A 67-year-old woman presents with complaints of a tender, progressively flattening arch on the left foot. She has no pain in the right foot, and modifying her shoe gear to softer, more "comfortable" styles has not helped alleviate her symptoms. Her symptoms began approximately 6 weeks ago when she heard a popping sound in her foot. Which of the following is the most likely diagnosis?
1) A Lisfranc's fracture dislocation
2) A form of arthritis
3) A stress fracture of the fifth metatarsal
4) A ruptured tibialis posterior tendon
