Being a bit of an old f*)& (disturbing that I came across the attached paper as a postgrad!) gives me some early insights -- Engel's BioPsychoSocial model is still not widely followed in medicine -- especially, perhaps due to the way "the old language" is still used -- curiously enough though, the person who did much to try to push for it, George Engel, showed how it could be used in physical medicine, not just in mental health (the modern euphemism for "psychiatric services") -- but see the attached, where he applies it to myocardial infarction -- not always an easy paper to find!
interestingly, again, he refined his thoughts from an earlier 1951 paper of his