Percutaneous lumbar and thoracic pedicle screws: a trauma experience.

DESIGN: Retrospective case study. OBJECTIVE: Percutaneous pedicle screw (PPS) techniques do not allow direct visualization and may lead to erroneous screw placement. A technique utilizing only fluoroscopy is described. Verification of its accuracy and morphometric validation are presented. BACKGROUND: Minimally invasive spine surgical techniques, particularly PPS placement, have been growing in popularity. The purported benefits of minimally invasive spine surgical stated may be even more advantageous in the trauma setting. METHODS: Jamshidi needles were docked in the typical starting position verified with posterior-anterior image. Jamshidi needle (20 mm) was advanced ensuring that the tip remained lateral to the medial pedicle wall. A Kirschner (K-wire) was placed through the needle. Once all the K-wires were placed, a lateral image was taken confirming the correct trajectory and that the wire passed the posterior vertebral body wall. Patients with PPS fixation were retrospectively studied with postoperative computed tomography to verify screw accuracy. Screw grade was assessed as grade I when completely within the pedicle, II <2 mm, III 2-4 mm, and IV >4 mm outside the pedicle. Morphometrically, 40 thoracic and lumbar computed tomography scans of patients (<40 y) without spine fractures were reviewed. The pedicle length was defined as the distance from the dorsal cortical margin to the posterior vertebral body in the pedicle's midaxis. RESULTS: A total of 172 screws were placed. Eighteen percent were found to have cortical breach, but only 2.9% were found to have >grade II breach. The morphometric study demonstrated the pedicle length to range from 14.4 to 22.1 mm. The shortest was in the upper thoracic and the longest at L1-L2. CONCLUSIONS: The morphometric study demonstrates if a K-wire is placed 20 mm into the bone and remains lateral to the medial pedicle wall and the tip just engages the vertebral body, the screw trajectory is safe particularly in the lower thoracic and upper lumbar spine. A smaller distance may be utilized in the upper thoracic. Breach rates are similar to other reports using other techniques; none were clinically significant. The advantage of this technique is the use of only PA fluoroscopy for placing all the wires percutaneously.

Thoracic pedicle subtraction osteotomy in a pediatric patient: a case report.

STUDY DESIGN: Case report. OBJECTIVE: To describe a case of thoracic pedicle subtraction osteotomy (PSO) for congenital kyphosis in a child. BACKGROUND INFORMATION: Although congenital kyphosis is rare, it is a challenging cause of pediatric myelopathy and frank paralysis. Even less common is the use of PSO for the surgical management of focal congenital kyphosis. We present the case of a child with congenital kyphosis that was managed with a pedicle subtraction osteotomy. METHODS: A detailed history and physical examination were performed with careful review of the patient's medical records and x-ray studies. A PSO at T11 was performed along with T9 through L1 instrumented posterolateral fusion. CASE DESCRIPTION: A 10-year-old girl was evaluated for walking difficulty and a lump on her back. Physical examination revealed a sharp gibbus kyphosis in the lower thoracic spine with tenderness and bilateral back muscle spasms. The patient displayed difficulty with balance lacking a smooth, regular gait rhythm. Clonus and radiculopathy were not present. Plain x-ray of the thoracolumbar spine revealed hyperkyphosis and failure of anterior wall segmentation between T10 and T11 vertebral bodies. Cobb's angle measured 65 degrees. Due to her symptoms and degree of correction required, we elected to perform a PSO at T11 along with T9 to L1 posterolateral instrumentation fusion. No intraoperative complications occurred. There was a significant improvement in her posture and gait. DISCUSSION: A thoracic PSO for congenital kyphosis was safely performed with an excellent outcome. To our knowledge, this is the first PSO procedure performed in Uganda.

Oblique lumbar interbody fixation: a biomechanical study in human spines.

STUDY DESIGN: In vitro spine biomechanics. OBJECTIVE: To determine the biomechanical properties of oblique lumbar interbody fixation (OLIF) in human cadaveric spines. SUMMARY OF BACKGROUND DATA: OLIF has been used for stabilization of degenerative spondylolisthesis at the lumbosacral junction. Biomechanical properties and mode of failure of OLIF as a standalone device for motion segments without sagittal deformity has not yet been investigated. We hypothesize that the biomechanical properties of OLIF will be comparable with the contemporary standard of pedicle screw (PS) fixation. METHOD: Randomly matched motion segments from L1 to L5 were allocated into 2 groups: (A) OLIF (group 1, n=5) or (B) PS (group 2, n=5). The intact and instrumented motion segments with and without anterior interbody graft were first tested under a combination of 200N axial compression and 5 Nm bending moments in flexion-extension and in lateral bending. Range of motion (ROM) and neutral zone were determined and compared between intact, OLIF and PS. A final load to failure test was carried out for each motion segment in either flexion or extension. RESULT: OLIF resulted in reduction of flexion-extension ROM to 36%±14% of intact whereas PS resulted in reduction to 27%±22% of intact. The reduction of lateral bending ROM were 32%±13% and 32%±24% of intact with OLIF and PS. There were no significant difference in ROM between OLIF and PS (P=0.39). The mean failure loads with OLIF and PS in flexion were 1284 and 1158N, and in extension were 1879 and 1934N, respectively. Failure occurred at the ventral screw bone interface without pedicle fracture. CONCLUSIONS: These results indicate that stiffness and load to failure of the OLIF is comparable with PS fixation. OLIF failure occurred ventrally through the anterior cortical rim without concomitant pedicle fracture.

T8 spinal cord transection in a 6-year-old child.

STUDY DESIGN: Case report. OBJECTIVE: To describe a case of spinal cord transection in a 6-year-old child. BACKGROUND INFORMATION: Non-missile injury of the spinal cord is not common and its incidence varies according to the country. In addition, to our knowledge, there are no published reports of spinal cord injury (SCI) from a penetrating nail. Here, we report the case of a child who developed complete SCI because of cord transection by a nail. METHODS: A detailed history and physical examination were performed along with careful review of the patient's medical records. In addition, a review of the literature was conducted to assess the incidence and treatment of similar injuries. CASE DESCRIPTION: A 6-year-old boy was admitted to the hospital after falling from a tree and landing on a nail. His physical examination revealed an emaciated child with multiple decubitus ulcers, lying on his side in bed. Visible was a well-healed posterior puncture wound at the T8 vertebral level. On neurological examination, the patient had 0/5 muscle strength in his lower extremities, symmetrical areflexia, and hypoesthesia below the T8 level. Plain x-ray of the thoracolumbar spine was normal. Magnetic resonance imaging revealed a transected spinal cord at the T8 vertebra, consistent with his nail puncture wound. DISCUSSION: This report describes an unusual case of a complete SCI in a pediatric patient caused by penetrating trauma from a nail. To our knowledge, this is the first case to report on complete SCI due to trauma from a nail.

Pedicle screw insertion angle and pullout strength: comparison of 2 proposed strategies.

OBJECT: Minimally invasive pedicle screws inserted vertically (that is, dorsoventrally) through the pedicle, as opposed to the more common coaxial technique, offer potential advantages by minimizing soft-tissue stripping during screw placement. The screws are designed for insertion through a medial starting point with vertical trajectory through the pedicle and into the vertebral body. As such, no lateral dissection beyond the insertion point is necessary. However, the effects of this insertion technique on the screw biomechanical performance over a short- and long-term are unknown. The authors investigated the pullout strength and stiffness of these screws, with or without fatigue cycling, compared with comparably sized, traditional screws placed by coaxial technique. METHODS: Twenty-one lumbar vertebrae (L-3, L-4, and L-5) were tested. Each pedicle of each vertebra was instrumented with either a traditional, coaxial pedicle screw (Group A), placed through a standard starting point, or a vertically oriented, alternative-design screw (Group B), with a medial starting point and vertical trajectory. The specimens were divided into 2 groups for testing. One group was tested for direct pullout (10 specimens) while the other was subject to pullout after tangential (toggle) cyclic loading (11 specimens). The screws were cycled in displacement control (± 5 mm producing ~ 4-Nm moment) at a rate of 3 Hz for 5000 cycles. Pullout tests were performed at a rate of 1 mm/minute. RESULTS: Two-way ANOVA showed that Group B screws with a medial starting point (2541 ± 1090 N for cycled vs 2135 ± 1323 N for noncycled) had significantly higher pullout loads than Group A screws with a standard entry point (1585 ± 766 N for cycled vs 1417 ± 812 N noncycled) (p = 0.001). There was no significant effect of cycling or screw insertion type on pullout stiffness. Tangential stiffness of the Group B screws was significantly less than that of the Group A screws (p = 0.001). The stiffness of both screws in the toe region was significantly affected by cycling (p = 0.001). CONCLUSIONS: The use of Group B screws inserted through a medial starting point showed greater pullout load than a Group A screw inserted through a standard starting point. The greater pullout strength in Group B screws may be due to screw thread design and increased cortical bone purchase at the medial starting point. Nevertheless, anatomical considerations of the medial starting point, that is, pedicle or lateral vertebral body cortex breach, may limit its application. The medial starting point of the Group B screw was frequently in the facet at the L-3 and L-4 pedicle entry points, which may have clinical importance.

The difference in spine specimen dual-energy X-ray absorptiometry bone mineral density between in situ and in vitro scans.

BACKGROUND CONTEXT: Human cadaveric specimens are commonly used to evaluate bone-implant interface strength in osteoporotic spine fixation. Dual-energy X-ray absorptiometry (DXA) scans are usually carried out on explanted spine specimens to measure bone mineral density (BMD) before in vitro biomechanical studies are carried out. PURPOSE: The purposes of this study were to verify and quantify the difference in DXA BMD between unexplanted (in situ) and explanted (in vitro) scans and to develop and validate a correction factor (CF) between in vitro and in situ DXA BMD. STUDY DESIGN: This is a retrospective analysis of past DXA scans of explanted specimens and a repeated measure scan rescan study of in situ and in vitro spine specimens. METHODS: Dual-energy X-ray absorptiometry scans were previously carried out on 106 male and 83 female lumbar specimens. Using multiple regressions, the correlation functions between Z score, BMD, and age were determined for male and female groups. The CF was developed based on difference in BMD between mean in vitro and population data. Next, in situ DXA scans were carried out on the lumbar spine of four full human cadavers, and subsequently, in vitro scans were repeated after explantation. The CF was applied to these in vitro scan data and the resulting corrected BMD compared with in situ scan values. RESULTS: The specimens had significantly lower Z score than population mean. The mean Z score was -0.7+/-1.4 (p<.001) for male and -0.3+/-1.3 (p=.03) for female specimens. The difference between in situ and in vitro scans was quantified to be 0.06 g/cm(2) for male specimens and to be a function of age (6.80 Age(-0.5)-3.76 Age(-0.365)) for female specimens. In vitro BMD was 96+/-11% of in situ BMD and was significantly different (p=.04). Corrected BMD after application of CF was 97+/-11% of in situ BMD and was not significantly different (p=.13). CONCLUSIONS: In vitro BMD scan on explanted specimens measured lower DXA values than in situ BMD scans on full cadavers. A CF when used resulted in more accurate measure of the in situ BMD.

Hydroxyapatite-coated tapered cementless femoral components in total hip arthroplasty.

Tapered cementless femoral fixation provides a reliable option for routine primary total hip arthroplasty (THA). The use of hydroxyapatite (HA)-coated stems is increasing as a result of mounting evidence that HA may improve the reliability of bone osseointegration and improve overall THA outcomes. These trends are based on a growing body of literature that supports both the theoretical and clinical rationale of this approach. There is solid clinical evidence that the combination of tapered geometry with an HA coating increases the likelihood of reliable femoral fixation. A comprehensive review of this literature evaluating the clinical use of cementless femoral components that use an HA coating is presented, and reveals that HA-coated stems have significantly improved proximal femoral fixation with less stress shielding and superior osseous remodeling. Although these advantages have not been shown to significantly increase long-term durability, there is sufficient data to support the routine use of HA-coated, tapered cementless femoral stems in THA.

Posterolateral spinal cord decompression in patients with metastasis: an endoscopic assisted approach.

Spinal tumors that are radioresistant or cause bony compression of the spinal cord often require surgical decompression to protect or restore neurological function. Metastatic lesions and primary tumors such as multiple myeloma usually arise in the vertebral body, which can collapse and become unstable, and can compress the anterior columns of the cord. Laminectomy is often ineffective in these patients, and direct anterior decompression through thoracotomy is the widely-accepted solution to the neurological problem. The anterior surgical approach is particularly challenging in the upper thoracic spine. Patients with limited pulmonary reserve due to pneumonectomy or pulmonary metastasis might not tolerate the loss of lung capacity necessitated by either thoracotomy or thoracoscopy. Because posterior instrumentation is usually needed to provide stability following corpectomy and spinal cord decompression, posterolateral approaches to spinal cord decompression have gained favor in recent years. Posterolateral decompression offers advantages over the combined anterior and posterior approach, reducing operative time, morbidity, and hospital stay. Drawbacks to traditional posterolateral decompressions include poor visualization of the tumor immediately anterior to the spinal cord and the need to manipulate the spinal cord to completely remove a tumor adherent to the dura. Endoscopically assisted posterolateral decompression allows decompression of the anterior surface of the spinal cord, the point of pressure in most circumstances. Endoscopic video assistance facilitates vertebrectomy, cord decompression, and anterior reconstruction, all performed through the same posterior incision. Endoscopic assisted spinal cord decompression dramatically reduces morbidity, ICU requirements, and inpatient hospitalization and has proven useful for a variety of metastatic tumors at every level of the spinal column.

Hip and knee arthroplasty in the geriatric population.

Osteoarthritis is the leading cause of hip and knee pathology in the geriatric population. Hip and knee arthroplasty are the definitive interventions to alleviate pain and restore physical functioning. Complications related to these procedures do occur: the most com-mon of these are infection, thromboembolism, dislocations, and periprosthetic fractures. New improvements related to minimally invasive and computer-assisted navigation surgery techniques are promising and already have shown excellent outcomes in patients exposed to joint arthroplasty.

The dual specificity phosphatase Cdc25C is a direct target for transcriptional repression by the tumor suppressor p53.

The cdc25C gene has been shown to be a novel target for transcriptional downregulation by p53. Two independent mechanisms contribute to the p53-dependent repression of the cdc25C gene. First, an element in the cdc25C promoter consisting of a binding site for p53 plus an adjacent 8 base pairs confers p53-dependent repression. Mutation of either the p53 binding site or the adjacent 8 bp sequence abolishes this effect. The element conferring p53-dependent repression also contains a binding site for the transcription factor Sp1 and a mutant p53 protein that retains the ability to interact with the p53-binding site is defective in mediating repression. Second, a minimal promoter lacking the p53 binding site but containing a previously characterized CDE/CHR element is also repressed by p53. This repression is abrogated when a 5 bp mutation is introduced in the CHR sequence. These results support a model for p53 downregulating cdc25C expression, in part, by direct binding to a promoter element that is likely to require cooperation with an additional cellular factor.

Recurrent anterior glenohumeral instability with onset after forty years of age: the role of the anterior mechanism.

Recurrent instability in patients over forty years of age is felt to occur primarily as a result of an associated rotator cuff tear. This is often referred to as the "posterior mechanism." We reviewed our patients over the age of forty who underwent an anterior shoulder repair to identify the incidence of capsulolabral detachments and the role of an "anterior mechanism" in this patient population. A retrospective review of all patients from 1985 to 2000 was performed to identify patients who had surgery for recurrent instability that began after forty years of age. Of the 265 patients records reviewed, 11 patients were identified who fulfilled the inclusion criteria. Of the 11 patients identified, 9 patients underwent anterior capsulolabral reconstruction for recurrent instability; the remaining two patients underwent repair of large rotator cuff tears. All 9 patients had a capsulolabral detachment, 4 had a rotator interval defect, 2 had anterior and inferior capsular redundancy, 1 had a small rotator cuff tear and 1 had an anterior capsular avulsion from the humeral head. At minimum follow-up of 32 months none of the patients reported episodes of instability. The reported incidence of rotator cuff tears in patients over the age of forty following an initial traumatic anterior glenohumeral dislocation ranges from 35% to 100%. When recurrent instability occurs, it is postulated to occur via a "posterior mechanism" (i.e., secondary to a significant full-thickness rotator cuff tear). However, all of our patients had an anterior capsulolabral detachment as the "common lesion" associated with recurrent instability. Although small, this series emphasizes the role of the "anterior mechanism" in patients who develop recurrent instability after the age of forty. A high rate of success was achieved by addressing the pathoanatomic changes identified.

Revision anterior shoulder repair for recurrent anterior glenohumeral instability.

Although the operative management of recurrent anterior glenohumeral instability has received significant attention in literature, the outcome of revision anterior shoulder repair is much less frequently reported. We report the results of our experience with this challenging problem. Retrospective chart review identified 29 patients who underwent revision anterior shoulder repair. Prior procedures included eight Bankart repairs, seven capsular shifts, 10 combined Bankart and capsular shift procedures, three Putti-Platt procedures, two staple capsulorrhaphies, two Bristow procedures, seven arthroscopie procedures, and one Magnuson-Stack. The average age of the patients was 31.6 years (range: 18 to 52 years) and the dominant extremity was involved in 69%. Findings at the time of revision anterior shoulder repair included 22 patients with capsulolabral detachment, 24 with capsular redundancy, and 14 with rotator interval defects. Twenty-three of the 29 patients were available for at least a two-year follow-up. Twenty-one (91%) remain stable. One patient was non-compliant with the postoperative immobilization and re-dislocated within the first month. The second patient, who had a prior Bankart procedure followed by a capsular shift two years later, underwent a capsular shift for significant capsular laxity. He re-dislocated approximately 15 months postoperatively. Our success rate of 91% in this small series approaches the results of primary open repair for recurrent glenohumeral instability. To achieve a successful outcome, it is essential to address all pathology at the time of revision repair.

DNA damage-induced downregulation of Cdc25C is mediated by p53 via two independent mechanisms: one involves direct binding to the cdc25C promoter.

The Cdc25C phosphatase mediates cellular entry into mitosis. The cdc25C gene is a target for transcriptional downregulation by the tumor suppressor protein p53, and this repression can be shown to contribute to p53-dependent cell cycle arrest. Two independent mechanisms have been identified. One involves the direct binding of p53 to a site in the cdc25C promoter, and the second involves a CDE/CHR element. Both of these mediate p53-dependent repression at levels of p53 comparable to those produced by DNA damage. Three CCAAT elements in the cdc25C promoter that were previously implicated in p53-dependent repression fail to do so at physiologically relevant levels of p53. Repression of Cdc25C by p53 represents an additional mechanism for p53-dependent cell cycle arrest in response to DNA damage. Importantly, this is a clear demonstration of p53-mediated transcriptional downregulation that is dependent on sequence-specific DNA binding by p53.