Mechanical implications of collagen fibre orientation in cortical bone of the equine radius.

Mechanical test specimens were prepared from the cranial and caudal cortices of radii from eight horses. These were subjected to destructive tests in either tension or compression. The ultimate stress, elastic modulus and energy absorbed to failure were calculated in either mode of loading. Analysis was performed on the specimens following mechanical testing to determine their density, mineral content, mineral density distribution and histological type. A novel technique was applied to sections from each specimen to quantify the predominant collagen fibre orientation of the bone near the plane of fracture. The collagen map for each bone studied was in agreement with the previously observed pattern of longitudinal orientation in the cranial cortex and more oblique to transverse collagen in the caudal cortex. Bone from the cranial cortex had a significantly higher ultimate tensile stress (UTS) than that from the caudal cortex (160 MPa vs 104 MPa; P < 0.001) though this trend was reversed in compression, the caudal cortex becoming relatively stronger (185 MPa vs 217 MPa; P < 0.01). Bone from the cranial cortex was significantly stiffer than that from the caudal cortex both in tension (22 GPa vs 15 GPa; P < 0.001) and compression (19 GPa vs 15 GPa; P < 0.01). Of all the histo-compositional variables studied, collagen fibre orientation was most closely correlated with mechanical properties, accounting for 71% of variation in ultimate tensile stress and 58% of variation in the elastic modulus. Mineral density and porosity were the only other variables to show any significant correlation with either UTS or elastic modulus. The variations in mechanical properties around the equine radius, which occur in close association with the different collagen fibre orientations, provide maximal safety factors in terms of ultimate stress, yet contribute to greater bending of the bone as it is loaded during locomotion, and thus lower safety factors through the higher strains this engenders.

Aetiopathogenesis of canine elbow osteochondrosis: a study of loose fragments removed at arthrotomy.

Twenty-five ununited coronoid processes (UCP) and 24 osteochondritis dissecans (OD) flaps were examined by light and transmission electron microscopy. Chondrocytes showed degenerative changes but remained viable and continued to secrete matrix components, even though the organisation of the matrix was altered. Differences in the histological and ultrastructural appearance of the two lesions tend to suggest that they are two separate disease entities, although they may occur together in the same joint. It is hypothesised that OD results from incorrect cartilage maturation and endochondral ossification. The aetiology of UCP is unclear but there is a possibility of its being a subchondral fracture, with an ineffective fibrous repair in some cases.

The response of equine cortical bone to loading at strain rates experienced in vivo by the galloping horse.

The behaviour of cortical bone under load is strain rate-dependent, i.e. it is dependent on the rate at which the load is applied. This is particularly relevant in the galloping horse since the strain rates experienced by the bone are far in excess of those recorded for any other species. In this study the effect of strain rates between 0.0001 and 1 sec-1 on the mechanical properties of equine cortical bone were assessed. Initially, increasing strain rates resulted in increased mechanical properties. Beyond a critical value, however, further increases in strain rate resulted in lower strain to failure and energy absorbing capacity. This critical rate occurred around 0.1 sec-1 which is within the in vivo range for a galloping racehorse. Analysis of the stress-strain curves revealed a transition in the type of deformation at this point from pseudo-ductile to brittle. Bones undergoing brittle deformation are more likely to fail under load, leading to catastrophic fracture and destruction of the animal.

Post natal development of the canine elbow joint: a light and electron microscopical study.

The elbows of 13 puppy cadavers were dissected, samples were taken for light and electron microscopy, and the thickness of the articular cartilage of the distal humerus and proximal ulna was measured. Throughout post natal development differences were found in the arrangement of the growth plate and articular chondrocytes. At birth, the articular surface had remnants of a fibrous limiting membrane that was continuous with the perichondrium, a finding not previously recorded in dogs. Orientation of the collagen fibrils within the matrix of the articular cartilage was initially lacking but became established by three weeks. In the humerus cartilage canals were present up to 12 weeks old. The articular cartilage of the humeral condyle varied in thickness across the joint surface, being thicker on the medial than on the lateral side; it was also thicker at the apex of the medial coronoid process. These regions of thick cartilage correspond with the sites where cartilage defects arise in elbow osteochondrosis. No histological evidence was found that the medial cornoid process of the ulna is a separate centre of ossification.

Equine synovial tendon sheaths and bursae: a transmission electron microscope study.

A transmission electron microscope study was undertaken to investigate the details of the synovial tendon sheath and bursal lining in horses. The lining cells appeared to be fibroblasts and were buried in a finely granular ground substance. Generally these cells had poor cytoplasmic organelles, sparse short profiles of rough endoplasmic reticulum (RER), few scattered ribosomes and, occasionally, a poorly developed Golgi complex. However, a few lining cells appeared more active, having pronounced RER with dilated cisternane. The surface of the lining cells, particularly those with dilated RER, had filipodia of different shapes, which in some instances appeared to surround a detached matrix. This feature might indicate that these cells are capable of phagocytosis. In young animals, the lining was more or less akin to that of the adult. However, the lining cells were virtually indistinguishable from the fibroblasts in the subconnective tissue.

Equine synovial tendon sheaths and bursae: an histological and scanning electron microscopical study.

The structure of equine synovial tendon sheaths and bursae has been examined by light and scanning electron microscopy. Tissue samples were obtained from horses of various types and ages with no clinical evidence of sheath or bursal disorders. The interior of both structures was lined by a cellular layer superimposed on a vascular zone supported by a fibrous layer. The pattern of cell distribution of the lining varied from site to site within the same structure depending on the nature of the underlying tissue and on the amount of movement to which the structure was subjected. The cellular layer was predominantly fibrous in nature with scanty, widely separated fibroblasts (eg where it lines the palmar ligament, tendons and paratendons). In the mesotendon and bursal extremities, where the lining is subjected to a positive degree of movement, the cellular layer was areolar in type with well established folds populated by abundant cells oval to round in shape. In foals and yearlings, the supportive layer was mainly around the areolar with patches of adipose tissue; which were gradually replaced by fibrous tissue as the animal grew.

Orthopaedic problems in old dogs.

With advancing years a dog may suffer from a variety of conditions of its musculoskeletal system which adversely affect its ability to exercise and may cause it to be retired from activities in work and sport for which it has been trained. Arthritis is common, and in many cases arises from developmental errors suffered in puppyhood, such as hip dysplasia, osteochondrosis and growth plate disorders. Trauma to joints (ligament ruptures, dislocations and fractures) may also be the precursor of degenerative joint changes later in life. It is important, therefore, for all such conditions to be corrected as effectively as possible if joint disease is to be minimised as the dog grows older. Preventive action is also required for some conditions for which correction may not be entirely feasible, so the identification of modes of inheritance is important if those are to be controlled by breeding. Certain spinal disorders also tend to increase in prevalence with age, particularly spondylosis deformans, neoplasms and chronic degenerative radiculomyelopathy. As it happens, spondylosis in mild to moderate degree affects pet dogs very little, but a reduction in spinal flexibility can cause problems for dogs required to be agile in work or sport. In common with other body tissues, neoplasm of the locomotor system increases in occurrence in older dogs, and although the overall incidence of tumours of bones, joints, nervous tissue and muscle is relatively low, these are the most serious of all the limb and spinal conditions encountered because of their life threatening propensities. The treatment required covers a wide range from simple changes of management in order to reduce exercise, to the use of analgesics and anti-inflammatory drugs and to surgery to remove diseased tissue, stabilise joints or reduce pain with forms of arthroplasty or arthrodesis.

Use of contrast radiography in the investigation of tenosynovitis and bursitis in horses.

Contrast radiography, using a 25 per cent solution of sodium diatrizoate, has been used for the investigation of tenosynovitis and bursitis in horses. The procedure was undertaken on a series of 32 clinical cases and on specimens obtained at autopsy. Lesions affecting the extensor tendon sheaths at the carpus, the digital sheath, the tarsal sheath and the bursae at the elbow, hock and fetlock were examined by this means. The results showed the procedure offered the clinician useful information about the nature of the interior of these structures, particularly as regards the presence of adhesions and anastomoses between adjacent sheaths and joint capsules. Together with other clinical and laboratory findings, contrast radiography can assist in assessing the prognosis and in formulating appropriate treatment.

Radiographic anatomy of tendon sheaths and bursae in the horse.

Contrast radiography was used to determine the position, shape, relationship and capacity of a number of tendon sheaths and bursae which have clinical significance in the horse. It was possible to establish the normal range of radiographic anatomy for these structures. Some variation in the extent and form of tendon sheaths were found between individual horses and between foals and adults.

Tendon injuries in horses treated with carbon fibre implants.

Implants of carbon fibre, made by plaiting a tow of 10,000 filaments of Grafil type HT-S, were used to treat strains and ruptures of digital flexor tendons in 46 horses. The relevant clinical data, the techniques employed and an analysis of the results are described. Apart from two horses in which the implant was extruded and had to be removed, there were minimal untoward consequences of the surgery. Of the 34 horses with acute or chronic tendinitis, 14 returned to racing, seven were used as hunters and seven as hacks. Among the former group, seven suffered a further strain while racing but the others performed well for some time. Twelve horses with severed tendons recovered well and only in one did infection occur. Overall the results in the latter were better than had previously been achieved using other repair materials.

Disturbance in the growth of the tibia and femur in dogs.

The clinical and radiographic features associated with premature cessation of the growth of the tibia (four) and femur (eight) in 12 dogs are described. Surgical correction of the resultant deformity was possible in only a few cases. Trauma was thought to be the cause of the local growth plate disorder.