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Introduction: Bridge plating of distal femur fractures with lateral locking plates is susceptible to varus collapse, fixation failure, and nonunion. While medial and lateral dual plating has been described in clinical series, the biomechanical effects of dual plating of distal femur fractures have yet to be clearly defined. The purpose of this study was to compare dual plating to lateral locked bridge plating alone in a cadaveric distal femur gap osteotomy model. Materials and Methods: Gap osteotomies were created in eight matched pairs of cadaveric female distal femurs (average age: 64 yrs (standard deviation ± 4.4 yrs); age range: 57–68 yrs;) to simulate comminuted extraarticular distal femur fractures (AO/OTA 33A). Eight femurs underwent fixation with lateral locked plates alone and were matched with eight femurs treated with dual plating: lateral locked plates with supplemental medial small fragment non-locking fixation. Mechanical testing was performed on an ElectroPuls E10000 materials testing system using a 10 kN/100 Nm biaxial load cell. Specimens were subject to 25,000 cycles of cyclic loading from 100-1000 N at 2 Hz. Results: Two (2/8) specimens in the lateral only group failed catastrophically prior to completion of testing. All dual plated specimens survived the testing regimen. Dual plated specimens demonstrated significantly less coronal plane displacement (median 0.2 degrees, interquartile range [IQR], 0.0–0.5 degrees) compared to 2.0 degrees (IQR 1.9-3.3, p = 0.02) in the lateral plate only group. Dual plated specimens demonstrated greater bending stiffness compared to the lateral plated group (median 29.0 kN/degree, IQR 1.5–68.2 kN/degree vs median 0.50 kN/degree, IQR 0.23–2.28 kN/degree, p = 0.03). Conclusion: Contemporary fixation methods with a distal femur fractures are susceptible to mechanical failure and nonunion with lateral plates alone. Dual plate fixation in a cadaveric model of distal femur fractures underwent significantly less displacement under simulated weight bearing conditions and demonstrated greater stiffness than lateral plating alone. Given the significant clinical failure rates of lateral bridge plating in distal femur fractures, supplemental fixation should be considered, and dual plating of distal femurs augments mechanical stability in a clinically relevant magnitude.

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This study explored the relationship between gay identity-related factors (gay community involvement, gay bar attendance, gay identity importance, and self-homophobia) and unprotected anal sex (UA) in the past 3 months among men who have sex with men (MSM) of three different race/ethnicity groups. Four hundred eighty-three MSM (mean age 34) were recruited in the San Francisco Bay Area (33% African American, 34% Latino and 33% White). Compared with White MSM, African American and Latino MSM were less likely to identify as gay, and to attend gay bars/clubs, and more likely to report self-homophobia. Just over one third of the sample reported UA (did not vary by race). Gay community involvement was associated with receptive UA with all partners (adjusted odds ratio [AOR = 1.30, 95% Confidence Interval (CI) = 1.06-1.60). Gay bar attendance was associated with insertive UA with all partners (AOR = 1.20, 95% CI = 1.01-1.43) and with HIV-discordant partners (AOR = 1.35, 95% CI = 1.08-1.69). Implications for prevention include addressing community norms and encouraging alternatives to bars as settings in which to meet and socialize with other MSM.

Objective: To assess the interest of out-of-treatment methamphetamine-using men who have sex with men (MSM) seen at public health STD clinics in an intervention specifically targeting their drug use. Study Design: An anonymous, self-administered survey of MSM who use methamphetamine attending public health STD clinics in Seattle and San Francisco. Results: Among 174 men surveyed, 36% reported being considerably or extremely troubled or bothered by their methamphetamine use, 62% reported a considerable or extreme desire to reduce or stop their use of methamphetamine, and 52% reported considerable or extreme interest in attending a program to stop or decrease methamphetamine use. While 70% of the men surveyed had attempted to stop using methamphetamine, only 12% had ever been in drug treatment. Conclusions: In a two-city sample of MSM who use methamphetamine, interest in an intervention to help men stop or decrease their methamphetamine use is high. Interventions that target methamphetamine use and are delivered through the public health system merit further investigation.

Objective To examine the prevalence of negotiated safety (NS) in a diverse sample of HIV-negative men who have sex with men (MSM), characteristics of MSM practicing NS, and adherence to NS. Methods This was a cross-sectional survey of San Francisco MSM recruited from venues and community organizations. NS relationships were defined as those in which HIV-negative men were in seroconcordant primary relationships for >/=6 months, had unprotected anal intercourse (UA) together, and had rules prohibiting UA with others. Adherence to NS was determined from self-reported sexual behavior in the prior 3 months. Presence of an agreement with NS partners to disclose rule breaking was also determined. Results Of 340 HIV-negative participants, 76 (22%) reported a current seroconcordant primary relationship for >/=6 months. Of these 76 men, 38 (50%) had NS relationships, 30 (39%) had no UA with primary partners, and 8 (11%) had UA with primary partners without rules prohibiting UA with others. In multivariate analysis, NS was more common than no UA with primary partners in younger men. Among 38 NS men, 29% violated their NS-defining rule in the prior 3 months, including 18% who reported UA with others, and 18% reported a sexually transmitted infection (STI) in the prior year. Only 61% of NS men adhered fully to rules and agreed to disclose rule breaking. Conclusions Although NS was commonly practiced among HIV-negative men in seroconcordant relationships, some men violated NS-defining rules, placing themselves and potentially their primary partners at risk for HIV infection. Prevention efforts regarding NS should emphasize the importance of agreement adherence, disclosure of rule breaking, and routine STI testing.

The objective of this study was to estimate frequency and correlates of discussing HIV viral load (VL) with serodiscordant sex partners to guide decisions about sexual activities among men who have sex with men (MSM). We conducted a cross-sectional survey of 573 San Francisco MSM. Among 507 who knew their HIV status, 397 (78%) were familiar with the term 'viral load', and half (n=199) had a serodiscordant partner in the prior year. These 199 respondents (n=130 [65%] HIV-positive; n=69 [35%] HIV-negative) were the focus of this analysis. A majority (n=111, 56%) discussed VL in the prior year with serodiscordant partners specifically to guide decisions about sexual risk behaviour. Discussion was more common among HIV-positive than HIV-negative participants (adjusted odds ratio [AOR], 3.5; 95% confidence interval [CI], 1.6-7.6), and African Americans compared to whites (AOR, 3.7; 95% CI, 1.5-9.5). HIV-negative men who discussed VL were more concerned about becoming infected, but also more willing to engage in risky behaviour with a partner whose VL is undetectable, than men not discussing VL. Some HIV-negative men may be discussing VL to engage in higher risk behaviour upon learning of an HIV-positive partner's undetectable VL. Interventions targeting MSM should explain that while risk of transmission is likely reduced with a low blood plasma VL, it is not necessarily eliminated.

Objectives: There is evidence that methamphetamine and sildenafil (Viagra) use are associated with sexual risk behaviour among men who have sex with men (MSM). We investigated the association of methamphetamine, sildenafil, and other substance use with unprotected receptive and insertive anal sex among MSM by conducting an encounter specific analysis. Methods: Data were from a cross sectional, community based survey of MSM in San Francisco regarding behaviour during their most recent anal sex encounter. Mulitvariate regression analysed independent associations of specific substance use and demographic variables with unprotected anal sex behaviours. Results: The sample (n = 388) was diverse in race/ethnicity, age, income, education, HIV status, and homosexual/bisexual identification. More than half (53%) reported unprotected anal sex, including insertive (29%) and receptive (37%) during their most recent anal sex encounter; 12% reported unprotected insertive and 17% reported unprotected receptive anal sex with an HIV discordant or unknown partner. Methamphetamine was used by 15% and sildenafil was used by 6% of the men before or during the encounter; 2% used both drugs. In multivariate analysis controlling for demographic factors and other substance use, methamphetamine use was associated with unprotected receptive (odds ratio (OR), 2.03; 95% confidence interval (CI), 1.09 to 3.76) and sildenafil use was associated with unprotected insertive (OR, 6.51; CI, 2.46 to 17.24) anal sex. Effects were stronger with HIV discordant or unknown sex partners specifically. Conclusion: Encounter specific associations of methamphetamine and sildenafil use with unprotected receptive and insertive anal sex, respectively, indicate the importance of assessment specificity and tailoring risk reduction efforts to address certain drugs and sexual behavioural roles among MSM.

Objectives: To assess the prevalence of and factors associated with 'barebacking' as a sociocultural phenomenon in a sample of HIV-positive and -negative men who have sex with men (MSM), and to assess the reasons for barebacking and venues for meeting partners. Design: A cross-sectional survey of MSM recruited in the San Francisco Bay Area from July 2000 to February 2001. Methods: Barebacking, defined as 'intentional anal sex without a condom with someone other than a primary partner', was assessed among men who had heard of the term. Participants were recruited outside multiple venues and interviewed later at community locations. Chi-square and multivariate logistic regression were used for analysis. Results: The sample (n = 554) of MSM were African-American (28%), Latino (27%), white (31 %) and other race/ethnicity (14%); 35% reported being HIV-positive. Seventy per cent of the men had heard of barebacking. Among men aware of the term, 14% had barebacked in the past 2 years (22% of HIV-positive versus 10% of HIV-negative men, P < 0.001); 10% of the full sample did so. The prevalence of barebacking did not differ by race/ethnicity or sexual orientation identification. Men tended to report bareback partners who had the same HIV serostatus; however, a sizeable proportion of men had partners of different or unknown serostatus. Increased physical stimulation and emotional connectedness were the primary reasons for barebacking. Conclusion: New approaches are needed to reduce bareback behavior and the risk of HIV transmission, including innovative health-promoting behavioral and biomedical interventions.

Context: HIV risk behavior among urban gay/bisexual men has recently increased. High-risk sexual activity and drug use may be particularly high during circuit party (CP) weekends, during which gay/bisexual men congregate for social activities and dancing. Objectives: To compare prevalence of risk behaviors during CP weekends with those during non-CP weekends. Design: Cross-sectional study. Participants: 295 gay/bisexual men from the San Francisco Bay Area. Main Outcome Measures: Drug use and sexual risk behavior during a San Francisco CP weekend, a CP weekend held in another geographic area (distant weekends), and two non–CP weekends. Results: During their most recent distant CP weekend, 80% of participants used methylenedioxymethamphetamine (ecstasy), 66% ketamine, 43% crystal methamphetamines, 29% gamma-hydroxybutyrate or gamma-butyrolactone (GHB/GBL), 14% sildenafil (Viagra), and 12% amyl nitrites (poppers); 53% used four or more drugs. Drug use prevalence was greater during CP than non-CP weekends (p < .001). Unprotected anal sex with partners of unknown or opposite HIV serostatus was most prevalent during distant CP weekends, reported by 21% of HIV-positive and 9% of HIV-negative participants. In multivariate analysis, predictors of unprotected anal sex with opposite or unknown HIV serostatus partners included being HIV-positive (odds ratio [OR], 3.2; 95% confidence interval [CI], 1.4–7.5), and weekend use of crystal methamphetamines (OR 2.4; 95% CI, 1.1–4.9), sildenafil (OR, 3.8; 95% CI, 2.0–7.3), and amyl nitrites (OR, 2.2; 95% CI, 1.3–4.0). Conclusions: Prevalence of high-risk activity during these weekends suggests significant potential for HIV transmission in this population. Public health programs in communities hosting CPs should aim to reduce rates of drug use and sexual risk behavior among CP participants, especially HIV-positive men.

OBJECTIVES: This study described HIV prevalence, risk behaviors, health care use, and mental health status of male-to-female and female-to-male transgender persons and determined factors associated with HIV. METHODS: We recruited transgender persons through targeted sampling, respondent-driven sampling, and agency referrals; 392 male-to-female and 123 female-to-male transgender persons were interviewed and tested for HIV. RESULTS: HIV prevalence among male-to-female transgender persons was 35%. African American race (adjusted odds ratio [OR] = 5.81; 95% confidence interval [CI] = 2.82, 11.96), a history of injection drug use (OR = 2.69; 95% CI = 1.56, 4.62), multiple sex partners (adjusted OR = 2.64; 95% CI = 1.50, 4.62), and low education (adjusted OR = 2.08; 95% CI = 1.17, 3.68) were independently associated with HIV. Among female-to-male transgender persons, HIV prevalence (2%) and risk behaviors were much lower. Most male-to-female (78%) and female-to-male (83%) transgender persons had seen a medical provider in the past 6 months. Sixty-two percent of the male-to-female and 55% of the female-to-male transgender persons were depressed; 32% of each population had attempted suicide. CONCLUSIONS: High HIV prevalence suggests an urgent need for risk reduction interventions for male-to-female transgender persons. Recent contact with medical providers was observed, suggesting that medical providers could provide an important link to needed prevention, health, and social services.

Background: Research suggests that because of economic necessity, many male-to-female (MTF) transgender individuals trade sex for money, drugs, housing, and other things they may need. To date, no studies have quantitatively assessed psychosocial correlates of condom use with this population. Methods: We conducted a cross sectional study with 190 MTF transgender individuals involved in sex trade in San Francisco, California. Multivariate logistic regression was used to determine factors independently associated with inconsistent condom use during receptive anal sex with exchange partners. Results: About one fifth of our participants reported inconsistent condom use during receptive anal sex in the past 6 months. In the multivariate model, low self-esteem [adjusted odds ratio (AOR) = 3.09; 95% confidence interval (CI) (1.28, 7.47)], a history of forced sex or rape [AOR = 2.91; 95% CI (1.06, 8.01)], and use of crack-cocaine [AOR = 2.59; 95% CI (1.09, 6.13)] were independently associated with inconsistent condom use. Conclusions: Our findings highlight an urgent need for multilevel risk reduction interventions for MTF transgender individuals involved in sex trade. Such interventions will be most effective if they address the psychosocial context of sexual risk taking by focusing on issues such as low self-esteem, sexual violence, and illicit drug use.

This paper considers the response of various types of elastic collision cross sections to functional variations in the intermolecular potential. The following cross sections are considered differential, total, effective diffusion, and effective viscosity. A very simple expression results for the diffusion and viscosity cross sections at high energy relating the variations to the classical deflection function. Attention is first given to the forward sensitivity densities δσ(E)/δV(R) [i.e., the functional derivative of cross sections σ(E) with respect to the potential surface V(R)]. In addition inverse sensitivity densities δV(R)/δσ(E) are obtained. These inverse sensitivity densities are of interest since they are the exact solution to the infinitesimal inverse scattering problem. Although the inverse densities do not in themselves form an inversion algorithm, they do give a quantitative measure of the importance of performing particular measurements for the ultimate purpose of inversion. In addition, the ...

A general technique is described for gaining insight into inversion processes. Upon solving the equation of motion associated with a given physical model, specialized inverse coefficients are calculated to address questions on inverse modeling. The number of accessible independent inverse coefficients is shown to be directly related to the number of independent pieces of modeling data taken as available. Although the inverse coefficients do not in themselves form an inversion algorithm, they do give a quantitative measure of the importance of performing certain additional measurements for the ultimate purpose of inversion. The concepts are illustrated by some simple dynamical models. The calculations show that the normal forward sensitivities and the new inverse coefficients generally exhibit disparate behavior in accord with the differing physical quantities being addressed.

This paper considers the response of various rotational energy transfer processes to functional variations about an assumed model intermolecular potential. Attention is focused on the scattering of an atom and a linear rigid rotor. The collision dynamics are approximated by employing both the infinite order sudden (IOS) and exponential distorted wave (EDW) methods to describe Ar–N2 and He–H2, respectively. The following cross sections are considered: state‐to‐state differential and integral, final state summed differential and integral, and effective diffusion and viscosity cross sections. Attention is first given to the forward sensitivity densities δ0/δV(R,r) where 0 denotes any of the aforementioned cross sections, R is the intermolecular distance, and r is the internal coordinates. These forward sensitivity densities (functional derivatives) offer a quantitative measure of the importance of different regions of the potential surface to a chosen cross section. Via knowledge of the forward sensitivities...

The functional relation between elastic total cross sections and interatomic potentials is examined. The forward scattering process is explored by the sensitivity densities δσ( E )/δ V ( R ) and in a similar fashion inverse scattering is probed by the densities δ V ( R )/δσ( E ). Both densities provide valuable information about the relation between structure in the cross section and potential.