Effects of bone cement volume and distribution on vertebral stiffness after vertebroplasty.

STUDY DESIGN: The biomechanical behavior of a single lumbar vertebral body after various surgical treatments with acrylic vertebroplasty was parametrically studied using finite-element analysis. OBJECTIVES: To provide a theoretical framework for understanding and optimizing the biomechanics of vertebroplasty. Specifically, to investigate the effects of volume and distribution of bone cement on stiffness recovery of the vertebral body. SUMMARY OF BACKGROUND DATA: Vertebroplasty is a treatment that stabilizes a fractured vertebra by addition of bone cement. However, there is currently no information available on the optimal volume and distribution of the filler material in terms of stiffness recovery of the damaged vertebral body. METHODS: An experimentally calibrated, anatomically accurate finite-element model of an elderly L1 vertebral body was developed. Damage was simulated in each element based on empirical measurements in response to a uniform compressive load. After virtual vertebroplasty (bone cement filling range of 1-7 cm3) on the damaged model, the resulting compressive stiffness of the vertebral body was computed for various spatial distributions of the filling material and different loading conditions. RESULTS: Vertebral stiffness recovery after vertebroplasty was strongly influenced by the volume fraction of the implanted cement. Only a small amount of bone cement (14% fill or 3.5 cm3) was necessary to restore stiffness of the damaged vertebral body to the predamaged value. Use of a 30% fill increased stiffness by more than 50% compared with the predamaged value. Whereas the unipedicular distributions exhibited a comparative stiffness to the bipedicular or posterolateral cases, it showed a medial-lateral bending motion ("toggle") toward the untreated side when a uniform compressive pressure load was applied. CONCLUSION: Only a small amount of bone cement ( approximately 15% volume fraction) is needed to restore stiffness to predamage levels, and greater filling can result in substantial increase in stiffness well beyond the intact level. Such overfilling also renders the system more sensitive to the placement of the cement because asymmetric distributions with large fills can promote single-sided load transfer and thus toggle. These results suggest that large fill volumes may not be the most biomechanically optimal configuration, and an improvement might be achieved by use of lower cement volume with symmetric placement.

Transforaminal lumbar interbody fusion: technique, complications, and early results.

OBJECTIVE: To demonstrate the safety, surgical efficacy, and advantages of the transforaminal approach for lumbar interbody fusion when combined with pedicle screw fixation. METHODS: We retrospectively reviewed the records of 22 patients (age range, 34-63 yr; mean, 49 yr) with Grade I or II spondylolisthesis who underwent transforaminal lumbar interbody fusion. Nineteen patients presented with low back pain and associated radiculopathy, and three presented with low back pain only. Transforaminal lumbar interbody fusion was performed at L4-L5 in 8 patients, L5-S1 in 11 patients, L3-L4 and L4-L5 in 2 patients, and L4-L5 and L5-S1 in 1 patient. Periodic follow-up took place 1 to 12 months after surgery (mean, 5.3 mo). Decompression is performed according to clinical circumstances. Pedicle screws are placed, and a discectomy is carried out. The cartilaginous endplates are removed. The interspace is gradually distracted, resulting in lost disc height being regained, and interbody fusion cages are positioned. The pedicle screw-and-rod construct is then compressed, restoring lumbar lordosis. RESULTS: Low back pain completely resolved in 16 patients, moderate relief from pain was achieved in 5 patients, and the pain was unchanged in one patient. Nonneurological complications included intraoperative durotomy in one patient and postoperative wound infection in two. In one patient, postoperative mild L5 motor paresis resolved. One patient had a temporary brachial plexopathy due to intraoperative positioning, and one patient had peripheral polyneuropathy secondary to prolonged intraoperative blood pressure cuff inflation. CONCLUSION: Transforaminal lumbar interbody fusion is a safe and effective method for achieving circumferential spinal fusion via a single-stage procedure. This procedure is particularly useful in restoring disc space height and lumbar lordosis.

Spinal chondrosarcoma following adenocarcinoma of the breast: case report.

BACKGROUND: Chest wall chondrosarcomas have been reported rarely in breast cancer patients treated with chest wall radiation therapy. However, there are no prior reports of spinal chondrosarcomas arising in patients with a history of breast adenocarcinoma. CASE DESCRIPTION: A neurologically intact 53-year-old woman with breast adenocarcinoma and new onset back pain was evaluated. Magnetic resonance imaging of the spine revealed a tumor of the posterior elements of T7, impinging upon the spinal cord. A computed tomography guided needle biopsy of the spinal mass failed to yield diagnostic results. The patient underwent an open surgical biopsy and complete excision of a low-grade chondrosarcoma. The patient's thoracic pain resolved after surgical excision of her thoracic tumor. She remained neurologically intact. Pathological examination of the tumor revealed a low-grade chondrosarcoma. CONCLUSION: We present the first reported case of chondrosarcoma of the spine arising in a patient with a history of breast adenocarcinoma without prior irradiation. Solitary spinal tumors in patients with breast adenocarcinoma should not be assumed to be metastatic lesions, and chondrosarcoma should be included in the differential diagnosis of spinal lesions in this patient population. Experimentally, chondrosarcomas have been shown to be sensitive to circulating levels of estrogens, and this might explain an association with adenocarcinoma of the breast treated with tamoxifen.

Quantification of axonal damage in traumatic brain injury: affinity purification and characterization of cerebrospinal fluid tau proteins.

Diffuse axonal injury is a primary feature of head trauma and is one of the most frequent causes of mortality and morbidity. Diffuse axonal injury is microscopic in nature and difficult or impossible to detect with imaging techniques. The objective of the present study was to determine whether axonal injury in head trauma patients could be quantified by measuring levels of CSF tau proteins. Tau proteins are structural microtubule binding proteins primarily localized in the axonal compartment of neurons. Monoclonal antibodies recognizing the form of tau found in the CSF of head trauma patients were developed by differential CSF hybridoma screening using CSF from head trauma and control patients. Clones positive for head trauma CSF tau proteins were used to characterize this form of tau and for ELISA development. Using the developed ELISA, CSF tau levels were elevated >1,000-fold in head trauma patients (mean, 1,519 ng/ml of CSF) when compared with patients with multiple sclerosis (mean, 0.014 ng/ml of CSF; p < 0.001), normal pressure hydrocephalus (nondetectable CSF tau), neurologic controls (mean, 0.031 ng/ml of CSF; p < 0.001), or nonneurologic controls (nondetectable CSF tau; p < 0.001). In head trauma, a relationship between clinical improvement and decreased CSF tau levels was observed. These data suggest that CSF tau levels may prove a clinically useful assay for quantifying the axonal injury associated with head trauma and monitoring efficacy of neuroprotective agents. Affinity purification of CSF tau from head trauma patients indicated a uniform cleavage of approximately 18 kDa from all six tau isoforms, reducing their apparent molecular sizes to 30-50 kDa. These cleaved forms of CSF tau consisted of the interior portion of the tau sequence, including the microtubule binding domain, as judged by cyanogen bromide digestion. Consistent with these data, CSF cleaved tau bound taxol-polymerized microtubules, indicating a functionally intact microtubule binding domain. Furthermore, epitope mapping studies suggested that CSF cleaved tau proteins consist of the interior portion of the tau sequence with cleavage at both N and C terminals.

Compression of the upper cervical spinal cord causing symptoms of brainstem compromise. A case report.

STUDY DESIGN: A case is reported in which a flexion-induced compression of the upper cervical spinal cord caused symptoms of brainstem compromise in the absence of radiographic evidence of osseous instability. OBJECTIVES: A 41-year-old woman developed postoperative cervical instability with flexion-induced neurologic symptoms referable to the brainstem. The instability was caused by direct compression at the third cervical vertebral body, which in turn was caused by differential movements between the neuraxis and skeletal elements in the upper cervical spine. SUMMARY OF BACKGROUND DATA: Pathologic processes at the craniocervical junction may cause brainstem compromise with neurologic symptoms. The mechanism of brainstem involvement is usually either vertebrobasilar insufficiency or direct mechanical compression. In cases where the brainstem is compressed by skeletal elements, the compressing osseous structures usually are the walls of the foramen magnum or the odontoid process, or, less frequently, the atlas or axis vertebrae. Symptoms of brainstem dysfunction caused by dynamic compression at the level of the third cervical vertebra in the absence of hindbrain herniation are unusual and, to the best of the authors' knowledge, have not been described previously. METHODS: The patient underwent initial examination, evaluation, and periodic follow-up examination with magnetic resonance imaging from the time of her first visit until 26 months after the surgical treatment. The patient experienced postsurgical instability with dynamic compression by the C3 vertebral body, which caused brainstem compromise. Surgical treatment consisted of decompressive C3 corpectomy and fusion of C2 to C6, supplemented by anterior fixation. RESULTS: After undergoing surgical decompression of C3, reconstruction, and anterior internal fixation of C2 to C6, the patient had dramatic neurologic improvement. Diplopia, paresthesia, and nystagmus disappeared immediately after surgery. Swallowing difficulties, hoarseness, and vertigo improved gradually. At follow-up examination 26 months after surgery, the patient was asymptomatic. Magnetic resonance imaging showed good position of the construct, with no evidence of compression of the spinal cord or brainstem. CONCLUSIONS: Instability of the cervical spine may result in symptoms of brainstem dysfunction, even in the absence of hindbrain herniation. This instability is explained by the differential movement between the bony structures and neuraxis in the upper cervical region. Diagnosis and adequate management of this instability alleviates the neurologic symptoms and prevents possible hazardous complications.

Traumatic cranial defects reconstructed with the HTR-PMI cranioplastic implant.

Titanium mesh, polymethyl methacrylate application, and autogenous bone grafting have been used to reconstruct traumatic cranial defects, with varying success. A more recent technique utilizing hard tissue replacement-patient matched implants (HTR-PMIs) involves the production of a cranioplastic implant using three-dimensional computed tomography imaging. It has proven less time-consuming and provides an excellent cosmetic result for the patient. The authors present two case reports using this technique to correct traumatic cranial defects. Both patients exhibited satisfactory results and no postoperative complications. The authors believe this relatively new technique represents an advance in the management of large cranial defects.

Traumatic subarachnoid-pleural fistula: case report.

Traumatic subarachnoid-pleural fistula was recently diagnosed in an 18-year-old male after a gunshot wound in the chest and spinal column. The diagnosis was suggested by persistent pleural drainage and headache in the setting of signs of spinal injury at the thoracic level. Computed tomographic myelography delineated the dural injury. The fistulous connection was defined and repaired at operation. This paper describes the diagnostic and therapeutic features encountered in the management of this rare disorder.

Local protective effects of nerve growth factor-secreting fibroblasts against excitotoxic lesions in the rat striatum.

Neurotrophic factors, such as nerve growth factor (NGF), in addition to their role in neuronal development, have protective effects on neuronal survival. Intracerebral implantation of cells genetically altered to secrete high levels of NGF is also found to promote neuronal survival in experimental lesioning models of the brain. The range of activity for such biological delivery systems has not yet been well described either spatially or temporally. Therefore, the authors chose to study the local and distant protective effects of an NGF-secreting rat fibroblast cell line implanted in an excitotoxic lesion model of Huntington's disease. They found that preimplantation of NGF-secreting fibroblasts placed within the corpus callosum reduced the maximum cross-sectional area of a subsequent excitotoxic lesion in the ipsilateral striatum by 80% when compared to the effects of a non-NGF-secreting fibroblast graft, and by 83% when compared to excitotoxic lesions in ungrafted animals (p < 0.003). However, NGF-secreting cells placed in the contralateral corpus callosum failed to affect striatal lesion size significantly when compared to contralateral or ipsilateral non-NGF-secreting cell implants. Of note, fibroblasts were clearly visible within the graft site at 7 and 18 days after implantation; however, few cells within the grafts stained positively for NGF peptide or for the messenger ribonucleic acid (mRNA) encoding the transfected NGF gene-construct at either time point. These results show that biological delivery systems for NGF appear to have a profound but local effect on neuronal excitotoxicity, which will necessitate careful neurosurgical placement for maximum effect. Furthermore, the ability of this genetically altered cell line to synthesize NGF mRNA and peptide appears to decrease spontaneously in vivo, a characteristic that will need to be addressed before this method of biological delivery can be utilized as a treatment for chronic degenerative diseases.

Authentic and artifactual detection of the E. coli lacZ gene product in the rat brain by histochemical methods.

The accurate detection of a marker gene is fundamental to the assessment of any gene delivery protocol. The use of E. coli lacZ as such a marker gene has become common in studies on gene transfer to the central nervous system. The straightforward histochemical assay that is available to detect the gene product, beta-galactosidase; has made it an attractive system. However, using standard protocols, we have found dramatic non-E. coli lacZ staining in cells with neuronal, glial and endothelial morphology in the normal, adult rat brain. This false staining is primarily in the brainstem, but is evident in cortical and subcortical regions as well. This endogenous reactivity is independent of substrate concentration within the range tested, but is exquisitely sensitive to even small fluctuations in pH. In light of these findings, one must carefully examine any findings of E. coli lacZ gene expression in the rat brain based solely on histochemical analysis of tissue sections.

Cervical disc herniation presenting as a mass lesion posterior to the odontoid process. Report of two cases.

The authors report two cases of herniated intervertebral disc presenting as a mass posterior to the odontoid process and causing myelopathy in previously healthy elderly women. The differential diagnosis of a mass at the craniovertebral junction is reviewed, and the implications of these cases are discussed.

Contralateral trigeminal dysaesthesias associated with second cervical nerve compression: a case report.

This 70-year-old woman presented with a left C2 solitary metastatic lesion producing ipsilateral occipital pain associated with contralateral fronto-orbital dysaesthesias. Examination revealed analgesia in the left C2 dermatome and hyperaesthesia in the right forehead. These symptoms and findings resolved following a course of radiation therapy to the C2 metastasis. Ipsilateral trigeminal dysaesthesias produced by cervical lesions have been described, however, contralateral cervicogenic trigeminal dysaesthesias have not. Relevant experimental data are analysed; neural pathways are suggested by which a cervical lesion, especially at C2 or C3, may produce trigeminal dysaesthesias referred ipsilaterally or contralaterally.