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Biomedical subjects

J B Carr

Publications and source records attributed to J B Carr.

At least 19 recordsLinked to original sources
PubMed1997

Internal fixation of experimental intraarticular calcaneal fractures: a biomechanical analysis of two fixation methods.

OBJECTIVE: To evaluate and compare the mechanical stability of two different fixation techniques on experimentally induced calcaneus fractures. METHODS: Thirteen fresh frozen cadaver lower limbs had intraarticular calcaneal fractures produced with an impact loading device. Internal fixation was then performed through lateral and medial approaches using 3.5-mm interfragmentary screws fixed to the posterior facet. Next, either a five-hole 1/3 tubular or five-hole reconstruction plate was placed on the lateral cortex. Radiographs were obtained to confirm reduction. The foot was then cyclically loaded for 500 cycles with a compressive load of 98 N, followed by loading to failure. RESULTS: The displacement at the posterior facet fracture line between the loaded and unloaded foot at the 500th cycle was 0.30 +/- 0.08 mm and 0.39 +/- 0.18 mm for the tubular and reconstruction plates, respectively. These displacements were not statistically significant (Student's t test p > 0.3). The load and displacement at failure for the tubular plate were 2021 +/- 1050 N and 6.10 +/- 1.75 mm, respectively. Those for the reconstruction plate were 1923 +/- 697 N and 4.57 +/- 1.32 mm (p > 0.09). CONCLUSION: This study supports the mechanical viability of using less prominent plates for the fixation of intra-articular calcaneal fractures.

Aged↗
PubMed1996

Repeated oral benzene exposure alters enzymes involved in benzene metabolism.

Benzene is a known carcinogen and hematopoietic toxin in humans and experimental animals. The effect of acute, high-dose exposure to benzene on hepatic bioactivation and detoxication enzymes has been defined, while little is known about the effect of repeated, low-dose benzene exposure on these enzymes. Our objective was to determine whether repeated, oral benzene exposure alters enzymes involved in benzene metabolism. Specifically, we were concerned with cytochrome P-450-2E1, a bioactivation enzyme, and glutathione transferase and aldehyde dehydrogenase, two detoxifying enzymes. Female CD-1 mice were treated by gavage for 3 wk with benzene doses of 5 mg/kg (0.064 mmol/kg) or 50 mg/kg (0.646 mmol/kg) in corn oil. These doses of benzene produced 0.048 and 0.236 mumol muconic acid/d, respectively. We found that repeated exposure to 50 mg benzene/kg/d decreased P-450-2E1 activity by 34% and induced glutathione transferase activity by 30% without affecting aldehyde dehydrogenase activity. These changes in enzyme activities may serve a protective role against repeated exposure to benzene.

Administration, Oral↗
PubMed1996

Biomechanics of rigid tibial nail insertion sites.

The use of a very proximal insertion site for rigid intramedullary nailing was evaluated in a biomechanical study. The purpose of this study was to compare the bursting strains generated in a proximal tibia fracture fragment during rigid nailing, using the recommended insertion sites versus a more proximal site just anterior to the tibial plateau in the midline. Proximal one-third tibia fractures were created in 12 pairs of fresh cadaver specimens. Strain gauges were applied to the medial and lateral cortices of the proximal fragments. Lottes nails, Grosse-Kempf nails, and unreamed Russell-Taylor nails were inserted in four successive pairs of specimens. In each pair, one side used the recommended starting point, and the other side used the proximal insertion site. The strain was recorded at successive 2- to 4-cm depth intervals during nail insertion. In the Lottes group, much larger bursting strains were generated in the lateral cortex when using a distal starting point (P < 0.05). In the unreamed Russell-Taylor group, the anteromedial surface strains were significantly increased using a distal starting point (P < 0.05). The Grosse-Kempf group showed no significant difference in strains associated with any insertion point during tibial intramedullary nailing.

Adult↗
PubMed1995

Increased endobiotic fatty acid methyl esters following exposure to methanol.

Human exposure to methanol is likely to increase in the future due to its proposed use as an alternate automobile fuel. Since alcohols are known to esterify the fatty acids in the body and some of those esterified esters are toxic, we studied the formation of fatty acid esters of methanol in Long-Evans male rats given a single oral dose of 3.5 g/kg body weight of methanol in saline. Animals given an equal volume of saline served as control. Three rats were euthanized at 1, 3, 6, 12 and 24 hr following the treatment. Fatty acid methyl esters, extracted from whole blood, liver, pancreas, and brown fat were separated by thin-layer chromatography and quantitated by gas chromatography (GC). Their identity was then confirmed by GC-mass spectrometry. Average levels as high as 596, 5293, 2239, 1106, 9665, 7728, 562, and 2792 micrograms/g (wet weight basis) of 14:0, 16:0, 16:1, 18:0, 18:1, 18:2, 18:3, and 20:4 fatty acid methyl esters, respectively, were found in the pancreas of methanol-treated rats. The average concentration of total fatty acid methyl esters was computed to be 4513, 29594, 22871, 18956, 17014, and 9702 micrograms/g in the pancreas compared to 1.9, 25.4, 36.8, 18.5, 18.9, and 14.2 micrograms/g in the liver at 0, 1, 3, 6, 12, and 24 hr, respectively, following methanol exposure. On dry lipid weight basis, the levels were significantly higher again in pancreas followed by brown fat and liver. In whole blood, only low levels of 16:0, 18:0, and 20:4 fatty acid methyl esters could be detected at all time points. The highest concentration of total fatty acid methyl esters in the pancreas, liver, and brown fat was detected at 1, 3, and 24 hr, respectively. Most of the fatty acid methyl esters found in the liver and pancreas decreased after 6 hr of methanol exposure. The fatty acid methyl esters of higher concentrations were 16:0 in the whole blood, 18:0, 18:1, 18:2, and 20:4 in liver, 18:1, and 18:2 in pancreas and 16:0, 18:1, and 18:2 in brown fat. These fatty acid methyl esters were also detected in the tissues of control rats indicating their endogenous formation. Significant increase in methylation of the fatty acids during methanol exposure, as found in this study, may serve as a defense mechanism for preventing available methanol from oxidative metabolism to render toxicity. However, the biological significance of these fatty acid methyl esters is yet to be understood.

Adipose Tissue, Brown↗
PubMed1995

Pathophysiology of spinal cord injury. Recovery after immediate and delayed decompression.

We evaluated the effect of the timing of decompression of the spinal cord after compression of 50 per cent of the diameter of the spinal cord at the fourth lumbar level in thirty purebred dogs. The dogs were divided into five groups of six dogs each on the basis of the duration of the compression. Decompression was performed immediately (Group I), one hour (Group II), six hours (Group III), twenty-four hours (Group IV), or one week (Group V) after the compression. Monitoring of somatosensory evoked potentials, daily neurological examinations, and histological and electron microscopic studies at the time of the autopsy were performed for all of the dogs. Initially, all of the dogs were paraplegic after the compression of the spinal cord. The dogs that had immediate decompression or decompression after one hour of compression recovered the ability to walk (grades 4 and 5, according to Tarlov's system) as well as control of the bowel and bladder, and the somatosensory evoked potentials improved an average of 85 and 72 per cent, respectively. However, when compression lasted six hours or more, there was no neurological recovery and there was progressive necrosis of the spinal cord. Somatosensory evoked potentials improved 29 per cent in Group III, 26 per cent in Group IV, and 10 per cent in Group V. The percentage of recovery of the somatosensory evoked potentials by six weeks after the decompression was significantly related to the duration of the compression (p < 0.0008).

Animals↗
PubMed1994

Surgical techniques useful in the treatment of complex periarticular fractures of the lower extremity.

Treatment of complex periarticular fractures of the lower extremity is guided by the principle of soft-tissue preservation. A skin incision through the subcutaneous tissue to incise the periosteum, followed by judicious application of implants will incur the least amount of iatrogenic damage. The concept of "sufficient stability" can replace the need for "rigid fixation" in many instances. Operative treatment should be considered a complementary extension to the well-founded principles of nonoperative treatment rather than the antithesis. In the final analysis, the approach of a biologist or gardener will yield better results than a strictly mechanical or saw bone laboratory approach.

Ankle Injuries↗
PubMed1994

Surgical treatment of the intra-articular calcaneus fracture.

The acute displaced intra-articular calcaneus fracture should be approached on a rational basis. Minimally displaced fractures are best treated with early motion and delayed bearing of weight. Reconstructible, displaced fractures are probably best treated with exact open reduction and internal fixation, assuming contraindications such as poor skin condition or underlying disease are not present. The severely displaced, Sanders-type IV fractures remain a dilemma, and these may demonstrate a role for primary fusion in select instances. If one chooses to treat a calcaneus fracture surgically, it should be recognized that the result will be related to the exactness of the reduction. This surgery is very challenging, with an arduous learning curve. Importantly, if one cannot obtain an anatomic reduction, the patient may have been better off treated nonoperatively.

Arthroplasty↗
PubMed1993

Fracture blisters: clinical and pathological aspects.

Fracture blisters are tense vesicles or bullae that arise on markedly swollen skin directly overlying a fracture. There is very little objective data in the literature detailing their characteristics and management. All fracture blisters that occurred over a 3 1/2-year period were studied retrospectively at four hospitals, of which three were level I trauma centers. A total of 53 blisters developed in 51 patients. They occurred in characteristic locations along the human musculoskeleton, most commonly overlying the tibia, ankle, and elbow. They arose within 24-48 h of acute injury in most instances. The timing of surgical intervention affected the occurrence of fracture blisters. Those patients with acute fractures who underwent open reduction internal fixation (ORIF) within 24 h of injury had the lowest incidence of fracture blisters (2.0%) compared with those delayed for > 24 h (8.0%) (p < 0.001). In those patients with fracture blisters present at time of surgery, patient care was affected in 10 of 13 cases (71%). Two of these were major complications occurring as postoperative wound infections. Other management problems consisted of delaying surgery, and changing in the operative plan. There were no adverse affects on patient care when the fracture blister developed postoperatively. Twenty-one fractures with blisters were treated by closed means, with the presence of fractures blisters delaying closed reduction and casting in two. Biopsy examination of 15 blisters supported the clinical impression that fracture blisters are subepidermal vesicles. The blister fluid was found to be a sterile transudate. Microbial evaluation of 11 ruptured fracture blisters demonstrated colonization (primarily with skin pathogens), occurred soon after blister rupture, and continued until reepithelialization.

Adult↗
PubMed1993

A simplified method of total contact casting for diabetic foot ulcers.

A simplified method of total contact casting for diabetic plantar ulcerations is described in which a standard, well-molded short-leg walking cast is applied. Weekly cast changes are performed initially, followed by longer cast change intervals. Either fiberglass or plaster casting tape appears equally efficacious. Healing of all ulcers was demonstrated in 12 patients treated with this technique.

Aged↗
PubMed1993

A comparison of femoral neck fixation with the reconstruction nail versus cancellous screws in anatomic specimens.

Femoral neck fixation techniques were applied to five matched pairs of autopsy specimens to evaluate the fixation of the Russell-Taylor femoral nail in ipsilateral neck and shaft fractures of the femur. Reconstruction nail fixation of the femoral neck was compared with that of three parallel screws. The intact and postfixation femora were subjected to an applied bending moment in 0 degrees, 30 degrees, and 90 degrees of simulated hip flexion. The bending stiffness was determined from the load deformation data for each intact femur and then after the appropriate fixation. The fatigue response of the fixation, presence of osteopenia, degree of fracture reduction, and device alignment showed that the stiffness ratio (fixed to normal) of the nail was greater in most specimens. There was no statistical difference in retained stiffness after cyclic loading between the nail and cancellous screw fixations. The ultimate strength of the nail was 2.5 times the strength of the screw fixation of the femoral neck. Thus, the nail provided biomechanically sound fixation of the femoral neck.

Aged↗
PubMed1993

Mechanism and pathoanatomy of the intraarticular calcaneal fracture.

The mechanism and pathoanatomy of the acute intraarticular calcaneal fracture is produced by axial loading. A combination of shear and compression forces produce two characteristic primary fracture lines. Shearing forces produce a fracture dividing the calcaneus into medial and lateral portions. This fracture line typically splits the posterior facet and can extend anteriorly to involve the anterior and cuboid facets. Compression forces divide the calcaneus into anterior and posterior portions. This fracture line can extend medially to involve the middle facet. Loss of calcaneal height and length are readily explained by this mechanism.

Calcaneus↗