Correlation of racing performance with radiographic changes in the proximal sesamoid bones of 487 Thoroughbred yearlings

REASONS FOR PERFORMING STUDY

Proximal sesamoiditis has been a common and confusing radiographic diagnosis in Thoroughbred yearling surveys. This study categorised the radiographic appearance of yearling proximal sesamoid bones and determined their effect on the number of races started and earning potential for racing at ages 2 and 3 years.

HYPOTHESIS

Yearlings with moderate to severe proximal sesamoiditis have decreased performance at age 2 and 3 years.

METHODS

Survey radiographs of 487 Thoroughbred yearlings were reviewed. Proximal sesamoid bones were examined and findings placed into 7 categories, 5 of which measured size, shape, and number of vascular canals, and 2 examined the radiographic shape of the sesamoid abaxial surface. Records of horses age 2 and 3 years were reviewed to obtain the number of races completed and money won in those races.

RESULTS

Vascular canals with parallel sides < 2 mm in width in any number were normal. Yearlings with 1 or 2 abnormally conformed vascular canals (nonparallel sides and > 2 mm in width) had a decrease in number of race starts at age 2 years when compared to normal horses. This same change in the fore- or hindlimbs was associated with decreases in starts and earnings at age 2 years. If uniformly present in both fore- and hindlimbs there was no difference from normal horses. Yearlings with > 2 irregular vascular canals had a decrease in number of race starts and earnings at age 2 and 3 years. Changes in proximal sesamoid bone contour did not affect performance.

CONCLUSIONS

Horses with enlarged vascular canals, within their sesamoids as yearlings, start fewer races and earn less prize money than horses with normal vascular canals.

POTENTIAL RELEVANCE

One or two enlarged canals affected horses as 2-year-olds. Three or more enlarged vascular canals affected horses at ages 2 and 3 years, which should be taken into account when examining radiographs for potential purchase of young horses.

A study on the pathogenesis of equine sesamoiditis: the effects of experimental occlusion of the sesamoidean artery

In this study the potential role of circulatory disturbances in the pathogenesis of sesamoiditis was investigated by studying the clinical and histological effects of experimental occlusion of the sesamoidean artery, which is the main nutrient artery of the proximal sesamoid bone (PSB). For this purpose, five adult Dutch Warmblood horses were used in which the sesamoidean artery was occluded with polyvinyl alcohol foam particles. Bone labelling was carried out with oxytetracycline and calcein. All animal were checked clinically three times a week and radiographically at days 14, 21, 28 and 35. At day 35 the animals were killed and the fetlock was dissected and macroscopically evaluated. The PSBs were isolated and radiographed and the soft tissues adjacent to the abaxial side of the PSBs were histologically examined [routine histology and for the neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP)]. The PSBs were divided into bony slices which were radiographed and evaluated histologically (routine, SP, CGRP, fluorescence). All horses showed a slight lameness that gradually diminished. Radiographically enlarged vascular channels were seen in only one horse. Histological data showed that on average 60% (range 37-89%) of the total area had been deprived of vascularization. In two horses an increase in the extent of the arterial network from the basal side of the PSB was seen. Only in the horse with the greatest extent of occlusion were bone necrosis and a reactively increased uptake of fluorochromes adjacent to the occluded arteries found. Bone density did not change. The distribution of neuropeptides in the surrounding soft tissues was not affected by the occlusion. From this study, it can be concluded that a large part of the arterial supply to the PSB can be interrupted without provoking histological and/or radiographic changes that are consistent with clinical sesamoiditis. Therefore, it seems very improbable that circulatory disturbances are a primary aetiopathogenic factor in the disease.

Laminar microvascular flow, measured by means of laser Doppler flowmetry, during the prodromal stages of black walnut-induced laminitis in horses

OBJECTIVE

To measure changes in laminar microvascular blood flow (LMBF) over time in healthy horses and horses in the prodromal stage of black walnut-induced laminitis and to determine the effects of glyceryl trinitrate application on LMBF in horses with acute laminitis.

ANIMALS

10 healthy adult horses.

PROCEDURE

Laser Doppler flowmetry was used to measure LMBF Baseline measurements were obtained, horses were given deionized water via a nasogastric tube, and measurements were obtained hourly for 12 hours. Twenty-four hours later, baseline measurements were again obtained, and horses were given black walnut extract. Measurements were obtained hourly for 12 hours or until development of Obel grade-3 laminitis. At this time, 5 horses were treated with phenylbutazone, and the other 5 were treated with phenylbutazone and glyceryl trinitrate, and measurements were obtained hourly for an additional 12 hours.

RESULTS

LMBF was significantly decreased 1 and 2 hours after administration of the black walnut extract but then returned to near-baseline values for the next 6 hours. Eight hours after extract administration, there was a second significant decrease in LMBF that persisted until the end of the study. Glyceryl trinitrate had no effect on LMBF. Clinical signs of laminitis developed 8 to 12 hours after extract administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that in horses with black walnut-induced laminitis, there is an early decrease in LMBF followed by reperfusion prior to onset of clinical signs. Treatment with glyceryl trinitrate after development of clinical signs of laminitis did not have a significant effect on LMBF.

[The proximal sesamoid bone of the horse; vascular and neurologic characteristics]

Sesamoiditis is characterized clinically by repeated lameness and radiologically by changes in the proximal sesamoid bones. This thesis, which was defended in June 1997, investigated two characteristics of sesamoiditis, namely the arterial blood supply and the innervation of the proximal sesamoid bones, in order to gain more insight into the etiopathogenesis of sesamoiditis. Experiments with patient material showed that the proximal sesamoid bones have an enormous arterial reserve, due in part to the formation of an arterial shift. Moreover, the sesamoid bones have their own sensory innervation, provided by a branch of the medial and lateral palmar nerve. This branch is called the sesamoid nerve in this article. A special technique was developed to anaesthetize this nerve and can be used for further differentiation of pastern lameness. That the sesamoid bones are sensitive to pain was demonstrated by detection of the so-called nociceptive neuropeptides, substance P and calcitonin gene-related peptide, which are specifically involved in pain sensation. However, the adjacent ligament appear to be even more sensitive. The etiopathogenesis of sesamoiditis is discussed, as are a number of clinical implications of pain in the sesamoid bones. A number of potential future developments are mentioned.

The arterial shift features in the equine proximal sesamoid bone

Sesamoidosis in horses is characterised by lameness and radiographic changes in the proximal sesamoid bones and the aetiology is attributed to either mechanical factors or circulatory disturbances. In this study arteriograms of proximal sesamoid bones were investigated in 17 lame patients suffering from sesamoidosis, 6 sound horses and 4 yearlings. The arterial patterns of the proximal sesamoid bones from the patients, showed a shift from an abaxial to a basal arterial blood supply. This shift was only found in radiographically changed bones. Histological evaluation showed a significantly higher percentage of arteries with a large diameter in sections from the base of proximal sesamoid bones that showed an arterial shift. The presence of the shift appeared to be related to a change in shape of the bone, in particular to new bone formation along the abaxial border. The results of this study suggest that in horses suffering from sesamoidosis changes in the arterial pattern arise which might be a compensatory mechanism in respons to a vascular iischaemic challenge. Further investigations are needed to characterise the initial stimulus that induces this compensation and to determine if the compensation is sufficient to maintain a continuous and adequate blood supply.

Clinical relevance of the microvasculature of the equine proximal sesamoid bone

The blood supply to the proximal sesamoid bone of the equine forelimb was examined in 18 cadaver limbs from adult horses, using x-ray computed tomography and a tissue-clearing (Spalteholz) technique. Results of the study indicated that the proximal sesamoid bones were supplied by multiple branches of the medial and lateral palmar digital arteries, which entered the proximal half of the bones on their non-articular, abaxial surface. After entering the bone, the vessels traverse dorsally, axially, and distally, arborizing into several smaller branches that appear to supply the entire bone. The major branches of these vessels reside in bony canals, the orientation and distribution of which parallel the radiographic lucencies seen in horses with sesamoiditis and correspond to the configuration of apical fracture patterns.

Treatment and pathogenesis of navicular disease ('syndrome') in horses

The future directions of navicular disease research are unclear. Often researchers investigate only one of the multitude of factors likely to be important in understanding the disease. Two exceptions to this is work done by Wright in this issue of EVJ and by MacGregor (1988) who compared a number of the treatment regimens (e.g. rest, warfarin, isoxsuprine, shoeing with egg bars) and found that approximately 75% of the horses improved in their performance. Perhaps this percentage of 'recovered' horses from this disease is what can be realistically expected, as often horses with navicular disease remain undiagnosed until the disease has advanced to the stage where problems exist in the foot or to where the conformation-balance of the hoof is irrecoverable. Perhaps the key to controlling the disease is prevention by maintaining good overall hoof husbandry in a conservative and consistent manner. I would advocate that efforts be made to evaluate hoof 'balance' and the validity of the hoof wall-pastern axis being parallel, as these are clearly of importance in this debilitating disease.

The blood supply to the great toe sesamoids

The purpose of this study was to define the intraosseous and extraosseous blood supply of the hallucal sesamoids by studying a total of 10 fresh-frozen, below-knee specimens with no evidence of vascular disease. Most specimens were injected with high grade India ink, cleared using a standard Spalteholz technique, and processed to delineate the extraosseous and intraosseous blood supply to include soft tissue dissection and coronal sectioning. Two additional specimens were injected with blue Mercox acrylic solution to further define the extraosseous vasculature. The major extraosseous blood supply to the sesamoids is via the posterior tibial artery. This vessel then branches into the medial plantar artery which further divides upon entering the medial and lateral sesamoids in their proximal poles. Vessels in the peripheral soft tissues, although abundant, do not seem to penetrate the cortex of the sesamoids. The intraosseous blood supply to the sesamoids seems to be threefold. Mainly, sesamoid arteries enter the lateral and medial sesamoids from the proximal aspect via a single vessel. This proximal vessel proceeds distally with a network of branching. Plantar, nonarticular vessels enter the sesamoids, constituting a second source of vascularity. Finally, small vessels also enter the sesamoids through medial and lateral capsular attachments. Based on this study, a possible explanation for avascular necrosis and nonunion of sesamoids is proposed, and an optimal surgical approach is discussed.(ABSTRACT TRUNCATED AT 250 WORDS)

The microvasculature of the sesamoid complex: its clinical significance

The microvascular anatomy of the sesamoid complex was investigated in 15 cadaver specimens using histology and tissue clearing (Spalteholz) techniques. It was found that both sesamoids appeared equally well vascularized and the vascular supply to each sesamoid originated from two major sources (proximal and plantar) and one minor source (distal). Proximally, vessels originating from the first plantar metatarsal artery enter the sesamoid at its attachment to the flexor hallucis brevis. In addition, vessels enter the plantar surface of the sesamoid near the midline and arborize throughout the bone, anastamosing with the proximal vessels. The distal vascular supply to the sesamoids originates from its distal capsular attachment and appears to contribute minimally to the overall vascular scheme. The lateral attachments of the sesamoids to the plantar plate and joint capsule were relatively avascular. In two bipartite specimens examined, the major blood supply originated from the proximal and distal poles of the sesamoid. No vessels were observed entering the plantar surface of these specimens. The results of this study suggest that injury to the proximal or plantar aspects of the sesamoids could disrupt the vascular supply to these bones. These areas should, therefore, be avoided during the surgical approach to the sesamoids.

The arterial supply of the sesamoid bones of the hallux: the course and source of the nutrient arteries as an anatomical basis for surgical approaches to the great toe

The arterial supply of the hallux sesamoids was studied in 29 human feet by anatomical dissection. Eight of them underwent radiographic analysis prior to dissection. The sesamoid arteries branch off from the digital plantar arteries of the hallux, which, in turn, are derived from the medial plantar artery and the plantar arch (type A), the plantar arch (type B), or the medial plantar artery (type C). The respective frequencies of types A, B, and C were 52%, 24%, and 24%. The number of sesamoid arteries varied from one (55%) to three (10%) and the number increased with the size of the sesamoid bones. Anatomical knowledge of the course and distribution of these vessels may be of great help to the orthopedist in the understanding of the pathogenesis of avascular necrosis and may provide insight into several technical aspects regarding surgery of the hallux.

[Chronic disease of the two sesamoid bones of the lower foot of the horse]

The aetiology and pathogenesis of navicular bone disease and sesamoidosis are discussed on the basis of findings reported in the literature and research. A marked similarity is found to be present between the clinical presentation, aetiology and pathogenesis of these two diseases. In addition, the intra and juxta-articular signs of degeneration as seen in these diseases are similar to those seen in various forms of arthrosis. Circulatory disturbances resulting from partial or complete arterial occlusion, caused by arteriosclerosis, are likely to play an important role in the cause of degeneration of various anatomical structures occurring in navicular bone disease and sesamoidosis. In contrast, it is unlikely that overloading is a major factor in the aetiology of navicular bone disease and sesamoidosis, although it may be of importance in its pathogenesis. For a full understanding of the cause of arteriosclerosis, far more fundamental research is required.

Dimensions and arterial vascular supply of the sesamoid bones of the human hallux

The arterial supply of the ossa sesamoidea hallucis was studied in 13 subjects of both sexes by gross anatomical dissection. The majority of the ossa sesamoidea, i.e. 63% of the medial and 58% of the lateral sesamoid bones (SB), were supplied by a single artery. 26% of the medial and 32% of the lateral SB received 2 sesamoid arteries. In left feet only, 3 sesamoid arteries were found to supply 11% of the medial and 10% of the lateral SB. The actual number of sesamoid arteries proved to correspond to the dimensions and compactness (robusticity) of the ossa sesamoidea hallucis as well as to several other parameters, such as anthropometric dimensions, sex and footedness of the individuals.

The effect of artificial occlusion of the Ramus navicularis and its branching arteries on the navicular bone in horses: an experimental study

The clinical, radiographic, arteriographic, scintigraphic and histological effects of experimental occlusion of the Ramus navicularis (R. Navicularis) and its branching arteries are evaluated. Occlusion of the R. navicularis and its branching arteries creates changes, arteriographically and histologically, which resemble those of navicular disease. The increased bone remodelling, the shift in arterial pattern, the formation of collaterals and the increased connective tissue in the synovial membrane and nutrient foramina, as a reaction to the reduction of the distal arterial supply of the navicular bone, are also pathological features in the navicular bones of horses with navicular disease. The results of the present study support the theory that a reduced distal arterial supply of the navicular bone is important in the pathogenesis of navicular disease.

The effect of unilateral resection of segments of both palmar digital arteries on the navicular bone in ponies: an experimental study

Clinical, radiographical, scintigraphical and histological effects on the navicular bone after resection of the medial and lateral palmar digital arteries in the pastern of one forelimb in ponies are evaluated. The acute disruption of the main blood supply of the distal extremity causes lameness due to the suddenness of the resection in which the collateral circulation is insufficiently developed. Because of the compensatory collateral circulation, no permanent symptoms of ischaemia occur despite the partial resection of both palmar digital arteries. Histologically the percentage of relative osteoid volume of the operated limb was significantly higher than in the control limb.

Development of the navicular bone in foetal and young horses, including the arterial supply

A macroscopic, arteriographic and histological study of the development and the arterial anatomy of the navicular bone of 33 foetuses and 55 young horses is described. After 125 days of gestation the blood supply consists of two routes: one situated in the superficial layer of the fibrocartilage and the other similar to the blood supply of the navicular bone of the normal mature horse. After 270 days gestation, the blood vessels in the fibrocartilage gradually regressed and retracted until they have disappeared at six months after birth. At two months after birth the first macroscopic thinning of the fibrocartilage was noticed. From seven months to one year about 45 per cent of the navicular bones showed a slight thinning of the fibrocartilage. A positive correlation was found between radiographic abnormalities (ie enlargement of the nutrient foramina) and the frequency of thinning of the fibrocartilage. Radiographic abnormalities were first recognised 14 days after birth, whereas the arteriogram showed the first changes such as fewer or no arteries entering distally at the distal extremities at 10 weeks after birth. At four weeks after birth the first arterial wall changes were found, ie intimal thickening with or without splitting of the internal elastic membrane. From that age onward, the number of navicular bones with arterial wall changes gradually increased. Starting at five months after birth only 6 to 20 per cent of the arteries in the navicular bones without radiographic abnormalities showed arterial wall changes. However, the navicular bones with radiographic abnormalities showed arterial wall changes in 25 to 80 per cent of the arteries.

The arterial supply of the navicular bone in the normal horse

An arteriographic and histological study of the arterial blood supply of 35 navicular bones, from 19 adult horses with no clinical or radiographical signs of navicular disease, is described. The arteries enter the navicular bone from four directions: distal, proximal, medial, and lateral. The navicular bone can be divided into areas which receive arteries from one, two, or three directions, whereas the distal supply covers the largest part of the navicular bone. The distal arteries enter the navicular bone through the nutrient foramen which contains loose connective tissue, nutrient vessels and myelinated nerves. At least 77 per cent of the nutrient foramina contains synovial membrane. Twelve per cent of the arteries in the navicular bone show histological changes. Thickening of the intima with or without splitting of the internal elastic membrane and hyalinization, fibrosis and hypertrophy of the media were observed.

The arterial supply of the navicular bone in adult horses with navicular disease

A macroscopical, arteriographical and histological study was made of the arterial supply of the navicular bones of horses with clinical and/or radiographic signs of navicular disease. Based on the clinical and radiological findings the navicular bones of 40 Warmblood horses are divided into four different groups. In the pattern of the arteriogram obvious changes are noticed: an imbalance and a distal to proximal shift between the distal and proximal arterial supply occur, indicating a reduction of the distal blood supply with a compensatory reaction of the proximal, medial and lateral supply. The changes in the pattern of the arteriogram are histologically defined by arterio(lo) sclerosis and newly formed arteries. The presence of radiologically visible nutrient foramina is associated with a changed pattern in the arteriogram, increased bone remodelling and fibrosis. Ischaemia and increased pressure (hypertension and/or increased intra-articular pressure) are considered to be responsible for changes in form and number of radiologically visible nutrient foramina.