Abstract
BackgroundsThe purpose of this study was to investigate the occurrence and factors associated with postoperative shoulder imbalance (PSI) in Lenke type 1A curve.MethodsThis study included 106 patients with Lenke Type 1A curve who were followed up more than two years after posterior correction surgery. Pedicle screw (PS) constructs were used in 84 patients, and hybrid constructs in 22. The upper instrumented vertebra was rostral to the upper-end vertebra (UEV) in 70 patients, at UEV in 26, and below UEV in 10. The clavicle angle and T1 tilt angle were measured as PSI indicators, and correlations between radiographic parameters of shoulder balance and other radiographic parameters and associations between PSI and clinical parameters were investigated. For statistical analyses, paired and unpaired t-tests were used.ResultsThe mean Cobb angles of the main and proximal thoracic curves were 54.6 ± 9.5 and 26.7 ± 7.9 degrees before surgery, 14.5 ± 7.5, and 14.9 ± 7.1 at follow-up. Clavicle angle and T1 tilt angle were −2.9 ± 2.8 and −2.6 ± 6.3 before surgery, 2.4 ± 2.8 and 4.4 ± 4.3 immediately after surgery, and 1.8 ± 2.1 and 3.4 ± 5.5 at follow-up. Twenty patients developed distal adding-on. Clavicle angle at follow-up correlated weakly but significantly with preoperative clavicle angle (r = 0.34, p = 0.001) and with the correction rates of the main thoracic curve (r = 0.34, p = 0.001); it correlated negatively with the proximal curve spontaneous correction rate (r = −0.21, p = 0.034). The clavicle angle at follow-up was significantly larger in patients with PS-only constructs (PS 2.1 degrees vs. hybrid 0.9, p = 0.02), and tended to be smaller in patients with distal adding-on (adding-on 1.1 vs. non adding-on 2.0, p = 0.09).ConclusionsPSI was more common with better correction of the main curve (using PS constructs), in patients with a larger preoperative clavicle angle, and with a larger and more rigid proximal curve. Distal adding-on may compensate for PSI.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2474-15-366) contains supplementary material, which is available to authorized users.
Highlights
Adolescent idiopathic scoliosis, of which etiology remains to be clarified [1], is classified into six types by Lenke et al [2]
Maximal correction of the main thoracic curve can cause the left shoulder to elevate, even in Lenke type 1 curves, because a proximal thoracic curve often has enough rigidity to prevent a spontaneous correction equivalent to correction achieved by instrumented fusion in the main thoracic curve [12]
The correction rate of the main thoracic curve was 75.4 ± 11.3% in patients treated with all-pedicle screw (PS) constructs, and 66.4 ± 16.2% in those treated with hybrid constructs (p = 0.003)
Summary
Adolescent idiopathic scoliosis, of which etiology remains to be clarified [1], is classified into six types by Lenke et al [2]. Lenke type 1 curve is a single thoracic curve with non-structural flexible curves in the proximal thoracic and lumbar spine. Lenke type 1 has three modifiers—A, B, and C—that indicate the configuration and magnitude of the distal lumbar curve. Maximal correction of the main thoracic curve can cause the left shoulder to elevate, even in Lenke type 1 curves, because a proximal thoracic curve often has enough rigidity to prevent a spontaneous correction equivalent to correction achieved by instrumented fusion in the main thoracic curve [12]. If postoperative shoulder imbalance (PSI) persists, the left shoulder becomes quite prominent, and this may cause patients to be dissatisfied with the results of the surgery [12,13,14]
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