the.com/knees

The body's most complicated hinge, betraying every athlete who ever trusted it.

means The joints in the middle of your legs that bend, connecting thigh to shin and letting you walk, kneel, and crouch.

from From Old English 'cneow,' a word with deep Germanic roots and likely a far cousin to Latin 'genu' and Greek 'gony' — all tracing back to the same ancient Proto-Indo-European root for 'knee.' The silent 'k' we still spell but no longer say is a fossil of a time when English speakers actually pronounced that opening consonant, before centuries of lazy mouths quietly dropped it.

largest joint: The knee is the biggest joint in the body
no muscle: It moves entirely via tendons and ligaments
late bloomer: Kneecaps don't fully harden until age three
weak link: ACL tears end more careers than any injury
weight bearing: Carries forces several times your body weight

for instance

knee of the curve — skateboarding trick where rider bends knees at extreme angle, popularized in vert skating since 1970s

housemaid's knee — bursitis condition affecting people who kneel frequently, documented medical condition since victorian era

knee replacement surgery — orthopedic procedure performed over 1 million times annually in the us alone