Background: The impact of total knee arthroplasty (TKA) on patients' informal caregivers (eg, family members, friends) has gone largely ignored. The goals of this study are to measure the impact of TKA on the caregiver and identify factors contributing to higher burden.; Methods: One hundred fifty primary TKA patients and their designated caregivers were prospectively enrolled. The Caregiver Strain Index (CSI) was completed by caregivers preoperatively, at 4 weeks, and at 1 year after surgery.