About four years ago my Achilles tendon started hurting and I was told it was Achilles tendinitis.
Literal
4 years [about-ほど] before [at-に] Achilles-tendon [subject-が] painful became Achilles-tendonitis [quotative-と] was-told.
アキレス腱 'Achilles tendon' uses the katakana rendering of Achilles + 腱 (tendon). アキレス腱炎 appends 炎 'inflammation' — a standard medical naming pattern. ~といわれました 'was told' — passive quotative, common for reporting a diagnosis.