There are several common causes of numbness at the knee joint: 1. Nerve damage to the dermal nerve around the knee joint due to inflammation, infection, injury, stimulation by adverse factors, and systemic underlying diseases, resulting in sensory numbness of the nerve. Common causes include acute injury to the knee joint, chronic strain, osteoarthritis of the knee joint, and peripheral dermal neuritis, as well as systemic diseases, such as diabetes. These are all harmful to the local nerves of the knee joint, resulting in the above symptoms.2. To consider problems with the high nerve center, a common cause is a herniated lumbar disc. Due to the high location of the sensory branch of the knee joint, see the herniated discs of the lumbar 2 and 3 vertebrae, which can compress the nerve roots of the knee joint, thus leading to numbness around the knee joint. This condition is relatively uncommon in clinical practice, but can also be examined.3. See the third transverse process syndrome of the lumbar spine, which is prone to strain inflammation due to the anatomical characteristics of the transverse process of the lumbar spine and the surrounding tendons and ligament stops, thus stimulating the surrounding passing blood vessels and nerves and causing numbness around the knee joint.