Final answer:
A postoperative low-grade temperature in a patient after knee replacement surgery, which deviates from the expected critical pathway outcome of being afebrile, is called a negative variance.
Step-by-step explanation:
The finding of a low-grade temperature in a patient after knee replacement surgery, when the patient was expected to be afebrile according to a critical pathway, is known as a variance. In clinical practice, a variance refers to a departure from the anticipated plan of care. When an outcome is not as expected or there are unmet goals, it is considered a negative variance because it indicates a deviation from the desired or expected condition (which would be afebrile, normotensive, and eupneic in this case).