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3.
J Spinal Disord Tech ; 24(6): E49-56, 2011 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-21685804

RESUMO

STUDY DESIGN: An in vitro biomechanical cadaver study. OBJECTIVES: To evaluate the pull-out strength after 5000 cyclic loading among 4 revision techniques for the loosened iliac screw using corticocancellous bone, longer screw, traditional cement augmentation, and boring cement augmentation. SUMMARY OF BACKGROUND DATA: Iliac screw loosening is still a clinical problem for lumbo-iliac fusion. Although many revision techniques using corticocancellous bone, larger screw, and polymethylmethacrylate (PMMA) augmentation were applied in repairing pedicle screw loosening, their biomechanical effects on the loosened iliac screw remain undetermined. METHODS: Eight fresh human cadaver pelvises with the bone mineral density values ranging from 0.83 to 0.97 g/cm were adopted in this study. After testing the primary screw of 7.5 mm diameter and 70 mm length, 4 revision techniques were sequentially established and tested on the same pelvis as follows: corticocancellous bone, longer screw with 100 mm length, traditional PMMA augmentation, and boring PMMA augmentation. The difference of the boring technique from traditional PMMA augmentation is that PMMA was injected into the screw tract through 3 boring holes of outer cortical shell without removing the screw. On an MTS machine, after 5000 cyclic compressive loading of -200∼-500 N to the screw head, axial maximum pull-out strengths of the 5 screws were measured and analyzed. RESULTS: The pull-out strengths of the primary screw and 4 revised screws with corticocancellous bone, longer screw and traditional and boring PMMA augmentation were 1167 N, 361 N, 854 N, 1954 N, and 1820 N, respectively. Although longer screw method obtained significantly higher pull-out strength than corticocancellous bone (P<0.05), the revised screws using these 2 techniques exhibited notably lower pull-out strength than the primary screw and 2 PMMA-augmented screws (P<0.05). Either traditional or boring PMMA screw showed obviously higher pull-out strength than the primary screw (P<0.05); however, no significant difference of pull-out strength was detected between the 2 PMMA screws (P>0.05). CONCLUSIONS: Wadding corticocancellous bone and increasing screw length failed to provide sufficient anchoring strength for a loosened iliac screw; however, both traditional and boring PMMA-augmented techniques could effectively increase the fixation strength. On the basis of the viewpoint of minimal invasion, the boring PMMA augmentation may serve as a suitable salvage technique for iliac screw loosening.


Assuntos
Cimentos para Ossos , Parafusos Ósseos , Ílio/cirurgia , Vértebras Lombares/cirurgia , Falha de Prótese , Idoso , Fenômenos Biomecânicos , Feminino , Humanos , Fixadores Internos , Masculino , Pessoa de Meia-Idade , Reoperação
4.
Zhonghua Yi Xue Za Zhi ; 91(15): 1041-6, 2011 Apr 19.
Artigo em Chinês | MEDLINE | ID: mdl-21609639

RESUMO

OBJECTIVE: To investigate vertebral augmentation with a novel reticulate bone filling container system by polymethyl methacrylate (PMMA) injection in cadaveric simulated vertebral compressive fracture and explore the effect of reticulate bone filling container on cement distribution controlling within vertebral body and the restoration of biomechanical properties after augmentation. METHODS: A total of 28 freshly frozen human vertebrae specimens were randomly divided into 4 groups. After the measurements of bone mineral density (BMD) and vertebral height, each vertebra received an axle load by a MTS (material testing system) machine to test the initial strength and stiffness. Subsequently a simultaneous compressive fracture model was created to measure the stiffness and height of fractured vertebrae. Then the augmentation procedure was performed. Afterward the biomechanical properties and the vertebral height were similarly measured as pre-operatively. The expansion of bone filling container and the distribution of cement within vertebral body were morphologically observed by crossing the specimens in sagittal midline and also integrated with the radiographic results. RESULTS: Stiffness was significantly restored comparing with that of fractured level (P < 0.05). And the bipedicular groups had better restoration results than the unipedicular groups. The strength and height of specimens significantly increased after the augmentation procedure but without difference among groups. In axial radiographic view, the distribution of cement in vertebral body was oval or long oval-shaped in double-layer bone filling container groups while it was irregular in single-layer groups. After crossing, the double-layer version expanded well in vertebral body and could enwrap most of injected cement. There was only a little leakage near the vessel layer. But the single-layer version had a poor expansion and a large amount of cement leakage. CONCLUSION: This novel reticulate bone void filling container system with different layers may restore both the biomechanical properties and the height of fractured vertebrae. But, with the benefit of reducing cement leakage, a double-layer design can enwrap most of injected PMMA and has a brighter prospect of clinical application.


Assuntos
Substitutos Ósseos , Estresse Mecânico , Vertebroplastia/instrumentação , Fenômenos Biomecânicos , Densidade Óssea , Humanos , Vértebras Lombares , Fraturas da Coluna Vertebral/cirurgia , Vértebras Torácicas , Vertebroplastia/métodos
5.
Clin Biomech (Bristol, Avon) ; 26(6): 556-61, 2011 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-21345556

RESUMO

BACKGROUND: Iliac screw loosening has been a clinical problem in the lumbo-pelvic reconstruction. Although iliac screws are commonly inserted into either upper or lower iliac column, the biomechanical effects of the two fixations and their revision techniques with bone cement remain undetermined. The purpose of this study was to compare the anchoring strengths of the upper and lower iliac screws with and without cement augmentation. METHODS: 5 pairs of formalin fixed cadaveric ilia with the bone mineral density values ranged from 0.82 to 0.97 g/cm(2) were adopted in this study. Using screws with 70-mm length and 7.5-mm diameter, 2 conventional iliac screw fixations and their revision techniques with cement augmentation were sequentially established and tested on the same ilium as follows: upper screw, upper cement screw, lower screw, and lower cement screw. Following 2000 cyclic compressive loading of -300 N to -100 N to the screw on a material testing machine, the maximum pull-out strengths were measured and analyzed. FINDINGS: The average pull-out strengths of upper, upper cement, lower, and lower cement screws were 964 N, 1462 N, 1537 N, and 1964 N, respectively. The lower screw showed significantly higher pull-out strength than the upper one (P=0.008). The cement augmentation notably increased the pull-out strengths of both upper and lower screws. The positive correlation between pull-out strength and bone mineral density value was obtained for the 4 fixations. INTERPRETATION: The lower iliac screw technique should be the preferred choice in lumbo-pelvic stabilization surgery; cement augmentation may serve as a useful salvage technique for iliac screw loosening; preoperative evaluation of bone quality is crucial for predicting fixation strength of iliac screw.


Assuntos
Cimentos para Ossos/química , Parafusos Ósseos , Idoso , Fenômenos Biomecânicos , Densidade Óssea , Feminino , Humanos , Ílio/química , Masculino , Pessoa de Meia-Idade , Ossos Pélvicos/patologia , Pelve/patologia , Estresse Mecânico
6.
Clin Biomech (Bristol, Avon) ; 25(9): 867-72, 2010 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-20655639

RESUMO

BACKGROUND: Although both single and dual iliac screw techniques are used in spino-pelvic reconstruction following sacrectomy for treating sacral tumors, the basis for choosing between the two techniques for different instability types remains undetermined. The purpose of this study was to evaluate the effects of the extent of sacrectomy on the stability of the lumbo-iliac fixation construct using single and dual iliac screw techniques. METHODS: Nine human L2-pelvic specimens were tested for their intact condition simulated by L3-L5 pedicle screw fixation. Sequential partial sacrectomies and L3-iliac fixation using bilateral single and dual iliac screws were conducted on the same specimens as follows: under-S1 sacrectomy+single screw, under-½S1 sacrectomy+single screw, one-side sacroiliac joint resection+single screw, total sacrectomy+single screw, and total sacrectomy+dual screw. Biomechanical testing was performed on a material testing machine for evaluating the stiffness of the L3-iliac fixation construct in compression and torsion. FINDINGS: Single iliac screw technique was found to effectively restore the local stability in under-½S1 sacrectomy. However, it could not provide adequate stability for further resection of one-side sacroiliac joint in torsion and total sacrectomy in compression (P<0.05). On the other hand, dual iliac screw technique could restore the stability to the intact condition after total sacrectomy in both compression and torsion. INTERPRETATION: The single iliac screw technique for L3-iliac fixation could effectively restore the local stability for under-½S1 sacrectomy. However, for instabilities of the under-½S1 sacrectomy with one-side sacroiliac joint resection or total sacrectomy, the dual iliac screw technique should be considered.


Assuntos
Parafusos Ósseos , Ílio/cirurgia , Fixadores Internos , Adulto , Idoso , Fenômenos Biomecânicos , Feminino , Humanos , Vértebras Lombares/cirurgia , Masculino , Pessoa de Meia-Idade , Articulação Sacroilíaca/cirurgia , Sacro/cirurgia , Fusão Vertebral/métodos , Estresse Mecânico
7.
Spine (Phila Pa 1976) ; 35(15): E714-20, 2010 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-20535041

RESUMO

STUDY DESIGN: A prospective clinical trial was conducted. OBJECTIVE: To compare the clinical and radiologic late results of monosegmental transpedicular fixation versus short-segment pedicle instrumentation (SSPI) in management of thoracolumbar burst fractures and evaluate the efficacy of monosegmental transpedicular fixation. SUMMARY OF BACKGROUND DATA: SSPI (1 level above and 1 below the fracture level) are accepted by many surgeons as an accepted technique for the treatment of thoracolumbar burst fractures. To preserve more motion segments, some authors have advocated monosegmental pedicle instrumentation (MSPI). The recent developments showed that MSPI yielded good clinical results; however, there were no report about comparison of clinical outcome between monosegmental and biosegmental transpedicular fixation in management of thoracolumbar burst fractures. METHODS: Eighty-five patients with thoracolumbar burst fractures fulfilling the inclusion criteria were included in the study. The patients were randomized by a simple method into 2 groups. Group 1 were treated with monosegmental transpedicular fixation (n = 47), and group 2 were treated with biosegmental transpedicular fixation (n = 38). Clinical (Low Back Outcome Score and Oswestry Disability Index) and radiologic (load-sharing classification index, sagittal index, and percentage of anterior body height compression) outcomes were analyzed. RESULTS: The 2 groups were similar in age, follow-up period, and severity of the deformity and fracture. The postoperative and follow-up sagittal index, local kyphosis, percentage of anterior body height compression, and average correction loss in local kyphosis in both groups were not significantly different. The failure rate between the 2 surgical approaches was also not significantly different (group 1 = 6.38% and group 2 = 5.26%). Oswestry Disability Index improved in both groups by >25 points in a similar amount (P = 0.23). The average follow-up Low Back Outcome Score was 74.9 and 60.2 for group 1 and group 2, respectively (P = 0.033). CONCLUSION: In conclusion, radiologic parameters demonstrated that both MSPI and SSPI are the effective and reliable operative techniques for selected thoracolumbar burst fractures. MSPI shortened the operative time and decreased the amount of blood loss significantly and, thus, offered better clinical results. Nevertheless, long-term studies are supposed to be performed to support the outcomes.


Assuntos
Fixação Interna de Fraturas/métodos , Vértebras Lombares/cirurgia , Fraturas da Coluna Vertebral/cirurgia , Vértebras Torácicas/cirurgia , Adulto , Parafusos Ósseos , Avaliação da Deficiência , Feminino , Fixação Interna de Fraturas/instrumentação , Humanos , Dor Lombar/diagnóstico , Dor Lombar/etiologia , Vértebras Lombares/lesões , Masculino , Pessoa de Meia-Idade , Complicações Pós-Operatórias/diagnóstico , Complicações Pós-Operatórias/etiologia , Estudos Prospectivos , Reprodutibilidade dos Testes , Vértebras Torácicas/lesões , Resultado do Tratamento
8.
Eur Spine J ; 19(7): 1121-8, 2010 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-20195650

RESUMO

The development of iliac screws has provided a markedly easier way for spino-pelvic instrumentation than the classical Galveston technique. However, high rates of iliac screw loosening and breakage are usually reported, especially in cases where bilateral single iliac screws are used. Therefore, there is a need for exploring more stable iliac fixation techniques. Thus, the objective of this study was to compare the biomechanical effects of bilateral single and dual iliac screws on the stability of L3-iliac fixation construct under total sacrectomy condition. In this study, L2-pelvic specimens were harvested from seven fresh human cadavers. After biomechanically testing the intact state simulated by L3-L5 pedicle screw fixation, destabilization was introduced by total sacrectomy. Upon destabilization, L3-iliac screw-rod reconstructions were performed by four different techniques as follows: (1) bilateral single short iliac screws (Single-Short); (2) bilateral single long iliac screws (Single-Long); (3) bilateral dual short iliac screws, placed in the upper and lower iliac columns (Dual-UL); and (4) bilateral dual short iliac screws, all placed in the lower iliac column (Dual-Lower). These four iliac screw fixation techniques were sequentially preformed in the same specimen, and the lengths of the short and long iliac screws were 70 and 130 mm, respectively. Biomechanical testing was performed on a material testing machine under 800 N compression and 7 Nm torsion loading modes to evaluate the construct stiffness. In compression, the stiffness of the L3-iliac fixation constructs of Single-Short, Single-Long, Dual-UL, and Dual-Lower techniques were 73, 76, 98, and 108% of the intact state, respectively. No significant differences were detected between Single-Short and Single-Long (P = 0.589) techniques. However, the compressive stiffness of these two techniques was significantly lower than the intact state, and the Dual-UL and Dual-Lower techniques (P < 0.05). There was no statistical difference between the intact condition and the Dual-Lower technique (P = 0.109). Interestingly, Dual-Lower exhibited notably higher compressive stiffness than Dual-UL (+10.3%, P = 0.049). In torsion, the stiffness of Single-Short, Single-Long, Dual-UL, and Dual-Lower techniques were 72, 79, 105, and 109% of the intact condition, respectively. No significant differences were detected between Single-Short and Single-Long techniques (P = 0.338), and also among Dual-UL, Dual-lower techniques, and the intact state (P > 0.05). However, Single-Short and Single-Long techniques provided markedly lower construct torsional stiffness than the other three groups (P < 0.05). For lumbo-illiac reconstruction after total sacrectomy, even the use of bilateral single, long iliac screws do not help in restoring the local stability to the intact condition. However, dual iliac screws provide much higher construct stability than single iliac screw techniques. Therefore, dual iliac screw technique should be preferred for treating the unstable situation caused by total sacrectomy.


Assuntos
Fixação Interna de Fraturas/métodos , Ílio/cirurgia , Vértebras Lombares/cirurgia , Adulto , Idoso , Análise de Variância , Fenômenos Biomecânicos , Parafusos Ósseos , Feminino , Fixação Interna de Fraturas/instrumentação , Humanos , Fixadores Internos , Masculino , Pessoa de Meia-Idade
9.
Spine (Phila Pa 1976) ; 35(19): E925-31, 2010 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-20098349

RESUMO

STUDY DESIGN: An in vitro laboratory study. OBJECTIVE: (i) To evaluate the effect of osteoporotic degree in determining the strength of sacral screw fixation and (ii) to compare the strength of unaugmented bicortical pedicle screw and polymethylmethacrylate (PMMA) augmented unicortical pedicle screw in sacral fixation. SUMMARY OF BACKGROUND DATA: Screw loosening is a clinical problem in lumbosacral fusions, especially in osteoporotic patients. To improve the screw anchoring strength of sacrum, bicortical and PMMA augmented sacral pedicle screw fixation techniques are widely used in clinical practice. However, the biomechanical strength of the bicortical and PMMA augmented sacral screw fixations remains undetermined in different degrees of osteoporosis. METHODS: Twenty-five fresh osteoporotic cadavers were used in this study. According to the value of lumbar bone mineral density (BMD) assessed by DEXA, specimens were divided into 3 groups: group A (N=9): BMD=0.7 to 0.8 g/cm, group B (N=8): BMD=0.6 to 0.7 g/cm, and group C (N=8): BMD<0.6 g/cm. In each specimen, S1 pedicle screw was inserted bicortically on the left side, and S1 pedicle screw with PMMA augmentation was inserted unicortically on the right side of the sacrum. Following a dynamic cyclic loading from 30 to 250 N on the screw head for 2000 cycles, the subsidence displacement and axial pull-out strength of each screw were measured. RESULTS: No anchoring failure (defined as the subsidence displacement exceeding 2 mm within 2000 loading cycles) occurred in group A and B. However, in group C, 6 cases (75%) in bicortical fixation and 5 cases (63%) in PMMA augmented fixation failed during cyclic loading. In group A, no significant difference between the bicortical and PMMA augmented fixations was detected in terms of the subsidence and maximal pull-out strength. In group B, significantly less subsidence and higher maximal pull-out strength were demonstrated in the PMMA augmented technique than that in the bicortical fixation. Both techniques exhibited lower subsidence of the screw in group A than in group B. The bicortical technique exhibited higher maximum pull-out strength in group A than that in group B. However, statistical difference in terms of PMMA augmentation was not detected between group A and B. CONCLUSION: For BMD value more than 0.70 g/cm, bicortical sacral pedicle screw fixation could obtain sufficient anchoring strength comparable with the PMMA augmented technique. When BMD value is within 0.6 to 0.7 g/cm, the PMMA augmented technique would be more beneficial in improving the fixation strength than the bicortical fixation. For BMD values less than 0.6 g/cm, early screw loosening may occur in both bicortical and PMMA augmented fixations.


Assuntos
Cimentos para Ossos/uso terapêutico , Parafusos Ósseos , Vértebras Lombares/cirurgia , Osteoporose/complicações , Polimetil Metacrilato/uso terapêutico , Sacro/cirurgia , Fraturas da Coluna Vertebral/cirurgia , Fusão Vertebral/instrumentação , Absorciometria de Fóton , Idoso , Idoso de 80 Anos ou mais , Fenômenos Biomecânicos , Densidade Óssea , Cadáver , Análise de Falha de Equipamento , Humanos , Técnicas In Vitro , Vértebras Lombares/diagnóstico por imagem , Vértebras Lombares/lesões , Teste de Materiais , Pessoa de Meia-Idade , Osteoporose/diagnóstico por imagem , Desenho de Prótese , Falha de Prótese , Sacro/diagnóstico por imagem , Sacro/lesões , Índice de Gravidade de Doença , Fraturas da Coluna Vertebral/diagnóstico por imagem , Fraturas da Coluna Vertebral/etiologia , Estresse Mecânico
10.
J Spinal Disord Tech ; 23(6): 404-9, 2010 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-20087222

RESUMO

STUDY DESIGN: An in vitro biomechanical cadaver study. OBJECTIVES: To compare the subsidence displacement after cyclic loading among 4 sacral pedicle screw fixations of bicortical, tricortical, standard polymethylmethacrylate (PMMA) augmentation, and sub-endplate PMMA augmentation in osteoporotic condition. SUMMARY OF BACKGROUND DATA: Implant failure caused by screw loosening is a clinical problem for lumbosacral fusions, especially in osteoporotic patients. To improve sacral screw anchoring strength, the main fixation techniques need to be evaluated biomechanically. METHODS: For this study, 11 fresh osteoporotic cadaver sacra were harvested and bone mineral density was measured with dual-energy radiograph absorptiometry. A 7 mm diameter monoaxial pedicle screw (S1) was randomly assigned by side (left vs. right) and placed bicortically or tricortically. The 2 screws, followed 2000 cyclic compression loading of 30 to 250 N, were removed. The screw tracts were filled up with PMMA, then, screws 5 mm shorter than the bicortical or tricortical fixation were reinserted (defined as standard and sub-endplate PMMA augmented sacral screw fixations, respectively). The PMMA augmented screws were then retested as before. Screw subsidence displacement after 2000 cyclic loading was measured and compared. RESULTS: The average bone mineral density of 11 specimens was 0.71 g/cm, ranged from 0.65 to 0.78 g/cm. No significant difference of subsidence displacement was detected between tricortical and standard PMMA augmented screws (P>0.05), however, the 2 fixations exhibited markedly less subsidence than bicortical screw (P<0.05). Sub-endplate PMMA augmented screw showed the least subsidence among all the screws (P<0.05). CONCLUSIONS: PMMA augmentation can increase the bonding strength of sacral screw-bone interface and the sub-endplate PMMA augmented sacral screw could obtain the highest stability among the 4 fixation techniques in osteoporotic condition.


Assuntos
Osteoporose/cirurgia , Sacro/cirurgia , Fusão Vertebral/métodos , Idoso , Idoso de 80 Anos ou mais , Fenômenos Biomecânicos/fisiologia , Densidade Óssea/fisiologia , Parafusos Ósseos , Feminino , Humanos , Fixadores Internos , Modelos Lineares , Masculino , Pessoa de Meia-Idade , Osteoporose/fisiopatologia , Sacro/fisiopatologia , Fusão Vertebral/instrumentação , Suporte de Carga
11.
J Spinal Disord Tech ; 22(8): 545-50, 2009 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-19956027

RESUMO

STUDY DESIGN: Comparison of the biomechanical fixation strengths offered by 3 iliac screw fixation techniques: short screw, short screw augmented with cement, and long screw. OBJECTIVE: Evaluate the effect of screw length and bone cement augmentation on the fixation strength of iliac screw upon fatigue loading. SUMMARY OF BACKGROUND DATA: Iliac screws have been used in treating spinal disorders such as spinal deformity, spondylolisthesis, and sacral tumor. In clinical practices, both short screws and long screws are being used. It has been reported that short iliac screws have a higher rate of loosening. Therefore, short iliac screws are being used with bone cement augmentation to improve fixation. To date, no biomechanical study has compared the strengths of these 3 different iliac screw fixation techniques. METHOD: Fresh, frozen human cadaveric pelvis specimens (n = 18, 12 males, 6 females, average age 61 y) were used. Bone density was measured to characterize bone quality. The specimens were randomly divided into 2 groups. In group 1 (n = 8), short screws of 7.0-mm diameter and 70 + or - 4 mm length (as the length of exceeding over ischial notch) and long screw of 7.0-mm diameter and 120 + or - 4 mm length were placed on either side of the pelvis (left and right). In group 2 (n = 10), short iliac screws were placed after augmentation with polymethyl methacrylate bone cement on 1 side of the pelvis and long iliac screw were placed on the other side (left and right). Cyclic loading ranging from 20 to 200 N was applied to each screw at a frequency of 2 Hz up to 5000 cycles. Pullout tests were then conducted at the rate of 5 mm/min after the fatigue test, and the maximum pullout strength for each screw was recorded and analyzed. RESULTS: The maximum pullout strength of the long screw and short screw groups after fatigue conditioning were 2386 + or - 1470 and 833 + or - 681 N respectively. Significant difference was found between the 2 groups (P < 0.05). The short iliac screw had a higher loosening rate. The pullout force of the short screw fixation with augmentation and the long screw fixation after cyclic loading were 2436 + or - 915 and 2529 + or - 1055 N, respectively. No significant difference was found between the 2 groups (P > 0.05). CONCLUSIONS: Short iliac screws are susceptible to loosening after cyclic loading. Bone cement augmentation of short screws has demonstrated a significant increase in the fixation strength of short screws to an extent similar to that of long iliac screws. Thus, short iliac screw fixation after augmentation with bone cement will be a viable clinical option for spino-pelvic reconstruction.


Assuntos
Cimentos para Ossos/normas , Parafusos Ósseos/normas , Ílio/cirurgia , Complicações Pós-Operatórias/prevenção & controle , Fusão Vertebral/instrumentação , Fusão Vertebral/métodos , Fenômenos Biomecânicos/fisiologia , Cimentos para Ossos/uso terapêutico , Densidade Óssea/fisiologia , Cadáver , Falha de Equipamento , Análise de Falha de Equipamento/métodos , Feminino , Humanos , Ílio/anatomia & histologia , Ílio/fisiologia , Instabilidade Articular/cirurgia , Vértebras Lombares/cirurgia , Masculino , Pessoa de Meia-Idade , Polimetil Metacrilato/normas , Polimetil Metacrilato/uso terapêutico , Complicações Pós-Operatórias/etiologia , Complicações Pós-Operatórias/fisiopatologia , Procedimentos Cirúrgicos Reconstrutivos/instrumentação , Procedimentos Cirúrgicos Reconstrutivos/métodos , Curvaturas da Coluna Vertebral/cirurgia , Estresse Mecânico , Suporte de Carga/fisiologia
12.
Spine (Phila Pa 1976) ; 34(16): E565-72, 2009 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-19770599

RESUMO

STUDY DESIGN: Comparison of feasibility and safety of the placement of short and long iliac screws by anatomic and biomechanical evaluations as they apply to lumbo-iliac fixation construct. OBJECTIVE: To compare the stability of the short and long iliac screw fixations for lumbo-iliac reconstruction by anatomic and biomechanical evaluations. SUMMARY OF BACKGROUND DATA: Spinopelvic reconstruction remains a challenge to spine surgeons. Despite the advent of many fixation methods, the use of iliac screws seems most favorable so far. Various lengths of iliac screws are applied in surgical treatments; however, no biomechanical comparison has been reported based on the screw length. METHODS: For anatomic observation, CT scan data of 60 Chinese adults were used to measure the details of the iliac spine structures. For biomechanical evaluation, 7 adult human cadavers (L3-pelvis) were observed. L4-S1 pedicle screw fixation was performed with posterior spinal fixation system. On the basis of the lengths of iliac screws, 2 groups were tested (short screw group using 70 mm screws and long screw group using 138 mm screws). In this study, short and long iliac screws were placed in the same specimen. Biomechanical testing was performed on a material testing machine under 800 N compression and 7 Nm torsion loading modes for stiffness evaluations. Finally, pullout testing was performed for all the iliac screws to measure the maximum pullout force. RESULTS: The length of the line between posterior superior iliac spine and anterior inferior iliac spine was 140.6 +/- 1.1 mm, and the distance between this line and the greater sciatic notch was 18.3 +/- 0.8 mm. The length of the line between posterior superior iliac spine and the second narrowest point was 67.1 +/- 0.62 mm in men and 70.1 +/- 1.4 mm in women. Insertion lengths of the short and long iliac screws were 70 +/- 2 mm and 138 +/- 4 mm, respectively. The lumbo-pelvic reconstruction using short and long iliac screws restored 53.3% +/- 13.6% and 57.6% +/- 16.2% of the initial stiffness in compression testing respectively. In torsion testing, the use of short and long iliac screws harvested 55.1% +/- 11.9% and 62.5% +/- 9.2% of the initial stiffness, respectively. No significant difference was detected between the 2 reconstructions in terms of compressive and torsional stiffness (P > 0.05). However, the maximum pullout strength of long iliac screw group was significantly higher than the short screw group (P < 0.05). CONCLUSION: The local stability is rather difficult to be restored to the original levels regardless the length of iliac screws. Obviously, long iliac screws resisted significantly greater axial pullout force. However, under physiologic, torsional, and compressive loading conditions, the mechanical stability of lumbo-pelvic fixation construct with short iliac screws was comparable with that of the long ones. Therefore, the use of short iliac screws, which are only about half the length of the long iliac screws, could reduce the implantation risk without significantly compromising on the stability of the construct.


Assuntos
Parafusos Ósseos , Ílio/cirurgia , Vértebras Lombares/cirurgia , Fusão Vertebral/métodos , Adolescente , Adulto , Idoso , Fenômenos Biomecânicos , Cadáver , Estudos de Viabilidade , Feminino , Humanos , Ílio/diagnóstico por imagem , Ílio/fisiopatologia , Vértebras Lombares/diagnóstico por imagem , Vértebras Lombares/fisiopatologia , Masculino , Pessoa de Meia-Idade , Modelos Anatômicos , Fusão Vertebral/instrumentação , Tomografia Computadorizada por Raios X , Adulto Jovem
13.
Zhonghua Wai Ke Za Zhi ; 46(15): 1179-82, 2008 Aug 01.
Artigo em Chinês | MEDLINE | ID: mdl-19094686

RESUMO

OBJECTIVE: To biomechanically compare the stability of the short and long iliac screw fixation constructs in lumbo-iliac reconstruction. METHODS: Seven adult human embalmed cadavers (L(3)-pelvis) were used. Using posterior spinal fixation system, L(4)-S(1) pedicle screw fixation was performed. This was defined as intact state of the sacroiliac joint. After the intact test, total sacrum resection and L(4)-L(5)-pelvis reconstruction by pedicle screw and iliac screw with different lengths were performed as follow: short screw group (as the length of exceeding 2 mm over ischial notch) and long screw group (as the length of exceeding 2 mm over anterior inferior iliac spine). Using the 858 MTS material testing machine, biomechanical testing was performed under 800 N compression and 7 Nm torsion loading modes. At last, the axial pullout test of two iliac screws was executed. Construct stiffness in compression and torsion test, and maximum pullout force were analyzed. RESULTS: Insertion lengths of the short and long iliac screw were (70 +/- 2) mm and (138 +/- 4) mm respectively. The lumbo-pelvic reconstruction using short and long iliac screw, respectively restored 53.3% +/- 13.6% and 57.6% +/- 16.2% of the initial stiffness in compression testing, and respectively harvested 55.1% +/- 11.9% and 62.5% +/- 9.2% of the initial stiffness in torsion testing. No significant difference was detected between the two reconstructions (P > 0.05), however, the compressive and torsional stiffness of the two techniques were markedly less than the intact condition (P < 0.05). The maximum pullout strength of long iliac screw was significantly higher than short screw (P < 0.05). CONCLUSIONS: Under the physical loading, lumbo-pelvic fixation construct using the short iliac screw may obtain mechanical stability comparable to that by long iliac screw. The short iliac screw is only the half of the long iliac screw by length, could reduce the implantation risk. However, the long iliac screw behaves greater axial pullout force, should be applied as far as possible in the osteoporosis patient. The lumbo-pelvic reconstruction utilizing any length of iliac screw is difficult to restore the local stability.


Assuntos
Ílio/cirurgia , Vértebras Lombares/cirurgia , Ossos Pélvicos/cirurgia , Adulto , Idoso , Fenômenos Biomecânicos , Parafusos Ósseos , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Sacro/cirurgia , Fusão Vertebral/métodos
14.
Spine (Phila Pa 1976) ; 28(14): 1573-80, 2003 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-12865847

RESUMO

STUDY DESIGN: Pedicle screw fixation alone for sequential spinal instabilities was biomechanically compared with pedicle screw fixation using interbody cages. OBJECTIVE: To evaluate biomechanical effects of interbody cages on construct stiffness, pedicle-screw strain, and the adjacent level in posterior lumbar reconstruction using pedicle screw fixation. SUMMARY OF BACKGROUND DATA: It remains undetermined what types of spinal instability require interbody support in posterior lumbar reconstruction. METHODS: For this study, 10 calf spines (L3-L6) were used. Sequential destabilization was performed at L4-L5 followed by posterior reconstruction using pedicle screw fixation (PS) and interbody cages as follows: intact + PS (I-PS), medial facetectomy + PS (MF-PS), total facetectomy + PS (TF-PS), partial discectomy + PS (D-PS), and D-PS + interbody cages (PLIF). Biomechanical testing was performed under flexion and extension loading modes. Construct stiffness (L4-L5), rod-screw bending strain, and range of motion (ROM) at the upper adjacent level (L3-L4) were analyzed. RESULTS: In terms of construct stiffness (L4-L5), all the reconstructions except D-PS demonstrated higher construct stiffness than the intact spine (P < 0.05). The PLIF showed the highest stiffness among all the reconstructions (P < 0.05). In terms of ROM (L3-L4), all the reconstructions increased the ROM, as compared with the intact state (P < 0.05). Importantly, PLIF showed significantly greater ROM than all the other reconstructions except I-PS (P < 0.05). In terms of rod-screw strain, the D-PS resulted in higher strain than the other groups (P < 0.05). The PLIF presented less strain than the other reconstructions (P < 0.05). CONCLUSIONS: For spinal instability with preserved anterior load sharing, pedicle screw fixation alone is biomechanically adequate, and interbody cages should not be used because they further increase segmental motion at the adjacent segment. However, PS alone provides insufficient stability and high implant strain in case of damaged anterior column. In such cases, additional interbody cages significantly increase construct stiffness and decrease hardware strain. However, they increase ROM at the adjacent segment as well.


Assuntos
Parafusos Ósseos , Vértebras Lombares/cirurgia , Procedimentos Ortopédicos/métodos , Doenças da Coluna Vertebral/cirurgia , Animais , Fenômenos Biomecânicos , Parafusos Ósseos/normas , Bovinos , Técnicas In Vitro , Fixadores Internos , Vértebras Lombares/fisiopatologia , Movimento (Física) , Procedimentos Ortopédicos/instrumentação , Doenças da Coluna Vertebral/fisiopatologia
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