An equine cadaver study investigating the relationship between cervical flexion, nuchal ligament elongation and pressure at the first and second cervical vertebra.

Pressure in the atlanto-axial region due to hyperflexion ('rollkur') may influence the development of a nuchal bursa, as adventitious bursae may be caused by pressure. Investigating the pressure between the nuchal ligament and atlas/axis in a flexed position may provide information on the pathogenesis of nuchal bursitis. In this study, ten equine head and neck specimens with one side of the soft tissues over the cervical vertebral spine removed were placed in lateral recumbency on a table in neutral, mildly flexed, and hyperflexed head and neck positions. Angulations of the neck were measured using markers placed on the nuchal ligament and drilled into the skull, vertebrae and withers. In six specimens, the pressure between the nuchal ligament and the atlas and the axis was measured using an inflatable air pouch. Hyperflexion was associated with the highest nuchal ligament length and with the highest pressure values at the site of the nuchal bursa over the atlas (99±24mmHg, more than four times the pressure in the neutral position) and over the axis (77±30mmHg, more than twice the pressure values of the neutral position). Also, over the three head and neck positions, neck flexion angles were highly correlated with pressure values and with nuchal ligament length. This marked increase in pressure at the level of atlas and axis caused by head and neck hyperflexion should be considered during training of horses at risk of, or diagnosed with, nuchal bursitis.

The influence of trimming of the hoof wall on the damage of laminar tissue after loading: An in vitro study.

Laminitis is associated with failure of the suspensory apparatus of the distal phalanx (SADP) connecting the distal phalanx to the hoof wall. The specific aim of this study was to examine in vitro whether thinning of the hoof wall leading to increased deformability influences the damage of the laminar tissue created by loading of the hoof. Paired cadaver forelimbs from twelve horses were used. For each pair, the hoof wall from one hoof was thinned by 25%; this was ascertained by radiography. The contralateral hooves were used as controls. In a material testing machine, hooves were loaded in a proximodistal direction at 0.5mm/s until a cut-off value of 8kN or 14mm was reached. Afterwards, samples of the SADP were taken for histology. Image-based evaluation of the destruction of the SADP was performed using quantitative histogram analysis. Additionally, three examiners masked to treatment (trimmed/untrimmed) qualitatively evaluated SADP destruction. During hoof loading with forces from 0.5 to 1.8 times the body mass of the donor horses, hooves with thinned hoof wall underwent significantly more deformation (P<0.05). Quantitative histogram analysis detected a shift to higher brightness values and a higher pixel intensity in control hooves, representing disruption in the histologic analysis. Qualitative evaluation of histology sections showed significantly more disruption of the SADP in untrimmed hooves (P=0.03). These results confirm the hypothesis that reduced hoof wall thickness can decrease disruption of laminar tissue in vitro, thus supporting the evaluation of hoof wall reduction as a prophylactic measure in horses at imminent risk of SADP failure.

Comparative need for spinal stabilisation between quadrupedal and bipedal locomotion.

Sheep are commonly used as an animal model for the human lumbar spine, but similarities in trunk muscle activity of humans and sheep during functional tasks such as locomotion have not been investigated. Therefore, the aim of the study was to evaluate trunk and pelvic limb muscle activity during walk and run/trot gaits in man and sheep. Electromyography of the muscles erector spinae (ES), gluteus maximus (GM), rectus abdominis (RA), obliquus externus (OE) and obliquus internus (OI) were collected in 24 humans and 15 sheep during treadmill walk and run/trot. Kinematic data from the tarsus (human) or metatarsus (sheep) were obtained to define motion cycles and determine stride characteristics. Mean and range of normalised muscle activity were calculated. In phasic muscles, the occurrence of the maximum was reported. At walk, mean activity was greater in humans for all three abdominal muscles (all p<0.01). At the run/trot, mean activity of ES was significantly greater in sheep (p<0.05) and mean activity of right OI was greater in humans (p=0.016). At the walk, range of ES activity was significantly greater in humans compared to sheep (p<0.01), but significantly smaller in humans in RA and right OE (p<0.05). At the run/trot, range of activity was significantly greater in humans compared to sheep in all muscles (p<0.05), except right RA and OI. Compared to humans, occurrence of maximum activity was earlier in sheep for ES right during walk (p=0.005), and later for GM during walk and run/trot (p<0.001). The results suggest that numerous differences in trunk muscle activity exist between man and sheep during treadmill walk and run/trot, and that these differences are muscle-and gait-specific. Trunk muscle activity should therefore be regarded as species-specific which suggests differences in stabilization strategies. This should be taken into consideration when extrapolating animal model findings to the human spine.

From maturity to old age: tasks of daily life require a different muscle use in horses.

In vertebrates ageing is characterized by reduced viscoelasticity of the ligamentous and tendineous structures and fibre changes in muscle. Also, some vertebral joint degeneration develops with ageing. The aim of this study was to apply dynamic time warping to compare the temporal characteristics of the surface electromyography (sEMG) data and to illustrate the differences in the pattern of muscle use during tasks of daily life in old and mature horses. In vivo kinematics (24 skin markers) and sEMG measurements of neck extensors and flexors were taken in five mature horses (age 10 ± 2 years, half of mean life expectancy) and five old horses (age 25 ± 5 years, older than the mean life expectancy). All horses had the same level of activity in the 12 months prior to the measurement. Tasks measured were neck flexion and neck extension as well as neutral neck position. Muscle activation, minimum and maximum muscle activation were collected. Quartiles of muscle activity based on the maximum observed activity of each muscle were calculated to document the relative increase of activity level during the task. Kinematics as well as overall muscle activity patterns were similar across horses and age groups. However, in the neutral position old horses showed increased extensor activity compared to mature horses, indicating that old equine muscle requires more activity to counteract gravity. Dynamic time warping specified optimal temporal alignments of time series, and different temporal performances were identified. The age groups differed during the flexion task, while extension and neutral were more similar. The results of this study show that even in the second half of life and in the absence of muscle disuse the muscular strategy employed by horses continues to be adapted.

Hyperinsulinaemia increases vascular resistance and endothelin-1 expression in the equine digit.

REASONS FOR PERFORMING STUDY: Insulin leads to overexpression of endothelin-1 (ET-1) in the endothelium of insulin-resistant rodents. If this is also the case in equine laminar tissue, this could explain the predisposition of insulin-resistant horses to laminitis. OBJECTIVES: To investigate the effect of hyperinsulinaemia on metabolism and vascular resistance of the isolated equine digit in a model of extracorporeal perfusion. STUDY DESIGN: Randomised, controlled study with interventional group, with blinded evaluation of histology results. METHOD: After exsanguination, equine digits (n = 11) and autologous blood were collected at an abattoir. One digit served as a hyperinsulinaemic pilot limb, 5 digits were assigned to the hyperinsulinaemic perfusion (IP) group and 5 to the control perfusion (CP) group. Digits were perfused for 10 h at a defined perfusion rate of 12 ml/min/kg. After the first hour of perfusion (equilibration period), insulin was added to the reservoir of the IP digits. Perfusion pressure, glucose consumption, lactate and lactate dehydrogenase were monitored. Vascular resistance was calculated as perfusion pressure (in millimetres of mercury) in relation to the flow rate (in millilitres per minute). After perfusion, histology samples of the dorsal hoof wall (haematoxylin & eosin or periodic acid-Schiff) were evaluated. Immunohistology with a polyclonal rabbit-derived anti-endothelin antibody was used for detection of ET-1. RESULTS: In the IP group, the mean insulin concentration in the plasma of the perfusate was 142 ± 81 µiu/ml, while insulin concentration was <3 µiu/ml in the CP group. Mean vascular resistance was significantly higher (P<0.01) in the IP group (2.04 ± 1.13 mmHg/ml/min) than in the CP group (1.31 ± 0.55 mmHg/ml/min). Histology of the IP group samples showed significantly more vessels with an open lumen, increased width of the secondary epidermal lamellae and formation of oedema. In the lamellar vessels (veins and arteries) and nerve fibres, ET-1 expression was much more prominent in the IP group than in the CP group samples. CONCLUSIONS: Short-term hyperinsulinaemia leads to increased vascular resistance in the equine digit and increased expression of ET-1 in the laminar tissue.

Evaluation of a signal-adapted filter for processing of periodic electromyography signals in horses walking on a treadmill.

OBJECTIVE: To evaluate an adaptive-filter method for use in analysis of periodic electromyography (EMG) signals in which the transfer function of the filter is matched to characteristics of the signal. ANIMALS: 15 adult horses without clinical signs of back pain. PROCEDURE: Electromyography signals of the left and right longissimus dorsi muscles, middle gluteal muscles, and triceps brachii muscle were recorded from horses walking on a treadmill, using bilaterally placed surface electrodes. A reflective marker was placed on the hoof of the left hind limb for simultaneous kinematic measurement of motion cycles. Absolute value of the measured EMG signal was convoluted by use of a filter signal equivalent to the length of 3 motion cycles. The signal-to-noise ratio (SNR) was calculated from the autocorrelation function and compared with the SNR of the unfiltered and the low-pass filtered signals. RESULTS: The signal-adapted filter significantly increased SNR (by 7.3 dB, compared with the low-pass filter, and by 11.1 dB, compared with the unfiltered EMG signal). CONCLUSIONS AND CLINICAL RELEVANCE: The signal-adapted filter eliminates signal parts that are not correlated to periodic motion. The method reported here improves the applicability of periodic EMG signals as a clinical tool.

Treadmill study of the range of back movement at the walk in horses without back pain.

OBJECTIVE: To evaluate back movement during walking in horses. ANIMALS: 22 adult horses with no history or signs of back pain. PROCEDURE: 3-dimensional movements of markers on the hooves, head, and back were measured with a motion analysis system while the horses were walking on a treadmill. The positions of markers on the hooves, head, and the skin above the spinous processes of T5, T10, T16, L3, and 2 sacral vertebrae were recorded. From a minimum of 6 walking motion cycles/horse, marker movement and the time of occurrence of minimum and maximum marker positions within the motion cycle were determined. Angles were calculated between the markers on the head, T16, and S4 or S5 and between the markers on T5, T16, and S4 or S5. RESULTS: Lateral back movement was maximal at L3, where it reached (mean +/- SD) 3.5 +/- 0.8% of the horses' height at the withers. Maximum dorsoventral back movement was found at the sacrum, where it reached 4.7 +/- 1.3% of the height at the withers. In the horizontal plane, the angle between T5, T16, and S4 or S5 was altered by 11 +/- 2.5 degrees during the motion cycle. In the sagittal plane, the angle between the head, T16, and S4 or S5 was altered by 7 +/- 3 degrees. CONCLUSIONS AND CLINICAL RELEVANCE: Results of this study may be used as basic kinematic reference data for evaluation of back movement in horses.