Systems and methods utilize a strain sensor to monitor the status of bone fusion. The systems include a sensor system that measures an initial strain in a medical device implanted in or disposed on a bony structure to obtain an initial strain value, and measures a subsequent strain in the medical device to obtain a subsequent strain value. The systems also include a reader or a processor that calculates a magnitude of the difference between the subsequent strain value and the initial strain value or a magnitude of the difference between a current strain value and a previous strain value. If the magnitude of the difference is greater than the predeter mined difference value, the sensor system measures multiple strain values, and the processor calculates an average slope based on the multiple measured strain values, and, if the average slope is less than the predetermined slope, generates a notification that bone fusion in a bony structure has occurred.