Table 6 Associations between the spinal flexibility and bracing outcomes

Cheung [30]

Supine flexibility rate (30.20%)

First in-brace correction rate (41%)

r = 0.650; p < 0.001

Curve progression

Supine flexibility can predict in-brace correction and risk of curve progression

Cheung [14]

Supine Cobb angle/supine flexibility rate

(22.5°/70.6%)

Immediate in-brace Cobb angle/in-brace correction rate (18.9°/85.1%)

r = 0.740; p < 0.001

Immediate in-brace Cobb

Supine radiographs have predictive value for in-brace correction of AIS, the in-brace Cobb angle is 0.809 of the supine Cobb angle

He [15]

Supine flexibility (40%)

Initial in-brace correction (41%)

r = 0.660; p > 0.05

Initial in-brace correction

The spinal flexibility in the prone position is the closest to and most correlated with the initial in-orthosis correction among the four studied positions. The prone position could be an effective method to predict the initial effect of orthotic treatment on the patients with AIS

Prone flexibility (42%)

r = 0.750; p > 0.05

Flexibility of sitting with lateral bending (143%)

r = 0.040; p < 0.05

Flexibility of prone with lateral bending (127%)

r = 0.030; p < 0.05

He [33]

Supine Cobb angle (radiograph) (18.8°)

In-brace Cobb (16.6°)

r = 0.730; p < 0.05

In-brace Cobb

The recumbent curvatures (especially prone curvature) could be a predictor of the initial effect of orthotic treatment in the patients with AIS

Supine curvature (ultrasound) (10.7°)

In-brace curvature (11.2°)

r = 0.760; p = 0.27

In-brace curvature

Prone curvature (ultrasound) (10.7°)

r = 0.870; p = 0.16

Curvature of sitting with lateral bending (ultrasound) ( − 6.5°)

r < 0.30; p < 0.05

Curvature of prone with lateral bending (ultrasound) ( − 3.5°)

r < 0.30; p < 0.05

Ohrt-Nissen [31]

Supine bending curve flexibility rate (60%)

Immediate in-brace correction (61%)

NA

Curve progression

A decrease in curve flexibility, as determined by supine lateral bending radiograph, was an independent predictor of curve progression

Ohrt-Nissen [32]

Supine bending curve flexibility rate (63%)

Initial in-brace correction (63%)

NA

Initial in-brace Cobb

Supine lateral bending radiographs may serve as a key prognostic parameter in patients with AIS before initiating brace treatment

Wong [28]

Supine flexibility rate (23.2%)

First in-brace correction rate (33.7%)

NA

Curve progression

Flexibility was found to be significantly predictive of curve for curve progression; A higher supine flexibility (18.1%) predicted a lower risk of progression

Kuroki [34]

Flexibility index (NA)

Initial correction rate (NA)

NA

Curve progression

Curve flexibility did not affect the clinical results of brace treatment. However, success rate was insignificantly higher in the cases whose Cobb angle in brace was smaller than that in hanging position

Cheung [6]

Supine flexibility rate (30%)

First in-brace correction rate (41%)

NA

Curve regression; Curve progression

Despite a trend for patients with curve regression to have higher baseline flexibility, after controlling for other factors, no clinically important differences was found with increased flexibility

Kawasaki [36]

Supine flexibility rate (22%)

Initial in-brace correction rate (31.7%)

NA

Curve progression

Those with higher flexibility are at risk of curve progression

Strube [17]

Curve flexibility (NA)

In-brace correction (NA)

NA

Curve progression

Treatment failure depended significantly on major curve flexibility (p = 0.005)

Falbo [16]

Curve flexibility (59.64%)

In-brace correction (23.57%)

NA

In-brace curve correction

Curve flexibility alone cannot predict coronal curve correction. Additional factors must be considered when predicting success of brace treatment for AIS

Kwan [29]

Supine flexibility (43.9%)

Immediate in-brace correction rate (47.9%)

NA

Curve progression

Curve flexibility was associated with an increased risk of curve progression

Kuroki [35]

Hanging Cobb angle (21.1°)

Initial in-brace Cobb (20.3°)

r = 0.762; p < 0.001

Initial brace Cobb angle

Hanging total spine X-ray is useful for confirmation of adequate correction by the OMC brace in idiopathic scoliosis