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Biomedical subjects

W T Jackson

Publications and source records attributed to W T Jackson.

At least 19 recordsLinked to original sources
PubMed1992

Leukotriene B4 receptor antagonists: the LY255283 series of hydroxyacetophenones.

A series of hydroxyacetophenones was prepared for evaluation as leukotriene B4 (LTB4) receptor antagonists, culminating in 1-[5-ethyl-2-hydroxy-4-[[6-methyl-6-(1H-tetrazol-5- yl)heptyl]oxy]phenyl]ethanone (compound 35, LY255283). Using an assay for inhibition of specific [3H]LTB4 binding to human PMN, we found that substitution of a nonpolar substituent in the 5-position was required for activity. Best activity was realized with hydrogen in the 3-position, hydroxyl in the 2-position, short chain alkyl ketone in the 1-position, and a six- or eight-carbon chain linking the oxygen in the 4-position with an unsaturated terminal function. Compound 35, having an IC50 of 87 nM in the binding assay, was chosen for further preclinical evaluation.

Acetophenones↗
PubMed1992

Effects of tibial rotations on patellar tracking and patello-femoral contact areas.

The object of this study is to determine the effect of tibial rotations on the three-dimensional patello-femoral motions and contact areas during a physiological loading condition, the knee-extension exercise. A commercially available device, the 3-SPACE digitizer and tracker system, was used to collect the motion data, utilizing cadaveric human lower limbs as well as the geometric measurements describing the articular surfaces at the patello-femoral joint. It was found that tibial rotations caused statistically significant differences, at the 0.05 level, in patellar tilt, patellar rotation and patellar medial-lateral shift. It was also found that while the magnitude of the total contact area at a given knee flexion angle did not change significantly with tibial rotations, medial and lateral components of the total contact areas were affected by tibial rotations. Medical femoral contact areas increased with internal tibial rotations at all flexion angles; lateral femoral contact areas increased with external tibial rotations at all flexion angles. This correlates well with the kinematic data since it was found that the patella shifted medially with internal tibial rotations at all flexion angles, and titled more medially near full-extension causing an increase in the medial contact areas and a decrease in the lateral contact areas.

Biomechanical Phenomena↗
PubMed1992

Danger zone of the acetabulum.

The danger zone of the acetabulum is defined by Marvin Tile as that part of the posterior wall and column at the mid-acetabulum lying above the ischial spine. Screws inserted in the danger zone are at risk of violating the hip joint. Unfortunately, this zone is frequently used in the fixation of posterior wall and column fractures. Cadaveric studies were performed analyzing 1-cm cross-sections through the acetabulum for the purpose of studying the anatomical configuration of the danger zone. The plane of the cross-section was perpendicular to the posterior column. Each cross-section had the medial boundary of the acetabulum projected onto the posterior column. The cross-sections were then assembled to form the original acetabulum. By analyzing the projections on the posterior column, the exact configuration of the danger zone was determined. Screws placed at the margin of the danger zone and directed perpendicular to the posterior column violated the hip joint. Through analysis of the cross-sections, safe anatomic pathways were developed for screw placement. Cortical screws (4.5 mm), placed at entry points of 2 cm and 3 cm medial to the lateral acetabular margin and angled medially 45 degrees and 15 degrees, respectively, did not violate the hip joint. The angulation was respective to the perpendicular to the posterior column. In this study, the average width of the posterior column at the mid-acetabular level was 4.8 cm. Computed tomography scan of the acetabulum yielded valuable information regarding screw placement in the posterior column.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetabulum↗
PubMed1992

Anatomical considerations of posterior tibialis tendon entrapment in irreducible lateral subtalar dislocation.

Irreducible lateral subtalar dislocation is associated with posterior tibialis tendon entrapment. Mulroy and Leitner have proposed conflicting theories regarding the exact mechanism of tendon entrapment. Cadaveric analysis of lateral subtalar dislocation supported Leitner's contention that tearing of the flexor retinaculum promotes posterior tibialis tendon entrapment. Retinacular disruption allowed tendon subluxation over the medial malleolus and talar head to the entrapped position. Entrapment of the flexor digitorum longus only occurred in the Leitner model. When the flexor retinaculum and deep posterior compartment fascia were preserved, the muscle failed at the musculotendinous junction. Flexor hallucis longus entrapment could not be produced in either experimental model. Plantarflexion of the great and lesser toes, noted on clinical presentation, is caused by functional lengthening of the route coursed by the flexor digitorum longus and flexor hallucis longus.

Cadaver↗
PubMed1992

A three-dimensional morphometrical study of the distal human femur.

The objective of this paper is to present a method to describe the three-dimensional variations of the geometry of the three portions forming the distal part of the human femur: the medial and lateral femoral condyles and the intercondylar fossa. The contours of equally spaced sagittal slices were digitized on the distal femur to determine its surface topography. Data collection was performed using a digitizer system which utilizes low-frequency, magnetic field technology to determine the position and orientation of a magnetic field sensor in relation to a specified reference frame. The generalized reduced gradient optimization method was used to reconstruct the profile of each slice utilizing two primitives: straight-line segments and circular arcs. The profile of each slice within the medial femoral condyle was reconstructed using two circular arcs: posterior and distal. The profile of each slice within the lateral femoral condyle was reconstructed using three circular arcs: posterior, distal and anterior. Finally, the profile of each slice within the intercondylar fossa was reconstructed using two circular arcs: proximal-posterior and anterior, and a distal-posterior straight-line segment tangent to the proximal-posterior circular arc. Combining the data describing the profiles of the different slices forming the distal femur, the posterior portions of each of the medial and lateral femoral condyles were modelled using parts of spheres having an average radius of 20 mm. The anterior portion of the lateral condyle was approximated to a right cylinder having its circular base parallel to the sagittal plane with an average radius of 26 mm. The anterior portion of the intercondylar fossa was modelled using an oblique cylinder having its circular base parallel to the sagittal plane with an average radius of 22 mm. Furthermore, it is suggested that the distal portion of the lateral femoral condyle could be modelled using parts of two oblique cones while the distal portion of the medial femoral condyle could be modelled using a part of a single oblique cone, all cones having their circular bases parallel to the sagittal plane. It is also suggested that the posterior portion of the intercondylar fossa could be modelled using two oblique cones: a proximal cone having its base parallel to the sagittal plane and a distal cone having its base parallel to the frontal plane.

Femur↗
PubMed1992

Low lumbar burst fractures: comparison between conservative and surgical treatments.

Twenty-two low lumbar burst fractures (L3-L5) were treated, with an average follow up of 56.2 and 39.0 months in the conservative and surgically treated groups, respectively. Twenty patients were available for review; seven were treated conservatively and 13 were stabilized surgically. All patients were evaluated clinically for work status, activity level, residual pain, and subsequent development of neurologic symptoms. Roentgenograms were reviewed for severity of initial fracture, canal compromise, and maintenance of initial correction. In general, neurologically intact patients in both groups returned to similar postinjury employment levels. Persistent back pain was found to be more disabling in the surgically treated group, in which a fusion incorporating four or five lumbar segments was performed. There was no evidence of significant loss of initial reduction, and no patients experienced late neurological compromise in the surgical group. An average follow-up kyphosis of 9.2 degrees and 31% loss of vertebral height were observed in the conservative group, while a follow-up lordosis of 1 degree and 19% loss of vertebral height were observed in the surgical group. Conservative treatment of low lumbar burst fracture is a viable option in neurologically intact patients, but loss of lordosis and vertebral height may persist. Biomechanical and anatomic characteristics of the low lumbar spine differ from the thoracolumbar region and may account for the inherent stability of these injuries. If surgery is chosen, a long fusion with distraction instrumentation should be avoided in the low lumbar spine. A short rigid fixation with pedicular instrumentation may be of greater benefit.

Adolescent↗
PubMed1992

Specific inhibition of leukotriene B4-induced neutrophil activation by LY223982.

LY223982, (E)-5-(3-carboxybenzoyl)-2-((6-(4-methoxyphenyl)-5- hexenyl)oxy)benzenepropanoic acid, is a newly discovered potent inhibitor of specific binding of leukotriene B4 (LTB4) to its receptor on human neutrophils. This study demonstrated that the compound is also a specific antagonist of LTB4-induced neutrophil activation under both in vitro and in vivo conditions. LY223982 was found to be 189-fold more effective in displacing [3H]LTB4 than 35S-N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) from their corresponding receptors on human neutrophils. The concentration inhibiting 50% of response (IC50) for displacement of [3H]LTB4 (13.2 nM) was only 6.8-fold higher than the value for nonradioactive LTB4. The compound inhibited the aggregation of guinea pig neutrophils caused by LTB4 more strongly than FMLP or platelet-activating factor. The IC50 for inhibition of LTB4-induced responses (74 nM) was 93- and > 135-fold lower than the IC50 for inhibition of the corresponding FMLP and platelet-activating factor-induced effects. LY223982 was also a potent antagonist of the aggregation of human neutrophils by LTB4 (IC50, 100 nM). Chemotaxis of human neutrophils induced by LTB4 was only modestly inhibited by the compound (IC50 = 6 microM) but it had even less effect on cell movement caused by FMLP. LY223982 inhibited transient leukopenia induced in rabbits with LTB4 (ED50, 3 mg/kg) but not with FMLP. It had no agonist activity in any of the test systems. In summary, the results indicate that LY223982 is a potent specific antagonist of LTB4-induced neutrophil activation.

Animals↗
PubMed1992

Characterization of the spatial arrangement of the two acid-binding sites on the human neutrophil LTB4 receptor.

A series of lipophilic benzophenone dicarboxylic acids have been shown to be inhibitors of the binding of LTB4 to its receptors on intact human neutrophils (Gapinski et al. (1990). Structure-activity relationships indicated that maximum activity was achieved when an acid group was attached at the meta position of each ring. In this report, the conformation of these inhibitors that binds best to the LTB4 receptor was determined. Inhibition concentration profiles of four rigid xanthone isomers that mimicked the four major conformational states of this type of benzophenone dicarboxylic acid were compared. LY264086, 3-[4-[7-carboxy-3-[decyloxy]-9-oxo-9H-xanthene]]propanoic acid, was the most potent inhibitor. The distance between the two carboxyl groups in this isomer was found to be 9.8 A, implying that the two acid binding sites on the receptor are separated by similar dimensions. Molecular modeling studies with low energy conformers of the xanthone isomers and LTB4 suggested a configuration of the agonist when it is bound to the receptor but did not exclude all other possibilities. These experiments further support the existence of two acid-binding sites on the human neutrophil LTB4 receptor.

Benzophenones↗
PubMed1992

Internal fixation of radial neck fracture in a fracture dislocation of the elbow. A case report.

A 27-year-old manual laborer presented with dislocation of the right elbow, complete separation of the radial head at the neck level, and avulsion of the coronoid process. Closed reduction of the elbow resulted in ulnohumeral instability. As an alternative to silastic implant, the radial head was reduced, internally fixed, and used as a spacer to restore elbow stability. The radial head fracture healed with no sequelae. At two years follow-up examination, the patient had a stable elbow with nearly full range of motion.

Adult↗
PubMed1992

Anatomic considerations of pin placement in the proximal tibia and its relationship to the peroneal nerve.

Peroneal nerve impalement is a recognized complication of percutaneous placement of wires, which is gaining increased usage with the application of the techniques of Ilizarov, Monticelli, and Spinelli. Dissections of the peroneal nerve in the proximal tibia were performed in ten anatomic specimens (20 legs) to define (1) its relationship to palpable landmarks, (2) distribution of major branches to the musculature, and (3) safe zones of placement of percutaneous wires in the proximal tibia. The anterior recurrent tibial nerve was frequently in an area of risk where it courses proximally in the anterior compartment. A safe zone is located anterior to the palpable portion of the fibular head and up to 2 cm distal to the tip of the fibular head.

Humans↗
PubMed1992

Magnetic resonance imaging after pedicular screw fixation of the spine.

Magnetic resonance imaging (MRI) of the thoracolumbar spine is valuable in the diagnosis of acute and chronic spine injuries. It allows evaluation of the nerve roots, spinal cord, and the supporting bony and ligamentous structures. Magnetic resonance imaging can be used to detect sequelae of spinal cord injury and any mechanical impingement on the spinal cord or nerve roots. Pedicular screw fixation of the spine is becoming the procedure of choice for stabilization of the lumbar spine, yet it limits the postoperative use of MRI because of marked imaging artifacts arising from the ferromagnetic properties of the used stainless steel implants. The authors have compared extensive artifacts produced by the stainless steel implants with those produced by titanium implants. Titanium implants produced fewer artifacts in the spinal canal. The use of MRI compatible materials in thoracolumbar spine stabilization would permit detailed examinations by serial MR imaging.

Alloys↗
PubMed1992

Titanium hip implants for improved magnetic resonance and computed tomography examinations.

The value of magnetic resonance imaging (MRI) for assessment of the hip has been demonstrated, particularly in cases of avascular necrosis. Magnetic resonance imaging can be used to provide anatomic evaluation of the femoral head, acetabulum, hip joint, joint fluid, and the surrounding structures. MR examinations of two patients with hip fractures fixed with stainless steel hip implants were compared with nine patients with hip fractures fixed with titanium hip implants, one of which showed avascular necrosis of the femoral head. The titanium implants resulted in less MRI artifacts, allowing for improved depiction of the femoral head and surrounding soft tissue. For this reason titanium fixation devices are recommended as a substitute for stainless steel in the hip joint region in a patient who may need future MR examination.

Bone Nails↗
PubMed1991

Effects of hypotensive anesthesia, nonsteroidal antiinflammatory drugs, and polymethylmethacrylate on bleeding in total hip arthroplasty patients.

One hundred forty patients ranging in age from 26 to 88 years, who had primary total hip arthroplasty (performed by the same surgeon and lateral surgical approach), were analyzed for intraoperative and postoperative blood loss. The factors affecting blood loss, which include bleeding disorders, medications, duration of surgery, the mean intraoperative blood pressure, and use of cement, were all recorded. A significant reduction in the intraoperative blood loss was observed in the group of patients with hypotensive anesthesia (greater than 20 mmHg drop in the mean intraoperative blood pressure using inhalation anesthetics) compared to the group of patients who did not have hypotensive anesthesia. The patients who had been on aspirin or nonsteroidal antiinflammatory drugs prior to surgery had increased intraoperative and postoperative blood loss compared to the patients who did not take such medications. The effect of cementing with methylmethacrylate on bleeding was also observed; the patients with uncemented implants had a greater blood loss after operation than the patients who had cemented prosthetic components.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1991

Anatomic considerations in posterior plating of the cervical spine.

We evaluated the anatomic structures at risk during posterior plating of the cervical spine and outlined a safe technique for screw insertion. Three cadaveric specimens were evaluated anatomically and radiographically. Screws and wires were inserted into the articular masses at different locations and angulations. The relationship of the neurovascular structures to the screws and wires was noted. To avoid injury to the nerve roots, vertebral artery, and spinal cord, the screw should be placed in the center of the articular masses perpendicular to the vertebral plane with 15 degrees lateral angulation.

Bone Plates↗
PubMed1991

Assessment of tibial fracture union by 35-45 degrees internal oblique radiographs.

Thirty-five to 45 degrees internal oblique radiographs were used in the assessment of tibial fracture healing. This view is particularly helpful when routine radiographic examinations (anteroposterior and lateral) are nondiagnostic in assessing tibial fracture healing. The technique was helpful in the diagnosis of four occult nonunions as well as in showing the position of a bone graft when used. The authors recommend this view when a decision about tibial fracture healing cannot be made from routine radiographs. They recommend this view before resorting to tomograms of the tibia.

Fractures, Ununited↗