A 59-year-old woman presents with 6 months of bilateral hand and wrist joint pain. It is associated with morning stiffness that lasts at least 2 hours. She has had an involuntary weight loss of 4.4 kg (10 lb) in the past 3 months and low-grade fevers. Her past medical history is unremarkable, and she takes no medications. On physical examination, there is mild swelling, warmth, and tenderness at most of her metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints. Anti-cyclic citrullinated peptide (anti-CCP) antibodies and rheumatoid factor are positive, and a diagnosis of rheumatoid arthritis (RA) is confirmed. What other skeletal area is most likely to be affected by this patient’s disease?