From Longman Dictionary of Contemporary Englishknee capˈknee cap noun [countable] 
HBHthe bone at the front of your knee
HBHthe bone at the front of your kneeExamples from the Corpus
knee cap• Indiana was without Patterson, its leading scorer and rebounder, because of a slight dislocation of his left knee cap.• Jokes about the subject suggest the punch-line might be followed by the odd shattered knee cap. 