Scoliosis uses the 45 to 50° threshold as a result of the well-documented, plus or minus 5° measurement error that can occur while measuring Cobb angles. Surgeons who are specialized in spine surgery perform surgery for scoliosis. To completely straighten a scoliotic spine is usually impossible, but for the most part, significant corrections are achieved. The two main types of surgery are: One or both of these surgical procedures may be needed. The surgery may be done in one or two stages and, on average, takes four to eight hours. A 50-year follow-up study published in the "Journal of the American
Supernumerary body part Supernumerary body part Supernumerary body parts are most commonly a congenital disorder involving the growth of an additional part of the body and a deviation from the body plan. Body parts may be easily visible or hidden away, such as internal organs. Many additional body parts form by the same process as conjoined twins: the zygote begins to split but fails to completely separate. This condition may also be a symptom of repeated occurrences of continuous inbreeding in a genetic line. Specific types of additional body parts include: Vestigial structures are anatomical structures of organisms in a species which are