Cervical spine pedicle screws: a biomechanical comparison of two insertion techniques.

STUDY DESIGN: Biomechanical testing of the pullout strengths of pedicle screws placed by two different techniques in adult human cadaveric cervical spines. OBJECTIVES: To determine whether there is a significant difference in screw purchase of two commonly proposed methods of cervical pedicle screw insertion. SUMMARY OF BACKGROUND DATA: Wiring techniques remain the gold standard for posterior cervical fixation. However, absent or deficient posterior elements may dictate the use of alternative fixation techniques. Cervical pedicle screws have been shown to have significantly higher pullout strength than lateral mass screws. METHODS: Fifty fresh disarticulated human vertebrae (C3-C7) were evaluated with computed tomography for anatomic disease and pedicle morphometry. The right and left pedicles were randomly assigned to either a standard method or the Abumi insertion method. In the latter technique the cortex and cancellous bone of lateral mass are removed with a high-speed burr, which provides a direct view of the pedicle introitus. The pedicle is then probed and tapped and a 3.5-mm cortical screw inserted. Each screw was subjected to a uniaxial load to failure. RESULTS: There was no significant difference in the mean pullout resistance between the Abumi (696 N) and standard (636.5 N) insertion techniques (P = 0.41). There was no difference in pullout resistance between vertebral levels or within vertebral levels. Two (4%) minor pedicle wall violations were observed. CONCLUSION: In selected circumstances pedicle screw instrumentation of the cervical spine may be used to manage complex deformities and patterns of instability. Surgeons need not be concerned about reduced screw purchase when deciding between the Abumi method and its alternatives.

Cervical pedicle screws: comparative accuracy of two insertion techniques.

STUDY DESIGN: Independently assessed radiographic and anatomic comparison of device implantation methods. OBJECTIVES: To compare the relative accuracy of two techniques of inserting cervical pedicle screws. SUMMARY OF BACKGROUND DATA: In an attempt to define the anatomic risks of cervical pedicle screw insertion, image-guided stereotactic technology was shown to be superior to some other methods in vitro.- Meanwhile, in vivo experience with Abumi's technique of screw insertion has had few clinically relevant instances of screw malposition. There has been no direct comparison between current image-guided technology and Abumi's fluoroscopically assisted technique. METHODS: The pedicles (C3-C7) of human cadaveric cervical spines were instrumented with 3.5-mm screws with either of two techniques. Cortical integrity and potential neurovascular injury were independently assessed by computed tomographic (CT) scans and anatomic dissection. A cortical breach was considered "critical" if the screw encroached on any vital structure. If any part of the screw violated the cortex of the pedicle but no vital structure was at risk for injury, the breach was classified as "noncritical." RESULTS: In Group I (StealthStation; Sofamor-Danek, Memphis, TN), 82% of screws were placed in the pedicle, and 18% had a critical breach. In Group II (Abumi technique), 88% of screws were placed in the pedicle, and 12% had a critical breach. No statistically significant differences were demonstrated between each group (P = 0.59). Regarding pedicle dimensions and safety of insertion, a critical pedicle diameter of 4.5 mm was determined to be the size below which a critical breach was likely, but above which there was a significantly greater likelihood for safe screw placement. The most common structure injured in each group was the vertebral artery. CONCLUSIONS: The use of a computer-assisted image guidance system did not enhance safety or accuracy in placing pedicle screws compared with Abumi's technique. Both techniques have a noteworthy risk of injuring a critical structure if inserted into the pedicles with a diameter of less than 4.5 mm. Under laboratory conditions, pedicles with a diameter of more than 4.5 mm have a significantly greater likelihood of being safely instrumented by either technique. These data indicate that cervical pedicle screw placement is feasible, but it should be reserved for selected circumstances with clear indications and in the presence of suitable pedicle morphology.

Osteoinductive bone graft substitutes.

This review will summarize the major efforts currently underway to develop osteoinductive bone graft substitutes for minimally invasive spine fusions. The primary categories of substitute include purified bone growth factors, recombinant bone growth factors, and growth factors delivered by gene therapy approaches. Clinical trials are underway for the purified and recombinant bone growth factors and pre-clinical studies have yielded promising results for a variety of gene therapy techniques for generating bone.

Rapid-staged strategy for concomitant critical carotid and left main coronary disease with left ventricular dysfunction: IABP use.

BACKGROUND: Few reports address the high-risk patient population with concomitant critical carotid and left main coronary disease with left ventricular dysfunction. To decrease the risks involved with the simultaneous and traditional staged surgical approaches, we developed a rapid staging strategy using an intraaortic balloon pump. METHODS: Between 1992 and 1996, 20 patients presented with a high-risk "triad" defined by greater than 70% stenosis of the left main coronary artery, ejection fraction less than 0.30, and greater than 90% stenosis of the internal carotid artery. An intraaortic balloon pump was placed immediately before carotid endarterectomy under angiographic guidance. Less than 24 hours later (mean, 18 hours) coronary artery bypass grafting was performed, and the intraaortic balloon pump was removed the day of coronary artery bypass grafting in all cases (total IABP duration, <36 hours). RESULTS: Eighteen patients (18/20) were extubated on the day of coronary artery bypass grafting (mean, 12 hours). Sixteen patients (16/20) were transferred from the intensive care unit within 48 hours, with total hospital stay ranging from 6 to 12 days (mean, 8 days). There were no 30-day postoperative deaths, myocardial infarctions, or neurologic, vascular, bleeding, or other major complications. At a mean 29.4-month follow-up, there were two noncardiac deaths and no neurologic events. Six-month, 1-year, and 2-year follow-up ultrasounds showed all operative carotid arteries remained patent. CONCLUSIONS: A rapid staged procedure with angiographically guided placement of the intraaortic balloon pump was safe and effective in this very high risk patient population. It may be an option to decrease the risks involved with simultaneous operations and increase the efficiency and safety of "traditional" staged carotid and coronary artery bypass grafting procedures.

Purification and functional characterization of a chaperone from Methanococcus jannaschii.

A chaperone from Methanococcus jannaschii has been purified to homogeneity with a single chromatographic step. The chaperone was identified and characterized using activity assays for characteristic chaperone abilities. The M. jannaschii chaperone binds unfolded proteins, protects proteins against heat-induced aggregation, and has a strongly temperature dependent ATPase activity. The chaperone has also been shown to inhibit the spontaneous refolding of a mesophilic protein at low temperatures. The purified chaperone complex has a M(r) of about 1,000,000 and consists of a single type of subunit with an approximate M(r) of 60,000. Analysis of partial sequence data reveals that this chaperone is the predicted protein product of the previously identified chaperonin gene in M. jannaschii (BULT et al., 1996). To our knowledge, this is the first functional characterization of a chaperone from a methanogen.

Protein folding stability can determine the efficiency of escape from endoplasmic reticulum quality control.

A fraction of each secreted protein is retained and degraded by the endoplasmic reticulum (ER) quality control apparatus that restricts export to correctly folded proteins. The intrinsic biophysical attributes that determine efficiency of escape from this proofreading process have been examined by expressing mutants of bovine pancreatic trypsin inhibitor (BPTI) in yeast. Secretion efficiency is strongly correlated with thermodynamic stability for a series of six point mutations of BPTI. No correlation of secretion efficiency with either oxidative folding or refolding rates in vitro is found; both the rapidly folded Y35L BPTI mutant and the slowly unfolded G36D BPTI mutant exhibit low secretion efficiency. Elimination of cysteines 14 and 38 by mutagenesis does not increase secretion efficiency, indicating that intramolecular thiol/disulfide rearrangements are not primarily responsible for retention and degradation of destabilized BPTI variants. Mutant yeast strains with diminished ER-associated degradation do not secrete BPTI more efficiently, indicating that retention and degradation are separable processes. These data support a model for ER quality control, wherein protein folding is functionally reversible and the relative rates of folding, unfolding, vesicular export, and retention determine secretion efficiency.

Secretion efficiency in Saccharomyces cerevisiae of bovine pancreatic trypsin inhibitor mutants lacking disulfide bonds is correlated with thermodynamic stability.

Bovine pancreatic trypsin inhibitor (BPTI) has been widely used as a model protein to investigate protein structure and folding pathways. To study the role of its three disulfide bonds in folding, proofreading, and secretion of BPTI in an intact eucaryotic cell, BPTI was expressed and secreted from a synthetic gene in the yeast Saccharomyces cerevisiae. Site-directed mutagenesis was used to create all possible single and pairwise cysteine to alanine BPTI mutants, and the effect of these mutations on secretion efficiency was determined. The 5-55 disulfide bond is found to be essential for secretion-loss of either Cys5, Cys55, or both prevents secretion. Removal of the 14-38 disulfide bond results in a small reduction of secretion, but individual Cys14 or Cys38 replacements reduce secretion efficiency by 30%. Cys30 and Cys30-51 mutants are secreted at half the level of wild-type BPTI, while secretion of the Cys51 mutant is reduced by 90%. BPTI containing only a single disulfide bond (5-55) is not secreted. No relationship is observed between secretion efficiency and in vitro folding or unfolding rates, but mutant BPTI secretion is directly correlated with the in vitro unfolding temperature Tm and the free energy of stabilization provided by each of the three disulfides. These results indicate that structural fluctuations rather than the time-averaged structure observed by NMR or X-ray crystallography may determine recognition of a protein as misfolded and subsequent retention and degradation.

Reliability of roentgenogram evaluation of pedicle screw position.

STUDY DESIGN: This was a human cadaver study of the accuracy of biplanar roentgenography in determining pedicle screw position. OBJECTIVE: To determine the independent accuracy of radiologic evaluation of screw placement and to determine if there are any particular screw malpositions that are more likely to produce a false sense of acceptable screw position. SUMMARY OF BACKGROUND DATA: Other investigators have reported the correlation between radiologic evaluation and anatomic dissection. However, in those studies the radiologic evaluation was not independent of the surgeons placing the screws. There has been no comment in the literature regarding particular screw malpositions that would lead the surgeon into a false sense of successful screw placement. METHODS: Pedicle screws were placed in cadaver spines, and biplanar roentgenograms of the specimens were evaluated by independent observers. The results of the roantgenogram evaluation then were compared to those of the anatomic dissection. RESULTS: The accuracy of roentgenogram evaluation varied from 73% to 83%, depending on the experience of the surgeon grading the roentgenograms. Screws misplaced medially into the spinal canal are more likely to give the surgeon a false sense of successful screw placement. CONCLUSIONS: The surgeon must not rely solely on the roentgenograms, but instead continue to use tactile sensory skills, anatomic knowledge, and additional modalities such as electromyography monitoring.

A neural-network approach to nonparametric and robust classification procedures.

In this paper algorithms of neural-network type are introduced for solving estimation and classification problems when assumptions about independence, Gaussianity, and stationarity of the observation samples are no longer valid. Specifically, the asymptotic normality of several nonparametric classification tests is demonstrated and their implementation using a neural-network approach is presented. Initially, the neural nets train themselves via learning samples for nominal noise and alternative hypotheses distributions resulting in near optimum performance in a particular stochastic environment. In other than the nominal environments, however, high efficiency is maintained by adapting the optimum nonlinearities to changing conditions during operation via parallel networks, without disturbing the classification process. Furthermore, the superiority in performance of the proposed networks over more traditional neural nets is demonstrated in an application involving pattern recognition.

Familial predisposition for degenerative disc disease. A case-control study.

STUDY DESIGN: This case-control study was undertaken to determine if relatives of patients who had been admitted for surgery for degenerative disc disease-related problems were at increased risk for lower back pain or sciatica. OBJECTIVES: To determine if familial factors play a role in placing a person at risk for development of degenerative disc disease of the lumbar spine. SUMMARY OF BACKGROUND DATA: It is known that smoking and various occupational factors can place a person at risk for degenerative disc disease problems. It is not known if a familial predisposition may also exist. METHODS: The family members and relatives of 65 patients who had undergone surgery for lumbar degenerative disc disease were interviewed with a standardized questionnaire and compared with a control group of 67 patients who had been admitted to hospital for non-spine-related orthopedic procedures. The same interview and standardized questionnaire was used for both groups by a single observer. RESULTS: In the study group of 65 patients who had undergone surgery for degenerative disc disease, 44.6% were noted to have a positive family history, whereas 25.4% of the patients in the control group had a positive family history. Eighteen and one-half percent of relatives in the study group had a history of having spinal surgery, compared with only 4.5% of the control group. CONCLUSIONS: The results indicate that a familial predisposition to degenerative disc disease can exist along with other risk factors.

Distribution-free graphical and statistical analysis of serial dependence in neuronal spike trains.

Two-dimensional 'joint' interval distributions of sequential interspike (ISIs) are a commonly used tool in neuronal spike train analysis. We present and evaluate here a modification of the joint interval plot using ranked ISIs. This modification provides clearer graphical evaluation of serial dependence in ISI sequences, a distribution-free basis for isolating changes in serial dependence across experimental treatments from changes in ISI distributions, and a basis for unambiguous statistical tests of serial dependence and stationarity. To validate this method and illustrate the advantages of its use we have applied it to both single-neuron spike trains recorded from cultured mammalian spinal cord neurons and artificial spike trains generated by stochastic models with defined burst envelopes and serial dependencies.

Results of intervertebral diskectomy without fusion at L4-5 versus L5-S1.

The results of diskectomy without fusion at L4-5 were compared with those at L5-S1. Strict indications for surgery had been applied to each group. Evaluation was carried out using the Oswestry Disability scale, as well as a modified Smiley-Webster scale, and a subjective improvement rating scale, as well as documenting work status, whether any future surgery was required, and other factors. Results were placed into categories based on these evaluation methods and were analyzed statistically. Average follow-up was 51 months with a minimum of 24 months. Overall excellent and good results occurred in 81% of patients in both groups. No difference in reoperation rate was detected between the two groups. Women were more likely to undergo a subsequent procedure, usually fusion. Equally satisfactory results can be obtained at L4-5 and L5-S1 if strict selection criteria are used.

Management of the coronary-subclavian steal syndrome with balloon angioplasty. A case report and review of the literature.

A fifty-two-year-old woman with angina pectoris due to coronary-subclavian steal syndrome through a left internal mammary artery graft placed distal to a left anterior descending artery stenosis is presented. Retrograde flow through the mammary artery graft due to severe left subclavian stenosis was observed angiographically. Accordingly, left subclavian balloon angioplasty was performed, restoring normal antegrade flow through the internal mammary artery graft and resulting in resolution of the patient's symptoms. The patient was subsequently discharged with no evidence of angina. Carotid-subclavian bypass surgery was avoided, reducing patient discomfort, procedural risk, and expense.

The results of surgical treatment for adult scoliosis.

This study was done to define and characterize those adult patients with scoliosis who will have problems of pain and/or progression leading to a surgical procedure and to review the results of these surgical procedures. The authors reviewed the cases of 49 adult patients who had undergone surgical treatment for scoliosis (average follow-up, 34 months; range, 24-140 months). The patients were categorized according to age, which allowed analysis of the data comparing age and the incidence and level of pain, age versus the degree of curvature, and age versus the incidence of progression. The relative incidence of pain and progression as indications for surgery were found to vary with respect to age. In the younger groups, progression was more often the indication for surgery than in the older groups. The younger groups also had larger curves than did the older groups, on average. The degree of pain was not found to correlate with the magnitude of the deformity. Surgical complications occurred in 20 patients; however, 14 of these were minor complications during the perioperative period, which did not result in any sequelae. Surgical treatment can be done with a relatively low serious complication rate and good results in terms of pain relief and reasonable correction of the deformity.

Malignant memories. Reluctance to utilize mental health services after a disaster.

This report describes the reluctance of individuals exposed to a man-made disaster to utilize formal mental health services. Measures were obtained in an initial screening 6 months after a shooting for 24 exposed school personnel. Data from the initial screening were compared for those who did not participate in a follow-up screening 12 months later (N = 11) and those who did (N = 13). Follow-up nonparticipants reported: more posttraumatic stress disorder symptoms, especially avoidance; recall of life threat during the event; feeling depressed; and an increase in positivity toward victims but not about their work or mental health professionals. The authors conclude that some individuals may avoid formal mental health services because they serve as cues for malignant memory retrieval and discuss implications for service delivery.

Malignant memories: PTSD in children and adults after a school shooting.

Sixty-four children and 66 adults were screened for post-traumatic stress disorder 6 to 14 months after a school shooting. Although there were no differences in overall frequencies of DSM-III-R diagnoses or cluster endorsements, there were developmental influences. Post-traumatic stress disorder was associated more with emotional states recalled from the disaster than with proximity. Emotional states mediated the formation of malignant memories leading to symptomatology, suggesting that postdisaster intervention be offered on the basis of degree of emotional reaction as well as proximity.

Temporal consistency of the WAIS-R Memory/Freedom from Distractibility factor in a nonclinical sample.

The temporal consistency of the WAIS-R Memory/Freedom from Distractibility factor and its intrafactorial components were measured over a 4-wk. period in a nonclinical sample of 22 undergraduates. A modest but significant consistency coefficient of .49 was obtained for Memory/Freedom from Distractibility. Neither intrafactorial component manifested significant temporal consistency over four weeks. Significant retest improvements were expected and observed on Memory/Freedom from Distractibility and Advanced Computation. These retest improvements were interpreted in terms of task familiarity rather than specific content recall. The reported temporal consistency coefficients appear to represent the lowest consistency for these neuropsychological constructs. The routine use of Memory/Freedom from Distractibility was questioned pending more comprehensive measurement of reliability.

Posttraumatic stress disorder after a school shooting: effects of symptom threshold selection and diagnosis by DSM-III, DSM-III-R, or proposed DSM-IV.

OBJECTIVE: The purpose of the study was to investigate the effect of symptom threshold and criteria set selections on the diagnosis of posttraumatic stress disorder (PTSD) in adults and children exposed to a man-made disaster and determine how well DSM-III and its successors agree. METHOD: Data gathered in the course of a voluntary clinical screening for PTSD in 66 adults and 64 children 6 to 14 months after exposure to a school shooting were analyzed according to DSM-III, DSM-III-R, and proposed DSM-IV criteria for PTSD diagnosis and cluster endorsement using liberal (occurring at least a little of the time), moderate (occurring at least some of the time), and conservative (occurring at least much or most of the time) symptom thresholds. RESULTS: Within DSM-III, DSM-III-R, and proposed DSM-IV, selection of liberal, moderate, and conservative symptom thresholds had robust effects on rates of diagnoses; liberal thresholds allowed the greatest frequencies of diagnosis. Compared with DSM-III and proposed DSM-IV, DSM-III-R generally diagnosed the fewest cases. Agreements between DSM-III-R and proposed DSM-IV were good, while agreements between DSM-III and its successors varied for children and adults. CONCLUSIONS: Diagnostic rates and agreements were complexly influenced by interactions among threshold and revisions in symptom clusters. The present study suggests that attempts to refine PTSD classification consider specification of symptom threshold intensity and supports the view that modification of criteria sets be undertaken with caution.