Calcified tissue structure in the distal condyle of the third metacarpal bone in young Thoroughbred horses

Abstract

Aims: To determine improvements in third metacarpal (Mc3) condylar microanatomy attributable to preconditioning exercise. To investigate developmental causes of Mc3 condylar fracture.Methods: Twelve Thoroughbred horses were raised at pasture; six received preconditioning exercise from 10 days. Calcein labels were administered 19 and 11 days prior to euthanasia at 18 months. Six horses also received 2 seasons of race-training and were euthanised at 3 years. Slices were taken from the distal Mc3 condyle in the frontal and dorsal-and palmar-oblique frontal planes, scanned with DXA and macerated (frontal slices) or embedded in PMMA (oblique slices).Articular calcified cartilage (ACC) and subchondral bone (SCB) in oblique slices were imaged using confocal scanning light microscopy and quantitative backscattered electron scanning electron microscopy. ACC and SCB in the palmar slice lateral parasagittal grooves were imaged using µCT and nanoindentation tested. Results: Characteristic spatial variations in ACC and SCB histomorphometric parameters were present, none of which was significantly related to preconditioning exercise. Thickened, aberrantly mineralised ACC was found in 13/24 parasagittal grooves in the palmar slices and on the sagittal ridge of 4/12 dorsal slices of 18-month-old horses. Deep to thickened ACC, SCB had an open marrow structure, having not adopted the buttress morphology of the normal SCB plate. SCB in 3-year-old horses had incorporated early ACC defects as notches in parasagittal grooves and a hyaline cartilage island in a sagittal ridge. ACC was less stiff and SCB more stiff in affected than unaffected parasagittal grooves. Chondroclastic resorption in the parasagittal groove may be retarded as early as 3-6 months, possibly due to localised inhibition of Dr Naomi Boxall has guided me through the PhD experience; as one of the several PhD students 5 Attribution I knew while an undergraduate at Massey University she gave me insight into coping with the varied challenges that postgraduate study entails. Naomi also helped correct my sometimes dubious spelling, grammar and punctuation while preparing documents for submission. Jen Swindlehurst provided a number of images of equine metacarpals from her own studies that I was kindly allowed to use in my presentations. Jen's work also (conveniently) supported my own, and it was nice to have a colleague who was so intimately familiar with the problem of condylar fracture. Several of Professor

The Bone Cartilage Interface and Osteoarthritis

“…That the layers represent differences in the degree of mineralization which occurred at successive time intervals seems intuitively obvious, but it is also proven by the visualisation of time given by tetracycline and calcein labels seen with CSLM imaging overlaid on to the BSE imagery (Fig. 1c) [8][9][10].…”

“…where the palmar/plantar condyles are loaded by the proximal sesamoid bones and it is likewise obvious in the relevant locations in human hip and knee OA (Figs. [8][9][10][11]. Continued heavy loading leads to continued infilling of potential fatty marrow space with new, immature, woven bone (Fig.…”

“…In any event, the HAC is lost locally and bone to bone contact established causing bone wear and eburnation (Figs. [8][9][10][11].…”

“…The depths of the holes show intense activities of resorption and the deposition of new tissues, including woven bone, dense fibrous connective tissue and newly formed cartilage (Figs. [8][9][10][11].…”

“…MUGES: 14 two-year-old TB fillies reared entirely at pasture: seven underwent training: the other 7 fillies were confined to large grass paddocks and not trained [5][6][7][8][9][10][11][12][13].…”