Condividete mi raccomando! Pubblichiamo un breve estratto relativo allintroduzione in Nuova Zelanda a livello nazionale della tecnica Pennhip a far data dal 2014. Ai veterinari di quel paese(per quello che conta) il mio personale plauso per esser riusciti per primi a superare i problemi che nel resto del mondo fanno prevalere gli interessi al benessere animale a dispetto dellevidenza scientifica oggi disponibile, Auspichiamo che prima o poi anche da noi qualcuno si metterà una mano sulla coscienza! The science behind hip laxity and the distraction index (PennHIP®) From January 2014 the NZVA will no longer be offering a hip-extended scoring system. Instead the NZVA will be recommending that NZ dog breeders use the PennHIP® method to determine hip status for breeding purposes. Background to the change in policy Canine hip dysplasia (CHD) is characterised by the early onset of arthritis induced by abnormal development of the hip, which occurs during adolescence. Lack stability of the hip leads to the hip moving “in and out of joint” as the dog walks. This leads to wear of the cartilage that we recognise as osteoarthritis (which is progressive and cannot be reversed). CHD is a multifactorial trait, which is genetically determined but influenced by environmental factors. We do not currently have a genetic test for CHD so in order to select the best dogs for breeding, we have to recognise the features of CHD clinically or on x-rays. Features of CHD on x-ray include the presence of arthritis and how “loose” the hips appear. Laxity (looseness) of the hip was identified as an important factor in the development of CHD in the 1960’s. Clinically, veterinarians recognise loose hips by using x-rays, or feeling the laxity of the hips under anaesthesia. Detecting signs of arthritis on x-ray is relatively straightforward in older dogs. But the ability to detect loose hips on standard x-rays is influenced by positioning, depth of sedation/anaesthesia and the way the dog’s hips are held. The extent to which arthritis is present is highly age dependant. In other countries, dogs have to be greater than 24 months of age for accreditation. But in NZ we allow dogs as young as 12 month of age to be scored. At this age the extent of arthritis can be underestimated and the diagnosis relies on detection of a “loose” hip. Unfortunately the position of the standard x-ray (legs stretched out behind) is the exact position in which the hip joint is at it’s tightest. Why does the traditional hip-extended x-ray method under-estimate the presence of hip laxity? The hip joint is enclosed within a capsule, and the ball is held within the socket by a strong ligament. However the most important stabilisers of the hip joint are the surrounding muscles, which pull the ‘ball’ up into the ‘socket’ and the surface tension effect of the close-fitting ball and socket stuck together by a thin film of joint fluid. The joint capsule and femoral head ligament have to be loose enough to allow motion. Only at the extremes of motion (e.g. with the legs stretched out behind) are the capsule and ligament tight. In the stretched out position the capsule and ligament “wind-up” and help force the ball deeper into the socket. This means that the positioning the NZVA (or BVA/AVA/OFA) scheme uses is actually the tightest position of the hip and can underestimate the extent of laxity. As laxity is key to diagnosing CHD in dogs at only 12 months of age, our current scheme can yield false negatives, dogs that actually have the genes for CHD but are given low scores. Andrew Worth, Convenor of the NZVA Hip and Elbow Dysplasia Schemes. 1 Worth AJ, Bridges, JP, Jones, G. Trends in the phenotypic hip status of selected breeds of dog as measured by the New Zealand Veterinary Association Hip Dysplasia scheme (1990-2008). New Zealand Veterinary Journal, 59: 2, 67-74, 2011 2 Worth AJ Bridges JP, Jones G. Reduction in the incidence of elbow dysplasia in four breeds of dog as measured by the New Zealand Veterinary Association scoring scheme. New Zealand Veterinary Journal, Volume 58(4), 190-195, 2010 3 Worth, Laven, Erceg. An assessment of the agreement between the New Zealand Veterinary Association Hip Dysplasia Scoring System and the PennHIP Distraction Index in German Shepherd dogs. New Zealand Veterinary Journal, 57 (6), 338-345 December 2009
Posted on: Wed, 22 Oct 2014 07:09:04 +0000
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