In 1931 the Rottweiler was officially recognised by the American Kennel Club. In 1936, Rottweilers were exhibited in Britain at Crufts. In 2017, the American Kennel Club ranked the Rottweiler as the eighth-most popular pure-breed in the United States. The color and markings of a Rottweiler are very distinctive. A Rottweiler is always, by any breed club standards, black with well-defined mahogany or rust-colored markings that do not take up more than ten percent of the dog's body color. All Rottweilers standard to AKC specifications have one mahogany dot above each eye on the inner brow ridge, on the cheeks, one strip on each side of the snout; cheek markings do not cross over the bridge of the nose, the top of the nose should remain black. For this reason the various Rottweiler breed clubs have had x-ray testing regimens in place for many years. Osteochondritis dissecans, a condition affecting the shoulder joints, can also be a problem due to the breed's rapid growth rate.