Long incomplete longitudinal fractures of the third metacarpal and metatarsal bone in horses

Five horses with long incomplete longitudinal fractures of the third metacarpal bone and three horses with similar fractures of the third metatarsal bone were examined. In three of the metacarpal fractures a long incomplete fissure extended proximomedially, in association with the more common lateral condylar fracture of the third metacarpal bone, and in the other two cases the fracture originated from the medial aspect of the distal articular surface. In the three horses with fractures of the third metatarsal bone the fractures had a consistent spiral configuration.     

Nuclear scintigraphic evaluation of third metacarpal and metatarsal bone fractures in three horses

Nuclear scintigraphy was used to evaluate healing of third metacarpal bone (MC III) fractures in 2 horses (horses 1 and 2) and a third metatarsal bone fracture in 1 horse (horse 3) after stabilization of each fracture with 2 broad dynamic compression plates. In horse 1, the fracture had uniform uptake of 99mTc methylene diphosphonate on days 1, 15, and 30 after surgery. The fracture healed, and the horse was discharged from the clinic on day 52. In horse 2, a 6-cm photopenic region (ie, area of low radioactivity) was seen over the diaphysis of MC III on day 3. The region persisted and became more distinct by day 32. The diaphysis of MC III sequestered, and horse 2 was euthanatized on day 44. In horse 3, vascularity was seen bridging the fracture on day 5, with a 3-cm photopenic region over the dorsal diaphysis of the third metatarsal bone. By days 18 and 32, uptake of 99mTc methylene diphosphonate in the region had increased, indicating vascularization of the site. the fracture healed, and horse 3 was discharged from the clinic on day 47. Our findings indicated that serial nuclear scintigraphy can be used to evaluate fracture vascularization after surgery in horses.     

Effects of exercise on chondrocyte viability and subchondral bone sclerosis in the distal third metacarpal and metatarsal bones of young horses

The objective was to determine the effects of early exercise on the articular cartilage and subchondral bone at specific sites of the distal third metacarpal and metatarsal bones of 12 young Thoroughbred horses allowed free choice exercise at pasture. Six of the horses had additional controlled exercise 5 days per week from mean age of 21+/-20 days of age (range: 3-83 days) until 17.1 months of age. Confocal laser scanning microscopy was used to quantify viable and non-viable chondrocytes. Proteoglycan scoring and modified Mankin scoring was performed and subchondral bone mineral density measured by computed tomography. The number of viable chondrocytes was significantly greater in the conditioned group, which also had a higher Safranin O/Fast Green (SOFG) score than did the group which could exercise only at pasture. There was no difference in mean bone mineral density between groups, nor was there relationship between subchondral bone mineral density and chondrocyte viability. The apparent beneficial effects of early conditioning exercise may support the use of exercise to optimise development of articular cartilage in young individuals.     

Propagation of a dorsal cortical fracture of the third metacarpal bone in two horses

Seemingly, propagation of a dorsal cortical fracture in the third metacarpal bone developed after continued race performance in 2 horses. Historically, both horses had intermittent lameness that had responded to nonsteroidal anti-inflammatory drugs and brief rest periods. However, lameness in both horses had increased in severity. Radiography revealed a dorsal cortical fracture of the third metacarpal bone, with propagation of the fracture plane proximally. Fractures were incomplete and healed with stall rest in both horses.     

Changes in salivary and plasma cortisol levels in Purebred Arabian horses during race training session

Physical activity and stress both cause an increase in cortisol release ratio. The aim of this study was to evaluate the use of saliva samples for the determination of cortisol concentrations indicating the work‐load level in horses during race training. Twelve Purebred Arabian horses aged 3–5 years were studied during the routine training session. After the warm‐up, the horses galloped on the 800 m sand track at a speed of 12.8 m/s. Three saliva samples, and three blood samples were collected from each horse. Both types of samples were taken at rest, immediately after return from the track and after 30 min restitution. The concentrations of blood lactic acid (LA), and cortisol in saliva and plasma samples were measured and analyzed. Blood LA, plasma and salivary cortisol levels increased significantly after exercise (P < 0.05). Salivary cortisol concentration determined 30 min after the exercise correlated significantly with plasma cortisol level obtained immediately after exercise (P < 0.05) as well as measured 30 min after the end of exercise (P < 0.05). The determination of cortisol concentration in saliva samples taken from racehorses 30 min after the end of exercise can be recommended to use in field conditions to estimate the work‐load in racehorses.     

Gender differences in exercise - induced intravascular haemolysis during race training in thoroughbred horses

Exercise-induced intravascular haemolysis and “sport anemia” are widely reported in human sports medicine. It has been recognized also in horses, however, the clinical importance and the onset of this condition seem different than in human. In this study we investigated the episodes of intravascular haemolysis, indicated by the increase in plasma haemoglobin and the decrease in serum haptoglobin levels, after routine training sessions in race horses. Heart rate and changes in haematological parameters confirmed, that the exertion was relatively high. Intravascular haemolysis did not appear in stallions but was detected in mares after two training sessions. It has been determined that serum haptoglobin levels were higher in mares than in stallions before and after all training sessions. It is postulated that intravascular haemolysis induced by training is of limited clinical importance because it occurred only in mares which are better adapted due to higher haptoglobin level at rest, and it had no cumulative effect. Therefore gender differences should be taken into consideration in experiments with athletic horses.     

Computed tomographic diagnosis of incomplete palmar cortical (fatigue) fracture of the third metacarpal bone in two young adult endurance horses

Two young adult endurance horses were presented for investigation of sudden-onset forelimb lameness during competition. Clinical examination revealed a severe forelimb lameness and pain on palpation of the proximal palmar metacarpal area. Initial radiographic survey of the affected forelimb was unremarkable in both cases. A week of box rest resulted in only a mild improvement in the lameness. A second radiographic examination did not reveal any significant abnormalities. In both cases, scintigraphic examination was suggested, but was declined by the owner, and the lameness had significantly improved after local infiltration of 3 mL of anaesthetic solution in the proximal suspensory region. Radiographic and ultrasonographic examinations of the carpus and proximal suspensory region were unremarkable in Case 2. Case 1 had increased thickness of the medial lobe of the proximal aspect of the suspensory ligament. A computed tomographic examination was performed and an incomplete longitudinal (fatigue) fracture of the proximal third metacarpal bone was detected. After 8 months of box rest and rehabilitation, re-examination revealed resolution of the lameness in both cases. Advanced diagnostic imaging should be considered in young endurance horses with severe lameness during competition or training, in which radiographic and ultrasonographic examinations are unremarkable or do not explain the severity of the lameness. Computed tomography imaging is considered a useful diagnostic imaging technique to detect incomplete longitudinal palmar metacarpal cortical (fatigue) fractures due to its ability to provide excellent bone detail.     

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.     

Incomplete palmar fracture of the proximal extremity of the third metacarpal bone in horses: ten cases (1981-1986)

In 4 adult horses, simple, nondisplaced, incomplete fracture of the proximal extremity of the third metacarpal bone (MC3) was identified radiographically only on the dorsopalmar projection. Lameness was slight to moderate. Although nerve blocks of the foot and fetlock did not alter the lameness, high palmar regional nerve block improved the gait in 1 of the 2 horses on which it was performed. Pain on palpation or swollen distal accessory (inferior check) ligament, flexor tendons, and suspensory ligament were not found in any horse. The fracture was localized to the palmar surface of the proximal extremity of the MC3 on the basis of the intense uptake of radiopharmaceutical (99MTc-labeled sodium medronate) observed in that area during the soft tissue and delayed bone phases of a nuclear scintigraphic examination (nuclear scan) performed concurrently with radiography. Of 4 horses evaluated 6 months after the initial diagnosis, 3 had medullary sclerosis without radiographic evidence of fracture; results of follow-up nuclear scintigraphy performed in one of these horses at the same time were normal. Incomplete fracture also was suspected in another 6 adult horses with clinical lameness referable to the proximal extremity of the MC3. Although a fracture line could not be seen radiographically, trabecular hypertrophy and/or medullary sclerosis of the proximal extremity of the MC3 were detected on the dorsopalmar projection. Further, during nuclear scintigraphy, an intense uptake of the radiopharmaceutical was observed on the palmar aspect of the proximal extremity of the MC3 in all 6 horses.(ABSTRACT TRUNCATED AT 250 WORDS)     

Biochemical markers of bone activity in young standardbred horses during different types of exercise and training

Seven untrained Standardbred horses were used in a training programme of 6 weeks to evaluate the effects of exercise and training on bone metabolism. The horses were exercised on a treadmill according to a standardized exercise test (SET 1: six incremental steps, 5 min duration each; start 5 m/s, increase 1 m/s). SET 1 was followed by a training programme of 6 weeks. In alternating order: high-speed exercise (HSE): 15 min duration, start at VLa4, continuous increase in speed every 60 s by 0.3 m/s (14 incremental steps); low-speed exercise (LSE): constant velocity at VLa2.5, duration: approximately 60-90 min (total training programme: eight HSE and eight LSE sessions). SET 2 finished the training programme and a deconditioning period of 12 weeks followed. Blood samples for lactate, total plasma protein (TPP), osteocalcin, and ICTP (cross-linked C-telopeptide of type I collagen) were collected. ICTP increased during SET 1 and SET 2, whereas osteocalcin decreased to below resting concentration 24 h after SET 1. A rise in ICTP was observed during LSE 1 and LSE 8, which was followed by a drop 24 h after exercise. No changes in osteocalcin were noted during LSE 1, but 24 h after LSE 1 osteocalcin dropped to below pre-exercise levels. LSE 8 resulted in an increase in osteocalcin, followed by a drop 24 h after LSE 8. Osteocalcin and ICTP were not affected by HSE. Baseline osteocalcin levels dropped during the course of training. The acute response of biochemical bone markers indicates a direct influence of a single bout of exercise on bone metabolism.     

Comparison of two grafting methods in 4.0-mm drill defects in the third metacarpal bone of horses.

In 6 horses, bilateral metacarpal vertical series of three 4.0-mm unicortical drill holes were made. At random, one of each series of 3 holes was filled using a sternal 4.0-mm cancellous bone cylinder or a slurry of cancellous bone injected into the hole or left as an empty control. All horses had lateral metacarpal xeroradiographs at monthly intervals. Three horses (6 metacarpi) were examined post mortem after 4 months and 3 others after 6 months. Immediate through 4-month post-operative xeroradiographs demonstrated increased density in the holes with cancellous cylinders and no difference could be seen between the untreated controls and holes injected with slurry. From 5 months, no radiographic difference could be seen between the treatment groups. No consistent histological difference between treatment groups could be detected. In conclusion, no justification for clinical grafting of 4.0-mm unicortical dorsal metacarpal drill holes could be found.     

Musculoskeletal responses of 2-year-old Thoroughbred horses to early training. 6. Bone parameters in the third metacarpal and third metatarsal bones

AIM: To determine the effect of a known training regimen on the size and mineral content of the third metacarpal (Mc3) and third metatarsal (Mt3) bones of 2-year-old Thoroughbred horses trained on racetracks. METHODS: Mc3 and Mt3 of seven horses trained on grass and sand tracks were scanned at several sites using conventional quantitative and peripheral computed tomography (CT). Bone dimensions and density in the diaphysis and epiphysis were compared with those from seven untrained horses. Calcein label was injected in two clusters, during Weeks 9 and 12. The extent and rate of diaphyseal modelling was determined by confocal fluorescent microscopic examination of thin plane parallel sections of the mid-metacarpal region. RESULTS: Volumetric bone mineral density (BMDv) of the epiphysis was markedly higher and of the diaphysis was slightly higher in trained compared with untrained horses, but greater bone size in the trained horses had the greatest effect on an index of bone strength. Active osteons, defined as Haversian systems containing calcein label, were fewer, of smaller diameter at the time of calcein injection, and had a greater bone apposition rate in trained than in untrained horses. CONCLUSIONS: Conventional training of 2-year-old Thoroughbred racehorses over a 13-week period had a significant effect on bone size, density and strength index when compared to untrained horses. CLINICAL RELEVANCE: Bone responded rapidly to early training. The data provide reference values and sites for use in longitudinal studies of commercial training regimens.     

Musculoskeletal responses of 2-year-old Thoroughbred horses to early training. 6. Bone parameters in the third metacarpal and third metatarsal bones

AIM: To determine the effect of a known training regimen on the size and mineral content of the third metacarpal (Mc3) and third metatarsal (Mt3) bones of 2-year-old Thoroughbred horses trained on racetracks.

METHODS: Mc3 and Mt3 of seven horses trained on grass and sand tracks were scanned at several sites using conventional quantitative and peripheral computed tomography (CT). Bone dimensions and density in the diaphysis and epiphysis were compared with those from seven untrained horses. Calcein label was injected in two clusters, during Weeks 9 and 12. The extent and rate of diaphyseal modelling was determined by confocal fl uorescent microscopic examination of thin plane parallel sections of the mid-metacarpal region.

RESULTS: Volumetric bone mineral density (BMDv) of the epiphysis was markedly higher and of the diaphysis was slightly higher in trained compared with untrained horses, but greater bone size in the trained horses had the greatest effect on an index of bone strength. Active osteons, defined as Haversian systems containing calcein label, were fewer, of smaller diameter at the time of calcein injection, and had a greater bone apposition rate in trained than in untrained horses.

CONCLUSIONS: Conventional training of 2-year-old Thoroughbred racehorses over a 13-week period had a significant effect on bone size, density and strength index when compared to untrained horses.

CLINICAL RELEVANCE: Bone responded rapidly to early training. The data provide reference values and sites for use in longitudinal studies of commercial training regimens.     

Stress reactions and stress fractures of the proximal palmar aspect of the third metacarpal bone in horses: 58 cases (1980-1990).

The case records, radiographs, and nuclear bone scans of 58 horses with stress reactions or stress fractures of the proximal palmar aspect of the third metacarpal bone (MC3) were reviewed. There were 47 Standardbreds, 4 Quarter Horses, 3 Thoroughbreds, 2 Arabians, 1 Oldenburg, and 1 Pony of America. Fifty-six of the horses were racehorses or performance horses. The mean and median ages of affected horses were 4 and 3 years, respectively. Lameness ranged from mild to severe. Physical findings were usually subtle and included signs of pain on deep palpation of the proximal palmar aspect of MC3 and slight effusion of the middle carpal joint in some cases. Lameness was commonly improved by high palmar and palmar metacarpal nerve blocks or anesthesia of the middle carpal joint. Fifty-three horses had higher than normal radiopharmaceutical uptake in the proximal palmar aspect of MC3 in the left or right limb. The other 5 horses had higher than normal radiopharmaceutical uptake bilaterally. Fifty-six of the 63 limbs with abnormal bone scans also had abnormal radiographs. Treatment consisted of a variable period of rest (1 to 6 months). Healing was best assessed by follow-up bone scans. Of the 45 horses for which follow-up information was adequate, 29 (64%) returned to their previous level of performance.     

Advanced imaging of an incomplete fracture and exostosis of the third metacarpal bone in a young Warmblood horse

A 5-year-old Hanoverian gelding with acute moderate right forelimb lameness underwent nuclear scintigraphy, which identified marked increase in radiopharmaceutical uptake of the proximomedial aspect of the right metacarpus. Ultrasonography and radiography identified sclerosis and exostosis of the proximomedial aspect of the metacarpal bone III in-between the suspensory ligament and the second metacarpal bone, and presence of a suspected fracture. The owner requested euthanasia of the gelding, and post-mortem computed tomography and magnetic resonance imaging identified marked bone sclerosis and thickening of the palmar cortex of the metacarpal III (McIII), presence of an incomplete fracture in the palmar cortex of McIII and expansive exostosis from McIII extending in a palmar direction between the suspensory ligament and the second metacarpal bone. Histopathological examination confirmed the imaging findings of sclerosis and led to final diagnosis of a fracture of the palmar cortex of the McIII associated with an exostosis encroaching the medial aspect of the suspensory ligament. No abnormalities were present in the suspensory ligament or metacarpal bone II (McII).     

Effects of age and diet on the development of mechanical strength by the third metacarpal and metatarsal bones of young horses

The application of transmission ultrasonics to the equine cannon holds promise as a method of monitoring metacarpal and metatarsal development, quality and integrity under a variety of experimental and field conditions. The validity of relating the velocities of sound pulses transmitted through the cannon to the mechanical breaking strengths of these bones was tested in two studies. Breaking strengths calculated from the sound velocities through sections of the metacarpal bones from 14 yearling ponies and 12 yearling horses were highly correlated with the mechanical breaking strengths of those sections (r = .907 and .927, respectively; P less than .01). Sound velocities through the cannons of the horses before sacrifice ranged from 2,453 to 3,130 m/s and were correlated with their mechanically determined breaking strengths (193 to 262 X 10(6) N/M2; r = .673; P less than .01). The correlation coefficient increased to .912 when the sound velocities were adjusted for the sound-delaying effects of the overlying soft tissues. In a third study, 13 horses were weaned at 2 to 4 mo of age and were fed diets providing either 100 or 130% of National Research Council (NRC) energy and protein recommendations. Metacarpal and metatarsal development was monitored monthly for 15 mo via transmission ultrasonics. Sound velocities, breaking strengths calculated from velocities adjusted for estimated soft tissue cover, measured bone mediolateral diameters and cannon diameters minus estimated soft tissue increased as quadratic functions of chronologic age (r greater than .840; P less than .0001). None of these variables was significantly affected by diet, leg or sex. These studies have demonstrated that the use of transmission ultrasonics to estimate and monitor metacarpal and metatarsal breaking strengths in the live horse is reliable, reproducible, simple, accurate and valid. They also suggest that NRC energy and protein recommendations meet the requirements for maximum bone growth and development in well-managed young equines.     

Effects of treadmill exercise on cortical bone in the third metacarpus of young horses.

The effects of exercise and relative inactivity on cortical bone were compared in young horses. Two groups were used; one was given a 14-week programme of exercise (n = 6) and the other kept as unexercised controls (n = 6). The first nine weeks of exercise involved trotting and cantering (2 to 4 km d-1 at speeds up to 12 m s-1) on a treadmill set at an incline of 3 degrees. Over the next five weeks the horses were trained at near maximal speeds (that is, up to 14.5 m s-1) with no incline of the treadmill. At the end of the programme marked differences in cortical porosity and distribution of subperiosteal osteogenesis at the mid-shaft of the third metacarpal bone were found between the groups. Histomorphometrical examination of the dorsal cortex showed minimal bone remodelling in the exercised horses, but extensive modelling as evidenced by the large amount of subperiosteal bone formation. In contrast, the unexercised horses had significantly more bone remodelling and less formation of subperiosteal bone. The histomorphometric and microradiographic findings provided an explanation for changes in the non-invasive bone measurements that occurred during training. Bone mineral content of the mid-metacarpus was found to increase more in the exercised than the unexercised horses despite a lower overall growth in bodyweight. In those horses that completed the full training programme, ultrasound speed increased significantly by the end of the training programme. It remained unchanged in the horse that did not complete the full exercise programme and decreased slightly in the unexercised horses. The difference in ultrasound speed between the groups was considered to reflect differences in intracortical bone porosity, endosteal bone formation and alterations in skin thickness. The stiffness of cortical bone increased significantly in the exercised horses but remained unaltered in the unexercised horses.