Introduction: Treatment of burst fractures involves stabilization of the unstable site. Classical biomechanical models have involved thoracic spines disarticulated from the ribcage. However, the biomechanical influence of the rib cage on fracture stabilization and the use of short segment constructs versus long segment constructs for mid-thoracic fractures have yet to be fully investigated.

Methods: Eight human cadaveric spines, C7 – L1 with intact ribcage were tested using a robotic spine testing system (KUKA, Germany). A continuous pure moment (±5 Nm) was applied to simulate flexion-extension (FE), lateral bending (LB), and axial rotation (AR). Intersegmental rotations were measured using an optoelectronic system (Optotrak, Northern Digital Inc.). Intact specimens were tested first, then after surgically induced fracture at T9 and sequential placement of four construct patterns: 3 above/2 below (3A/2B), 1 above/1 below (1A/1B), 1 above/1 below with vertebral body augmentation (1A/1B VA), and vertebral body augmentation alone (VA). Statistical tests were used to compare the segmental range of motion (ROM) between surgical treatments (T8 - T10).

Results: Mean ROM increased by 86%, 151% and 31% in LB, FE and AR respectively after fracture. In LB, there was significant reduction for only three construct patterns: 3A/2B (92%, p = 0.0004), 1A/1B (63%, p = 0.0132) and 1A/1B w/VA (66%, p = 0.0150). In FE, only 3A/2B showed a significant reduction in motion (90%, p = 0.0113). For AR, three construct patterns, 3A/2B (66 %, p = 0.0001), 1A/1B (53 %, p = 0.0001) and 1A/1B w/VA (51%, p = 0.0002) significantly reduced motion. We found that statistically, only three construct patterns (3A/2B, 1A/1B and 1A/1B w/VA) showed comparable stability in all three motion planes.

Conclusions: Thus far, our findings would support that a shorter construct with or without vertebral augmentation can stabilize the spine to the extent that a longer construct would.

Patient Care: With the knowledge that the intact ribcage and sternum does contribute enough stability to the thoracic spine, we should be able to treat unstable thoracic burst fractures with a shorter 1 above/1below construct. This shorter construct should result in a smaller incision, less muscle dissection, less blood loss, shorter operative time, and less post-operative pain.

Learning Objectives: By the conclusion of this session, participants should be able to do the following: 1) Understand the biomechanical contribution of the ribcage and sternum to the thoracic spine, 2) Understand that of the 4 proposed constructs in the thoracic spine for stabilization of a burst fracture, 1 level above and below the fracture in the setting of intact ribcage and sternum is as stable as a rigid 3 above and 2 below construct. 3) Understand the limitations of this project to be a biomechanical study with the next step to involve clinical application.

References: 1. Watkins et al ., Spine (Phila Pa 1976). 2005 Jun 1;30(11):1283-6. 2. Acosta et al, Neurosurg Spine. 2008 Apr; 8(4):341-6. 3. Parker et al ., Spine (Phila Pa 1976). 2000 May 1;25(9):1157-70.