Complications with the variable spinal plating system

Spinal Pedicle Morphometry using Multidetector CT—An experience from the Indian Subcontinent

Introduction For safe pedicle screws placement, knowledge of pedicle morphometry is essential, because an inconsistency between pedicle width and the screw diameter may lead to severe complications like nerve, vessel or visceral injuries.

Objectives To study the spinal pedicle width and height of lumbar spine, using multidetector CT (MDCT), among the Indian population.  To study the spinal pedicle angulation of lumbar spine, using MDCT, among the Indian population.

Method The study was conducted at a tertiary care multispecialty hospital. In the present study, a total of 321 patients were included, who underwent MDCT scan without contrast at our institution, over a period of 2 years, from May 2017 to May 2019. The study population (n = 321) was divided into different subgroups on the basis of the age. The data was taken from the workstation. Comparison was made separately between each subgroup.

Results In our subset of population, the 10 to 90 years age group, pedicle dimensions are as follow: The pedicle diameter from L1 to L5 is 4.46 to 11.92 mm. The pedicle height from L1 to L5 is 7.38 to 11.01 mm. The pedicle axial angulation from L1 to L5 is 22.27 to 36.08 degree. The pedicle lateral angulation from L1 to L5 is 16.12 to 22.47 degree.

Conclusion Knowledge of the pedicle morphometry (pedicle width, height and angulation) of lumbar spine will help the neurosurgeons standardize the size of pedicle screws which is required for spinal fixation surgery at various lumbar vertebra levels.

Superiority of Multidetector Computed Tomography With 3-Dimensional Volume Rendering Over Plain Radiography in the Assessment of Spinal Surgical Instrumentation Complications in Patients With Cancer

OBJECTIVE

The objective of this study was to compare multidetector computed tomography (MDCT) images with volume-rendered translucent display (VRTLD) series to plain radiographs for evaluating spinal surgical instrumentation after resection and reconstruction for spinal malignancies.

METHODS

In 44 patients with tumor resection and spinal reconstruction, 17 with complications, 3 neuroradiologists evaluated plain radiographs, MDCT images alone, VRTLD images alone, and MDCT images with VRTLD images for identifying complications in 3 categories: subsidence/migration, construct fracture, and screw loosening. Each category was scored as 1 (complications), 2 (no complications), or 3 (not sure), and the minimum score was used for analyses. Clinical/surgical outcomes were the reference standard.

RESULTS

Sensitivity, specificity, and accuracy (95% confidence interval), respectively, were as follows: MDCT/VRTLD, 100%, 100%, 100% (91.96%-100.00%); MDCT alone, 88.24%, 100%, 95.45% (84.53%-99.44%); VRTLD alone, 82.35%, 96.3%, 90.91% (78.33%-97.47%); plain radiographs, 52.94%, 100%, 81.82% (67.29%-91.81%).

CONCLUSIONS

Multidetector computed tomography with VRTLD series seems best for evaluation of spinal instrumentation after tumor resection and reconstruction.

Long-term outcomes of long level posterolateral fusion in lumbar degenerative disease: comparison of long level fusion versus short level fusion: a case control study

Background

We sought to evaluate the long-term outcomes of long-level instrumented posterolateral fusion (PLF) directly compared to those with short level instrumented PLF for degenerative spinal stenosis.

Methods

From 1987–2002, patients who underwent instrumented PLF with wide decompression for degenerative spinal stenosis were reviewed. A total of 295 patients were available for follow-up over 10 years (mean, 14 years). These patients were divided into Group 1 (fusion of 1 or 2 levels) and Group 2 (fusion of three or more levels). Clinical and radiological outcomes were evaluated.

Results

On clinical outcomes, Group 1 showed better results than Group 2 based on the Katz’s Activities Daily Living index (p = 0.024), Kirkaldy-Willis criteria (p = 0.001) and the Korean version of the Oswestry disability index (p = 0.01). However, excellent and good outcome was noted in more than 64.5 % in Group 2. For radiological outcomes, overall fusion rate was higher in Group 1 compared with Group 2, but not significantly different (p = 0.35). However, the metal problems and surgical complications were more developed in Group 2 (p < 0.001). Although the radiologic changes on adjacent segments increased in accordance with the follow-up period, particularly in Group 2 (p < 0.001), no correlation with clinical symptoms was found.

Conclusions

The long-level fusion group maintained acceptable clinical and radiological outcomes compared to the short-level fusion group at minimum of 10 years of follow-up.

Electrical stimulation threshold in chronically compressed lumbar nerve roots: Observational study

OBJECTIVES

Intraoperative neuromonitoring (IONM) is a common practice in spinal surgery, mostly during pedicle screw placement. However, there is not enough information about the factors that can interfere with IONM data. One of these factors may be existing damage of the nerve root whose function must be preserved. The main purpose of the present study is to evaluate the effect of chronic compression in lumbar nerve roots in terms of stimulation thresholds during direct nerve stimulation.

PATIENTS AND METHODS

Direct electrical stimulation was performed in 201 lumbar nerve roots during lumbar spinal procedures under general anaesthesia in 80 patients with different lumbar spinal pathologies. Clinical and radiological data were reviewed in order to establish the presence of chronic compression.

RESULTS

Chronically compressed nerve roots showed a higher stimulation threshold than non compressed nerve roots (11.93 mA vs. 4.33 mA). This difference was confirmed with intra-subject comparison (paired sample t test, p=0.012). No other clinical factors were associated with this higher stimulation threshold in lumbar nerve roots.

CONCLUSION

A higher stimulation threshold is present in compressed lumbar nerve roots than non compressed roots. This needs to be taken into consideration during pedicle screw placement, where intraoperative neurophysiological monitoring is being used.

Novel pedicle screw and plate system provides superior stability in unilateral fixation for minimally invasive transforaminal lumbar interbody fusion: an in vitro biomechanical study

Purpose

This study aims to compare the biomechanical properties of the novel pedicle screw and plate system with the traditional rod system in asymmetrical posterior stabilization for minimally invasive transforaminal lumbar interbody fusion (MI-TLIF). We compared the immediate stabilizing effects of fusion segment and the strain distribution on the vertebral body.

Methods

Seven fresh calf lumbar spines (L3-L6) were tested. Flexion/extension, lateral bending, and axial rotation were induced by pure moments of ± 5.0 Nm and the range of motion (ROM) was recorded. Strain gauges were instrumented at L4 and L5 vertebral body to record the strain distribution under flexion and lateral bending (LB). After intact kinematic analysis, a right sided TLIF was performed at L4-L5. Then each specimen was tested for the following constructs: unilateral pedicle screw and rod (UR); unilateral pedicle screw and plate (UP); UR and transfacet pedicle screw (TFS); UP and TFS; UP and UR.

Results

All instrumented constructs significantly reduced ROM in all motion compared with the intact specimen, except the UR construct in axial rotation. Unilateral fixation (UR or UP) reduced ROM less compared with the bilateral fixation (UP/UR+TFS, UP+UR). The plate system resulted in more reduction in ROM compared with the rod system, especially in axial rotation. UP construct provided more stability in axial rotation compared with UR construct. The strain distribution on the left and right side of L4 vertebral body was significantly different from UR and UR+TFS construct under flexion motion. The strain distribution on L4 vertebral body was significantly influenced by different fixation constructs.

Conclusions

The novel plate could provide sufficient segmental stability in axial rotation. The UR construct exhibits weak stability and asymmetrical strain distribution in fusion segment, while the UP construct is a good alternative choice for unilateral posterior fixation of MI-TLIF.

CT-Guided Transfacet Pedicle Screw Fixation in Facet Joint Syndrome: A Novel Approach

Axial microinstability secondary to disc degeneration and consequent chronic facet joint syndrome (CFJS) is a well-known pathological entity, usually responsible for low back pain (LBP). Although posterior lumbar fixation (PIF) has been widely used for lumbar spine instability and LBP, complications related to wrong screw introduction, perineural scars and extensive muscle dissection leading to muscle dysfunction have been described. Radiofrequency ablation (RFA) of facet joints zygapophyseal nerves conventionally used for pain treatment fails in approximately 21% of patients. We investigated a "covert-surgery" minimal invasive technique to treat local spinal instability and LBP, using a novel fully CT-guided approach in patients with axial instability complicated by CFJS resistant to radioablation, by introducing direct fully or partially threaded transfacet screws (transfacet fixation - TFF), to acquire solid arthrodesis, reducing instability and LBP. The CT-guided procedure was well tolerated by all patients in simple analogue sedation, and mean operative time was approximately 45 minutes. All eight patients treated underwent clinical and CT study follow-up at two months, revealing LBP disappearance in six patients, and a significant reduction of lumbar pain in two. In conclusion, CT-guided TFF is a fast and safe technique when facet posterior fixation is needed.

Intraoperative 3-dimensional imaging (O-arm) for assessment of pedicle screw position: Does it prevent unacceptable screw placement?

Background

Pedicle screws are biomechanically superior over other spinal fixation devices. When improperly positioned, they lose this advantage and put adjacent structures at risk. Accurate placement is therefore critical. Postoperative computed tomography (CT) scans are the imaging gold standard and have shown malposition rates ranging from 2% to 41%. The O-arm (Medtronic Navigation, Louisville, Colorado) is an intraoperative CT scanner that may allow intervention for malpositioned screws while patients are still in the operating room. However, this has not yet been shown in clinical studies. The primary objective of this study was to assess the usefulness of the O-arm for evaluating pedicle screw position by answering the following question: What is the rate of intraoperative pedicle screw revision brought about by O-arm imaging information? A secondary question was also addressed: What is the rate of unacceptable thoracic and lumbar pedicle screw placement as assessed by intraoperative O-arm imaging?

Methods

This is a case series of consecutive patients who have undergone spine surgery for which an intraoperative 3-dimensional (3D) CT scan was used to assess pedicle screw position. The study comprised 602 pedicle screws (235 thoracic and 367 lumbar/sacral) placed in 76 patients, and intraoperative 3D (O-arm) imaging was obtained to assess screw position. Action taken at the time of surgery based on imaging information was noted. An independent review of all scans was also conducted, and all screws were graded as either optimal (no breach), acceptable (breach ≤2 mm), or unacceptable (breach >2 mm). The rate of pedicle screw revision, as detected by intraoperative 3D CT scan, was determined.

Results

On the basis of 3D imaging information, 17 of 602 screws (2.8%) in 14 of 76 cases (18.4%) were revised at the time of surgery. On independent review of multiplanar images, 11 screws (1.8%) were found to be unacceptable, 32 (5.3%) were acceptable, and 559 (92.9%) were optimal. All unacceptable screws were revised to an optimal or acceptable position, and an additional 6 acceptable screws were revised to an optimal position. Thus, by the end of the cases, none of the 602 pedicle screws in the 76 surgical procedures was in an unacceptable position.

Conclusion

The new-generation intraoperative 3D imaging system (O-arm) is a useful tool that allows more accurate assessment of pedicle screw position than plain radiographs or fluoroscopy alone. It prompted intraoperative repositioning of 2.8% of pedicle screws in our series. Most importantly, it allowed identification and revision of all unacceptably placed pedicle screws without the need for reoperation.

The seasonality of postoperative infection in spine surgery

OBJECT

Studies from many disciplines have found an association with the summer months, elevated temperature, humidity, and an increased rate of infection. The "July effect," a hypothesis that the inexperience of new house staff at the beginning of an academic year leads to an increase in wound complications, has also been considered. Finally, an increase in trauma-related admissions in the summer months is likely to result in an increased incidence of postoperative infections. Two previous studies revealed mixed results concerning perioperative spinal wound infections in the summer months. The purpose of this study was to determine the months and/or seasons of the year that display significant fluctuation of postoperative infection rate in spine surgery. Based on the idea that infection rates are susceptible to seasonal factors, the authors hypothesized that spinal infections would increase during the summer months.

METHODS

Inclusion criteria were all spine surgery cases at a single tertiary referral institution between January 2005 and December 2009; 8122 cases were included. Patients presenting with a contaminated wound or active infection were excluded. Infection rates were calculated on a monthly and seasonal basis and compared.

RESULTS

A statistically significant increase in the infection rate was present on both a seasonal and monthly basis (p = 0.03 and p = 0.024) when looking at the seasonal change from spring to summer. A significant decrease in the infection rate was seen on a seasonal basis during the change from fall to winter (p = 0.04). The seasonal rate of infection was highest in the summer (4.1%) and decreased to the lowest point in the spring (2.8%) (p = 0.03).

CONCLUSIONS

At the authors' institution, spine surgeries performed during the summer and fall months were associated with a significantly higher incidence of wound infection compared with the winter and spring. These data support the existence of a seasonal effect on perioperative spinal infection rates, which may be explained by seasonal variation in weather patterns and house staff experience, among other factors.

Is surgical case order associated with increased infection rate after spine surgery?

STUDY DESIGN

Retrospective database review.

OBJECTIVE

To determine whether surgical site infections are associated with case order in spinal surgery.

SUMMARY OF BACKGROUND DATA

Postoperative wound infection is the most common complication after spinal surgery, with incidence varying from 0.5% to 20%. The addition of instrumentation, use of preoperative prophylactic antibiotics, length of procedure, and intraoperative blood loss have all been found to influence infection rate. No previous study has attempted to correlate case order with infection risk after surgery.

METHODS

A total of 6666 spine surgery cases occurring between January 2005 and December 2009 were studied. Subjects were classified into 2 categories: fusion and decompression. Case order was determined, with each procedure labeled 1 to 5 depending on the number of previous cases in the room. Variables such as the American Society of Anesthesiologists score, number of operative levels, wound class, age, sex, and length of surgery were also tracked. A step-down binary regression was used to analyze each variable as a potential risk factor for infection.

RESULTS

Decompression cases had a 2.4% incidence of infection. Longer surgical time and higher case order were found to be significant risk factors for lumbar decompressions. Fusion cases had a 3.5% incidence of infection. Posterior approach and revision cases were significant risk factors for infection in cervical cases. For lumbar fusion cases, longer surgical time, higher American Society of Anesthesiologists score, and older age were all significant risk factors for infection.

CONCLUSION

Decompressive procedures performed later in the day carry a higher risk for postoperative infection. No similar trend was shown for fusion procedures. Our results identify potential modifiable risk factors contributing to infection rates in spinal procedures. Specific risk factors, although not defined in this study, might be related to contamination of the operating room, cross-contamination between health care providers during the course of the day, use of flash sterilization, and mid-day shift changes.

SOFT STABILIZATION OF THE LUMBAR SPINE USING THE GRAF SYSTEM FOR SPINAL INSTABILITY SYNDROMES AND PSEUDOARTHROSIS — 5 YEARS' RESULTS

There is considerable controversy in the diagnosis and management of lumbar spinal instability. Most clinicians agree that patients suffering from the chronic low back syndrome who have suspected instability and have not responded to conservative measures, should be considered for operative treatment with stabilization using rigid or semi-rigid systems to reduce or eliminate movement at the painful segment.

The concept of soft stabilization was introduced by Henri Graf in 1988 and has become a routine procedure in various centres throughout the world for stabilization for clinical instability syndromes.

The Graf system was introduced into Western Australia in October, 1991. The aim of this paper is to report the independently reviewed retrospective results of the first 25 patients with respect to clinical outcome and radiological features.

The clinical outcomes were consistent with other reported treatment measures for the chronic low back pain syndrome. The radiological results do not show any evidence of implant loosening or breakage.

Perioperative surgical complications of transforaminal lumbar interbody fusion: a single-center experience

OBJECT

Since its original description in 1982, transforaminal lumbar interbody fusion (TLIF) has grown in popularity as a means for achieving circumferential fusion. The authors sought to define the perioperative complication rates of the TLIF procedure at a large academic medical center.

METHODS

For all eligible patients from a consecutive series of 531 TLIF procedures, the institution's complication database and the medical record were reviewed to identify complications. Medical, nonprocedure-related complications such as myocardial infarction and pulmonary embolism were excluded due to inconsistency in the recording of these complications in the database. Rates were calculated for each type of complication, and subgroup analysis was performed to investigate the effect of previous lumbar surgery, and of multilevel versus single-level interbody fusion on complication rates. Odds ratios were calculated and evaluated using chi-square analysis.

RESULTS

Five hundred thirty-one patients underwent a TLIF procedure during the study period. Two hundred forty-four patients (46%) had undergone a previous lumbar operation. Interbody fusion was performed at 1 level in 317 patients, at 2 levels in 188 patients, at 3 levels in 24 patients, and at 4 levels in 2 patients. One hundred thirty-five patients (25.4%) had at least one procedure-related complication. The most common complications were durotomy (14.3% of patients) and infection (3.8% of patients). Symptomatic screw misplacement (2.1% of patients) and interbody cage migration (1.8% of patients) were less common complications. The overall complication rate was greater in those patients who had undergone a previous operation (OR 1.75, 95% CI 1.18-2.59; p < 0.01) and in those who had multilevel surgery (OR 1.54, 95 % CI 1.04-2.28; p = 0.03), and the incidence of durotomy was higher in patients who had a previous operation (OR 1.75, 95% CI 1.07-2.87; p = 0.03). These differences were statistically significant. Durotomy also occurred more frequently in patients who had multilevel interbody fusion (OR 1.49, 95% CI 0.92-2.43; p = 0.13). A trend toward higher infection rates in those patients who underwent multilevel interbody fusion was observed (OR 1.5, 95% CI 0.62-3.68; p = 0.49), but this was not statistically significant. Infection rates did not differ between revision and first-time surgeries.

CONCLUSIONS

Transforaminal lumbar interbody fusion has gained widespread popularity as a procedure for achieving arthrodesis in the lumbar spine. Complications occurred more often in patients undergoing revision surgery or multilevel interbody fusion. Durotomy and infection were the most common complications in this series.

Infections in the operated spine: update on risk management and therapeutic strategies

Among the possible risks of spine surgery, surgical site infection (SSI) is far from negligible. Incidence is higher than in other locomotor system procedures, with more severe local and general impact. Certain broad guidelines can be formulated. The risk of SSI should be taken into account in the choice of treatment options discussed with the patient. Antibiotic prophylaxis, surgical prevention of iatrogenic infection and an SSI surveillance protocol should be implemented. SSI should be suspected in case of any abnormality in postoperative course, and biological and imaging (MRI or CT) measures should be taken. Local sampling for bacteriological identification is mandatory. Treatment strategy should ideally be discussed in a multidisciplinary coordination meeting, and adapted in the light of local bacterial ecology and resistance data. The information provided to the patient should be transparent and adapted to the patient's individual context.

LEVEL OF EVIDENCE

Level V.

Co-registration of Sequential Multidetector Computed Tomography Studies for the Evaluation of Surgical Instrumentation following Resection of Spinal Tumors

Surgical resection of spinal tumors involves complex reconstructive procedures. The stability and integrity of the surgical construct are evaluated with multidetector computed tomography (MDCT). As coregistration, or fusion, of different imaging modalities, especially positron emission tomography/computed tomography (PET/CT), is common practice, we sought to determine if this technique could be applied to sequential, postoperative MDCT studies of the spine. Herein, we demonstrate that by utilizing the Hermes workstation, co-registration of MDCT spine studies can be performed. This technique allows sequential MDCT examinations of the post-operative spine to be viewed together as one study and may aid in evaluation of the position and integrity of the surgical construct over time. Further study and refinement of this technique will be necessary before clinical implementation.

In vivo three-dimensional morphometric analysis of the lumbar pedicle isthmus

STUDY DESIGN

In vivo noninvasive study.

OBJECTIVE

To properly quantify pedicle anatomic parameters, using subject-based CT three-dimensional models and compare the data from 2-dimensional transverse-CT images.

SUMMARY OF BACKGROUND DATA

Accurate measurement of morphometric parameters of pedicle isthmus is important for transpedicular procedures. Anatomically, the lumbar pedicle is known to be elliptical cross-sectionally and slightly inclined in the vertical plane in the lower lumbar levels. Therefore, measurement of the pedicle isthmus may be overestimated when transverse images are used. More accurate measurement of the 3-dimensional geometry of the pedicle is therefore needed. To the best of our knowledge, 3-dimensional geometry of the pedicle has not been reported as the literature values are based on 2-dimensional image data.

METHODS

In vivo measurements of the lumbar pedicle isthmus were performed on the 3-dimensional subject-based CT models, using custom-developed software in 89 volunteers.

RESULTS

The least axis of pedicle, the longest axis of pedicle and the transverse plane width were largest at L5 in both genders. The isthmus angle declined in the lower levels. The ratio of the transverse plane width to the least axis of pedicle was largest at L5.

CONCLUSION

Our results showed that the least axis of pedicle, the longest axis of pedicle and the transverse plane width peaked at L5, and the transverse plane width became approximately twice as long in the lower levels compared to the upper levels. The ratio of the transverse plane width to the least axis of pedicle increased by about 40% at L5. These findings highlight the fact that measuring the isthmus width from CT transverse images leads to overestimation, especially in the lower lumbar spine. Therefore, a 3-dimensional inclination of the least axis of the pedicle should be taken into account for the determination of the pedicle diameter in the lower lumbar vertebrae.

Biomechanical rigidity of an all-polyetheretherketone anterior thoracolumbar spinal reconstruction construct: an in vitro corpectomy model

BACKGROUND CONTEXT

Polyetheretherketone (PEEK) is gaining favor as a spinal implant material for interbody and corpectomy cages as well as stabilizing rods. However, there has been little correlation to a relevant and reproducible clinical model. Biomechanical data on PEEK rod constructs have not been reported.

PURPOSE

To quantify the stabilizing effects of PEEK versus titanium (Ti) instrumentation in a thoracolumbar corpectomy model.

STUDY DESIGN

Corpectomy and randomized instrumentation with an all-Ti, all-PEEK, and hybrid cage/rod construct were performed on cadaveric spines to assess biomechanical differences.

METHODS

Pure unconstrained bending moments were applied to the intact spine and subsequent test constructs in the three physiologic planes using a load control protocol. Motion tracking and analysis were carried out to quantify and compare the range of motion (ROM) between different test constructs in each plane.

RESULTS

Flexion ROM did not show significant changes compared with intact, whereas the all-Ti and hybrid construct reduced ROM significantly in extension. Lateral bending was significantly reduced in all the treatment groups. Rotational stability of the construct was significantly compromised by an all-PEEK spinal construct.

CONCLUSION

The rigidity of the corpectomy construct increased as the amount of Ti in the construct increased. A hybrid construct incorporating a PEEK corpectomy cage and Ti rods may provide adequate stability for an anterior thoracolumbar reconstruction in the sagittal and coronal planes. An all-PEEK construct may provide adequate stability in the coronal and sagittal planes but may compromise the stability significantly in axial rotation. Consideration should be given for supplemental posterior instrumentation if an all-PEEK construct is used in an anterior thoracolumbar spinal reconstruction procedure.

Is aggressive surgery necessary for acute postoperative deep spinal wound infection?

STUDY DESIGN

A retrospective study of the clinical results of conservative treatment of patients with acute postoperative deep spinal infection.

OBJECTIVE

To determine the efficacy of antibiotic only treatment of postoperative deep spinal infection.

SUMMARY OF BACKGROUND DATA

Traditionally, aggressive surgical treatment combined with antibiotics has been viewed as the gold standard for treating postoperative deep spinal infection. There are, however, disadvantages to surgical treatment including higher treatment cost, multiple anesthesia and surgeries, and the risk of perioperative morbidity and mortality particularly in immunocompromised patients. Although many new antibiotics and new methods of antibiotic treatment have recently become available, the role of conservative treatment using antibiotics alone to treat postoperative acute infection has not yet been determined.

METHODS

Ten consecutive patients with acute postoperative spinal infection were treated using antibiotics alone. The mean onset of the symptoms of infection after surgery was 15.4 days (range, 5-18 days). Seven patients had purulent wound drainage; 3 had healed wounds without discharge. Bacterial culture of the discharge showed methicillin-resistant Staphylococcus aureus (1 patient), methicillin-resistant coagulase negative Staphylococcus (4 patients), methicillin-sensitive coagulase negative Staphylococcus (1 patient). One patient had a negative culture. Patients with wound drainage were treated with intravenous vancomycin or teicoplamin for 4 to 6 weeks followed by oral antibiotics (quinolone with/without rifampin) for 1 to 3 months. All other patients were treated with oral antibiotics for 3 months.

RESULTS

One patient could not complete treatment because of allergy to antibiotics. Infection was controlled in the remaining patients without surgical intervention and did not reoccur. All wound drainage ceased within 2 weeks. The C-reactive protein level of most patients returned to normal range within 10 weeks.

CONCLUSION

Antibiotic treatment alone may be effective in the treatment of acute postoperative spinal infection when diagnosis is prompt. Aggressive surgery may be not necessary and may be reserved for patients who fail conservative treatment.

Pedicle and spinal canal parameters of the lower thoracic and lumbar vertebrae in the achondroplast population

STUDY DESIGN

Retrospective morphometric population study.

OBJECTIVE

To characterize pedicle and spinal canal morphology of the achondroplastic lower thoracic and lumbar vertebrae and to suggest dimensions for improving pedicle screw selection and placement.

SUMMARY OF BACKGROUND DATA

Although morphometric population studies exist for various races, to our knowledge, no such analysis has been made in achondroplastic patients.

METHODS

With computer software, we measured pedicle parameters on the computed tomography images of 19 adult achondroplastic patients.

RESULTS

Pedicle and chord lengths ranged from 9.5-12.5 mm and 29.5-36.4 mm, respectively. Transverse pedicle diameter increased from T9 (5.5 mm) to L5 (14.2 mm). Sagittal pedicle diameter declined from L1 (11.6 mm) to L5 (7.8 mm). Transverse angulation was greatest at L5 (15.7 degrees ) and smallest at T12 (1.1 degrees ). Pedicles were directed cranially at all levels, ranging from 3.8 degrees -15.6 degrees . Interpedicular distance and cross-sectional area were smallest at L4 (14.9 mm and 119 mm, respectively). Pedicle starting points diverged from T9 (13.6 mm) to L5 (19.2 mm2).

CONCLUSION

Achondroplastic pedicle morphology differs markedly from those of the normal spine: chord lengths are substantially shorter, pedicles are inclined cranially, pedicle starting points diverge progressively in the lumbar spine, and pedicle shape transitions from vertically to horizontally oriented ellipsoids along the lumbar spine. Consideration of this variation could maximize the effectiveness and safety of pedicle instrumentation.

Stepwise Methodology for Plain Radiographic Assessment of Pedicle Screw Placement: A Comparison With Computed Tomography

OBJECTIVE

The objective of this study is to evaluate the effectiveness of a specific methodology for plain radiographic assessment of lumbar pedicle screw position.

PURPOSE

To evaluate the effectiveness of using orthogonal plain radiographs and a systematic method of interpretation, developed by the senior author, in assessing the placement of lumbar and lumbosacral pedicle screws.

STUDY DESIGN

This was an adult cadaver study of the accuracy of using plain radiographs or computed tomography to assess pedicle screw position. Plain radiographs were performed and compared with computed tomography (CT) scans. Gross anatomic dissections were performed to directly confirm screw position. Variables, including screw material, radiographic view, and screw dimensions, were assessed for their effect on the ability of physicians to determine pedicle screw position. Multiple readers were included in the study, including 1 spine Fellow, 3 experienced orthopedic spine surgeons, and 1 neuroradiologist.

METHODS

Five adult cadaveric spines were instrumented with titanium pedicle screws from L1 to S1. Screws were placed outside the confines of the pedicle in all 4 quadrants or within the pedicle using a Latin-Square design. Each cadaver was imaged with orthogonal radiographs and high-resolution CT scans. The spines were then reimaged after the instrumentation was replaced with stainless steel screws placed in the identical position. Finally, each spine was dissected to assess the exact position of the screws. Images were read in a blinded fashion by 1 spine fellow, 2 staff surgeons, and a staff radiologist. The results were compared with the known screw positions at dissection.

RESULTS

In total, 120 pedicle screws were placed, 44 (38%) outside the confines of the pedicle. Sensitivity, defined as the percent of the misplaced screws that were correctly identified, was similar across the 3 diagnostic tests, but markedly improved when all CT formats were considered together. Similarly, specificity, defined as the percent of screws correctly read as being placed within the pedicle, was independent of radiographic examination. Sensitivity of the radiographic technique was 70.1% and specificity was 83.0%, whereas sensitivity for CT scans was 84.7% and specificity was 89.7%. There was an observed association with anatomic level, with a consistently less accuracy in detecting screw position at L1 with plain x-ray (P=0.001). Additionally, correct position of stainless steel screws was more difficult to detect as compared with titanium (P=0.033) using either x-rays or CT. Other variables examined, such as screw length and screw diameter, did not have an effect on the ability to read the positioning.

CONCLUSIONS

CT scans, often considered the "gold standard" for clinical assessment of pedicle screw placement, have limitations when validated with gross anatomical dissection. The described systematic method for evaluating pedicle screw placement using orthogonal plain radiographs attained accuracy comparable to high-resolution CT scans.

Is High Level of Disability an Indication for Spinal Fusion?

OBJECTIVE

Posterior lumbar interbody fusion is a recognized procedure for the treatment of back pain associated with degenerative disc disease and segmental instability. It allows decompression of the spinal canal and circumferential fusion through a single posterior incision.

METHODS

Sixty-five consecutive patients who underwent posterior lumbar interbody fusion using carbon cages and pedicle fixation between 1993 and 2000 were recruited and contacted with a postal survey. Clinical outcome was assessed by the postoperative clinical findings and complications and the fusion rate, which was assessed using the scoring system described by Brantigan and Steffee. Functional outcome was measured by using improvement in the Oswestry Disability Index, return to work, and satisfaction with the surgical outcome. The determinants of functional relief were analyzed against the improvement in disability using multiple regression analysis.

RESULTS

The mean postoperative duration at the time of the study was 4.4 years. Overall radiologic fusion rate was 98%. There was a significant improvement in Oswestry Disability Index (P < 0.01). There was 84% satisfaction with the surgical procedure and 61% return to predisease activity level and full employment. We found preoperative level of disability to be the best determinant of functional recovery irrespective of age or the degree of psychological morbidity and litigation (P < 0.01).

CONCLUSION

The combination of posterior lumbar interbody fusion and posterior instrumented fusion is a safe and effective method of achieving circumferential segmental fusion. A direct relationship between preoperative level of disability and functional recovery suggests that disability should be measured preoperatively and spinal fusion should be performed to alleviate disability caused by degenerative spine.

Correction of adolescent idiopathic scoliosis using thoracic pedicle screw fixation versus hook constructs

This retrospective study was undertaken to determine the effectiveness and cost of thoracic pedicle screws versus laminar and pedicle hooks in patients undergoing surgical correction of adolescent idiopathic scoliosis (AIS). Immediate preoperative and 6-week postoperative radiographs were examined in 25 consecutive cases of children with AIS who were divided into two groups, those with thoracic pedicle screw constructs and those with thoracic hook constructs. Endpoints collected included radiographic measures, complications, surgical time, implant cost, and quality-of-life measures. Ten children underwent spinal fusion using thoracic pedicle screw fixation and 15 underwent thoracic constructs composed of hooks. Similar sex and age distribution were noted in both groups, and among the 20 girls and 5 boys the average age was 14.5. The mean preoperative Cobb angle was 53.5 degrees for the screw group and 52.5 degrees for the hook group. Correction averaged 70.2% for the screw group and 68.1% for the hook group. There were no significant differences between the two patient groups in terms of percentage of or absolute curve change after surgery. The apical vertebral translation, end vertebral tilt angle, and coronal balance did not differ significantly between the two patient groups. Comparison of operative time and quality of life revealed no significant differences. Screw constructs were significantly more expensive than hook constructs. The correction obtained from thoracic pedicle screw fixation is comparable to traditional hook constructs in AIS. Surgery using either construct effectively corrects AIS.

Surgical treatment for the painful motion segment: matching technology with the indications: posterior lumbar fusion

STUDY DESIGN

A convenience literature-based review of the different techniques of posterior lumbar fusion.

OBJECTIVE

To describe the history, specific techniques, and outcomes of different methods of posterior lumbar fusion. The specific methods that were described include 1) uninstrumented posterior, posterolateral, and facet fusion, and 2) instrumented fusion using pedicle screws or facet screws.

SUMMARY OF BACKGROUND DATA

There are various posterior fusion techniques available for the treatment of degenerative lumbar spine conditions. Each individual technique has specific technical demands, indications, advantages, and disadvantages which should be taken into consideration when performing these procedures.

METHODS

The published scientific literature on the different methods of posterior lumbar fusion was reviewed. The history, indications, advantages, disadvantages, and clinical and radiographic outcomes were described based on the literature search.

RESULTS/CONCLUSIONS

Posterior fusion techniques have been and will continue to be among the most commonly performed procedures in lumbar spine surgery. The different methods of fusion are well defined, as are the possible complications and outcomes. They are effective techniques when performed on appropriately selected patients by a surgeon knowledgeable in the techniques and indications. Further studies are needed regarding promising but relatively unproven developments such as minimally invasive surgery and the use of osteoinductive agents.

Clinical analysis of percutaneous facet screw fixation after anterior lumbar interbody fusion

Object. The authors performed a retrospective study to evaluate the results of percutaneous facet screw fixation (PFSF) after anterior lumbar interbody fusion (ALIF) in comparison with the gold standard, post-ALIF pedicle screw fixation (PSF).

Methods. Of 84 patients treated for degenerative spondylolisthesis or degenerative disc disease at the authors' institution, 44 underwent PFSF (Group 1) and 40 underwent PSF (Group 2 [control population]) after ALIF. Function was assessed using the Oswestry Disability Index (ODI) scoring system, and outcome was measured using the Macnab criteria. At 3, 6, 12, and 24 months after surgery, dynamic lateral (flexion—extension) radiography and computerized tomography scanning were conducted to evaluate the osseous union status. After a minimum follow-up period of 2 years, analysis showed no intergroup statistical difference in terms of ODI score and Macnab outcome criteria (p > 0.05).

Excellent or good outcome was obtained in 40 (90.9%) of the 44 patients in Group 1 and 37 (92.5%) of the 40 patients in the control Group 2 (p > 0.05). No patient required a blood transfusion in either group. At 24 months after surgery fusion rates were 95.8% in Group 1 and 97.5% in Group 2.

Conclusions. The results of PFSF following ALIF appear to be clinically equivalent to those achieved after PSF, and the procedure represents a safe and minimally invasive modality with which to achieve solid fusion in the lumbar spine.

Surgical management of lumbar stenosis: decompression and indications for fusion

Review of the clinical, neuroradiological, and surgical management of lumbar spinal stenosis reveals that 90 to 95% of congenital or acquired variants may be adequately managed by means of decompression without fusion. These decompressive procedures often simultaneously treat disc herniations, limbus fractures, degenerative spondylolisthesis, rare selected cases of spondylolisthesis accompanied by lysis in older patients, and degenerative scoliosis. Fusion should be reserved for the approximately 5 to 10% of patients in whom there is clinical evidence of instability prior to surgery or for the few who develop slippage following laminectomy and facetectomy.

A biomechanical comparison of facet screw fixation and pedicle screw fixation: effects of short-term and long-term repetitive cycling

STUDY DESIGN

A biomechanical study was conducted to assess the stabilization performance of transfacet pedicle screw fixation.

OBJECTIVE

To compare the biomechanical effects of short-term and long-term cyclic loading on lumbar motion segments instrumented with either a pedicle screw or a transfacet pedicle screw construct.

SUMMARY OF BACKGROUND DATA

Facet screw fixation is an alternative to pedicle screw fixation that permits the use of a minimally invasive strategy. It is not known whether facet screw fixation can provide stability equivalent to pedicle screw fixation during cyclical loading. Therefore, transfacet pedicle screw fixation and standard pedicle screw fixation techniques were compared biomechanically.

METHODS

Lumbar motion segments were tested under short-term and long-term cyclic loading conditions. For the short-term phase, specimens were tested intact for six cycles (to 400 N or 4 Nm) in compression, flexion, extension, lateral bending, and torsion. The specimens then were instrumented with bilateral semicircular interbody spacers and pedicle screw instrumentation or transfacet pedicle screws, and the testing sequence was repeated. For the long-term phase, 12 specimens were instrumented in a similar manner and loaded to 6 Nm of flexion bending for 180,000 cycles.

RESULTS

For the short-term phase, both fixation systems had significantly greater stiffness and reduced range of motion, as compared with the intact state. No differences were observed between the fixation systems except in flexion, wherein transfacet pedicle screw specimens were significantly stiffer than traditional pedicle screw specimens. For the long-term phase, the stiffness and range of motion did not significantly increase or decrease over repetitive cycling of the instrumented specimens. Furthermore, no significant difference between the fixation systems was observed.

CONCLUSIONS

The stability provided by both transfacet pedicle screw fixation and traditional pedicle screw fixation was not compromised after repetitive cycling. In this model, transfacet pedicle screw fixation appears equivalent biomechanically to traditional pedicle screw fixation.

Complications and problems related to pedicle screw fixation of the spine

This retrospective study analyzes the complications and the problems developed during and after pedicle screw fixation in patients with spinal disorders and trauma. One hundred twelve patients were treated using the Cotrel-Dubousset pedicle screw fixation system for degenerative disease (57 patients), trauma (42 patients), infection (eight patients), and tumor (five patients) of the lumbar or thoracolumbar spine. The average age of the patients was 47 years and the average followup was 35 months. Forty-seven general complications were seen in 41 patients (36.5%). In addition, hardware failures were observed in 12 patients (10.7%), junctional problems were seen in five patients (4.5%), problems in the instrumented segments were seen in 39 patients (34.7%), and problems of balance occurred in five patients (4.5%). Although the rate of the reported complications was high, the final outcome of the patients was not affected significantly. Placement of the pedicle screws in the thoracolumbar and lumbar spine is a technically demanding procedure. It should be used by experienced and qualified surgeons who are aware of the pitfalls associated with its use.

Measurements of the lumbar pedicles in the Eastern Anatolian population

Pedicle screw fixation of the spine has become one of the most stable and versatile methods of spine fixation, and knowledge of pedicle morphology is crucial for the safe application of these systems. We undertook this study because only a few reports have investigated Eastern populations. Lumbar pedicle anatomy, i.e., pedicle width (PW) and pedicle height (PH), transverse and sagittal pedicle angles (TPA, SPA), and pedicle length (PL), were assessed in the following two groups: (1) computed tomography scans of 29 normal adults, and (2) 16 dried lumbar spines obtained from the Anatomy Department. Interpedicular distance was different in each group. PW ranged from 4 mm to 14 mm. In both groups, the narrowest PH was 8.2 mm, the widest 19.7 mm. TPA ranged from 6(o) to 19(o) and increased from L1 to L5. In the sagittal plane, the pedicles angled caudally at L5. PL was longest at L1 and shortest at L5. In conclusion, pedicle dimensions and angles may show individual and structural differences. Our data were not significantly different from previous reported data. A detailed knowledge of these relationships is important for any surgery involving screw purchase via a pedicle, to prevent screw cutout and failure of fixation or neurological injury. Selection of the proper diameter of screw is an important issue for safe placement. Knowledge of the pedicle axis length is essential in choosing screw lengths but should always be checked intraoperatively with fluoroscopic control during screw insertion.

Spinal somatosensory evoked potential evaluation of acute nerve-root injury associated with pedicle-screw placement procedures: an experimental study

Pedicle screws for spinal fixation risk neural damage because of the proximity between screw and nerve root. We assessed whether spinal somatosensory evoked potential (SSEP) could selectively detect pedicle-screw-related acute isolated nerve injury. Because pedicle screws are too large for a rat's spine, we inserted a K-wire close to the pedicle in 32 rats, intending not to injure the nerve root in eight (controls), and to injure the L4 or L5 root in 24. We used sciatic-nerve-elicited SSEP pre- and postinsertion. Radiologic, histologic, and postmortem observations confirmed the level and degree of root injury. Sciatic (SFI), tibial (TFI), and peroneal function indices (PFI) were calculated and correlated with changes in potential. Although not specific for injuries to different roots, amplitude reduction immediately postinsertion was significant in the experimental groups. Animals with the offending wire left in place for one hour showed a further non-significant deterioration of amplitude. Electrophysiologic changes correlated with SFI and histologic findings in all groups. SSEP monitoring provided reliable, useful diagnostic and intraoperative information about the functional integrity of single nerve-root injury. These findings are clinically relevant to acute nerve-root injury and pedicle-screw insertion. If a nerve-root irritant remains in place, a considerable neurologic deficit will occur.

Radiologic evaluation of adjacent superior segment facet joint violation following transpedicular instrumentation of the lumbar spine

STUDY DESIGN

The location of pedicle screws in relation to adjacent superior segment facet joints in 106 patients after lumbar spinal fusion was assessed using computed tomography and plain radiographs.

OBJECTIVES

To document the incidence of adjacent superior segment facet joint violation following transpedicular instrumentation in the lumbar spine.

SUMMARY OF BACKGROUND DATA

Review of the literature failed to show any documented study examining this incidence.

METHODS

A total of 106 patients (212 top-level facet screws) undergoing lumbar spinal fusion surgery using transpedicular instrumentation between 1996 and 1999 were prospectively evaluated with a computed tomography scan and plain radiographs at 6 months following surgery. These were blindly and independently evaluated by a consultant radiologist and a spinal research fellow to document the incidence of superior segment facet joint violation. Calculation of the kappa coefficient and chi2 analysis were carried out.

RESULTS

The spinal research fellow noted the incidence of facet joint violation on the computed tomography scan to be present in 20% of the screws and 32% of the patients, whereas the consultant radiologist noted this to be the case in 23% and 35%, respectively. The kappa coefficient for computed tomography scan was 0.88, whereas for the plain radiographs it was 0.39. The incidence of facet joint violation was noted to be independent of the sex, level, and diagnosis. There was also an almost uniform incidence in each of the years from 1996 to 1999.

CONCLUSION

Facet joint violation occurred in just >30% of the patients and 20% of the screws in this study. This, therefore, raises the theoretical possibility of long-term deterioration in the clinical results following the use of transpedicular instrumentation.

Effect of spinal disease on successful arthrodesis in lumbar pedicle screw fixation

OBJECT

Pedicle screw fixation with transverse process fusion has gained widespread acceptance since its inception. Improved rates of arthrodesis have been demonstrated when this technique is used. The authors present one of the largest series of patients to undergo this procedure at a single center; one of the goals was to correlate construct length and spinal disease with rates of successful arthrodesis by conducting a prospective analysis of lumbar fusion in which pedicle screws were placed.

METHODS

During a 7-year period, the senior author performed pedicle screw fixation with posterolateral fusion in 457 patients; the mean follow-up period was 28.4 months. Indications for fusion included metastatic tumor, single-level degenerative disc disease (DDD), trauma, degenerative scoliosis, and translational vertebral instability. Successful fusion was based on the radiographic demonstration of a bilateral contiguous osseous bridge over the transverse processes and absence of movement on dynamic x-ray films. Fusion rates were lowest in cases of tumors (54%) and highest in cases of trauma (96%). In patients with single-level DDD the rate was 91%, and in those with translational instability it was 89%. Fusion rates, however, declined steeply in relation to each additional motion segment in the translational instability group. In this group a strong linear trend for proportion was demonstrated (p < 0.001). The overall fusion rate in patients with degenerative scoliosis was 70%. The overall fusion rate for the entire group was 86%.

CONCLUSIONS

The data in this study can be used as a benchmark with which to compare newer technologies. Although overall pedicle screw-assisted fusion rate in cases of trauma or selected degenerative lesions approached 90%, the arthrodesis rates are not uniform for the different diagnoses. This appears to be related to the underlying spinal disease and the number of segments included in the fusion.

Biomechanical analysis of biodegradable interbody fusion cages augmented With poly(propylene glycol-co-fumaric acid)

STUDY DESIGN

Three different types of biodegradable poly(L-lactide-co-D,L-lactide) cages with and without augmentation of a biodegradable poly(propylene glycol-cofumaric acid) scaffold were compared with autograft and metallic cages of the same design and size by determining the stiffness and failure load of the L4-L5 motion segment of cadaveric human spines.

OBJECTIVES

To determine how these devices limit the range of motion in the lumbar spine compared with a metallic cage. If biomechanically equivalent, biodegradable spinal fusion systems ultimately could reduce local stress shielding and diminish the incidence of clinical complications, including device-related osteopenia, implant loosening, and breakage.

SUMMARY OF BACKGROUND DATA

Previous studies in dogs and humans have demonstrated vertebral body osteopenia as a result of instrumented spine fusions. To the authors' knowledge, neither an in vitro nor an in vivo biomechanical analysis of a biodegradable interbody fusion system has been performed.

METHODS

Forty-eight L4-L5 motion segments were isolated from 22 male and 26 female human donors with an average age of 49.6 +/- 2.7 years (range 36-55 years). Cages of similar dimensions and design, including a threaded, hollow, porous titanium BAK cage and three different BIO cages (BIO cage 1, pure polymer; BIO cage 2, polymer plus hydroxyapatite buffer; BIO cage 3, polymer plus nano-sized hydroxyapatite), produced from the same poly(L-lactide-co-D,L-lactide) polymer were tested in a comparative analysis to intact motion segment, interbody implantation of autograft, and a BIO cage augmented with an expandable biodegradable foam-scaffold fashioned from poly(propylene glycol-cofumaric acid).

RESULTS

All cages were able to increase stiffness and failure load of the unstable motion segment significantly (P < 0.01). In comparison with the bone graft, the BAK cage (P < 0.01) and BIO cages 1 and 3 (P < 0.05) were able to increase stiffness and failure load. There was no significant difference between BIO cage 2 and the bone graft. Augmentation of BIO cage 1 with the foaming PPF scaffold resulted in higher stiffness and similar failure load as seen with the BAK cage.

CONCLUSION

By comparison, the in vitro lumbar spinal motion segment stiffness and failure load produced by implantation of a biodegradable interbody fusion cage augmented with an expandable PPF scaffold is similar to that of the titanium BAK cage. This suggests that biodegradable anterior interbody fusion systems could be further developed for clinical applications.

Pedicle screws with high electrical resistance: a potential source of error with stimulus-evoked EMG

STUDY DESIGN

Clinically relevant aspects of pedicle screws were subjected to electrical resistance testing.

OBJECTIVES

To catalog commonly used pedicle screws in terms of electrical resistance, and to determine whether polyaxial-type pedicle screws have the potential to create a high-resistance circuit during stimulus-evoked electromyographic testing.

SUMMARY OF BACKGROUND DATA

Although stimulus-evoked electromyography is commonly used to confirm the accuracy of pedicle screw placement, no studies have documented the electrical resistance of commonly used pedicle screws.

METHODS

Resistance measurements were obtained from eight pedicle screw varieties (5 screws of each type) across the screw shank and between the shank and regions of the screw that would be clinically accessible to stimulus-evoked electromyographic testing with a screw implanted in a pedicle. To determine measurement variability, resistance was measured three times at each site and with the crown of the polyaxial-type screw in three random positions.

RESULTS

Resistance across the screw shank ranged from 0 to 36.4 ohms, whereas resistance across the length of the monoaxial-type screws ranged from 0.1 to 31.8 ohms. Resistance between the hexagonal port and shank of polyaxial-type screws ranged from 0 to 25 ohms. In contrast, resistance between the mobile crown and shank of polyaxial-type screws varied widely, ranging from 0.1 ohms to an open circuit (no electrical conduction). Polyaxial-type screws demonstrated an open circuit in 28 of 75 measurements (37%) and a high-resistance circuit (exceeding 1000 ohms) in 5 of 75 measurements (7%).

CONCLUSIONS

Polyaxial-type pedicle screws have the potential for high electrical resistance between the mobile crown and shank, and therefore may fail to demonstrate an electromyographic response during stimulus-evoked electromyographic testing in the setting of a pedicle breech. To avoid false-negative stimulus-evoked electromyographic testing, the cathode stimulator probe should be applied to the hexagonal port or directly to the screw shank, and not to the mobile crown.

Moving toward a standard for spinal fusion outcomes assessment

Previous spinal fusion outcomes assessment studies have been complicated by inconsistencies in evaluative criteria and consequent variations in results. As a result, a general consensus is lacking on how to achieve comprehensive outcomes assessment for spinal fusion surgeries. The purpose of this article is to report the most validated and frequently used assessment measures to facilitate comparable outcomes studies in the future. Twenty-seven spinal fusion outcomes studies published between 1990 and 2000 were retrospectively reviewed. Study characteristics such as design, evaluative measures, and assessment tools were recorded and analyzed. Based on the reviewed literature, an outcomes assessment model is proposed including the Short Form-36 Health Survey, the Oswestry Disability Questionnaire, the North American Spine Society Patient Satisfaction Index, the Prolo Economic Scale, a 0-10 analog pain scale, medication use, radiographically assessed fusion status, and a generalized complication rate.

Treatment of idiopathic scoliosis with CD-instrumentation: lumbar pedicle screws versus laminar hooks in 66 patients

We studied whether the pedicle screw is better than laminar hooks for fixation of the lumbar spine in the treatment of idiopathic scoliosis. 66 consecutive patients with idiopathic scoliosis (King I and II) were studied retrospectively. Group S included 33 patients (25 females) treated with pedicle screws. Their mean age at operation was 17 (13-54) years. Group H included 33 patients (30 females) treated exclusively with hooks. Their mean age at operation was 16 (1140) years. The preoperative mean angles of the thoracic curve in group S was 66 (42.115) degrees, and in group H 65 (42-121) degrees. The lumbar curve averaged 46 (20-85) degrees in group H and 53 (33-86) degrees in group S. All patients were fused only posteriorly with Cotrel-Dubousset instrumentation and an autogenic bone graft. The mean follow-up time was 4 (2-7) years. Mean correction of the thoracic curve was 45% in group S and 50% in group H. The lumbar curve was corrected by 50% in group S and 51% in group H. Loss of correction of the thoracic curve occurred in 5% in group S and 6% in group H and of the lumbar curve in 3% in group S and 10% in group H (p = 0.04). Group S better maintained the correction of the lateral tilt of the uninstrumented segment adjacent to the fusion (p = 0.04). Derotation, according to Perdriolle, in the distal segment adjacent to the fusion was 6% in group S and 2% in group H. We found no difference between correction of the thoracic and lumbar curves using pedicle screws and laminar hooks in the lumbar spine. Pedicle screws better maintained the correction of the lumbar curve and the lateral tilt in the distal segment adjacent to fusion.

Anterior/posterior lumbar fusion versus transforaminal lumbar interbody fusion: analysis of complications and predictive factors

No previous study has compared the complications between anterior/posterior and transforaminal interbody fusions. We performed a retrospective analysis of 164 patients to compare the complications and associated predictive factors of the two techniques of circumferential lumbar fusion. Fifty-three had same-day anterior/posterior fusion (group 1), and 111 had transforaminal interbody fusion (group 2). Mean operating time (p < 0.0001) and hospital stay (p < 0.0001) was significantly longer for group 1 patients. Average blood loss was greater for group 1 patients (p < 0.01). Higher complication rates were found in group 1 patients (p < 0.004). Wound infection occurred more frequently in patients with adjunctive treatment (p < 0.04). Hospital stay was an independent predictor of complications in both groups. In group 1, body mass index was independently associated with complications. In group 2, both hospital stay and adjunctive treatment were predictive of complications. Transforaminal lumbar interbody fusion is the preferred technique because it is associated with shorter operating time, less blood loss, shorter hospital stay, and lower incidence of complications.

The use of evoked EMG in detecting misplaced thoracolumbar pedicle screws

STUDY DESIGN

Experimental study performed using an animal model.

OBJECTIVES

To determine if EMG responses generated by the electrical stimulation of thoracolumbar pedicle screws could be used to predict the screw position.

SUMMARY OF BACKGROUND DATA

Evoked EMG has been used successfully to predict pedicle screw position in the lumbar spine. No data have been published on its effectiveness in the thoracic spine.

METHODS

A total of 91 screws were inserted into the pedicles from T8 to L2 in six sheep. Monitoring electrodes were placed into transversus abdominus at three levels, the lower two intercostal spaces, and into psoas. A constant voltage stimulus was applied to a probe inserted into each pedicle, and then to each pedicle screw after it had replaced the probe. The threshold voltage required to evoke EMG activity in the relevant myotome was noted. After monitoring the position of each screw was determined by gross dissection.

RESULTS

EMG responses in abdominal and intercostal muscles were successfully evoked by thoracic pedicle screw stimulation. Of the 91 screws, 50 were within the pedicle and required an average voltage of 15.12 V to stimulate an EMG response, compared with the 41 misplaced screws that had an average voltage of 7.63 V (P < 0.0001). Using a threshold of 10 V the technique has a sensitivity of 94% and a specificity of 90%.

CONCLUSION

Electrical stimulation of pedicle screws and EMG recording in abdominal and leg muscles in sheep provide a reliable indication of pedicle screw position. This technique can be directly applied to human thoracolumbar surgery, but differences in pedicle size would mean that new threshold voltage criteria would need to be established.

Acute lower gastrointestinal bleeding as a late complication of spinal instrumentation

Posterior or anterior fusion with spinal instrumentation is a well-known operation for scoliosis. There are multiple potential complications; the most common are blood loss during the initial surgery and wound infection. Vascular injury has been reported. However, to the authors' knowledge, acute gastrointestinal bleeding has not been reported. The authors report on a child who presented 6 years after posterior spinal instrumentation with massive acute lower gastrointestinal bleeding resulting from internal iliac artery injury and bowel perforation. The etiology, diagnosis, and management of such bleeding is reviewed.

Can insertional torque predict screw loosening and related failures? An in vivo study of pedicle screw fixation augmenting posterior lumbar interbody fusion

STUDY DESIGN

An investigation of the relation between intraoperative insertional torque of pedicle screws, bone mineral density of the vertebra, and development of screw loosening in vivo.

OBJECTIVES

To determine the usefulness of intraoperative measurement of the insertional torque of pedicle screws.

SUMMARY OF BACKGROUND DATA

Some biomechanical studies have demonstrated that the insertional torque is highly correlated with bone mineral density and the stability of pedicle screws in vitro.

METHODS

Pedicle screw fixation was performed with posterior lumbar interbody fusion in 62 consecutive patients. The mean age of the patients at the time of surgery was 58 years. The insertional torque of pedicle screws was measured intraoperatively in all patients. The mean follow-up period was 2.7 years.

RESULTS

The mean insertional torque was 1.28 +/- 0.37 Nm in patients with screw loosening and 1.50 +/- 0. 40 Nm in patients without the problem. The mean insertional torque in patients with compression fractures in the upper vertebra adjacent to the fixed segment was 0.83 +/- 0.23 Nm. There was no significant difference between the mean insertional torque in patients with screw loosening and those without the condition. The mean insertional torque in patients without screw loosening was significantly greater than in patients with compression fractures (P < 0.01). A high correlation was found between insertional torque and bone mineral density (P < 0.01).

CONCLUSIONS

Although a high correlation was found between the insertional torque of pedicle screws and bone mineral density in vivo, the insertional torque could not objectively predict screw loosening.

The radiologic anatomy of the lumbar and lumbosacral pedicles

STUDY DESIGN

An anatomic and radiologic study of lumbar and lumbosacral pedicle anatomy.

OBJECTIVES

To define the radiologic anatomy of the lumbar and first sacral pedicle in the coaxial projection.

SUMMARY OF BACKGROUND DATA

Fluoroscopic assistance for pedicle screw placement requires radiologic landmarks. The radiologic landmarks have previously been assumed. Detailed study of the correlation between anatomy and radiology is required.

METHODS

Lumbar vertebrae and sacra were marked with radiopaque material to demonstrate the pedicle cortical borders. The vertebrae were then imaged in the coaxial projection to determine the correlation between the pedicle cortex and the radiologic image. Pedicle dimensions were recorded.

RESULTS

Pedicle dimensions were consistent with known measurements, yet the long axis of the L4 and L5 pedicle ellipse was oblique to the vertical. Consequently, the minor diameter of the pedicle ellipse was considerably less than the measured pedicle width at L5. The radiologic pedicle image was consistently within the true pedicle cortex, by up to 3 mm, and probably represents the inner cortical border of the pedicle. The S1 pedicle has reliable anatomic landmarks, yet only the medial and superior borders were visualized.

CONCLUSIONS

The radiologic pedicle image in the lumbar and lumbosacral spine is a reliable guide to the true bony cortex of the pedicle. At S1 the pedicle image is less well correlated with the cortical borders of the pedicle, yet other reliable anatomic landmarks exist.

Vascular complications in lumbar spinal surgery: percutaneous endovascular treatment

Four patients underwent endovascular treatment of vascular injuries complicating lumbar spinal surgery. In two patients with massive retroperitoneal hemorrhage, the extravasating lumbar arteries were successfully embolized with microcoils. Two patients with large iliac arteriovenous fistula (AVF) were treated, one with embolization using a detachable balloon and coils, which failed, and the other with placement of a stent graft after embolization of distal runoff vessels, which occluded the fistula. We conclude that acute arterial laceration or delayed AVF complicating lumbar spinal surgery can be managed effectively with selective embolization or stent-graft placement, respectively.

Complications associated with pedicle screws

BACKGROUND

The safety and the effectiveness of pedicle-screw instrumentation in the spine have been questioned despite its use worldwide to enhance stabilization of the spine. This review was performed to answer questions about the technique of insertion and the nature and etiology of complications directly attributable to the screws.

METHODS

We performed a retrospective review of all of the pedicle-screw procedures that were done by us from January 1, 1984, to December 31, 1993. We inserted 4790 screws during 915 operative procedures on 875 patients; 668 (76.3 percent) of the patients had a lumbosacral arthrodesis. The mean duration of follow-up was three years (range, two to five years). The accuracy of screw placement was assessed on intraoperative, immediate postoperative, and follow-up radiographs with use of a technique that was developed by one of us (F. D.); this technique has yet to be validated to determine the prevalence of various types of error.

RESULTS

Of the 4790 screws, 4548 (94.9 percent) had been inserted within the pedicle and the vertebral body. One hundred and thirty-four (2.8 percent) of the screws had perforated the anterior cortex, and this was the most common type of perforation. One hundred and fifteen (2.4 percent) of the screws were associated with complications that could be ascribed to the use of pedicle screws. The most common problem was late-onset discomfort or pain related to a pseudarthrosis or perhaps to the screws; this problem was associated with 1102 (23.0 percent) of the screws, used in 222 (24.3 percent) of the procedures. The symptoms necessitated removal of the instrumentation with or without repair of the pseudarthrosis. A pseudarthrosis was found during forty-six (20.7 percent) of the 222 procedures. Irritation of a nerve root occurred after nine procedures (1.0 percent) and was caused by eleven screws (0.2 percent); it was more commonly caused by medially placed screws. Three patients had residual neurological weakness despite removal of the screws. Twenty-five screws (0.5 percent), used in twenty procedures (2.2 percent), broke. The screws that broke were of an early design. A pseudarthrosis was found in thirteen of twenty patients who had broken screws. Sixteen of the twenty patients had an exploration; three of them were found to have a solid fusion, and thirteen were found to have a pseudarthrosis. The remaining four patients had evidence of a solid fusion on radiographs and had no pain.

CONCLUSIONS

There are few problems associated with the insertion of screws, provided that the surgeon is experienced and adheres to the principles and details of the operative technique. Our review revealed a low rate of postoperative complications related to pedicle screws. The problem of late-onset pain may be related to the implants or to the stiffness of the construct; however, it is difficult to accurately identify its exact etiology.

Simultaneous somatosensory evoked potential and electromyographic recordings during lumbosacral decompression and instrumentation

OBJECTIVE

Both motor and sensory neurological deficits have been reported after decompression and instrumentation of the lumbosacral spine. In this report, we describe a simple and effective method by which sensory and motor functions can be monitored simultaneously, using somatosensory evoked potentials (SSEP), spontaneous electromyographic (EMG) activity, and compound muscle action potential monitoring. The concomitant use of these monitoring techniques allows ongoing functional evaluation of the cauda equina and spinal cord during patient positioning, surgery, wound closure, and anesthetic emergence.

METHODS

SSEPs were recorded continuously in response to peroneal or tibial nerve stimulation. EMG activity (both spontaneous and evoked) was recorded bilaterally from appropriate lower extremity muscle groups. All recordings (SSEP and EMG activity recordings) were obtained, stored, and reviewed simultaneously.

RESULTS

SSEPs and EMG activity were simultaneously recorded for 44 patients. All patients in the study underwent surgical procedures to decompress and stabilize the lumbosacral spine, using pedicle screw instrumentation. In two cases, changes in SSEPs and spontaneous EMG activity were noted and were correlated with postoperative patient complaints.

CONCLUSION

This report describes the concomitant use of powerful and simple tools that provide immediate, "early-warning" feedback to the surgical team concerning the sensory and motor functioning of the spinal cord and cauda equina. In addition, compound muscle action potential recording provides a tool for the identification of both levels and structures in the lumbosacral spine.