Biomechanical analysis on of anterior transpedicular screw-fixation after two-level cervical corpectomy using finite element method

BackgroundAnterior cervical trans-pedicle screw fixation was introduced to overcome some of the disadvantages associated with anterior cervical corpectomy and fusion. In vitro biomechanical studies on the trans-pedicle screw fixation have shown excellent pull-out strength and favorable stability. Comprehensive biomechanical performance studies on the trans-pedicle screw fixation, however, are lacking.MethodsThe control computed tomography images (C2-T2) were obtained from a 22-year-old male volunteer. A three dimensional computational model of lower cervical spine (C3-T1) was developed using computed tomography scans from a 22 year old human subject. The models of intact C3-T1 (intact group), anterior cervical trans-pedicle screw fixation (trans-pedicle group), and anterior cervical corpectomy and fusion (traditional group) were analyzed with using a finite element software. A moment of 1 N·m and a compressive load of 73.6 N were loaded on the upper surface and upper facet joint surfaces of C3. Under six conditions, four parameters such as the range of motion, titanium mesh plant stress, end-plate stress, and bone-screw stress were measured and compared on two treatment groups.FindingsCompared with the intact model, the range of motions for treatment groups were decreased. Compared with cervical corpectomy and fusion, the titanium plant, C4 upper end-plate and C7 lower end-plate stresses in trans-pedicle group were reduced. No significant difference was discovered on bone-screw stress between the two groups for lateral flexion and rotation, but bone-screw stress is smaller in trans-pedicle group when compared with traditional group. With exception of individual difference, trans-pedicle group had better biomechanical results than traditional group in range of motions, titanium mesh plant stress, end-plate stress and bone-screw stress.InterpretationThe trans-pedicle method has better biomechanical properties than the anterior cervical corpectomy and fusion making it a viable alternative for cervical fixations.     

下颈椎前路内固定联合后路经关节金属螺钉置入固定的生物力学稳定性

背景：对退变性颈椎管狭窄单纯采用前路椎体次全切除或椎间盘切除或单纯后路单开门椎管扩大成行均不能彻底完成脊髓减压和脊柱三柱稳定。目的：探讨下颈椎前路固定联合后路经关节螺钉固定的生物力学稳定性。方法：正常成人尸体颈椎标本,每具分别制作以下两种模型：①经后路C3～C7单开门和下颈椎前路C5椎体次全切除钛网支撑植骨、ORION内固定模型（对照组）。②经后路C3～C7单开门和经关节螺钉内固定及下颈椎前路C5椎体次全切除钛网内植骨、ORION内固定模型（实验组）。结果与结论：实验组在前屈、后伸、左、右侧屈及左、右旋转移位角度均小于对照组（P〈0.001）。提示：①在生物力学实验中,下颈椎前路固定联合后路经关突节螺钉固定的生物力学性能优良,对抗前屈、后伸、左、右旋转的作用力更强,颈椎可获得更可靠的稳定性。②下颈椎前路固定联合后路经关节螺钉固定在对抗颈椎前屈运动时力学稳定性更为强大。     

The traumatic spondylolisthesis of the axis. A biomechanical in vitro evaluation of an instability model and clinical relevant constructs for stabilization

OBJECTIVE: Stepwise destabilization of the traumatic spondylolisthesis C2 with an increasing anterior defect of C2-C3 was investigated. The three-dimensional stabilizing capabilities of posterior transpedicle screw osteosynthesis and two anterior plate systems C2-C3, the H-plate and the titanium locking plate were tested. DESIGN: A biomechanical in vitro study was performed using a standardized experimental protocol in a spine tester. BACKGROUND: The extent of the instability of the traumatic spondylolisthesis of C2 within its different types remains unclear. Posterior and anterior approaches for stabilization exist for patients with isthmusfractures at C2, the stabilizing effect has not been demonstrated yet. METHODS: The motion levels from C2-C3 in six human specimen were tested in flexion, extension, right and left lateral bending and left and right axial rotation. The specimens were tested intact, after destabilization and after stabilization. RESULTS: In extension and axial rotation, each step of destabilization decreased the moment significantly, to achieve the range of motion of the intact specimen. In flexion a statistical significant destabilization after separation of the posterior longitudinal ligament was present. The flexibility tests showed an increasing range of motion of the posterior transpedicle screws, with increasing anterior instability markedly in flexion and extension. After H-plate and locking plate fixation, a significant decrease of the range of motion resulted in flexion. The stiffness in flexion and extension increased consecutively, while in lateral bending and axial rotation the transpedicle screw fixation showed the highest stiffness. CONCLUSIONS/RELEVANCE: The traumatic spondylolisthesis of C2 is a significantly unstable injury in case of additional segmental damage of C2-C3. Anterior stabilization in these injuries is mandatory.     

Posterior cervical spine crisscross fixation: Biomechanical evaluation

BackgroundBiomechanical/anatomic limitations may limit the successful implantation, maintenance, and risk acceptance of posterior cervical plate/rod fixation for one stage decompression-fusion. A method of posterior fixation (crisscross) that resolves biomechanical deficiencies of previous facet wiring techniques and not reliant upon screw implantation has been devised. The biomechanical performance of the new method of facet fixation was compared to the traditional lateral mass plate/screw fixation method.MethodsThirteen human cadaver spine segments (C2-T1) were tested under flexion-compression loading and four were evaluated additionally under pure-moment load. Preparations were evaluated in a sequence of surgical alterations with intact, laminectomy, lateral mass plate/screw fixation, and crisscross facet fixation using forces, displacements and kinematics.FindingsCombined loading demonstrated significantly lower bending stiffness (p < 0.05) between laminectomy compared to crisscross and lateral mass plate/screw preparations. Crisscross fixation showed a comparative tendency for increased stiffness. The increased overall motion induced by laminectomy was resolved by both fixation techniques, with crisscross fixation demonstrating a comparatively more uniform change in segmental motions.InterpretationThe crisscross technique of facet fixation offers immediate mechanical stability with resolution of increased flexural rotations induced by multi-level laminectomy. Many of the anatomic limitations and potentially deleterious variables that may be associated with multi-level screw fixation are not associated with facet wire passage, and the subsequent fixation using a pattern of wire connection crossing each facet joint exhibits a comparatively more uniform load distribution. Crisscross wire fixation is a valuable addition to the surgical armamentarium for extensive posterior cervical single-stage decompression-fixation.     

Biomechanical comparison of cervical discectomy/fusion model using allograft spacers between anterior and posterior fixation methods (lateral mass and pedicle screw)

BackgroundThe purpose of this study is to investigate effects of different fixation methods on the physical stress on allospacers, endplate-vertebral body, and implants using finite element model analyses.MethodsStress distribution and subsidence risk according to the fixation methods under the condition of hybrid motion control were analyzed. The detailed finite element model of a previously validated, three-dimensional, intact cervical spinal segment model, with C5–C6 segmental fusion using allospacer, was used to evaluate the biomechanical characteristics of different fixation combinations, such as anterior plate/screws, lateral mass screw, and posterior pedicle screw.FindingsThe load sharing on allospacers increased in extension in order of posterior pedicle screws (21.4%), lateral mass screws (31.5%), and anterior plate/screws (56.6%). lateral mass screw demonstrated the highest load sharing (68.1%) on the allospacer in flexion. The Peak von Mises stress of the allospacer was the lowest in flexion and axial rotation but the highest in extension with anterior plate/screws. Allospacer subsidence risk was the lowest in extension, lateral bending, and axial rotation with posterior pedicle screws but the lowest in flexion with anterior plate/screws. The bone-screw loosening risk was the lowest in all modes with posterior pedicle screws but the highest with anterior plate/screws.InterpretationPosterior pedicle screws demonstrated the best mechanical stability of allospacer failure-subsidence and the lowest risk of screw loosening. Different motion restrictions depending on the fixation method should be considered for implant and allospacer safety.     

Effectiveness of cervical zero profile integrated cage with and without supplemental posterior Interfacet stabilization

BackgroundConditions requiring cervical decompression and stabilization are commonly treated using anterior cervical discectomy and fusion using an anterior cage-plate construct. Anterior zero profile integrated cages are an alternative to a cage-plate construct, but literature suggests they may result in less motion reduction. Interfacet cages may improve integrated cage stability. This study evaluated the motion reduction of integrated cages with and without supplemental interfacet fixation. Motion reduction of integrated cages were also compared to published cage-plate results.MethodsSeven cadaveric (C2-T1) spines were tested in flexion-extension, lateral bending, and rotation. Specimens were tested: 1) intact, 2) C6-C7 integrated cage, 3) C6-C7 integrated cage + interfacet cages, 4) additional integrated cages at C3-C4 and C4-C5, 5) C3-C4, C4-C5 and C6-C7 integrated cages + interfacet cages. Motion, lordosis, disc and neuroforaminal height were assessed.FindingsIntegrated cage at C6-C7 decreased flexion-extension by 37% (P = .06) and C3-C5 by 54% (P < .01). Integrated + interfacet cages decreased motion by 89% and 86% compared to intact (P < .05). Integrated cages increased lordosis at C4-C5 and C6-C7 (P < .01). Integrated + interfacet cages returned C3-C5 lordosis to intact values, while C6-C7 remained more lordotic (P = .02). Compared to intact, neuroforaminal height increased after integrated cages at C3-C5 (P ≤ .01) and at all levels after interfacet cages (P < .01).InterpretationAnterior integrated cages provides less stability than traditional cage-plate constructs while supplemental interfacet cages improve stabilization. Integrated cages provide more lordosis at caudal levels and increase neuroforaminal height more at cranial levels. After interfacet cages, posterior disc height and neuroforaminal height increased more at the caudal segments.     

How does a novel knitted titanium nucleus prosthesis change the kinematics of a cervical spine segment? A biomechanical cadaveric study

BackgroundTotal disc replacement is a possible treatment alternative for patients with degenerative disc disease, especially in the cervical spine. The aim is to restore the physiological flexibility and biomechanical behavior. A new approach based on these requirements is the novel nucleus prosthesis made of knitted titanium wires.MethodsThe biomechanical functionalities of eight human cervical (C4-C7) spine segments were investigated. The range of motion was quantified using an ultra-sound based motion analysis system. Moreover, X-rays in full flexion and extension of the segment were taken to define the center of rotation before and after implantation of the nucleus prosthesis as well as during and after complex cyclic loading.FindingsThe mean range of motion of the index segment (C5/6) in flexion/extension showed a significant reduction of range of motion from 9.7° (SD 4.33) to 6.0° (SD 3.97) after implantation (P = 0.037). Lateral bending and axial rotation were not significantly reduced after implanting and during cyclic loading in our testing. During cyclic loading the mean range of motion for flexion/extension increased to 7.2° (SD 3.67). The center of rotation remained physiological in the ap-plane and moved cranially in the cc-plane (−27% to −5% in cc height) during the testing.InterpretationThe biomechanical behavior of the nucleus implant might lower the risk for adjacent joint disorders and restore native function of the index segment. Further in vivo research is needed for other factors, like long-term effects and patient's satisfaction.     

Assessment of motion in the cervico-thoracic spine in patients with subacute whiplash-associated disorders.

OBJECTIVE: To investigate the distribution of segmental flexion mobility in the cervico-thoracic spine of men and women with whiplash-associated disorders. The study also assesses the relationship between cervical mobility and segmental flexion mobility, and whether hypomobility in C7-T1 is associated with neck pain and weakness in the hands. Finally, the study investigates the impact of fear of movement/(re)injury and pain intensity on cervical mobility. METHOD: The data in this longitudinal study was obtained from a previous trial on 47 patients. Assessments were performed at baseline and 3 and 9 months following randomization using a cervical range of motion instrument, the cervico-thoracic ratio, a Grippit, a visual analogue scale, a Painmatcher, and the Tampa Scale for Kinesiophobia. RESULTS: Women exhibited hypomobility in C7-T1. There was no significant association between the 2 cervical measurement techniques. The correlation between flexion mobility in C7-T1 and grip strength was weak but significant (r=-0.3) (p<0.05). There was also a weak but significant negative correlation between total cervical mobility and neck pain intensity. No significant correlation was found between fear of movement/(re)injury and cervical mobility. CONCLUSION: Women with whiplash-associated disorders seem to exhibit flexion hypomobility in C7-T1. The flexion mobility in C7-T1 was weakly, but significantly, correlated with grip strength, but was not shown to predict neck pain. Neck pain may give rise to restricted range of motion.     

Biomechanical comparison of the stable efficacy of two anterior plating systems

OBJECTIVE: To compare the immediate stable efficacy and load sharing effect of two types of anterior cervical screw-plating instrumentations: the Morscher Synthes titanium locking screw-plate system and the Caspar trapezoidal screw-plate system. DESIGN: Fresh porcine cervical spines with intact, two surgery unstable models, and then reconstructed with or without screw-plating instruments were compared in three physiological loading conditions. BACKGROUND: Two markedly instrumentation systems--Morscher Synthes titanium cervical locking screw-plate and Caspar trapezoidal screw-plate systems are commonly used in management of complex cervical spine disorders. Although the biomechanical study showed that the lower cost Caspar system performed superior in extension before and after plate fatigue, the clinic evaluations of two systems were contradictory. So (1) does the titanium cervical locking plate system pay for its higher cost? and (2) what is the load sharing character of strut graft in one level corpectomy?METHODS: Eight fresh ligamentous porcine cervical spines from C3 to C7 were undergone axial compression, rotation and sagittal flexion tests. The biomechanical experiment was sequentially repeated for the intact, C5-6 discectomy, C5 corpectomy, and then stabilized by either type of plate fixation devices with or without polymethylmethacrylate bone cement grafting. Strains measured by an extensometer across the operated motion segment were used as the index of stability. RESULTS: Analysis of the strain data showed both types of anterior fixation plate systems provided adequate-restored stability for the spinal column only aided with polymethylmethacrylate construction. Statistically, there was no significant difference in biomechanical evaluation for the stability effect between much cost Morscher Synthes plate and Caspar plate system (p<0.005). The spinal disc bore as much as 75% of axial loading. While the strut graft functioned as the disc substitute and spacer, it bore more than 90% of axial loading. In high degree of flexion, the transmitted compressive load was shifted anteriorly to the screw-plate. This might unload the polymethylmethacrylate graft and resulted in the strut graft in tensile fatigue failure. CONCLUSIONS: Statistically both systems showed similar stable efficacy, however, the Morscher Synthes cervical locking plate system might provide better stable effect in higher degrees of flexion motion. The strut graft played as the major load-bearing role in axial compression and sagittal flexion, while in axial rotation, the applied torque was mainly resisted by facet joint and screw-plate system complex. RELEVANCE: The minor discrepancy of two plating systems may be due to the nature of plate geometry and design but not the material properties. Combination of bone graft and either plating systems provides adequate fusion stability under physiological loadings. The high degree flexion may cause the posterior portion of polymethylmethacrylate graft in tensile fracture and then result in polymethylmethacrylate failure in clinic observation.     

体外生物力学评价上胸椎前路钛板内固定装置的三维运动稳定性

背景：国内外少见颈前路带锁钢板重建上胸椎的体外生物力学报道。目的：从生物力学角度评价自行研制的上胸椎前路钛板内固定装置。方法：15具成人尸体上胸椎标本分成3组,即上胸椎前路钛板内固定组（B）,颈前路钛板预弯内固定组（C）,颈前路钛板未预弯内固定组（D）。对完整标本进行三维活动度测量,分别安装好各组内固定再次进行标本在前屈、后伸和侧弯及旋转状态下的三维运动稳定性测量,并与完整状态（A）进行对比。结果与结论：在完整状态下B、C、D3组标本的三维运动稳定性差异无显著性意义（P〉0.05）。前屈稳定性排列：B〉D〉C〉完整,B、A之间差异有显著性意义（P=0.012）;后伸稳定性排列：B〉C〉A〉D,B与A,C,D之间差异有显著性意义（P=0.001,0.021,0.01）;旋转状态下的稳定性排列：B〉C〉A〉D,各组差异无显著性意义;侧弯稳定性排列：A〉B〉C〉D,A和C,D之间差异有显著性（P=0.005,0.002）。提示上胸椎前路钛板装置具有较好的三维稳定性,如果采用颈前路钛板内固定建议塑型。     

体外生物力学评价上胸椎前路钛板内固定装置的三维运动稳定性

背景:国内外少见颈前路带锁钢板重建上胸椎的体外生物力学报道。目的:从生物力学角度评价自行研制的上胸椎前路钛板内固定装置。方法:15具成人尸体上胸椎标本分成3组,即上胸椎前路钛板内固定组(B),颈前路钛板预弯内固定组(C),颈前路钛板未预弯内固定组(D)。对完整标本进行三维活动度测量,分别安装好各组内固定再次进行标本在前屈、后伸和侧弯及旋转状态下的三维运动稳定性测量,并与完整状态(A)进行对比。结果与结论:在完整状态下B、C、D3组标本的三维运动稳定性差异无显著性意义(P>0.05)。前屈稳定性排列:B>D>C>完整,B、A之间差异有显著性意义(P=0.012);后伸稳定性排列:B>C>A>D,B与A,C,D之间差异有显著性意义(P=0.001,0.021,0.01);旋转状态下的稳定性排列:B>C>A>D,各组差异无显著性意义;侧弯稳定性排列:A>B>C>D,A和C,D之间差异有显著性(P=0.005,0.002)。提示上胸椎前路钛板装置具有较好的三维稳定性,如果采用颈前路钛板内固定建议塑型。     

Upper and lower adjacent segment range of motion after fixation of different lumbar spine segments in the goat: an in vitro experiment

ObjectivesThe purpose of this study was to examine the biomechanical effects of fixation on range of motion (ROM) in the upper and lower adjacent segments of different lumbar spine segments in a goat spine model.MethodsFifteen goat spine specimens (vertebrae T12–S1) were randomly divided into three groups: A (single-segment fixation), B (double-segment fixation), and C (triple-segment fixation). Motion in different directions was tested using a spinal motion simulation test system with five external loading forces. Transverse, forward–backward, and vertical displacement of the upper and lower adjacent segments were measured.ResultsAs the external load increased, the upper and lower adjacent segment ROM increased. A significantly greater ROM in group C compared with group A was found when the applied external force was greater than 75 N. The upper adjacent segment showed a significantly greater ROM than the lower adjacent segment ROM within each group.ConclusionsAdjacent segment ROM increased with an increasing number of fixed lumbar segments. The upper adjacent segment ROM was greater than that of the lower adjacent segments. Adjacent segment stability after lumbar internal fixation worsened with an increasing number of fixed segments.     

C2 椎弓根螺钉置入内固定治疗Hangman骨折的生物力学评价

背景:C2椎弓根钉置入内固定治疗Hangman骨折因固定可靠,无生理功能的丢失而受到众多学者的青睐,根据文献报道,单节段固定治疗Hangman骨折的适应证差异较大,并且缺乏生物力学依据.目的:评价C2椎弓根螺钉置入内固定治疗Hangman骨折的生物力学性能.设计、时间和地点:2004-05/08在解放军第一军医大学全军生物力学重点实验室完成的对比观察实验.材料:材料采用AO通用的钛合金颈椎椎弓根螺钉,长度18～25mm,直径3.5 mm.6具新鲜C1～C4颈椎标本依次制成Ⅰ型、ⅡA型和Ⅱ型Hangman骨折模型.方法:椎弓根螺钉固定后在非破坏方式下用脊柱三维运动实验机进行测量,通过加载盘对标本施加2.0 N·m的纯力偶矩,使标本产生前届/后伸、左/右侧弯和左/右轴向旋转6种生理运动:每次测试重复3次加载/卸载循环,在第3次循环时进行运动学测量.主要观察指标:由激光扫描仪(精度0.1%)摄取在零载荷和最大载荷时的脊柱运动图像,并用相应软件系统进行图像分析,计算出标本的三维运动范围.结果:1型骨折C2椎弓根螺钉固定后相对稳定性在屈曲、后伸、侧弯及旋转达到了对照组的100.62%,96.91%,99.19%,97.12%(P＞0.05).ⅡA型骨折C2椎弓根螺钉固定后旋转稳定性达到了对照组的61.86%(P＜0.05).Ⅱ型骨折C2椎弓根螺钉固定后相对稳定性在屈曲、后伸、侧弯及旋转为对照组的47.84%,21.29%,65.98%,41.69%(P＜0.05).结论:生物力学评估提示,Hangman Ⅰ型、ⅡA型骨折基本适合C2椎弓根螺钉置入治疗,置入固定后骨折可达生理性固定或稳定性较好;Ⅱ型骨折固定后稳定性较差,不适合单纯椎弓根钉内固定置入.     

Impact of multilevel facetectomy on segmental spinal flexibility in patients with thoracic adolescent idiopathic scoliosis

BackgroundThe aim of this study was to intraoperatively assess the effects of multilevel facetectomy on segmental spinal flexibility in patients with thoracic adolescent idiopathic scoliosis.MethodsTwenty patients who underwent posterior thoracic adolescent idiopathic scoliosis curve correction were evaluated. Compressive or distractive loaded force of 50N was applied on the handle of a compressor or distractor connected to the necks of pedicle screws inserted at T7 to T11. Segmental spinal flexibility rates were calculated based on the distance between screw heads under the loaded and unloaded conditions. In addition, the flexibility rates were obtained before and after multilevel facetectomy.FindingsAbsolute flexibility rates of all segments significantly increased after multilevel facetectomy under both compressive and distractive forces (P < 0.01). The absolute change in the flexibility rate was significantly higher at the concave side than at the convex side under both compressive (P < 0.01) and distractive loaded forces (P = 0.046). No significant correlation was found between change in the flexibility rates and preoperative Cobb angle or preoperative curve flexibility.InterpretationFrom a biomechanical point of view, multilevel facetectomy provides proper spinal flexibility to improve the correction rate of posterior adolescent idiopathic scoliosis surgery. The effects are higher at the concave side than at the convex side.     

Biomechanical effects of uncinate process excision in cervical disc arthroplasty

BackgroundStudies on the role of uncinate process have been limited to responses of the intact spine and patient's outcomes, and procedures to perform the excision. The aim of this study was to determine the role of uncinate process on the biomechanical response at the index and adjacent levels in three artificial discs used in cervical disc arthroplasty.MethodsA validated finite element model of cervical spine was used. Flexion, extension, and lateral moments and follower load were applied to Bryan, Mobi-C, and Prestige LP artificial discs at C5-C6 level with and without uncinate process. Ranges of motion at index level and adjacent caudal and cranial segments, intradiscal pressures at adjacent segments, and facet loads at index level and adjacent segments were obtained. Data were normalized with respect to the preservation of uncinate process.FindingsUncinate process removal increased motions up to 27% at index and decreased up to 10% at adjacent levels, decreased disc pressures up to 14% at adjacent segments, decreased facet loads at adjacent segments up to 14%, while at index level, change in loads depended on mode and arthroplasty, with Mobi-C responding with up to 51% increase and Bryan disc up to 11% decrease, while Prestige LP increased loads by 17% in extension and decreased by 9%% in lateral bending.InterpretationAs surgical selection is based on morphology and surgeon's experience, the present computational findings provide quantitative information for an optimal choice of the device and procedure, while further studies (in vitro/clinical) would be required.     

Biomechanical investigation of potential prophylactic scoliosis treatments following various sizes of chest wall resection

BackgroundA well-known problematic sequela of chest wall resections is development of scoliosis. Despite the seriousness and frequency of scoliosis following chest well resection, the etiology and biomechanical information needed to understand this progression aren't well-known.MethodsRange of motion of six specimen (C7–L2) was captured using a custom-built six degrees-of-freedom machine in each of three physiological rotation axes. Left posterior ribs were sequentially resected 7cm from the rib head, starting at the 5^th rib and continuing until the 10^th rib. Injured specimen were instrumented with unilateral anterior rod fixation and then with additional unilateral posterior fixation, each starting at T4 and then extended distally as ribs were resected. Relative motion between the constructs' proximal and distal ends was measured in all three axes for the intact, injured, unilateral anterior, and unilateral anterior with unilateral posterior constructs.FindingsRaw motion of the injured specimen increased in a stepwise manner as ribs were resected. Averaged across all injury sizes, the unilateral anterior construct significantly reduced motion by 47.0±13.4% in lateral bending (P=.001). The combined anterior-posterior construct significantly reduced motion by 57.6±15.9% in flexion/extension (P<.001), 70.3±12.2% in lateral bending (P<.001), and 51.1±14.5% in axial rotation (P<.001). Combined anterior-posterior fixation was significantly more stable than anterior-only fixation in flexion/extension (P=.002).InterpretationRegardless of injury size, posterior rib resection did not create significant immediate instability of the thoracic spine. Concurrent spinal stabilization was shown to maintain thoracic spine stability. Combined anterior-posterior fixation proved to be significantly more rigid than an anterior-only construct.     

Functional radiographic examination of the cervical spine in patients with post-traumatic headache

The segmental extension-flexion motion of the cervical spine and the overall C1-C7 motion were measured on functional X-rays in 19 patients with post-traumatic headache and 19 age- and sex-matched controls. The extension-flexion C1-C7 motion was reduced in patients with post-traumatic headache due to reduced motion in three segments: C2-C3, C5-C6 (p less than 0.05), and C6-C7 (p less than 0.01). In both groups a negative correlation between the C1-C7 motion and age was found, but the regression coefficients were different. Only in the control group could a negative correlation between segmental motion and age be demonstrated. In the patients with post-traumatic headache a statistically significant negative correlation between the log (pain index) and the age-corrected C1-C7 motion was found (p less than 0.04). On the segmental level a negative correlation between the log (pain index) and the age-corrected C1-C2 and C5-C6 motion could be demonstrated (p less than 0.05). Regarding C6-C7 there was a tendency to negative correlation. Furthermore, a negative correlation between the frequency of associated symptoms (dizziness, visual disturbances and ear symptoms) and the age-corrected C5-C6 motion was found. Consequently the decrement of motion primarily affected C2-C3, C5-C6, and C6-C7, whereas the analysis of correlation with pain index indicated C1-C2 and C5-C6 (C6-C7) as the most important segments involved.     

Normal kinematics of the upper cervical spine during the Flexion-Rotation Test - In vivo measurements using magnetic resonance imaging

The Flexion-Rotation Test (FRT) is proposed to assess mobility primarily at C1-C2. However, there is no in vivo measurement investigating the validity of the FRT. The purpose of this study was 1) to examine measurement reliability of segmental upper cervical movements using magnetic resonance imaging and 2) to investigate the content validity of the FRT. Nineteen asymptomatic female subjects (mean age: 22.2 years) were evaluated with a 0.2-T horizontally open MRI unit. The segmental rotation angles from Occiput-C1 to C3-C4 and the C4 vertebra were assessed with the head maximally rotated to both the right and the left in two conditions - neck in neutral and in flexion. Good reliability of the method of measurement was suggested by error considerations. A repeated measure ANOVA revealed an interaction between the two different neck starting positions and segment levels (P < 0.0001). Post-hoc analysis revealed that there were significant reductions in the flexed position (P < 0.0001) except for at Occiput-C1. While there was only a 16.3% reduction in rotation range at C1-C2, the reduction was 68.1% at C2-C3, 61.4% at C3-C4, and 76.9% at segments below C4, respectively, supporting the content validity of the FRT as a clinical measure of atlanto-axial mobility.     

Immediate effects of a new microprocessor-controlled prosthetic knee joint: a comparative biomechanical evaluation

Bellmann M, Schmalz T, Ludwigs E, Blumentritt S. Immediate effects of a new microprocessor-controlled prosthetic knee joint: a comparative biomechanical evaluation.ObjectiveTo investigate the immediate biomechanical effects after transition to a new microprocessor-controlled prosthetic knee joint.DesignIntervention cross-over study with repeated measures. Only prosthetic knee joints were changed.SettingMotion analysis laboratory.ParticipantsMen (N=11; mean age ± SD, 36.7±10.2y; Medicare functional classification level, 3–4) with unilateral transfemoral amputation.InterventionsTwo microprocessor-controlled prosthetic knee joints: C-Leg and a new prosthetic knee joint, Genium.Main Outcome MeasuresStatic prosthetic alignment, time-distance parameters, kinematic and kinetic parameters, and center of pressure.ResultsAfter a half-day training and an additional half-day accommodation, improved biomechanical outcomes were demonstrated by the Genium: lower ground reaction forces at weight acceptance during level walking at various velocities, increased swing phase flexion angles during walking on a ramp, and level walking with small steps. Maximum knee flexion angle during swing phase at various velocities was nearly equal for Genium. Step-over-step stair ascent with the Genium knee was more physiologic as demonstrated by a more equal load distribution between the prosthetic and contralateral sides and a more natural gait pattern. When descending stairs and ramps, knee flexion moments with the Genium tended to increase. During quiet stance on a decline, subjects using Genium accepted higher loading of the prosthetic side knee joint, thus reducing same side hip joint loading as well as postural sway.ConclusionsIn comparision to the C-Leg, the Genium demonstrated immediate biomechanical advantages during various daily ambulatory activities, which may lead to an increase in range and diversity of activity of people with above-knee amputations. Results showed that use of the Genium facilitated more natural gait biomechanics and load distribution throughout the affected and sound musculoskeletal structure. This was observed during quiet stance on a decline, walking on level ground, and walking up and down ramps and stairs.     

Biomechanical evaluation of anterior lumbar interbody fusion with various fixation options: Finite element analysis of static and vibration conditions

BackgroundAnterior lumbar interbody fusion combined with supplementary fixation has been widely used to treat lumbar diseases. However, few studies have investigated the influence of fixation options on facet joint force and cage subsidence. The aim of this study was to explore the biomechanical performance of anterior lumbar interbody fusion with various fixation options under both static and vertical vibration loading conditions.MethodsA previously validated finite element model of the intact L1–5 lumbar spine was employed to compare five conditions: (1) Intact; (2) Fusion alone; (3) Fusion combined with anterior lumbar plate; (4) Fusion combined with Coflex-F fixation; (5) Fusion combined with bilateral pedicle screw fixation. The models were analyzed under static and vertical vibration loading conditions respectively.FindingsBilateral pedicle screws provided highest stability at surgical level. Applying supplementary fixation diminished the dynamic responses of lumbar spine. Compared with anterior lumbar plate and Coflex-F device, bilateral pedicle screws decreased the stress responses of the endplates and cage under both static and vibration conditions, while increased the facet joint force at adjacent levels. As for comparison between Coflex-F device and anterior lumbar plate, results showed a similarity in biomechanical performance under static loading, and a slightly higher dynamic response of the latter under vertical vibration.InterpretationThe biomechanical performance of lumbar spine was significantly influenced by the variation of fixations under both static and vibration conditions. Bilateral pedicle screws showed advantages in stabilizing surgical segment and relieving cage subsidence, but may increase the facet joint force at adjacent levels.