Radiographic changes in degenerative thoracolumbar junctional kyphosis: sagittal balance and compensatory mechanism

English Keywords:Degenerative thoracolumbar junctional kyphosis  Degenerative lumbar kyphosis  Pelvis retroversion  Thoracic kyphosis  Sagittal balance

English Abstract:

  【Abstract】 Objectives: To compare the radiological parameters in patients with or without degenerative thoracolumbar junctional kyphosis(DTLJK), and to analyze the compensatory mechanism of sagittal balance. Methods: From March 2016 to May 2017, 77 patients with degenerative lumbar kyphosis(sagittal imbalance due to lumbar kyphosis or marked loss of lumbar lordosis) were enrolled in our radiographic study, including 30 males and 47 females with an average age of 65.8±8.0 years(range, 48-82 years). According to thoracolumbar junctional angle(TLJA), these patients were divided into two groups, degenerative thoracolumbar junctional kyphosis(DTLJK) group(group A, TLJA≥10°, 43 patients) and non-degenerative thoracolumbar junctional kyphosis(NDTLJK) group(group B, TLJA<10°, 34 patients). Complete spino-pelvic radiographic parameters were compared between two groups, including C7-sagittal vertical axis, thoracic kyphosis, lumbar lordosis, pelvic incidence, pelvic tilt and sacral slope. Results: The lumbar lordosis of group A and B was 17.30°±11.55° and 22.54°±8.72°, respectively. The thoracolumbar junctional angle(TLJA) in patients of group A and B was -15.26°±3.65° and -3.67°±4.74°, respectively. In group A, lumbar lordosis showed correlation with thoracic kyphosis(r=-0.345, P=0.024), sacral slope(r=0.595, P=0.000) and pelvic tilt(r=-0.363, P=0.017). In group B, lumbar lordosis showed correlation with thoracic kyphosis(r=-0.400, P=0.019), sacral slope(r=0.681, P=0.000) and C7-sagittal vertical axis(r=-0.402, P=0.018). There were significant differences in lumbar lordosis(t=2.230, P=0.029), thoracic kyphosis(t=3.325, P=0.001), sacral slope(t=2.939, P=0.004) and pelvic incidence (t=2.130, P=0.036) between two groups. Conclusions: Degenerative thoracolumbar junctional kyphosis is common and may be generated from special characteristics of morphology and biomechanics of the thoracolumbar junction. To maintain sagittal balance, pelvis retroversion may be more important in patients with DTLJK, while thoracic curves changes may be more important in patients without DTLJK.