The Collaborative International Dictionary of English v.0.48:

Subluxation \Sub`lux*a"tion\, n. [Pref. sub + luxation: cf. F.
   subluxation.] (Surg.)
   An incomplete or partial dislocation.
   [1913 Webster]

WordNet (r) 3.0 (2006):

subluxation
    n 1: partial displacement of a joint or organ