As we consider in-brace curve correction and review the literature that indicates better in-brace results produce better final results, we must also consider the basic principals of compression and distraction as described by Hueter and Volkmann. 27 If a brace reduces a curve only 50 percent, the resultant curve has a concave and convex aspect, and thus we have compression at the concave aspect and distraction at the convex aspect. It must then be concluded that the compression and distraction forces decrease proportionately as the curve is reduced in magnitude, and if the curve is corrected beyond 100 percent (overcorrected), the compression and distraction forces are negated.
Early part-time and nighttime brace wear studies used the existing protocol of previous full-time brace wear studies and included single and double curves with Cobb angle magnitudes as great as 49°. However, more recent studies indicate that certain groups of patients respond better to nighttime brace wear than do others. 1,2,5 Katz et al. 5 noted that single curves with a Cobb angle of less than 35° responded comparably to treatment with the Boston brace worn full-time and the Charleston brace worn only at nighttime. Trivedi and Thomson 28 also noted that patient selection was important in the use of nocturnal wear with the Charleston brace.
Part-time and nighttime brace wear studies have overwhelmingly indicated that both alter the natural history of IS. Bowen et al. 26 reported that nighttime bracing of flexible curves demonstrated a success rate statistically comparable to the Wilmington full-time brace. Kehl and Morrissy 9 demonstrated success with part-time brace wear and indicated that curves of less than 35 percent and absent of vertebral wedging would respond as well with part-time bracing as full-time bracing. Allington and Bowen 12 reported no statistical difference in the results of curves ≥40° when treated with part-time bracing or full-time bracing. Federico and Renshaw 1 reported observing results of nighttime treatment with the Charleston bending brace to be at least as good as reported results for full-time brace treatment for curves ≤40°. 3 Trivedi and Thomson 28 demonstrated favorable results in altering the natural history of adolescent IS (AIS) using nighttime treatment with the Charleston bending brace, and suggested that single curves responded best to nighttime-only treatment.
There have been many investigators of part-time and nighttime brace wear for the patient with AIS, and all investigators agree that both alter the natural history of AIS. The confusion and disagreement that have been reported are focused on patient selection, curve location, curve magnitude, and curve type (single or double). Nocturnal bracing has been a part of every treatment regimen since bracing for AIS began. During the process of weaning from brace wear, nocturnal wear is the last to be discontinued. Price et al. 6 have demonstrated that growth hormones are more active during the sleep hours, so the benefit of nocturnal bracing is heightened. d’Amato et al. 4 described nighttime bracing as a stronger dose of correction during a shorter period because of the far greater amount of in-brace correction nocturnal braces are able to achieve.
Since 1979, investigators have accepted the fact that a large number of patients will not comply with a full-time brace wear treatment regimen. Time-modified treatment regimens using braces designed to be worn in an upright and recumbent position have proven to be successful in altering the natural history of AIS. Nighttime brace treatment regimens have proven to be successful in altering the natural history of AIS. There is still controversy regarding the comparison of part-time and nighttime treatment regimens to full-time brace wear treatment regimens. The data reviewed suggest that single curves with Cobb angle magnitudes of less than 35° respond statistically as well with nighttime brace treatment. The data also suggest that nighttime braces can achieve much better in-brace curve correction, and the nonupright position offers favorable biomechanical positioning.
Double curves present some difficulty for nighttime brace design. The ability of the orthotist is instrumental for in-brace correction of double curves when using a nighttime brace. The data suggest that double curves with magnitudes of less than 30° can be treated effectively with a well-designed nighttime brace; however, the design of such a brace is difficult for the orthotist who is not well trained in scoliosis bracing.
Continued research of nighttime brace treatment for the treatment of AIS is necessary; however, the data as of this date are promising. If nighttime brace treatment of AIS is accepted as advantageous for small curves and it is determined that larger curves need additional time in a brace, it would appear to this author that the addition of another brace for daytime wear is appropriate. Obviously, the braces offer a vastly different biomechanical approach, and the brace that achieves the most favorable in-brace positioning cannot be worn while the patient is upright.
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