a natural tendency to move left, therefore in the open space most people and animals come full circles left. Right-sidedness is observed only in highly-developed mammals, including horses [17
]. It is manifested while starting galloping with so called left leg more willingly, while the left thoracic limb is the leading one, so it is put forward first during horse’s action while running. A right-sided horse has a natural tendency to ‘break’ left, which means that when a horse gets scared of something, it usually nips out left. It was also observed that facing an obstacle, horses more frequently break left in front of it [17
The fact the unequal loading inspired a lot of scientists and doctors to examine the influence of the unequal loading, not only on shaping but also on exposure to injuries of particular structures of the locomotor’s system of the bilateral limbs.
Comparison of the bilateral long bones of limbs in horses was conducted by morphometric methods. The studies confirmed the phenomenon of asymmetry regarding the femoral bones in this species [18
] and the equine third metacarpal [19
]. Importantly recent study found that the majority of proximal phalanx fractures in horses occur in the right leg [20
In contrast to human medicine, where the pQCT method is becoming more frequently used [21
] it is rarely applied in horses. It is related with species specificity, e.g. difficulty with keeping the animal still for several minutes, dimensions etc. [24
Unfortunately, even tests on isolated equine bones with the use of the pQCT method are performed very rarely. So far, the above method has been used on radius and tibia [24
], third metacarpal bone [26
] and the distal sesamoid bone [27
]. According to the authors’ knowledge, there is still insufficient number of research studies on comparative analysis of both densitometric and geometric parameters of the both front legs proximal phalanges in horses with the use of pQCT.
There is still lack of writing touching upon the issue of influence of the increased loading of one side of horse body on shaping of microstructure of long bones in bilateral limbs. The umber of studies that thoroughly compare densitometric and geometric parameters between bilateral ones of limbs in this species are still insufficient.
Due to the lack of studies that focus on how increased one-side load affects the microstructure of long bones in bilateral limbs and their densitometric features, studies that do address the issue are very important because of their cognitive value. Moreover, research on the possible influence of asymmetrical load on the pastern bone parameters may provide information on the nature of remodeling in the pastern bone tissue as a result of load.
The aim of this study was to compare the densitometric and geometric parameters between the both front legs proximal phalanges in the equine forelimb at 15%, 50% and 85% of bone length with the use of pQCT. It was also analyzed whether the right or left bone preference affected the values of the above parameters at the three measurement levels.