Biomechanical Comparison of a Headless Compression Screw Fastener and AO Cortical Bone Screw for Fixation of a Simulated Equine Third Carpal Bone Slab Fracture.

Frontal plane slab fractures account for the majority of third carpal bone (C3) fractures in racing and performance horses. Recommended treatment is stabilization with a lagged AO cortical screw. Associated complications are fragment splitting, fragment spinning, and irritation of dorsal soft tissue structures. A novel, headless, cannulated screw with interlocking threads the Headless Compression Screw Fastener (HCSF) has been developed to resist multidirectional forces and bending moments; however, it has not been applied in the horse. Simulated C3 frontal plane slab fractures were created in nine paired carpi from equine cadaver limbs, fixed with either the HCSF or AO cortical bone screw, and loaded in shear to failure. The effect of screw type on stiffness, maximum load to failure, and yield load was assessed in separate linear mixed models. No significant (P< .05) difference between screw types was detected in terms of maximum load to failure (P= .084), stiffness (P= .26), or yield load (P= .088). Mode of failure was screw bending in all specimens. For some samples in both groups, failure was associated with the sagittal fracture at the screw-bone interface. The HCSF was successfully used to repair simulated third carpal bone fractures. The different head and thread pitches of the HCSF effectively compressed the fracture. The headless design eliminates the need for counter sinking. There was no significant difference in maximum load to failure, stiffness, nor yield load compared to the cortical screws. These results invite clinical application to be investigated.

Hand and body position during locomotor behavior in the aye-aye (Daubentonia madagascariensis).

Aye-ayes (Daubentonia madagascariensis) have unique hands among primates, with extraordinarily long fingers in relation to body size. These long digits may be vulnerable to damage from forces during locomotion, particularly during head-first descent-a locomotor mode that the aye-aye utilizes frequently. Previous behavioral studies of aye-aye locomotion reported that Daubentonia must curl its fingers during horizontal quadrupedalism and/or descent to reduce potential stresses on its long fingers. To test this hypothesis, we examined hand and body position in three captive adult aye-ayes while they walked quadrupedally on horizontal and oblique branches. Substantial variation in hand position was observed among individuals for each substrate orientation. While hand postures with curled fingers were preferred by one individual during descent, they were not preferred by the other two individuals, contrary to our expectations. Differences in body position were more consistent among all three individuals. The angle of the body relative to the substrate was significantly reduced during descent (8.4 degrees ) compared to horizontal locomotion (16.9 degrees ). These results suggest that changes in body position, rather than hand position, may help reduce stresses on the digits. A biomechanical model is proposed that demonstrates how a reduction in the body angle in relation to substrate may act to move the center of mass more caudally. This mechanism of moderating loads by altering body position, rather than hand position, may represent an important functional aspect of arboreal locomotion in aye-ayes and other primates.

Hereditary compulsive self-mutillating behaviour in laboratory rabbits.

During the last few years an increasing number of cases of extensive automutilation has been observed in a rabbit breeding colony of Checkered crosses. Digits and pads of the front feet were traumatized. No other behavioural abnormalities or signs of disease were evident. Self-mutillation was seen both in stock, breeding and experimental animals, in rabbits kept singly in cages and in those housed in groups on the ground, in rabbits kept in different buildings and under the care of different staff members. This behavioural abnormality of Checkered crosses has also been observed in animals after being placed into other institutions or private homes. No evidence of an agent responsible for the occurrence of self-injury could be found with parasitological, mycological, histological, clinical or haematological examination. Twelve to 16 animals are affected yearly in a colony varying in size between 130 and 230 rabbits. Following complete healing, relapses occurred up to 3 times per year, on either the same or the opposite front foot. In the last 21 cases episodes of automutillation could be regularly interrupted with the dopamine antagonist, haloperidol. Similar signs of auto-mutillation were never seen in animals of another breeding line kept in the same building and under the same conditions nor in animals brought in from other breeding colonies. A relatively high coefficient of inbreeding can be presupposed in this 15-year-old breeding colony of Checkered crosses. A genetic predisposition for the behavioural anomaly described appears very likely.