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Biomedical subjects

L A Whitaker

Publications and source records attributed to L A Whitaker.

At least 73 records · Page 4Linked to original sources
PubMed1987

The craniofacial dysostoses: guidelines for management of the symmetric and asymmetric deformities.

Although great diversity marks the craniosynostoses, our experience related to that from other centers allows us to draw certain conclusions for their management. For the asymmetric synostoses, operative intervention should be carried out in infancy or early childhood. Although the unilateral approach is our preferred method, the bilateral approach can yield equally satisfactory results. Surgeons should, therefore, familiarize themselves with both methods and individualize for the given deformity. Mild symmetric (upper face) synostoses are best managed in infancy or early childhood, utilizing bilateral orbital advancement with the expectation that the need for additional major surgery will be at worst 50 per cent and likely significantly less. For moderate to severe synostoses, delaying major intervention to later childhood or adolescence maximizes the chance of obtaining a satisfactory result by a single procedure, either an extended LeFort III or monoblock advancement. Individualization of each case is essential, and the need for brain and eye protection or the psychologic needs of the patient may dictate a modification of the treatment guidelines. Patients and parents must be aware that growth and development subsequent to surgery is not entirely predictable, and there may be a need for a second major intervention at a subsequent time, despite these established guidelines.

Acrocephalosyndactylia↗
PubMed1986

Effect of age on horizontal eye movement latency.

Reaction time to initiate an eye movement to a target which suddenly appeared 2.8 degrees from fixation was measured for older and younger adults. Healthy men and women were tested in a series of trials; on one-half of these trials prior knowledge of the target's location was given (simple reaction time), whereas on the remaining trials the target could appear to left or right of fixation with equal probability (choice reaction time). For both simple and choice trials, the mean reaction times for younger adults were significantly faster than for older adults. Simple reaction time trials were no faster than choice trials for either age group. In addition to mean reaction times, the distribution of the response times were examined for each age group. The shapes of the two distributions were symmetric; however, the SD of the older adults' scores was greater than that of the younger adults.

Adolescent↗
PubMed1986

Aesthetic surgery of the supraorbital ridge and forehead structures.

A physical anthropologic basis for aesthetic evaluation of the supraorbital ridges and forehead is described. The structures included for evaluation and possible treatment are the supraorbital ridges, relation of the orbital walls to the eyes, the temporal ridges, and slope of the forehead. All can be altered by reduction contouring or augmentation using methods described. Twenty-one patients are presented having procedures for purely aesthetic reasons. If more than 5 to 6 mm of augmentation or reduction is desired, the deformity is more than aesthetic and should be treated by a craniofacial team. The aesthetic restructuring procedures described are done using tissue localized to the cranium and have proven to be safe and free of complications in the patients treated. Physical anthropology helps to put the aesthetics of these procedures on a firmer basis and to determine which patients may require more than an extracranial aesthetic procedure.

Adolescent↗
PubMed1986

Facial form analysis of the lower and middle face.

Structural form analysis identifies the major structural members of the middle and lower face through their high- and low-light areas, provides measurements and relationships between the key points, and explains the angular relationships in constructing a geometric form corresponding to these members. The six key points define the superior and inferior and anterior and posterior angles. The angles and planes then lead to a geometric form of the lower and middle face. The final construction provides a framework for examining the facial form and making aesthetic judgments which lead directly to surgical decisions. A study of 50 Caucasian women ages 22 to 30 was performed. Specific patient examples with analyses are provided.

Adult↗
PubMed1985

Psychosocial adjustment and craniofacial malformations in childhood.

Forty-three children between the ages of 6 and 13 years with congenital facial anomalies underwent psychosocial evaluation prior to surgery. Also evaluated were healthy children matched to the craniofacial subjects by sex, age, intelligence, and economic background. Relative to this comparison group, the craniofacial children were found to have poorer self-concept, greater anxiety at the time of evaluation, and more introversion. Parents of the craniofacial children noted more frequent negative social encounters for their children and more hyperactive behavior at home. Teachers reported more problematic classroom behavior. Examination of these results revealed craniofacial malformations to be associated with psychosocial limitations rather than marked deficits. These children tended to function less well than the comparison children, but with few exceptions, they were not functioning in a psychosocially deviant range. Explanations for the observed circumscribed impact of facial deformity include the use of denial as a coping mechanism, possible diminished significance of appearance for younger children, and the restricted environment experienced by most of the subjects. It can be predicted that time would render these protective influences ineffective, so that adolescent and young adult patients could be at far greater psychosocial risk.

Adolescent↗
PubMed1985

The early revascularization of membranous bone.

The experimental finding that membranous onlay bone grafts maintain volume and viability to a greater extent than do endochondral grafts may be related to the more rapid vascularization of membranous bone. Microangiographic techniques were used to study the rates of vascularization of membranous and endochondral bone grafts in adult white New Zealand rabbits at 1, 3, 7, 14, and 21 days after bone grafting. Vascularization patterns were quantified microscopically using a modified point-counting technique. At 3 days, membranous bone grafts demonstrated vessel ingrowth from both soft tissue and host bone. Little ingrowth was seen in endochondral grafts. By day 7, 2.5 vessels per square were identified entering membranous grafts, while an average of 0.6 vessels per square were counted for endochondral bone grafts. At day 14, there was an average of greater than 20 vessels per square for membranous grafts versus 1.8 for their endochondral counterparts. At 21 days, the endochondral grafts demonstrated persistent avascular central areas not seen in membranous grafts. Membranous onlay bone grafts in the rabbit are more rapidly vascularized than endochondral grafts. This factor may affect the greater volume maintenance seen in experimental membranous grafts.

Animals↗
PubMed1984

Cranial base dynamics in craniofacial dysostosis.

Cephalometric analyses of twenty-one patients with Crouzon's disease were undertaken to correlate the cranial base abnormalities to altered facial morphology. Angular deformities of the cranial base, i.e., the vertical sloping of the anterior cranial fossa and the angulation of the cranial base flexure were found to correlate well to observed exorbitism and midface retrusion , respectively. Normal craniofacial growth and clinical implications of these data are discussed.

Adolescent↗
PubMed1984

The influence of the recipient site on bone grafts to the face.

This study investigates the relationship of resorptive and depository surfaces to the maintenance of bone graft volume in the growing rabbit facial skeleton. Bone grafts fare best (1) when their periosteal surface is placed in contact with soft tissue and their cancellous surface in contact with bone and (2) when bone is grafted to periosteal depository recipient sites. Fluorescent microscopy failed to demonstrate any difference in the rates of calcification in any of the grafts studied.

Animals↗
PubMed1984

Selective alteration of palpebral fissure form by lateral canthopexy.

A method is described for altering the shape and position of the palpebral fissure at the lateral canthus. Three steps are essential to alter shape and position. They are (1) identification of a lateral canthal soft-tissue mass consisting of periosteum, lateral canthal ligament, and orbicularis muscle, (2) extensive subperiosteal soft-tissue mobilization of the lateral canthal soft-tissue mass (LCSTM) from a point just superior to the zygomaticofrontal suture and inferiorly along the infraorbital rim to a point corresponding with a vertical line drawn from the pupil downward, and (3) cutting of all soft tissue, including orbicularis muscle from dermis to bone and from bone to conjunctiva, from the lateral canthal soft-tissue mass medially to a point equal to a vertical line drawn from the pupil downward. After tension-free shifting laterally and superiorly has been accomplished, the lateral canthal soft-tissue mass is fixed into bone with minimal overcorrection. If there is still soft-tissue skin resistance, then overcorrection is desirable. The most difficult judgments in the procedure are the amount of superior and lateral tension to be placed on the palpebral fissure. As an aid in these judgments, the lateral-most extent of the palpebral fissure should be approximately 3 mm above the medial canthus horizontally and 3 to 4 mm medial to the medial-most portion of the lateral orbital rim. If overcorrection occurs, it can be released relatively simply.

Cephalometry↗
PubMed1983

Item analysis of a single response dichotic listening test.

Ten left-handed and eight right-handed subjects were tested on five replications of a single-response dichotic listening test. Nine CV dichotic pairings of the six stop consonants plus /a/ were used. Computer synthesis guaranteed that these pairs differed on only a single phonemic feature, thus permitting fusion. Mean laterality scores were significantly higher (greater right ear advantage) for right-handers than for left-handers. Selective attention instructions did not alter laterality scores. Test-retest correlation coefficients were consistently high (greater than .70 for all adjacent replication comparisons). Error rates were low (averaging 5.5%) and 39% of these were psychoacoustic confusions rather than true (guessing) errors. These confusions were found for only two of the nine pairs. Stimulus dominance, as opposed to ear dominance, was considered separately. Two dichotic pairs had such strong stimulus dominance for all subjects that little ear advantage information was available from those pairs. It was recommended that the three dichotic pairs prone to psychoacoustic confusions and/or overwhelming stimulus dominance be removed from the test.

Dominance, Cerebral↗
PubMed1983

Membranous versus endochondral bone: implications for craniofacial reconstruction.

Based on observations in the human suggesting improved membranous bone graft take, an experimental study was undertaken in 15 rabbits and 7 monkeys to evaluate the differences in take between membranous and endochondral bone grafts. Using vital stains, serial cephalograms, direct measurements, and point-counting techniques, the grafts were compared. In both types of experimental animals, membranous bone maintained its volume to a significantly greater extent than endochondral bone when autografted in the craniofacial region. The loss of volume with endochondral grafts was at the end of the experiment more than three times that of membranous grafts in the rabbit (65 percent endochondral loss versus 19.5 percent membranous loss) and more than four times volume loss in the monkey (17.2 percent membranous volume loss versus 88 percent endochondral loss). The uptake of vital stains (tetracycline and alizarin) was greater with membranous bone, and point counting demonstrated more living membranous bone (40.5 percent membranous versus 28.1 percent endochondral) at the end of the experiment. These studies confirm the increased resorption of endochondral bone grafts when compared with membranous grafts and substantiate clinical impressions that cranial donor sites are preferable for craniofacial recipient areas when clinically feasible.

Animals↗
PubMed1982

Stimulus-response compatibility for left-right discriminations as a function of stimulus position.

In two experiments, choice response times to visual stimuli (word and arrow) were measured. The stimuli were presented briefly (180 msec) in left and right visual half-field (VHF). Each stimulus required a left-right discrimination; however, half the stimuli were positive (e.g., LEFT), and half were negative (e.g., NOT RIGHT). In Experiment 1, button-pressing responses in the midsagittal plane were used; in Experiment 2, vocal responses were used. There was a strong stimulus-response (S-R) compatibility effect, influenced by the interaction of negation (positive vs. negative) and stimulus position (VHF). Latencies were faster to positive stimuli whose direction and VHF matched than to positive stimuli whose direction and VHF did not correspond. Conversely, latencies were faster to negative stimuli when response direction and VHF did not match than when direction and VHF did correspond. These results replicate the S-R compatibility effect found by Whitaker (1980) using foveal stimuli. The results were analyzed with regard to a hemisphere activation model proposed by Cotton, Tzeng, and Hardyck (1980) but were found to fit Whitaker's (1980) model better.

Discrimination Learning↗