Knee joint injection is a procedure commonly performed for pain management of osteoarthritis. Although several techniques have been described, it is usually performed by either medial or lateral approach with the lower limb extended on the examination table. We present the case of a patient who developed saphenous neuropathy following knee joint injection via medial approach. The clinical picture suggests that the needle pierced the nerve during the procedure. The patient was moderately obese. This is the first case report in the literature of saphenous nerve injury following medial knee joint injection. Practitioners should be aware of this complication in choosing an approach to the knee joint injection, especially when the patient is obese and the anatomic landmarks are obscured.