6. Biomechanical investigation of the potential development and prevention of scoliosis following various sizes of chest wall resection

Abstract

BACKGROUND CONTEXT Chest wall resection is used to treat several thoracic disorders including tumor removals. A well-known problematic sequela of chest wall resections is development of scoliosis. Literature shows that the degree of the induced curvature correlates to the number of resected ribs. Despite the seriousness and frequency of scoliosis following chest well resection, the etiology and biomechanical information needed to understand this deformity development are not well-known. PURPOSE The objective of the present study was to investigate the effect of chest wall resections, ranging in size from 1 to 6 ribs, on the biomechanical stability of the spine. Further, the study compared anterior-only fixation with a combined anterior-posterior approach in reducing range of motion (ROM) following chest wall resection. STUDY DESIGN/SETTING Biomechanics/laboratory. METHODS The range of motion (ROM) of six specimens (C7–L2) was captured using a custom-built six degrees-of-freedom machine in each of three physiological rotation axes: flexion extension (FE), lateral bending (LB), and axial rotation (AR). Left posterior ribs were sequentially resected 7 cm from the rib head, starting at the 5th rib and continuing until the 10th rib. Injured specimens were instrumented first with unilateral anterior rod fixation (UA) and then with additional unilateral posterior fixation (UA+UP), each starting at T4 and then extended distally as ribs were resected. Relative motion between the proximal and distal ends of the construct was measured in all three axes for the intact, injured, UA, and UA+UP constructs. RESULTS Raw ROM of the injured specimen increased in a stepwise manner as additional ribs were resected, with an average increase of 0.90°±0.52° in FE, 0.98°±0.40° in LB, and 2.75°±1.50° in AR. No statistically significant differences in ROM normalized to the intact specimen were found between operative constructs for any injury size (p>.05). Across all injury sizes, the UA construct reduced motion, and the UA+UP construct further reduced motion in all FE (22.0±12.3% vs 58.4±13.2%), LB (51.0±9.8% vs 74.4±9.0%), and AR (25.4±9.0% vs 58.7±11.2%). The impact of fixation was slightly greater as more ribs were resected. CONCLUSIONS The stepwise ROM increase for the injured model as more ribs were resected can likely be attributed to the additional motion segment, suggesting that the etiology of scoliosis following chest wall resection may not be purely biomechanical in nature. Overall, the UA+UP construct may be a more optimal construct than UA in reducing motion and potentially assisting in limiting the risk of scoliosis development. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.