The friction of explanted hip prostheses

Charnley prostheses, retrieved at revision surgery, were studied to assess the effects of friction on the total hip replacement procedure. Frictional resistance was measured using the Durham hip function simulator under both dry and lubricated conditions. The friction factor values (f) for the explanted prostheses were found to have a non- Gaussian distribution with medians of 0.13 [inter-quartile range (IQR) 0.10-0.16] and 0.06 (IQR 0.005-0.08) for dry and lubricated (n = 0.01 Pa s) regimes, respectively. New Charnley prostheses had values of f equal to 0.11 +/- 0.025 and 0.04 +/- 0.01 under the same conditions, and showed no large deviation from a Gaussian distribution. There was found to be a statistically significant difference in the medians of the friction factors for new and retrieved prostheses in the lubricated regime. Ingression of cement into the worn region of the cup was found to increase the friction factor significantly under dry conditions. There was no evidence of an increase in the friction factor or torque for those joints that had a loose socket with respect to those that were fixed at revision. A decrease in the frictional torque against number of cycles undergone by the joint in vivo may indicate that a fatigue-type process may have a role in the loosening of the socket. However, this relationship was found not to be significant for friction measured under lubricated conditions and it seems unlikely that the frictional torque generated in this type of prosthesis will contribute significantly to the long-term loosening of the socket.      

Intraoperative measurement of cortical blood flow adjacent to cerebral AVM using laser Doppler velocimetry

Standard methods for measurement of cerebral blood flow (CBF) are not optimal for continuous intraoperative recording. Laser Doppler velocimetry has been used for evaluation of microcirculatory flow in a variety of human tissues, including skin, muscle, and retina. The authors report the use of this technique for measuring flow in human cerebral cortex. The physiological changes associated with excision of a cerebral arteriovenous malformation are interpreted using CBF recorded intraoperatively with the laser Doppler probe.     

Apparent unilateral visual neglect in MPTP-hemiparkinsonian monkeys is due to delayed initiation of motion

Monkeys made hemiparkinsonian by infusion of a solution of MPTP into one carotid artery appeared to ignore food presented from the contralateral side. Initial observations suggested neglect of visual stimuli presented as fruit treats by automated delivery system in the half-field contralateral to MPTP treatment. Further studies in which fruit treats were left in the 'neglected' visual field indicated that this apparent neglect, unlike neglect attending cortical lesions, was rather a marked delay in initiating movements (unilateral hypokinesia). These observations may explain apparent subcortical neglect and are consistent with the known role of nigrostriatal dopaminergic neurones in movement regulation. This is a useful animal model in which difficulties in initiation of movement (hypokinesia). a cardinal symptom of Parkinson's disease, can be studied separately from other deficits in motor performance.     

A comparison of histological and immunohistochemical methods for quantifying the pathological lesions of Pick's disease

Counts of Pick bodies (PB), Pick cells (PC), senile plaques (SP) and neurofibrillary tangles (NFT) were made in the frontal and temporal cortex from patients with Pick's disease (PD). Lesions were stained histologically with hematoxylin and eosin (HE) and the Bielschowsky silver impregnation method and labeled immunohistochemically with antibodies raised to ubiquitin and tau. The greatest numbers of PB were revealed by immunohistochemistry. Counts of PB revealed by ubiquitin and tau were highly positively correlated which suggested that the two antibodies recognized virtually identical populations of PB. The greatest numbers of PC were revealed by HE followed by the anti-ubiquitin antibody. However, the correlation between counts was poor, suggesting that HE and ubiquitin revealed different populations of PC. The greatest numbers of SP and NFT were revealed by the Bielschowsky method indicating the presence of Alzheimer-type lesions not revealed by the immunohistochemistry. In addition, more NFT were revealed by the anti-ubiquitin compared with the anti-tau antibody. The data suggested that in PD: (i) the anti-ubiquitin and anti-tau antibodies were equally effective at labeling PB; (ii) both HE and anti-ubiquitin should be used to quantitate PC; and (iii) the Bielschowsky method should be used to quantitate SP and NFT.     

Septicaemia as a hospital hazard

In 1 year there were 135 episodes of septicaemia in a large referral hospital serving a population of 400,000 people. Of these, 52 were hospital-acquired giving a nosocomial septicaemia rate of 2.08 per 1000 admissions. The mortality rate rose with the number of antibiotics used; from 15% in those receiving one drug to 50% in those receiving three. A wide variety of organisms were encountered, the largest group being Staphylococcus aureus, 12 episodes; and Escherichia coli, nine episodes. Staphylococcus epidermis was pathogenic in seven patients with one death. A review of possible aetiological factors showed that 28 episodes occurred postoperatively with surgery considered directly responsible in 20. Intravenous cannulae were in place in 39 patients at the time of development of infection; they were causal in at least five; with two deaths. Urinary catheters were in situ in 14 patients and causal in at least six, with two deaths. Immunosuppression by drugs carried a worse prognosis than when infection occurred in patients with immunosuppressive disease.     

The effect of fetal mesencephalon implants on primate MPTP-induced parkinsonism. Histochemical and behavioral studies

Parkinsonism or hemiparkinsonism was induced by administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in four rhesus monkeys, which then received homologous fetal mesencephalon implants into the caudate nuclei. Cavities were prepared in the medial caudate nucleus 2 to 5 weeks before the fetal grafts were implanted. Control studies were conducted in unoperated MPTP-treated animals. Significant behavioral improvement, which occurred within weeks of implantation of fetal mesencephalon, was sustained for up to 7 months. No recovery was seen in the unoperated control animals. Histological examination revealed numerous surviving tyrosine hydroxylase (TH)-immunoreactive cell bodies. In addition to the graft, abundant TH-immunoreactive fibers were observed in the host caudate nucleus ventral to the region of the implanted and the nonimplanted cavities. Since TH-immunoreactive cell bodies of the substantia nigra compacta (A-9 cells) were destroyed by MPTP treatment and the ventral tegmental area (A-10) remained intact, it is concluded that sprouting of remaining host dopaminergic fibers occurs. These newly formed fibers appeared to emanate from the mesolimbic projection to the striatum. It is likely that the newly sprouted dopaminergic fibers account for the motor improvement elicited by precavitation and fetal mesencephalon implantation. These results suggest that the mechanism of recovery of parkinsonian primates after implantation of fetal dopaminergic tissue into the caudate nucleus is by stimulation of sprouting from host neurons. They also suggest that, with identification of the factors responsible for the formation of the new dopaminergic neuronal processes and with further development, tissue implantation may be an effective therapy for Parkinson's disease in humans.     

The effect of temperature on the tuning and physiology of insect auditory receptors

The characteristic sound frequency, maximum spike response, spontaneous activity and rate of adaptation of individual auditory receptors in locusts increase as the ambient temperature increases. For changes in the ambient temperature between 22 degrees C and 32 degrees C the characteristic frequency shifted by 0.1 to 0.2 octaves per degree centrigrade with an average thermal Q10 of 2.93 and the maximum rate of production of action potentials of individual receptors doubled. These effects exceed those expected from temperature dependent changes in mechanical properties of the tympanic membrane or the auditory organ. It is therefore concluded that the receptors contain a temperature dependent cellular process that contributes to the tuning of the sensilla.     

Basilar venous plexus of the posterior fossa: a potential source of error in petrosal sinus sampling

Sampling of serum from the inferior petrosal sinus can provide important information about the source of elevated adrenocorticotropic hormone (ACTH) levels. This often leads to improved results of pituitary surgery for Cushing disease. The authors describe a successful catheterization technique and illustrate the venous anatomy of the inferior petrosal sinuses and basilar plexus.