Search PubMed⌕ Search

Biomedical subjects

Mark S Cohen

Publications and source records attributed to Mark S Cohen.

34 records · Page 2Linked to original sources
PubMed2005

Thermal tissue damage caused by ultrasonic cement removal from the humerus.

BACKGROUND: Ultrasound devices can selectively remove cement during revision arthroplasty. These instruments initially were designed for the hip and knee but also have been applied to the upper extremity. We describe a patient in whom a radial nerve palsy and a pathologic humeral fracture developed after ultrasonic cement removal was performed because of an infection at the site of a total elbow arthroplasty. Biopsies of the humerus, the triceps muscle, and the radial nerve showed widespread necrosis consistent with thermal injury. METHODS: A study involving six human cadaveric specimens was conducted to measure temperature elevations in bone and adjacent soft tissue during cement removal with use of an ultrasound device with and without irrigation. RESULTS: While temperature increased only minimally during cement polymerization, ultrasonic melting and removal of cement with use of constant energy delivery led to markedly elevated temperatures in the humeral cortex, the triceps muscle, and the radial nerve. These temperatures were above the known thresholds for thermal injury and necrosis. Subsequently, strategies designed to allow for safe ultrasonic cement removal from the humerus were applied, including intermittent delivery of energy and the use of cold irrigation between probe passes. These strategies resulted in markedly lower maximum temperatures in all tissues tested. CONCLUSIONS: Temperatures in the humerus, triceps, and, most importantly, the radial nerve can reach potentially dangerous levels when ultrasound technology is used to remove cement from the humerus. We suggest intermittent cold irrigation of the humeral canal, no tourniquet use, education of surgeons with regard to proper techniques designed to limit heat generation, and consideration of exposure and protection of the radial nerve when ultrasound devices are used.

Aged↗
PubMed2004

Fractures of the coronoid process.

Proper treatment of coronoid fractures requires an understanding of the bony and soft tissue anatomy of the elbow and the various injury mechanisms that occur. Newer fracture classifications help direct treatment based on the size and location of the fracture, injury mechanism, and associated stability of the elbow.

Elbow Joint↗
PubMed2004

Concurrent EEG/fMRI analysis by multiway Partial Least Squares.

Data may now be recorded concurrently from EEG and functional MRI, using the Simultaneous Imaging for Tomographic Electrophysiology (SITE) method. As yet, there is no established means to integrate the analysis of the combined data set. Recognizing that the hemodynamically convolved time-varying EEG spectrum, S, is intrinsically multidimensional in space, frequency, and time motivated us to use multiway Partial Least-Squares (N-PLS) analysis to decompose EEG (independent variable) and fMRI (dependent variable) data uniquely as a sum of "atoms". Each EEG atom is the outer product of spatial, spectral, and temporal signatures and each fMRI atom the product of spatial and temporal signatures. The decomposition was constrained to maximize the covariance between corresponding temporal signatures of the EEG and fMRI. On all data sets, three components whose spectral peaks were in the theta, alpha, and gamma bands appeared; only the alpha atom had a significant temporal correlation with the fMRI signal. The spatial distribution of the alpha-band atom included parieto-occipital cortex, thalamus, and insula, and corresponded closely to that reported by Goldman et al. [NeuroReport 13(18) (2002) 2487] using a more conventional analysis. The source reconstruction from EEG spatial signature showed only the parieto-occipital sources. We interpret these results to indicate that some electrical sources may be intrinsically invisible to scalp EEG, yet may be revealed through conjoint analysis of EEG and fMRI data. These results may also expose brain regions that participate in the control of brain rhythms but may not themselves be generators. As of yet, no single neuroimaging method offers the optimal combination of spatial and temporal resolution; fusing fMRI and EEG meaningfully extends the spatio-temporal resolution and sensitivity of each method.

Brain↗
PubMed2004

Current concepts in the treatment of distal radial fractures.

Surgical indications for the treatment of distal radial fractures are evolving. It is important to identify the various articular fragments and their significance to facilitate optimal surgical treatment of these fragments from the standpoint of both internal and external fixation. New techniques in the visualization and stabilization of the articular surface and the treatment of defects in the metaphysis, including the use of cement to buttress the articular surface, have been brought to the forefront. A treatment algorithm for associated injuries to the distal radioulnar joint is also helpful.

Algorithms↗
PubMed2003

Preiser's disease: identification of two patterns.

PURPOSE: A large series of patients with Preiser's disease was reviewed to compare 2 potentially different categories of this disorder: complete versus partial vascular impairment of the scaphoid bone as determined by magnetic resonance imaging (MRI). METHODS: Nineteen patients with Preiser's disease were identified retrospectively from 2 institutions. Using MRI criteria, 2 disease patterns were identified: diffuse necrosis and/or ischemia of the scaphoid (type 1 disease, 11 cases) and segmental vascular impairment of the scaphoid (type 2 disease, 8 cases). Risk factors for osteonecrosis, treatment methods, and serial radiographs were reviewed in all cases. Sixteen patients were examined for the purpose of this study at an average follow-up of 25 months. RESULTS: MRI signal changes of necrosis and/or ischemia involved 100% of the scaphoid in type 1 cases and on average approximately 42% in type 2 cases (range, 33% to 66%). In type 1 cases, regardless of the treatment used, the scaphoid typically fragmented and collapsed. In type 2 cases, scaphoid architecture was altered minimally after similar treatment methods. A history of wrist trauma was significantly more common in type 2 cases, and the results of treatment were generally better in this group of patients (mean Mayo modified wrist scores, 86 vs 58 points). CONCLUSIONS: This study supports the concept of 2 patterns of scaphoid involvement in Preiser's disease. Type 1 cases are characterized by MRI signal changes of necrosis and/or ischemia involving the entire scaphoid bone. Patients in this group have a propensity for scaphoid deterioration. Type 2 cases have MRI signal changes involving only part of the scaphoid. These patients commonly report a history of wrist trauma, show fewer tendencies toward scaphoid fragmentation, and may have a more favorable clinical outcome.

Adult↗
PubMed2003

The Fibonacci sequence: relationship to the human hand.

PURPOSE: The motion path of the digits follows the path of an equiangular spiral in which a constant angle is formed by all radial vectors along the curve. This implies that the lengths of the metacarpals, proximal, middle, and distal phalanges approximate a Fibonacci sequence in which the ratio of any 2 consecutive numbers approaches the number 1.61803 (phi). This study tested the hypothesis that the metacarpal and phalangeal bone lengths follow the Fibonacci relationship. METHODS: Standardized x-rays were taken of the hands of 100 healthy volunteers. The proximal phalanx length was subtracted from the sum of the lengths of the middle and distal phalanges and the metacarpal length was subtracted from the sum of the lengths of the middle and proximal phalanges. Confidence intervals for the quotients of the measured lengths of the adjacent bones of the hand also were used for statistical analysis. RESULTS: Only 1 of 12 bone length ratios contained the ratio phi in the 95% confidence interval, that of the small finger metacarpal and proximal phalanx. The largest variability was seen in the small finger phalangeal relationships. CONCLUSION: The application of the Fibonacci sequence to the anatomy of the human hand, although previously accepted, is a relationship that is not supported mathematically. The difference between individual bone lengths as measured at the joint line and the center of rotation of the joints may explain our finding.

Bone and Bones↗
PubMed2003

Partial olecranon excision: the relationship between triceps insertion site and extension strength of the elbow.

PURPOSE: Partial excision with triceps reattachment is an accepted method for treating comminuted fractures of the olecranon. The currently recommended site for reattachment is along the articular margin of the remaining olecranon process. With computer models suggesting that this may lead to weakness of elbow extension, this study was performed to evaluate different sites for triceps reattachment with respect to extension strength of the elbow. METHOD: Ten fresh frozen human cadavers were potted and the elbow placed in varying degrees of flexion (45 degrees, 90 degrees, and 135 degrees ). Incremental loads were applied to the triceps mechanism and the force generated was recorded using an Instron materials testing machine (Instron Corp., Canton, MA). A 50% olecranon excision was then performed, simulating a comminuted olecranon fracture. The triceps tendon was attached either anteriorly along the articular margin or posteriorly along the cortical margin. All specimens were tested at both insertion sites in random order. RESULTS: A significant decrease in extension strength was observed between intact specimens and anterior attachment of the triceps tendon at all angles of elbow flexion. A decrease was only observed with posterior reattachment at 90 degrees. Posterior reattachment provided greater extensor strength than anterior attachment, with greatest differences seen at increasing positions of elbow extension. CONCLUSIONS: Although anterior reattachment of the triceps tendon after partial excision of the olecranon is currently recommended by some, this results in diminished strength of the triceps mechanism. A greater mechanical advantage with increased strength is provided by a more posterior reattachment using the technique described. These differences are greatest at increasing positions of elbow extension where triceps strength is more functionally important.

Biomechanical Phenomena↗
PubMed2003

Comparison of multiple sclerosis lesions at 1.5 and 3.0 Tesla.

OBJECTIVE: To evaluate the relative sensitivity of MR scanning for multiple sclerosis (MS) at 1.5 Tesla (T) and 3.0 T using identical acquisition conditions, as is typical of multicenter clinical trials. METHODS: Twenty-five subjects with MS were scanned at 1.5 T and 3.0 T using fast spin echo, and T(1)-weighted SPGR with and without gadolinium contrast injections. Image data, blinded to field strength, were analyzed using automated segmentation and lesion counting. RESULTS: Relative to scanning at 1.5 T, the 3.0 T scans showed a 21% increase in the number of detected contrast enhancing lesions, a 30% increase in enhancing lesion volume and a 10% increase in total lesion volume. DISCUSSION: The improved detection ability using high-field MR imaging is prominent even when sequence parameters are optimized around the midfield units. Multicenter trials using both 1.5 T and 3.0 T instruments may be affected by these sensitivity differences.

Adolescent↗
PubMed2003

The assessment and management of the stiff elbow.

Posttraumatic loss of elbow motion can cause substantial disability, limiting the ability to put one's hand in the volume of a sphere in space. Although a number of conditions can lead to loss of motion, a greater understanding of the functional anatomy of the elbow has led to advances in surgical management. Elbow stiffness has been classified in a number of ways, but the consistent feature is capsular contracture. Treatment of the stiff elbow begins with clinical evaluation of elbow stiffness and identification of indications for surgical intervention. Techniques of open and arthroscopic elbow contracture release are evolving. Assessment and management of elbow contracture associated with heterotopic ossification, and treatment of distal humerus nonunion should be done early to restore elbow motion.

Arthroscopy↗
PubMed2003

Difficult elbow fractures: pearls and pitfalls.

Complex elbow fractures are exceedingly challenging to treat. Treatment of severe distal humeral fractures fails because of either displacement or nonunion at the supracondylar level or stiffness resulting from prolonged immobilization. Coronal shear fractures of the capitellum and trochlea are difficult to repair and may require extensile exposure. Olecranon fracture-dislocations are complex fractures of the olecranon associated with subluxation or dislocation of the radial head and/or the coronoid process. The radioulnar relationship usually is preserved in anterior but disrupted in posterior fracture-dislocations. A skeletal distractor can be useful in facilitating reduction. Coronoid fractures can be classified according to whether the fracture involves the tip, the anteromedial facet, or the base (body) of the coronoid. Anteromedial coronoid fractures are actually varus posteromedial rotatory fracture subluxations and are often serious injuries. These patterns of injury predict associated injuries and instability as well as surgical approach and treatment. The radial head is the bone most commonly fractured in the adult elbow. If the coronoid is fractured, the radial head becomes a critical factor in elbow stability. Its role becomes increasingly important as other soft-tissue and bony constraints are compromised. Articular injury to the radial head is commonly more severe than noted on plain radiographs. Fracture fragments are often anterior. Implants applied to the surface of the radial head must be placed in a safe zone.

Fractures, Bone↗
PubMed2002

Simultaneous EEG and fMRI of the alpha rhythm.

The alpha rhythm in the EEG is 8-12 Hz activity present when a subject is awake with eyes closed. In this study, we used simultaneous EEG and fMRI to make maps of regions whose MRI signal changed reliably with modulation in posterior alpha activity. We scanned 11 subjects as they rested with eyes closed. We found that increased alpha power was correlated with decreased MRI signal in multiple regions of occipital, superior temporal, inferior frontal, and cingulate cortex, and with increased signal in the thalamus and insula. These results are consistent with animal experiments and point to the alpha rhythm as an index of cortical inactivity that may be generated in part by the thalamus. These results also may have important implications for interpretation of resting baseline in fMRI studies.

Adult↗
PubMed2002

Inhibition of medullary thyroid carcinoma cell proliferation and RET phosphorylation by tyrosine kinase inhibitors.

BACKGROUND: Most medullary thyroid carcinomas (MTCs) result from gain-of-function mutations in the RET proto-oncogene, which encodes a transmembrane tyrosine kinase receptor. Systemic therapies have not been effective in treating this disease. We evaluated the effects of 3 tyrosine kinase inhibitors (TKIs) on MTC cell growth and RET tyrosine kinase activity by using an in vitro model. METHODS: An MTC cell line (TT cells, RETc634 mutant) cultured in RPMI medium was exposed to varying concentrations of STI571, genistein, or allyl-geldanamycin with controls (no TKI) for 3 to 48 hours. Cellular protein was analyzed by immunoprecipitated Western blot analysis probing with a monoclonal antiphosphotyrosine antibody. Cell proliferation was determined by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) and 5-bromo-2'-deoxyuridine (BrdU) assays. RESULTS: RET phosphorylation was inhibited at 24 hours of exposure to 5 to 20 micromol/L STI571 and 48 hours of exposure to genistein (200 micromol/L) and allyl-geldanamycin (6 micromol/L). RET protein was detected in equal concentrations in all experimental conditions. MTT and BrdU assays demonstrated a dose-dependent decrease in TT cell proliferation with exposure to the 3 TKIs. CONCLUSIONS: These TKIs selectively inhibit cell growth and RET tyrosine kinase activity of MTC cells in vitro in a dose manner. This study suggests the use of TKIs in human trials as a systemic therapy for MTC.

Benzamides↗
PubMed2002

Recruitment of anterior dorsolateral prefrontal cortex in human reasoning: a parametric study of relational complexity.

Reasoning and problem solving depend on the ability to represent and integrate complex relationships among stimuli. For example, deciding whether an animal is dangerous requires integrating information about the type of animal, its size, its distance from oneself, and one's proximity to shelter. Relational complexity increases with the number of such interdependent elements that must be simultaneously considered to solve a problem. We used functional magnetic resonance imaging to identify brain regions that respond selectively in processing high levels of relational complexity. Performance on nonverbal reasoning problems in which relational complexity was varied parametrically was compared with performance on control problems in which relational complexity was held constant while difficulty was manipulated by adding distractor forms to the problems. Increasing complexity and adding distractors both led to increased activation in parietal and in dorsolateral prefrontal cortex, with high levels of relational complexity selectively activating anterior left prefrontal cortex. Our data provide evidence that brain regions specific to integrating complex relations among stimuli are distinct from those involved in coping with general task difficulty and with working-memory demands.

Adult↗
PubMed2002

Gastrointestinal manifestations of multiple endocrine neoplasia type 2.

OBJECTIVE: To determine the clinical features, natural history, and role of surgery for gastrointestinal manifestations of the multiple endocrine neoplasia type 2 (MEN 2) syndromes. SUMMARY BACKGROUND DATA: The MEN 2 syndromes are characterized by medullary thyroid carcinoma and other endocrinopathies. In addition, some patients with MEN 2A develop Hirschsprung's disease (HD), and all patients with MEN 2B have intestinal neuromas and megacolon that can cause significant gastrointestinal problems. METHODS: From 83 families with MEN 2A, eight patients with HD were identified (MEN 2A-HD). These and all patients with MEN 2B followed at the authors' institution (n = 53) were sent questionnaires to describe the onset and type of gastrointestinal symptoms and treatment they had before the diagnosis of MEN 2. Records of all patients responding were reviewed, including radiographic imaging, histology, surgical records, and genetic testing. RESULTS: Thirty-six of the 61 patients (59%) responded (MEN 2A = 8, MEN 2B = 28) to the questionnaires. All patients with MEN 2A-HD were operated on for HD 2 to 63 years before being diagnosed with MEN 2. All patients responding were underweight as infants and had symptoms of abdominal pain, distention, and constipation. Eighty-eight percent had hematochezia, 63% had emesis, and 33% had intermittent diarrhea before surgery. All patients with MEN 2A-HD had rectal biopsies with a diverting colostomy as the initial surgical procedure. This was followed by a colostomy takedown and pull-through procedure at a later interval. Ninety-three percent of patients with MEN 2B had gastrointestinal symptoms 1 to 24 years before the diagnosis of MEN 2. Symptoms included flatulence (86%), abdominal distention or being underweight as a child (64%), abdominal pain (54%), constipation or diarrhea (43%), difficulty swallowing (39%), and vomiting (14%). Seventy-one percent of patients with MEN-2B with gastrointestinal symptoms had radiographic imaging, 32% were admitted to the hospital, and 29% underwent surgery. CONCLUSIONS: Patients with MEN 2A-HD had a typical HD presentation and always required surgery. Patients with MEN 2B have significant gastrointestinal symptoms, but less than a third had surgical intervention. Understanding the clinical course and differences in these patients will improve clinical management.

Adolescent↗