Assessment of backside wear from the analysis of 55 retrieved tibial inserts

Fifty-five retrieved tibial inserts with four different locking mechanisms were evaluated for evidence for polyethylene wear between the inferior surface of the tibial insert and metal tray. This type of wear will be referred to as backside wear. Backside wear was assessed by evaluating manufacturer's stamped markings on the inferior polyethylene surface. Because these markings are embossed into the polyethylene surface, they were used as indicators of backside wear. Decreases in the depths of markings indicated that backside wear was clearly evident, regardless of design, in 24 (44%) of the inserts. In eight of these 24 inserts, the manufacturer's stamped markings were removed completely. The amount of polyethylene wear was as a high as 591 mg from the inferior surface. This corresponds to a polyethylene wear rate from the backside of the tibial insert of greater than 100 mg per year, which is two to four times higher than wear rates associated with total hip replacements. The current work provides direct evidence of backside wear in all four tibial insert designs. Backside wear of tibial inserts can be a significant contributor to polyethylene wear in total knee arthroplasty. Close attention should be given to the fixation of tibial inserts to metal trays by manufacturers and surgeons.     

Amygdalo-cortical sprouting continues into early adulthood: implications for the development of normal and abnormal function during adolescence

Adolescence is a critical stage for the development of emotional maturity and diverse forms of psychopathology. The posterior basolateral nucleus of the amygdala is known to mediate fear and anxiety and is important in assigning emotional valence to cognitive processes. The medial prefrontal cortex, a homologue of the human anterior cingulate cortex, mediates emotional, attentional, and motivational behaviors at the cortical level. We postulate that the development of connectivity between these two corticolimbic regions contributes to an enhanced integration of emotion and cognition during the postnatal period. In order to characterize the development of this relay, injections of the anterograde tracer biocytin were stereotaxically placed within the posterior basolateral nucleus of the amygdala of rats at successive postnatal time points (postnatal days 6-120). Labeled fibers in the medial prefrontal cortex were evaluated using a combination of brightfield, confocal, and electron microscopy. We found that the density of labeled fibers originating from the posterior basolateral nucleus shows a sharp curvilinear increase within layers II and V of the anterior cingulate cortex and the infralimbic subdivisions of medial prefrontal cortex during the late postweanling period. This increase was paralleled by a linear rise in the number of axospinous and axodendritic synapses present in the neuropil. Based on these results, we propose that late maturation of amygdalo-cortical connectivity may provide an anatomical basis for the development and integration of normal and possibly abnormal emotional behavior during adolescence and early adulthood.     

Ligand binding and protein dynamics in neuroglobin

Neuroglobin (Ngb) is a recently discovered protein in vertebrate brain tissue that belongs to the globin family of proteins. It has been implicated in the neuronal response to hypoxia or ischemia, although its physiological role has been hitherto unknown. Ngb is hexacoordinate in the ferrous deoxy form under physiological conditions. To bind exogenous ligands like O(2) and CO, the His E7 endogenous ligand is displaced from the sixth coordination. By using infrared spectroscopy and nanosecond time-resolved visible spectroscopy, we have investigated the ligand-binding reaction over a wide temperature range (3-353 K). Multiple, intrinsically heterogeneous distal heme pocket conformations exist in NgbCO. Photolysis at cryogenic temperatures creates a five-coordinate deoxy species with very low geminate-rebinding barriers. The photodissociated CO is observed to migrate within the distal heme pocket even at 20 K. Flash photolysis near physiological temperature (275-353 K) exhibits four sequential kinetic features: (i) geminate rebinding (t < 1 micros); (ii) extremely fast bimolecular exogenous ligand binding (10 micros < t < 1 ms) with a nontrivial temperature dependence; (iii) endogenous ligand binding (100 micros < t < 10 ms), which can be studied by using flash photolysis on deoxy Ngb; and (iv) displacement of the endogenous by the exogenous ligand (10 ms < t < 10 ks). All four processes are markedly nonexponential, suggesting that Ngb fluctuates among different conformations on surprisingly long time scales.     

Predictive factors for neoplasia and malignancy in a neck mass

OBJECTIVE: To determine clinical factors that are able to predict the likelihood of neoplasia and malignancy of cervical masses. DESIGN: Retrospective review of case series. Data were collected for age, sex, a history of alcohol and tobacco use, mass location, number, bilaterality, size, and duration. Logistic regression was performed to determine which clinical variables were significant in a prediction model for neoplasia and malignancy in a cervical mass. SETTING: An academic general otolaryngology practice. RESULTS: Review of 160 open neck biopsies yielded 95 complete cases for regression analysis. Thirty cases of neoplasia (31.6%) and 12 cases of malignancy (12.6%) were noted. For the prediction of neoplasia, logistic regression analysis identified patient age, duration, and size of the mass to be statistically significant. The overall model for neoplasia had positive and negative predictive values of 63.6% and 78.1%, respectively, and an overall accuracy of 74.7%. For the prediction of malignancy, only age was found to be significant. The model for malignancy failed to show any classification utility beyond that of clinical judgment. CONCLUSIONS: On the basis of clinical factors, a logistic regression model can distinguish patients who have a low chance for neoplasia in a neck mass, and thereby help avoid unnecessary biopsy. It is not as useful in selecting patients for early biopsy. The strict prediction of malignancy on the basis of clinical variables alone is difficult.     

The effects of dietary selenomethionine on polyamines and azoxymethane-induced aberrant crypts

We evaluated the effects of dietary selenomethionine supplementation on colonic polyamine levels and the ability of L-selenomethionine supplementation to modulate the carcinogenic activity of azoxymethane (AOM) in the rat colon. Four-week-old male F344 rats were treated with 15 mg/kg body weight of AOM once a week for 2 weeks. Dietary selenomethionine at a concentration of either 1 or 2 ppm was administered in AIN-76A rodent diet to AOM-treated animals for 16 weeks. Aberrant crypt foci (ACF), precursor lesions of colon cancer, were investigated after the 16 week treatment course. Selenomethionine given in the diet at 2 ppm markedly reduced the number of aberrant crypt foci. The multiplicity of ACFs (i.e. the number of aberrant crypts/focus) and the percentage of microadenomas were also affected by selenomethionine in a dose dependent manner. However, evaluation of the colonic tissue polyamine levels between control and treated groups showed no significant difference. These results demonstrate that selenomethionine can modulate the development of AOM-induced premalignant lesions through a polyamine-independent mechanism.