Biomedical subjects

L Nokes

Publications and source records attributed to L Nokes.

16 recordsLinked to original sources

PubMed2006

The functional anatomy of Kager's fat pad in relation to retrocalcaneal problems and other hindfoot disorders.

Kager's fat pad is a mass of adipose tissue occupying Kager's triangle. By means of a combined magnetic resonance imaging, ultrasound, gross anatomical and histological study, we show that it has three regions that are closely related to the sides of the triangle. Thus, it has parts related to the Achilles and flexor hallucis longus (FHL) tendons and a wedge of fat adjacent to the calcaneus. The calcaneal wedge moves into the bursa during plantarflexion, as a consequence of both an upward displacement of the calcaneus relative to the wedge and a downward displacement of the wedge relative to the calcaneus. During dorsiflexion, the bursal wedge is retracted. The movements are promoted by the tapering shape of the bursal wedge and by its deep synovial infolds. Fibrous connections linking the fat to the Achilles tendon anchor and stabilize it proximally and thus contribute to the motility of its tip. We conclude that the three regions of Kager's fat pad have specialized functions: an FHL part which contributes to moving the bursal wedge during plantarflexion, an Achilles part which protects blood vessels entering this tendon, and a bursal wedge which we suggest minimizes pressure changes in the bursa. All three regions contribute to reducing the risk of tendon kinking and each may be implicated in heel pain syndromes.

Achilles Tendon↗

PubMed2005

Review of the vascularisation of the human Achilles tendon.

A region of avascularity mid-way along the length of the Achilles tendon has long been associated with rupture. Whilst it is agreed that this region is the location most common to rupture, the exact vascular distribution appears unclear. Regions of avascularity identified within the tendon have included the origin and insertion, as well as the midsection. This review aims to analyse critically and summarise all previous studies of the vascularisation of the healthy human Achilles tendon, in order to determine the most likely region of avascularity and, thereby establish whether a relationship exists between vascularisation and rupture. Whilst no definitive conclusion was reached, it was concluded that the vascularisation does affect the tensile strength and so rupture vulnerability of the healthy Achilles tendon, although it is unlikely to be either the sole, or most significant, contributor. Other factors, such as thinning and twisting of the tendon at the midsection are mechanical influences that will increase the incidence of rupture by increasing the concentration of stress.

Achilles Tendon↗

PubMed2004

Effect of a bisphosphonate, disodium pamidronate, on the quasi-static flexural properties of Palacos R acrylic bone cement.

Aseptic loosening is a major complication of joint replacements and is thought to be associated with a heavy macrophage infiltrate in response to wear particles. Bisphosphonates are compounds known to inhibit osteoclastic activity and are used to reduce osteolysis in Paget's disease, osteoporosis, and metastatic bone disease. Oral bisphosphonates have also been used to decrease osteolysis and therefore prevent aseptic loosening of joint replacements. It has been suggested that bisphosphonates mixed in bone cement can reduce bone resorption in joint replacement surgery. This would be an excellent therapeutic option to prevent or control osteolysis. The present aim was to study the mechanical properties of a commercially available acrylic bone cement, Palacos R, mixed with the bisphosphonate pamidronate. The liquid monomer of Palacos R was mixed with liquid pamidronate. Two groups of bone-cement strips were produced, one with added pamidronate and one without. The flexural properties of the cement strips were examined. A significant reduction in both the bending modulus and bending strength of the specimens with added pamidronate was found. In conclusion, the use of liquid pamidronate mixed with the acrylic bone cement Palacos R in order to reduce osteolysis is not recommended because of its effect on the mechanical properties of Palacos R.

Algorithms↗

PubMed2001

Visual and visuospatial development in young children with Williams syndrome.

This study investigated the relation between sensory visual problems and the severity of visuospatial difficulties in a large group of young children with Williams' syndrome (WS). A questionnaire describing visual and associated problems was completed by the families of 108 children with WS and detailed follow-up assessments were conducted, including visual, spatial, motor, visuocognitive, and linguistic tests of 73 of these children (mean age 7 years 3 months; 40 males, 73 females). Children with WS showed a much higher incidence of common paediatric sensory vision problems (strabismus, visual acuity loss, amblyopia, reduced stereopsis) than normally developing children. It was found that delays with respect to age normative values increased with age on all tests. No significant correlation was found between the presence of a visual deficit and the severity of the visuospatial problems, suggesting that the difficulties children with WS have in understanding spatial arrangements are not simply a result of their earlier sensory visual problems. Results confirm the dissociation between visuospatial and language abilities in children with WS, and support the neurobiological model of a split between ventral and dorsal stream processing of visual information with a generalized deficit in dorsal stream processing in young children with WS.

Amblyopia↗

PubMed2001

The use of handheld cement sample as a guide to the setting of in situ cement mantle.

During cemented joint arthroplasties, it is necessary to monitor the hardening of the cement to know when it is soft enough to allow insertion of the prosthesis but viscous enough to maintain bone interlock. Most often, a small piece of cement is left out and checked for hardening. These cement pieces are exposed to different fates, which include being held in the hand, held between fingers and kneaded, and left on the instrument table. The value of any of these techniques for predicting the cement's hardening has not been investigated formally. During 9 total hip arthroplasties, polymethyl methacrylate bone-cement was used in cementing the femoral component. Three 1-cm(3) samples collected from each operation site were exposed to the aforementioned 3 different conditions. The fingertip-held and kneaded cement specimens most closely predicted the time to setting of the cement mantle at the operation site.

Adult↗

PubMed1997

A specific deficit of dorsal stream function in Williams' syndrome.

Williams' syndrome (WS) is a rare, genetically based disorder of cognitive development. Affected individuals show a severe deficit of spatial cognition but a relative sparing of language and face recognition. To examine the possible neural basis of the spatial deficit, we tested a group of WS children, aged 4-14 years, on two measures specific to dorsal cortical stream function: global motion coherence thresholds, in comparison with an analogous form-coherence test, and visuo-manual accuracy in posting a card through a slot, compared with matching the slot orientation. Deficits in these tasks provide the first evidence of specific involvement in WS of the dorsal stream, the cortical system believed to encode information about spatial relationships and the visual control of action.

Adolescent↗

PubMed1996

Visual function and perinatal focal cerebral infarction.

AIMS: To evaluate the visual function of infants with perinatal cerebral infarction in whom the site and size of the lesion has been determined using magnetic resonance imaging (MRI). METHODS: Twelve infants with cerebral infarction on MRI were studied with a battery of tests specifically designed to evaluate visual function in infancy. This included tests: for visual attention (fixation shifts); of cerebral asymmetry (optokinetic nystagmus, visual fields); for assessment of acuity (forced choice preferential looking); and neurophysiological measures of vision (phase reversal and orientation reversal visual evoked potential). RESULTS: A considerable incidence of abnormalities on at least one of the tests for visual function used was observed. The presence or severity of visual abnormalities could not always be predicted by the site and extent of the lesion seen on imaging. CONCLUSIONS: Early focal lesions affecting the visual pathway can, to some extent, be compensated for by the immature developing brain. These data suggest that all the infants presenting with focal lesions need to be investigated with a detailed assessment of various aspects of vision.

Cerebral Infarction↗

PubMed1995

Coverage of routine neonatal metabolic screening in children born to women known to be infected with HIV-1.

Unlinked anonymous HIV-1 testing of neonatal samples routinely collected for metabolic screening is now carried out in many parts of the United Kingdom. The purpose of this study was to assess the completeness of screening coverage in infants born to women known to be infected with HIV-1. Research nurses at family HIV clinics in three London hospitals searched for Guthrie cards from all infants born to known infected residents of North East, North West, and South West Thames regions over a 32 month period. If no card was found initially, mothers were approached for more information. Overall coverage was estimated to be 96.4% (94.6% in infants of African origin and 100% in white infants). These figures are similar to recent general population coverage estimates in inner London. We conclude that the anonymous newborn HIV testing programme is providing sufficiently accurate information on both absolute levels and time trends in maternal seroprevalence.

Africa↗

PubMed1995

Antibody responses to Haemophilus influenzae type b and Streptococcus pneumoniae vaccines in children with human immunodeficiency virus infection.

Antibody responses to Haemophilus influenzae type b (Hib) conjugate (ActHIB; Pasteur Merieux) and pneumococcal (Pneumovax II; Morson) vaccines were measured in 56 infected children (VI) and 44 uninfected children (U) older than 18 months of age, born to human immunodeficiency virus-positive mothers. Preimmunization, 21% U and 20% VI had protective concentrations of anti-Hib polysaccharide antibodies. Postimmunization, 100% U and 86% VI achieved protective titers (P = 0.008). The geometric mean increase in anti-Hib polysaccharide antibody was 7.6 (95% confidence interval, 3.5 to 16.3; P = 0.0001) times higher in U than in VI children after adjusting for age and ethnicity. Sixty-one percent U compared to 54% VI showed a 2-fold increase in antibody levels to at least one of the four pneumococcal vaccine serotypes (3, 6, 19, 23) measured (P = 0.4). For both vaccines there was a significant trend toward poorer responses in children with acquired immunodeficiency syndrome but no correlation with age adjusted CD4 counts. These data suggest that human immunodeficiency virus-infected children should be immunized with these polysaccharide vaccines early in the course of their disease.

Antibodies, Bacterial↗

PubMed1995

Pharmacokinetics of zidovudine and dideoxyinosine alone and in combination in children with HIV infection.

The pharmacokinetics of zidovudine (ZDV) and dideoxyinosine (ddI) were investigated following administration alone and in combination to children with symptomatic HIV disease. The children were studied on three separate occasions and received ZDV 200 mg m-2, ddI 100 mg m2 or a combination of ZDV 200 mg m-2 plus ddI 100 mg m-2. The administration of ddI did not significantly alter ZDV pharmacokinetics. The area under the curve (AUC) was 14.2 +/- 4.9 and 15.8 +/- 7.2 mumol l-1 h and elimination half-life (t1/2, z) was 1.4 +/- 0.4 and 1.2 +/- 0.2 h in the absence and presence of ddI respectively. The peak concentration (Cmax), time to peak (tmax) and apparent oral clearance (CL/F) were also unchanged. The administration of ZDV had no significant effect on ddI Cmax, tmax, t1/2,z, or CL/F, however the AUC was reduced by 19% (5.9 +/- 2.9 to 4.8 +/- 2.7 mumol l-1 h; P < 0.05). This study suggests that ZDV and ddI may be co-administered to children with symptomatic HIV disease without concern of a clinically relevant pharmacokinetic drug interaction.

Administration, Oral↗

PubMed1994

Impact characteristics of two types of police baton.

A comparison study of the American style ASP extendible police baton with the conventional UK police wooden truncheon was performed. It was found that the ASP baton generated approximately twice the contact pressure than the conventional wooden truncheon. A discussion on the medical/legal aspects of the results are given.

Biomechanical Phenomena↗

PubMed1994

The mechanics of stab wounding.

The dynamics of stab wounds were investigated using a load cell connected to microcomputer-based measuring equipment. Two types of knife blade were attached to the load cell to assess the characteristics of stab wounds caused in pig tissue. The results show that as the blade progresses through the tissue it is resisted mostly by the skin, but a significant secondary resistance exists in the deeper muscle layers.

Animals↗

PubMed1985

Vibration analysis in the assessment of conservatively managed tibial fractures.

A simple and quantitative method for the assessment of fracture healing has been developed. this method depends on a technique of vibration analysis evolved from a study of 30 intact human tibiae and has been applied to the study of 22 tibial fractures. Real time vibration analysis will allow quantitative comparisons of different methods of non-operative fracture management, and, in addition to providing a uniquely powerful research tool, may have value in aiding clinical management decisions.

Biomedical Engineering↗

PubMed1984

Direct and indirect determination of tibial natural frequency--a comparison of frequency domain analysis and fast Fourier transform.

The natural frequency of in vivo mechanical systems has been derived in the past by signal conditioning techniques. For the living tibia the accuracy of this derived method was not validated. In addition the use of Fast Fourier Transform is time consuming, tedious and expensive. Direct measurement yields results which are more accurate, more easily obtained, and more clinically applicable.

Biomechanical Phenomena↗

PubMed1984

Vibration analysis of human tibia: the effect of soft tissue on the output from skin-mounted accelerometers.

The vibration response of bone can be recorded from a skin-mounted accelerometer, but only if it is sufficiently preloaded to overcome the damping effect of the interposed soft tissue. Excessive preload results in distortion of the recorded signal by a high-frequency component which probably originates in the supporting apparatus of the accelerometer. The required preload is proportional to the soft tissue thickness, but for any given soft tissue thickness, the range of allowable preload is fairly wide.

Acceleration↗

PubMed1984

Abdominal girth: an unreliable measure of intra-abdominal bleeding.

The measurement of abdominal girth in an attempt to detect intra-abdominal bleeding may be dangerously misleading. It is an inaccurate measure of intra-abdominal collection of fluid. The results show that measurements are heavily biased by the expectations of observers, with the result that a considerable change in girth is likely to be ignored. The error caused by observer bias is much greater than the distension which actually occurs when fluid collects in the abdomen over a short period.

Abdomen↗