Prediction of Thoracic Dimensions and Spine Length Based on Individual Pelvic Dimensions. Another Standard for Evaluation of Outcome in Early Onset Spinal Deformity
Purpose: To determine predictors of normal chest and thoracic spine dimensions that are patient-specific for comparison in patients with severe chest/spine abnormalities at any age, size, or stage of growth. An internal, individualized standard for chest and spine dimensions would provide a basis of evaluation of spine and thoracic treatment outcomes in patients not following the usual patterns of growth and development.
Methods: IRB approval was obtained for review of existing chest and abdominal CT scans in previously healthy patients evaluated for trauma or new onset malignancy. Conditions or surgeries which may have influenced dimensions or normal growth were excluded. After a pilot investigation and statistical analysis a pre-determined uniform distribution of genders and ages ranging from 0 to 21 years were determined and 187 CT scans meeting those criteria selected for measurement. On average 5 of each gender for each age year were selected. Mean age was 9.5 +/- 6.0 years. There was no significant difference in age between the 76 females (9.0 +/- 6.1) and 111 males (9.8 +/- 5.8) (p = 0.39). Measurements made on CT scan included maximum inner chest width (CW), chest depth, thoracic spine height, lumbar spine height, and pelvic inlet width (PW). Analysis of variance and linear regression analysis were used to assess the correlation between chest dimensions and pelvic width, age and gender.
Results: Multiple linear regression indicated that pelvic inlet width (beta = 1.72, t = 32.24, p<0 .0001) and gender (beta="" 1.90, t="" 6.70, p<0.0001) provided the best model fit in establishing normal ranges of chest width (adjust R-squared="" 0.86). Age contributed no additional information beyond that by pelvic sex. Pelvic inlet provides an age-independent parameter for prediction thoracic dimensions. Gender-based CW based on PW were constructed using 95% confidence intervals. Normal (CW) cm. can be predicted (PW) formulas:
Females: Chest Width = 2.8 + 1.7 x PW + 2
Males: Chest Width = 2.8 + 1.7 x PW + 4
Significance: Early onset spinal deformity can be associated with late pulmonary insufficiency and diminished trunk height, or so-called “thoracic insufficiency syndrome”. Treatments include early arthrodesis, instrumentation without fusion, and more recently expansion thoracostomy and VEPTR (vertical expandable prosthetic titanium rib) insertion. Evaluation of anatomic outcomes in this group of patients is in part hindered by the inability to measure the effect of treatment on predicted thoracic and spine dimensions. It is anticipated that these individual patient-based standards will aid in assessing the effect of treatment on thoracic growth in this severely affected group of patients.