Bilateral stress-related patellar fractures after total knee arthroplasty associated with traditional Japanese dance: A case report with biomechanical analysis

Background Patellar fracture after total knee arthroplasty (TKA) is uncommon and usually associated with trauma or surgical factors. Stress-related fractures due to postoperative activity are rarely reported. Case presentation An 81-year-old female professional instructor of traditional Japanese dance developed bilateral non-traumatic inferior pole patellar fractures after staged posterior-stabilized TKA with patellar resurfacing. Postoperative alignment was satisfactory, and she resumed dance training three months after surgery. Radiographs at six and nine months revealed bilateral patellar fractures without trauma. Conservative treatment with activity cessation and teriparatide achieved union within six months. After fracture healing, motion analysis performed on the patient herself demonstrated substantially higher external knee flexion moments during dance movements than during normal gait, with peak values up to 1.06 Nm/kg compared with 0.25 Nm/kg. Conclusions Traditional Japanese dance movements involving sustained quadriceps activity may increase patellofemoral loading and contribute to stress-related patellar fractures after TKA.