In vitro method for assessing the biomechanics of the patellofemoral joint following total knee arthroplasty.

The patellofemoral joint is a common site of pain and failure following total knee arthroplasty. A contributory factor may be adverse patellofemoral biomechanics. Cadaveric investigations are commonly used to assess the biomechanics of the joint, but are associated with high inter-specimen variability and often cannot be carried out at physiological levels of loading. This study aimed to evaluate the suitability of a novel knee simulator for investigating patellofemoral joint biomechanics. This simulator specifically facilitated the extended assessment of patellofemoral joint biomechanics under physiological levels of loading. The simulator allowed the knee to move in 6 degrees of freedom under quadriceps actuation and included a simulation of the action of the hamstrings. Prostheses were implanted on synthetic bones and key soft tissues were modelled with a synthetic analogue. In order to evaluate the physiological relevance and repeatability of the simulator, measurements were made of the quadriceps force and the force, contact area and pressure within the patellofemoral joint using load cells, pressure-sensitive film, and a flexible pressure sensor. The results were in agreement with those previously reported in the literature, confirming that the simulator is able to provide a realistic physiological loading situation. Under physiological loading, average standard deviations of force and area measurements were substantially lower and comparable to those reported in previous cadaveric studies, respectively. The simulator replicates the physiological environment and has been demonstrated to allow the initial investigation of factors affecting patellofemoral biomechanics following total knee arthroplasty.

Low torque levels can initiate a removal of the passivation layer and cause fretting in modular hip stems.

Taper connections of modular hip prostheses are at risk of fretting and corrosion, which can result in reduced implant survival. The purpose of this study was to identify the minimum torque required to initiate a removal of the passivation layer at the taper interface as a function of assembly force and axial load. Titanium stems and cobalt-chromium heads were assembled with peak impaction forces of 4.5 kN or 6.0 kN and then mounted on a materials testing machine whilst immersed in Ringer's solution. The stems were subjected to a static axial load (1 kN or 3 kN) along the taper axis. After a period of equilibration, a torque ramp from 0 to 15 Nm was manually applied and the galvanic potential was continuously recorded. Prostheses assembled with a force of 6 kN required a significantly higher torque to start a removal of the passivation layer compared to those assembled with 4.5 kN (7.23±0.55 Nm vs. 3.92±0.97 Nm, p=0.029). No influence of the axial load on the fretting behaviour was found (p=0.486). The torque levels, which were demonstrated to initiate surface damage under either assembly force, can be readily reached during activities of daily living. The damage will be intensified in situations of large weight and high activity of the patient or malpositioning of the prosthesis.

The basalis of the primate endometrium: a bifunctional germinal compartment.

Radioautographic analysis of epithelial and stromal cell proliferation in the primate endometrial functionalis and basalis (rhesus monkey) has identified horizontal zonal patterns of mitotic activation and inhibition during natural menstrual cycles. At 1 h after a single i.v. injection of [3H]thymidine, mitotic activity in endometrial biopsies (hysterotomy) was determined on 9 days from the late proliferative to the late luteal phase (-2 days to + 14 days relative to the estrogen [E2]peak). Labeling indices (LIs) were determined within glandular segments of the 4 horizontal endometrial zones: Transient functionalis Zone I (luminal epithelium) and Zone II (uppermost gland); Germinal basalis: Zone III (middle gland) and Zone IV (basal gland). The size of the dividing epithelial populations (LI) differed zonally. During E2 dominance (-2 days to +3 days), the epithelial LIs of functionalis I (10 +/- 0.3%) and II (9.8 +/- 1.0%) were greater than those of basalis III (5.8 +/- 0.2%) and basalis IV (3.7 +/- 0.8%). During progesterone (P) dominance (+5 days to +14 days), epithelial mitosis was strongly inhibited in functionalis I (4.3 +/- 1.9%), functionalis II (0.8 +/- 0.2%), and basalis III (1.4 +/- 0.5%). Thus germinal basalis III was linked functionally with transient functionalis I and II by periovulatory uniformity in epithelial proliferation and postovulatory mitotic inhibition. A unique mitotic pattern set basalis IV apart from other zones by a steady rise in LI from 1% (-2 days) to 11% (+10 days). The LIs for stromal fibroblasts remained quite uniform in basalis IV but varied in other zones. Thus the postovulatory primate basalis was a distinct bipartite compartment in which the mitotic rate in basalis IV glandular epithelium increased steadily whereas that of basalis III was strongly inhibited. The remarkable enhancement of epithelial mitotic activity in basalis IV may reflect expansion of the stem-progenitor cell population for gestational growth or for post-menstrual regeneration.

A zonal pattern of cell proliferation and differentiation in the rhesus endometrium during the estrogen surge.

The cellular and tissue basis of endometrial renewal in the rhesus monkey is being investigated by radioautographic localization of proliferating cell populations. Here we report our findings on epithelial cell proliferation during the midcycle estrogen surge. Endometrial biopsies were obtained by hysterotomy at approximately 1 h after a single intravascular injection of [3H] thymidine ([3H]T). Light and electron microscopic radioautography was performed on 7 specimens obtained from 4 monkeys in relation to the serum estradiol (E2) peak as follows: -2, -1, 0, +1, +2, and +3 days (+/- 1 day). Cell proliferation and differentiation were analyzed according to the 4 horizontal histologic endometrial zones (Bartelmez et al., 1951). Epithelial labeling indices were higher in the functionalis (Zone I, luminal epithelium, 9-12%; Zone II, uppermost gland segments, 7-14%) than in the basalis (Zone III, middle gland segments, 5-7%; and Zone IV, basal gland segments, 1-7%). Despite the large and rapid serum E2 fluctuations during the surge from -2 days to +3 days E2 peak, proliferating epithelial populations within Zones I, II and III remained quite uniform in size. In the basalis, the proliferative patterns of Zones III and IV were dissimilar. The labeling index of Zone III remained quite uniform (5-7%), whereas in Zone IV, it increased progressively from 1% (-2 days) to 7% (+3 days). These data establish the bipartite nature of the basalis. Radioautographic evidence indicates that endometrial cell proliferation is tightly coupled to progressive cell differentiation in the functionalis and basalis. Thus intrinsic positional differences exist in the responsiveness of the primate endometrium to common hormonal stimulation during the E2 surge and the initial postovulatory rise of progesterone.