Anterior Single Solid Rod Instrumentation in Thoracolumbar Adolescent Idiopathic Scoliosis With and Without the Use of Interbody Structural Support

Introduction: The use of interbody structural support is often recommended in conjunction with anterior instrumentation for the treatment of thoracolumbar AIS. Purpose: To compare pre and postoperative coronal and sagittal parameters in patients treated with an anterior single solid rod construct with and without the use of interbody structural support.

Materials and Methods: Thirty–nine patients (mean age 15.9 years) with thoracolumbar AIS underwent anterior surgery using a single 6mm solid rod construct (3 male, 36 female). Structural interbody support was used in 24 patients and packed morselized autograft bone alone was used in 15 patients. No patients were braced postoperatively. Each patient had minimal follow–up of 2 years. Preoperative, initial and most recent follow–up radiographs were reviewed to determine Cobb measurements of the primary and compensatory curves (thoracic and lumbar), apical and end vertebra rotation, apical translation, last instrumented vertebra (LIV) angulation and translation, global coronal and sagittal balance and segmental sagittal Cobb measurements from T2–12, T5–12, T12–L2, T12–LIV, T12–sacrum, and the instrumented levels.

Results: Along with achieving maximal curve correction, as well as coronal and sagittal balance, obtaining horizontalization and derotation of the LIV are major surgical goals. Primary Cobb correction averaged 74%. Spontaneous correction of the uninstrumented curves was 29% for the thoracic and 72% for the lumbar. The mean sagittal profile of the instrumented segments was –2° preoperatively and +2° postoperatively. There were no statistical differences in any of the coronal or sagittal measurements between patients in which interbody structural support was utilized versus patients in which only morselized bone autograft was used. Achieving horizontalization of the LIV correlated statistically with preoperative measurements of apical translation of the primary curve (<48mm, p<0.05), translation of the lowest instrumented vertebra (<30mm, p<0.01), global coronal imbalance (<30mm, p<0.05), and instrumentation that included the horizontal vertebra on the reverse bending radiograph(p<0.01).

Conclusions: The use of interbody structural support may not be necessary to maintain appropriate sagittal and coronal profile when a rigid single rod construct is used for the treatment of thoracolumbar AIS. Parameters predicting horizontalization and derotation of LIV were identified which if achieved help establish normal relationships between the uninstrumented segments and may therefore prevent late degenerative changes.