Tennis Elbow is pain on the outside of the elbow.
There are a number of muscles that attach to the outside of the elbow, and when these muscles are overused, pain can develop.
A good example is the Extensor Carpi Radialis Longus muscle.
The lower neck and upper back, when dysfunctional, can cause tension to develop in the muscles around the elbow and lead to tennis elbow.
Treatment will normally involve deep massage or acupuncture and spinal manipulation.