Stability and Trunnion Wear Potential in Large-diameter Metal-on-Metal Total Hips: A Finite Element Analysis

Background

Large-diameter femoral heads for metal-on-metal THA hold theoretical advantages of joint stability and low bearing surface wear. However, recent reports have indicated an unacceptably high rate of wear-associated failure with large-diameter bearings, possibly due in part to increased wear at the trunnion interface. Thus, the deleterious consequences of using large heads may outweigh their theoretical advantages.

Questions/purposes

We investigated (1) to what extent femoral head size influenced stability in THA for several dislocation-prone motions; and the biomechanics of wear at the trunnion interface by considering the relationship between (2) wear potential and head size and (3) wear potential and other factors, including cup orientation, type of hip motion, and assembly/impaction load.

Methods

Computational simulations were executed using a previously validated nonlinear contact finite element model. Stability was determined at 36 cup orientations for five distinct dislocation challenges. Wear at the trunnion interface was calculated for three separate cup orientations subjected to gait, stooping, and sit-to-stand motions. Seven head diameters were investigated: 32 to 56 mm, in 4-mm increments.

Results

Stability improved with increased diameter, although diminishing benefit was seen for sizes of greater than 40 mm. By contrast, contact stress and computed wear at the trunnion interface all increased unabatedly with increasing head size. Increased impaction forces resulted in only small decreases in trunnion wear generation.

Conclusions

These data suggest that the theoretical advantages of large-diameter femoral heads have a limit. Diameters of greater than 40 mm demonstrated only modest improvement in terms of joint stability yet incurred substantial increase in wear potential at the trunnion.

Clinical Relevance

Our model has potential to help investigators and designers of hip implants to better understand the optimization of trunnion design for long-term durability.     

Anxiety Reduction Among Breast-Cancer Survivors Receiving Hypnotic Relaxation Therapy for Hot Flashes

Anxiety is common among breast-cancer survivors. This analysis examined the effect of a hypnotic relaxation therapy, developed to reduce hot flashes, on anxiety levels of female breast-cancer survivors. Anxiety was assessed using a numeric analog scale and the Hospital Anxiety and Depression Scale-Anxiety subscale. Significant reductions in anxiety were found from pre- to postintervention for each weekly session and were predictive of overall reductions in anxiety from baseline to after the last intervention. In this analysis, hypnotizability did not significantly predict for anxiety reductions measured before and after each session or from baseline to exit. These data provide initial support for the use of hypnotic relaxation therapy to reduce anxiety among breast-cancer survivors.     

Stress and quality of sleep among individuals diagnosed with diabetes

Several studies have suggested that stress and sleep may be related to diabetic disease progression. Cortisol is one physiological indicator of stress that has been well validated in previous research. The primary objectives of the present study were (1) to examine the experiences of stress among patients diagnosed with diabetes and (2) to evaluate the quality of sleep among these participants. Participants (mean age = 34.99 years) were 20 adolescents and adults with Diabetes Mellitus; 13 had Type 1 and 17 were female. Primary measures included actigraphy, the Pittsburgh Sleep Quality Index (PSQI), salivary cortisol and the Perceived Stress Scale (PSS). Participants reported a moderate amount of stress (mean PSS scores = 20.2), slept an average of 6.51 h and exhibited at least one clinical indicator of sleep disturbance. Objectively measured total sleep time was associated with awakening cortisol (r = 0.62, p = 0.004) and PSQI Global scores (r = ‐0.51, p = 0.021). Awakening cortisol and PSS scores were not associated with PSQI Global scores, but were related to specific self‐reported sleep disturbances. Given the interacting physiological pathways of stress and sleep, both of which were evident in this small sample, these variables warrant further study. Copyright © 2009 John Wiley & Sons, Ltd.     

Pelvic ultrasound findings in different forms of sexual precocity

Recently produced reference curves for various ultrasound dimensions were used to retrospectively assess 67 pelvic ultrasound scans carried out at the initial presentation in girls with sexual precocity. At presentation the group with precocious puberty had significantly increased uterine lengths and ovarian volumes compared with the normal population, and a significantly increased fundal–cervical ratio. Ovarian volume was also significantly increased in thelarche and thelarche variant. The fundal–cervical ratio was significantly increased in thelarche variant. There was considerable overlap between individuals with sexual precocity and normal subjects. The ultrasound findings that best discriminated early or precocious puberty from other forms of sexual precocity were the presence of a midline endometrial echo, and a uterine length above the 97th centile for age. An entirely normal pelvic ultrasound at presentation did not rule out the possibility of precocious puberty.     

African green monkeys provide a useful nonhuman primate model for the study of human parainfluenza virus types-1, -2, and -3 infection

Human parainfluenza virus (HPIV) types-1, -2, and -3 are significant causes of both upper and lower respiratory tract disease in infants and children. Although there are two live attenuated vaccines for the prevention of HPIV-3 disease in phase 1 clinical trials, vaccines are not currently available for prevention of HPIV-1 or -2 disease. Our laboratory is developing candidate vaccines for the prevention of HPIV-1, -2, and -3 disease, and a suitable nonhuman primate model is needed for evaluation of these vaccine candidates prior to administration to humans. We evaluated the replication of HPIV-1 and -2 in six different species of nonhuman primates and found both viruses to replicate most efficiently in African green monkeys and chimpanzees. We then compared the replication of HPIV-3 in African green monkeys to that in rhesus macaques, which we have used previously, and found that HPIV-3 replicated to higher titer in African green monkeys. In summary, African green monkeys provide a very useful nonhuman primate for the evaluation of HPIV-1, -2, and -3 vaccine candidates, especially for the evaluation of various combinations of these PIV vaccines and for vaccine strategies that employ sequential immunization.     

Substance use by indigenous and non-indigenous primary school students

OBJECTIVE: Recent Australian research with adolescents aged 13 to 17 years has found that Indigenous youth are more likely than non-Indigenous adolescents to smoke tobacco and cannabis, although they may be less likely to use alcohol. The objective of this study was to examine whether this pattern exists among younger children. METHOD: A school-based, self-report survey was conducted in primary schools that had high proportions of Aboriginal and Torres Strait Islander children. Four schools were located in metropolitan Brisbane and three in Far North Queensland (sample n = 507 students: 270 girls, 237 boys, aged 9-13 years). RESULTS: Significant numbers of these children had started to experiment with recreational drugs. Twenty-two per cent had attempted to smoke at least one cigarette, 14% smoked in the preceding year, while 3% had smoked more than 10 cigarettes in their lives. Thirty-eight per cent had had at least one drink of alcohol, while 6% had smoked marijuana at least once. There was no significant association between Indigenous/non-Indigenous background and risk of smoking tobacco or marijuana, while Indigenous children were less likely than non-Indigenous children to report experience with alcohol. CONCLUSIONS: Contrary to data from secondary school students, Indigenous youth in primary schools were not more likely than non-Indigenous children to have experimented with tobacco or marijuana, or to be frequent tobacco smokers. It appears therefore that the excessive uptake of drug use among Indigenous youth occurs in the early stages of secondary school. This finding underlines the importance of preventive education in primary schools, especially for Indigenous children who have a high risk of making the transition to drug use in adolescence.