3 Preoperative Evaluation and Imaging Techniques in Adolescent Idiopathic Scoliosis



10.1055/b-0038-160334

3 Preoperative Evaluation and Imaging Techniques in Adolescent Idiopathic Scoliosis

Kenny Kwan, Kenneth M.C. Cheung, and Michael To

Introduction


Optimal care for patients with adolescent idiopathic scoliosis (AIS) involves performing an appropriate preoperative clinical evaluation and requesting relevant imaging procedures for surgical planning. In the majority of patients, a proper history and a thorough physical examination, supplemented with plain standing radiographs of the whole spine, are all that is needed for diagnosis and treatment decision making. Additional evaluations may be needed for planning for surgery or bracing. The standing whole spine radiographs enable an appreciation of the two-dimensional deformities of the curvatures, whereas dynamic radiographs are important in determining curve flexibilities, which in turn influences the surgical approach, technique, and fusion levels. Computed tomography is occasionally needed to help delineate the bony anatomy and to exclude congenital causes. Magnetic resonance imaging is occasionally required to define the soft tissues and neural structures. This chapter discusses the preoperative clinical and radiological assessments in the planning of AIS surgery.



Preoperative Evaluation



History and Clinical Evaluation


Proper preoperative evaluation for patients with AIS should start by taking a history and performing a physical examination to exclude nonidiopathic neuromuscular, congenital, and syndromal causes. The history should address the age of onset and rate of progression, and the presence of symptoms and associated conditions. The age of onset defines if the scoliosis is considered early onset (before the age of 10 years) or adolescent onset. The main complaint is usually one of cosmesis; in other cases, the deformity has been discovered by a screening program or as an incidental finding in a routine clinical examination. 1 , 2 Thus, patients presenting with any symptoms related to the curvature should be thoroughly investigated. Night pain and back discomfort causing limitation in daily activities warrant more detailed investigations for underlying malignancy, chronic inflammatory disorders, and intraspinal abnormalities. The age of onset of puberty should be noted, which helps in assessing the skeletal maturity and the remaining growth potential; this age is easier to determine in girls, as the onset of menarche can usually be recalled, whereas in boys there is no clear clinical marker. The change of voice and the onset of growth spurt in boys may help to determine the skeletal maturity. The neurologic development of the child should also be properly evaluated to exclude possible underlying neuromuscular diseases. It is important to obtain a family history as well, as 30 to 50% of AIS patients have a positive family history. 3 The past medical history may provide a clue to the possible underlying diagnoses and is useful in determining fitness for surgery ( Table 3.1 ).























Table 3.1 Causes of scoliosis

Spinal Causes


Extraspinal Causes


Congenital


Pelvic obliquity


Neuromuscular


Leg length discrepancy


Syndromes (e.g., Marfan syndrome)


Sciatica


Idiopathic


Posture


The physical examination should confirm the diagnosis of AIS, evaluate the general fitness of the child, and assess the spinal malalignment and the flexibility of the scoliosis.


Adolescent idiopathic scoliosis is a diagnosis of exclusion, arrived at by ruling out other causes. Clinical features suggestive of syndromal diseases, skeletal dysplasia, and neuromuscular causes should not be overlooked. Café-au-lait skin lesions should alert the practitioner to the possibility of neurofibromatosis. Likewise, disproportionately long and slender limbs with long fingers and toes, joint laxity, and a high arched palate should raise the suspicion of Marfan′s syndrome. The presence of sacral dimples, especially those associated with a tuft of hair, may suggest underlying spinal anomalies such as myelomeningocele and spina bifida. Patients with dwarfism, especially the ones with disproportionate short stature, should be assessed for skeletal dysplasia. A comprehensive neurologic examination is important to exclude spinal tumors, spinal cord anomalies (e.g., syringomyelia and tethered cord), and myopathies. Limb length should be measured to exclude secondary scoliosis from limb length discrepancy and pelvic obliquity. The presence of a joint contracture can affect the surgical decision making and needs to be carefully evaluated.


Although AIS is a three-dimensional deformity of the spinal column, its effects can extend to the whole truncal appearance and balance, which needs to be considered in the physical evaluation. With the child in the standing position, the front, back, and side should be properly assessed. Clinical determination of the structural curve(s) should be made, which, in our experience, is a useful adjunct to radiographic assessment. A proximal thoracic curve is indicated by a higher left shoulder and a trapezius line together with a prominent left scapula on forward bending ( Fig. 3.1 ), whereas a main thoracic curve is indicated by the presence of a rib hump ( Fig. 3.2 ), and a lumbar curve, by a loin hump ( Fig. 3.3 ). Rotational profile changes are best seen with the patient in the 90-degree-forward bending position and with the observer viewing from the back. In addition, with the patient in this position, have the patient actively bend to the left and right, which provides the examiner with a good sense of the amount of rotational correction of the curvature with coronal correction of the deformity ( Fig. 3.4 ).

Fig. 3.1 A proximal thoracic curve is indicated by a prominent left scapula on forward bending.
Fig. 3.2 A main thoracic curve is indicated by the presence of a rib hump on forward bending.
Fig. 3.3 A thoracolumbar curve is indicated by a thoracic and loin hump on forward bending.
Fig. 3.4 Active side bending with the patient in the forward bent position can help to assess the amount of rotational correction and the flexibility of the curvature. Bending to the left (a) leads to an increase in the size of the hump, whereas right bending into the curve (b) results in a reduction in the curve and the size of the hump.

Listing, which represents the lateral translation of the head away from the midline, should be documented. It can be assessed by using a plumb line hanging down from C7 and by quantifying the lateral translation of the C7 relative to the gluteal cleft. Truncal shift refers to the lateral translation of the rib cage in relation to the pelvis. Such assessment is particularly important in patients who have full head compensation with the head and neck back to the midline. Listing alone does not completely reflect the severity of the spinal deformity.


Proper recognition of the preoperative unleveled shoulders for the consideration of proximal thoracic (PT) curve fusion can help to prevent postoperative shoulder imbalance. In our experience, the preoperative left-elevated shoulder often necessitates the fusion of PT curve because sole correction of the right main thoracic (MT) curve can further elevate the left shoulder, whereas the preoperative right-elevated shoulder suggests that the PT curve fusion may not be required because the left shoulder elevation from the MT curve correction may be able to compensate the preexisting right-elevated shoulder.



Neck Balance Evaluation


When evaluating the shoulder height in AIS patients, surgeons should not ignore the neck balance, especially in Lenke type 2 (double thoracic curve pattern) patients. In these patients, the T1 tilts to the right side due to the left proximal thoracic curve. The T1 can be considered as the “ground base” of the cervical spine. The T1 tilt is strongly associated with the neck tilt. Therefore, the neck also tilts to the right in these patients. It has been found that the neck tilt is distinct from shoulder imbalance. 4 Clinical neck tilting has poor correlation with clinical shoulder imbalance. Lenke type 2 patients with a preoperative right-elevated shoulder have good shoulder balance after partial fusion or non-fusion of the PT curve. However, these patients complain of postoperative deteriorated neck tilting due to the increased T1 tilt result from decompensation of the unfused PT curve ( Fig. 3.5 ). Full fusion of the PT curve with the correction of T1 tilt may be helpful in preventing the deterioration of neck tilting in these patients ( Fig. 3.6 ).

Fig. 3.5 (a,c) A 19-year-old man with preoperative radiographic right-elevated shoulder fused to T3. The neck tilt increased from (b) 4 degrees preoperatively to (d) 11 degrees at the last follow-up. Although this patient had a leveled postoperative shoulder, the neck tilt deteriorated.
Fig. 3.6 (a,c) A 12-year-old girl with preoperative right-elevated shoulder fused to T1. The neck tilt was corrected from (a) 13 degrees preoperatively, to (d) 6 degrees at the last follow-up. This patient had both good neck balance and shoulder symmetry.

We also assess the shoulder imbalance and asymmetry in AIS patients by determining the following: (1) shoulder height ( Fig. 3.7 ), (2) shoulder area index 1 ( Fig. 3.8 ), (3) shoulder area index 2 ( Fig. 3.9 ), (4) shoulder angle ( Fig. 3.10 ), and (5) axilla angle ( Fig. 3.11 ). 5 These parameters can serve to supplement the radiographic parameters in surgical decision making for AIS patients.

Fig. 3.7 Shoulder height (SH): The horizontal line through the higher axilla intersects the arms at P (left) and Q (right), the plumb line through the midpoint of the neck intersects this horizontal line at O, and the trisection lines of OP, OQ intersect the shoulders at A′, B′ (right). The difference between the heights of A and A′ is defined as the inner shoulder height (SHi), and that between B and B′ is defined as the outer shoulder height (SHo)
Fig. 3.8 Shoulder area index 1 (SAI1): The area surrounded by m, l1, the superior margin of the shoulders and the outer margin of the upper arms, is divided by the plumb line through the midpoint of the neck into area a1 and area a2; the ratio a1/a2 is defined as SAI1. [m is the line connecting the two inflection points (right and left) between the shoulder and neck; l1 is the horizontal line through the higher axilla.]
Fig. 3.9 Shoulder area index 2 (SAI2): The area surrounded by m, l2, the superior margin of the shoulders, is divided by the plumb line through the midpoint of the neck into area b1 and area b2; the ratio b1/b2 is defined as SAI2. [m is the line connecting the two inflection points (right and left) between the shoulder and neck; l2 is the horizontal line through the lower inflection point between the shoulder and the upper arm.]
Fig. 3.10 Shoulder angle: the angle between the horizontal line and the line through two inflection points of the shoulders and upper arms.
Fig. 3.11 Axilla angle: the angle between the horizontal line and the line through both axillae.

Sagittal balance in AIS should not be overlooked. Patients with AIS develop thoracic hypokyphosis as a result of the rotational deformity. Some may also have reduced lumbar lordosis. Further reduction of thoracic kyphosis after surgery may lead to adjacent-segment disease and compensatory decrease in lumbar lordosis, resulting in disk degeneration, back pain, and poor quality of life. 6 , 7


The findings regarding shoulder imbalance, listing, truncal asymmetry, abnormal thoracic, and lumbar deformity should correlate with the radiological assessment, so that all the information can be combined to address the correc tion of the scoliosis and the level of fusion. As the goal of AIS surgery is to restore the alignment of the spine and improve the cosmesis, the coronal and sagittal malalignment should be carefully assessed.

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May 21, 2020 | Posted by in ORTHOPEDIC | Comments Off on 3 Preoperative Evaluation and Imaging Techniques in Adolescent Idiopathic Scoliosis
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