A SDD surgery, performed under either general anesthesia + epidural OR under ‘regional’ anesthesia / sedation + epidural, is generally used where 1) an individual has problems that are not related to dysplasia, 2) are too severe or in too expansive of a location to be addressed by a hip arthroscopy (because the scope would not be able to access all of the areas that require repair), or 3) had a scope and it failed. These problems are often times caused by Femoroacetabular Impingement (FAI). FAI is a condition of too much friction in the hip joint. Basically, the ball (head of the femur) and socket of the pelvis (acetabulum) rub abnormally creating damage to the hip joint, which may be caused by CAM, PINCER, or MIXED impingement. These impingements can cause damage to the cartilage, labrum, or bone. Click [HERE!] for more info on FAI.
In addition, individuals who have Acetabular Retroversion (where the acetabulum is tipped too far forward) often need to have SDD surgery (click [HERE!] for more info on Acetabular Retroversion).
SDD surgery starts with a 6-10″ incision. Once inside, the surgeon breaks a small section of the thigh bone (called the greater trochanter) in a procedure called a trochanteric osteotomy. This little section of bone is the attachment point for several leg and glute muscles. By performing the trochanteric osteotomy, the surgeon is able to move the attached muscles (as opposed to cutting them and having to reattach them later) which provides the surgeon with access to the hip joint. The surgeon can then remove (dislocate) the entire ball of the femur from the socket (the acetabulum) of the pelvis (which, in my mind, is CRAZY because your leg is effectively disconnected from the body).
Once dislocated from the socket, the surgeon will repair the impingement(s) which can include shaving down parts of bone and smoothed. The surgeon can also repair the cartilage and the labrum. The surgeon will put the leg through its paces, making it move in every way the person who owns the leg will eventually use it. The purpose of this is to make sure that the impingement is totally gone. After the shaving and fixing is complete, the portion of the femur that was previously broken is put back into place and screwed into position. Voila! SDD surgery.
Check out this site and video that shows how a SDD works. The video was provided by Dr. John Clohisy, a well known and well respected orthopedic hip surgeon. The video is not at all gory — if anything, it suggests that SDD surgery is a walk in the park.
Sometimes, the surgeon may not put back all of the trochanter or may move the trochanter further down the femur in a procedure called a trochanteric advancement (http://www.thedenverclinic.com/services/hip/trochanteric-advancement.html). Sometimes this procedure is performed in conjunction with a PAO surgery. Each patient is different so the specifics of the procedure are case by case specific.
Here is a GREAT link to more info on FAI at Hospital for Special Surgery: http://www.hss.edu/conditions_femoroacetabular-impingement-a-patient-guide-to-hip-mobility-and-hip-arthroscopy.asp.