Trauma had previously been found to be associated with PsA in smaller studies,, which in turn had led to the idea of a «deep Koebner» phenomenon playing a role in PsA, mirroring the superficial Koebner phenomenon seen in skin psoriasis.5 Koebner found that when an area of skin in
people with psoriasis became traumatised following injury, a psoriatic lesion often appeared in the same location.