Essentially it is the meeting of three bones: your arm bone called the humerus forms a complex joint with the two forearm bones called the radius and the ulna. The bottom part of the humerus forms two large roundish knuckles called condyles. A bony bump on the inside knuckle is called the medial epicondyle, and a similar bump on the outside knuckle is called the lateral epicondyle.
Tennis elbow is officially known as Lateral Epicondylagia, or Lateral Epicondylitis – though the two terms are not technically referring to the same problem. Sometimes you may come across the name Lateral Epicondylosis, but this is an inappropriate name as it simply means that you have a lateral epicondyle.
As in the case of Achilles Tendinitis, Tennis Elbow pain is usually due to pathology in or around the tendon. Tendons are the tissues that muscle turns into before joining onto bone. Many people will experience pain in the outside of their elbow at the site of the lateral epicondyle. The achilles tendon (which is the focus of the problem in Achilles Tendinitis) and the tendon of the extensor muscles of the forearm (which is the focus of the problem in Tennis Elbow) are regarded as the most likely tendons to cause people pain due to repetitive work or sporting activities.
One study in Finland of 5871 people between the ages of 30 and 64 years old found that 1.2% of them had lateral epicondylagia. Or to put it another way, just over 1 out of every 100 adults had tennis elbow. The numbers of men and women with the condition were similar. Being a past or present smoker, or being obese, did increase the likelihood of someone having the condition. Some sporting activities do have a higher tendency than others to cause the condition.
For example a study of five very active tennis clubs discovered that about half of 194 tennis players, who played tennis 4 times a week and had done so for at least one year, had experienced tennis elbow. However, often those who experience the condition are not tennis players, but rather those who have occupations involving repetitive manual work.
Treatment can include surgery but this is typically not necessary. In fact, of 85,318 patients with tennis elbow (Lateral epicondylagia) only 1,694 were treated with an operation. In other words, only 2% of people with tennis elbow received surgery. 
Most people with Tennis Elbow will get better without needing surgery or one or more corticosteroid injections.
Compared to physiotherapy treatment, treatment of Tennis Elbow with cortisone injections (also known as corticosteroid injections) results in symptoms that are worse even 3 months after injection. Also, people who have had steroid injections are more likely to have their symptoms recur, than after treatment with physiotherapy.  Perhaps the most surprising result from research was the study involving 165 patients who received ‘treatment’ consisting of either corticosteroid injection or placebo injection. It was found that one year after the treatment that the steroid injection resulted in worse clinical outcomes than the placebo. These poorer outcomes included a greater recurrence rate (54%) in the corticosteroid group compared to the placebo group (12%) during the year after the patients received treatment.  Cortisone injections have also been found to be a worse form of treatment than ‘wait and see’ treatment at 6 and 12 months.
We have had the opportunity of helping people with Tennis Elbow. Over the course of weeks, is often successful. So the goods news is that Tennis Elbow pain can go away; it can resolve. The same good news applies to Achilles Tendonitis, but more will be written about that condition in the future.