Osteochondral lesions in distal tarsal joints of Icelandic horses reveal strong associations between hyaline and calcified cartilage abnormalities

Osteochondral lesions in the joints of the distal tarsal region of young Icelandic horses provide a natural model for the early stages of osteoarthritis (OA) in low-motion joints. We describe and characterise mineralised and non-mineralised osteochondral lesions in left distal tarsal region joint specimens from twenty-two 30 ±1 month-old Icelandic horses. Combinations of confocal scanning light microscopy, backscattered electron scanning electron microscopy (including, importantly, iodine staining) and three-dimensional microcomputed tomography were used on specimens obtained with guidance from clinical imaging. Lesion-types were described and classified into groups according to morphological features. Their locations in the hyaline articular cartilage (HAC), articular calcified cartilage (ACC), subchondral bone (SCB) and the joint margin tissues were identified and their frequency in the joints recorded. Associations and correlations between lesion-types were investigated for centrodistal joints only. In centrodistal joints the lesion-types HAC chondrocyte loss, HAC fibrillation, HAC central chondrocyte clusters, ACC arrest and ACC advance had significant associations and strong correlations. These lesion-types had moderate to high frequency in centrodistal joints but low frequencies in tarsometatarsal and talocalcaneal-centroquartal joints. Joint margin lesion-types had no significant associations with other lesion-types in the centrodistal joints but high frequency in both the centrodistal and tarsometatarsal joints. The frequency of SCB lesion-types in all joints was low. Hypermineralised infill phase lesion-types were detected. Our results emphasise close associations between HAC and ACC lesions in equine centrodistal joints and the importance of ACC lesions in the development of OA in low-motion compression-loaded equine joints

Timing of Vertical Head, Withers and Pelvis Movements Relative to the Footfalls in Different Equine Gaits and Breeds

Knowledge of vertical motion patterns of the axial body segments is a prerequisite for the development of algorithms used in automated detection of lameness. To date, the focus has been on the trot. This study investigates the temporal synchronization between vertical motion of the axial body segments with limb kinematic events in walk and trot across three popular types of sport horses (19 Warmbloods, 23 Iberians, 26 Icelandics) that are known to have different stride kinematics, and it presents novel data describing vertical motion of the axial body segments in tölting and pacing Icelandic horses. Inertial measurement unit sensors recorded limb kinematics, vertical motion of the axial body at all symmetrical gaits that the horse could perform (walk, trot, tölt, pace). Limb kinematics, vertical range of motion and lowest/highest positions of the head, withers and pelvis were calculated. For all gaits except walk and pace, lowest/highest positions of the pelvis and withers were found to be closely related temporally to midstance and start of suspension of the hind/fore quarter, respectively. There were differences in pelvic/withers range of motion between all breeds where the Icelandic horses showed the smallest motion, which may explain why lameness evaluation in this breed is challenging

Radiographic closure time of appendicular growth plates in the Icelandic horse

<p>Abstract</p> <p>Background</p> <p>The Icelandic horse is a pristine breed of horse which has a pure gene pool established more than a thousand years ago, and is approximately the same size as living and extinct wild breeds of horses. This study was performed to compare the length of the skeletal growth period of the "primitive" Icelandic horse relative to that reported for large horse breeds developed over the recent centuries. This information would provide practical guidance to owners and veterinarians as to when the skeleton is mature enough to commence training, and would be potentially interesting to those scientists investigating the pathogenesis of osteochondrosis. Interestingly, osteochondrosis has not been documented in the Icelandic horse.</p> <p>Methods</p> <p>The radiographic closure time of the appendicular growth plates was studied in 64 young Icelandic horses. The results were compared with previously published closure times reported for other, larger horse breeds. The radiographs were also examined for any signs of developmental orthopaedic diseases. In order to describe further the growth pattern of the Icelandic horse, the total serum alkaline phosphatase (ALP) activity was determined and the height at the withers was measured.</p> <p>Results</p> <p>Most of the examined growth plates were fully closed at the age of approximately three years. The horses reached adult height at this age; however ALP activity was still mildly increased over baseline values. The growth plates in the digits were the first to close at 8.1 to 8.5 months of age, and those in the regions of the distal radius (27.4 to 32.0 months), tuber olecrani (31.5 to 32.2 months), and the stifle (27.0 to 40.1 months) were the last to close. No horse was found to have osteochondrosis type lesions in the neighbouring joints of the evaluated growth plates.</p> <p>Conclusion</p> <p>The Icelandic horse appears to have similar radiographic closure times for most of the growth plates of its limbs as reported for large new breeds of horses developed during the past few centuries. It thus appears that different breeding goals and the intensity of breeding have not altered the length of the growth period in horses. Instead, it can be assumed that the pristine and relatively small Icelandic horse has a slower rate of growth. The appendicular skeleton of Icelandic horses has completed its bone growth in length at approximately 3 years of age, and therefore may be able to enter training at this time.</p

Bone spavin in Icelandic horses : aspects of predisposition, pathogenesis and prognosis

Bone spavin is an osteoarthrosis (OA) of the centrodistal tarsal joint (CD), the tarsometatarsal joint (TMT) and occasionally the proximal intertarsal joint (PIT). In order to detect and describe the earliest changes compatible with OA, specimens from the CD of young Icelandic horses were examined by high detail radiography (0-6 year, n = 111) and histology (0-4 year, n = 82). Histological chondronecrosis was seen in 33% of the joints, located both medially and laterally. Radiographic sclerosis of the subchondral bone was recorded in 60% of the specimens, most often medially. The medial subchondral bone sclerosis was not correlated with the chondronecrosis, but laterally the bone sclerosis was considered to be secondary to the cartilage lesions.In a field survey, 614 Icelandic horses in the age range of 6-12 year (mean age 7.9 year), and in use for riding were examined radiographically and clinically for OA in the distal tarsal joints, to estimate the prevalence and clinical relevance of the disease in the riding horse population, to evaluate the effect of potential (environmental and intrinsic) risk factors and to estimate the heritability ofthe disease. Radiographic signs ofOA in the distal tarsal joints (RS) were found in 30.3% of the horses and hindlimb lameness after flexion test ofthe tarsus was found in 32.4%. There was a significant correlation between the two diagnostic methods and 16.4% ofthe horses had both ofRS and lameness after flexion test. The survival culling rate ofthe horses in the five following years was significantly affected by RS and horses with the combination of RS and a positive flexion test had the poorest prognosis.The prevalence of RS was strongly correlated to age and tarsal angle (increased as the tarsal angle decreased). The birthplace was also significantly associated with RS, and considered to be an indirect genetic effect. The prevalence oflameness after flexion test was not influenced by age but a significant effect of sire was established. The prevalence was higher for horses that were broken to saddle late (6 year or older) and for horses that had not participated in a stud show. The heritability of age-at-onset of RS, reflecting the predisposition for OA, was estimated to be 0.33 and a similar figure was found for the heritability oflameness after flexion test.It was concluded that bone spavin is a common disease in Icelandic horses affecting their durability, although often subclinically manifested. The high prevalence of histological findings in the young horses (1-4 year) and radiographical findings in the 6-12 year old horses demonstrated a progressive nature of the disease although the progression may be slow. The initiation of the disease was unrelated to the use of the horses for riding and workload was not found to effect the development ofthe disease negatively. The mediumhigh heritability together with the association to the tarsal angle and the radiographic pattern of uneven distribution of load in the CD joint, strongly indicate that poor tarsal conformation or architecture of the distal tarsal joints is the main etiological factor ofthe disease