Ingrowth and formation of bone in defects in an uncemented fiber-metal total hip-replacement model in dogs.

An osseous defect was created in the acetabulum and femur of twenty dogs, and then a fiber-metal total hip prosthesis was inserted. A comparison was made between the effects of leaving the defects unfilled, filling the defects with an autogenous bone graft, and filling them with a 50:50 mixture of autogenous bone graft and a biphasic ceramic composed of hydroxyapatite and tricalcium phosphate. The characteristics of formation of bone within the sites of the defects and the extent of the ingrowth of bone into the underlying porous surface were analyzed. At six and twelve weeks after implantation, the dogs in the control group (unfilled defects) had the least amount of bone in the sites of the defects. In the dogs that had had an autogenous bone graft and those in which the defects had been filled with a mixture of autogenous bone graft and biphasic ceramic, there were excellent osteoconductive properties in the filling of the sites of the defects with new bone. A comparison was made between the amount of bone that formed in the osseous defects and the amount that formed in the spaces of the porous-surfaced fiber-metal components of the prostheses, directly underlying and adjacent to the defects. At six weeks, the greatest amount of ingrowth of bone into the spaces of the underlying titanium fiber-metal acetabular components was seen in the control group (22 per cent of the porous surface), followed by the group in which the defects had been filled with a mixture of autogenous bone graft and biphasic ceramic (19 per cent). The defects that had been filled only with autogenous bone graft had poor ingrowth of bone into the porous surface (4 per cent) and predominantly fibrous ingrowth. At twelve weeks, these defects again showed the least amount of ingrowth of bone (15 per cent) compared with the defects in the control group (24 per cent) and those that had been filled with a mixture of autogenous bone graft and biphasic ceramic (24 per cent). No statistically significant differences were found in the amount of ingrowth of bone into the defects that had been created in the femur in the three groups of dogs at either six or twelve weeks. However, the trends appeared to correlate with the data for the acetabular defects.

A non-linear finite element analysis of some early collapse processes in femoral head osteonecrosis.

Some aspects of the early collapse biomechanics of the segmentally necrotic adult human femoral head were studied, using a small-deformation plane strain, elasto-plastic finite element model. The computational procedure used was based upon the initial stress technique, and permitted study of stress and strain fields and of the progression of failure regions as a function of incrementally applied joint loads. The results consistently demonstrated both subchondral and deep cancellous failure patterns similar to those seen clinically. There was a clear distinction, however, between these two failure regimes, dependent primarily upon the relative strength deficits input for the subchondral versus the deep cancellous regions. Usually, the failure zone was appreciable only at significantly supra-physiological loads, reflecting the likely importance of fatigue events in the clinical collapse process. Although subchondral failure was always limited to the entire base region of the infarction wedge, the zones of deep failure varied considerably with changes in lesion geometry, usually being concentrated within the infarct near the underlying necrotic/viable interface.

Anterior stability of the glenohumeral joint. A dynamic model.

This study defines the interaction of the rotator cuff musculature and the glenohumeral ligaments in providing anterior stability to the glenohumeral joint. Eight cadaveric shoulders were studied using a testing frame that individually simulated the forces of the subscapularis, the supraspinatus, and the infraspinatus/teres minor musculature. The application of these forces abducted the humerus to approximately 90 degrees. The cocking phase of throwing was then simulated through the use of an Instron. With random variation of the rotator cuff forces, we investigated the effects that each force had on the rotation of the humerus and the strain of the inferior glenohumeral ligament. Our results demonstrate that the infraspinatus/teres minor muscle group was the most effective in controlling external rotation of the humerus and in reducing ligamentous strain. These observations are pertinent in the treatment of anterior instability syndromes of the shoulder.

Group encounters and territoriality in wild Alaotran gentle lemurs (Hapalemur griseus alaotrensis).

During a 3 month field study, 18 group encounters between four groups of Alaotran gentle lemurs (Hapalemur griseus alaotrensis) were observed in the Lake Alaotra marshland in Madagascar. Behaviors observed during group encounters are described, and quantitative data on intergroup interactions and ranging patterns are discussed in the context of territoriality. Intergroup interactions varied in their intensity, ranging from visual monitoring, scent marking, and display locomotion to penetrating the neighboring range. A quarter (27%) of the encounters were aggressive, involving chases and confrontation displays, and no affiliative interactions were observed. Both adult males and females were involved in intergroup encounters, with males playing more active roles. All encounters took place in the small overlapping areas of neighboring home ranges. The outcome of an aggressive encounter was determined by its location, with the resident group always driving out the intruding one. The Alaotran gentle lemur actively advertised and consistently defended a large area of its home range against intrusion of neighboring groups and can therefore be considered territorial.

Characterization of thin polymer and biopolymer layers by ellipsometry and evanescent field technology.

The characterization of sensitive layers is the prerequisite for the optimization of chemical and biochemical sensors. The application of SE (Spectral Ellipsometry) and SPR (Surface Plasmon Resonance) as methods of characterization of such sensitive layers is discussed. In combination with infrared spectroscopy, the properties of polymer networks, micro-porous polymers, liquid crystals, and biomimetic polymers can be examined regarding their applicability for optical sensing. Apart from the basic principles regarding the characterization approaches, applications in the area of environmental sensing, optimization of hydrogel layers for antigen/antibody interaction, and discrimination of analytes in homologous series of alcohols are discussed. The effects of analytes on the phase transition in combination with disordering of liquid crystals are given.

Social organization of the Alaotran gentle lemur (Hapalemur griseus alaotrensis).

Knowledge of the social organization of lemurs is still limited for most species. Where there is sufficient information, it has been shown that lemur social organization differs in essential points from that of other primates. In the field study reported here, demographic structure and life-history processes were investigated in order to characterize the social organization of the Alaotran gentle lemur (Hapalemur griseus alaotrensis). Data were obtained through captures and observations. Alaotran gentle lemurs were found in small groups of up to nine individuals. Although most groups contained just one breeding female, a substantial proportion of groups (35%) had two breeding females. Therefore, Alaotran gentle lemurs cannot be classed as being organized in monogamous family groups. An extended birth season was found, and groups with two breeding females had significantly higher breeding output per adult than groups with a single adult female. Limited data suggest that females emigrate from their natal group while still subadult, whereas males can stay in the natal group until they are fully grown and disperse as adults. Variability in group composition, significantly higher reproductive output per adult in groups with two breeding females, and delayed dispersal of males suggest that Alaotran gentle lemurs pursue a resource-defense mating strategy, rather than a female-defense mating strategy. The suggestion that extant social lemurs may have evolved from a monogamous system, could explain the differences between lemur social systems and those of other primates.

Dyeless optical detection of ammonia in the gaseous phase using a pH-responsive polymer--characterization of the sorption process.

pH-responsive polymers enable the dyeless optical detection of acidic or basic pollutants in air. The characterization of the sorption process and the optimization of the response time of the sensitive layers were high-lighted. The swelling of a pH-responsive polysiloxane induced by sorption of gaseous ammonia was investigated by measurement techniques such as spectroscopic ellipsometry (SE) and infrared spectroscopy (IR). Furthermore, the pH-responsive polymer was applied for the detection of gaseous ammonia using the LED-based reflectometric interference spectroscopy set-up (RIfS4lambda). A limit of detection of 0.30 mg/m3 ammonia and a response time (t90%) of 35 s could be verified. The application of pH-responsive polymers can be a powerful alternative to dye-based optical sensing, since photobleaching or leaching of the sensitive functional unit cannot occur applying this approach, and since the properties of the sensitive layer proved to be very promising.

Measurement of brachial plexus strain in arthroscopy of the shoulder.

The purpose of this study was to measure the strain on the brachial plexus that results from traction loads applied at various arm positions and to correlate this with visibility through the arthroscope. We mounted strain gauges to the upper trunk, lateral cord, median nerve, and radial nerve of five fresh human cadavers. Each cadaver was placed in a lateral decubitus position, with the head fixed in a neutral position, as for shoulder arthroscopy, and the strain on the plexus was measured as a function of arm position and traction load. A final cadaver was used to determine the accessibility and visibility in the arthroscope at each of the arm positions. At a given flexion angle, increasing abduction is associated with decreasing strain. At a given abduction angle, increasing flexion results in decreased strain. The minimum overall strain was noted at 90 degrees of flexion and 0 degree of abduction. Visibility at this position is limited. We conclude that the ideal arthroscopic position is a combination of two positions that would maximize visibility while minimizing strain to the nerves. These two positions are 45 degrees of forward flexion and 90 degrees of abduction in combination with 45 degrees of forward flexion and 0 degree of abduction.