Variation in the Quantity of Elastic Fibres with Degeneration in Canine Cranial Cruciate Ligaments from Labrador Retrievers.

Objectives This study aims to quantify numbers of elastic fibres in cranial cruciate ligaments from a dog breed at high risk of cranial cruciate ligament disease. Methods Macroscopically normal cranial cruciate ligaments were harvested from six Labrador retrievers. Sequential histological sections were assessed for extracellular matrix degeneration (haematoxylin and eosin stain) and elastic fibre staining (Miller's stain). Elastic fibres were semi-quantified using previously published scoring systems. Each section was scored twice by two observers. Results Increased numbers of elastic fibres were seen with increasing cranial cruciate ligament degeneration (p = 0.001). Labrador retriever cranial cruciate ligaments had lower elastic fibre staining when compared with previous published findings in the racing greyhound. Clinical Significance The cranial cruciate ligaments from a dog breed at high risk of cranial cruciate ligament disease vary in the quantity of elastic fibres in association with ligament degeneration. Breed variation in the quantity of elastic fibres may reflect differing risk of cranial cruciate ligament disease.

The organisation of elastin and fibrillins 1 and 2 in the cruciate ligament complex.

Although elastin fibres and oxytalan fibres (bundles of microfibrils) have important mechanical, biochemical and cell regulatory functions, neither their distribution nor their function in cruciate ligaments has been investigated. Twelve pairs of cruciate ligaments (CLs) were obtained from 10 adult dogs with no evidence of knee osteoarthritis. Elastic fibres were identified using Verhoeff's and Miller's staining. Fibrillins 1 and 2 were immunolocalised and imaged using confocal laser scanning microscopy. Hydrated, unfixed tissue was analysed using Nomarski differential interference microscopy (NDIC), allowing structural and mechanical analysis. Microfibrils and elastin fibres were widespread in both CLs, predominantly within ligament fascicles, parallel to collagen bundles. Although elastin fibres were sparse, microfibrils were abundant. We described abundant fibres composed of both fibrillin 1 and fibrillin 2, which had a similar pattern of distribution to oxytalan fibres. NDIC demonstrated complex interfascicular and interbundle anatomy in the CL complex. The distribution of elastin fibres is suggestive of a mechanical role in bundle reorganisation following ligament deformation. The presence and location of fibrillin 2 in oxytalan fibres in ligament differs from the solely fibrillin 1-containing oxytalan fibres previously described in tendon and may demonstrate a fundamental difference between ligament and tendon.