Answer:

trickknee

AnswerCrossword Clue
TRICKKNEEJoint where you never know what to expect?
TRICKKNEETroublesome leg joint
TRICKKNEEQuirky joint
TRICKKNEEMagician's joint?
TRICKKNEEAthlete's problem
TRICKKNEEIt may require joint checking
TRICKKNEEUnpredictable joint
TRICKKNEEIt may require joint checking?
TRICKKNEEAffliction that may be helpful in a proposal?
TRICKKNEEEx-athlete's ailment, perhaps