Tennis Elbow occurs when the muscles which attach to the elbow become overloaded and start to tear the tendon attached to the elbow. The arm - in particular the forearm - can experience muscular spasms and a local weakness which serves to protect it from further damage.
There are many excellent textbooks on osteopathy. One of my favourites is Cranial Manipulation Theory and Practice (Osseous and Soft Tissue Approaches) by Leon Chaitow, published by Churchhill Livingstone. This is beautifully-illustrated textbook - which comes with an excellent CD - combines traditional osteopath approaches with cranial osteopathy.