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      Drugs & Diseases > Orthopedic Surgery

      Idiopathic Scoliosis Workup

      Updated: Jan 03, 2023
      • Author: Charles T Mehlman, DO, MPH; Chief Editor: Jeffrey A Goldstein, MD  more...
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      Workup

      Laboratory Studies

      Laboratory workup for patients with scoliosis consists primarily of preoperative testing. Most, if not all, patients undergo preoperative assessment of hemoglobin and hematocrit levels. A type and screen is obtained, if not a complete type and crossmatch for packed red blood cells.

      Autologous blood can be drawn preoperatively to avoid the need for allogenic blood transfusion. However, there are concerns related to obtaining autologous blood, such as possible wastage of blood products if there is no significant intraoperative blood loss and possible inappropriate transfusion out of a felt need to use the autologous blood already obtained. [66]  If there is a small interval of time between when the autologous blood is obtained and when the surgical procedure is performed, using this blood can result in lower hemoglobin and hematocrit levels at the start of the surgical case.

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      Imaging Studies

      Radiography

      Multiple authors have cited the value of bending radiographs, including those over a fulcrum. [67] Klepps and Lenke et al found that thoracic fulcrum bending radiographs worked best for them when dealing with isolated main thoracic curves. [68]

      After the publication of the King classification in the early 1980s, the thoracic curve patterns found in adolescent idiopathic scoliosis were commonly classified according to this system. [69] Subsequently, significant questions were raised regarding its reliability and reproducibility. [70, 71] In addition, it was noted that the King classification alone (in its original form) does not allow comprehensive curve classification (eg, lumbar and thoracolumbar curve patterns). [72]  Many now regard the King classification as primarily of historical interest. The Lenke classification (see below) has become more commonly used for adolescent idiopathic scoliosis. [73]

      Multiple authors have analyzed the ability of orthopedic surgeons to reliably measure scoliosis radiographs. Morrissy et al used 50 radiographs and four examiners (two experienced orthopedic surgeons, one fellow, and one senior resident) to study their ability to make Cobb angle measurements. With the examiners choosing end vertebrae and measuring scoliotic curves accordingly, intraobserver variability was 4.9°. [74]

      Carman et al used eight scoliosis radiographs measured by five examiners (four orthopedic surgeons, one physical therapist) to evaluate interobserver and intraobserver variation. They found that a 10° measurement difference is necessary before there is a 95% confidence level that one Cobb angle measurement is truly different from another. [75]

      Lenke classification

      Currently, the Lenke classification system is commonly used to categorize adolescent idiopathic scoliosis. This system, first published in 2001, includes the following three components [73] :

      • Curve type (1, 2, 3, 4, 5, or 6)
      • Lumbar spine modifier (A, B, or C)
      • Sagittal thoracic modifier (–, N, or +)

      On coronal and sagittal radiographs, the six types specified by Lenke et al have specific characteristics that distinguish structural and nonstructural curves in the proximal thoracic (PT), main thoracic (MT), thoracolumbar (TL), and lumbar (L) regions. [73]  Regional curves are measured, the major curve is identified, and a determination is made as to whether the minor curve is structural. The curve is then assigned to the appropriate numeric type (1 through 6).

      The lumbar spine modifier is based on the relation of the center sacral vertical line (CSVL) to the apex of the curve. If the CSVL passes between pedicles of apical lumbar vertebrae, the modifier A is assigned; if it touches a pedicle, the modifier B is assigned; and if it does not touch apical lumbar vertebrae, the modifier C is assigned.

      54-degree Lenke 1A curve. 54-degree Lenke 1A curve.
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      The sagittal thoracic modifier is based on the sagittal Cobb angle from T5 to T12. If the angle is less than 10º (hypokyphotic), the modifier – is assigned; if it is 10-40º (normal), the modifier N is assigned; and if it exceeds 40º (hyperkyphotic), the modifier + is assigned.

      Further application of this classification system to the surgical instrumentation and fusion planning are discussed in the "Surgical Therapy" section below.

      Magnetic resonance imaging

      It has been suggested that magnetic resonance imaging (MRI) is indicated primarily in patients who have idiopathic scoliosis with unusual complaints (eg, severe unexplained headaches), as well as in those with atypical clinical findings (eg, ataxia, cavus foot deformity, severe kyphosis, or syndromic features). [76]  In cases of infantile and juvenile idiopathic scoliosis, it is more common to obtain a total spine MRI to look for intraspinal pathology (eg, tethered cords, syrinx, and Chiari malformations), especially when the curve exceeds 20º.

      Routine MRI evaluation of all patients with adolescent idiopathic scoliosis is not recommended but can be warranted in the setting of a rapidly progressing curve, associated kyphosis, or other atypical features (eg, a left-side thoracic curve). [77]

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      Other Tests

      Bone age radiographs

      Left-hand radiographs are used to determine skeletal maturity in adolescents with scoliosis. The Sanders classification is used to score the hand radiographs and is more accurate than the Risser classification in prediciting the stage of adolescent growth velocity. [78]

      Pulmonary function testing

      Pulmonary function studies have been used extensively in the evaluation of patients with idiopathic scoliosis. [7, 79, 80, 81] In general, patients whose scoliosis surgery does not involve disruption of the chest wall can be expected to experience improved postoperative pulmonary function. [82, 60] Other authors have suggested that an impairment in respiratory mechanics may persist after successful scoliosis surgery. [83] Preoperative pulmonary function testing is of questionable value in patients with moderate deformity (average Cobb angle, 48°), in that most of these patients can be expected to have normal or only mildly abnormal results. [84]

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      Histologic Findings

      Scoliosis is clearly a disease that is strongly influenced by, if not completely rooted in, spinal growth. It has even been referred to by some as "an unsynchronized growth." [85]

      Hsu et al studied muscle biopsies from 27 patients with idiopathic scoliosis who were undergoing posterior spinal fusion. Specimens were obtained from the paraspinal musculature of both the convex and the concave side. All patients had thoracic curves in the range of 37-81°. [86]  In all, 68% of the patients demonstrated abnormalities in muscle fiber distribution. The abnormalities were similar on the convex and concave sides, the most notable being a reversal of the normal type 2 fiber ratio, so that type 2A fibers predominated over type 2B fibers. These changes are similar to those seen in endurance training and might be due to the extra work of trying to maintain posture in the setting of scoliosis.

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