Periprosthetic knee fracture (PPKF) following total knee arthroplasty (TKA) can be difficult to treat. A PPKF can be treated both operatively and nonoperatively, and the treatment varies between fracture sites. This study aimed to assess the risk of reoperation according to the fracture site and treatment of the PPKF.This study is a nationwide cohort study using register data from 1997 to 2022. Cruciate-retaining or posterior-stabilized primary TKA were identified from the Danish Knee Arthroplasty Register. Subsequent PPKFs, fracture treatments, and later reoperations were identified through the International Classification of Diseases, tenth edition (ICD-10) diagnosis and procedure codes in the Danish National Patient Register. In addition, indications for revision total knee arthroplasty (rTKA) in the Danish Knee Arthroplasty Register were used to identify PPKFs and the reason for reoperation.We included 1,931 PPKFs (1,494 femoral, 207 patellae, and 230 tibial) with an overall two-year reoperation risk of 20% (95% confidence interval (CI): 18 to 23). Femoral PPKFs had a two-year reoperation risk of 16% (CI: 12 to 22) after nonoperative treatment and 21% (CI: 18 to 24) after operative treatment. Patellar PPKFs had a two-year reoperation risk in five to 17 after nonoperative treatment and 46% (CI: 30 to 69) after operative treatment. Tibial PPKFs had a two-year reoperation risk of 17% (CI: 11 to 27) after nonoperative treatment and 36% (25 to 53) after operative treatment.The overall two-year reoperation risk was 20% (CI: 18 to 23). Operative-treated PPKFs had a higher risk of reoperation across all fracture locations. The highest reoperation risk was found after operatively treated patella and tibial PPKFs (46 and 36%, respectively), and the lowest reoperation risk was found after nonoperative-treated patella PPKFs.