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P156. Rod Derotation vs. Direct Incremental Segmental Translation: A Biomechanical Analysis
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Proceedings of the NASS 24th Annual Meeting / The Spine Journal 9 (2009) 1S-205S
RESULTS: Of 184 patients, 62 were smokers (22 M, 40F; age 52.8 yrs) and 122 nonsmokers (45 M, 77F; age 57.5 yrs). Average 12-month Lenke score across all subsets was 1.07 (smokers 1.08; nonsmokers 1.07). At 24 months, average Lenke score across all subsets was 1.03 (smokers 1.00, non smokers 1.02). There were no infections, neurologic complications or plate breakages. One patient, a 59 year-old diabetic male smoker, developed a pseudarthrosis; at the 6-month follow-up, the patient remained asymptomatic and declined re-operation. CONCLUSIONS: The combination of a demineralized bone matrix-local bone contained within allograft dowels or PEEK spacer resulted in similar fusion rates (O 97%) for both smokers and nonsmokers at 12 months and 24 months postoperatively. FDA DEVICE/DRUG STATUS: PEED Spacers: Approved for this indication; Allograft Dowels: Approved for this indication. doi: 10.1016/j.spinee.2009.08.415
P155. DBM Use in 2-Level PLIFs: Fusion Comparison of Smokers and Non-Smokers W.B. Rodgers, MD, Curtis S. Cox, MD, Edward J. Gerber, MD; Jefferson City, MO, USA BACKGROUND CONTEXT: Smoking has been cited to potentiate postoperative infections and interfere with bone graft incorporation in fusion procedures. As such, higher pseudarthrosis (non-union) rates have been historically reported in this population subset. PURPOSE: Rates of fusion are presented between smokers and nonsmokers, using a commercially available demineralized bone matrix (DBM) coupled with bone marrow aspirate and local bone in 2-level posterolateral interbody fusion (PLIF) procedures. STUDY DESIGN/SETTING: Prospective, nonrandomized clinical and radiographic assessment. PATIENT SAMPLE: Of our single-site consecutive series of 110 twolevel PLIF patients, 47 smoked at the time of surgery. OUTCOME MEASURES: Clinical and radiographic measures were prospectively collected and evaluated to assess comorbidities, complications, and fusion results at 12 and 24 months postop. METHODS: 110 instrumented, 2-level PLIF procedures were performed by a single surgeon using a graft composite were prepared from ground lamellar bone, supplemented with DBM and posterior iliac crest bone marrow aspirate (BMA). The composite was placed in the aperture of PEEK or machined allograft spacers (to achieve interbody fusion) and along the intertransverse membrane (to achieve posterolateral fusion). Anteroposterior and lateral flexion and extension radiographs, obtained at three-, six-, and twelve-months, were evaluated utilizing Lenke’s criteria for intertransverse fusion and modified Lenke criteria of interbody fusion. Global fusion was defined as either: Lenke or modified Lenke score of 1; or Lenke score 2þmodified Lenke score 2. RESULTS: 46 smokers and 62 non-smokers, ranging in age from 33-85 years (average age557.42 years) presented for 12-month follow-up. Intertransverse/interbody scores for smokers51.89/1.20 and for nonsmokers51.69/1.25. To date, 32 smokers and 40 non-smokers have presented for 24 month follow-up. Lenke scores for smokers at 24 months postop were 1.81/1.25; non smokers 1.63/1.18. Similar complication rates were observed in both groups; 6 re-operations were performed for adjacent segment disease. CONCLUSIONS: Smoking is often identified as a contributing factor to increased pseudarthrosis (non-union) rates in spinal fusion surgeries. The fusion rates for smokers and non-smokers were 97.8% and 98.4% at 12 months respectively, and 97% and 97.5% at 24 months; no significant difference was shown between the two groups. Slightly better (intertransverse) Lenke scores were noted in the nonsmokers.
FDA DEVICE/DRUG STATUS: PEEK Spacers: Approved for this indication; Allograft Dowels: Approved for this indication. doi: 10.1016/j.spinee.2009.08.416
P156. Rod Derotation vs. Direct Incremental Segmental Translation: A Biomechanical Analysis Xiaoyu Wang, PhD1, Carl-Eric Aubin, PhD1, Hubert Labelle, MD2, Dennis Crandall, MD3; 1Ecole Polytechnique & Sainte-Justine University Hospital Center, Montreal, Quebec, Canada; 2Sainte Justine University Hospital Center, Montreal, Quebec, Canada; 3Sonoran Spine Center, Mesa, AZ, USA BACKGROUND CONTEXT: Scoliosis is corrected by different maneuvers applied to the spine via a mechanical constructs, with rods usually bent to desired sagittal profile. Basic techniques involve vertebral translation, rod derotation, direct vertebra derotation, compression and distraction, and in situ rod contouring. In order to maintain the correction rods are fully seated and locked into the slot of each implant, making it difficult to fine-tune the implant-rod relative location and control the force distribution amongst the implants. Direct incremental segmental translation (DIST) was proposed to provide a better control on the vertebra location with respect to the rod. The most distinguishing point of this concept is the ability to translate each implant toward and fixed on the rod from any distance and at any angle. PURPOSE: Compare the forces at the bone-screw interface during scoliosis correction using rod derotation vs. DIST. STUDY DESIGN/SETTING: We analyzed the biomechanics of two instrumentation paradigms: rod derotation technique (RDT) vs. a direct incremental segmental translation approach (DIST). PATIENT SAMPLE: Reduction techniques documented using pre- and post-op radiographs as well as intra-operative video of surgical maneuvers of 10 cases were used to develop a model for computer simulation of correction techniques for scoliosis. OUTCOME MEASURES: Computer simulation of scoliosis correction. METHODS: A common curve pattern (thoracolumbar curve) for adolescent idiopathic scoliosis was chosen. Simulations with both the RDT and
Figure. Simulated forces and their orientation at the vertebra-implant connections for the RDT (a) and DIST (b) techniques. The length of the arrows is proportional to the forces.
Proceedings of the NASS 24th Annual Meeting / The Spine Journal 9 (2009) 1S-205S DIST techniques were performed using the same patient biomechanical model built using biplanar X-rays, with same instrumentation levels and rod shape. The correction maneuvers and resulting effects were analyzed and compared. RESULTS: The vertebra position relative to the rod for the DIST is determined by 5 independent variables (position, orientation) vs. 2 for the RDT; thus increasing the possible correction of the connected vertebra. The DIST allows the spine deformity to be reduced by either gradually pulling the spine towards the rod through helical connections or translating it by pivoting the posts. Load at the vertebra-implant connection was on average 18% lower for the DIST, and better distributed (lower STD). CONCLUSIONS: The direct incremental segmental translation approach allows more control with better load sharing amongst implants. SIGNIFICANCE: This analysis provides insight into the different biomechanical effects of the 2 instrumentation paradigms. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs.
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their coronal tilts and unique pedicle footprints. It is important to distinguish a Type I from Type II L5 pedicle as a Type II pedicle is wider, has a more lateral pedicle center relative to the MLP, and has the potential for lateral screw placement while still remaining within the pedicle.
doi: 10.1016/j.spinee.2009.08.417
P157. An Anatomical Study which Describes the Relationship of the Pedicle Center to the Mid-Lateral Pars (MLP) in the Lower Lumbar Spine as a Guide to Pedicle Screw Placement Brian Su1, Paul Kim, MD2, Thomas Cha, MD2, Joseph Lee, MD2, Ernest April, PhD2, Mark Weidenbaum, MD2, Alexander R. Vaccaro, MD, PhD1; 1The Rothman Institute, Philadelphia, PA, USA; 2Columbia University, New York, NY, USA BACKGROUND CONTEXT: Traditional medial-lateral starting points for lumbar pedicle screws use the facet as an anatomical reference for all lumbar levels. The facet is often a difficult landmark to use secondary to degenerative changes and the desire to minimize damage to the facet capsule in the most cephalad level. These techniques can also result in pedicle violation particularly in the lower lumbar spine. Use of the non-arthritic MLP is proposed in this study as an alternative anatomical reference point for the pedicle center. PURPOSE: Describe morphometric data of the lower lumbar pedicles, the unique coronal pedicle footprints of L4 and L5, and their impact on the relationship of the pedicle center to the MLP. STUDY DESIGN/SETTING: Human Cadaver Study for morphometric data. PATIENT SAMPLE: Not applicable. OUTCOME MEASURES: Not Applicable. METHODS: Seventy-two pedicles (L3-S1) from embalmed cadaveric spines were used. Linear and angular dimensions of the pedicle were measured including the degree of coronal pedicle tilt of L4 and L5. The center of the pedicle relative to the MLP and relative to the midline of the base of the transverse process was measured. The axial superior facet angle and angle of pedicle screw insertion was also measured. RESULTS: The minimum pedicle width was 10.9 mm and 12.4 mm and the coronal pedicle tilt was 36 and 55 for L4 and L5 respectively. A classification of two types of L5 pedicles relevant to pedicle center location was developed. In the medial-lateral direction, the pedicle center is 2.9 mm lateral to the MLP at L3 and L4. At L5, it is 1.5 mm and 4.5 mm lateral to the MLP for a Type I and Type II pedicle respectively. In the superior-inferior direction, the pedicle center is 1 mm superior to the midline of the transverse process base for all lower lumbar levels. Significant differences between a Type I and II L5 pedicle were a larger pedicle width and distance of the pedicle center to the MLP for a Type II pedicle. The difference between the axial pedicle screw insertion angle and anatomic superior facet angles was 8 from L4-S1. CONCLUSIONS: The MLP is a reliable anatomic reference point for the center of the pedicle in the lower lumbar spine. Consideration needs to be taken when inserting pedicle screws at L4 and L5 because of the degree of
Figure.
FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. doi: 10.1016/j.spinee.2009.08.418
P158. The Surgical Approach to the Cervico-Thoracic Junction: Can a Standard Smith-Robinson Approach Be Utilized? Woojin Cho, MD, PhD1, Takeshi Maeda, MD, PhD2, Yung Park, MD, PhD3, Jacob Buchowski, MD, MS1, K. Daniel Riew, MD1; 1Washington University School of Medicine, St, Louis, MO, USA; 2Spinal Injuries Center, Fukuoka City, Japan; 3Yonsei University School of Medicine, Seoul, South Korea BACKGROUND CONTEXT: A number of techniques for exposing the anterior cervico-thoracic junction have been described. However most are associated with significant morbidity. PURPOSE: There are few reports that describe techniques for determining when a standard Smith-Robinson approach is adequate and when a more invasive approach, such as a sternal splitting approach is necessary. We undertook this study to help clarify this issue. STUDY DESIGN/SETTING: Case Series Report. PATIENT SAMPLE: The records and radiographs of all patients who had undergone anterior cervico-thoracic arthrodesis to T1 or below by a single surgeon at an academic institution were evaluated by independent surgeons. OUTCOME MEASURES: Descriptive Obsevational Study. METHODS: The senior author’s technique for preoperatively determining whether a standard Smith-Robinson approach could be utilized to expose the intended caudal segment was based on preoperative lateral x-rays. A line was drawn from the intended skin incision site to the top of the manubrium (at the suprasternal notch) to the level of the disc space. This line represented the trajectory of the approach. If it appeared to allow adequate
Proceedings of the NASS 24th Annual Meeting / The Spine Journal 9 (2009) 1S-205S
RESULTS: Of 184 patients, 62 were smokers (22 M, 40F; age 52.8 yrs) and 122 nonsmokers (45 M, 77F; age 57.5 yrs). Average 12-month Lenke score across all subsets was 1.07 (smokers 1.08; nonsmokers 1.07). At 24 months, average Lenke score across all subsets was 1.03 (smokers 1.00, non smokers 1.02). There were no infections, neurologic complications or plate breakages. One patient, a 59 year-old diabetic male smoker, developed a pseudarthrosis; at the 6-month follow-up, the patient remained asymptomatic and declined re-operation. CONCLUSIONS: The combination of a demineralized bone matrix-local bone contained within allograft dowels or PEEK spacer resulted in similar fusion rates (O 97%) for both smokers and nonsmokers at 12 months and 24 months postoperatively. FDA DEVICE/DRUG STATUS: PEED Spacers: Approved for this indication; Allograft Dowels: Approved for this indication. doi: 10.1016/j.spinee.2009.08.415
P155. DBM Use in 2-Level PLIFs: Fusion Comparison of Smokers and Non-Smokers W.B. Rodgers, MD, Curtis S. Cox, MD, Edward J. Gerber, MD; Jefferson City, MO, USA BACKGROUND CONTEXT: Smoking has been cited to potentiate postoperative infections and interfere with bone graft incorporation in fusion procedures. As such, higher pseudarthrosis (non-union) rates have been historically reported in this population subset. PURPOSE: Rates of fusion are presented between smokers and nonsmokers, using a commercially available demineralized bone matrix (DBM) coupled with bone marrow aspirate and local bone in 2-level posterolateral interbody fusion (PLIF) procedures. STUDY DESIGN/SETTING: Prospective, nonrandomized clinical and radiographic assessment. PATIENT SAMPLE: Of our single-site consecutive series of 110 twolevel PLIF patients, 47 smoked at the time of surgery. OUTCOME MEASURES: Clinical and radiographic measures were prospectively collected and evaluated to assess comorbidities, complications, and fusion results at 12 and 24 months postop. METHODS: 110 instrumented, 2-level PLIF procedures were performed by a single surgeon using a graft composite were prepared from ground lamellar bone, supplemented with DBM and posterior iliac crest bone marrow aspirate (BMA). The composite was placed in the aperture of PEEK or machined allograft spacers (to achieve interbody fusion) and along the intertransverse membrane (to achieve posterolateral fusion). Anteroposterior and lateral flexion and extension radiographs, obtained at three-, six-, and twelve-months, were evaluated utilizing Lenke’s criteria for intertransverse fusion and modified Lenke criteria of interbody fusion. Global fusion was defined as either: Lenke or modified Lenke score of 1; or Lenke score 2þmodified Lenke score 2. RESULTS: 46 smokers and 62 non-smokers, ranging in age from 33-85 years (average age557.42 years) presented for 12-month follow-up. Intertransverse/interbody scores for smokers51.89/1.20 and for nonsmokers51.69/1.25. To date, 32 smokers and 40 non-smokers have presented for 24 month follow-up. Lenke scores for smokers at 24 months postop were 1.81/1.25; non smokers 1.63/1.18. Similar complication rates were observed in both groups; 6 re-operations were performed for adjacent segment disease. CONCLUSIONS: Smoking is often identified as a contributing factor to increased pseudarthrosis (non-union) rates in spinal fusion surgeries. The fusion rates for smokers and non-smokers were 97.8% and 98.4% at 12 months respectively, and 97% and 97.5% at 24 months; no significant difference was shown between the two groups. Slightly better (intertransverse) Lenke scores were noted in the nonsmokers.
FDA DEVICE/DRUG STATUS: PEEK Spacers: Approved for this indication; Allograft Dowels: Approved for this indication. doi: 10.1016/j.spinee.2009.08.416
P156. Rod Derotation vs. Direct Incremental Segmental Translation: A Biomechanical Analysis Xiaoyu Wang, PhD1, Carl-Eric Aubin, PhD1, Hubert Labelle, MD2, Dennis Crandall, MD3; 1Ecole Polytechnique & Sainte-Justine University Hospital Center, Montreal, Quebec, Canada; 2Sainte Justine University Hospital Center, Montreal, Quebec, Canada; 3Sonoran Spine Center, Mesa, AZ, USA BACKGROUND CONTEXT: Scoliosis is corrected by different maneuvers applied to the spine via a mechanical constructs, with rods usually bent to desired sagittal profile. Basic techniques involve vertebral translation, rod derotation, direct vertebra derotation, compression and distraction, and in situ rod contouring. In order to maintain the correction rods are fully seated and locked into the slot of each implant, making it difficult to fine-tune the implant-rod relative location and control the force distribution amongst the implants. Direct incremental segmental translation (DIST) was proposed to provide a better control on the vertebra location with respect to the rod. The most distinguishing point of this concept is the ability to translate each implant toward and fixed on the rod from any distance and at any angle. PURPOSE: Compare the forces at the bone-screw interface during scoliosis correction using rod derotation vs. DIST. STUDY DESIGN/SETTING: We analyzed the biomechanics of two instrumentation paradigms: rod derotation technique (RDT) vs. a direct incremental segmental translation approach (DIST). PATIENT SAMPLE: Reduction techniques documented using pre- and post-op radiographs as well as intra-operative video of surgical maneuvers of 10 cases were used to develop a model for computer simulation of correction techniques for scoliosis. OUTCOME MEASURES: Computer simulation of scoliosis correction. METHODS: A common curve pattern (thoracolumbar curve) for adolescent idiopathic scoliosis was chosen. Simulations with both the RDT and
Figure. Simulated forces and their orientation at the vertebra-implant connections for the RDT (a) and DIST (b) techniques. The length of the arrows is proportional to the forces.
Proceedings of the NASS 24th Annual Meeting / The Spine Journal 9 (2009) 1S-205S DIST techniques were performed using the same patient biomechanical model built using biplanar X-rays, with same instrumentation levels and rod shape. The correction maneuvers and resulting effects were analyzed and compared. RESULTS: The vertebra position relative to the rod for the DIST is determined by 5 independent variables (position, orientation) vs. 2 for the RDT; thus increasing the possible correction of the connected vertebra. The DIST allows the spine deformity to be reduced by either gradually pulling the spine towards the rod through helical connections or translating it by pivoting the posts. Load at the vertebra-implant connection was on average 18% lower for the DIST, and better distributed (lower STD). CONCLUSIONS: The direct incremental segmental translation approach allows more control with better load sharing amongst implants. SIGNIFICANCE: This analysis provides insight into the different biomechanical effects of the 2 instrumentation paradigms. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs.
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their coronal tilts and unique pedicle footprints. It is important to distinguish a Type I from Type II L5 pedicle as a Type II pedicle is wider, has a more lateral pedicle center relative to the MLP, and has the potential for lateral screw placement while still remaining within the pedicle.
doi: 10.1016/j.spinee.2009.08.417
P157. An Anatomical Study which Describes the Relationship of the Pedicle Center to the Mid-Lateral Pars (MLP) in the Lower Lumbar Spine as a Guide to Pedicle Screw Placement Brian Su1, Paul Kim, MD2, Thomas Cha, MD2, Joseph Lee, MD2, Ernest April, PhD2, Mark Weidenbaum, MD2, Alexander R. Vaccaro, MD, PhD1; 1The Rothman Institute, Philadelphia, PA, USA; 2Columbia University, New York, NY, USA BACKGROUND CONTEXT: Traditional medial-lateral starting points for lumbar pedicle screws use the facet as an anatomical reference for all lumbar levels. The facet is often a difficult landmark to use secondary to degenerative changes and the desire to minimize damage to the facet capsule in the most cephalad level. These techniques can also result in pedicle violation particularly in the lower lumbar spine. Use of the non-arthritic MLP is proposed in this study as an alternative anatomical reference point for the pedicle center. PURPOSE: Describe morphometric data of the lower lumbar pedicles, the unique coronal pedicle footprints of L4 and L5, and their impact on the relationship of the pedicle center to the MLP. STUDY DESIGN/SETTING: Human Cadaver Study for morphometric data. PATIENT SAMPLE: Not applicable. OUTCOME MEASURES: Not Applicable. METHODS: Seventy-two pedicles (L3-S1) from embalmed cadaveric spines were used. Linear and angular dimensions of the pedicle were measured including the degree of coronal pedicle tilt of L4 and L5. The center of the pedicle relative to the MLP and relative to the midline of the base of the transverse process was measured. The axial superior facet angle and angle of pedicle screw insertion was also measured. RESULTS: The minimum pedicle width was 10.9 mm and 12.4 mm and the coronal pedicle tilt was 36 and 55 for L4 and L5 respectively. A classification of two types of L5 pedicles relevant to pedicle center location was developed. In the medial-lateral direction, the pedicle center is 2.9 mm lateral to the MLP at L3 and L4. At L5, it is 1.5 mm and 4.5 mm lateral to the MLP for a Type I and Type II pedicle respectively. In the superior-inferior direction, the pedicle center is 1 mm superior to the midline of the transverse process base for all lower lumbar levels. Significant differences between a Type I and II L5 pedicle were a larger pedicle width and distance of the pedicle center to the MLP for a Type II pedicle. The difference between the axial pedicle screw insertion angle and anatomic superior facet angles was 8 from L4-S1. CONCLUSIONS: The MLP is a reliable anatomic reference point for the center of the pedicle in the lower lumbar spine. Consideration needs to be taken when inserting pedicle screws at L4 and L5 because of the degree of
Figure.
FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. doi: 10.1016/j.spinee.2009.08.418
P158. The Surgical Approach to the Cervico-Thoracic Junction: Can a Standard Smith-Robinson Approach Be Utilized? Woojin Cho, MD, PhD1, Takeshi Maeda, MD, PhD2, Yung Park, MD, PhD3, Jacob Buchowski, MD, MS1, K. Daniel Riew, MD1; 1Washington University School of Medicine, St, Louis, MO, USA; 2Spinal Injuries Center, Fukuoka City, Japan; 3Yonsei University School of Medicine, Seoul, South Korea BACKGROUND CONTEXT: A number of techniques for exposing the anterior cervico-thoracic junction have been described. However most are associated with significant morbidity. PURPOSE: There are few reports that describe techniques for determining when a standard Smith-Robinson approach is adequate and when a more invasive approach, such as a sternal splitting approach is necessary. We undertook this study to help clarify this issue. STUDY DESIGN/SETTING: Case Series Report. PATIENT SAMPLE: The records and radiographs of all patients who had undergone anterior cervico-thoracic arthrodesis to T1 or below by a single surgeon at an academic institution were evaluated by independent surgeons. OUTCOME MEASURES: Descriptive Obsevational Study. METHODS: The senior author’s technique for preoperatively determining whether a standard Smith-Robinson approach could be utilized to expose the intended caudal segment was based on preoperative lateral x-rays. A line was drawn from the intended skin incision site to the top of the manubrium (at the suprasternal notch) to the level of the disc space. This line represented the trajectory of the approach. If it appeared to allow adequate