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A PI is hired to find a missing girl born without arms or legs. What he finds is a doctor taking people like the girl and grafting insect limbs on them and using them in a high end brothel. There are dogs, a yellow car and two of the doctors henchmen killing people.

This is only a partial match from my reading of some of the plot summaries out there but in case you've confused two books or the summaries are incomplete it is worth mentioning.

Dr. Adder (1984) by K.W. Jeter

Set in a future where the United States has largely broken down into reluctantly cooperating enclaves run by a wide variety of strongmen and warlords, with a veneer of government control that seems largely interested in controlling technology. Dr. Adder is an artist-surgeon, who modifies sexual organs of his patients to satisfy the weirdest of perversion; he is clearly depicted as a partly criminal, partly countercultural figure in a future Los Angeles.

This review gives a bit more information that seems at least like a partial match to the story you are looking for.

Dr. Adder is a brilliant surgeon in the horrible wreck of future Los Angeles, a messianic figure who earns his keep by re-sculpting the various teenage runaways of Orange County into the whores of Los Angeles - amputating and reconfiguring various body parts, wiping away their minds if necessary. This sickeningly sick character is an unrepentant woman-hater and homophobe; he is also the wildly popular and beloved symbol of freedom for both L.A. and the O.C. John Mox is a brillant corporate strategist and voice of moral authority in the drug-addled suburban sprawl of future Orange County, a messianic figure who keeps his power by out-maneuvering his fellow corporate shareholders and by addressing the denizens of Southern California during his daily televised hour of folksy, grandfatherly sermons. This sickeningly sick character is an unrepentant hater of all things associated with the body's desires; he is also the commander of a legion of bloodthirsty stormtroopers called The Moral Force. E Allen Limmit is a disaffected young man, fresh off the giant-mutated-chicken farm, once a soldier and later the manager of the farm's mutated-chicken-whore brothel. A somewhat bland and often irritable lad with vague ambitions to be somebody, do something, whatever, just getting the hell off of the farm. Limmit travels to The Interface - a terminally seedy street that functions as a meeting place for the degraded, drugged-up, fuck-happy denizens of L.A. & O.C. And he has brought a terrifyingly effective death-weapon with him - an instant-massacre machine. Woot! Guess who gets caught between a rock and a hard place.

I found this with the Google query "book" "doctor" "insect" "limbs" brothel.