Posterior Spinal Fusion Hardware¶
Overview¶
Posterior spinal fusion is the most common instrumented spinal surgery. Pedicle screws are placed through the pedicles into the vertebral bodies and connected by rods to stabilize the spine while bony fusion occurs. Understanding the expected hardware appearance and recognizing complications is essential for radiologists.
Normal Hardware Appearance¶
Pedicle Screws¶
- Screws should be contained within the pedicle and vertebral body
- The tip should not breach the anterior vertebral body cortex
- Medial pedicle breach may compress the thecal sac or nerve roots
- Lateral breach is generally less clinically significant
Rods¶
- Connect the pedicle screws bilaterally
- Should be smoothly contoured following the spinal alignment
Cross-links¶
- Connect the bilateral rods transversely for added stability
Imaging Evaluation¶
Radiography¶
- AP and lateral views assess overall hardware position and alignment
- Look for screw breakage, rod fracture, screw pullout, and cage migration
CT¶
- Best modality for detailed hardware assessment
- Evaluate pedicle screw trajectory (medial or lateral breach)
- Assess bony fusion — bridging bone between vertebral bodies or posterolateral gutters
- Lucency around screws (>2 mm halo = loosening)
MRI¶
- Limited by metal artifact, but MARS techniques improve visualization
- Evaluates epidural space, neural compression, and soft tissues
Clinical Pearl
A 2 mm lucent halo around a pedicle screw on CT suggests loosening. Loosening can result from pseudarthrosis (failure of fusion), infection, or poor bone quality. Always correlate with clinical symptoms and other findings — asymptomatic lucency may simply represent stress remodeling at the bone-screw interface.
Key Points¶
- Pedicle screws should be contained within the pedicle and vertebral body
- CT is the best modality for hardware and fusion assessment
- Lucency >2 mm around screws suggests loosening
- Medial pedicle breach is more clinically significant than lateral
- Always assess fusion status — hardware alone does not indicate successful fusion
References¶
- Wuertzer SD, Pohl EC, Stevens EA, Geer CP. Spinal Fusion: Role of Perioperative Radiography. RadioGraphics. 2023;43(4):e220061. doi:10.1148/rg.220061.
- Ghodasara N, Yi PH, Clark K, Fishman EK, Farshad M, Fritz J. Postoperative Spinal CT: What the Radiologist Needs to Know. RadioGraphics. 2019;39(6):1840-1861. doi:10.1148/rg.2019190050.
- Rutherford EE, Tarplett LJ, Davies EM, Harley JM, King LJ. Lumbar spine fusion and stabilization: hardware, techniques, and imaging appearances. RadioGraphics. 2007;27(6):1737-1749. doi:10.1148/rg.276065205.
- Ha AS, Petscavage-Thomas JM. Imaging of current spinal hardware: lumbar spine. AJR Am J Roentgenol. 2014;203(3):573-581. doi:10.2214/AJR.13.12217.
- Wu X, Shi J, Wu J, Cheng Y, Peng K, Chen J, Jiang H. Pedicle screw loosening: the value of radiological imagings and the identification of risk factors assessed by extraction torque during screw removal surgery. J Orthop Surg Res. 2019;14(1):6. doi:10.1186/s13018-018-1046-0.
- Gertzbein and Robbins classification of pedicle screw position. Radiopaedia.org. https://radiopaedia.org/articles/gertzbein-and-robbins-classification-of-pedicle-screw-position. Accessed May 13, 2026.