17.2.1 Shoulder Balance in Normal Adolescents

The normal, healthy adolescent is considered to have level shoulders. The head and pelvis are aligned, and both sides of the body are symmetric. The central sacral vertical line (CSVL) bisects the trunk into two halves that match in shape and function. Any asymmetry is assumed to be pathologic. Shoulder imbalance may be the result of diseases of the shoulder girdle (atrophy, tumors) or rib cage (rib anomalies or fusions). Spinal deformities may also result in rib cage, trunk, and/or shoulder asymmetry. However, even in the absence of any pathology, shoulder imbalance is possible in the “normal” adolescent. ¹

Kuklo et al ² defined shoulder balance for AIS patients as a less than 1 cm side-to-side difference between the shoulders on clinical examination. Interestingly, Akel et al ¹ found that 28% of patients in their study of healthy adolescents had shoulder asymmetry greater than 1 cm. The study also reported any imbalance greater than 1 cm as abnormal and that only 19% of healthy subjects had truly balanced shoulders. The average shoulder asymmetry in the study was 7.5 mm with a range from 1 to 27 mm. Of note, patient questionnaires revealed that none of the subjects felt they had any asymmetry.

The challenge lies in the correlation between a surgeon’s assessment of patient alignment and the patient’s perception, which is arguably paramount. Matamalas et al ³ evaluated 80 adolescents and young adults with only moderate scoliosis and found that 62% of patients had balanced shoulders by clinical examination. However, 47% of patients in the clinically unbalanced group perceived themselves as completely balanced with patient-reported outcomes questionnaires and the Spinal Appearance Questionnaire (SAQ). Furthermore, 10% of patients in the balanced group, with a shoulder height angle (SHA) of less than 3 degrees, perceived their shoulders to be significantly asymmetric.

The SAQ is a validated and reliable assessment of a patient’s perception of his or her appearance. ⁴ The SAQ was administered to 1,800 AIS patients with curves ranging from 10 to 120 degrees. The assessment includes domains for appearance and expectations. The questionnaire was found to have excellent test–retest reliability (α> 0.8) as well as having significant correlations with curve magnitude. The SAQ demonstrated significant differences between those patients who were in the observation range and those who required surgery. The SAQ includes several questions regarding a patient’s perception and expectation of shoulder balance.

17.2.2 Relationship of Shoulder Balance with Outcome Scores

Achieving body symmetry and improved clinical appearance following scoliosis surgery are important patient and surgeon goals. Patients’ perception of their appearance can play a considerable role in their overall satisfaction and self-esteem. Raso et al ⁵ reported that shoulder and scapular imbalance as well as waist asymmetry accounted for 75% of patient’s perceptions of trunk deformity in AIS. Theologis et al ⁶ found that the appearance of the trunk and shoulders was of “critical importance” to the adolescent with idiopathic scoliosis. Tones et al ⁷ found that adolescents with scoliosis exhibited poorer psychosocial functioning, body image, and health-related quality-of-life scores than their healthy peers. Body image concerns appeared to be qualitatively different for adolescent males and females and significantly less of a concern for adults with scoliosis. An earlier study by Bengtsson et al ⁸ found that patients with severe scoliosis had higher rates of insecurity and hypersensitivity compared to normal adolescent female counterparts. Importantly, the study demonstrated that the severity of the deformity correlated with worsening psychosocial adjustment with their condition.

Edgar and Mehta ⁹ reviewed the long-term follow-up of 168 AIS patients with or without fusion at least 10 years after reaching skeletal maturity. The authors found that fusion reduced the incidence of severe pain and allowed patients to perform heavy physical work. However, over 50% of the patients in the surgical and nonsurgical groups complained of being self-conscious or depressed about their body shape. Rib prominence and asymmetry were the main features of concern and distress for these patients. Smyrnis et al ¹⁰ reported decreased outcome scores with shoulder asymmetry greater than 2 cm.

Koch et al ¹¹ performed an extensive psychological assessment on 42 AIS patients before and after spinal fusion. The authors found that the majority of the patients (73%) were satisfied with their postoperative appearance. However, 75% of the patients who were dissatisfied with their clinical appearance exhibited feelings of sadness and low body satisfaction prior to surgery. The study recommended a referral for a preoperative psychological evaluation if any signs of depression and/or poor body image are present. The authors found that early psychological intervention in at-risk patients might help them better cope with the postoperative recovery, reduce anxiety, and improve their overall satisfaction with the surgery. A second subset of patients who were satisfied with their appearance preoperatively but dissatisfied postoperatively was also reviewed. This subgroup of patients had likely unmet and/or unrealistic expectations with the surgical outcome and had hoped for a “substantially improved appearance after surgery.” Analysis of these two groups highlights the significant psychological component of spinal deformity, its effect on adolescents, and the possible positive impact that can occur with early preoperative psychological intervention/counseling.

17.3.1 Clinical Evaluation of Shoulder Balance

Studies have demonstrated that there is more than one aspect of clinical shoulder alignment and that they relate differently to various radiographic parameters. Ono et al ¹⁴ described two distinct regions of shoulder height asymmetry. The “medial” shoulder is best represented by trapezial prominence. This can be assessed by the trapezial angle (TA) and trapezial angle ratio (TAR). (Fig. 17‑1). TA is described as the angle between the horizontal line and the line connecting the intersections of the sternocleidomastoid muscle and the trapezius. TAR is calculated by taking the ratio of the left/right area created by taking the line connecting the acromia, the perpendicular line through the intersection of the sternocleidomastoid and trapezius muscle, and the margin of the trapezial muscle. The “lateral” prominence is best represented by the clavicle angle. Clavicle angle is the angle between the line connecting the top margin of the soft tissues immediately superior to the acromioclavicular joint and the horizontal line. Similarly, the clinical shoulder height is the difference (in millimeters) between the right and left acromioclavicular joints (Fig. 17‑2). The lateral prominence is what is more commonly referred to when studies report on “clinical shoulder balance.”

Qiu et al ¹⁵ described the evaluation of shoulder alignment based on the inner and outer shoulder heights, similar to the medial and lateral prominence described earlier. The authors also described the axilla angle, which is the angle between the horizontal line and a line through the posterior fold of both axillae (Fig. 17‑3). However, there was no correlation with axilla angle and any radiographic parameters, consistent with other attempted evaluations of lateral shoulder alignment.

In the literature, the clinical evaluation of shoulder imbalance has been inconsistently assessed from both an anterior and posterior perspective. Proponents of the posterior clinical assessment feel that this is how the surgeon sees the patient in the clinic, on a posteroanterior radiograph, and on the operating room table. While these points are certainly valid, the authors of this chapter feel strongly that the gold standard clinical evaluation of shoulder balance for the patient and the surgeon should be from an anterior perspective, as, ultimately, the patients’ perception of their shoulder alignment is paramount.

17.3.2 Radiographic Evaluation of Shoulder Balance

Many radiographic parameters have been evaluated in an effort to find an assessment that has a reliable association with shoulder balance. Qiu et al ¹⁵ reported excellent intra- and interobserver reliability (correlation coefficients > 0.9) with the radiographic parameters listed later. However, as an example, Kuklo et al ² reported that clavicle angle provided the best radiographic prediction of postoperative shoulder alignment. Conversely, Qiu et al ¹⁵ did not identify any radiographic parameters that accurately reflected the clinical appearance of the shoulders. The discordance between the clinical and radiographic assessment of shoulder alignment is unfortunately not uncommon. Chung et al ¹⁶ demonstrated that nearly half (46.5%) of Lenke 1 and 67.5% of Lenke 2 AIS patients had discordant medial and lateral shoulder balance prior to surgery.

Radiographic Parameters

T1 tilt: The angulation of the upper endplate of T1 to the horizontal, considered “positive” if the left proximal corner is elevated relative to the right (Fig. 17‑4).

First rib angle: The tilt of a tangential line that connects both the superior borders of the first ribs (Fig. 17‑5).

Clavicle angle (radiographic): The intersection of a horizontal line and the tangential line connecting the highest two points of each clavicle (Fig. 17‑6).

Radiographic shoulder height (RSH): Determined by the difference in the soft-tissue shadow directly superior to the acromioclavicular joint. Kuklo et al ² graded these differences as Grade 0: RSH < 1 cm; Grade 1: 1 cm ≤ RSH < 2 cm; Grade 2: 2 cm ≤ RSH ≤ 3 cm; Grade 3: RSH > 3 cm (Fig. 17‑7).

Coracoid height difference: Graded height difference (in millimeters) between the right and left coracoid process (Fig. 17‑8).

Clavicle chest cage angle difference (CCAD) ¹⁷ (Fig. 17‑9):

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  A line (center chest cage line or CCL) is drawn from the centroid of T1 to the centroid of T12.

  
  
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  A line is drawn perpendicular to the first line.

  
  
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  Another line is drawn from the middle of the proximal end of the clavicle to the middle of the distal end of the clavicle in both the right and left clavicles.

  
  
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  The angle formed by the intersection of these lines is the clavicle chest angle (CCA).

  
  
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  CCAD is measured as the subtraction of the values of the left CCA from the corresponding values of the right CCA.

  

Yagi et al ¹⁷ extensively evaluated the CCAD, reporting excellent intra- and interobserver reliability of this relatively novel radiographic assessment and a significant correlation between preoperative CCAD and postoperative shoulder balance (p = 0.01). Only 13% of patients with a grade 3 CCAD (>10 degrees) had balanced shoulders postoperatively, while 54% of patients with a preoperative grade 3 CCAD (>10 degrees) had unbalanced shoulders postoperatively.

17.3.3 Authors’ Recommendation

These radiographic assessments, along with a myriad of others, have all proven to provide the surgeon with objective information on shoulder alignment in some capacity and are provided here for completeness. However, performing a litany of radiographic measurements may not always be practical for the surgeon. The authors recommend that, at a minimum, the surgeon should always have an appreciation of the proximal thoracic (PT) Cobb, T1 tilt, and RSH when evaluating radiographic shoulder alignment.

17.3.4 Relationship of Clinical and Radiographic Shoulder Balance

The importance of T1 tilt has been evaluated in multiple studies with conflicting results. Akel et al ¹ demonstrated that T1 tilt was the most accurate predictor of clinical shoulder balance. However, Lee et al ¹⁸ found that T1 tilt had no correlation with shoulder balance. Amir et al ¹⁹ demonstrated that correcting the PT curve and leveling T1 was associated with improved medial shoulder balance. However, the lateral shoulder balance was less predictably controlled relative to T1 tilt, leading the authors to state that “leveling the PT curve and T1 does not guarantee balanced shoulders.”

Bagó et al ²⁰ evaluated several radiographic measurements in comparison with clinical shoulder height. The authors reported only a moderate correlation coefficient between clinical shoulder height and T1 tilt: 0.54; first rib inclination: 0.63; and coracoid process height: 0.96. Qiu et al ¹⁵ demonstrated that the first rib angle (FRA) had the highest correlation coefficient with inner shoulder height, but this was only 0.8. Other parameters including T1 tilt, clavicle angle, and coracoid process height also had significant correlation with inner and outer shoulder height, but the correlation coefficient was less than 0.8 for all parameters. Thus, the authors stated that radiographic parameters could only partially reflect the clinical shoulder appearance. Given that none of the radiographic and clinical assessments had a strong correlation to one another, the authors recommended that the clinical shoulder parameters “serve as a supplement” to the radiographic parameters in the evaluation of shoulder alignment.

Ono et al ¹⁴ described two components of shoulder balance: medial (trapezial prominence) and lateral (clinical shoulder balance). The authors comment that this difference exists in part because there is no direct contact between the shoulder and the spine as the spine articulates with the ribs, which then connect to the scapula. Thus, the more direct measures of spinal alignment (T1 tilt, FRA, and PT Cobb) have a better correlation with medial trapezial prominence than lateral shoulder balance. Amir et al ¹⁹ identified a similar weak correlation between the correction of the PT deformity and improvement in lateral shoulder balance. They state that this is likely due to the overall improvement in the trunk/thoracic cage deformity, as the shoulders lay on these structures. However, given that there is not a solid direct connection between the spine and the outer shoulders, this correction of lateral shoulder balance relative to spinal deformity correction is not linear, and thus is less predictable.

17.4.1 Magnitude and Flexibility of the Proximal Thoracic Curve

The concept of a structural PT curve that warrants treatment has been recognized since the Ponseti classification in 1950. ²¹ As correction methods and instrumentation improved, it was recognized that correction of the main thoracic (MT) curve alone in the presence of a significant PT curve would produce postoperative shoulder imbalance. King et al ²² classified the double thoracic curve pattern as a Type V and recommended fusion of both thoracic curves. In a later article, Lenke et al ²³ recommended that the PT curve be fused if the Cobb angle was greater than 30 degrees and corrected to no better than 20 degrees. Subsequently, the landmark AIS classification study by Lenke et al ²⁴ established criteria for a “structural” PT curve, which did not bend down below 25 degrees on side-bending films. This defined the structural PT curve, which they recommended to include in the fusion construct.

These findings were reproduced utilizing pedicle screw instrumentation in a more recent study by Li et al. ²⁵ The authors evaluated 25 consecutive Lenke type 2 patients in which the PT and MT curves were fused according to the Lenke classification of inclusion of the PT curve if it did not bend to less than 25 degrees. Inclusion of the structural PT curve in the fusion resulted in 84% of patients with level shoulders postoperatively, and the remaining 16% had only minor shoulder asymmetry of 1 to 2 cm.

Kuklo et al ² performed an extensive evaluation of 112 King V (Lenke type 2) patients with an upper instrumented vertebra (UIV) of T2, T3, or T4, assessing a multitude of radiographic and clinical parameters. In this study, the PT Cobb magnitude and flexibility as well as T1 tilt did not play a significant role in predicting postoperative shoulder balance, regardless of the UIV. The study found the preoperative clavicle angle, followed by the coracoid height (described later), to be the best predictors of postoperative shoulder balance.

17.4.2 Preoperative Shoulder Imbalance

The importance of properly assessing preoperative shoulder balance and the PT curve has been described since the 1960s. ²⁶ In 1993, Lee et al ¹⁸ reported that the most important determinant of postoperative shoulder balance was preoperative shoulder balance. The authors recommended fusion of the PT curve in patients with preoperative left shoulder elevation in the setting of a typical right thoracic AIS deformity. Suk et al ¹³ recommended that a PT curve of greater than 25 degrees coupled with a preoperative level or elevated left shoulder should be considered a true double thoracic curve and the PT curve should be included in the fusion. The authors reported that the left shoulder had to be at least 12 mm below the right shoulder prior to surgery to warrant not fusing the PT curve.

Kuklo et al ² reported that the clavicle angle was the lone radiographic parameter that was significantly predictive for postoperative shoulder alignment. A negative clavicle angle preoperatively (which correlates with right shoulder elevation) did not require fusion of the PT curve regardless of the orientation of T1 tilt and/or the presence of a structural PT curve. The authors demonstrated that correction of the right MT curve would appropriately elevate the depressed left shoulder. In the case of a positive clavicle angle (elevated left shoulder) preoperatively, fusion or at least partial fusion of the PT curve was recommended.

More recently, Zang et al ²⁷ in a study of 49 patients with AIS found preoperative RSH to be an independent predictor of “aggravation” of postoperative RSH; however, the odds ratio was only 0.9. Hong et al ²⁸ also demonstrated that patients with smaller preoperative shoulder imbalance had a higher chance of postoperative shoulder imbalance. Gotfryd et al ²⁹ reported that for every 1 degree measured for clavicle angle, there was a corresponding elevation of 0.14 degrees of the ipsilateral shoulder. An elevated left shoulder postoperatively was most common in patients who had only mild or no shoulder imbalance preoperatively.

Han et al ³⁰ evaluated the effect of the preoperative clinical chest cage angle (CCAD, described earlier) on postoperative shoulder balance. The preoperative CCAD was found to be significantly greater in patients with unbalanced shoulders postoperatively. The preoperative CCAD was also shown to be greater in patients with unsatisfied postoperative outcomes. The authors identified a preoperative CCAD threshold of ≥ 5.5 degrees that would predict postoperative radiographic shoulder imbalance and patient satisfaction. However, the preoperative CCAD was not able to predict postoperative clinical shoulder balance.

17.4.3 Authors’ Recommendation

The preoperative assessment of shoulder balance, clinically and radiographically, appears to have a more substantial role than the size of the PT curve in determining the proper UIV.

17.5.1 Upper Instrumented Vertebra Selection

The main surgical goal for posterior spinal fusion (PSF) for AIS is arresting progression of the spinal deformity and safely maximizing the coronal, sagittal, and axial plane correction. However, the patient and family’s focus may be more toward the overall appearance/body image. As stated earlier, the importance of the appreciation of shoulder balance before and after surgery has been discussed since the 1960s. The King V double thoracic curve pattern was subsequently classified as a Lenke type 2 curve. In this setting, the PT curve is at least 25 to 30 degrees and has minimal flexibility, bending down to greater than 25 degrees. A PT curve that does not bend down to less than 25 degrees on side bending is therefore deemed a “structural curve” and was recommended to be included in the fusion construct. ²⁴

As stated earlier, the preoperative shoulder alignment also can play a significant role in the UIV level selection. Lee et al ¹⁸ recommended fusion of the PT curve if the left shoulder was elevated preoperatively in an effort to achieve postoperative shoulder asymmetry. Suk et al ¹³ reiterated these recommendations with all pedicle screw constructs. The authors stated that the PT curve should be included in the fusion when the left shoulder is at the same level or higher than the right shoulder. The PT curve does not have to be fused if the right shoulder is at least 12 mm higher than the left preoperatively.

Kuklo et al ² also reiterated these findings in their study of 112 King V (Lenke type 2) patients, all of who had a PT Cobb greater than 20 degrees and underwent PSF with a UIV of T2–T4. The authors did not find a statistically significant difference in postoperative shoulder alignment with a UIV of T2 versus T3 versus T4. Furthermore, the authors did not find that preoperative T1 tilt, PT Cobb magnitude, and/or flexibility played a role in predicting postoperative shoulder alignment. This study found the clavicle angle alone to be a reliable predictor of postoperative shoulder balance. Similar to the aforementioned parameters, the authors found satisfactory results with the inclusion of the PT curve in the fusion only if the clavicle angle was positive (elevated left shoulder) preoperatively. Otherwise, the PT curve did not need to be included in the construct. With these parameters, the authors reported that 76% of the patients were clinically balanced postoperatively and 74% were either happy or very happy with their overall appearance.

Rose and Lenke ³¹ published operative treatment guidelines for patients with AIS. This report recommended fusion to T4 or T5 if the right shoulder was elevated prior to surgery, patients with neutral preoperative shoulders should be fused to T3, and the fusion should extend to T2 if the left shoulder is higher preoperatively. Bjerke et al ³² later evaluated these criteria and found that 16% of patients had postoperative shoulder asymmetry when these guidelines were strictly followed. Furthermore, 15% had unbalanced shoulders postoperatively when the guidelines were not followed. These findings highlight the likely multifactorial nature of postoperative shoulder alignment.

Most recently, Brooks et al ³³ evaluated 626 AIS patients with a UIV of T2, T3, or T4. The authors demonstrated an improved correction of the PT curve when the UIV was T2 or T3 versus T4. Conversely, a significantly greater percentage of postoperative shoulder asymmetry was noted with a more proximal UIV. Patients fused to T2 had unbalanced shoulders (>1 cm) in 45% of cases, 48% if the UIV was T3, and in only 34% if the UIV was T4 (p = 0.008). These results held true even in the setting of an elevated left shoulder preoperatively. Thus, in this study, the selection of T4 as the UIV resulted in a significantly higher percentage of patients with level shoulders postoperatively compared to T2 and T3 regardless of which shoulder was elevated.

The majority of the studies assessing shoulder balance focus primarily on Lenke type 1 and 2 curves. Yaszay et al ³⁴ evaluated the preoperative and postoperative shoulder alignment for primary thoracolumbar curves (Lenke type 5). In their study, 53% of patients had an elevation of the shoulder opposite the thoracolumbar curve prior to surgery, which was associated with a larger MT curve (average: 31 vs. 24 degrees for level shoulders vs. 21 degrees for a lower shoulder; p = 0.01). Postoperatively, 64% had shoulder asymmetry less than 1 cm, and 93% had shoulder asymmetry less than 2 cm. Interestingly, the inclusion of the MT curve in the fusion did not influence the postoperative shoulder balance regardless of the preoperative shoulder alignment. These findings are similar when compared to those of Kuklo et al, ² who demonstrated that a more proximal UIV and inclusion of the PT curve in the fusion did not significantly improve postoperative shoulder balance.

There is unfortunately little discussion in the literature regarding the sagittal plane for the PT curve. Newton et al ³⁵ demonstrated through a detailed assessment of three-dimensional reconstructions utilizing modern imaging techniques that the thoracic spine is often much more hypokyphotic or even lordotic than initially appreciated on traditional two-dimensional radiographs. Careful attention should be paid to the sagittal alignment of the PT curve preoperatively and intraoperatively. Inclusion of the PT spine in the construct is required regardless of the coronal Cobb if significant PT kyphosis is present, as this renders the PT curve “structural.” ²⁴ Furthermore, the surgeon must be aware that in the setting of significant MT lordosis, an inflection point may exist between this point and the beginning of PT kyphosis. Similar to the general principles for the thoracolumbar junction, the authors of this chapter recommend that the surgeon not stop the construct at the apex of a sagittal inflection point and, thus, include the PT spine in the fusion construct.