Biomechanical evaluation of the medial collateral ligament of the elbow

Anatomical dissection and biomechanical testing were used to study twenty-eight cadaveric elbows in order to determine the role of the medial collateral ligament under valgus loading. The medial collateral ligament was composed of anterior, posterior, and occasionally transverse bundles. The anterior bundle was, in turn, composed of anterior and posterior bands that tightened in reciprocal fashion as the elbow was flexed and extended. Sequential cutting of the ligament was performed while rotation caused by valgus torque was measured. The anterior band of the anterior bundle was the primary restraint to valgus rotation at 30, 60, and 90 degrees of flexion and was a co-primary restraint at 120 degrees of flexion. The posterior band of the anterior bundle was a co-primary restraint at 120 degrees of flexion and a secondary restraint at 30 and 90 degrees of flexion. The posterior bundle was a secondary restraint at 30 degrees only. The reciprocal anterior and posterior bands have distinct biomechanical roles and theoretically may be injured separately. The anterior band was more vulnerable to valgus overload when the elbow was extended, whereas the posterior band was more vulnerable when the elbow was flexed. The posterior bundle was not vulnerable to valgus overload unless the anterior bundle was completely disrupted. The intact elbows rotated a mean of 3.6 degrees between the neutral position and the two-newton-meter valgus torque position. Cutting of the entire anterior bundle caused an additional 3.2 degrees of rotation at 90 degrees of flexion, where the effect was greatest. CLINICAL RELEVANCE: Physical findings in a patient who has an injury of the anterior bundle may be subtle, and an examination should be performed with the elbow in 90 degrees of flexion for greatest sensitivity. As the anterior bundle is the major restraint to valgus rotation, reconstructive procedures should focus on anatomical reproduction of that structure. Parallel limbs of tendon graft placed from the inferior aspect of the medial epicondyle to the area of the sublimis tubercle will simulate the reciprocal bands of the anterior bundle. Temporary immobilization with the elbow in flexion may relax the critically important anterior band of the reconstruction during healing.     

Responses of MT and MST neurons to one and two moving objects in the receptive field

To test the effects of complex visual motion stimuli on the responses of single neurons in the middle temporal visual area (MT) and the medial superior temporal area (MST) of the macaque monkey, we compared the response elicited by one object in motion through the receptive field with the response of two simultaneously presented objects moving in different directions through the receptive field. There was an increased response to a stimulus moving in a direction other than the best direction when it was paired with a stimulus moving in the best direction. This increase was significant for all directions of motion of the non-best stimulus and the magnitude of the difference increased as the difference in the directions of the two stimuli increased. Similarly, there was a decreased response to a stimulus moving in a non-null direction when it was paired with a stimulus moving in the null direction. This decreased response in MT did not reach significance unless the second stimulus added to the null direction moved in the best direction, whereas in MST the decrease was significant when the second stimulus direction differed from the null by 90 degrees or more. Further analysis showed that the two-object responses were better predicted by taking the averaged response of the neuron to the two single-object stimuli than by summation, multiplication, or vector addition of the responses to each of the two single-object stimuli. Neurons in MST showed larger modulations than did neurons in MT with stimuli moving in both the best direction and in the null direction and the average better predicted the two-object response in area MST than in area MT. This indicates that areas MT and MST probably use a similar integrative mechanisms to create their responses to complex moving visual stimuli, but that this mechanism is further refined in MST. These experiments show that neurons in both MT and MST integrate the motion of all directions in their responses to complex moving stimuli. These results with the motion of objects were in sound agreement with those previously reported with the use of random dot patterns for the study of transparent motion in MT and suggest that these neurons use similar computational mechanisms in the processing of object and global motion stimuli.     

HIV-1 disease progression and AIDS-defining disorders in rural Uganda

BACKGROUND: The majority of people infected with HIV-1 live in Africa, yet little is known about the natural history of the disease in that continent. We studied survival times, disease progression, and AIDS-defining disorders, according to the proposed WHO staging system, in a population-based, rural cohort in Uganda. METHODS: In 1990 we recruited a random sample of people already infected with HIV-1 (as prevalent cases) detected during the initial survey round of a general-population study to form a natural-history cohort. Individuals from the general-population cohort who seroconverted between 1990 and 1995 (incident cases) were also invited to enroll. Participants were seen routinely every 3 months and when they were III. FINDINGS: By the end of 1995, 93 prevalent cases and 86 incident cases had been enrolled. Four patients in the prevalent group were in stage 4 (AIDS) at the initial visit. During the next 5 years, 37 prevalent cases progressed to AIDS. Seven incident cases progressed to AIDS and the cumulative progression to AIDS at 1, 3, and 5 years after seroconversion was 2%, 6%, and 22%, respectively. The cumulative probability of AIDS at 4 years from entering stages 1, 2, and 3 was 11%, 33%, and 58%, respectively. There were 47 deaths among prevalent cases and seven among incident cases during follow-up. The cumulative mortality 4 years after patients entered stages 1, 2, 3, and 4 was 9%, 33%, 56%, and 86%, respectively. The median survival after the onset of AIDS was 9.3 months. INTERPRETATION: Our results are important for the setting of priorities and rationalisation of treatment availability in countries with poor resources. We found that progression rates to AIDS are similar to those in developed countries for homosexual cohorts and greater than for cohorts infected by other modes of transmission. However, we have found that the rates of all-cause mortality are much higher and the progression times to death are shorter than in developed countries.     

False-positive WBC imaging secondary to a distended bladder and fecal retention

We present the sonographic findings of a fetus with a vesicoallantoic cyst. The cyst was first identified at 17 weeks of gestation; it was associated with an omphalocele, and disappeared spontaneously at 29 weeks. The fetal urinary bladder was not visualized thereafter. An omphalocele and exstrophia of the urachus were found at birth and repaired. Non-visualization of the fetal urinary bladder suggested rupture of the covering membrane of the omphalocele and allantois during fetal life. A defect in the wall of the omphalocele supported our hypothesis.     

Role of permanent stents

Brain dead patients are ideal donors for organ transplantation. The lack of organs has aroused new interest in other kinds of patients who are called non-heart-beating donors. In these donors the warm ischaemia time should be as short as possible. This problem has led to a discrepancy between a proper diagnosis of death and a fast organ procurement. In non-heart-beating donor protocols the death should be determined in an unambiguous manner that can also be accepted in other situations. The best solution would be to create one set of criteria of death that can be applied to all situations. Brain death as the criterion of death also in patients with asystole would serve this purpose.     

New directions in breast cancer research

Research in breast cancer extends in many directions, stimulated by concerns related to the high incidence of the disease and the relative unpredictability of its clinical course. Examples of work in several directions are presented here arranged by four levels of analysis. 1) Molecular, intracellular events (molecular genetics). Recent identification of genes that predispose to breast cancer, and the isolation of those genes and their protein products, permit investigations of the most critical issues: the roles of these genes in normal development and breast differentiation, and how their alteration permits or contributes to tumor initiation. Thus, we expect that understanding the functions of the genes involved in inherited susceptibility to breast cancer will also be informative for sporadic breast cancers. 2) Cellular biology (cellular models for preneoplastic disease). We examine models of breast cancer development and ask how they help to validate a morphologic sequence for human breast neoplasia and whether they permit investigation of how to modify disease progression. Two useful models, one in transgenic mice and the other using human breast stem cells capable of culture and xenograft growth, are now available. 3) Tissue and organ (the tumor and its local environment). We look at the relationship of the tumor cell population to its local environment (stroma, blood vessels, etc.). This leads naturally to questions of how neighboring tissues and cytokines may modify tumor growth. 4) The individual as an organism and member of a population (hormonal rise and chemoprevention). We address identification of the primarily hormonal risk factors and a possible related mode of cancer prevention.     

First year serologic response to treatment for syphilis: a model for prediction of seroreversion

There is no straightforward test available, within weeks of treatment for syphilis, to assess adequacy of serologic response. We propose a method to predict non-treponemal seroreversion based on short term response. To develop and illustrate this method, we used data from 370 individuals with infectious syphilis. Individual serologic response appears to be a linear function of (log) time, suggesting the possibility of using rapid plasma reagin titres recorded in the first few months after treatment to determine the slope of the linear treatment response line. The slope of the response line, during the first year after treatment, is an important predictor of seroreversion but must be considered in conjunction with pre-treatment titre. We recommend development of an action line be developed based on these variables. Such a line would indicate the necessity for retreatment if the line plotted from the patient's first year response failed to fall below the action line.     

Genetic diversity of feline immunodeficiency virus: dual infection, recombination, and distinct evolutionary rates among envelope sequence clades

For the rapid genetic analysis of feline immunodeficiency virus (FIV), we developed a heteroduplex mobility assay (HMA) that utilizes a PCR-amplified fragment of the FIV envelope gene spanning the third and fourth variable regions of the envelope surface protein coding sequence. Viral sequences were successfully amplified from blood specimens from 98 naturally infected cats from Australia, Canada, Germany, Italy, South Africa, and the United States. Eighty were clearly assignable to the A or B envelope sequence subtypes. Three belonged to subtype C, one was dually infected with viruses harboring the A and B env subtypes, and several were categorized as outliers to any of the established subtypes or as probable intersubtype recombinants. Some geographic clustering was evident, with subtypes A and B found in greater frequency in the western and eastern regions of the United States, respectively. Subtypes A, B, and C were found on more than one continent, and countries with more than two samples analyzed contained at least two subtypes. The broadest representation of subtypes was found in Munich, Germany, where three subtypes and one virus that was not classifiable by HMA were found. Thirteen samples were selected for DNA sequence determination over the same region of env used for HMA. Analysis of all available FIV env sequences from this and previous studies revealed the existence of recombinant viruses generated from subtype A/B, B/D, and A/C envelope gene sequences. Subtype A env sequences were less diverse than subtype B sequences, although both groups had well-supported clusters. Furthermore, the mutational pattern giving rise to diversification in the two subtypes differed, with the subtype A viruses showing half as many synonymous site mutations compared to subtype B yet showing similar levels of nonsynonymous site changes. These results are consistent with the hypothesis that FIV-B is an older virus group and is possibly more host adapted than FIV-A.