1. Having the spine damaged
   "a broken-backed book"; "a broken-backed old horse"
    
2. (of a horse) having bones of the back united by a bony growth
   "The broken-backed horse was retired from racing"
    
3. (of a ship) so weakened as to sag at each end
   "The broken-backed hull of the old ship needed extensive repairs";
   - hogged

See also: bulging, convex, damaged, unfit