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Biomedical subjects

W T Jackson

Publications and source records attributed to W T Jackson.

At least 37 records · Page 2Linked to original sources
PubMed1996

Talar neck fractures: anatomic considerations for posterior screw application.

The bony window available for posterior screw placement in the talus and the morphology of the talar neck were studied in 50 dry tali. In addition, 12 cadaver specimens were used to study the posterolateral approach. The bony window was bounded medially by the lateral tubercle of the posterior process of the talus, laterally by the fibular facet, superiorly by the trochlear articular surface, and inferiorly by the posterior calcaneal facet. The average vertical thickness at 2-mm increments was recorded across the talar neck to define the bony mass available for screw insertion. The smallest thickness of the talar neck was at a point 2 mm medial to the lateral border. The thickness progressively increased in a medial direction. The superior talar neck surface was found to have an average width of 18.4 +/- 1.6 mm. The angle formed between the superior and lateral surfaces of the talar neck averaged 29.3 degrees, which would account for the better delineation of the lateral border of the neck under fluoroscopy of the talus with the foot in pronation. The diameter of the screw in relation to the window height should be considered.

Adolescent↗
PubMed1996

Recombinant human secretory phospholipase A2 released thromboxane from guinea pig bronchoalveolar lavage cells: in vitro and ex vivo evaluation of a novel secretory phospholipase A2 inhibitor.

The primary objective of this study was to develop a functional assay that could provide rapid and reliable information on some pharmacologic characteristics of a novel inhibitor of human secretory phospholipase A2 (sPLA2). Guinea pig bronchoalveolar lavage (BAL) fluid, containing predominantly macrophages, eosinophils and epithelial cells, released thromboxane A2, as measured by thromboxane B2, in a concentration-dependent manner on exposure to recombinant human sPLA2 (rh-sPLA2). Similarly, n-formyl-L-methionyl-L-leucyl-L-phenylalanine (n-F-Met-Leu-Phe) or arachidonic acid also released this lipid mediator. Indomethacin, a cyclooxygenase inhibitor, blocked synthesis of thromboxane in response to these agents. p-Bromophenacylbromide-inactivated rh-sPLA2 was substantially less effective than the untreated enzyme in causing release of thromboxane. LY311727 is a potent indole-derived inhibitor of the isolated enzyme (IC50 = 23 nM). Incubation of this agent with BAL cells, just before addition of rh-sPLA2, reduced release of thromboxane with an IC50 = 1.8 x 10(-6) M. Specificity for sPLA2 was demonstrated in that LY311727, unlike indomethacin, did not reduce synthesis and subsequent release of thromboxane A2 in response to arachidonic acid. Using this technique as a basis, we determined whether LY311727 could sufficiently accumulate in lung after i.v. administration to inhibit rh-sPLA2-induced thromboxane A2 release from BAL cells. The compound, given i.v. to guinea pigs 5 min before collecting BAL fluid, produced a dose-dependent inhibition of rh-sPLA2 with an ED50 = 50 mg/kg. Thus, new in vitro and ex vivo assays were developed that permit functional evaluation of novel sPLA2 inhibitors. These techniques should serve as secondary assays for evaluation of human sPLA2 inhibitory activity from a chemical series and in addition provide initial data related to metabolic stability and distribution to the lung.

Animals↗
PubMed1995

Synthetic and structure/activity studies on acid-substituted 2-arylphenols: discovery of 2-[2-propyl-3-[3-[2-ethyl-4-(4-fluorophenyl)-5- hydroxyphenoxy]-propoxy]phenoxy]benzoic acid, a high-affinity leukotriene B4 receptor antagonist.

Structural derivatives of LY255283 have been studied as receptor antagonists of leukotriene B4. Substitution of the 2-hydroxyacetophenone subunit of 1 (LY255283) with a 2-arylphenol group provided entry into several new series that feature various mono- and diacidic core functionality. These new analogues, the subject of a broad structure-activity investigation, displayed significantly increased in vitro and in vivo activity as receptor antagonists of LTB4. A series of diaryl ether carboxylic acids demonstrated especially interesting activity and led to the discovery of compound 43b, 2-[2-propyl-3-[3-[2-ethyl-4-(4- fluorophenyl)-5-hydroxyphenoxy]-propoxy]phenoxy]benzoic acid (LY293111), a 2-arylphenol-substituted diaryl ether carboxylic acid which displayed potent binding to human neutrophils (IC50 = 17 +/- 4.6 nM) and guinea pig lung membranes (IC50 = 6.6 +/- 0.71 nM), inhibition of LTB4-induced expression of the CD11b/CD18 receptor on human neutrophils (IC50 = 3.3 +/- 0.81 nM), and inhibition of LTB4-induced contraction of guinea pig lung parenchyma (pKB = 8.7 +/- 0.16). In vivo, 43b demonstrated potent activity in inhibiting LTB4-induced airway obstruction in the guinea pig when dosed by the oral (ED50 = 0.40 mg/kg) or intravenous (ED50 = 0.014 mg/kg) routes. A specific LTB4 receptor antagonist, 43b had little effect on inhibiting contractions of guinea pig lung parenchyma induced by leukotriene D4 (LTD4), histamine, carbachol, or U46619. Compound 43b has been chosen as a clinical candidate and is currently in phase I studies for a variety of inflammatory diseases.

Airway Obstruction↗
PubMed1995

Anatomic relationships of the cervicothoracic junction.

STUDY DESIGN: This study analyzed the anatomic relationships between bony structures and soft tissues of the cervicothoracic junction. OBJECTIVES: To provide composite reference data for intrasegmental and intersegmental gradients of anatomic variation within the cervical-thoracic junction. SUMMARY OF BACKGROUND DATA: Because the risk of soft tissue damage during posterior spinal stabilization, an understanding of bony and soft tissue changes in the cervicothoracic junction is necessary. METHODS: Three-hundred-twenty-four cross-sectional spinal segments from nine spines were analyzed to characterize cervicothoracic junctional anatomy. RESULTS: There were predictable cranial-to-caudal alterations in both bone and soft tissue anatomy of the cervicothoracic junction. Neural and vascular structures directly anterior to the lateral mass or transverse process and lateral to the pedicle tend to decrease in frequency, whereas measured parameters of the vertebrae increase in size from C5-T3, except for pedicle dimensions that tend to increase at the C7-T1 junction. CONCLUSION: The anatomic changes that occur within the cervicothoracic junction are consistent and predictable, and their recognition should lead to a better appreciation of their clinical implications.

Aged↗
PubMed1995

Morphometric evaluation of the first sacral vertebra and the projection of its pedicle on the posterior aspect of the sacrum.

STUDY DESIGN: This study directly measured the dimensions of the first sacral vertebra based on dry bony specimens. OBJECTIVES: To measure the dimensions of the S1 pedicle, vertebral body, and spinal canal, and determine the projections of the S1 pedicle on the posterior aspect of the sacrum. SUMMARY OF BACKGROUND DATA: Sacral screw fixation remains a challenging clinical problem because of the unique anatomy of the first sacral vertebra. The anatomic data of S1 have rarely been described in the literature. METHODS: Sacrums from 50 carefully prepared bony spines were used. Linear measurements included the dimensions of the vertebral body, spinal canal, and pedicle. Pedicle width was measured in two segments, pedicle zones 1 and 2. Angular measurements of the pedicle relative to the sagittal plane were also included. RESULTS: In pedicle zone 1, the average medial angle of the pedicles was 10.2 degrees for men and 10.7 degrees for women, average width was 10.9 mm for men and 10.4 mm for women, average length of the pedicles was 34.6 mm for men and 34.9 mm for women. In pedicle zone 2, the average medial angle of the pedicles was 39.4 degrees for both men and women, average width was 15.6 mm for men and 14.7 mm for women, average length of the pedicles was 43.7 mm for men, and 41.7 mm for women. The projections of pedicle zones 1 and 2 on the posterior aspect of S1 were determined. CONCLUSIONS: The investigators proposed the concept of pedicle zones 1 and 2. The safer area for S1 pedicle screw insertion was found in pedicle zone 2.

Adult↗
PubMed1995

Response of the lateral meniscus of the dog to wide incision and repair of the meniscotibial ligament.

The effects of extensive incision and reattachment of the coronary ligaments on meniscal healing in the canine were examined. Through an extensile exposure to the lateral tibial plateau, nine mongrel dogs underwent wide incision, reflection, and subsequent reattachment of their meniscotibial ligaments. At intervals of 3, 6, and 9 weeks, three dogs were killed and a gross and microscopic evaluation of their menisci and perimeniscal tissues was performed. At 3 weeks, a small region of the central meniscal periphery was found to be devoid of a vascular network. By 6 weeks, the entire peripheral vasculature had reconstituted. No specimen demonstrated histologic evidence of meniscal necrosis or degeneration. Healing occurred by fibrovascular scar.

Animals↗
PubMed1995

The treatment of tibial nonunion with angular deformity using an Ilizarov device.

Nine patients with nonunion of the tibia associated with angular deformity were treated using the Ilizarov device. Eight of these went on to heal the nonunion and had acceptable correction of the angular deformity. One patient with an atrophic nonunion and severe bone loss received a below knee amputation. The authors recommend the use of circular ring fixation as an alternative in the treatment of selected cases of stiff nonunion of the tibia combined with angular deformity, particularly if there is active infection, prior use of an external fixator, or poor soft tissue coverage.

Adolescent↗
PubMed1995

Coronal fracture of the body of the hamate.

Fractures of the body of the hamate are unusual. Eleven patients with coronal fractures of the hamate bone, all involving dislocation of the hamate-metacarpal joint, are reported. Routine roentgenograms were not helpful in delineating the presence of the injury in five patients; therefore, fracture diagnosis was not initially made in those patients. The average delay in diagnosis of this group was 10 days. A 30-degree pronated view, tomograms, and computed tomography scans may be necessary in the diagnosis of this injury. This fracture was found to be highly unstable. Ten patients underwent surgery for stabilization of their fractures and restoration of the congruity of the hamate-metacarpal joint. Four patients were treated with open reduction and internal fixation of the fracture. Six patients were treated with closed reduction and percutaneous pinning. All patients treated surgically had maintenance of reduction of their joints. One patient was treated with closed reduction and casting; reduction in this case was lost, and the patient developed residual subluxation of the hamate-metacarpal joint.

Adolescent↗
PubMed1995

Metaphyseal nonunion: a diagnostic dilemma.

Twenty-eight patients with metaphyseal nonunion were evaluated retrospectively. Initially, all patients were thought to have healing of their fractures. Mild pain and/or instability with weightbearing or discomfort localized around the hardware were common symptoms of this nonunion; however, substantial pain was not a predominant feature. In the majority of cases, routine roentgenograms were not helpful in establishing the diagnosis. Overlapping hardware made visualization difficult; furthermore, the presence of a callus gave a false impression of fracture healing. Tomograms were done in 13 patients, but were not helpful in four patients. Stress views and examination under fluoroscopy were reliable means of making this diagnosis, particularly around the knee region. It was done, however, only in a few patients. Subtle changes in the position of hardware or the position of the fragments are also an indication of failure of union. The average time from the initial injury to the diagnosis of nonunion was 36 weeks. Five patients whose pain was attributed to the hardware were found to have a nonunion intraoperatively at time of attempted hardware removal. In one patient, the nonunion was diagnosed during a quadricepsplasty. In two patients, the diagnosis was missed a second time following revision of fixation and bone grafting. Diagnosis of metaphyseal nonunion requires a high index of suspicion, because it occurs among all age groups. It is not as rare as previously described and poses many difficulties. The authors recommend the use of additional studies, including tomograms or stress views, oblique to establish difficult diagrams.

Adolescent↗
PubMed1995

Arthroscopy of the subtalar joint: establishing a medial portal.

One of the recently introduced procedures for studying the posterior subtalar joint is subtalar arthroscopy. There is no reference in the literature to the possibility of a medial portal that might be used either for arthroscopic insertion, probing, or instrumental manipulation. The two portals mentioned in the literature are the anterolateral and the posterolateral portals. For evaluating the possibility of establishing a medial portal, six embalmed adult cadaver feet were used to study the anatomical relations to the proposed medial portal. The subtalar joints of another six fresh adult cadaver feet were then arthroscoped, after distraction of the joint, using the anterolateral, posterolateral, and medial portals. Findings indicated that the medial portal gives good visualization of the posterior subtalar joint. Clinical application has not yet been assessed.

Adult↗
PubMed1995

Osteosynthesis of the cervical spine with an anterior plate.

Osteosynthesis with an anterior plate is indicated for stabilization of the cervical spine. It is used for reconstruction of the vertebral body following corpectomy and for cervical instability due to fractures, fracture-dislocations, and post-laminectomy. In these situations, a well-keyed anterior graft or posterior fusion alone may be inadequate to attain stability. The authors retrospectively review 25 cases of osteosynthesis of the cervical spine using the AO H-plate. All the patients were stable enough postoperatively to allow early mobilization with a cervicothoracic orthosis. Average follow up was 31.2 months. All the grafts fused; however, complications occurred in 36% of the cases. The majority of these complications did not affect the long-term clinical result. This method involves potential risks to the spinal cord, esophagus, carotid structures, and laryngeal nerve. It should therefore be used in carefully selected cases.

Adult↗
PubMed1995

Difficulty in removal of the distal locking device of the Brooker-Wills tibial nail.

Complications in removal of the Brooker-Wills tibial nail were encountered in eight patients, and breakage of the distal fins occurred in four of these patients. Although none of the patients experienced residual effects related to removal of the tibial nail, the procedure is associated with potential risks such as infection or nonunion. Three methods of nail removal are described.

Adult↗
PubMed1995

Anatomy of C7 lateral mass and projection of pedicle axis on its posterior aspect.

A specimen study focused on the measurements of C7 lateral mass and pedicle as well as the projection of pedicle axis on the posterior aspect of the lateral mass was done, based on 56 whole clean, dry, well-preserved spines of skeletally mature adults, 32 males and 24 females. Lateral mass widths averaged 11.7 mm. Lateral mass heights averaged 14.8 mm. The average thickness of the lateral mass was 6.8 mm. The average pedicle widths were 6.2 mm, and the average heights were 7.0 mm. Small, but statistically significant differences were found between the averages of the aforementioned dimensions in the male and female groups. The angulation between pedicle axis and the posterior aspect of the lateral mass averaged 107.0 degrees in the transverse plane and 76.2 degrees in the sagittal plane, respectively. Differences in angulations were not significant when compared according to side or sex of group. Distances from the projection point of pedicle axis to a line passing through the mid-line of the transverse process ranged from 2 mm superior to the line to 4.5 mm inferior, with an average 1.2 mm inferior on right side and 0.3 mm inferior on the left. Distances from the pedicular axial projection point to the outer margin of the lateral mass ranged from 0.0 mm to 5.4 mm, with an average 2.4 mm on the right side and 2.9 mm on the left side. Differences of distance related to left or right side were statistically significant, whereas the distances when related to the sex of the group were not.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Vulnerability of the posterior interosseous nerve during proximal radius exposures.

This study describes the anatomy of the posterior interosseous nerve and proposes how to protect it during the different approaches to the proximal radius. Based on the findings presented here, the choice of the approach and the pitfalls that might cause posterior interosseous nerve injury were defined. Three surgical approaches were used on 30 cadaveric upper limbs: modified Henry's anterior approach, Thompson's posterior approach, and a modified Gordon-Boyd's approach. Important anatomic structures were localized, marked, and shown on radiographs. Plates and screws were applied through the different approaches to determine the relationship of the hardware to the posterior interosseous nerve. Measurements were taken between the humeroradial joint, as a reference point, and different important anatomic structures. It was concluded that the anterior approach to the proximal radius is relatively safe and offers the possibility of proximal and distal extension. Caution should be taken while applying screws, however, to avoid posterior interosseous nerve injury. The radius is superficial posteriorly, and many surgeons favor Thompson's approach for exposure of the proximal radius; nonetheless, it carries the risk of posterior interosseous nerve injury with exposure of the most proximal portion of the radius. The modified Gordon-Boyd's approach offers the advantage of exposing both the radius and the ulna, but necessitates excessive muscle stripping.

Bone Plates↗
PubMed1994

Morphometric evaluation of the cervico-thoracic junction. Practical considerations for posterior fixation of the spine.

STUDY DESIGN: Linear and angular measurements were performed on 128 vertebrae (16 spines) from C5 to T5. OBJECTIVES: Vertebrae were studied to characterize vertebral shape and size changes in the cervico-thoracic region. SUMMARY OF BACKGROUND DATA: Analysis of vertebral anatomy has been extensive and well characterized. Regions of transitional anatomy necessitate further study due to the often abrupt changes in anatomic relationships. METHODS: Two observers performed linear and angular measurements including pedicle width, height, and length, as well as pedicle-body, pedicle-lamina, lamina-transverse process, and pedicle-lamina angular measurements. Pedicle axis projection on the posterior aspect of the lamina was also calculated. RESULTS: The mean pedicle width ranged from 7.8 mm (T1) to 4.4 mm (T5). The body-pedicle angle decreased > 4 degrees per level in the transverse plane, from 50 degrees (C5) to 11 degrees (T5). The axial projection of the pedicle changed throughout the region (compared with level above) and was significant for T1. CONCLUSIONS: Because of the complexities of the cervico-thoracic junction, additional characterization increases the knowledge of the anatomic relationships in this region.

Adult↗