During a visit by Venezuelan President Hugo Chavez this week, Castro was shown vigorously shaking hands - with his right arm - and standing unassisted for several minutes at a time.
The 78-year-old has not started walking, however - at least not in public.
"His ability to recover and be back in public and doing his normal daily routine is testament to his good health," said Los Angeles-based Dr. Lawrence D. Dorr, who has led several medical missions to Cuba to provide hip and knee replacements.
The Cuban leader made headlines when
A few weeks later, Cuban television showed Castro sitting in a wheelchair, his arm in a sling, during a surprise visit by Chavez in early November.
The Cuban leader then surprised many when he suddenly stood up from his wheelchair during a state visit by Chinese President Hu Jintao on Nov. 23, a month after the fall. He leaned on a metal cane with an arm support while the Chinese and Cuban national anthems played.
This week, during a military ceremony attended by Chavez, Castro again popped up from his wheelchair, this time standing for several minutes with no support. Later Tuesday, he stood again after signing agreements with Chavez to deepen trade relations, bracing himself on a table at first, then standing tall.
After the fall, presidents and high-profile friends sent Castro get-well wishes. American director Oliver Stone sent the Cuban leader a letter saying he could play the movie role of "Superman's grandfather" for handling the operations and recovery so well.
In recent years, Castro's knees have seemed more wobbly, his step less steady. But given his age, he appears to be strong, and maintains a busy schedule that frequently includes all-night meetings with aides and visitors.
Requests to speak with Castro's doctors were not immediately granted. A Cuban official privately said he was pleased that Castro appeared to be recovering so well.
Dorr, the American doctor, guessed that Castro was already walking a bit in private, albeit stiffly. He said it could take several more months for the leader to be able to walk comfortably again.
"After that kind of injury, healing could take as long as six months," Dorr said.
The biggest problem after breaking a kneecap is being able to bend the knee comfortably again, according to the doctor.
"The longest recovery for (Castro) will be in activities like climbing stairs," Dorr said.
By Vanessa Arrington