A 55-year-old woman with a 10-year history of rheumatoid arthritis presents with progressive bilateral hand deformities. On examination, she has swan-neck deformity of the fingers and hyperextension at the proximal interphalangeal (PIP) joint with flexion at the distal interphalangeal (DIP) joint. She also has a positive rheumatoid factor and elevated CRP. Her current regimen includes methotrexate and a TNF-α inhibitor. Which of the following best explains the pathomechanical basis of swan-neck deformity in rheumatoid arthritis?