The Collaborative International Dictionary of English v.0.48:

Humpbacked \Hump"backed`\, a.
   Having a humped back.
   [1913 Webster]

WordNet (r) 3.0 (2006):

humpbacked
    adj 1: characteristic of or suffering from kyphosis, an
           abnormality of the vertebral column [syn: crookback,
           crookbacked, humped, humpbacked, hunchbacked,
           gibbous, kyphotic]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "humpbacked":
   arched, arciform, arclike, arcual, bandy, bowed, bowlike,
   bunchbacked, camelback, concave, convex, crookbacked, embowed,
   gibbose, gibbous, humped, humpy, hunchbacked, hunched, hunchy,
   kyphotic, oxbow, vaulted