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Biomedical subjects

J C Yuen

Publications and source records attributed to J C Yuen.

At least 19 recordsLinked to original sources
PubMed2001

Sensitivity of damage predictions to tissue level yield properties and apparent loading conditions.

High-resolution finite element models of trabecular bone failure could be used to augment current techniques for measuring damage in trabecular bone. However, the sensitivity of such models to the assumed tissue yield properties and apparent loading conditions is unknown. The goal of this study was to assess the sensitivity of the amount and mode (tension vs. compression) of tissue level yielding in trabecular bone to these factors. Linear elastic, high-resolution finite element models of nine bovine tibial trabecular bone specimens were used to calculate the fraction of the total tissue volume that exceeded each criterion for apparent level loading to the reported elastic limit in both on-axis and transverse compression and tension, and in shear. Four candidate yield criteria were studied, based on values suggested in the literature. Both the amount and the failure mode of yielded tissue were sensitive to the magnitudes of the tissue yield strains, the degree of tension-compression asymmetry of the yield criterion, and the applied apparent loads. The amount of yielded tissue was most sensitive to the orientation of the applied apparent loading, with the most tissue yielding for loading along the principal trabecular orientation and the least for loading perpendicular to it, regardless of the assumed tissue level yield criterion. Small changes in the magnitudes and the degree of asymmetry of the tissue yield criterion resulted in much larger changes in the amount of yielded tissue in the model. The results indicate that damage predictions based on high-resolution finite element models are highly sensitive to the assumed tissue yield properties. As such, good estimates of these values are needed before high-resolution finite element models can be applied to the study of trabecular bone damage. Regardless of the assumed tissue yield properties, the amount and type of damage that occurs in trabecular bone depends on the relative orientations of the applied apparent loads to the trabecular architecture, and this parameter should be controlled for both experimental and computational damage studies.

Animals↗
PubMed2001

The accuracy of SM-HCV rapid test for the detection of antibody to hepatitis C virus.

OBJECTIVE: Conventional tests for antibody to hepatitis C virus (HCV) require considerable time before results are available. The aim of this study is to examine the accuracy of a new quick test (SM-HCV Rapid Test) for the detection of antibody to hepatitis C virus with reference to the well-established third generation enzyme immunoblot assay (EIA-3; Abbott Laboratories, Chicago, IL). METHODS: A total of 290 subjects (100 patients with chronic hepatitis C infections, 95 patients with other chronic liver diseases, 95 healthy subjects) were recruited. Thirty microliters of serum was tested for anti-HCV by SM-HCV Rapid Test according to the manufacturer's instruction. Liver function tests and serum HCV RNA by polymerase chain reaction (PCR) were measured. RESULTS: In the 100 patients positive for anti-HCV by EIA-3, 98 of these patients were also positive for anti-HCV by SM-HCV Rapid Test. In the 95 patients with other chronic liver diseases, 94 samples were negative for anti-HCV by both EIA-3 and SM-HCV Rapid Test. The remaining one patient was positive for anti-HCV by the EIA-3 but negative by the SM-HCV Rapid Test. In the 95 controls, which were negative for anti-HCV by EIA-3, all were also negative for anti-HCV by SM-HCV Rapid Test and HCV RNA by PCR. Using EIA-3 as the gold standard screening test for anti-HCV, the sensitivity and the specificity of SM-HCV Rapid Test were 98% and 100%, respectively. The positive predictive value and negative predictive value of SM-HCV Rapid Test were 100% and 97.9%, respectively. CONCLUSIONS: SM-HCV Rapid Test is a reliable test with high sensitivity and specificity. The anti-HCV result can be available within a very short period of time. It is a useful screening test for anti-HCV.

Adolescent↗
PubMed2000

High-resolution finite element models with tissue strength asymmetry accurately predict failure of trabecular bone.

The ability to predict trabecular failure using microstructure-based computational models would greatly facilitate study of trabecular structure-function relations, multiaxial strength, and tissue remodeling. We hypothesized that high-resolution finite element models of trabecular bone that include cortical-like strength asymmetry at the tissue level, could predict apparent level failure of trabecular bone for multiple loading modes. A bilinear constitutive model with asymmetric tissue yield strains in tension and compression was applied to simulate failure in high-resolution finite element models of seven bovine tibial specimens. Tissue modulus was reduced by 95% when tissue principal strains exceeded the tissue yield strains. Linear models were first calibrated for effective tissue modulus against specimen-specific experimental measures of apparent modulus, producing effective tissue moduli of (mean+/-S.D.) 18.7+/-3.4GPa. Next, a parameter study was performed on a single specimen to estimate the tissue level tensile and compressive yield strains. These values, 0.60% strain in tension and 1.01% strain in compression, were then used in non-linear analyses of all seven specimens to predict failure for apparent tensile, compressive, and shear loading. When compared to apparent yield properties previously measured for the same type of bone, the model predictions of both the stresses and strains at failure were not statistically different for any loading case (p>0.15). Use of symmetric tissue strengths could not match the experimental data. These findings establish that, once effective tissue modulus is calibrated and uniform but asymmetric tissue failure strains are used, the resulting models can capture the apparent strength behavior to an outstanding level of accuracy. As such, these computational models have reached a level of fidelity that qualifies them as surrogates for destructive mechanical testing of real specimens.

Animals↗
PubMed2000

Distinguishing laser Doppler flowmetric responses between arterial and venous obstructions in flaps.

This study emphasizes the differences in laser Doppler flowmetric responses between arterial and venous obstruction of flaps, by using an experimental model and a clinical review. Monitoring free flaps in the early postoperative period is valuable in the salvage of failing flaps. When combined with clinical observation, the laser Doppler flowmeter can provide the surgeon with an early indication of impending flap failure, which enhances the success rate of flap salvage. Understanding the difference in laser Doppler flowmetric response between venous and arterial occlusion allows for improved interpretation of the perfusion data. The authors monitored 12 epigastric skin island flaps in six male Sprague-Dawley rats, comparing flow data between venous and arterial occlusion. Arterial occlusion consistently led to an abrupt fall below the critical value within 1 min, while venous occlusion consistently showed a more gradual decline over 15 min and beyond. In the authors' clinical series of 13 failing flaps recorded by the laser Doppler, three cases of arterial occlusion showed an abrupt decline in flow values, while 10 cases of venous obstruction showed a gradual decline to critical value, usually over several hours. When monitoring free flaps using the laser Doppler, it is crucial to pay special attention to any gradual decline in flow values, in order to detect impending flap failure and to expedite reexploration.

Adult↗
PubMed2000

Endovascular treatment of a pseudoaneurysm of a recipient external carotid artery following radiation and free tissue transfer.

Radical resection and reconstruction after preoperative radiation has become routine treatment for patients with certain types and stages of head and neck cancers. When microvascular flap reconstruction is required, the recipient vessels have been subjected to radiation, making them more thrombogenic and friable, thus increasing the risks of postoperative complications. The authors report a patient who received preoperative radiation therapy for rhabdomyosarcoma of the infratemporal fossa and who underwent a radical resection and free rectus musculocutaneous flap reconstruction. The free flap covered the base of the brain from the nasopharynx and closed an intraoral defect. The donor artery was anastomosed end to side to the external carotid artery stump. The patient developed a pseudoaneurysm of the external carotid artery stump 1 month postoperatively, which was treated with endovascular coil embolization without loss of the flap. Percutaneous transcatheter endovascular treatment of pseudoaneurysms that develop after free tissue transfer in head and neck reconstruction has not been reported previously. One month after surgery, endovascular occlusion of the main arterial supply to the flap did not compromise its viability because of collateral revascularization from the peripheral tissue bed, despite the patient's history of radiation.

Adolescent↗
PubMed2000

Monitoring free flaps using the laser Doppler flowmeter: five-year experience.

Over a 5-year period, 232 microvascular composite-tissue transfers to the head and neck, trunk, and extremities were monitored using the laser Doppler flowmeter. Thirteen free flaps (5.6 percent) developed vascular complications, all within 4 days after surgery. The laser Doppler flowmeter detected vascular compromise in all cases with no false positives or negatives. Failure to monitor the flap according to protocol by nursing staff occurred in one patient, which led to a delay in detection of venous compromise and subsequent flap loss. The salvage rate was 69.2 percent, leading to an overall flap viability of 98.3 percent. Our series of free-flap monitoring using the laser Doppler flowmeter is the largest reported to date. Review of the English literature shows consistent support by numerous clinical series for the use of the laser Doppler as a valuable postoperative monitor after free-flap transfers.

Adolescent↗
PubMed1999

Convergence behavior of high-resolution finite element models of trabecular bone.

The convergence behavior of finite element models depends on the size of elements used, the element polynomial order, and on the complexity of the applied loads. For high-resolution models of trabecular bone, changes in architecture and density may also be important. The goal of this study was to investigate the influence of these factors on the convergence behavior of high-resolution models of trabecular bone. Two human vertebral and two bovine tibial trabecular bone specimens were modeled at four resolutions ranging from 20 to 80 microns and subjected to both compressive and shear loading. Results indicated that convergence behavior depended on both loading mode (axial versus shear) and volume fraction of the specimen. Compared to the 20 microns resolution, the differences in apparent Young's modulus at 40 microns resolution were less than 5 percent for all specimens, and for apparent shear modulus were less than 7 percent. By contrast, differences at 80 microns resolution in apparent modulus were up to 41 percent, depending on the specimen tested and loading mode. Overall, differences in apparent properties were always less than 10 percent when the ratio of mean trabecular thickness to element size was greater than four. Use of higher order elements did not improve the results. Tissue level parameters such as maximum principal strain did not converge. Tissue level strains converged when considered relative to a threshold value, but only if the strains were evaluated at Gauss points rather than element centroids. These findings indicate that good convergence can be obtained with this modeling technique, although element size should be chosen based on factors such as loading mode, mean trabecular thickness, and the particular output parameter of interest.

Adult↗
PubMed1999

Microsurgical flaps for limb salvage in children.

We evaluated the results of microsurgical flaps for wound coverage in limb salvage cases at Arkansas Children's Hospital. Ages ranged from one to 18 years with a mean of 7.7 years. Sixteen children with soft tissue defect in 18 limbs were reconstructed with 19 free tissue transfer. Only one out of 19 free flaps failed, which necessitated a second free flap, giving an overall initial flap success rate of 95%. One flap developed superficial muscle necrosis, requiring debridement followed staged skin graft. All limbs were successfully salvaged. Our series confirms that microsurgical flap surgery is safe and effective in children, with limb salvage approaching 100 percent.

Adolescent↗
PubMed1998

Staged sequential reconstruction of a total lower lip, chin, and anterior mandibular defect.

The combination of a total lower lip, chin, and anterior mandibular defect following cancer resection is an extremely complex problem that requires a sequence of operations to optimize functional and aesthetic results. One patient is presented in whom the defect was reconstructed with a free fibular flap followed by a series of ancillary procedures using both modern and traditional techniques. At the time of tumor ablation, the through-and-through oromandibular defect was reconstructed with a fibular osteocutaneous flap. The lower lip and gingivolabial sulcus was reconstructed later with a tongue flap. Tissue expansion was subsequently used to replace the fibular skin with expanded submental hair-bearing skin. A polyethylene implant was added later to the fibular bone for chin augmentation. Subsequently the lower lip was supported with a tendinous graft suspended to the anterior masseter bilaterally. Lastly, the vermilion border was elevated by removing a rim of the tongue flap and covering the secondary wound with a full-thickness skin graft. At the end of the reconstructive procedures, lip seal and oral aperture were good with no drooling and excellent speech.

Carcinoma, Squamous Cell↗
PubMed1998

Reduced cost of extremity free flap monitoring.

We analyzed the results and cost-effectiveness of our protocol for free flap monitoring in extremity patients. Of 70 consecutive free flaps to the upper and lower extremity that were monitored by laser Doppler flowmeter, 62 were managed on the hospital ward immediately after recovery from general anesthesia. The duration of laser Doppler monitoring was 5 days. Perfusion compromise occurred in three flaps, two of which occurred in the recovery room and were initially detected by the laser Doppler and successfully salvaged by early exploration. The average equipment cost for the use of the laser Doppler flowmeter for 5 days was significantly less than the cost of an intensive care unit bed for a single day. Our experience confirms that monitoring free flaps with laser Doppler is cost-effective and indicates that a specialized care bed after the recovery room is not necessary in routine extremity cases. Since no vascular complication occurred beyond the second postoperative day, this study suggests that the duration of laser Doppler monitoring can be discontinued on the third postoperative day.

Adolescent↗
PubMed1996

A neurovascular island flap for volar-oblique fingertip amputations. Analysis of long-term results.

A neurovascular island flap has been developed to reconstruct volar-oblique fingertip amputations. This study analyzes the data collected on 16 patients who were treated with this flap and had at least 2 years follow-up. The average active/passive range of motion was 54/55 degrees at the DIP joint, 96/98 degrees at the PIP joint, and 83/83 degrees at the MP joint. Twelve out of 16 flaps (75%) had two-point discrimination better than 10 mm. Moderate and severe problems included cold intolerance (six patients), hypersensitivity (three patients), stiffness (three patients), and numbness (two patients). Out of the 16 patients treated with this technique, 14 were satisfied with their surgical outcome. In experienced hands, this technique is a safe and reliable method with which to reconstruct volar-oblique fingertip amputations.

Adult↗
PubMed1996

Double skin paddle fibular flap for a through-and-through oromandibular defect.

The fibular osteocutaneous free flap has become the most versatile method for reconstructing composite defects of the mandible. The complexity of the reconstruction increases substantially when both intraoral and extraoral defects are present, possibly dictating the need for an additional flap. For the smaller through-and-through defects, a single skin island may be sufficient, but may be limited by inadequate reach. Although not routinely necessary, the skin island may be split completely to enhance the effective reach of the second paddle. One patient report is presented for which a moderately sized through-and-through defect of the mandible was reconstructed using a double skin paddle fibular osteocutaneous free flap.

Carcinoma, Squamous Cell↗
PubMed1996

Free flap coverage for knee salvage.

Soft-tissue reconstruction using free flaps was reviewed in 11 consecutive knee wounds complicated by joint exposure or adjacent osteomyelitis and unavailability of adequate local flaps. Ten free muscle flaps and one fasciocutaneous flap were used successfully. Eight limbs presented with wide exposure of the knee joint, including 4 patients with wound infection involving the joint. Three other patients suffered osteomyelitis immediately adjacent to the knee. All knees were successfully salvaged with a single free flap operation, except for one knee that required a second free flap after flap necrosis. Follow-up in nine flaps ranged from 7 weeks to 19 months (mean, 12 months). For patients without preexisting conditions affecting the knee, free flap coverage provided excellent return of knee function. The choice of recipient vessels was determined mainly by the region of the knee requiring coverage. The recipient arteries utilized included the distal superficial femoral artery, anterior tibial artery, popliteal artery, and small arteries, which included the saphenous artery and descending branch of the lateral circumflex femoral artery. The use of small arteries and venae comitantes as recipient vessels increased the effective reach of the free flaps and eliminated the need for vein grafts.

Adolescent↗
PubMed1996

Versatility of the subcuticular purse-string suture in wound closure.

This paper presents a useful extension of the purse-string continuous subcuticular suture technique for management of circular or oval wounds. This strategy can provide primary skin closure in small defects. It can be used in large skin defects, reducing the amount of skin graft required. In large composite defects, it can reduce the size of the flap. The purse-string can be applied to elliptical defects as well as circular ones and can be employed in all regions of the body. The versatility of the subcuticular purse-string suture in wound closure has been demonstrated.

Dermatologic Surgical Procedures↗