During his residency at UCLA, Jannetta was in the laboratory dissecting a set of cranial nerves when he noticed that a blood vessel was unexpectedly pressing on one of the nerves. Jannetta suspected that this abnormal impingement of the nerve might be the cause of the painful facial condition known as trigeminal neuralgia. He devised the microvascular decompression procedure to treat patients with the condition. In addition to helping trigeminal neuralgia patients, the procedure became a treatment option for several related conditions.[2]
He was a faculty member and division chief at Louisiana State University before moving to a similar role with the University of Pittsburgh in 1971.[1] In 1995, he spent a year as Secretary of Health for the Commonwealth of Pennsylvania.[2] Jannetta practiced at Allegheny General Hospital for a few years before he retired.[3]