Acute elbow pain with a snap sensation in a pitcher is always concerning for a UCL injury and possible need for Tommy John surgery. Another less common injury that has a similar presentation is acute instability or snapping of the ulnar nerve.

The ulnar nerve sits in a groove on the inside part of the elbow. The nerve supplies sensation to the pinky and ring finger as well as activating the muscles of the forearm and hand.

The violent forces involved with throwing can dislocate the ulnar nerve from its groove. When the nerve dislocates, it creates the painful pop sensation in the inside part of the elbow. Once dislocated, the tissues surrounding the nerve are stretched and the result is persistent snapping where the nerve pops in and out of the groove with throwing and can even happen with less forceful elbow motions. Dysfunction of the nerve from the repeated dislocations can result in numbness and tingling in the pinky and ring finger and occasionally weakness in the hand muscles.

The diagnosis is made from physical examination where the ulnar nerve is observed to snap over the inside part of the humerus bone called the medial epicondyle. MRI and X Yay are frequently obtained to assess for other associated injuries such as a strain to the flexor muscles of the forearm or an injury to the UCL.

Unfortunately, once the nerve becomes unstable it is challenging to resume high velocity throwing without surgery. Bracing of the elbow with the elbow position towards full extension can manage acute symptoms and in some cases can allow a player to rehab and get back to throwing.

More commonly the snapping of the ulnar nerve is resolved with a surgical procedure called ulnar nerve transposition. In this procedure, the ulnar nerve is positioned in front of the arm and stabilized using either subcutaneous tissues or a dense tissue adjacent to the nerve called the intermuscular septum.

Recovery time for this surgery depends on the degree of injury to the ulnar nerve. Throwing can be resumed as early as six weeks in many cases.