Nerve injuries are a complication of knee replacement surgery. Most injuries are temporary improving in several days to months. Sometimes, the injury is permanent. This is more likely if severe scar tissue is present on or around the nerve. The symptoms can range from temporary to permanent problems in the legs and/or feet, including loss of feeling and strength of the affected area. Most commonly, there is a feeling of ankle weakness when lifting up your foot and numbness on the top of the foot.