The correct answer is:Saphenous
The saphenous nerve is a branch of the femoral nerve. This nerve, and the nerve to vastus medialis, are the only nerves found in the adductor canal. So, it makes sense that one of these structures was injured. The saphenous nerve is a sensory nerve only; it supplies the skin on the medial side of the leg. The patient's symptoms, as well as the type of procedure done, both point toward an injury to the saphenous nerve.
The femoral nerve does not travel in the adductor canal -- it ends by branching superior to the adductor canal, in the femoral triangle. If this nerve was injured, the quadriceps would be impaired, and the patient would have difficulty extending at the knee. The ilioinguinal nerve is a branch of the lumbar plexus which innervates muscles of the lower abdominal wall. The medial sural cutaneous nerve is a branch of the tibial nerve, responsible for providing cutaneous sensation to the upper posterior calf. The obturator nerve innervates the medial, adductor compartment of the thigh. Neither the symptoms nor the location of injury suggest that any of these other nerves were damaged.