The Big Bang Theory was able to hide Kaley Cuoco's horrible leg injury by giving Penny an odd but interesting new job in season 4. As the only original female character in the nerd-centric sitcom, Cuoco played her role in the CBS series for a total of 12 seasons, only missing a couple of episodes. This was despite being in a freak accident that resulted in her leg almost needing to be amputated. What made this worse was it happened while she and the rest of the cast were in the middle of production for one of the most important years of The Big Bang Theory.
Before becoming a successful pharmaceutical sales rep at Bernadette's company, Penny was an aspiring actress who moved to California from Nebraska. Everything that she did to earn money was primarily put towards her goal of eventually making big in Hollywood. Leonard and Sheldon being her neighbors helped in this regard because they can provide assistance whenever she was having financial issues. As she struggled to land acting gigs, however, she tried other jobs to fund her dream, which included being a Cheesecake Factory waitress. Thanks to it, The Big Bang Theory easily found a way to keep Cuoco working after her equestrian accident.
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Cuoco recalled how her horse was spooked during a riding lesson years ago, causing her to fall off of it. When it attempted to leap over her, it accidentally landed on her leg, resulting in her bones easily breaking. She almost lost her leg, but while the doctors were able to prevent that from happening, it forced her to miss two episodes of The Big Bang Theory season 4. At the time, the sitcom didn't make a big deal out of her absence. When she came back, however, CBS had to give Penny a new job to hide her injury - a bartender at The Cheesecake Factory.
In Jessica Radloff's The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series, series co-creator Chuck Lorre opened up about the matter and provided additional context. Not only was being a bartender help them hide the cast Cuoco was wearing, but it also allowed them to keep her off of her feet in longer sequences. Unfortunately, however, she wasn't good on the job, but they had to keep to her doing it to cater to her situation. Ultimately, Lorre credited Cuoco's real-life physical conditioning that allowed her to recover quickly.
Penny's time at The Cheesecake Factory was one of the most grueling periods of her life. Although she knew that it was just a temporary job as she worked to break into the acting industry, it still drained her. That being said, it also resulted in some of the best moments she's had with the rest of the Pasadena gang. When she became a bartender, however, The Big Bang Theory was able to fully highlight arguably one of her best qualities - being warm and empathetic. Multiple times, some of her friends would come and sit by the bar with their problems, and Penny would offer them advice.
The most memorable interactions Penny has had being a bartender was with Sheldon, however. After The Big Bang Theory debuted Missy but barely featured her, the socially-inept genius turned to his neighbor friend for some guidance whenever he had any problems. At one point, Penny decided to loosen up Sheldon by tricking him into drinking Long Island iced tea, resulting in the usually awkward character losing his inhibitions and just having fun.