Straight-Forward versus Bicortical Fixation Penetrating Endplate in Lumbosacral Fixation-A Biomechanical Study

OBJECTIVE: Many lumbosacral fixation techniques have been described to offer a more screw-bone purchase. The forward anatomical fixation parallel to the endplate is still the most preferred method. Literature revealed little knowledge regarding the mechanical stability of lumbosacral trans-endplate fixation compared to the traditional trans-pedicular screw fixation method. The aim of this study is to assess the pull-out strength of lumbosacral screws penetrating the end plate and comparing it to the conventional trans-pedicular screw insertion method.METHODS: Eight lumbar and eight sacral vertebrae, with average age 69.4 years, Left pedicles of the 5th lumbar vertebrae were used for trans-endplate screw fixation, group 1A, right pedicles were used for anatomical trans-pedicular screw fixation, group 1B. In the sacral vertebrae, the right side S1 pedicles were used for trans-endplate fixation, group 2A, left side pedicles were used for anatomical trans-pedicular screw fixation, group 2B. The biomechanical tests were performed using the axial compression testing machine. All tests were applied using 2 mm/min traction speed.RESULTS: The average pull-out strength values of groups 1A and 1B were 403.78±11.71 N and 306.26±17.55 N, respectively. A statistical significance was detected with p=0.012. The average pull-out strength values of groups 2A and 2B were 388.73±17.03 N and 299.84±17.52 N, respectively. A statistical significance was detected with p=0.012.CONCLUSION: The trans-endplate lumbosacral fixation method is a trustable fixation method with a stronger screw-bone purchase and offer a good alternative for surgeons specially in patients with osteoporosis.

Straight-Forward versus Bicortical Fixation Penetrating Endplate in Lumbosacral Fixation-A Biomechanical Study

OBJECTIVE: Many lumbosacral fixation techniques have been described to offer a more screw-bone purchase. The forward anatomical fixation parallel to the endplate is still the most preferred method. Literature revealed little knowledge regarding the mechanical stability of lumbosacral trans-endplate fixation compared to the traditional trans-pedicular screw fixation method. The aim of this study is to assess the pull-out strength of lumbosacral screws penetrating the end plate and comparing it to the conventional trans-pedicular screw insertion method. METHODS: Eight lumbar and eight sacral vertebrae, with average age 69.4 years, Left pedicles of the 5th lumbar vertebrae were used for trans-endplate screw fixation, group 1A, right pedicles were used for anatomical trans-pedicular screw fixation, group 1B. In the sacral vertebrae, the right side S1 pedicles were used for trans-endplate fixation, group 2A, left side pedicles were used for anatomical trans-pedicular screw fixation, group 2B. The biomechanical tests were performed using the axial compression testing machine. All tests were applied using 2 mm/min traction speed. RESULTS: The average pull-out strength values of groups 1A and 1B were 403.78±11.71 N and 306.26±17.55 N, respectively. A statistical significance was detected with p=0.012. The average pull-out strength values of groups 2A and 2B were 388.73±17.03 N and 299.84±17.52 N, respectively. A statistical significance was detected with p=0.012. CONCLUSION: The trans-endplate lumbosacral fixation method is a trustable fixation method with a stronger screw-bone purchase and offer a good alternative for surgeons specially in patients with osteoporosis.

Ideal Insertion Point and Angle of Cervical Pedicular Screws in Korean

STUDY DESIGN: A retrospective study. OBJECTIVES: Using computed tomography, it is to measure pedicle size of lower cervical spine in Koreas to find ideal insertion point and angle in fixating pedicular screws. SUMMARY OF LITERATURE REVIEW: Although techniques in pedicular screw fixation and pedicle's anatomical shape in foreign populations have been well documented and studied, no anatomical study on lower cervical pedicle in Korean population has been reported. MATERIALS AND METHODS: A total of 180 patients with computed tomography taken at our institution were selected for the study. Width, total length, and length of pedicle, insertion point and angle, and safe insertion angles were measured on axial view. On sagittal view, height of pedicle, insertion point and angle, and safe insertion angles were determined. RESULTS: Mean height of study subject was 164.2cm. Mean width of pedicle was 5.5mm, mean height 7.2mm, mean total length 31.2mm, and mean length 14.8mm. Mean insertion point from 3rd to 7th cervical spines was medially 3.3mm from lateral mass and downward 4.7mm from margin of upper facet. Mean insertion angles from 3rd to 7th cervical spines were 41.6degrees axially and 6.4degrees sagittally. Calculated safe insertion angles were 8degrees on medial and lateral sides and 14degrees on superior and inferior sides. CONCLUSIONS: Using computed tomography images, ideal insertion point and angle were measured for pedicular screw insertion, but, due to individual variation, preoperative measurement of insertion point and angle on computed tomography is necessary.

Efficiency of Implant Removal for Treatment of the Thoraco-lumbar Unstable Fractures: Multi Segments Fixation, Single Segment Fusion

STUDY DESIGN: A retrospective study. OBJECTIVES: To evaluate the safety and usefulness of implant removal based on fusion by radiological change analyses and non-fused segment motion angle after open reduction, multi-segment fixation, and single segment fusion. SUMMARY OF LITERATURE REVIEW: There have been reports that discuss possible fracture of fixator, loss of reduction, or failure of fixation in certain cases of single segment fixation consistent with thoracolumbar fracture. MATERIALS AND METHODS: We analyzed 83 patients who had undergone treatment by fixation of the top 2 segments and the bottom segment. The posterolateral fusions were performed for the top segment for thoracolumbar fractures. The mean follow-up was 21.3 months. Wedge and local kyphotic angles, anterior, and posterior heights of the vertebral body were measured on plain radiograph. The range of motion of each segment was recorded by flexion-extension lateral radiographs at 6 month after the removal of implants. RESULTS: Radiologic assessments performed on 83 patients demonstrated preoperative mean wedge angle, kyphotic angle, mean anterior body height of 20.1degrees, 18.5degrees and 62.0%, respectively, and, postoperatively, these were corrected by 9.0degrees, 9.3degrees and 24.6%, respectively. In the 44 cases that had the implants removed, the correction losses were 0.4degrees(P=0.258) and 3.7degrees(P=0.000), 0.5%(P=0.756), and at the last follow-up, compared to measurements prior to the removal. There was no statistical significance in wedge angle or anterior body height. The range of motion measured on the non-fused segment was 3.9degrees on average at 6-months after the hardware removal. CONCLUSIONS: The multi-segments fixation and single-segment fusion for the thoracolumbar fracture can preserve correction and the motion of non-fusion segment. Although the implant removal after union can sustain motion, further studies regarding degenerative change of the non-fused segment are necessary.

Avaliação clínica da estabilização dinâmica com dispositivo Dynesis em pacientes com dor lombar com seguimento mínimo de seis meses / Evaluation of clinical results of dynamic stabilization with the Dynesis dispositive in patients with lumbar pain with a 6 months minimum follow up

Objetivo: Avaliar o resultado clínico da estabilização dinâmica com o dispositivo Dynesis em pacientes com dor lombar e alteração degenerativa do disco intervertebral. Método: Os autores avaliaram 24 pacientes, com idade média de 43,2anos (26 a 57 anos) com queixa de dor lombar com no mínimo seis meses de tratamento conservador sem melhora e ressonância magnética com alteração degenerativa discal avaliado pela classificação de Pffirmann e preservação da altura do disco de pelo menos 40% na radiografia no plano sagital. Foi realizada a fixação com parafuso dinâmico (Dynesis). A avaliação foi realizada por meio da escala visual análoga para dor. Resultado: A escala visual análoga da dor pré-operatoriamente obteve média de 7,4 pontos e após seis meses caiu para 2,9 pontos de média. Conclusão: Neste estudo concluímos que há uma melhora da dor lombar após estabilização dinâmica com dispositivo Dynesis.

The Change of Adjacent Segment and Sagittal Balance after Thoracolumbar Spine Surgery

OBJECTIVE: To characterize perioperative biomechanical changes after thoracic spine surgery. METHODS: Fifty-eight patients underwent spinal instrumented fusions and simple laminectomies on the thoracolumbar spine from April 2003 to October 2008. Patients were allocated to three groups; namely, the laminectomy without fusion group (group I, n = 17), the thoracolumbar fusion group (group II, n = 27), and the thoracic spine fusion group (group III, n = 14). Sagittal (ADS) and coronal (ADC) angles for adjacent segments were measured from two disc spaces above lesions at the upper margins, to two disc spaces below lesions at the lower margins. Sagittal (TLS) and coronal (TLC) angles of the thoracolumbar junction were measured from the lower margin of the 11th thoracic vertebra body to the upper margin of the 2nd lumbar vertebra body on plane radiographs. Adjacent segment disc heights and disc signal changes were determined using simple spinal examinations and by magnetic resonance imaging. Clinical outcome indices were determined using a visual analog scale. RESULTS: The three groups demonstrated statistically significant differences in terms of angle changes by ANOVA (p < 0.05). All angles in group I showed significantly smaller angles changes than in groups II and III by Turkey's multiple comparison analysis. Coronal Cobb's angles of the thoracolumbar spine (TLC) were not significantly different in the three groups. CONCLUSION: Postoperative sagittal balance is expected to change in the adjacent and thoracolumbar areas after thoracic spine fusion. However, its prevalence seems to be higher when the thoracolumbar spine is included in instrumented fusion.

Biomechanics study on pull-out strength of thoracic extrapedicular screw / 吉林大学学报(医学版)

0.05).)Conclusion The extra-pedicular technique is feasible in biomechanics.

Effect of Insertion Status of a Pedicular Screw on its Mechanical Properties using the Finite Element Method / 대한정형외과학회잡지

PURPOSE: The structural performance of a fixation system was investigated in the case of screw insertion into the pedicular canal with or without its threads fastened in the cortex and in the broken pedicle. MATERIALS AND METHODS: The symmetric geometric model was used for the pull-out test, and the simplified 3-dimensional model at 3 level, namely, the 3rd, 4th and 5th lumbar vertebrae, was used for the axial compressive loading test. RESULTS: According to the result of the axial-loading test, bending moments and Von-Mises stresses were increased at the junction between the head and the 2nd and 3rd pitches of the lumbar pedicle screw and at the center of 4th lumbar vertebral body, in the models of intact, posterior elements removed and unstable fractured spines. As the results of flexibility, there is no difference in intra-cortical insertion compared to intra-medullary pedicle insertion in the intact spine model. However, flexibility of the laminectomy model was 8% better that of the intra-cortical insertion, and the unstable fracture model 2% better. CONCLUSION: There is no difference in the flexibility of intra-cortical and intra-medullary pedicle screw insertion. The stability of the posterior structure is more important than anterior pedicle screw fixation.

Direct Repair of Pars Defects in Symptomatic Lumbar Spondylolysis Using Pedicle Screws and Universal Hooks : Preliminary Report

OBJECTIVE: The authors introduce a technique of direct repair of pars defects in symptomatic lumbar spondylolysis using pedicle screws and universal hooks. METHODS: From March 2001 to September 2001, six patients with symptomatic lumbar spondylolysis and positive pars injection test underwent this procedure. Patients with lumbar instability and discogenic pain were excluded. After posterior midline incision, clearing of fibrous, cartilaginous and sclerotic tissues in and around the defects of pars was done until healthy bone was exposed. Strips of cancellous bone were taken from adjacent laminae and packed into the defects of pars. After insertion of the pedicle screws, universal hooks were placed in the lower margin of the lamina of the involved vertebra. With gentle compression between the head of screw and universal hook, the nut was fixed. Same procedures were done on the contralateral side. RESULTS: Postoperatively, all six patients experienced clinical improvement and there was no complication related with operation. CONCLUSION: This new technique is considered useful for direct repair of the defects in symptomatic lumbar spondylolysis without significant injury in the normal structures.

Deep Wound Infection after Lumbar Spine Fusion with Pedicular Screw Fixation / 대한척추외과학회지

STUDY DESIGN: Retrospective. OBJECTIVE: To define the preoperative risk factors for postoperative deep wound infection of instrumented spine and to analyze treatment modality and its result. SUMMARY OF LITERATURE REVIEW: When there have been postoperative deep wound infection after pedicular screw fixation of lumbar spine. there have been controversies, which was appropriate time of implants removal. MATERIALS AND METHODS: From January 1991 to December 1997, we performed 582 cases of posterior instrumentation using pedicular screws. We reviewed retrospectively seven cases who had suffered from postoperative wound infection in our hospital, and three referral cases from other hospitals. RESULTS: Six of ten cases have been exposed significant preoperative risk factors(i. e., diabetes, old age, malnutrition, concomitant infection, obesity, etc.). Infections was diagnosed at an average of 12.3 days after operation with fever & wound drainage as the most common presenting feature. Patients underwent prompt incision & drainage, susceptible antibiotics, multiple debride-ments(average: 1.77, range: 1-3). Seven of ten cases underwent removal of implant finally. At follow up evaluation, all cases except one had no recurrence of infection. But five cases showed pseudarthrosis. Four (80%) of them underwent removal of implant within 1 year after operation. Clinical results by criteria of Kirkaldy-Willis were 2 Good's, 7 Fair's and 1 Poor. CONCLUSION: Postoperative deep wound infection after pedicular screw fixation of lumbar spine leads to poor result. Especially early removal of implant within 1 year after operation was followed by pseudarthosis.

Additional Posterior Lumbar Interbody Fusion using Threaded Cage in Spondylolisthesis with Instability / 대한척추외과학회지

STUDY DESIGN: We studied retrospectively the comparison of the clinical and radiologic results of surgical treatment between additional posterior lumbar interbody fusion group and posterolateral fusion with transpedicular screw fixation alone group for spondylolisthesis with segmental instability. OBJECTIVES: To evaluate the efficacy of additional PLIF group using threaded cage in surgical treatment of spondylolisthesis with instability. SUMMARY OF LITERATURE REVIEW: The interbody gap produced by operative reduction of spondylolisthesis is potential risk factors for redisplacement, implant failure and pseudarthrosis. There have been many reports regarding surgical treatment of spondy-lolisthesis for preventing postoperative redisplacement or complication. However, there have been controversies, which was most effective procedure for maintenance of surgical correction of spondylolisthesis. MATERIAL AND METHOD: A fourteen patients with spondylolisthesis who underwent PLIF using threaded cage in addition to PLF from August 1998 to June 1999(Group A) were compared to twenty-one patients who underwent PLF alone from January 1993 to May 1995(Group B). We assessed the radiologic results of slip reduction(SR), sagittal angle correction(SAC) and disc height restoration(DHR) on preoperative, postoperative and last follow-up lumbar sagittal view and clinical outcomes according to Kirkaldy-Willis criteria. RESULTS: The Group A / Group B showed postoperative mean SR 13.2%/9.9%, SAC 3.7 degrees /2.3 degrees and DHR 24.1%/6.3%. At last follow up, the Group A / Group B showed mean SR loss 1.0/7.3%, SAC loss 1.2 degrees /5.4 degrees and DHR loss 1.5%/11% respectively. The clinical results were analyzed as 100%/81%(Group A/B) of excellent to good results. CONCLUSIONS: Additional posterior lumbar interbody fusion with threaded cage was more effective in reduction & maintenance of reduction and showed better clinical results than posterolateral fusion in spondylolisthesis with instability.

Surgical Management of Patients with Isthmic Spondylolisthesis with Transpedicular Screw Fixation and Posterior Lumbar Interbody Fusion using Posterior Movable Segment

Twenty three patients with isthmic spondylolisthesis were operated on from December 1993 to June 1995. There were 14 female and 9 male patients and the average age of the patients was 50(ranging 20-67) years old. Symptoms in the lower extremities had been present for 3 months to 10 years, although varying degrees of back pain had existed for longer periods. Disability was caused mainly by claudication in 20 patients. Diagnostic studies included plain films, tomography, CT scaning, and MRI. Single interspace was involved in 18 patients, and in five patients, two interspaces were involved. After wide decompression and discectomy, stabilization was reestablished by segmental pedicular screw fixation device(Diapason(R) pedicular system) and interbody fusion using posterior movable segment as graft material. Between 6 to 24 months postoperatively, all patients exhibited radiographic fusion. The results were excellent in 12 cases, good in 8 cases and fair in 3 cases. The authors believe that full four nerve roots decompression, pedicular screw fixation. Posterior lumbar interbody fusion using movable segment as graft material, and prevention of nerve root traction injury during insertion of graft bone are important points to get good post-operative results.

A Biomechanical Study on the Fixational Strength of the Trans-pedicular Screw: In vitro measurement / 대한정형외과학회잡지

With porcine vertebrae, the static and dynamic holding power of the pedicle screws under various conditions were measured to understand the biomechanical nature of the transpedicular screw fixation in spine. The objectives of the present study were; (1) to find the correlation between the insertion depth of the screw and the resulting holding power, (2) to determine the effect of bone cement augmentation on the screw fixation in a loosened hole, and (3) to assess the load-sharing mechanism between the cortical and the cancellous one surrounding the screw in this fixational system. The geomorphological characteristics of each porcine vertebra was measured directly with a micro-caliper. The bone mineral density of the specimens was also measured. Material with screw was holded in the fixed cross head of material testing system(Autograph E-10T). Testing force was applied and graph was obtained in the chart record. The results of the static pull-out tests in this study showed that there was a statistically-significant positive correlation between the screw diameter and the pull-out resistance(p < 0.05). The strength of the fixation did not actually increase as much as the insertion depth of the screw increased in these tests(r=0.457). In low-cycle fatigue tests, the increased number of cycles was required to clinical failure in the deeper-inserted crews. Considering the mechanical failure, a statistically-significant positive correlation between the failure cycle and the insertion depth was observed in both deep and shallow insertion groups(p < 0.05). Nonpressurized PMMA augmentation appeared to restore the ability of the screws to withstand pullout loading of the original value. On the effect of the cortical and cancellous bone, the most important factor was the cortical bone of the entrance near the screw.

Surgical Management of Spinal Stenosis with Degenerative Lumbar Scoliosis / 대한정형외과학회잡지

The coexistence of spinal stenosis and scoliosis in lumbar spines is becoming a more frequent problem in elderly persons. Decreased bone mass in most of these patients also complicates their management. Recently, the pedicle screw instrumentation systems offer the way to solve these difficult problems. Most of the cases with degenerative scoliosis itself don't require surgical intervention. However, the case with severe clinical manifestations need surgery. From Jan. 1988 to Oct. 1993, authors had treated operatively for 15 cases of spinal stenosis with degenerative lumbar scoliosis. After adequate posterior decompression, pedicular instrumentation was carried out and correction of scoliotic deformity was attempted. Cotrel-Dubousset instrumentation was used in six patients, Graf instrumentation in three patients, and combined(Steffee and Graf) instrumentation in six patients. Follow up was obtained at an average of 20.4 months(Range; 10

Rate of Pedicle Disruption after Screw Fixation / 대한정형외과학회잡지

Postoperative CT scans for accuracy of pedicular screw placement were assessed in 20 patients (82 pedicular screws) treated with several kinds of pedicular screws. When putting screws, the position of the guide pin was confirmed by the image intensifier. The measurement of canal encroachment from the medial border of the pedicle and the angle of insertion through the body of each vertebra were assessed; 1. Fifty-five(69.1%) were placed within the pedicle. 2. Ten(12.2%) were placed within 2mm of the medial border of the pedicle. 3. Three(3.6%) had 2mm to 6mm canal encroachment with the patient developing neurologic complication that was improved 8 months after the operation. 4.Fourteen(17.1%) perforated the lateral border of the pedicle, but they were not associated with neurologic complication. 5. The screws placed within 2mm of the medial border of the pedicle had higher angle of insertion than the screws exactly within the pedicle. Even with the use of image intensifier, there was a high rate of pedicle disruption. We have to insert the screws more exactly according to true anatomic angle of the pedicle on each level of every vertebra from the entry point avoiding high angle of insertion to prevent any disruption of the medial border of the pedicle which may result in neurologic complication.

CT and MRI Compatibility of Titanium Pedicular Screw System(DipasonTM)

After spinal fixation using conventional stainless steel screw fixation system, postoperative evaluation of spinal canal and identification of screw positions are very difficult because of severe image halation on computerized tomography(CT) or magnetic resonance imaging(MRI). As a result, diagnosis is interfered in cases of screw malposition, infection, and when demonstration of spinal decompression is needed. For this reason, titanium implants have been developed. Titanium is neither magnetic nor paramagnetic, so it produces minimal artifacts on CT or MRI. Titanium pedicular screw system(DipasonTM) is one of these instruments. In this study, the authors investigated the compatibility of this instrument with CT and MRI postoperatively. The use of titanium pedicular screw system permits high quality image of spinal cord, nerve root and screws on CT and MRI.