It is not uncommon for patients to feel numb after ACL surgery on their shin just past their incisions. While this does not occur in every patient, it is an expected consequence of undergoing surgery on the anterior (front) of the knee. Patients who have ACL reconstructions using their hamstring tendons or patellar tendons as grafts are at slightly higher risk for numbness compared to those who have reconstructions with quadriceps tendons. This numbness is a result of injury to very small superficial nerves that give sensation to the inside of the knee and along the front of the shin.
The nerves are branches of a larger nerve called the saphenous nerve and cross the knee going from the inside (medial aspect) toward the outside (lateral aspect). The saphenous nerve provides sensation to the skin surrounding the knee. Injury to these nerves can range from simple nerve irritation or stretch (neuropraxia) to being completely cut when incisions are made during surgery. Fortunately, much of the feeling on the shin does return over time. Nerves are one of the slowest structures to heal within the body and can take up to a year from surgery to heal. You can expect the patch of numbness over the shin to slowly become smaller with time as the nerve heals. If some numbness remains after a year has passed from surgery, it is more likely that this area of numbness will be permanent. The injury to the nerve will not affect your sense of balance in the knee or muscle control. While shin numbness after ACL is a common consequence of surgical reconstruction, patients can be reassured that such numbness should not hinder their overall recovery back to activity.