Clinical implications of an additional mediolateral implant option for a primary total knee system in an ethnically diverse population: 5-year interim results from a prospective, multicenter cohort study

Background Femoral component overhang can cause complications following primary total knee arthroplasty (TKA) and occurs more frequently in non-Caucasian populations due to anatomical differences insufficiently addressed by contemporary implants. The ANTHEM™ posterior-stabilized (PS) TKA system was designed to improve anatomical compatibility and reduce overhang. This prospective cohort study investigated implant survivorship, overhang frequency, and its clinical impact in Asian/Caucasian patients. Five-year interim results are reported. Methods 148 knees (120 patients; mean age 67.1 years; 77.5% female; 50% Asian, 50% Caucasian) underwent primary TKA for osteoarthritis at 6 international centers. Follow-up occurred at 6 weeks, 1, 2, and 5 years. Primary outcome was implant survivorship. Secondary outcomes included KOOS, 2011 KSS, EQ-VAS, EQ-5D3L, and radiographic assessments. Femoral component fit and safety events were collected. Results At 5 years, Kaplan–Meier survivorship estimates were 98.88% (95% CI: 92.29–99.84) for standard femorals and 96.88% (95% CI: 79.81–99.55) for narrow femorals. Six serious adverse device effects were reported − two possibly/directly related to the device/procedure. Radiographs showed 1 periprosthetic fracture and 5 non-progressive radiolucencies. No migration, loosening, osteolysis, or heterotopic ossification was observed. Overhang occurred in 12.8% of knees. All patient-reported outcomes improved significantly (p < 0.0001). Conclusion This knee system demonstrated excellent survivorship, strong clinical performance, minimal complications, and low overhang rates across diverse populations, supporting the value of enhanced anatomical fit in achieving optimal TKA outcomes.