EQUINE VETERINARY EDUCATION / AE / july 2022
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TABLE 1: Summary of the results Suture
Internasalis Internasalis Internasalis Internasalis Internasalis Nasofrontalis
Nasofrontalis (MMA)
Nasofrontalis
Nasofrontalis (MMA)
Nasofrontalis
Age Cell density Cell types 1 d High
1 d High
2 y Moderate– high
Fibrocytes Fibroblasts Some osteoblasts
Fibrocytes Fibroblasts Some osteoblasts
Fibrocytes Fibroblasts Some osteoblasts
6 y Moderate Predominantly Fibrocytes & fibroblasts
9 y Moderate Predominantly fibrocytes & fibroblasts
1 d High 1 d High
2 y Moderate– high
6 y Unable to evaluate
Fibrocytes Fibroblasts Some osteoblasts
Predominantly fibrocytes & fibroblasts
Fibrocytes Fibroblasts Some osteoblasts
9 y Moderate Predominantly fibrocytes & fibroblasts
Maxillolacrimalis 1 d High
Maxillolacrimalis 1 d Moderate– high
Maxillolacrimalis 5 d High
Maxillolacrimalis 2 y Moderate– high
Fibrocytes Fibroblasts Some osteoblasts
Predominantly fibrocytes & fibroblasts
Predominantly fibrocytes & fibroblasts
Predominantly fibrocytes & fibroblasts
Maxillolacrimalis 9 y Moderate Predominantly fibrocytes & fibroblasts
d, day; y, years.
fibrocytes (Fig 7). The bony interface is identified in the foals and 2-year-old horse by woven bone and medullary cavities; in the 6- and 9-year-old horses, this is replaced by cancellous bone with osteons (Figs 2b, 6 and 8).
Discussion
The aim of the present study was to histologically examine the internasal, nasofrontal and maxillolacrimal sutures in horses aged 1 day to 9 years and identify key histological features of facial sutures in horses of different ages. The sutures became increasing difficult to identify macroscopically on the skull – the Sutura maxillolacrimalis was not identifiable in the 6-year-old horse – however, all of the sutures examined were clearly visible on histology and contained connective tissue and blood vessels. There is
limited information as to proposed ages of fusion in facial sutures in horses; Butler et al. (2017) suggest that the nasofrontal suture is obliterated at 1 year of age, the left and right nasal bones (the internasal suture) do not fuse, and the maxillolacrimal suture is not specifically discussed, although the premaxilla suture is listed as being obliterated in the fourth year of life. However, as the authors are unaware of any previous studies examining facial suture patency in horses, these fusion times could be based on radiographic and gross visibility. The results of this study suggest that the patency of the facial sutures could be much longer than was previously thought and in fact, similar to that of the facial sutures in humans, which do not fuse until the seventh or eighth decade of life (Opperman 2000; Rice 2008). As the horse’s age increased, a progressive maturation of all three sutures was observed. This is evident through a
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Vascularisation Interdigitation High
High High
Moderate– high
Moderate– high
High
Moderate– high
High
Unable to evaluate Moderate– high
Moderate– high
High High High High
Moderate– high
Median width/lm
Moderate 260 Moderate 500 Moderate 560 Moderate 320 Tight
Moderate– tight
Unable to evaluate
Tight Tight Tight
Unable to evaluate
Tight
Unable to evaluate
Tight Tight 200 200 200 200 200 140 280 300 240 100 160
Widest point/lm
480 700 940 800 500 500 500 400 240 560 1300 800 420 400 360
Narrowest point/lm
60 420 340 160 80 100 100 50 100 60 80 200 180 40 60
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