A possible factor in persistent coccydynia is muscle dysfunction. It is common to find taut bands that are very painful when pressed. Taut bands are strongly contracted muscle fibers within an otherwise relatively normal muscle.
Rectal examination of the pelvic floor muscles is necessary to locate these contraction knots or myofascial trigger points. They are often found in the levator ani, sphincter ani and coccygeus muscles. Patients with these trigger points may complain of painful bowel movements and dyspareunia [painful sexual intercourse]. Other muscles that can cause coccydynia are the obturator internus, gluteus maximus and adductor magnus. Trigger points in the adductor magnus often cause pain in both the thigh and the pelvic floor.
Treatment of trigger points may include compression, dry needling, injection with procaine, manual stretching or myofascial release.
[The paragraphs above are adapted from a reply by Jan Dommerholt to a question on the NOI message board].
The gluteus maximus muscles are the powerful muscles in the buttocks that raise you from sitting to standing, and also lower you into a sitting position. The gluteus maximus is attached to the coccyx as well as to other bones. A spasm or tightness of this muscle can pull on the coccyx and cause pain when you move into a sitting position or raise yourself. It doesn't cause pain while you are sitting. The spasm, and the pain, is normally just on one side.
The features that distinguish gluteus maximus pain are:
If you have gluteus maximus pain, a manual practitioner who examines you will find muscle spasm, joint stiffness and tenderness at the lumbo-sacral joint on the same side as the pain. If the practitioner puts pressure on the point where the gluteus maximus is attached to the side of coccyx, this will reproduce the patient's pain.
Manual treatment of the back and buttock muscle should solve the problem, usually in 3 to 5 treatments, with clear improvement felt after the first treatment.
The information on gluteus maximus syndrome is based on information kindly supplied to me by Adrian Good, an osteopath and physiotherapist in Melbourne, Australia (email: firstname.lastname@example.org), and author of Pain Relief - Manual Therapies Can Help, Lothian Books, ISBN: 0734403240. The link is to the UK Amazon website, as it was not on the USA Amazon site.
One muscle which is often thought to be the cause of pain when sitting is the piriformis. You have two piriformis muscles, running horizontally from the lower spine to the top of each thighbone (femur). The piriformis runs over the sciatic nerve, and piriformis syndrome is thought to develop when the muscle becomes tight or spasms and places pressure on the sciatic nerve. This can cause pain in the lower back and/or pain that radiates to the buttocks and down the leg. Pain is often made worse by sitting.
According to one doctor, "Piriformis syndrome can cause pain in the low back, groin, perineum, buttock, hip and other areas, and can also cause dyspareunia (painful intercourse) and pain in the rectum during defecation. Piriformis problems are very diverse and very common, and fortunately respond very well to treatment in massage therapy".
Piriformis syndrome is usually diagnosed on the basis of the pattern of symptoms. One website, Neurography.com, says that special MRI scans can show up piriformis problems.
Trying to stretch the piriformis muscle has been suggested as a way of diagnosing the problem - if it hurts to stretch it, you may have piriformis syndrome. The instructions for stretching it are: Lie flat on your face on a bed. Bend your legs 90 degrees at the knee, lifting your feet in the air. Let the feet spread apart from each other, keeping the knees together and bent at 90 degrees.
Treatments include stretching the muscles, physical therapy, injections of corticosteriods.
There is detailed information on piriformis syndrome on the Spine-Health web site, and more general information on the International Society for pelvic pain site.