The founding of Mauritian endemic coffee trees by a synchronous long-distance dispersal event

The stochastic process of long-distance dispersal is the exclusive means by which plants colonize oceanic islands. Baker's rule posits that self-incompatible plant lineages are unlikely to successfully colonize oceanic islands because they must achieve a coordinated long-distance dispersal of sufficiently numerous individuals to establish an outcrossing founder population. Here, we show for the first time that Mauritian Coffea species are self-incompatible and thus represent an exception to Baker's rule. The genus Coffea (Rubiaceae) is composed of approximately 124 species with a paleotropical distribution. Phylogenetic evidence strongly supports a single colonization of the oceanic island of Mauritius from either Madagascar or Africa. We employ Bayesian divergence time analyses to show that the colonization of Mauritius was not a recent event. We genotype S-RNase alleles from Mauritian endemic Coffea, and using S-allele gene genealogies, we show that the Mauritian allelic diversity is confined to just seven deeply divergent Coffea S-RNase allelic lineages. Based on these data, we developed an individual-based model and performed a simulation study to estimate the most likely number of founding individuals involved in the colonization of Mauritius. Our simulations show that to explain the observed S-RNase allelic diversity, the founding population was likely composed of fewer than 31 seeds that were likely synchronously dispersed from an ancestral mainland species.

Biomechanical evaluation of calcaneocuboid distraction arthrodesis: a cadaver study of two different fixation methods

Calcaneocuboid distraction arthrodesis can be used to treat stage 2 posterior tibial tendon dysfunction. Nonunion, graft resorption, and implant failure have been reported after this procedure. This study compared two of the most commonly used methods for fixation of calcaneocuboid distraction arthrodesis. Twelve pairs of cadaver feet underwent simulated calcaneocuboid distraction arthrodesis. One specimen in each pair was fixed with two crossed 3.5 mm cortical lag screws. The contralateral specimen was fixed with a cervical H-plate. The calcaneus was fixed and a load was applied to the plantar aspect of the cuboid at a rate of 5 mm/minute until joint separation of 3 mm or fracture occurred. The average applied load to failure at 1.0 mm of joint separation was 30.5 +/- 11.6 N for the crossed screws and 77.7 +/- 36.4 N for the cervical H-plate (p = 0.001). The average stiffness at 1.0 mm of joint separation was 27.5 +/- 10.9 N/mm for the crossed screws and 43 +/- 21.2 N/mm for the cervical H-plate (p = 0.036). The higher stiffness and load to failure may account for the decreased nonunion rate noted anecdotally by some surgeons with H-plate fixation over crossed screw fixation for calcaneocuboid distraction arthrodesis.

Design enhancement of a solid ankle-foot orthosis: real-time contact pressures evaluation

The purpose of our study was to evaluate all contact pressures between the molded ankle-foot orthosis (MAFO) and the subject during activities of daily living. The MAFOs studied are used clinically to reduce plantar contact pressures associated with foot ulcers in adult neuropathic diabetic subjects, alleviating abnormal pressures by redistributing them to low-pressure plantar regions. While effective, MAFOs are often not used by the subject due to weight and comfort issues. An understanding of the contact pressures between the subject and the orthosis is a first step in improving basic MAFO design. Four nonimpaired, young adult males were tested in this study. A right-side MAFO was custom-molded and fitted for each subject by the same orthotist. Real-time pressures were obtained for the entire contact area using the F-Scan pressure measurement system. The data obtained demonstrated high contact pressures along the metatarsals of the foot, around the heel and ankle, and adjacent to the strap attachment sites. No contact pressures were noted along the posterior calf region during any of the activities performed. These data suggest the calf region would be a suitable site for material removal for weight reduction and increased comfort, especially in warm weather. In addition, these data may be useful to orthotists in improving the basic design and to researchers as a starting point for performing complex finite element analysis on the MAFO.

Calcaneocuboid joint pressures with lateral column lengthening (Evans) procedure

Calcaneocuboid joint pressures were evaluated with eight cadaver specimens. Real-time pressures were recorded using a TekScan 4200 sensor pad at lengths of 0, 5, and 10 mm in both unloaded and 350-newton loaded models. Recorded pressures exceeded 2.3 MPa in the loaded model at 10 mm lateral column lengthening. Although an acceptable procedure in the pediatric population, application of the Evans lateral column lengthening procedure for management of adult acquired flatfoot may generate excessive pressures leading to joint arthrosis. Lengthening by calcaneocuboid distraction arthrodesis may avoid this problem.

Bend testing of wrought wire removable partial denture alloys

The flexibility of the wrought wire clasp is related to a number of factors, including the type and gauge of the alloy. The purpose of this study was to compare the bend behavior of five wrought wire alloys used in removable partial dentures. The alloys and their gauge diameters (in millimeters) were Ticonium (18, 19, 20), platinum-gold-palladium (18, 19), Wironium (18, 20), Jelenko Standard (18, 19, 20), and Denture Clasp (18, 19, 20). A total of 12 to 15 samples of each dental alloy were tested. Three-point bending was performed on a servohydraulic testing system controlled by a computer at 1.00 mm/sec until fracture or actuator contact occurred. Maximum stress and elastic modulus in bending were determined for each gauge diameter. Analysis of variance and post hoc Scheffe statistical analyses revealed significant maximum stress and elastic modulus in bending differences for different alloys of the same gauge and for different gauges of the same alloy. The choice of material and the gauge diameter significantly influenced the mechanical property of bending for wrought wire removable partial denture alloys. The Ticonium alloy had the greatest elastic modulus (stiffest) at all levels and the Denture Clasp and the Jelenko Standard alloys had the lowest elastic modulus (most flexible). These data indicate that knowledge of the bending properties of an alloy is equally as important as the gauge size when selecting a wire clasp.

Initial failure strength of open and arthroscopic Bankart repairs

Surgical repair of recurrent anterior shoulder instability requires secure fixation of the separated inferior glenohumeral complex to bone. Many techniques of fixation are in use for both arthroscopic and open repair. The specific aim of this study was to compare the initial failure strength of eight repair techniques using a previously described canine model of Bankart repair. Intact capsule-to-bone complexes failed at the bony interface at 236 N. Traditional Bankart repair failed at 122.1 N (2 sutures) and 74.7 N (1 suture), Acufex TAG rod (Acufex Microsurgical, Mansfield, MA) at 143.5 N (2 sutures) and 79.8 N (1 suture), transglenoid suture technique (2 sutures) at 166.6 N, Mitek GII (Mitek, Norwood, MA) (1 suture) at 96.4 N, Zimmer Statak (Zimmer Inc, Warsaw, IN)(1 suture) at 95.2 N, and Acufex bioasbsorpable Suretac at 82.2 N. The two-suture repairs were statistically equivalent in strength to each other, as were the one-suture repairs and the Suretac device. Two-suture repairs were significantly stronger than the one-suture repairs (P < .01) failure. In the single-suture specimens, failure occurred by suture breakage in 46% (18 of 39) of specimens and soft-tissue failure around the suture in 54% (21 of 39). Failure in the two-suture techniques primarily occurred by soft-tissue failure (23 of 25) and this proved a statistically significant difference (P < .003). No device broke or pulled out of bone.

Tensile strength of the end-weave flexor tendon repair. An in vitro biomechanical study

A study was designed to investigate the tensile strength of the end-weave method of tendon repair. Flexor tendons were removed from 13 fresh-frozen human cadavers, transected and repaired with the end-weave technique varying from one to five weaves, with two suture techniques, the commonly used horizontal mattress suture and a new method we have termed the cross stitch. The repairs were then tested in tension to failure on a Materials Test System (MTS) biomechanical testing device. Comparisons were also made to tensile strengths of intact whole tendons, tendon-bone insertions, and distal reinsertion techniques. Tensile strength increased linearly with the number of weaves for both suture methods. The cross stitch was found to have significantly greater strength per weave compared to the horizontal mattress suture (P < 0.05). Three out of five trials of five weaves done with the cross stitch actually failed at the tendon itself first, rather than through the repair, which was the failure mode for all other trials. The results from this in vitro model suggest that active rehabilitative exercises might safely be performed in the immediate post-operative period after procedures that involve tendon weaving.

A programmable, computer-controlled cone-plate viscometer for the application of pulsatile shear stress to platelet suspensions

Described is a special purpose cone-plate viscometer that is capable of acceleration or deceleration through a step change in speed in less than 0.7s. The speed of the rotating cone is controlled by a microcomputer which can be programmed to generate speed vs time ramp functions of variable slope. Prior calibration of motor power required to shear Newtonian fluids of known viscosity at various speeds provides the basis for determination of apparent suspension viscosity and enables the viscometer automatically to compensate for changing sample viscosity during shear. The viscometer was used to carry out a series of preliminary studies in which platelet-rich plasma (PRP) was subjected to continuous and pulsatile shear stress at 37 degrees C. Shear-induced platelet aggregation (SIPAG) was significantly greater in response to pulsatile versus continuous shearing except at the lowest applied stress (10 dyn/cm2). Increases ranged from about 40 percent at a stress amplitude of 25 dyn/cm2 to nearly 55 percent at dyn/cm2. This increasing trend with stress amplitude might be interpreted as a positive correlation between SIPAG and the loading rate. Dense granule release, as indicated by serotonin release, was dependent on both stress amplitude and number of pulses even at the higher stress where SIPAG was independent of pulse number.

Structural details of boundary layer separation in a model human carotid bifurcation under steady and pulsatile flow conditions

We have used a dye-flow visualization technique to analyze the substructure of flow separation in a plastic model of the human carotid bifurcation under steady and pulsatile flow. Under steady conditions at a physiologic flow split (Q external carotid/Q common carotid = 0.30) and Reynolds number (500), a large region of separated fluid developed along the outside wall of the sinus, opposite the flow divider. Yellow dye injected into the boundary layer upstream from the bifurcation traveled slowly along the wall of the common carotid and entered directly into the separation. Blue dye injected into the central, high-velocity streamlines in the common carotid impacted on the flow divider, then traveled circumferentially and entered the separation. Mixing of these two sources was documented by the appearance of green fluid, which lingered in the region of separation. Pulsatile flow resulted in a smaller region of separation; mixing still occurred. Flow separation at the carotid bifurcation is a site of mixing of fluids previously subjected to prolonged low-shear wall contact and brief high-shear wall contact. Separation is itself a site of low shear, but this study reveals a mechanism whereby low and high shear may act independently or synergistically to explain the link between flow separation and atherogenesis.

Downstream anastomotic hyperplasia. A mechanism of failure in Dacron arterial grafts

The precise location and progression of anastomotic hyperplasia and its possible relationship to flow disturbances was investigated in femoro-femoral Dacron grafts in 28 dogs. In 13 grafts, the outflow from the end-to-side downstream anastomosis was bidirectional (BDO), and in 15 it was unidirectional (UDO) (distally). Grafts were electively removed at intervals of two to 196 days or at the time of thrombosis. Each anastomosis and adjacent artery was perfusion-fixed and sectioned sagittally. The mean sagittal section was projected onto a digitized pad, and the total area of hyperplasia internal to the arterial internal elastic lamina and within the adjacent graft was integrated by computer. The location of the hyperplasia was compared with previously established sites of flow separation and stagnation. The observation was made that hyperplasia is significantly greater at the downstream, as compared with the upstream, anastomosis in both groups (BDO = p less than 0.001 and UDO = p less than 0.001) (analysis of variance for independent groups). Furthermore, this downstream hyperplasia was progressive with time (BDO p less than 0.01) (UDO p less than 0.01); Spearman Rank Correlation. There was no significant increase in the extent of downstream hyperplasia where flow separation was known to be greater (BDO). Five grafts failed (three BDO, two UDO), as a result of complete occlusion of the downstream anastomosis by fibrous hyperplasia. Transmission electron microscopy showed the hyperplasia to consist of collagen-producing smooth muscle cells. Anastomotic hyperplasia is significantly greater at the downstream anastomosis, is progressive with time, and is the primary cause of failure of Dacron arterial grafts in this model. Quantitative analysis of downstream anastomotic hyperplasia may be a valuable measure of the biocompatibility of Dacron grafts.

A three dimensional multi-segmental analysis of the energetics of normal and pathological human gait

Segmental mechanical energy changes were studied in normal adults as a function of walking speed and in a group of subjects with pathologically impaired gait walking at their normal speed to determine the usefulness of this parameter in evaluating locomotor dysfunction. Of particular significance, the degree of exchange between potential and kinetic energy within and between limb segments was quantitatively evaluated. Due to the nature of most pathological gaits, no assumptions were made to impose symmetry between the right and left extremities and the translational as well as rotational kinetic energy of each of the limb segments was computed in three dimensions. Additionally, the torso was modeled as a group of segments with distributed mass in contrast to the commonly employed concentrated point mass model. In toto, a three dimensional twelve segment energetic analysis of the human body was developed and employed. In normal subjects, this analysis suggests a greater exchange between potential and kinetic energy near individually preferred walking speeds. Patterns of energy change noted in those subjects with locomotor dysfunction varied with the type of pathological disorder.

Flow studies in a model carotid bifurcation

Boundary layer separation in a plexiglass model carotid bifurcation was investigated in relation to the origin of atherosclerotic plaque clinically found in this region. Our model was comparable to a human carotid in both dimensions and geometry. Water flowed through the model at Reynolds numbers from 200 to 1200 under steady and pulsatile flow conditions, with outflow through the external and internal branches varied. The near-wall flow was visualized by slow injection of dye through ports machined in the model. Under steady flow at a physiological Reynolds number of 500 and a flow split at the bifurcation similar to that of a human carotid at rest, boundary layer separation was found to occur in a carotid sinus across from the external carotid origin, forming a shell of slowly moving fluid around the bifurcation. The rapidly moving mainstream impinged directly on the flow divider. The location of atherosclerotic plaque correlates best with the low shear region of separation and not with the region of high shear at the flow divider. Preliminary studies with pulsatile flow demonstrated little change from the steady flow results.