Prolotherapy ("Proliferative Injection Therapy") involves injecting a solution
of otherwise non-pharmacological substances into the body, generally in the
region of tendons or ligaments for the purpose of strengthening weakened tissues
and alleviating musculoskeletal pain.[1] Prolotherapy is also known as
"proliferation therapy" or "regenerative injection therapy."
Doctors and surgeons have given anecdotal accounts of successful treatment for
knee injuries, shoulder separation, and typical injuries to athletes
(epicondylitis, shoulder strain, lower back strain and injury, hip and knee
injury)[2][3][4] However, mainstream treatment is still pending further
investigation and consensus.

As of April 2005, doctors at the Mayo Clinic began supporting prolotherapy.
Robert D. Sheeler, MD (Medical Editor, Mayo Clinic Health letter) first learned
of prolotherapy through C. Everett Koop’s (former US Surgeon General) interest
in the treatment. Mayo Clinic doctors list the areas that are most likely to
benefit from prolotherapy treatment: back, ankles, knees, elbows, and the
sacroiliac joint. They report that "unlike corticosteroid injections — which may
provide temporary relief — prolotherapy involves improving the injected tissue
by stimulating tissue growth.'' [5]

Many solutions are used, including dextrose, lidocaine (a commonly used local
anesthetic), phenol, glycerine, or cod liver oil extract. The injection is given
into joint capsules or where tendon connects to bone. Many points may require
treatment. The solution placed into injured tissues triggers healing and pain
relief through the process of repair. In the case of weakened or torn ligaments,
it is beleived that release of growth factor at the sites of injury may result
in a 30-40% strengthening of the attachment points, although research evidence
supporting this process is still ongoing.

Prolotherapy treatment sessions are generally given every two to six weeks. Many
patients receive five to ten treatments. Then treatments at less and less
frequent intervals until treatments are required only once a year or even every
several years.[7] Allen R Banks, Ph.D., has described in detail the theory behind prolotherapy in
"A Rationale for Prolotherapy." [7]  A Cochrane Review, one of the gold standard references on Evidence Based
medicine, favors use of prolotherapy along with other forms of therapy (8).

Guidelines used by physicians as indications for prolotherapy for pain treatment.

Recurrent swelling or fullness involving a joint or muscular region
Popping, clicking, grinding, or catching sensations associated with pain with
activity or movement
A sensation of the “leg giving way” with associated back pain. 
Temporary benefit from chiropractic manipulation or manual mobilization that
fails to ultimately resolve the pain
Distinct tender points and “jump signs” along the bone at tendon or ligament
attachments
Numbness, tingling, aching, or burning, referred into an upper or lower
extremity
Recurrent headache, neck pain, back pain, face pain, jaw pain, ear pain
Chest pain with tenderness along the rib attachments on the spine or along the
front of the chest
Spine pain that respond poorly to drugs, other type of injections or surgery, or
whose origin is not clear or consistent based on extensive studies.
Prolotherapy is also used frequently for back pain treatment due to pain originating in soft tissues

M. A. Pappolla, MD, PhD. Back Pain Houston

References

1. ^"Injections to Kick-Start Tissue Repair". New York Times. 2007-08-07. http://www.nytimes.com/2007/08/07/health/07brod.html. Retrieved 2008-07-24. "Prolotherapy involves a series of injections designed to produce inflammation in the injured tissue. To appreciate the value of such a seemingly counterproductive measure, you need to know something about connective tissue and how the body normally repairs it. When tissues are injured, inflammation is a common natural response. It stimulates substances carried in blood that produce growth factors in the injured area to promote healing. Ligaments, tendons and cartilage have very poor blood supplies, which can result in incomplete healing." 
2. "Second Annual Prolotherapy Research Forum" (PDF). http://www.prolotherapy-hhf.org/Prolotherapy_insert%202006.pdf. 
3. Marc Darrow, Prolotherapy: Living Pain Free, Protex Press,
4. Ross A. Hauser, Marion A. Hauser, Prolo Your Pain Away, Beulah Land Press.
5. Mayo Clinic (2005). "Alternative treatments: Dealing with chronic pain". Mayo Clinic Health Letter 23 (4). 
6. Hauser, Ross. "The History of Prolotherapy.". http://getprolo.com/the_history_of_prolotherapy.htm. Retrieved 2007-08-26. "In 1955, at an American Medical Association meeting, Dr. Gustav Hemwall was astonished to see so many doctors at one particular exhibit. The presenter was talking about a very successful treatment for chronic low back pain. Nothing was worse at the time for Dr. Hemwall than having a chronic low back pain patient come to him, because the treatments he was able to offer were not very successful. The doctor doing the presentation was George S. Hackett, M.D., and he was discussing the technique of Prolotherapy. Once the crowd diminished, Dr. Hemwall asked Dr. Hackett how he could learn the treatment described in his book, Ligament and Tendon Relaxation Treated by Prolotherapy. Dr. Hemwall went to Dr. Hackett's office in Canton, Ohio, to learn the technique. Dr. Hemwall became so proficient at administering the technique that Dr. Hackett would later refer patients to him. Prolotherapy owes a great debt to Dr. Hemwall. Between 1955 until his retirement in 1996, he was the main instructor and proponent of Prolotherapy in the United States. He was not a researcher but a clinician, and perhaps the world's greatest Prolotherapist. He treated more than 10,000 patients world wide and collected data on 8,000 of these patients. In 1974, Dr. Hemwall presented his largest survey of 2,007 Prolotherapy patients to the Prolotherapy Association." 
7. Banks, Alan. "A Rationale for Prolotherapy". http://www.prolotherapy.com/articles/banks.htm. "Prolotherapy, the technology for strengthening lax ligaments, has found increased acceptance in recent years. However, despite its greater use, the mechanism of action of prolotherapy is not well understood. In the past few years a number of advances have been made in the understanding of wound repair. This author believes the increased knowledge which has been made available in the field of wound healing has application to a more complete understanding of prolotherapy. There follows a general discussion of wound healing and a hypothesis which provides a basis for understanding prolotherapy." 
8. Dagenais, S.; Yelland, M.; Del Mar, C.; Schoene, M.; Dagenais, S. (2007). "Prolotherapy injections for chronic low-back pain.". Cochrane database of systematic reviews (Online) (2): CD004059. Cochrane collaboration