In the picture, he sticks out his tongue and flashes the "hang loose" sign.
"I tore my ACL... but all is good. I opted for surgery so I can come back stronger than ever. Thank you to Dr Kvitne and his team at Kerlan-Jobe Surgery Center. I'll keep you updated as I heal and progress. Thanks for all the love and positivity," Efron, 31, tweeted.
The actor will next be seen in "Extremely Wicked, Shockingly Evil, and Vile", a biographical crime thriller on serial killer Ted Bundy.
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