A. Barneveld

Inertial properties of Dutch Warmblood horses

The complete set of three-dimensional inertial properties (mass, density, centre of mass, inertial tensor) was determined in 26 segments of six Dutch Warmblood horses. The measurements were performed with frozen segments similar to the procedure described by Lephart (1984, J. Biomechanics 17, 537-543). Based on these data linear regression models were developed for the estimation of inertial properties in living horses. The reproducibility of the dissection procedure was found to range between 2 and 9%. Both mean values and regression models are presented for all parameters. The mean standard error of estimation was 8% for the segment mass, 3% of the segment reference length for the position of the centre of mass, and 17% for the moments of inertia.

Kinematics of treadmill versus overground locomotion in horses

A kinematic analysis was carried out to compare treadmill and overground locomotion in horses at the trot. Stride variables and limb and trunk movements of 10 Dutch Warmblood horses were measured using the CODA-3 gait analysis system. Overground recordings were made on a rubber ground surface and on an asphalt track. Treadmill recordings were taken after a controlled habituation programme and at the same velocities as measured overground. On asphalt, a shorthened stride duration and a decreased vertical displacement of the withers were found compared with those on rubber ground. On the treadmill, stance duration of the forelimbs was longer than for either overground condition. Correspondingly, the hind limbs were placed earlier than the forelimbs in making diagonal ground contact in overground locomotion, but this changed to preceding forelimbs on the treadmill. Both forelimbs and hind limbs were moved more caudally during the retraction phase on the treadmill, while no differences were found in the protraction angle. The vertical movement of the hooves as well as the withers was smaller on the treadmill than on rubber ground. Treadmill belt velocity decreased by 9% during the stance phase. This is supposed to be an important reason for the differences in biomechanics and kinematics between treadmill and overground locomotion, which must be kept in mind when data obtained during treadmill locomotion have to be extrapolated to overground conditions.

Functional adaptation of equine articular cartilage: the formation of regional biochemical characteristics up to age one year.

Biochemical heterogeneity of cartilage within a joint is well known in mature individuals. It has recently been reported that heterogeneity for proteoglycan content and chondrocyte metabolism in sheep develops postnatally under the influence of loading. No data exist on the collagen network in general or on the specific situation in the horse. The objective of this study was to investigate the alterations in equine articular cartilage biochemistry that occur from birth up to age one year, testing the hypothesis that the molecular composition of equine cartilage matrix is uniform at birth and biochemical heterogeneity is formed postnatally. Water content, DNA content, glycosaminoglycan content (GAG) and biochemical characteristics of the collagen network (collagen content, hydroxylysine content and hydroxylysylpyridinoline [HP] crosslinks) were measured in immature articular cartilage of neonatal (n = 16), 5-month-old foals (n = 16) and yearlings (n = 16) at 2 predefined differently loaded sites within the metacarpophalangeal joint. Statistical differences between sites were analysed by ANOVA (P<0.01), and age correlation was tested by Pearsons product moment correlation analysis (P<0.01). In neonatal cartilage no significant site differences were found for any of the measured biochemical parameters. This revealed that the horse has a biochemically uniform joint (i.e. the cartilage) at birth. In the 5-month-old foals and yearlings, significant site differences, comparable to those in the mature horse, were found for DNA, GAG, collagen content and hydroxylysine content. This indicates that functional adaptation of articular cartilage to weight bearing for these biochemical parameters takes place during the first months postpartum. Water content and HP crosslinks showed no difference between the 2 sites from neonatal horses, 5-month-old animals and yearlings. At both sites water, DNA and GAG decreased during maturation while collagen content, hydroxylysine content and HP crosslinks increased. We propose that a foal is born with a uniform biochemical composition of cartilage in which the functional adaptation to weight bearing takes place early in life. This adaptation results in biochemical and therefore biomechanical heterogeneity and is thought to be essential to resist the different loading conditions to which articular cartilage is subjected during later life. As collagen turnover is extremely low at mature age, an undisturbed functional adaptation of the collagen network of articular cartilage at a young age may be of significant importance for future strength and resistance to injury.

The effect of platelet-rich plasma on the neovascularization of surgically created equine superficial digital flexor tendon lesions

The repair process of tendon injuries, which are common in both human and equine athletes, is slow and the quality of the repair tissue is often inferior to the original tendon tissue, which frequently leads to re‐injury. The relatively poor vascularization of tendons is considered to be one of the reasons for their limited healing potential. Recently, platelet‐rich plasma (PRP), an autologous concentrate of platelets, rich in growth factors, has been shown to enhance the repair process of injured tendons. This effect has been ascribed to the high levels of growth factors in PRP, several of which are known to be involved in tendon repair. Among many other growth factors, the vascular endothelial growth factor, a powerful stimulator of angiogenesis, is abundantly present in PRP, suggesting that enhancement of neovascularization might be one of the working mechanisms. In this study, the effect of PRP on neovascularization was studied in experimentally induced tendon injuries using color Doppler ultrasonography and immunological staining of Factor VIII. PRP induced significantly more neovascularization than the placebo treatment until at least 23 weeks after treatment, as detected by both Doppler ultrasonography and Factor VIII staining. Neovascularization might be one of the explanations for the long‐lasting effect of a single intratendinous treatment with PRP.

Contact areas and pressure distribution on the proximal articular surface of the proximal phalanx under sagittal plane loading.

The objective of this study was to map topographically contact areas and pressure distributions on the proximal articular surface (PAS) of the proximal phalanx (PI) under various clinically relevant loading conditions. Left and right forelimbs of 13 mature horses were transected halfway down the radius and loaded in a position mimicking the weightbearing attitude close to the midstance phase. Five loads were used which corresponded with loads that can be expected in different gaits or during athletic performance (stance: 1800 N, walk: 3600 N, trot: 5400 N, gallop: 10,500 N and jumping: 12,000 N). Contact areas and pressure distributions at the PAS of PI were determined using a methylene blue dye staining technique and 2 pressure sensitive films (low pressure: range 2.5-10 MPa and medium pressure: range 10-50 MPa). The contact area of PI was positively correlated (r = 0.86; P<0.01) with the applied load. The contact area increased from 63% at 1800 N to 95% at 12,000 N and gradually shifted to include more of the edges of the articular surface, but especially the dorsal articular margin of PI. Pressure distribution patterns were similar under the different loading conditions. Pressure was less at the palmar margin and in the central depression and highest at the dorsal articular margin. With increasing load, the highest peak pressures were measured at sites of the dorsal articular margin that are not loaded in the standing or walking horse. The results of this study suggest that the frequent occurrence of osteochondral lesions at the dorsal articular margin of PI is caused by the combination of the intermittent character and the high absolute values of loads at this site as they occur during athletic performance.

Development of biochemical heterogeneity of articular cartilage: Influences of age and exercise

The objective of this study was to document the development of biochemical heterogeneity from birth to maturity in equine articular cartilage, and to test the hypothesis that the amount of exercise during early life may influence this process. Neonatal foals showed no biochemical heterogeneity whatsoever, in contrast to a clear biochemical heterogeneity in mature horses. The process of formation of site differences was almost completed in exercised foals age 5 months, but was delayed in those deprived of exercise. For some collagen-related parameters, this delay was not compensated for after an additional 6 month period of moderate exercise. It is concluded that the functional adaptation of articular cartilage, as reflected in the formation of biochemical heterogeneity in the horse, occurs for the most part during the first 5 months postpartum. A certain level of exercise seems essential for this process and withholding exercise in early life, may result in a delay in the adaptation of the cartilage.

Correction models for skin displacement in equine kinematics gait analysis

Summary General mathematical models are presented to be used in equine kinematic gait analysis for the correction of the biological error that is caused by sliding of the skin over the underlying bony landmarks. Ten sites in the front limb and 8 in the hind limb were investigated. In the distal parts of the limbs a linear relationship with the angle of the adjacent joint was found. The more complex pattern in the proximal parts of the limbs could be satisfactorily represented by truncated Fourier series. Analyses were principally done in the Dutch Warmblood horse, but investigations in other breeds were carried out to verify the general applicability of the models. Skin displacement appeared to be negligible in the lower parts of the limbs, but reached large values in proximally located sites such as the caudal part of the greater trochanter of the femur. It is concluded that skin displacement in equine gait analysis may account for major errors in applied biomechanical research and therefore should be corrected, although it may be of less importance for clinical applications.

Topographical mapping of biochemical properties of articular cartilage in the equine fetlock joint

The aim of this study was to evaluate topographical differences in the biochemical composition of the extracellular matrix of articular cartilage of the normal equine fetlock joint. Water content, DNA content, glycosaminoglycan (GAG) content and a number of characteristics of the collagen network (total collagen content, levels of hydroxylysine- (Hyl) and the crosslink hydroxylysylpyridinoline, (HP) of articular cartilage in the proximal 1st phalanx (P1), distal 3rd metacarpal bone (MC), and proximal sesamoid bones (PSB) were determined in the left and right fetlock joint of 6 mature horses (age 5-9 years). Twenty-eight sites were sampled per joint, which included the clinically important areas often associated with pathology. Biochemical differences were evaluated between sampling sites and related with the predisposition for osteochondral injury and type of loading. Significant regional differences in the composition of the extracellular matrix existed within the joint. Furthermore, left and right joints exhibited biochemical differences. Typical topographic distribution patterns were observed for each parameter. In P1 the dorsal and palmar articular margin showed a significantly lower GAG content than the more centrally located sites. Collagen content and HP crosslinks were higher at the joint margins than in the central area. Also, in the MC, GAG content was significantly lower at the (dorsal) articular margin compared with the central area. Consistent with findings in P1, collagen and HP crosslinks were significantly lower in the central area compared to the (dorsal) articular margin. Biochemical and biomechanical heterogeneity of articular cartilage is supposed to reflect the different functional demands made at different sites. In the present study, GAG content was highest in the constantly loaded central areas of the joint surfaces. In contrast, collagen content and HP crosslinks were higher in areas intermittently subjected to peak loading which suggests that the response to a certain type of loading of the various components of the extracellular matrix of articular cartilage are different. The differences in biochemical characteristics between the various sites may help to explain the site specificity of osteochondral lesions commonly found in the equine fetlock joint. Finally, these findings emphasise that the choice of sampling sites may profoundly influence the outcome of biochemical studies of articular cartilage.

Dynamic pressure measurements for the detailed study of hoof balance: the effect of trimming

REASONS FOR PERFORMING STUDY Studies on hoof balance have, so far, only assessed the effects of strong and relatively unrealistic interventions due to technical limitations of measuring equipment. For the assessment of more subtle interventions, other techniques are necessary. OBJECTIVES To test a sensitive pressure measurement system during locomotion and to set a standard for further studies by using the system to evaluate the effects of trimming. METHODS Eighteen horses were measured before and after trimming with an interval of 4 weeks. Trimming was standardised to a straight hoof-pastern axis. The horses trotted over a pressure/force measuring system, with a temporal resolution of 240 Hz and a spatial resolution of 0.39 cm2. RESULTS The preferred way of landing was lateral, asymmetrical in both front and hind feet. The duration of landing was shorter in forelimbs than in hindlimbs with an equal decreasing trimming effect. Horses had a fixed hoof-unrollment pattern; the centre of pressure (CoP) travelled towards a maximum lateral deviation and returned towards the dorsopalmar/plantar axis of the hoof. Trimming decreased the intra-individual left/right difference in maximum lateral displacement. CONCLUSIONS The technique used provided easily accurate data to quantify hoof balance characteristics and to measure short-term trimming effects. POTENTIAL RELEVANCE Determination of CoP patterns has added value in gait analysis and can improve our understanding of the effects of different interventions on hoof balance.

Matrix metalloproteinase activity in equine synovial fluid: influence of age, osteoarthritis, and osteochondrosis

OBJECTIVE To investigate the influence of age, osteoarthritis (OA), and osteochondrosis (OC) on the matrix metalloproteinase (MMP) activity in the synovial fluid (SF) of equine joints. METHODS SF was collected from normal and osteoarthritic metacarpophalangeal joints (normal: 14 adult, 28 juvenile; OA: 22 adult). And from normal and osteochondrotic tarsocrural joints (5 months: 11 normal, 8 OC; 11 months: 7 normal, 6 OC). Subsequently, overall MMP activity was measured. RESULTS The level of active MMPs was almost twofold higher in SF from juvenile horses (age up to 11 months) than in SF from mature animals (4–30 years; p<0.001). In juvenile horses MMP activity was higher in 5 month old foals than in 11 month old foals (p<0.01). In adult horses MMP activity was independent of age. In OA joints the activity was nearly twice as high as in normal joints (p<0.001). In OC joints MMP activity was not significantly different from normal, age matched, control joints. CONCLUSIONS MMP activity in SF from normal adult joints is not related to age. In juvenile joints MMP activity is significantly higher than activity in joints from adult animals. It is hypothesised that the gradual decrease in MMP activity with increasing age reflects the declining metabolic activity resulting from ceasing growth and the accompanying decrease in cartilage remodelling. The increased MMP activity in osteoarthritic joints most likely reflects matrix destruction. In osteochondrosis MMP mediated matrix degradation appears not to be different from normal joints.