Relationship Between Pulmonary Function and Thoracic Morphology in Adolescent Idiopathic Scoliosis: A New Index, the "Apical Vertebra Deviation Ratio", as a Predictive Factor for Pulmonary Function Impairment.

STUDY DESIGN

A retrospective study.

OBJECTIVE

The aim of this study was to investigate the relationship between thoracic morphology (TM) and pulmonary function (PF) in patients with adolescent idiopathic scoliosis (AIS) and the feasibility of the "apical vertebra deviation ratio (AVDR)" as a predictor of PF impairment.

SUMMARY OF BACKGROUND

The PF of AIS is one of the key focuses of clinicians' attention. Early identification of AIS patients who are at risk of developing impaired PF is important for improving patient management.

METHODS

Preoperative PF and radiographic examination data of 108 patients with thoracic AIS were collected. The following TM data were collected: the costophrenic angle distance (CAD), distance between T1 and mean diaphragm height (T1-diaphragm), T1-T12 height, and AVDR. The correlation coefficient between PF and TM measurements was analyzed, and univariable and multivariable linear regressions were used to determine whether the TM measurements could predict PF.

RESULTS

The CAD, T1-diaphragm, and T1-T12 height were significantly positively correlated with forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), vital capacity, and total lung capacity (r = 0.54-0.74, P < 0.01). A linear equation between CAD and pulmonary volume could be established: FVC (L) = -3.46 + CAD (cm) × 0.27 (R2 = 0.54). If T1-T12 height is included, the correlation is further enhanced (R2 = 0.68). There was a significant negative correlation between the AVDR and predicted values of forced vital capacity (FVC%), FEV1%, predicted values of vital capacity, and predicted values of total lung capacity (r = -0.46 to -0.52, P < 0.01). The AVDR could predict the value of each of these variables. One of the linear equations is as follows: FVC% = 110.70-99.73 × AVDR (R2 = 0.272).

CONCLUSION

The two novel, two-dimensional TM measurements, CAD and AVDR, can be used as moderate to strong predictors of PF outcome in statistical terms. An AVDR >0.2 suggests that the patient may suffer from moderate or severe PF damage.Level of Evidence: 4.