Daniel G Kang1, Ronald A Lehman2, Scott C Wagner1, Adam J Bevevino1, Robert W Tracey1, Rachel E Gaume1, Anton E Dmitriev3. 1. Department of Orthopaedic Surgery, Walter Reed National Military Medical Center, 8901 Wisconsin Ave., Bldg 19, Rm #2101, Bethesda, MD 20889, USA. 2. Department of Orthopaedic Surgery, Walter Reed National Military Medical Center, 8901 Wisconsin Ave., Bldg 19, Rm #2101, Bethesda, MD 20889, USA; Division of Orthopaedics, Department of Surgery, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814, USA. Electronic address: armyspine@yahoo.com. 3. Department of Orthopaedic Surgery, Walter Reed National Military Medical Center, 8901 Wisconsin Ave., Bldg 19, Rm #2101, Bethesda, MD 20889, USA; Division of Orthopaedics, Department of Surgery, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814, USA.
Abstract
BACKGROUND CONTEXT: The use of a rod reduction device can have deleterious consequences on pedicle screw pullout strength (POS) in the thoracic spine. However, posterior-only osteotomies in the thoracic spine are often performed to improve flexibility of the spine and offset forces of deformity correction maneuvers. PURPOSE: To investigate the effect on pedicle screw POS caused by the rod reduction technique in the presence of facet osteotomies in the thoracic spine. STUDY DESIGN/ SETTING: The study is a biomechanical study using human cadaveric spine specimens. METHODS: Thoracic Ponte osteotomies were performed on 3 thoracic levels in 15 cadaveric specimens. The right rod was contoured with a 5-mm residual gap at the middle level and was reduced using a rod reduction device. On the left side (paired control), a rod with no mismatch was placed. Biomechanical testing was performed with tensile load to failure "in line" with the screw axis and POS measured in Newtons (N). RESULTS: After rod reduction, thoracic pedicle screw POS was significantly decreased (40%) compared with the control (419±426 N vs. 708±462 N, p=.002) and remained statistically significant after adjusting for bone mineral density (BMD) (p=.05). Eleven (73%) of the pedicle screws had visible pullout/failure during the reduction attempt and occurred irrespective of BMD. CONCLUSIONS: Despite thoracic Ponte osteotomies and increased flexibility of the spinal segments, the rod reduction device still significantly decreased pedicle screw POS, typically resulting in outright failure of the screw-bone interface. Therefore, rod reduction technique of any kind should be performed with caution as it frequently results in suboptimal pedicle screw fixation. Published by Elsevier Inc.
BACKGROUND CONTEXT: The use of a rod reduction device can have deleterious consequences on pedicle screw pullout strength (POS) in the thoracic spine. However, posterior-only osteotomies in the thoracic spine are often performed to improve flexibility of the spine and offset forces of deformity correction maneuvers. PURPOSE: To investigate the effect on pedicle screw POS caused by the rod reduction technique in the presence of facet osteotomies in the thoracic spine. STUDY DESIGN/ SETTING: The study is a biomechanical study using human cadaveric spine specimens. METHODS: Thoracic Ponte osteotomies were performed on 3 thoracic levels in 15 cadaveric specimens. The right rod was contoured with a 5-mm residual gap at the middle level and was reduced using a rod reduction device. On the left side (paired control), a rod with no mismatch was placed. Biomechanical testing was performed with tensile load to failure "in line" with the screw axis and POS measured in Newtons (N). RESULTS: After rod reduction, thoracic pedicle screw POS was significantly decreased (40%) compared with the control (419±426 N vs. 708±462 N, p=.002) and remained statistically significant after adjusting for bone mineral density (BMD) (p=.05). Eleven (73%) of the pedicle screws had visible pullout/failure during the reduction attempt and occurred irrespective of BMD. CONCLUSIONS: Despite thoracic Ponte osteotomies and increased flexibility of the spinal segments, the rod reduction device still significantly decreased pedicle screw POS, typically resulting in outright failure of the screw-bone interface. Therefore, rod reduction technique of any kind should be performed with caution as it frequently results in suboptimal pedicle screw fixation. Published by Elsevier Inc.