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Biomedical subjects

G R Evans

Publications and source records attributed to G R Evans.

At least 37 records · Page 2Linked to original sources
PubMed2000

Reconstruction of large sacral defects following total sacrectomy.

Total sacrectomies for cancer ablation often result in extensive defects that are challenging to reconstruct. In an effort to elucidate the criteria to select the most effective reconstructive options, we reviewed our experience with the management of large sacral wound defects. All patients who had a sacral defect reconstruction after a total sacrectomy at our institution between January of 1993 and August of 1998 were reviewed. The size of the defect, the type of reconstruction, postoperative complications, and functional outcome in each patient were assessed. A total of 27 flaps were performed in 25 patients for sacral defect reconstruction after a total sacrectomy. Diagnoses consisted of chordoma (n = 13), giant cell carcinoma (n = 2), sarcoma (n = 5), rectal adenocarcinoma (n = 4), and radiation induced necrosis (n = 1). The size of sacral defects ranged from 18 to 450 cm2 (mean, 189.8 cm2). Ten patients, including five who had preoperative radiation therapy, underwent transpelvic vertical rectus abdominis myocutaneous (VRAM) flap reconstruction for sacral defects with a mean size of 203.3 cm2. Of these, five patients (50 percent) had complications (four minor wound dehiscences and one seroma). Eight patients, including one who had preoperative radiation therapy, underwent bilateral gluteal advancement flap reconstruction for sacral defects with a mean size of 198.0 cm2. They had no complications. Two patients, both of whom had preoperative radiation therapy, underwent gluteal rotation flap reconstruction for sacral defects of 120 cm2 and 144 cm2. Both patients had complications (one partial flap loss and one nonhealing wound requiring a free flap). Three patients, including one who had preoperative radiation therapy, underwent reconstruction with combined gluteal and posterior thigh flaps for sacral defects with a mean size of 246 cm2; two of these patients had partial necrosis of the posterior thigh flaps. Three patients, all of whom had preoperative radiation therapy, underwent free flap reconstruction for sacral defects with a mean size of 144.3 cm2. They had no complications. Our experience suggests that there are three reliable options for the reconstruction of large sacral wound defects: bilateral gluteal advancement flaps, transpelvic rectus myocutaneous flaps, and free flaps. In patients with no preoperative radiation therapy and intact gluteal vessels, the use of bilateral gluteal advancement flaps should be considered. In patients with a history of radiation to the sacral area and in patients whose gluteal vessels have been damaged, the use of the transpelvic VRAM flap should be considered. If the transpelvic VRAM flap cannot be used because of previous abdominal surgery, a free flap should be considered as a last option.

Adult↗
PubMed2000

Postoperative adjuvant irradiation: effects on tranverse rectus abdominis muscle flap breast reconstruction.

The use of postoperative irradiation following oncologic breast surgery is dictated by tumor pathology, margins, and lymph node involvement. Although irradiation negatively influences implant reconstruction, it is less clear what effect it has on autogenous tissue. This study evaluated the effect of postoperative irradiation on transverse rectus abdominis muscle (TRAM) flap breast reconstruction. A retrospective review was performed on all patients undergoing immediate TRAM flap breast reconstruction followed by postoperative irradiation between 1988 and 1998. Forty-one patients with a median age of 48 years received an average of 50.99 Gy of fractionated irradiation within 6 months after breast reconstruction. All except two received adjuvant chemotherapy. Data were obtained from personal communication, physical examination, chart, and photographic review. The minimum follow-up time was 1 year, with an average of 3 years, after completion of radiation therapy. Nine patients received pedicled TRAM flaps and 32 received reconstruction with microvascular transfer. Fourteen patients had bilateral reconstruction, but irradiation was administered unilaterally to the breast with the higher risk of local recurrence. The remaining 27 patients had unilateral reconstruction. All patients were examined at least 1 year after radiotherapy. No flap loss occurred, but 10 patients (24 percent) required an additional flap to correct flap contracture. Nine patients (22 percent) maintained a normal breast volume. Hyperpigmentation occurred in 37 percent of the patients, and 56 percent were noted to have a firm reconstruction. Palpable fat necrosis was noted in 34 percent of the flaps and loss of symmetry in 78 percent. Because the numbers were small, there was no statistical difference between the pedicled and free TRAM group. However, as a group, the findings were statistically significant when compared with 1,443 nonirradiated TRAM patients. Despite the success of flap transfer, unpredictable volume, contour, and symmetry loss make it difficult to achieve consistent results using immediate TRAM breast reconstruction with postoperative irradiation. TRAM flap reconstruction in this setting should be approached cautiously, and delayed reconstruction in selected patients should be considered. Patients should be aware that multiple revisions and, possibly, additional flaps are necessary to correct the progressive deformity from radiation therapy.

Adult↗
PubMed2000

Clinical long-term in vivo evaluation of poly(L-lactic acid) porous conduits for peripheral nerve regeneration.

It was the purpose of this study to evaluate the clinical long-term effects of PLLA degradation in vivo on nerve regeneration in the rat sciatic nerve model. Thirty-one Sprague Dawley rats were utilized. Two groups of animals were selected. The control group of 10 animals received a 12 mm reversed isograft into the right sciatic nerve from 5 donor animals. The experimental group (n = 21) received a 12 mm empty PLLA conduits placed into a 12 mm defect in the right sciatic nerve. The left leg served as an internal control. Walking track analysis was performed monthly through 8 months. At the end of 4 and 8 months, animals in the control isograft and experimental group had the medial and lateral gastrocnemius muscles harvested and weighed for comparison. The midconduit/isograft and the distal nerve in these same animals were harvested and histomorphologically analyzed. Multiple samples were collected and expressed as means +/- standard error. A two-sample t-test and Wilcoxon rank sum test was used to compare the variables. Significance level was set at alpha = 0.05. After Bonferroni correction for multiple testing, a p value of < or = 0.01 was considered statistically significant. Throughout all time periods, the PLLA conduit remained structurally intact and demonstrated tissue incorporation and vascularization. There was no evidence of conduit collapse or breakage with limb ambulation. Moreover, there was no evidence of conduit elongation at 8 months as previously observed with the 75:25 poly(DL-lactic-co-glycolic acid) (PLGA) conduits. The mean absolute value of the sciatic functional index (SFI) demonstrated no group differences from isograft controls measured over the 8 months except at 3 months where the isograft values were higher (p = 0.0379) and at 7 months were the isograft group was significantly lower (p = 0.0115). At 4 and 8 months, the weight of the gastrocnemius muscles of the experimental group was not significantly different from isografts. At 4 months the number of axons/mm2 and nerve fiber density was not significantly different between the isograft control and experimental groups in either the midconduit/isograft or distal nerve. At 8 months the number of axons/mm2 was significantly lower in the isograft compared to the midconduit experimental group (p = 0.006). The number of axons/mm2 in the distal nerve and the nerve fiber density in the midconduit and distal nerve were not significantly different between the two groups. The study confirmed our initial hypothesis that PLLA conduits are a viable scaffold for clinical long-term nerve gap replacement. We are critically aware however that longer evaluation of polymer degradation is warrented. Further studies on these individual nerve components are continuing, with the ultimate goal being the fabrication of a bioactive conduit that meets or exceeds the functional results of isografts.

Animals↗
PubMed2000

Advances in head and neck reconstruction.

Head and neck deformities, which can be caused by trauma, congenital defects, infections, or neoplasms, produce a stereotypical constellation of functional and aesthetic deficits, depending on the specific anatomic region. These deformities can be classified into six major anatomic categories: intraoral, mandibular, midfacial, cranial base, cutaneous, and scalp. This article presents a reliable approach to the reconstruction of these six areas that is used at the University of Texas M. D. Anderson Cancer Center. The emphasis is on an analysis of the unique functional and aesthetic problems presented by each of these specific anatomic lesions, and the reconstructive options are selected to maximize outcomes. The problems and limitations of current methods are discussed, and areas of potential development are explored.

Face↗
PubMed1999

Measurement of blood flow and oxygen tension in adjacent tissues in pedicled and free flap head and neck reconstruction.

The purpose of this study was to evaluate blood flow and transcutaneous partial oxygen pressure (TcPO(2)) in adjacent tissues to free and pedicled flaps following reconstructive procedures used in conjunction with radical surgery for head and neck cancers. Fifty patients were included. Fourteen patients had reconstruction with pedicled flaps and 36 with free flaps. For each patient, TcPO(2) and laser Doppler flow measurements were taken at the center of the flap, in adjacent tissue, and in a corresponding contralateral site. Three laser Doppler measurements were performed at each site and a mean value recorded. All patients had undergone reconstruction up to 6 months prior to the time of the measurements. The collected data were analyzed using a Wilcoxon signed rank test. There were no statistically significant differences in partial oxygen tension or laser Doppler values between tissues adjacent to free compared to pedicled flaps. Although there is strong evidence to support that free flaps have improved blood flow and partial oxygen tension over pedicled flaps, further study is required to evaluate adjacent tissues. Flap choice may assist with alteration in blood flow in less favorable defects such as those in previously irradiated fields and those resulting from burn scars or chronic infections.

Adolescent↗
PubMed1999

In vivo evaluation of poly(L-lactic acid) porous conduits for peripheral nerve regeneration.

The present study provides in vivo trials of poly(L-lactic acid) (PLLA) as a porous biodegradable nerve conduit using a 10 mm sciatic nerve defect model in rats. The PLLA conduits, fabricated by an extrusion technique, had an inner diameter of 1.6 mm, an outer diameter of 3.2 mm, and a length of 12 mm. They were highly porous with an interconnected pore structure (of 83.5% porosity and 12.1 microm mean pore size). The conduits were interposed into the right sciatic nerve defect of Sprague Dawley rats using microsurgical techniques; nerve isografts served as controls. Walking track analysis was performed after conduit placement monthly through 16 weeks. At the conclusion of 6 and 16 weeks, sections from the isograft/conduit and distal nerve were harvested for histomorphometric analysis. The right gastrocnemius muscle was also harvested and its weight was determined. All conduits remained intact without breakage. Moreover, no conduit elongated during the 16 weeks of placement. Walking track analysis and gastrocnemius muscle weight demonstrated increasing regeneration over the 16 weeks in both the conduit and isograft control groups, with control values significantly greater. The nerve fiber density in the distal sciatic nerve for the PLLA conduits (0.16+/-0.07) was similar to that for the control isografts (0.19+/-0.05) at 16 weeks. The number of axons/mm2 in the distal sciatic nerve for the PLLA conduits was lower than that for the isografts (13 800+/-2500 vs. 10700+/-4700) at 16 weeks. The results for PLLA were significantly improved over those for 75:25 poly(DL-lactic-co-glycolic acid) of a previous study and suggest that PLLA porous conduits may serve as a scaffold for peripheral nerve regeneration.

Animals↗
PubMed1999

Postoperative irradiation: are there long-term effects on nerve regeneration?

This study investigates the histomorphologic and functional effects of external-beam irradiation on peripheral nerve regeneration in the rat model. All animals received a 1.5-cm interposition isogeneic nerve graft to the right posterior tibial nerve. Group 1 animals served as controls and Groups 2 and 3 received fractionated postoperative irradiation doses of 66 and 106 Gy, respectively. All animals were evaluated for functional recovery with monthly walking-track analysis. At the end of 8 months, the animals were sacrificed and segments of the grafted and distal nerve were harvested for histomorphologic analysis. A statistically significantly fewer number of axons were found in the distal segment of the irradiated specimens, compared to controls. There was no significant difference in the nerve-fiber density of the grafted or distal segments, compared to controls. Functional evaluation by walking-track analysis showed no difference between the irradiated groups and controls over the length of the study. These results suggest that acute nerve grafting of nerve defects in the face of planned postoperative irradiation is safe.

Animals↗
PubMed1999

The Fanconi anemia group E gene, FANCE, maps to chromosome 6p.

Fanconi anemia (FA) is a genetically heterogeneous autosomal recessive disease with bone marrow failure and predisposition to cancer as major features, often accompanied by developmental anomalies. The cells of patients with FA are hypersensitive to DNA cross-linking agents in terms of cell survival and chromosomal breakage. Of the eight complementation groups (FA-A to FA-H) distinguished thus far by cell fusion studies, the genes for three-FANCA, FANCC, and FANCG-have been identified, and the FANCD gene has been localized to chromosome 3p22-26. We report here the use of homozygosity mapping and genetic linkage analysis to map a fifth distinct genetic locus for FA. DNA from three families was assigned to group FA-E by cell fusion and complementation analysis and was then used to localize the FANCE gene to chromosome 6p21-22 in an 18.2-cM region flanked by markers D6S422 and D6S1610. This study shows that data from even a small number of families can be successfully used to map a gene for a genetically heterogeneous disorder.

Cell Fusion↗
PubMed1999

Tongue reconstruction: outcomes with the rectus abdominis flap.

Advanced carcinoma of the oral cavity is a devastating disease, with the potential for severe speech and swallowing dysfunction. This is a retrospective review documenting the outcome of 14 patients who underwent resection of at least 75 percent of their tongue with preservation of the larynx and an intact mandible. Reconstruction was accomplished with rectus abdominis free tissue transfer. There were seven male and seven female patients between the ages of 25 and 77 years (mean, 55 years) who underwent total (eight patients) or subtotal (six patients) glossectomy and reconstruction. Decannulation of the tracheostomy tube was performed in 12 patients (86 percent) at an average of 3.5 months postoperatively. One patient required interval laryngectomy for intractable aspiration 1 month postoperatively. Independent evaluation of speech, articulation, and deglutition was performed. Fifty percent of patients achieved oral intake of pureed foods or better. Sixty-four percent had acceptable speech. Reconstruction with rectus abdominis free tissue transfer is a viable method for rehabilitation, improving quality of life after total or subtotal glossectomy with laryngeal preservation.

Adult↗
PubMed1999

Skin graft survival after external beam irradiation.

Difficulties with skin graft ulceration after radiation therapy for cancer have led many to question the suitability of this method of soft-tissue coverage and its cost-effectiveness. The objective of this study was, therefore, to assess skin-graft integrity subjected to postoperative external beam irradiation in a rat model. The model consisted of a rectangular full-thickness skin graft raised and reapplied to its original bed on the dorsum of each rat. Five groups of adult male Sprague-Dawley rats (n = 8 per group) were established. Group A was the control group and was not given postoperative irradiation. Groups B, C, D, and E received postoperative unfractionated cobalt60 irradiation 4 weeks after grafting for a total dose of 15, 20, 25, or 30 Gy, respectively. Weekly skin-graft evaluation was performed for the 4 weeks after irradiation (8 weeks after surgery) by measuring areas of graft loss using computerized planimetry. After the animals were killed, histologic samples were obtained from normal unirradiated skin and from both intact and ulcerated skin-graft sites. Graft loss after irradiation of < or = 20 Gy was similar to that of the unirradiated controls. Occurring as early as 1 week after treatment, a two-fold increase in graft ulceration was observed with doses of > or = 25 Gy (p = 0.0007). Only partial healing of ulcerations was noted by the fourth week after treatment. Histologic changes associated with the irradiation of skin grafts using doses of 25 Gy or higher included hyaline degeneration, fibrinoid necrosis, telangiectasia, and edema. Granulation tissue predominated as a mechanism of healing in areas of graft ulceration. The intensity of inflammatory cell infiltrate did not correlate with radiation dose. The authors concluded that postoperative, unfractionated irradiation can induce skin-graft loss at doses of 25 Gy or higher. Fractionated irradiation or longer intervals between grafting and irradiation may increase skin-graft tolerance; however, further studies are warranted.

Animals↗
PubMed1999

Local recurrence risk after skin-sparing and conventional mastectomy: a 6-year follow-up.

In this study, the records of all patients at the University of Texas M. D. Anderson Cancer Center with T1 or T2 breast cancer who were treated between March of 1986 and November of 1990 with mastectomy followed by immediate breast reconstruction were reviewed for the presence of recurrent disease. Patients with in situ disease were not included. Patients were included in the study if a local recurrence occurred (regardless of the length of follow-up) or if a follow-up of 6 years or longer could be obtained. Patients were grouped according to the use or nonuse of skin-sparing mastectomy, by tumor stage, and by nuclear grade of the tumor. The series included 154 patients, of whom 114 had skin-sparing mastectomies and 40 had nonskin-sparing mastectomies. The local recurrence rate in the skin-sparing mastectomy group was 7.0 percent, whereas in the nonskin-sparing mastectomy group it was 7.5 percent. The sample size in the nonskin-sparing mastectomy group was too small for meaningful statistical analysis, but the data suggest that there is no clinically important difference in recurrence rates between the two groups. We conclude that the use of skin-sparing technique for early breast cancer patients does not significantly increase the risk of tumor recurrence after mastectomy.

Breast Neoplasms↗
PubMed1999

The effects of cisplatinum and vincristine on peripheral nerve regeneration.

Current treatment modalities for extremity sarcoma often include tumor extirpation plus neoadjuvant therapy. Limb-sparing surgery may require reconstruction of critical nerve defects. Neurotoxic side effects from adjuvant chemotherapy have been reported and raise concerns regarding the effects of chemotherapy on nerve regeneration. In an attempt to define the effects of adjuvant chemotherapy on peripheral nerve regeneration, cisplatin and vincristine were administered to rats following isografting of the posterior tibial nerve. Parameters used to assess peripheral nerve regeneration included walking track analysis and histomorphology. Sixty 250-g Sprague-Dawley rats were randomly allocated into one of three treatment groups. Each animal underwent a 15-mm reversed interposition nerve isograft from 30 donor rats into the right posterior tibial nerve. Ten animals served as control. The remaining animals were divided into two groups of 25 animals each. One group received cisplatin (75 mg/m2) and the other group received vincristine (1 mg/m2). Chemotherapy was administered at 4-week cycles for a total of six cycles (24 weeks). Walking track analysis was performed monthly. Nerve specimens were harvested from the grafted segment and the distal posterior tibial nerve for histomorphology. Walking track analysis demonstrated no statistical difference in print length between the control and chemotherapeutic groups at the conclusion of the study. The number of axons per square millimeter and nerve fiber density were not statistically different between control and chemotherapeutic groups. In the rodent posterior tibial nerve model, postoperative adjuvant therapy does not significantly alter functional outcome in peripheral nerve regeneration. The practice of immediate nerve grafting after tumor extirpation, despite planned postoperative chemotherapy, is supported.

Animals↗
PubMed1999

Engineering strategies for peripheral nerve repair.

Tissue engineering in the peripheral nervous system unites efforts by physicians, engineers, and biologists toward a common goal to create either natural or synthetic tubular nerve guidance channels as alternatives to nerve autografts for the repair of peripheral nerve defects. Guidance channels help direct axons sprouting from the regenerating nerve end, provide a conduit for diffusion of neurotropic and neurotrophic factors secreted by the damaged nerve stumps, and minimize infiltration of fibrous tissue. In addition to efforts to control these physical characteristics of nerve guidance channels, researchers are optimizing the incorporation of biologic factors and engineering interactive biomaterial that can specifically stimulate the regeneration process. It is believed that current and future research will ultimately result in biologically active and interactive nerve guidance channels that can support and enhance peripheral nerve regeneration over longer, more clinically relevant defect lengths.

Animals↗
PubMed1998

Drug-induced vasodilation: in vitro and in vivo study on the effects of lidocaine and papaverine on rabbit carotid artery.

Flap ischemia is often encountered during pedicled and free tissue transfer. In this study, the vascular effects of varying doses of lidocaine, papaverine, and a combination of the two agents were evaluated and compared in an in vitro and in vivo model in the rabbit carotid artery. In the in vitro study, 14 rings from the rabbit carotid artery were bathed in Krebs-Ringers solution and stretched progressively to an optimal tension of 3.7-4.2 grams. Their isometric contractile activity was measured. The specimens were precontracted with norepinephrine (1 microM), and a dose response curve was established by adding cumulatively either lidocaine (to 7 arterial rings) or papaverine (to 7 arterial rings) at increasing concentrations. In the in vivo study, microvascular anastomoses were performed bilaterally in the rabbit carotid artery in 30 animals using 9-0 nylon suture and standard microsurgical techniques. In each animal, one side was treated with heparinized sodium chloride and served as the control. The other side was treated blindly, during and after the anastomoses, with a topical application of 1 ml of either lidocaine 2% (n = 5), lidocaine 20% (n = 5), papaverine (30 mg/ml, n = 5), lidocaine 2% combined with papaverine (30 mg/ml, n = 5), or lidocaine 20% combined with papaverine (30 mg/ml, n = 5). For 30-60 minutes after the procedure, blood flow changes in the vessels were continuously monitored with a transonic doppler applied to both carotid arteries. The 20% lidocaine group was flushed with saline at the end of the first hour and monitored for an additional 60 minutes. Papaverine elicited a concentration-dependent relaxation of norepinephrine precontracted carotid artery rings in vitro. Lidocaine elicited a biphasic response, with low concentrations (10(-6)-10(-4) M) increasing the norepinephrine-induced contraction and high concentrations (10(-4)-10(-2) M) relieving this contraction. Microsurgical anastomosis produced a significant decrease of blood flow through the rabbit carotid artery as measured by the transonic doppler. Drug application did not alter the systemic blood pressure of the animals. Topical application of lidocaine 2% did not significantly change the blood flow after microvascular anastomosis. Topical application of lidocaine 20%, papaverine (30 mg/ml), or lidocaine (2% or 20%) combined with papaverine significantly increased the blood flow in the rabbit carotid artery. In the lidocaine 20% group, the blood flow remained significantly increased after the drug was flushed with heparinized saline solution. These results demonstrate that topical lidocaine 20%, papaverine, and lidocaine 2% or 20% combined with papaverine significantly increase blood flow in the rabbit carotid artery after microvascular anastomosis. The data confirm the use of papaverine and lidocaine 20%, alone or in combination, as spasmolytics during clinical microsurgery. This suggests that lidocaine 2% alone is not the ideal drug to relieve vascular constriction, and further studies on the clinical use of low concentrations of topical lidocaine in microsurgery is warranted.

Animals↗
PubMed1998

Soft tissue reconstruction following hemipelvectomy.

BACKGROUND: Resection of primary and metastatic pelvic bone disease may result in large soft tissue deficits. Guidelines for soft tissue reconstruction following pelvic bone resection were evaluated in a retrospective study. METHODS: Over a 5-year period 21 patients (31%) required soft tissue reconstruction following pelvic bone resection. Data on these patients were retrieved from case records. RESULTS: Twelve patients underwent immediate, planned reconstruction, 1 a two-stage reconstruction, and 8 patients required a delayed procedure for complications after bone resection and primary closure. Soft tissue reconstruction was usually accomplished with muscle-based flaps; (25 flaps in 20 patients: 20 pedicled, 5 free), or with skin grafts alone (1 patient). Specific postreconstruction complications occurred in 9 patients, 5 in flaps based on the ipsilateral rectus muscle. CONCLUSION: Flap closure is indicated to achieve primary closure and eliminate deadspace. The ipsilateral rectus muscle should be used with caution and contralateral-based rectus flaps considered. Indications for free flaps include the size and location of the defect and availability of tissue from an amputated limb.

Adult↗
PubMed1998

Manufacture of porous biodegradable polymer conduits by an extrusion process for guided tissue regeneration.

We have fabricated porous, biodegradable tubular conduits for guided tissue regeneration using a combined solvent casting and extrusion technique. The biodegradable polymers used in this study were poly(DL-lactic-co-glycolic acid) (PLGA) and poly(L-lactic acid) (PLLA). A polymer/salt composite was first prepared by a solvent casting process. After drying, the composite was extruded to form a tubular construct. The salt particles in the construct were then leached out leaving a conduit with an open-pore structure. PLGA was studied as a model polymer to analyze the effects of salt weight fraction, salt particle size, and processing temperature on porosity and pore size of the extruded conduits. The porosity and pore size were found to increase with increasing salt weight fraction. Increasing the salt particle size increased the pore diameter but did not affect the porosity. High extrusion temperatures decreased the pore diameter without altering the porosity. Greater decrease in molecular weight was observed for conduits manufactured at higher temperatures. The mechanical properties of both PLGA and PLLA conduits were tested after degradation in vitro for up to 8 weeks. The modulus and failure strength of PLLA conduits were approximately 10 times higher than those of PLGA conduits. Failure strain was similar for both conduits. After degradation for 8 weeks, the molecular weights of the PLGA and PLLA conduits decreased to 38% and 43% of the initial values, respectively. However, both conduits maintained their shape and did not collapse. The PLGA also remained amorphous throughout the time course, while the crystallinity of PLLA increased from 5.2% to 11.5%. The potential of seeding the conduits with cells for transplantation or with biodegradable polymer microparticles for drug delivery was also tested with dyed microspheres. These porous tubular structures hold great promise for the regeneration of tissues which require tubular scaffolds such as peripheral nerve, long bone, intestine, or blood vessel.

Biocompatible Materials↗