Search PubMed⌕ Search

Biomedical subjects

K L Armstrong

Publications and source records attributed to K L Armstrong.

28 records · Page 2Linked to original sources
PubMed1997

A biomechanical study of replacement of the posterior cruciate ligament with a graft. Part II: Forces in the graft compared with forces in the intact ligament.

UNLABELLED: A femoral load-cell was installed in twelve fresh-frozen knee specimens from cadavera, to measure the resultant force at the femoral origin of the posterior cruciate ligament during a series of tibial-loading tests. The posterior cruciate ligament was removed, and a ten-millimeter-wide bone-patellar ligament-bone graft was inserted. The knee was flexed to 90 degrees, the graft was pre-tensioned to restore the anterior-posterior laxity to that recorded after installation of the load-cell, and the loading tests were repeated. With the tibia locked in neutral rotation and a 200-newton posterior force applied to the tibia, the mean force generated in the intact posterior cruciate ligament ranged from 220 newtons at 90 degrees of flexion to thirty-six newtons at full extension. When the tibia was locked in external rotation during the posterior drawer test, the force was reduced when the knee was flexed 10 to 70 degrees; when the tibia was locked in internal rotation, the mean force was reduced at only 30 and 45 degrees of flexion. The mean forces in the graft were not significantly different, with the numbers available, from the corresponding values for the intact ligament during application of a straight posterior tibial force (neutral tibial rotation), during application of a fifteen-newton-meter flexion or extension moment (hyperflexion or hyperextension), during application of a ten-newton-meter varus or valgus moment, or during application of a ten-newton-meter internal or external tibial torque. With the numbers available, there were no significant differences between the mean tibial rotations associated with the intact posterior cruciate ligament and those associated with the graft at any angle of flexion, without or with applied tibial torque. CLINICAL RELEVANCE: The amount of force generated in the posterior cruciate ligament during the posterior drawer test depends on the angle of flexion at which the test is performed. When the angle of flexion is near 90 degrees, all of the posterior force applied to the tibia is transmitted to the ligament and the force in the ligament is not affected by the position of tibial rotation. When the test is performed at an angle of flexion near 30 degrees and in neutral tibial rotation, other structures (such as the collateral ligaments and the posterior part of the capsule) help to resist the posterior force applied to the tibia. The position of tibial rotation is important when the test is performed with the knee at an angle of flexion near 30 degrees, as secondary structures pre-tensioned by tibial torque act to reduce the amount of force carried by the posterior cruciate ligament even more. With a few minor exceptions, we found that the forces in a graft used to replace the posterior cruciate ligament were approximately the same as those in the intact ligament. Therefore, there appears to be little justification for restricting low-level rehabilitation activities once the fixation of the graft has healed. However, forces in the graft could be quite high during hyperextension and hypertension, as they are in the intact ligament. Thus, bracing in the early postoperative period may be advisable to prevent these motions.

Aged↗
PubMed1996

Effects of combined knee loadings on posterior cruciate ligament force generation.

Resultant forces in the posterior cruciate ligament were measured under paired combinations of posterior tibial force, internal and external tibial torque, and varus and valgus moment. The force generated in the ligament from a straight 100 N posterior tibial force was highly sensitive to the angle of knee flexion. For example, at 90 degrees of flexion the mean resultant force in the posterior cruciate ligament was 112% of the applied posterior tibial force, whereas at 0 degree, only 16% of the applied posterior force was measured in the ligament. When the tibia was preloaded by 10 Nm of external torque, only 9-13% of the 100 N posterior tibial force was transmitted to the posterior cruciate ligament at flexion angles less than 60 degrees; at 90 degrees of flexion, 61% was carried by the ligament. This "off-loading" of the posterior cruciate ligament also occurred when the tibia was preloaded by 10 Nm of internal torque, but only at knee flexion angles between 20 and 40 degrees. The addition of 10 Nm of valgus moment to a knee loaded by a 100 N posterior tibial force increased the mean force in the posterior cruciate ligament at all flexion angles except hyperextension; this represents a common and potentially dangerous loading combination. The addition of 10 Nm of varus moment to a knee loaded by a 100 N posterior tibial force decreased the mean force in the ligament between 10 and 70 degrees of flexion. External tibial torque (alone or combined with varus or valgus moment) was not an important loading mechanism in the posterior cruciate ligament. The application of internal torque plus varus moment at 90 degrees of flexion produced the greatest posterior cruciate ligament forces in our study and represented the only potential injury mechanism that did not involve posterior tibial force.

Aged↗
PubMed1994

The sleep patterns of normal children.

OBJECTIVES: To determine the range of sleep behaviour of normal children to age 38 months and to ascertain the level of parents' problems associated with their child's sleep behaviour. DESIGN AND SETTING: A cross-sectional survey by questionnaire of parents presenting with their children for routine well-child checks at child health centres, mobile clinics, flying doctor clinics and home visits throughout Queensland. Of 3383 questionnaires distributed 3269 (96.5%) were returned. MAIN OUTCOME MEASURES: 1. Sleep frequency and duration, settling procedures, time taken to settle at night, age when child first slept through the night and number of night-time wakenings requiring parental intervention. 2. Parents' problems with their child's sleep behaviour. RESULTS: There is a wide range of normal childhood sleep behaviour. Circadian rhythm is not well established until four months of age. Daytime sleep becomes less regular with increasing age. Frequent night-time wakening is common from four to 12 months. Night-time settling requires more parental input from 18 months. A large proportion of parents (28.6%) have a problem with their child's sleep behaviour. CONCLUSIONS: Parents require information from health care providers about the wide range of normal childhood sleep patterns. This information can help prevent misdiagnosis, inappropriate medication use, child abuse and parental depression when children's sleep patterns are a problem.

Child Behavior↗
PubMed1994

Variation among inbred and linecross mice in response to fescue toxicosis.

Variation in response to fescue toxicosis was examined in inbred and linecross mice. In Exp. 1, exposure to a 50% endophyte-infected tall fescue diet (E+) reduced ADG of males from six inbred lines, but ADG of males from one line was modestly higher on E+. Lines differed (P < .01) for reproductive organ weight, but the diet x line interaction was not significant. In Exp. 2, an apparently susceptible (C57) and an apparently resistant line (FVB) were mated to produce inbred and linecross offspring. The reduction in weight gain caused by the E+ diet did not differ significantly among the genetic groups. In Exp. 3, C57 and C57 backcrosses had smaller reductions in ADG during E+ vs control feeding periods than FVB and FVB backcrosses (P < .10). In Exp. 4, the E+ diet reduced litter size of mates of C57 males by one pup, whereas litter size of mates of FVB males was four pups larger (interaction P = .07). Neither diet, line, nor their interaction affected male reproductive organ weights or tissue proportions in testis cross-sections. In Exp. 5, the E+ diet did not affect weight gain of C57 or FVB males, but effects of the E+ diet on litter size of mates were similar to those in Exp. 4. Percentage of abnormal sperm was increased in C57 males on the E+ diet but decreased in FVB males (Exp. 5). Differences among inbred lines in susceptibility to fescue toxicosis may depend on severity of the challenge and life cycle stage when the challenge is imposed.

Analysis of Variance↗
PubMed1992

"Just a mother".

Explore the source record for details and available documents.

Attitude↗
PubMed1992

Mycobacterium haemophilum causing perihilar or cervical lymphadenitis in healthy children.

We describe five apparently immunologically normal children with infection caused by Mycobacterium haemophilum and resulting in perihilar or cervical lymphadenitis. Clinical distinction from Mycobacterium tuberculosis infection could be made by culture only, because differential Mantoux test results suggested tuberculosis. Treatment of these children involved chemotherapy or surgery or both, and outcome in all cases has been excellent. We believe that M. haemophilum should be added to the list of non-tuberculosis mycobacteria known to cause lymphadenitis in otherwise healthy children.

Antitubercular Agents↗
PubMed1991

Can infant death from child abuse be prevented?

OBJECTIVE: To assess the effectiveness of a child abuse surveillance and intervention program in protecting infants at risk. DESIGN AND SETTING: A retrospective review of all children discussed by the Suspected Child Abuse and Neglect Team of the Mater Misericordiae Children's Hospital, South Brisbane, over the five year period January 1986 to December 1990. PATIENTS: A total of 2126 children were discussed by the team; 375 were infants (less than 12 months of age) at the time of the initial discussion. Nine infants died suddenly and these nine deaths were examined in detail. RESULTS: All deaths were considered initially to be due to sudden infant death syndrome (SIDS), but autopsy findings in six suggested death was not accidental and in the other three significant doubt was raised by the history. Identifying risk factors for non-accidental injury were clearly present in all cases; however, there were major problems with notification to the appropriate authorities. Even in cases where appropriate identification and notification occurred planned interventions by multiple agencies failed to prevent death of these infants. CONCLUSIONS: There is a growing awareness of child abuse as a significant cause of morbidity and mortality in developed countries, but intervention is fraught with multiple difficulties and prevention programs are few. Recommendations are offered for improvement in recognition and notification of incipient child abuse as well as appropriate interventions to prevent infant deaths. Inappropriate death recording procedures may result in some sudden deaths being recorded as SIDS when in fact they are caused by child abuse.

Cause of Death↗
PubMed1991

Gastrointestinal bleeding with influenza virus.

Seven children who presented during the influenza A(H1N1) epidemic of 1988 are described. After a typical influenzal illness, they developed haematemesis of varying severity. Endoscopy revealed haemorrhagic gastritis. Laboratory evidence of influenza A(H1N1) virus infection was present. Two children died as a result of their illness. The association of virus and gastrointestinal haemorrhage is explored.

Child↗