Thoracolumbar Junction¶
Definition¶
The thoracolumbar junction (TLJ) is the transitional zone between the relatively rigid thoracic spine and the more mobile lumbar spine, typically defined as the T11–L2 segment. It is the most common site of spinal fractures due to the biomechanical stress concentration at this transition point.
Anatomy¶
Transitional Features¶
The TLJ represents a gradual transition between thoracic and lumbar morphology:
- Vertebral bodies: increase in size from thoracic to lumbar; T12 and L1 have intermediate dimensions
- Facet orientation: transitions from coronal (thoracic, allowing rotation) to sagittal (lumbar, restricting rotation); this transition typically occurs at the T12–L1 level
- Rib articulation: the last rib articulates with T12; L1 has no rib articulation, resulting in less posterior stabilization
- Kyphosis to lordosis: the thoracic kyphosis transitions to lumbar lordosis, with the inflection point typically at T12–L1
Biomechanical Significance¶
- The thoracic spine is stiffened by the rib cage, costovertebral joints, and coronal facet orientation
- The lumbar spine is relatively mobile with sagittal facet orientation
- The TLJ is the fulcrum where these two mechanically different regions meet
- Axial loads and flexion forces concentrate at this junction, explaining the high fracture rate
Important Structures¶
- Conus medullaris — the terminal end of the spinal cord, typically at the L1–L2 level (range T12–L3); injuries at the TLJ can directly damage the cord
- Artery of Adamkiewicz — typically enters between T9–T12; vulnerable during TLJ surgery or trauma
- Diaphragmatic crura — attach to the anterior surface of L1–L3 vertebral bodies; the aortic hiatus is at T12
Clinical Pearl
Approximately 50–60% of all spinal fractures occur at the thoracolumbar junction (T11–L2). The most common mechanism is flexion-compression, producing anterior wedge compression fractures. More severe mechanisms (flexion-distraction, burst) can result in posterior ligamentous complex disruption and spinal instability. The TLICS (Thoracolumbar Injury Classification and Severity) score integrates fracture morphology, PLC integrity, and neurologic status to guide surgical vs. conservative management.
Imaging Findings¶
Radiography¶
- AP view: assess vertebral body height symmetry, interpedicular distance (widening suggests burst fracture), and paraspinal soft tissue widening
- Lateral view: evaluate for anterior wedging (compression fracture), retropulsion of fragments, and kyphotic angulation
- A loss of >50% of anterior body height or kyphosis >30° suggests instability
CT¶
- Gold standard for fracture characterization at the TLJ
- Axial images: evaluate for burst fracture (retropulsed fragment in the canal), lamina fractures, and percent canal compromise
- Sagittal reformats: measure vertebral body height loss and kyphotic angle
- Coronal reformats: evaluate for lateral translation and asymmetric fractures
MRI¶
| Finding | Best Sequence | Significance |
|---|---|---|
| Marrow edema (acute fracture) | STIR/T2 fat-sat | Hyperintensity confirms acuity; distinguishes acute from chronic fracture |
| PLC injury | Sagittal STIR | High signal in the interspinous/supraspinous ligaments and ligamentum flavum indicates instability |
| Cord compression/contusion | Sagittal T2 | T2 hyperintensity within the cord indicates edema or contusion |
| Epidural hematoma | Sagittal/Axial T1 and T2 | Mixed-signal collection compressing the thecal sac |
Key MRI Finding
The posterior ligamentous complex (PLC) — comprising the supraspinous ligament, interspinous ligament, ligamentum flavum, and facet joint capsules — is the key determinant of surgical vs. conservative management in TLJ fractures. On sagittal STIR/T2 fat-sat MRI, PLC disruption appears as high-signal discontinuity of the normally low-signal ligaments between the spinous processes. Intact PLC generally supports conservative management; disrupted PLC typically requires surgery.
Key Points¶
- The thoracolumbar junction (T11–L2) is the most common site of spinal fractures
- The transition from rigid thoracic to mobile lumbar spine concentrates biomechanical stress
- The conus medullaris lies at this level, making cord injury possible with TLJ fractures
- CT is the primary modality for fracture characterization; MRI is essential for PLC and cord evaluation
- The TLICS scoring system guides management based on fracture morphology, PLC integrity, and neurologic status
- PLC integrity on MRI is the critical factor distinguishing stable from unstable injuries
References¶
- Fernández-de Thomas RJ, De Jesus O. Thoracolumbar Spine Fracture. StatPearls Publishing; updated 2023. https://www.ncbi.nlm.nih.gov/books/NBK562204/
- Fradet L, Petit Y, Wagnac E, Aubin CE, Arnoux PJ. Biomechanics of thoracolumbar junction vertebral fractures from various kinematic conditions. Med Biol Eng Comput. 2014;52(1):87-94. PMID: 24165806. https://pubmed.ncbi.nlm.nih.gov/24165806/
- Lee JY, Vaccaro AR, Lim MR, et al. Thoracolumbar injury classification and severity score: a new paradigm for the treatment of thoracolumbar spine trauma. J Orthop Sci. 2005;10(6):671-675. PMID: 16307197. https://pmc.ncbi.nlm.nih.gov/articles/PMC2779435/
- Jiménez-Almonte JH, King JD, Luo TD, Cassidy RC, Aneja A. Classifications in Brief: Thoracolumbar Injury Classification and Injury Severity Score System. Clin Orthop Relat Res. 2018;476(6):1352-1357. PMID: 29419629. https://pmc.ncbi.nlm.nih.gov/articles/PMC6263590/
- Masharawi Y, Rothschild B, Dar G, et al. Facet orientation in the thoracolumbar spine: three-dimensional anatomic and biomechanical analysis. Spine (Phila Pa 1976). 2004;29(16):1755-1763. PMID: 15303019. https://pubmed.ncbi.nlm.nih.gov/15303019/
- Saifuddin A, Burnett SJ, White J. The variation of position of the conus medullaris in an adult population. A magnetic resonance imaging study. Spine (Phila Pa 1976). 1998;23(13):1452-1456. PMID: 9670396. https://pubmed.ncbi.nlm.nih.gov/9670396/