Biomedical subjects

A Losken

Publications and source records attributed to A Losken.

29 records · Page 2Linked to original sources

PubMed1994

Internal calvarial bone distraction in rabbits with experimental coronal suture immobilization.

Correction of craniosynostosis involves removal of the coronal suture to allow for expansion of the developing brain and normal craniofacial growth. Frequently, however, the site reossifies, restricts growth, and requires additional surgery. The present study was designed to assess the effects of an internal, subperiosteal calvarial distractor on suturectomy site patency and compensatory craniofacial growth changes in an experimental rabbit model of coronal suture synostosis. In the present study, 43 1 1/2-week-old rabbits were used. Amalgam markers were placed across the frontonasal, coronal, and anterior lambdoidal sutures in all animals. Twenty-nine rabbits underwent bilateral coronal suture immobilization using methyl methacrylate. Fourteen rabbits were left untreated and served as sham controls. At 6 weeks of age, the immobilized rabbits were divided into three groups: (1) immobilized (controls), (2) suturectomy, and (3) suturectomy and distraction. The distractors were activated percutaneously at an average of 0.6 mm/week for 5 weeks (3 mm total). Lateral head radiographs were taken at 1 1/2, 6, 12, and 18 weeks of age. Results revealed that, by 6 weeks of age, animals with coronal suture immobilization exhibited significantly (p < 0.01) reduced growth across the coronal suture, resulting in shorter and inferiorly rotated cranial vaults compared with sham controls. By 12 weeks of age, rabbits with distraction returned to normal (sham control) coronal suture marker separation, whereas rabbits with immobilized sutures and suturectomy only showed significantly reduced marker distances. Rabbits with distraction also exhibited greater anterior cranial base lengths compared with the other experimental groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Development of a strain of rabbits with congenital simple nonsyndromic coronal suture synostosis. Part I: Breeding demographics, inheritance pattern, and craniofacial anomalies.

The lack of an animal model of congenital coronal suture (CS) synostosis has prompted the widespread use of an experimental rabbit model using adhesive immobilization of the CS. Such postnatal models have helped make significant scientific contributions but may still not fully represent all aspects of the human congenital condition. In the March 1993 issue of The Cleft Palate-Craniofacial Journal we reported a female rabbit born in our laboratory with complete bilateral CS synostosis. This follow-up study presents our attempts to breed this animal and establish a strain of craniosynostotic rabbits. To date, we have accomplished 10 back- and intercrosses with these animals and have produced a total of 71 live offspring; 10 animals exhibited complete nonsyndromic unilateral (plagiocephalic) or bilateral (brachycephalic) CS synostotic deformities at birth, and 19 animals exhibited partial CS synostosis that showed more than 75% growth retardation across the CS (well below the 95% confidence interval for normals). Results revealed that gestational time and litter size averages were consistent with those reported for the strain, although the average litter size decreased with increased inbreeding. By 1.5 weeks of age the completely synostosed animals already exhibited brachycephalic cranial vaults and midfacial hypoplasia compared to unaffected siblings. Initial pedigree analysis suggested an autosomal dominant inheritance pattern with incomplete penetrance and variable expressivity. The development of such a congenital rabbit model may prove useful in helping to understand the etiopathogenesis of this condition in human populations.

Animals↗

PubMed1994

Development of a strain of rabbits with congenital simple nonsyndromic coronal suture synostosis. Part II: Somatic and craniofacial growth patterns.

In the March 1993 issue of The Cleft Palate-Craniofacial Journal we reported a female rabbit born in our laboratory with complete bilateral coronal suture (CS) synostosis. This follow-up study presents our attempts to breed the animal and establish a strain of craniosynostotic rabbits. The second part of this study presents longitudinal somatic and craniofacial growth data in offspring with coronal suture synostosis. Serial growth data from 72 animals were collected for the present study. The sample consisted of 11 animals (10 offspring and the original female) with complete nonsyndromic unilateral (plagiocephalic) or bilateral (brachycephalic) CS synostosis, 19 animals with partial CS synostosis, and 42 unaffected control litter mates. At 10 days of age, all animals had radiopaque amalgam markers placed on either side of the frontonasal, coronal, anterior lambdoidal, and sagittal sutures. Body weights and serial lateral and dorsoventral head radiographs were taken at 1.5 (10 days), 6, 12, and 18 weeks of age. All animals showed similar body weights at 1.5 weeks of age, while completely synostosed animals exhibited a slight (about 12%), but significantly (p < .001) lowered body weight by 18 weeks of age. Results revealed that by 1.5 weeks of age the completely synostosed animals already exhibited brachycephalic cranial vaults, midfacial hypoplasia, and increased flattening of the cranial base compared to unaffected siblings. This pattern continued through 18 weeks of age, with the partially synostosed animals exhibiting intermediate morphologies.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Comparative cephalometric study of nasal cavity growth patterns in seven animal models.

Although primates have been the craniofacial growth models of choice, recent circumstances have stimulated the search for nonprimate models. In a series of studies we have described changes in various regions of the craniofacial complex for seven commonly used animal models. The present study examined the bony nasal cavity. One hundred and forty-four serial and cross-sectional lateral head x-rays were obtained for unoperated controls from previous growth studies. The sample consisted of data from 26 rats, 21 rabbits, 21 domestic cats, 23 domestic dogs, 17 baboons, 16 rhesus monkeys, and 20 chimpanzees. Comparative human data was taken from the Bolton Standards. The samples were divided into three age categories based on dental and somatic development. Midsagittal nasal cavity measurements included length, height, shape index, and area. Analysis was based on the percent increase in measures from the infant condition. Three major shapes were discerned at adulthood (1) vertical quadrangles (humans and cats); (2) triangles (chimpanzees, rhesus monkeys, and baboons), and (3) horizontal quadrangles (rabbits, rats, and dogs). Results showed that overall shape was best modeled by the chimpanzee and, as a nonprimate model, the laboratory cat. Rabbits and rats also showed similar percent changes for length or height dimensions at different ages, suggesting that these animals may be acceptable, inexpensive alternatives to primates in some experimental situations.

Adolescent↗

PubMed1993

Osseous guided tissue regeneration using a collagen barrier membrane.

The formation of mature, fibrous tissue in surgical osteotomy sites during the healing process can produce clinically undesirable results such as nonunion or encapsulation of alloplastic implants. The techniques of guided tissue regeneration have been used to ameliorate this problem by presenting a barrier to the invasion of fibrous tissue elements into the wound-site clot. The most frequently used barrier material, polytetrafluoroethylene is effective, but suffers the disadvantage of requiring surgical removal after clot organization is completed. A biocompatible, resorbable membrane that will effectively control the type of tissue that can invade and organize a clot would be advantageous, because it would not require surgical removal. In the present study, the efficacy of a collagen membrane to effect guided tissue regeneration in a rabbit zygomatic arch osteotomy model was tested. Complete, bilateral narrow (1 mm) or wide (5 mm) vertical osteotomies were created in eight adult New Zealand white male rabbits. On one side, the wound site was surrounded by a collagen barrier membrane prior to closure, while the other side was left uncovered (control side). Four animals were killed at 2 and 4 weeks postoperatively for gross radiologic and histologic examination of the wound site. The wide osteotomy sites without a barrier membrane showed invasion by fibroblasts resulting in fibrous nonunion, while the contralateral sides with the barrier membrane showed no fibrous tissue ingrowth and bony union by 4 weeks postoperatively. Although narrow wound sites without the barrier membrane showed fibrous tissue formation, the perimeter of the defects showed some new bone deposited at the periosteal surface, bridging the osteotomy site and producing osseous union.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Congenital bilateral coronal suture synostosis in a rabbit and craniofacial growth comparisons with experimental models.

Experimental rabbit models of postnatal coronal suture (CS) synostosis have helped make significant contributions towards the understanding and surgical management of human congenital craniosynostosis. The present study compares craniofacial growth patterns in animals with experimental CS immobilization and in a rabbit born in our laboratory with congenital CS synostosis. The study sample consisted of 10 sham controls, 14 experimental animals with bilateral CS immobilization, and one animal with congenital, bilateral CS synostosis. At 1.5 weeks of age, all animals had amalgam markers placed on either side of the frontonasal, coronal, and anterior lambdoid sutures. At this time, the experimental animals had bilateral CS immobilization using methyl-methacrylate. Serial lateral head x-rays were taken at 1.5, 6, 12, and 18 weeks of age. Results revealed that by 1.5 weeks of age the congenital animal already exhibited changes in the cranial vault, cranial base, midface, and orthocephalic cranial base angles compared to controls. By 6 weeks of age, animals with experimental immobilization showed compensatory growth patterns similar to the congenital animal, particularly at the calvarial sutures and upper midface. This pattern continued through 18 weeks. Results showed that experimental, postnatal CS immobilization produced similar craniofacial growth patterns to those observed for our single congenital animal, but to a lesser degree, and therefore validates, in part, findings from experimental rabbit models of synostosis.

Animals↗

PubMed1993

Experimental studies of DL-polylactic acid biodegradable plates and screws in rabbits: computed tomography and molecular weight loss.

A series of studies were designed to assess the potential of biodegradable DL-polylactic acid (DL-PLA) plates and screws for use in craniofacial surgery. We report on computed tomography (CT) scanning for visualization and postoperative follow-up and the short-term degradation sequelae of a biodegradable plate and screw system in an experimental animal model. Fractures of the nasal bones were created in 20 adult New Zealand white rabbits and rigidly fixed bilaterally with 4-hole plates and screws (n = 12), or left unrepaired for control data (n = 8). CT density, molecular weight, loss of plates and screws, and preliminary bone healing were assessed at 1, 2, 4, and 6 weeks postoperatively. Histologically, no differences in bone healing were noted between control and experimental animals at any time. Three-dimensional CT reconstruction of the skull was possible without artifacts, and no significant differences (p > 0.05) were found in specific CT scan density levels across postoperative intervals. However, significant (p < 0.001) molecular weight loss of the biodegradable plates was observed through 6 weeks postoperatively, reaching approximately 50% of the preoperative molecular weight. Molecular weight loss, however, was not detectable with CT density measurements. Results demonstrated that the use of biodegradable DL-PLA plates and screws had no adverse effect on fracture healing in this model and that CT scanning and three-dimensional reconstruction were possible without artifacts, independent of material degradation and molecular weight loss. These results suggest that this DL-PLA biodegradable system may have the potential for use in craniomandibulofacial surgery when short-term rigid fixation is necessary.

Analysis of Variance↗

PubMed1992

A comparative study of mandibular growth patterns in seven animal models.

The use of nonhuman primate experimental models has helped make significant contributions toward the clinical and surgical management of patients with craniofacial disorders. With concerns such as increasing cost, however, alternative models will have to be identified. The present comparative study describes baseline, age-related changes in mandibular growth patterns for seven commonly used animal models. The data was obtained from 144 serial and cross-sectional lateral head radiographs of unoperated control animals from a number of previous craniofacial growth studies. The sample consisted of 26 rats, 21 rabbits, 21 domestic cats, 23 domestic dogs, 17 baboons, 16 rhesus monkeys, and 20 chimpanzees. Comparative human data were taken from the Bolton Standards. The samples were divided into three age categories: infant, juvenile, and adult. Mandibular growth measurements included overall mandibular length, ramal height, and body height. Comparative analysis consisted of the calculation of percent increase from the infant condition. For all measurements, three major clusters could be discerned: 1) humans, chimps, and rhesus monkeys; 2) dogs and baboons; and 3) cats, rats, and rabbits. Results suggested that for the dimensions studied, long-term mandibular growth was best modeled by short-faced primates, and in particular, the chimpanzee. In addition, dogs and rats showed similar relative percent changes in different regions from juvenile through adulthood stages, which suggests that these animals may be acceptable, inexpensive alternatives to primates in certain experimental situations.

Adolescent↗

PubMed1992

Plate fixation of premaxillomaxillary suture and compensatory midfacial growth changes in the rabbit.

It has been suggested that rigid fixation of the developing craniofacial skeleton may lead to altered craniofacial growth. However, recent experimental studies have shown that microplate fixation of slow-growing calvarial sutures resulted in regional growth disturbances but had little effect on overall craniofacial growth. The present study was designed to assess the effects of microplate fixation of the more rapidly growing facial sutures on compensatory midfacial growth in the rabbit. Twenty-two 1.5-week-old rabbits were randomly divided into 2 groups: sham controls (n = 11) and animals with bilateral premaxillomaxillary suture fixation (n = 11). Fixation was accomplished using an intraoral approach, a 6-mm straight Luhr microplate, and two 2-mm long self-tapping screws across each suture. Serial lateral head radiographs were collected at 1.5, 3.5, 6, 12, and 18 weeks of age. Results revealed that by 3.5 weeks, animals with rigid fixation showed significantly shortened premaxillary lengths (p < 0.05), class III occlusal relationships, decreased midfacial heights, and abnormal palatocranial base angles compared with sham control animals. By 12 weeks of age, "catch-up" growth was evident in most dimensions in animals with fixation compared with shams. Gross examination of the cleaned and dried skulls revealed bony bridging across the premaxillomaxillary suture and osseous fracture lines extending superiorly from the site of screw fixation. Results demonstrated that rigid fixation of a rapidly growing facial suture did not impair long-term midfacial growth in the rabbit model and suggest that compensatory changes may have occurred at fracture lines from the self-tapping screws in these animals.

Adaptation, Physiological↗

PubMed1991

Frontal bone advancement and compensatory craniofacial growth changes in rabbits with experimental coronal suture immobilization.

Recent clinical advances in the surgical correction of coronal suture synostosis involve the overcorrection of a frontal bone segment to allow for unrestricted expansion of the developing neurocapsular matrix. However, the effects of such large-scale calvarial repositioning on subsequent brain mass growth trajectories and compensatory cranio-facial growth changes is unclear. This study was designed to investigate this relationship in an experimental rabbit model of bilateral coronal suture synostosis. Amalgam markers were placed across the frontonasal, coronal, and anterior lambdoid sutures in thirty-one 1.5-week-old rabbits. Twenty-one animals underwent bilateral coronal suture immobilization using methyl-methacrylate. Ten animals were left untreated and served as sham controls. At 6 weeks of age, the coronal suture was released by frontal bone craniotomy or frontal bone craniotomy with a 6-mm frontal bone advancement. Lateral head radiographs were taken at 1.5, 6, 7, 9, 12, and 18 weeks of age. Results revealed that by 6 weeks of age, animals with coronal suture immobilization exhibited growth disturbances across the various sutures resulting in altered craniofacial and cranial vault shape compared to control animals. Following coronal suture release, animals that underwent craniotomy showed rapid restenosis, which resulted in significantly altered cranial vault shape and cranial orthocephalization by 18 weeks of age. Animals that underwent frontal bone advancement exhibited normal overall craniofacial growth by 18 weeks of age compared with control animals but did exhibit regional compensatory growth disturbances at the frontonasal and anterior lambdoid sutures, possibly related to neural tissue distension.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1991

Frontal bone advancement stability with or without microplate fixation: an experimental study in rabbits.

Recent advancements in surgical correction of coronal suture craniosynostosis involve the overcorrection of a frontal bone segment to allow unrestricted growth of the developing brain. However, problems with segment stability and collapse have been reported. Such problems may be alleviated with microplate fixation of the segments. The present experimental study tests this hypothesis in a growing rabbit frontal bone advancement model. Sixteen 6-week-old rabbits were divided into three groups, consisting of animals with short bone segments advanced with two bone struts and fixed with Vicryl, long bone segments advanced with one bone strut and fixed with Vicryl, or long bone segments advanced with one bone strut and fixed with microplates. Frontal bone advancement collapse was assessed from lateral x-rays through 12 weeks postoperatively. Animals with microplate fixation exhibited significantly (p less than 0.01) less collapse (about 1% height reduction) compared to animals with short segments (about 30%) and long segments (about 45%). These results support, with experimental evidence, the utility of rigid three-dimensional fixation afforded by the microplate system in overcoming the effects of cranial growth and scalp and epicranial musculature closing tensions.

Analysis of Variance↗