H. M. S. Davies

Surface strain on the dorsal metacarpus of thoroughbreds at different speeds and gaits

Stacked rectangular rosette strain gages were used to measure surface bone strain on the dorsomedial cortex of the third metacarpal bones in 6 adult Thoroughbred horses during treadmill exercise. The peak principal compressive and tensile strains, angle of the peak strains and strain rate during loading were calculated and compared with speed and gait. At speeds from 4 to 14 m/s loading on the metacarpus resulted in compression of the dorsomedial cortex. Tension only occurred consistently in 1 forelimb of 1 horse at the walk (2 m/s). The angle of peak compression was within 10 degrees of the longitudinal axis of the bone, and the magnitude of compression was proportional to the speed of exercise. Mean maximum compressive strains in the 6 horses at 2 m/s were -668 mu strain, -1,204 mu strain at 4 m/s; -1,617 mu strain at 6 m/s; -2,127 mu strain at 8 m/s, and -2,533 mu strain at 10 m/s. Recordings from 3 horses gave a mean -3,206 mu strain at 12 m/s, and strains at 14 m/s approached -4,000 mu strain. Peak strains were similar in both forelimbs at the canter while strain rate tended to be higher in the leading forelimb.

Altered gene expression in early osteochondrosis lesions

Osteochondrosis is a condition involving defective endochondral ossification and retention of cartilage in subchondral bone. The pathophysiology of this condition is poorly characterized, but it has been proposed that the fundamental defect is failure of chondrocyte hypertrophy. The aim of the current study was to characterize phenotypic changes in chondrocytes associated with the initiation of osteochondrosis. Early lesions were induced in an equine model of osteochondrosis by feeding foals a high energy diet for 8 or 15 weeks. Lesions in articular‐epiphyseal growth cartilage were examined histologically and by quantitative PCR analysis of expression of a number of genes representative of pathways that regulate chondrocyte behavior during endochondral ossification. There were more cells present in clusters in the lesions compared to normal articular cartilage. Expression of matrix metalloproteinase‐13, type I collagen, type X collagen, and Runx2 mRNA was significantly greater in the lesions compared to normal cartilage from the same joint. Expression of vascular endothelial growth factor, type II collagen, connective tissue growth factor, aggrecan, Sox9, and fibroblast growth factor receptor 3 mRNA was not significantly different in lesions than in control cartilage. These observations suggest that osteochondrosis does not result from failure of chondrocytes to undergo hypertrophy.

Influence of Muscle-Tendon Wrapping on Calculations of Joint Reaction Forces in the Equine Distal Forelimb

The equine distal forelimb is a common location of injuries related to mechanical overload. In this study, a two-dimensional model of the musculoskeletal system of the region was developed and applied to kinematic and kinetic data from walking and trotting horses. The forces in major tendons and joint reaction forces were calculated. The components of the joint reaction forces caused by wrapping of tendons around sesamoid bones were found to be of similar magnitude to the reaction forces between the long bones at each joint. This finding highlighted the importance of taking into account muscle-tendon wrapping when evaluating joint loading in the equine distal forelimb.

Third metacarpal bone length and skeletal asymmetry in the Thoroughbred racehorse

In man, the dominant right hand is often larger than the nondominant left hand. However, in horses, skeletal asymmetry has not previously been reported. Skeletal asymmetry in the racehorse may influence the way it races and affect the incidence of lameness. The growth in length of the third metacarpal bone (McIII) in the horse has ceased by age 10 weeks (Fretz et al. 1984) and its length should therefore not be affected by subsequent training conditions. Horses are not trained at all until at least age 2 years. This means that measurements of the length of McIII may show any underlying asymmetry in the processes of growth present in racehorses that may affect their performance and the incidence of injury. The aim of this study was to establish whether there was a consistent difference in McIII length in two independent groups of Thoroughbred racehorses.

Surface strains around the midshaft of the third metacarpal bone during turning

REASONS FOR PERFORMING STUDY Bone strains quantify skeletal effects of specific exercise and hence assist in designing training programmes to avoid bone injury. OBJECTIVE To test whether compressive strains increase on the lateral surface of the inside third metacarpal bone (McIII) and the medial surface of the outside McIII in a turn. METHODS Rosette strain gauges on dorsal, medial and lateral surfaces of the midshaft of the left McIII in 2 Thoroughbred geldings were recorded simultaneously during turning at the walk on a bitumen surface. RESULTS Medial surface: Compression peaks were larger in the outside limb. Tension peaks were larger in the inside limb and in a tighter turn. On the lateral surface compression and tension peaks were larger on the inside limb, which showed the largest recorded strains (compression of -1400 microstrains). Dorsal compression strains were larger on the outside limb and on a larger circle. Tensile strains were similar in both directions and larger on a larger circle. CONCLUSIONS Compressive strains increased on the lateral surface of the inside McIII and medial surface of the outside McIII in a turn. POTENTIAL RELEVANCE Slow-speed turning exercise may be sufficient to maintain bone mechanical characteristics in the inside limb lateral McIII cortex. Further work is needed to confirm these findings and to determine whether faster gaits and/or tighter turns are sufficient to cause bone modelling levels of strain in the medial and lateral McIII cortex.

Transmucosal healing around peri-implant defects: crestal and subcrestal implant placement in dogs

OBJECTIVE This study was designed to evaluate the transmucosal healing response of implants placed with the junction of the smooth surfaces, either crestal or subcrestal, into simulated extraction defects after healing periods of 1 and 3 months. MATERIALS AND METHODS A total of 23 Straumann SP v3.3 mm NN, SLA 10 mm implants were placed in the mandibular premolar regions of three greyhound dogs 3 months after the teeth were removed. Five control implants were placed at the crestal bone level, and test implants with surgically created peri-implant defects of 1.25 mm wide x 5 mm depth were placed either at the crestal (nine implants) or at the 2 mm subcrestal (nine implants) bone level. Implants on the right side were placed 1 month before the dogs were sacrificed, and implants on the left side were placed 3 months before sacrifice. All dogs had daily plaque control following surgery and were sacrificed 3 months after implant placement for histological and histometric analyses. RESULTS Mesial-distal ground sections of the control and test implant specimens showed a greater %BIC in the coronal defect region after 3 months of healing. This healing response was incomplete for the test implants compared with the control implants after a 1-month healing period. The histometric measurements for test implants placed at the crestal bone level or 2 mm subcrestal with surgically created peri-implant defects were more coronal or closer to the implant margin compared with the control implants. Additionally, the degree of osseointegration between the newly formed bone and the implant surface was similar between the test implants. CONCLUSION Peri-implant defects of 1.25 mm width healed with spontaneous bone regeneration around implants placed transmucosally at crestal or 2 mm subcrestal with a high degree of osseointegration after a 3-month healing period.

Mechanical loading of the distal end of the third metacarpal bone in horses during walking and trotting

OBJECTIVE To assess the net mechanical load on the distal end of the third metacarpal bone in horses during walking and trotting. ANIMALS 3 Quarter Horses and 1 Thoroughbred. PROCEDURES Surface strains measured on the left third metacarpal bone of the Thorough-bred were used with a subject-specific model to calculate loading (axial compression, bending, and torsion) of the structure during walking and trotting. Forelimb kinematics and ground reaction forces measured in the 3 Quarter Horses were used with a musculoskeletal model of the distal portion of the forelimb to determine loading of the distal end of the third metacarpal bone. RESULTS Both methods yielded consistent data regarding mechanical loading of the distal end of the third metacarpal bone. During walking and trotting, the distal end of the third metacarpal bone was loaded primarily in axial compression as a result of the sum of forces exerted on the metacarpal condyles by the proximal phalanx and proximal sesamoid bones. CONCLUSIONS AND CLINICAL RELEVANCE Results of strain gauge and kinematic analyses indicated that the major structures of the distal portion of the forelimb in horses acted to load the distal end of the third metacarpal bone in axial compression throughout the stance phase of the stride.

Hypertrophy and physiological death of equine chondrocytes in vitro

REASON FOR PERFORMING STUDY Equine osteochondrosis results from a failure of endochondral ossification during skeletal growth. Endochondral ossification involves chondrocyte proliferation, hypertrophy and death. Until recently no culture system was available to study these processes in equine chondrocytes. OBJECTIVE To optimise an in vitro model in which equine chondrocytes can be induced to undergo hypertrophy and physiological death as seen in vivo. METHODS Chondrocytes isolated from fetal or older (neonatal, growing and mature) horses were cultured as pellets in 10% fetal calf serum (FCS) or 10% horse serum (HS). The pellets were examined by light and electron microscopy. Total RNA was extracted from the pellets, and quantitative PCR carried out to investigate changes in expression of a number of genes regulating endochondral ossification. RESULTS Chondrocytes from fetal foals, grown as pellets, underwent hypertrophy and died by a process morphologically similar to that seen in vivo. Chondrocytes from horses age >5 months did not undergo hypertrophy in pellet culture. They formed intramembranous inclusion bodies and the cultures included cells of osteoblastic appearance. Pellets from neonatal foals cultured in FCS resembled pellets from older horses, however pellets grown in HS underwent hypertrophy but contained inclusion bodies. Chondrocytes from fetal foals formed a typical cartilage-like tissue grossly and histologically, and expressed the cartilage markers collagen type II and aggrecan mRNA. Expression of Sox9, collagen type II, Runx2, matrix metalloproteinase-13 and connective tissue growth factor mRNA increased at different times in culture. Expression of fibroblast growth factor receptor-3 and vascular endothelial growth factor mRNA decreased with time in culture. CONCLUSIONS Freshly isolated cells from fetal growth cartilage cultured as pellets provide optimal conditions for studying hypertrophy and death of equine chondrocytes. POTENTIAL RELEVANCE This culture system should greatly assist laboratory studies aimed at elucidating the pathogenesis of osteochondrosis.

Morphometrical Study of Bony Elements of the Forelimb Fetlock Joints in Horses

There are many reports describing fractures in the bony elements of the equine fetlock joint and a few of these discuss possible relationships of these fractures to the mechanical loading of these bones. The likelihood of fracture must be related to the size and shape of bones involved, but information concerning the normal range in size and shape of these bones in horses is lacking. This study aimed to identify morphometrical variations of these bones within different groups of horses. Right and left metacarpal, proximal phalangeal and proximal sesamoid bones were collected from 10 Thoroughbreds (TB), five Standardbreds (SB) and eight Ponies (P) euthanized for non‐orthopaedic reasons. All bones were boiled, cleaned and dried. Dimensional parameters were measured using a custom‐built apparatus, calliper and plastic tape. The width and depth of the medial condyles of Mc3 were greater than the lateral condyles in all groups. The length to the lateral condyle was greater than the length to the medial condyle of Mc3, and the lengths of the lateral sides of the Mc3 and P1 bones were greater than the lengths of the medial sides in both forelimbs of all groups. The lateral sesamoids were similar to, or larger than, the medial sesamoids in all dimensions. There were some morphometrical variations in the bony elements of the equine fetlock joints in all groups.

Healing of Bio-Oss® grafted marginal gaps at implants placed into fresh extraction sockets of incisor teeth in dogs: a study on the effect of submerged vs. non-submerged healing.

OBJECTIVES To evaluate the effect of submerged vs. non-submerged (NS) protocols in healing outcomes of grafted marginal defects of immediate implants. MATERIALS AND METHODS The second maxillary incisors were extracted bilaterally in six greyhound dogs. Bone level reduced diameter implants were installed into the extraction sockets leaving orofacial gaps of 2 mm wide. Defects were filled with Bio-Oss(®) and covered with Bio-Gide(®). On the one side, the flap was advanced to fully submerge the implant, and on the other, the flap was sutured to allow NS healing. After 3 months of healing, the dogs were sacrificed and block biopsies were obtained to perform histological and morphometric analysis. RESULTS All implants were clinically healthy and well integrated into bone. In the majority of the specimens, the original bone in the coronal 2-3 mm of the buccal crest had completely resorbed and was replaced by a regenerated bone wall consisting of Bio-Oss(®) particles surrounded by newly formed bone. Horizontal and vertical resorption of the buccal bone resulted in ≥1 mm exposure of the implant surface in one-third of implants. Minor differences existed in some aspects of hard tissue healing between submerged and NS. CONCLUSION There was very little difference in healing outcomes as well as modelling of the facial bone wall between the submerged and NS protocols in relation to immediate implant placement in this dog model.