van der Zaag Ellen J, Weerts Erik A W S, van den Belt Antoon J M, Back Willem
Veterinary Clinic De Delta, Foppenpolder 1, NL-3155 EA, Maasland, The Netherlands.
Department of Pathobiology, Division Pathology, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 1, NL-3584 CL, Utrecht, The Netherlands.
BMC Vet Res. 2016 Apr 9;12:74. doi: 10.1186/s12917-016-0698-4.
Navicular bone partition is a rare condition reported in horses, which is during the evaluation of a lameness or prepurchase examination often misinterpreted for a parasagittal fracture. In this report, the clinicopathological findings of three cases of navicular bone partition are evaluated. The possible pathomechanisms underlying the condition are hypothesised, focusing on a potential origin of foetal vascular disturbance. This study is furthermore aiming at a clearer and earlier recognition of navicular bone partition, since this condition would finally predispose for a clinical lameness with a poor prognosis.
Case 1 was a 10-year-old Belgian Warmblood gelding with a Grade 3/5 chronic, recurrent left-forelimb lameness that had persisted for 4 months. Perineural palmar digital nerve block of the distal foot abolished the lameness. Radiographic examination revealed a bipartite navicular bone in the left forelimb. Unfortunately, the animal was lost to follow-up. Case 2 was a 7-year-old Quarter Horse stallion with a Grade 3/5 recurrent right forelimb lameness that had persisted for 2 years. The lameness switched to the contralateral left forelimb with a palmar digital nerve block. Radiographic examination identified a tripartite navicular bone in both forelimbs. Pathological examination additionally revealed chronic degenerative changes of the cartilage and subchondral bone with marked cystic changes. Case 3 was a 5-year-old Dutch Warmblood gelding with a Grade 3/5 recurrent left hindlimb lameness that had persisted for 6 months. Owing to the uncooperative behaviour of the horse, only a combined peroneal and tibial nerve block could be performed, which abolished the lameness. Radiographic examination revealed a bipartite navicular bone in the left hindlimb. Pathological examination showed a navicular bipartition in the left hindlimb, with microscopic changes comparable to those evident in Case 2; additionally, cartilage indentations were also found in the navicular bones of the right front- and hindlimb at a similar location as the partition site in the left hindlimb.
It is speculated that a navicular bone partition has a congenital origin and is caused by vascular disturbance during foetal development. This may lead to aberrant endochondral ossification or the formation of multiple ossification centres resulting in navicular bone partitioning. In the adult horse, chronic repetitive biomechanical challenges at the partition sites may induce local degenerative changes with subchondral cyst formation and thus would cause a gradually developing chronic lameness with a poor prognosis.
舟状骨分隔是马匹中一种罕见的病症，在评估跛行或购买前检查时，常被误诊为矢状面骨折。在本报告中，对三例舟状骨分隔病例的临床病理结果进行了评估。推测了该病症潜在的发病机制，重点关注胎儿血管紊乱的潜在起源。此外，本研究旨在更清晰、更早地识别舟状骨分隔，因为这种病症最终会导致临床跛行且预后不良。
病例1是一匹10岁的比利时温血 gelding，左前肢慢性复发性跛行，跛行程度为3/5级，持续了4个月。对足部远端进行掌侧指神经阻滞可消除跛行。X线检查显示左前肢舟状骨二分。不幸的是，该动物失访。病例2是一匹7岁的夸特马种公马，右前肢复发性跛行，跛行程度为3/5级，持续了2年。掌侧指神经阻滞使跛行转移至对侧左前肢。X线检查发现双前肢舟状骨三分。病理检查还显示软骨和软骨下骨有慢性退行性改变，并伴有明显的囊性改变。病例3是一匹5岁的荷兰温血 gelding，左后肢复发性跛行，跛行程度为3/5级，持续了6个月。由于马匹不配合，仅进行了腓总神经和胫神经联合阻滞，这消除了跛行。X线检查显示左后肢舟状骨二分。病理检查显示左后肢舟状骨二分，微观变化与病例2相似；此外，在右前肢和后肢的舟状骨中也发现了与左后肢分隔部位相似位置的软骨凹陷。
推测舟状骨分隔有先天性起源，是由胎儿发育过程中的血管紊乱引起的。这可能导致异常的软骨内成骨或多个骨化中心的形成，从而导致舟状骨分隔。在成年马中，分隔部位的慢性重复性生物力学挑战可能会诱发局部退行性改变并伴有软骨下囊肿形成，进而导致逐渐发展的慢性跛行且预后不良。
