It's not so much that it ruptures tendons, as they were some studies in dogs a while ago that showed that if you marinate canine achilles tendons in cipro some

It's not so much that it ruptures tendons, as they were some studies in dogs a while ago that showed that if you marinate canine achilles tendons in cipro some of the fibroblasts die off - which has the effect of diminishing the tendon structural integrity over time. The study was in achilles tendons, so you only ever heard about it being associated with achilles tendonitis. As a foundation of knowledge this was crap, but it made it into the med school curricula and textbooks. Which... well, when every med student in the country is taught "CIPRO = ACHILLES TENDONITIS" (and has it on their board exams that it can occur even years out), it's going to tend to create a certain bias for detecting and reporting. I mean, "Oh, my patient tore their achilles, and I treated them for a UTI three years ago. It must be the cipro!" I mean, no one would ever think that if they hadn't had it drilled into their heads in school. It's /probably/ bullshit... but there are better UTI meds, so most practitioners don't use it first-line regardless.