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Load sensing total knee replacement (TKR) implants are useful tools for monitoring prosthesis health and providing quantitative data to support patient claims of pain or instability. However, powering such devices throughout the entire life of the knee replacement is a challenge, and self-powered telemetry via energy harvesting is an attractive solution. In this study, we implemented vertical contact mode triboelectric energy harvesters inside a knee implant package to generate the power required for embedded digitization and communications circuitry. The harvesters produce small-scale electric power from physiologically relevant loads transmitted through the knee. Experiments were performed on a joint motion simulator with an instrumented package prototype between the polyethylene bearing and tibial tray. The amplitude and the pattern of the power output varied with the input loadings. Under sinusoidal loading the maximum apparent power harvested was around 7 μ W at (50-2000)N whereas, under vertical compressive gait loading the harvesters generated around 10 μ W at average human knee loads of (151-1950)N and 20 μ W when the maximum applied load was increased by 25%. Full six degrees of freedom (6-DoF) gait load/motions at 0.67Hz produced 50% less power due to the slower loading rate. The results show the potential of developing a triboelectric energy harvesting-based self-powered instrumented knee implant for long-term in vivo knee joint force measurement.