Major pain in rt leg from knee to anckel

Patient: I`m 62 and have partial knee replacement 20 yr`s ago .today I started to walk in doors and my rt knee gave out and I slightly bent forward to my rt and caught my self from falling. instant pain from knee to ankle right down the middle of leg to ankle.then 8 hrs latter went to bed. 3 hours in to sleep I woke up in pain to rt calf pain.very sore to I sat in chair and put my foot slightly back behind me to where my toes where bent and heal was up in the air for pain to go away. what might this be.

Symptoms: Pain in rt calf to the point it woke me up from a deep sleep