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Enigma of enostosis-like lesions in the horse
  1. Sue Dyson, MA, VetMB, PhD, DEO, FRCVS
  1. Centre for Equine Studies, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB8 7UU
  1. e-mail: sue.dyson{at}

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ENOSTOSIS-like lesions (ELLs) are an uncommon finding in the long bones of horses and their role in causing lameness remains challenging to determine. They have a characteristic radiological appearance: a focal area of increased opacity close to the nutrient foramen and contiguous with the endosteum, but with no cortical or periosteal reaction. This coincides with focal increased radiopharmaceutical uptake (IRU) of variable intensity. However, in many horses these lesions appear to be incidental abnormalities and were considered to be unrelated to lameness in 29 per cent (O'Neill and Bladon 2011), 50 per cent (Bassage and Ross 1998), 51 per cent (Ahern and others 2010) and 67 per cent (Ramzan 2002) of 21, 10, 79 and 12 horses respectively.

There are remarkably few horses in which pain causing lameness has been documented to arise from the region where an ELL has been identified. This in part reflects the nature of practices to which horses have been referred for scintigraphic assessment and not necessarily clinical investigation, but also the anatomical location of some ELLs in the humerus, radius, tibia and femur, regions where nerve blocking cannot be performed. Diagnosis must then be made by exclusion, but this should include perineural analgesia of the median and ulnar nerves in the forelimbs and tibial and fibular nerves in the hindlimbs, which has rarely been performed in the horses documented to date.

The presence of focal areas of IRU in several bones within …

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