He apparently broke his collarbone and some ribs in a 1992 bike accident. I don't know where it happened, Washington or Boston, and couldn't find anything from 1992 in the databases I searched. Maybe someone who has access to Boston papers from that time can search for info.
1992 Kerry broke ribs/collarbone in bike accident:
http://www.google.com/search?num=100&hl=en&lr=&ie=UTF-8&q=%22broke+his+collarbone%22+kerry