- Email: [email protected]
Biomechanical Effect of Increasing Magnitudes of Internal Annular Disruption
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Proceedings of the NASS 29th Annual Meeting / The Spine Journal 14 (2014) 1S–183S
30. In Vitro Endplate Strength after Iatrogenic Trauma Resulting from Lateral Interbody Spacer Implantation: Static Spacer Compared to Expandable Spacer William D. Hunter, Sr., MD1, Mark Moldavsky, MS2, Kanaan G. Salloum, BS2, Brandon Bucklen, PhD2; 1Gaston Memorial Hospital, Gastonia, NC, US; 2Globus Medical Inc., Audubon, PA, US BACKGROUND CONTEXT: Lateral interbody fusion, for indirect decompression, is an accepted method of treating disc degeneration. A significant complication of the lateral approach is interbody cage subsidence. Marchi et al found a 41% of subsidence in 46 patients undergoing lateral interbody surgery at 61 levels. Le et al found 14.3% radiographic subsidence in 140 patients, with most cases incorporating supplemental fixation. Immediate iatrogenic damage from impaction of the spacers can predispose theendplat3es to subsidence. PURPOSE: The current study investigates the vertebral bodyendplate strength after impaction of static and expandable lateral interbody spacers. Foraminal height restoration between both groups is also studied. STUDY DESIGN/SETTING: Biomechanical study. METHODS: Seven L2-L3 and L4-L5 functional spinal units, with DEXA scans, were evenly distributed between two groups. A physiological load of 222N was applied to the vertebral bodies and a lateral discectomy was performed. A static CoRoentÒ (NuVasive Inc.; San Diego, CA) and an expandable CALIBERÒ-L (Globus Medical Inc, Audubon, PA) were implanted with the goal of restoring intact disc height. After implantation, a metal stamp with the same footprint as the interbody spacers (18mm wide) was used to apply an axial load on the endplates at a rate of 5mm/min to a displacement of 3mm. Endplate strength and foraminal height restoration (‘‘implant foraminal height’’‘‘discectomy foraminal height’’) were reported. A paired two sample for means t-test was used to determine statistical significance between the groups (p#0.05). RESULTS: The T-scores for the vertebral bodies used in the static and expandable groups were -2.33 (61.55) and -2.58 (61.43) with no significant difference between the groups. The foraminal height restoration was 1.42mm (60.81) and 2.68mm (61.30) for the static and expandable groups respectively, and approached significance (p50.066).The maximum force of the endplates for static and expandable groups was 1764N (6966) and 2284N (6949) respectively, with a significant difference. CONCLUSIONS: When trialing under a physiological load with the same height restoration goals, the expandable spacer significantly restored more disc height compared to a static with the same height restoration goals. Furthermore, the endplates in the expandable group were able to withstand more compressive load (520N/117lbs) at the same displacement. The increased trialing required for a static spacer may lead to more iatrogenic endplate damage, which may result in less indirect decompression and weaker endplates. FDA DEVICE/DRUG STATUS: CoRoent (Approved for this indication), CALIBER-L (Approved for this indication).
6
University of Wisconsin Orthopedics and Rehabilitation, Madison, WI, US BACKGROUND CONTEXT: Tapping insertional torque (IT) is a metric used to estimate pedicle screw size. Prior studies have shown that obtaining a tapping IT value of 2.5 in-lbs predicts optimal pedicle fill when selecting screw size intraoperatively. Aside from utilization of an intraoperative torque meter, there are currently no guides to assess tapping IT values. PURPOSE: The purpose of this study was to determine if surgeons at all levels (intern to attending) could be trained to assess torque by ‘‘feel’’ to obviate the need for intraoperative gauges. STUDY DESIGN/SETTING: Biomechanical evaluation of insertional torque. OUTCOME MEASURES: Insertional torque. METHODS: Ten surgeons at our institution at different levels of training (attending, senior resident and junior resident) underwent a 30-repetition round of torque training with three separate tap sizes (4.5, 5.5, 6.5mm), followed by a round of testing. Each participant subsequently performed two additional rounds of testing spaced one week apart. Testing was performed utilizing polyurethane foam blocks at a density of 10 pounds/ft3 (pcf), which most closely resembled cancellous bone based on our pilot test. Torque values were recorded utilizing a digital torque gauge meter. Data were then analyzed with an ANOVA test with a post hoc comparison of means for any significant differences. RESULTS: We found no significant difference (p O 0.05) between each training level and our ‘‘perfect’’ model. We also found no significant difference between rounds of testing for all participants (p O 0.05). Additionally, there was no significant difference between the standard deviations measured between rounds (p O 0.05). We determined that junior level residents were not as accurate as either the senior level residents (p ! 0.05) or the attending surgeons (p ! 0.05), but there was no difference noted between junior residents and the ‘‘perfect’’ model (p O 0.05). CONCLUSIONS: Our data suggest that surgeons at all levels of training can be taught to accurately gauge 2.5 in-lbs of tapping insertional torque, and that this skill does not regress with subsequent testing at 1-week intervals. Therefore, resident and staff surgeons can be easily trained to assess intraoperative IT which obviates the need for an IT screw driver in the operating room. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. http://dx.doi.org/10.1016/j.spinee.2014.08.049
http://dx.doi.org/10.1016/j.spinee.2014.08.048
32. Biomechanical Effect of Increasing Magnitudes of Internal Annular Disruption Brian D. Stemper, PhD1, William H. Curry, DC1, Jason Przybylo, MD1, Kristen Kiehl1, Narayan Yoganandan, PhD1, Barry S. Shender, PhD2, Dennis J. Maiman, MD3; 1Medical College of Wisconsin, Milwaukee, WI, US; 2NAWCAD, Patuxent River, MD, US; 3Medical College of Wisconsin Department of Neurosurgery, Milwaukee, WI, US
31. Can Orthopedic Surgeons Be Trained to Accurately Gauge Tapping Insertional Torque? Daniel G. Kang, MD1, Ronald A. Lehman, Jr., MD2, Adam Bevevino, MD1, John P. Cody, MD3, Robert W. Tracey, MD4, Rachel E. Gaume, BS5, Scott Wagner, MD1, Paul A. Anderson, MD6; 1Bethesda, MD, US; 2 Potomac, MD, US; 3Washington, DC, US; 4Great Falls, VA, US; 5 Walter Reed National Military Medical Center, Bethesda, MD, US;
BACKGROUND CONTEXT: Internal disc disruption (IDD) results from tearing of inner annulus fibers while the external aspect remains intact. This condition occurs traumatically or degeneratively, is not identifiable using non-contrast CT, and induces painful symptoms. Due to its occult nature on routine imaging, IDD may be a source of idiopathic pain in the absence of obvious degenerative changes. The mechanism of pain is related to instability resulting from fundamental changes in segmental load sharing that contribute to discogenic pain mechanisms and acute nerve root compression. PURPOSE: Outline the effect of IDD on segmental biomechanics.
Refer to onsite Annual Meeting presentations and postmeeting proceedings for possible referenced figures and tables. Authors are responsible for accurately reporting disclosures and FDA device/drug status at time of abstract submission.
Proceedings of the NASS 29th Annual Meeting / The Spine Journal 14 (2014) 1S–183S STUDY DESIGN/SETTING: Measure basic biomechanical properties of lumbar motion segments prior to and following experimental induction of IDD. PATIENT SAMPLE: 12 lumbar motion segments were obtained from 8 minimally degenerated human lumbar spines (mean age: 54610yr). OUTCOME MEASURES: Segmental range of motion (RoM) under applied pure moments was quantified prior to and following IDD. Magnitude (percent cross-sectional area) and type (linear or concentrated) of disruption was quantified using axial MRI. Group differences were identified. METHODS: Axial MRI scans were obtained and intact specimens were then tested in pure bending (flexion, extension, lateral bending) to outline baseline biomechanics. IDD was induced using the Oliphant method (Clin Biomech 2006), which involves injection of pressurized nitrogen gas into the annulus through a catheter. MRI scans obtained following the IDD procedure were used to grade the level of annular disruption as the percentage of disc cross-sectional area affected. Specimens were again subjected to the pure moment protocol. Differences in biomechanical response were quantified as the change in post-disruption RoM. Differences were identified based on the type, location and magnitude of disruption. RESULTS: Four IDD types were identified: high (HMC) and low (LMC) magnitude concentrated disruptions, and linear disruptions in anterior (LA) and lateral (LL) disc regions. HMC and LMC disruptions affected 32% and 14.5% of the disc and were generally focused in the middle-right location. LA and LL disruptions affected 14.8% and 13.8% of the disc, were elongated in shape and located in anterior and right-lateral locations. The effect of IDD location was evident as LA and LL disruption types resulted in increased extension RoM (LA: 11%; LL: 14%), whereas LL disruptions did not affect and LA disruptions decreased flexion RoM (-9%). Both disruptions resulted in increased left lateral bending RoM (8.5%), and no change for right lateral bending. LMC disruptions had essentially no effect on RoM and HMC disruptions demonstrated considerable increases (8-23%) in RoM for all loading modes. CONCLUSIONS: This preliminary study demonstrated that the effect of IDD was dependent on the location, type and magnitude. Changes were most evident in loading modes that exercised disrupted fibers in tension, whereas compression of disrupted fibers generally resulted in no change from the intact condition. For the same magnitude, linear disruptions had a larger effect on segmental biomechanics than concentrated. However, disruption magnitude was evident when concentrated disruptions were increased to 32%, which had a large effect on biomechanics. These findings form the basis for further investigation of effects of IDD on segmental biomechanics and may provide a tool for clinicians to predict segmental instability based on the characteristics of IDD evident on axial MRI. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. http://dx.doi.org/10.1016/j.spinee.2014.08.050
33. Pfirrmann Grade as a Predictor of Range of Motion, Angular Stiffness and Relative Size of High-Flexibility Zone in the Lumbar Spine Muturi Muriuki, PhD1, Robert M. Havey, BS2, Leonard I. Voronov, MD, PhD3, Gerard Carandang1, Laurie Lomasney, MD4, Avinash G. Patwardhan, PhD5; 1Edward Hines Jr. VA Hospital, Hines, IL, US; 2 Hines, IL, US; 3Willowbrook, IL, US; 4Loyola University Medical Center, Maywood, IL, US; 5Loyola University Medical Center Department of Orthopaedic Surgery, Maywood, IL, US BACKGROUND CONTEXT: Pfirrmann Grade is used to assess intervertebral disc degeneration based on the appearance of the intervertebral
17S
space on T2-weighted MR images using disc signal intensity, disc height, and the ability to distinguish between the annulus and the nucleus of the disc. There is little biomechanical data on the correlation of Pfirrmann grade to quality of motion measures. PURPOSE: Determine if Pfirrmann disc grade predicts range of motion, stiffness and relative size of the high-flexibility zone. STUDY DESIGN/SETTING: Controlled laboratory study. PATIENT SAMPLE: 270 segments of 54 intact lumbar (L1-–sacrum) cadaveric spines (age 19–73 years; 34 M, 20 F). OUTCOME MEASURES: Pfirrmann grade, range of motion (ROM), angular stiffness, relative size of high-flexibility zone (HFZ). METHODS: Intervertebral discs were graded using T2-weighted MRI scans. Specimens were tested in flexion-extension with 0N and 400N follower preloads (flexion and extension limits of 8Nm and 6Nm, respectively). Vertebral motions were tracked using a 3D optoelectronic motion measurement system. A six-axis load transducer was used to measure applied moment. The data were used to calculate segmental ROM and stiffness in flexion and extension. ROM was decomposed into flexion and extension based on the specimen’s neutral posture as defined at the start of the experiments. HFZ (low-stiffness) and low-flexibility zone (LFZ) angular stiffness were calculated in flexion and in extension using custom MATLAB programs. Sizes of the HFZ zones relative to flexion or extension ROM were also calculated. Three disc grade-based groups were used in data analysis (Group I: grade 1 & 2; Group II: grade 3; Group III: grade 4 & 5). The effect of Pfirrmann grade on outcome measures was assessed using repeated measures ANOVA, with repeat factor applied follower load. RESULTS: Pfirrmann grade from the most to least common disc grades were 3 (n5141), 2 (n595), 4 (n526), 5 (n55) and 1 (n53). Lower lumbar motion segments were more likely to have a higher Pfirrmann grade (Pearson Chi-square: p50.001). L4-L5 and L5-S1 (40% of discs) had 5/5 of grade 5 discs, 19/26 (73%) of grade 4s, 59/141 (41%) of grade 3s, 25/95 (26%) of grade 2’s and 0 grade 1’s. Group I discs (n598) Compared to 0N, 400N follower preload caused a decrease in extension HFZ size (from 66% to 55% of ROM). The addition of compressive preload increased the flexion HFZ stiffness (from 1.25Nm/deg to 1.37Nm/deg). Mean HFZ size in flexion remained unchanged at 67% of ROM and total ROM increased slightly from 8.1 to 8.2 . Group II discs (n5141) Adding compressive preload caused a 0.2 decrease in total ROM to 8.4 , and a decrease in extension HFZ size (from 64% to 50% of ROM). Compressive preload increased the flexion HFZ stiffness (1.17Nm/deg to 1.26Nm/deg) and HFZ size in flexion (63% to 67% of ROM). Group III discs (n531) Compressive preload caused a decrease in total ROM (from 8.7 to 7.8 ), and in HFZ size in flexion and extension (from 66% to 59% and 61% to 44% of ROM respectively). Increases under compressive preload were observed in the flexion HFZ stiffness (from 1.27Nm/deg to 2.27Nm/deg). Group Comparisons: (400N Preload) Group III discs are almost one and half times stiffer in HFZ than the other groups. HFZ size as a percentage of ROM reduces with increased disc degeneration. Total ROM is 8.2 , 8.4 and 7.8 for the three groups respectively. The only significant difference is in HFZ size in extension between Group I and Group III discs. CONCLUSIONS: Our analysis found that, apart from HFZ size in flexion (p50.073), changes in the outcome measures used in this study are linked to Pfirrmann grade and application of compressive preload (p!0.0005). The changes observed are not as apparent without compressive preload, suggesting the importance of testing under compressive preload. Our results also suggest that Pfirrmann Grade 3 discs are more like Grade 1 & 2 discs than Grade 4 & 5 discs. This data adds to the few biomechanical studies of the correlation of Pfirrmann grade and biomechanical parameters. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. http://dx.doi.org/10.1016/j.spinee.2014.08.051
Refer to onsite Annual Meeting presentations and postmeeting proceedings for possible referenced figures and tables. Authors are responsible for accurately reporting disclosures and FDA device/drug status at time of abstract submission.
Proceedings of the NASS 29th Annual Meeting / The Spine Journal 14 (2014) 1S–183S
30. In Vitro Endplate Strength after Iatrogenic Trauma Resulting from Lateral Interbody Spacer Implantation: Static Spacer Compared to Expandable Spacer William D. Hunter, Sr., MD1, Mark Moldavsky, MS2, Kanaan G. Salloum, BS2, Brandon Bucklen, PhD2; 1Gaston Memorial Hospital, Gastonia, NC, US; 2Globus Medical Inc., Audubon, PA, US BACKGROUND CONTEXT: Lateral interbody fusion, for indirect decompression, is an accepted method of treating disc degeneration. A significant complication of the lateral approach is interbody cage subsidence. Marchi et al found a 41% of subsidence in 46 patients undergoing lateral interbody surgery at 61 levels. Le et al found 14.3% radiographic subsidence in 140 patients, with most cases incorporating supplemental fixation. Immediate iatrogenic damage from impaction of the spacers can predispose theendplat3es to subsidence. PURPOSE: The current study investigates the vertebral bodyendplate strength after impaction of static and expandable lateral interbody spacers. Foraminal height restoration between both groups is also studied. STUDY DESIGN/SETTING: Biomechanical study. METHODS: Seven L2-L3 and L4-L5 functional spinal units, with DEXA scans, were evenly distributed between two groups. A physiological load of 222N was applied to the vertebral bodies and a lateral discectomy was performed. A static CoRoentÒ (NuVasive Inc.; San Diego, CA) and an expandable CALIBERÒ-L (Globus Medical Inc, Audubon, PA) were implanted with the goal of restoring intact disc height. After implantation, a metal stamp with the same footprint as the interbody spacers (18mm wide) was used to apply an axial load on the endplates at a rate of 5mm/min to a displacement of 3mm. Endplate strength and foraminal height restoration (‘‘implant foraminal height’’‘‘discectomy foraminal height’’) were reported. A paired two sample for means t-test was used to determine statistical significance between the groups (p#0.05). RESULTS: The T-scores for the vertebral bodies used in the static and expandable groups were -2.33 (61.55) and -2.58 (61.43) with no significant difference between the groups. The foraminal height restoration was 1.42mm (60.81) and 2.68mm (61.30) for the static and expandable groups respectively, and approached significance (p50.066).The maximum force of the endplates for static and expandable groups was 1764N (6966) and 2284N (6949) respectively, with a significant difference. CONCLUSIONS: When trialing under a physiological load with the same height restoration goals, the expandable spacer significantly restored more disc height compared to a static with the same height restoration goals. Furthermore, the endplates in the expandable group were able to withstand more compressive load (520N/117lbs) at the same displacement. The increased trialing required for a static spacer may lead to more iatrogenic endplate damage, which may result in less indirect decompression and weaker endplates. FDA DEVICE/DRUG STATUS: CoRoent (Approved for this indication), CALIBER-L (Approved for this indication).
6
University of Wisconsin Orthopedics and Rehabilitation, Madison, WI, US BACKGROUND CONTEXT: Tapping insertional torque (IT) is a metric used to estimate pedicle screw size. Prior studies have shown that obtaining a tapping IT value of 2.5 in-lbs predicts optimal pedicle fill when selecting screw size intraoperatively. Aside from utilization of an intraoperative torque meter, there are currently no guides to assess tapping IT values. PURPOSE: The purpose of this study was to determine if surgeons at all levels (intern to attending) could be trained to assess torque by ‘‘feel’’ to obviate the need for intraoperative gauges. STUDY DESIGN/SETTING: Biomechanical evaluation of insertional torque. OUTCOME MEASURES: Insertional torque. METHODS: Ten surgeons at our institution at different levels of training (attending, senior resident and junior resident) underwent a 30-repetition round of torque training with three separate tap sizes (4.5, 5.5, 6.5mm), followed by a round of testing. Each participant subsequently performed two additional rounds of testing spaced one week apart. Testing was performed utilizing polyurethane foam blocks at a density of 10 pounds/ft3 (pcf), which most closely resembled cancellous bone based on our pilot test. Torque values were recorded utilizing a digital torque gauge meter. Data were then analyzed with an ANOVA test with a post hoc comparison of means for any significant differences. RESULTS: We found no significant difference (p O 0.05) between each training level and our ‘‘perfect’’ model. We also found no significant difference between rounds of testing for all participants (p O 0.05). Additionally, there was no significant difference between the standard deviations measured between rounds (p O 0.05). We determined that junior level residents were not as accurate as either the senior level residents (p ! 0.05) or the attending surgeons (p ! 0.05), but there was no difference noted between junior residents and the ‘‘perfect’’ model (p O 0.05). CONCLUSIONS: Our data suggest that surgeons at all levels of training can be taught to accurately gauge 2.5 in-lbs of tapping insertional torque, and that this skill does not regress with subsequent testing at 1-week intervals. Therefore, resident and staff surgeons can be easily trained to assess intraoperative IT which obviates the need for an IT screw driver in the operating room. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. http://dx.doi.org/10.1016/j.spinee.2014.08.049
http://dx.doi.org/10.1016/j.spinee.2014.08.048
32. Biomechanical Effect of Increasing Magnitudes of Internal Annular Disruption Brian D. Stemper, PhD1, William H. Curry, DC1, Jason Przybylo, MD1, Kristen Kiehl1, Narayan Yoganandan, PhD1, Barry S. Shender, PhD2, Dennis J. Maiman, MD3; 1Medical College of Wisconsin, Milwaukee, WI, US; 2NAWCAD, Patuxent River, MD, US; 3Medical College of Wisconsin Department of Neurosurgery, Milwaukee, WI, US
31. Can Orthopedic Surgeons Be Trained to Accurately Gauge Tapping Insertional Torque? Daniel G. Kang, MD1, Ronald A. Lehman, Jr., MD2, Adam Bevevino, MD1, John P. Cody, MD3, Robert W. Tracey, MD4, Rachel E. Gaume, BS5, Scott Wagner, MD1, Paul A. Anderson, MD6; 1Bethesda, MD, US; 2 Potomac, MD, US; 3Washington, DC, US; 4Great Falls, VA, US; 5 Walter Reed National Military Medical Center, Bethesda, MD, US;
BACKGROUND CONTEXT: Internal disc disruption (IDD) results from tearing of inner annulus fibers while the external aspect remains intact. This condition occurs traumatically or degeneratively, is not identifiable using non-contrast CT, and induces painful symptoms. Due to its occult nature on routine imaging, IDD may be a source of idiopathic pain in the absence of obvious degenerative changes. The mechanism of pain is related to instability resulting from fundamental changes in segmental load sharing that contribute to discogenic pain mechanisms and acute nerve root compression. PURPOSE: Outline the effect of IDD on segmental biomechanics.
Refer to onsite Annual Meeting presentations and postmeeting proceedings for possible referenced figures and tables. Authors are responsible for accurately reporting disclosures and FDA device/drug status at time of abstract submission.
Proceedings of the NASS 29th Annual Meeting / The Spine Journal 14 (2014) 1S–183S STUDY DESIGN/SETTING: Measure basic biomechanical properties of lumbar motion segments prior to and following experimental induction of IDD. PATIENT SAMPLE: 12 lumbar motion segments were obtained from 8 minimally degenerated human lumbar spines (mean age: 54610yr). OUTCOME MEASURES: Segmental range of motion (RoM) under applied pure moments was quantified prior to and following IDD. Magnitude (percent cross-sectional area) and type (linear or concentrated) of disruption was quantified using axial MRI. Group differences were identified. METHODS: Axial MRI scans were obtained and intact specimens were then tested in pure bending (flexion, extension, lateral bending) to outline baseline biomechanics. IDD was induced using the Oliphant method (Clin Biomech 2006), which involves injection of pressurized nitrogen gas into the annulus through a catheter. MRI scans obtained following the IDD procedure were used to grade the level of annular disruption as the percentage of disc cross-sectional area affected. Specimens were again subjected to the pure moment protocol. Differences in biomechanical response were quantified as the change in post-disruption RoM. Differences were identified based on the type, location and magnitude of disruption. RESULTS: Four IDD types were identified: high (HMC) and low (LMC) magnitude concentrated disruptions, and linear disruptions in anterior (LA) and lateral (LL) disc regions. HMC and LMC disruptions affected 32% and 14.5% of the disc and were generally focused in the middle-right location. LA and LL disruptions affected 14.8% and 13.8% of the disc, were elongated in shape and located in anterior and right-lateral locations. The effect of IDD location was evident as LA and LL disruption types resulted in increased extension RoM (LA: 11%; LL: 14%), whereas LL disruptions did not affect and LA disruptions decreased flexion RoM (-9%). Both disruptions resulted in increased left lateral bending RoM (8.5%), and no change for right lateral bending. LMC disruptions had essentially no effect on RoM and HMC disruptions demonstrated considerable increases (8-23%) in RoM for all loading modes. CONCLUSIONS: This preliminary study demonstrated that the effect of IDD was dependent on the location, type and magnitude. Changes were most evident in loading modes that exercised disrupted fibers in tension, whereas compression of disrupted fibers generally resulted in no change from the intact condition. For the same magnitude, linear disruptions had a larger effect on segmental biomechanics than concentrated. However, disruption magnitude was evident when concentrated disruptions were increased to 32%, which had a large effect on biomechanics. These findings form the basis for further investigation of effects of IDD on segmental biomechanics and may provide a tool for clinicians to predict segmental instability based on the characteristics of IDD evident on axial MRI. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. http://dx.doi.org/10.1016/j.spinee.2014.08.050
33. Pfirrmann Grade as a Predictor of Range of Motion, Angular Stiffness and Relative Size of High-Flexibility Zone in the Lumbar Spine Muturi Muriuki, PhD1, Robert M. Havey, BS2, Leonard I. Voronov, MD, PhD3, Gerard Carandang1, Laurie Lomasney, MD4, Avinash G. Patwardhan, PhD5; 1Edward Hines Jr. VA Hospital, Hines, IL, US; 2 Hines, IL, US; 3Willowbrook, IL, US; 4Loyola University Medical Center, Maywood, IL, US; 5Loyola University Medical Center Department of Orthopaedic Surgery, Maywood, IL, US BACKGROUND CONTEXT: Pfirrmann Grade is used to assess intervertebral disc degeneration based on the appearance of the intervertebral
17S
space on T2-weighted MR images using disc signal intensity, disc height, and the ability to distinguish between the annulus and the nucleus of the disc. There is little biomechanical data on the correlation of Pfirrmann grade to quality of motion measures. PURPOSE: Determine if Pfirrmann disc grade predicts range of motion, stiffness and relative size of the high-flexibility zone. STUDY DESIGN/SETTING: Controlled laboratory study. PATIENT SAMPLE: 270 segments of 54 intact lumbar (L1-–sacrum) cadaveric spines (age 19–73 years; 34 M, 20 F). OUTCOME MEASURES: Pfirrmann grade, range of motion (ROM), angular stiffness, relative size of high-flexibility zone (HFZ). METHODS: Intervertebral discs were graded using T2-weighted MRI scans. Specimens were tested in flexion-extension with 0N and 400N follower preloads (flexion and extension limits of 8Nm and 6Nm, respectively). Vertebral motions were tracked using a 3D optoelectronic motion measurement system. A six-axis load transducer was used to measure applied moment. The data were used to calculate segmental ROM and stiffness in flexion and extension. ROM was decomposed into flexion and extension based on the specimen’s neutral posture as defined at the start of the experiments. HFZ (low-stiffness) and low-flexibility zone (LFZ) angular stiffness were calculated in flexion and in extension using custom MATLAB programs. Sizes of the HFZ zones relative to flexion or extension ROM were also calculated. Three disc grade-based groups were used in data analysis (Group I: grade 1 & 2; Group II: grade 3; Group III: grade 4 & 5). The effect of Pfirrmann grade on outcome measures was assessed using repeated measures ANOVA, with repeat factor applied follower load. RESULTS: Pfirrmann grade from the most to least common disc grades were 3 (n5141), 2 (n595), 4 (n526), 5 (n55) and 1 (n53). Lower lumbar motion segments were more likely to have a higher Pfirrmann grade (Pearson Chi-square: p50.001). L4-L5 and L5-S1 (40% of discs) had 5/5 of grade 5 discs, 19/26 (73%) of grade 4s, 59/141 (41%) of grade 3s, 25/95 (26%) of grade 2’s and 0 grade 1’s. Group I discs (n598) Compared to 0N, 400N follower preload caused a decrease in extension HFZ size (from 66% to 55% of ROM). The addition of compressive preload increased the flexion HFZ stiffness (from 1.25Nm/deg to 1.37Nm/deg). Mean HFZ size in flexion remained unchanged at 67% of ROM and total ROM increased slightly from 8.1 to 8.2 . Group II discs (n5141) Adding compressive preload caused a 0.2 decrease in total ROM to 8.4 , and a decrease in extension HFZ size (from 64% to 50% of ROM). Compressive preload increased the flexion HFZ stiffness (1.17Nm/deg to 1.26Nm/deg) and HFZ size in flexion (63% to 67% of ROM). Group III discs (n531) Compressive preload caused a decrease in total ROM (from 8.7 to 7.8 ), and in HFZ size in flexion and extension (from 66% to 59% and 61% to 44% of ROM respectively). Increases under compressive preload were observed in the flexion HFZ stiffness (from 1.27Nm/deg to 2.27Nm/deg). Group Comparisons: (400N Preload) Group III discs are almost one and half times stiffer in HFZ than the other groups. HFZ size as a percentage of ROM reduces with increased disc degeneration. Total ROM is 8.2 , 8.4 and 7.8 for the three groups respectively. The only significant difference is in HFZ size in extension between Group I and Group III discs. CONCLUSIONS: Our analysis found that, apart from HFZ size in flexion (p50.073), changes in the outcome measures used in this study are linked to Pfirrmann grade and application of compressive preload (p!0.0005). The changes observed are not as apparent without compressive preload, suggesting the importance of testing under compressive preload. Our results also suggest that Pfirrmann Grade 3 discs are more like Grade 1 & 2 discs than Grade 4 & 5 discs. This data adds to the few biomechanical studies of the correlation of Pfirrmann grade and biomechanical parameters. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. http://dx.doi.org/10.1016/j.spinee.2014.08.051
Refer to onsite Annual Meeting presentations and postmeeting proceedings for possible referenced figures and tables. Authors are responsible for accurately reporting disclosures and FDA device/drug status at time of abstract submission.