has part has part characteristic of inheres in has modifier Abnormal patella morphology Patellar subluxation 2009-09-17T11:46:41Z HP:0010499 UMLS:C0857276 The kneecap normally is located within the groove termed trochlea on the distal femur and can slide up and down in it. Patellar subluxation refers to an unstable kneecap that does not slide centrally within its groove, i.e., a partial dislocation of the patella. Subluxation of patella Partial knee cap dislocation abnormal partially dislocated patella