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P161. CT and Biomechanical Analysis of Occipitocervical Stability Afforded by Three Fixation Techniques
Proceedings of the NASS 24th Annual Meeting / The Spine Journal 9 (2009) 1S-205S FDA DEVICE/DRUG STATUS: TranS1 Screw: Approved for this indication. doi: 10.1016/j.spinee.2009.08.421
P161. CT and Biomechanical Analysis of Occipitocervical Stability Afforded by Three Fixation Techniques Melvin Helgeson, MD1, Ronald A. Lehman, Jr., MD1, Anton E. Dmitriev, MSC2, Rick Sasso, MD3, Andrew Mack, MD2, K. Daniel Riew, MD4; 1 Washington, DC, USA; 2Walter Reed Army Medical Center, Washington, DC, USA; 3Indianapolis, IN, USA; 4Washingon School of Medicine, St. Louis, MO, USA BACKGROUND CONTEXT: Occipitocervical reconstruction and arthrodesis remain challenging. Treatment of occipitocervical instability is further complicated by the unique musculoskeletal, neurologic, and vascular anatomy, as well as the need to restrict motion in all three physiologic planes. PURPOSE: The objective of our study was to compare segmental stability and ROM of the standard occipitocervical screw/rod and plate constructs versus a new technique which incorporates occipital condyle fixation. STUDY DESIGN/SETTING: In vitro cadaveric study. PATIENT SAMPLE: Ten (10) human cadaveric occipitocervical spines OUTCOME MEASURES: Range of motion, peak failure moment. METHODS: Ten fresh frozen human cadaveric occipitocervical spines were radiographically evaluated to rule out spinal pathology and DEXA scanned for bone mineral density. Following intact analysis all specimens were instrumented bilaterally with C1 lateral mass screws and C2 pedicle screws. Additional occipital instrumentation was tested in random order under the following conditions: 1) Standard Occipitocervical plate/rod system, 2) Occipital condyle screws alone, 3) Occipital condyle screws with the addition of an eyelet screw placed into the occiput bilaterally. Following non-destructive ROM testing, specimens were evaluated under computed tomography (CT), and underwent destructive forward flexion failure comparing Group 1 to Group 3. RESULTS: There was no significant difference in occipitocervical (Occ to C1) axial rotation and flexion-extension range of motion between the standard occipitocervical plate/rod system (Group 1) and the occipital condyle screws with one eyelet screw bilaterally (Group 3) (p50.707 and p50.271, respectively). Furthermore, the occipital condyle screws alone (Group 2) did allow significantly more flexion-extension compared to Group 1. Interestingly, the two groups with occipital condyle screws (Groups 2 and 3) had significantly less lateral bending compared to Group 1 (p50.038 and p50.025, respectively). During CT analysis, the mean occipital condyle width was 10.8 mm (range 9.1-12.7 mm) and the mean condylar length was 24.3 mm (range 20.2-28.5). Upon destructive testing, there was no significant difference in forward flexion failure between Groups 1 and 3 (p50.348). CONCLUSIONS: With instrumentation across the mobile occipitocervical junction, our results indicate similar stability can be achieved with occipital condyle screws/eyelet screws compared to the standard occipitocervical rod/plate system. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. doi: 10.1016/j.spinee.2009.08.422
P162. Three-Level Lumbar ADR: A Clinical and Radiographic Analysis of Sagittal Motion Preservation at 2-6 Years Rick B Delamarter, MD1, Alexandre Rasouli, MD2, L.E.A. Kanim, MA1, Nomaan Ashraf, MD1, Brandon Strenge, MD1, Michael Kropf, MD1, Hyun Bae, MD1; 1The Spine Institute at Santa Monica, Santa Monica, CA, USA; 2The Spine Institute, Santa Monica, CA, USA BACKGROUND CONTEXT: The FDA-sponsored randomized controlled study of the Prodisc-L (Synthes Spine, Westchester, PA) lumbar
197S
disc replacement established superior clinical outcomes with preservation of motion at both surgical and adjacent levels, as compared to lumbar fusion. However, no previous study has reported on the radiographic characteristics of adjacent three-level lumbar disc replacements. PURPOSE: To evaluate clinical outcomes and the sagittal range of motion of three-level ProDisc-L disc replacements as well as motion at the adjacent unoperated segment. STUDY DESIGN/SETTING: Prospective Cohort. PATIENT SAMPLE: Forty-one patients receiving three-level adjacent ADR between L2 and S1. OUTCOME MEASURES: Lumbar range of motion was measured radiographically at the operated and unoperated lumbar segments. Oswestry Disability Index (ODI), Visual Analog Score Pain (VAS-P), and Visual Analog Score Satisfaction (VAS-S) data were also collected. METHODS: Patients were evaluated pre-operatively, at six weeks, three months, six months, and annually for 2-6 years postoperatively with lateral flexion-extension dynamic films and with completion of Oswestry and VAS surveys. RESULTS: At the motion segment adjacent to the ADR, the mean preoperative range of motion was 7.08 (SD 2.35 ), compared to 7.26 postoperatively (SD 2.38, pO0.05). The mean preoperative range of motion at all levels undergoing ADR was 8.53 (SD 1.66 ) versus 8.10 postoperatively (SD 2.80, p50.40), indicating no significant difference. At 2-6 years postoperatively, all patients had significant reductions in both ODI and VAS scores relative to preoperative levels (p!0.05). Of the 41 patients, one patient underwent revision surgery to a fusion. There were no surgeries at adjacent levels. CONCLUSIONS: The use of the three-level Prodisc-L ADR construct does not inhibit preservation of range of motion at the individual ADR levels. The nonoperative level adjacent to the construct maintains its preoperative range of motion at 2-6 years postoperatively. There was 0.02% reoperation rate for conversion to fusion and no operations at adjacent levels. Improvements in pain and disability were significant. FDA DEVICE/DRUG STATUS: ProDisc-L: Investigational/Not approved. doi: 10.1016/j.spinee.2009.08.423
P163. A Biomechanical Comparison of Integrated vs. Variable Cross-Connectors and Dual-Diameter vs. Single Diameter Screw Constructs at L5-S1 William Beutler, MD1, Walter Peppleman, Jr., MD2, Jeff Reuben, MD3, Aditya Muzumdar, MS4, Aditya Ingalhalikar, MS4, Brandon Bucklen, PhD4, Mark Moldavsky, BS4, Saif Khalil, PhD4; 1Harrisburg, PA, USA; 2 Pennsylvania Spine Institute, Harrisburg, PA, USA; 3Beaufort, SC, USA; 4 Globus Medical, Inc., Audubon, PA, USA BACKGROUND CONTEXT: The aim of this study is to evaluate the biomechanics of two instrumentation variables. A well known problem associated with any rod-screw fixation systems is screw backout, especially prevalent at the lumbosacral level. Cross-connectors have been utilized to bridge bilateral rods increasing torsional stability at L5-S1. Although the effect of screw diameter on fixation has been documented, dual outer diameter screw designs have not been fully characterized. PURPOSE: The purpose of this study was to examine the biomechanics of two fixation variables hypothesized to be important for torsional stability and fixation at L5-S1, namely the 1). influence of a integrated versus variable length cross connectors, and 2). screw thread design. STUDY DESIGN/SETTING: Cadaveric functional spinal units (FSU) were tested in physiological motions using a spine simulator (6 DOF machine, 0.5 degree/sec) with each construct type. Testing of integrated crossconnectors (RT) was compared to variable length connectors (T). Single diameter, standard screws (SS) and dual outer diameter screws (DOD) were tested on a uniaxial MTS machine. PATIENT SAMPLE: N/A.
P161. CT and Biomechanical Analysis of Occipitocervical Stability Afforded by Three Fixation Techniques Melvin Helgeson, MD1, Ronald A. Lehman, Jr., MD1, Anton E. Dmitriev, MSC2, Rick Sasso, MD3, Andrew Mack, MD2, K. Daniel Riew, MD4; 1 Washington, DC, USA; 2Walter Reed Army Medical Center, Washington, DC, USA; 3Indianapolis, IN, USA; 4Washingon School of Medicine, St. Louis, MO, USA BACKGROUND CONTEXT: Occipitocervical reconstruction and arthrodesis remain challenging. Treatment of occipitocervical instability is further complicated by the unique musculoskeletal, neurologic, and vascular anatomy, as well as the need to restrict motion in all three physiologic planes. PURPOSE: The objective of our study was to compare segmental stability and ROM of the standard occipitocervical screw/rod and plate constructs versus a new technique which incorporates occipital condyle fixation. STUDY DESIGN/SETTING: In vitro cadaveric study. PATIENT SAMPLE: Ten (10) human cadaveric occipitocervical spines OUTCOME MEASURES: Range of motion, peak failure moment. METHODS: Ten fresh frozen human cadaveric occipitocervical spines were radiographically evaluated to rule out spinal pathology and DEXA scanned for bone mineral density. Following intact analysis all specimens were instrumented bilaterally with C1 lateral mass screws and C2 pedicle screws. Additional occipital instrumentation was tested in random order under the following conditions: 1) Standard Occipitocervical plate/rod system, 2) Occipital condyle screws alone, 3) Occipital condyle screws with the addition of an eyelet screw placed into the occiput bilaterally. Following non-destructive ROM testing, specimens were evaluated under computed tomography (CT), and underwent destructive forward flexion failure comparing Group 1 to Group 3. RESULTS: There was no significant difference in occipitocervical (Occ to C1) axial rotation and flexion-extension range of motion between the standard occipitocervical plate/rod system (Group 1) and the occipital condyle screws with one eyelet screw bilaterally (Group 3) (p50.707 and p50.271, respectively). Furthermore, the occipital condyle screws alone (Group 2) did allow significantly more flexion-extension compared to Group 1. Interestingly, the two groups with occipital condyle screws (Groups 2 and 3) had significantly less lateral bending compared to Group 1 (p50.038 and p50.025, respectively). During CT analysis, the mean occipital condyle width was 10.8 mm (range 9.1-12.7 mm) and the mean condylar length was 24.3 mm (range 20.2-28.5). Upon destructive testing, there was no significant difference in forward flexion failure between Groups 1 and 3 (p50.348). CONCLUSIONS: With instrumentation across the mobile occipitocervical junction, our results indicate similar stability can be achieved with occipital condyle screws/eyelet screws compared to the standard occipitocervical rod/plate system. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. doi: 10.1016/j.spinee.2009.08.422
P162. Three-Level Lumbar ADR: A Clinical and Radiographic Analysis of Sagittal Motion Preservation at 2-6 Years Rick B Delamarter, MD1, Alexandre Rasouli, MD2, L.E.A. Kanim, MA1, Nomaan Ashraf, MD1, Brandon Strenge, MD1, Michael Kropf, MD1, Hyun Bae, MD1; 1The Spine Institute at Santa Monica, Santa Monica, CA, USA; 2The Spine Institute, Santa Monica, CA, USA BACKGROUND CONTEXT: The FDA-sponsored randomized controlled study of the Prodisc-L (Synthes Spine, Westchester, PA) lumbar
197S
disc replacement established superior clinical outcomes with preservation of motion at both surgical and adjacent levels, as compared to lumbar fusion. However, no previous study has reported on the radiographic characteristics of adjacent three-level lumbar disc replacements. PURPOSE: To evaluate clinical outcomes and the sagittal range of motion of three-level ProDisc-L disc replacements as well as motion at the adjacent unoperated segment. STUDY DESIGN/SETTING: Prospective Cohort. PATIENT SAMPLE: Forty-one patients receiving three-level adjacent ADR between L2 and S1. OUTCOME MEASURES: Lumbar range of motion was measured radiographically at the operated and unoperated lumbar segments. Oswestry Disability Index (ODI), Visual Analog Score Pain (VAS-P), and Visual Analog Score Satisfaction (VAS-S) data were also collected. METHODS: Patients were evaluated pre-operatively, at six weeks, three months, six months, and annually for 2-6 years postoperatively with lateral flexion-extension dynamic films and with completion of Oswestry and VAS surveys. RESULTS: At the motion segment adjacent to the ADR, the mean preoperative range of motion was 7.08 (SD 2.35 ), compared to 7.26 postoperatively (SD 2.38, pO0.05). The mean preoperative range of motion at all levels undergoing ADR was 8.53 (SD 1.66 ) versus 8.10 postoperatively (SD 2.80, p50.40), indicating no significant difference. At 2-6 years postoperatively, all patients had significant reductions in both ODI and VAS scores relative to preoperative levels (p!0.05). Of the 41 patients, one patient underwent revision surgery to a fusion. There were no surgeries at adjacent levels. CONCLUSIONS: The use of the three-level Prodisc-L ADR construct does not inhibit preservation of range of motion at the individual ADR levels. The nonoperative level adjacent to the construct maintains its preoperative range of motion at 2-6 years postoperatively. There was 0.02% reoperation rate for conversion to fusion and no operations at adjacent levels. Improvements in pain and disability were significant. FDA DEVICE/DRUG STATUS: ProDisc-L: Investigational/Not approved. doi: 10.1016/j.spinee.2009.08.423
P163. A Biomechanical Comparison of Integrated vs. Variable Cross-Connectors and Dual-Diameter vs. Single Diameter Screw Constructs at L5-S1 William Beutler, MD1, Walter Peppleman, Jr., MD2, Jeff Reuben, MD3, Aditya Muzumdar, MS4, Aditya Ingalhalikar, MS4, Brandon Bucklen, PhD4, Mark Moldavsky, BS4, Saif Khalil, PhD4; 1Harrisburg, PA, USA; 2 Pennsylvania Spine Institute, Harrisburg, PA, USA; 3Beaufort, SC, USA; 4 Globus Medical, Inc., Audubon, PA, USA BACKGROUND CONTEXT: The aim of this study is to evaluate the biomechanics of two instrumentation variables. A well known problem associated with any rod-screw fixation systems is screw backout, especially prevalent at the lumbosacral level. Cross-connectors have been utilized to bridge bilateral rods increasing torsional stability at L5-S1. Although the effect of screw diameter on fixation has been documented, dual outer diameter screw designs have not been fully characterized. PURPOSE: The purpose of this study was to examine the biomechanics of two fixation variables hypothesized to be important for torsional stability and fixation at L5-S1, namely the 1). influence of a integrated versus variable length cross connectors, and 2). screw thread design. STUDY DESIGN/SETTING: Cadaveric functional spinal units (FSU) were tested in physiological motions using a spine simulator (6 DOF machine, 0.5 degree/sec) with each construct type. Testing of integrated crossconnectors (RT) was compared to variable length connectors (T). Single diameter, standard screws (SS) and dual outer diameter screws (DOD) were tested on a uniaxial MTS machine. PATIENT SAMPLE: N/A.