A case with atypical clinical course diagnosed as osteoarthritis, osteonecrosis, subchondral insufficiency fracture, or rapidly destructive coxopathy.

Osteonecrosis (ON), subchondral insufficiency fracture (SIF), and rapidly destructive coxopathy (RDC) are considered to be clinically different disorders despite exhibiting several overlapping features. We encountered an elderly female patient with an atypical clinical course who was radiographically diagnosed as having osteoarthritis (OA), ON, SIF, and/or RDC over a long-term follow-up. In this case, radiographic diagnosis was apparently affected by the timing of imaging evaluation and was challenging because of radiographic overlap and atypical disease progression. The disorders of OA, SIF, ON, and RDC might share a similar pathophysiology.