A new spacer-guided, PCL balancing technique for cruciate-retaining total knee replacement

PURPOSE

The goal of this study was to investigate whether a new posterior cruciate ligament (PCL) balancing approach with a spacer technique during total knee arthroplasty (TKA) reproduced the correct tibiofemoral contact point (CP) location. It was hypothesized that it should be possible to adequately balance the PCL with this geometrical technique, obtaining correct position and stability of the medial femoral condyle, independent of insert shape.

METHODS

Nine fresh-frozen full-leg cadaver specimens were used. After native testing, prototype components of a new PCL-retaining implant were implanted using navigation and a bone-referencing technique. After finishing the bone cuts, the spacer technique was used to ascertain balancing of the PCL and the tibial cut was corrected if necessary. Passive and squat motions were performed before and after TKA using a dynamic knee simulator while tibiofemoral kinematics were recorded using six infrared cameras. CPs (native and implant) were calculated as the projections of the femoral condylar centres on the horizontal plane of the tibia.

RESULTS

The spacer technique resulted in correct PCL balancing in all specimens. The kinematic patterns of native and replaced knees showed no statistically significant differences in passive and squat motions. The medial CP after TKA was at the same position as in the native knee. No paradoxical sliding forward was seen after TKA, supporting our hypothesis.

CONCLUSIONS

The spacer technique can be applied by surgeons during PCL-retaining TKA and will lead to good PCL balancing, indicated by a correct CP, no lift-off in flexion and no posterior sag.

Can CT-based patient-matched instrumentation achieve consistent rotational alignment in knee arthroplasty?

PURPOSE

Long-term success of contemporary total knee replacements relies to a large extent on proper implant alignment. This study was undertaken to test whether specimen-matched cutting blocks based on computed axial tomography (CT) scans could provide accurate rotational alignment of the femoral component.

METHODS

CT scans of five fresh frozen full leg cadaver specimens, equipped with infrared reflective markers, were used to produce a specimen-matched femoral cutting block. Using those blocks, the bone cuts were made to implant a bi-compartmental femoral component. Rotational alignment of the components in the horizontal plane was determined using an optical measurement system and compared with all relevant rotational reference axes identified on the CT scans.

RESULTS

Average rotational alignment for the bi-compartmental component in the horizontal plane was 1.9° (range 0°-6.3°; standard deviation 2.6°). One specimen that showed the highest deviation from the planned alignment also featured a completely degraded medial articular surface.

CONCLUSIONS

The CT-based specimen-matched cutting blocks achieved good rotational alignment accuracy except for one specimen with badly damaged cartilage. In such cases, imaging techniques that visualize the cartilage layer might be more suitable to design cutting blocks, as they will provide a better fit and increased surface support.

The influence of malrotation and femoral component material on patellofemoral wear during gait

Complications involving the patellofemoral joint, caused by malrotation of the femoral component during total knee replacement, are an important cause of persistent pain and failure leading to revision surgery. The aim of this study was to determine and quantify the influence of femoral component malrotation on patellofemoral wear, and to determine whether or not there is a difference in the rate of wear of the patellar component when articulated against oxidised zirconium (OxZr) and cobalt-chrome (CoCr) components. An in vitro method was used to simulate patellar maltracking for both materials. Both rates of wear and changes in height on the patellar articular surface were measured. The mean rates of wear measured were very small compared to standard tibiofemoral wear rates. When data for each femoral component material were pooled, the mean rate of wear was 0.19 mm3/Mcycle (sd 0.21) for OxZr and 0.34 mm3/Mcycle (sd 0.335) for CoCr. The largest change in height on each patella varied from -0.05 mm to -0.33 mm over the different configurations.

The results suggest that patellar maltracking due to an internally rotated femoral component leads to an increased mean patellar wear. Although not statistically significant, the mean wear production may be lower for OxZr than for CoCr components.

Femoral component loosening in high-flexion total knee replacement

High-flexion total knee replacement (TKR) designs have been introduced to improve flexion after TKR. Although the early results of such designs were promising, recent literature has raised concerns about the incidence of early loosening of the femoral component. We compared the minimum force required to cause femoral component loosening for six high-flexion and six conventional TKR designs in a laboratory experiment.

Each TKR design was implanted in a femoral bone model and placed in a loading frame in 135° of flexion. Loosening of the femoral component was induced by moving the tibial component at a constant rate of displacement while maintaining the same angle of flexion. A stereophotogrammetric system registered the relative movement between the femoral component and the underlying bone until loosening occurred.

Compared with high-flexion designs, conventional TKR designs required a significantly higher force before loosening occurred (p < 0.001). High-flexion designs with closed box geometry required significantly higher loosening forces than high-flexion designs with open box geometry (p = 0.0478). The presence of pegs further contributed to the fixation strength of components.

We conclude that high-flexion designs have a greater risk for femoral component loosening than conventional TKR designs. We believe this is attributable to the absence of femoral load sharing between the prosthetic component and the condylar bone during flexion.

Anteroposterior positioning of the tibial component and its effect on the mechanics of patellofemoral contact

The biomechanics of the patellofemoral joint can become disturbed during total knee replacement by alterations induced by the position and shape of the different prosthetic components. The role of the patella and femoral trochlea has been well studied. We have examined the effect of anterior or posterior positioning of the tibial component on the mechanisms of patellofemoral contact in total knee replacement. The hypothesis was that placing the tibial component more posteriorly would reduce patellofemoral contact stress while providing a more efficient lever arm during extension of the knee.

We studied five different positions of the tibial component using a six degrees of freedom dynamic knee simulator system based on the Oxford rig, while simulating an active knee squat under physiological loading conditions. The patellofemoral contact force decreased at a mean of 2.2% for every millimetre of posterior translation of the tibial component. Anterior positions of the tibial component were associated with elevation of the patellofemoral joint pressure, which was particularly marked in flexion > 90°.

From our results we believe that more posterior positioning of the tibial component in total knee replacement would be beneficial to the patellofemoral joint.

Is there a biomechanical explanation for anterior knee pain in patients with patella alta?: influence of patellar height on patellofemoral contact force, contact area and contact pressure

The purpose of this study was to test the hypothesis that patella alta leads to a less favourable situation in terms of patellofemoral contact force, contact area and contact pressure than the normal patellar position, and thereby gives rise to anterior knee pain. A dynamic knee simulator system based on the Oxford rig and allowing six degrees of freedom was adapted in order to simulate and record the dynamic loads during a knee squat from 30 degrees to 120 degrees flexion under physiological conditions. Five different configurations were studied, with variable predetermined patellar heights. The patellofemoral contact force increased with increasing knee flexion until contact occurred between the quadriceps tendon and the femoral trochlea, inducing load sharing. Patella alta caused a delay of this contact until deeper flexion. As a consequence, the maximal patellofemoral contact force and contact pressure increased significantly with increasing patellar height (p < 0.01). Patella alta was associated with the highest maximal patellofemoral contact force and contact pressure. When averaged across all flexion angles, a normal patellar position was associated with the lowest contact pressures. Our results indicate that there is a biomechanical reason for anterior knee pain in patients with patella alta.

A comparison between internal and surface temperature measurement techniques during phacoemulsification cataract surgery: thermocamera versus thermocouple

PURPOSE

Corneal and scleral burns, one of the main complications that can occur during a cataract operation, are produced by overheating due to the use of the phacoemulsifier. The temperature of the anterior chamber of the eye can be measured both invasively using thermocouples and non-invasively, but only superficially, using a thermocamera.

METHODS

To compare the measures obtained from both techniques an in vitro experimental analysis was conducted on pigs' eyes. During a simulated phacoemulsification cataract operation both the surface temperature with a thermocamera and the temperature inside the anterior chamber with a thermocouple were recorded. For each procedure, the maximum temperature values measured by each technique were compared.

RESULTS

The results of this research show that the difference between the maximum values measured with the two techniques is on average 0.5 degrees C.

CONCLUSIONS

It is possible to employ a thermocamera technique instead of a thermocouple technique to provide an indication of the temperature inside the anterior chamber.

Imaging extracellular waves of glutamate during calcium signaling in cultured astrocytes

A growing body of evidence proposes that glial cells have the potential to play a role as modulators of neuronal activity and synaptic transmission by releasing the neurotransmitter glutamate (Arague et al., 1999). We explore the spatial nature of glutamate release from astrocytes with an enzyme-linked assay system and CCD imaging technology. In the presence of glutamate, L-glutamic dehydrogenase (GDH) reduces NAD(+) to NADH, a product that fluoresces when excited with UV light. Theoretically, provided that GDH and NAD(+) are present in the bathing saline, the release of glutamate from stimulated astrocytes can be optically detected by monitoring the accumulation of NADH. Indeed, stimuli that induce a wave of elevated calcium among astrocytes produced a corresponding spread of extracellular NADH fluorescence. Treatment of cultures either with thapsigargin, to deplete internal calcium stores, or with the membrane-permeant calcium chelator BAPTA AM significantly decreased the accumulation of NADH, demonstrating that this fluorometric assay effectively monitors calcium-dependent glutamate release. With a temporal resolution of 500 msec and spatial resolution of approximately 20 micrometer, discrete regions of glutamate release were not reliably resolved. The wave of glutamate release that underlies the NADH fluorescence propagated at an average speed of approximately 26 micrometer/sec, correlating with the rate of calcium wave progression (10-30 micrometer/sec), and caused a localized accumulation of glutamate in the range of 1-100 microM. Further analysis of the fluorescence accumulation clearly demonstrated that glutamate is released in a regenerative manner, with subsequent cells that are involved in the calcium wave releasing additional glutamate.

Regulation of exocytotic fusion by cell inflation

We have inflated patch-clamped mast cells by 3.8 +/- 1.6 times their volume by applying a hydrostatic pressure of 5-15 cm H2O to the interior of the patch pipette. Inflation did not cause changes in the cell membrane conductance and caused only a small reversible change in the cell membrane capacitance (36 +/- 5 fF/cm H2O). The specific cell membrane capacitance of inflated cells was found to be 0.5 microF/cm2. High-resolution capacitance recordings showed that inflation reduced the frequency of exocytotic fusion events by approximately 70-fold, with the remaining fusion events showing an unusual time course. Shortly after the pressure was returned to 0 cm H2O, mast cells regained their normal size and appearance and degranulated completely, even after remaining inflated for up to 60 min. We interpret these observations as an indication that inflated mast cells reversibly disassemble the structures that regulate exocytotic fusion. Upon returning to its normal size, the cell cytosol reassembles the fusion pore scaffolds and allows exocytosis to proceed, suggesting that exocytotic fusion does not require soluble proteins. Reassembly of the fusion pore can be prevented by inflating the cells with solutions containing the protease pronase, which completely blocked exocytosis. We also interpret these results as evidence that the activity of the fusion pore is sensitive to the tension of the plasma membrane.

Determination of glycated hemoglobins in the rat: comparison between two different chromatographic methods and application in experimental diabetology

Due to the unusual presence of several different hemoglobin components in the rat, determination of glycated hemoglobin (Hb) has been considered difficult and often unreliable in this animal species. In the present study, we compare a fully automated high-performance liquid chromatographic (HPLC) method of analysis of glycated hemoglobin that has been assessed for clinical use with an affinity chromatography technique using boronate micro-columns; we used blood samples taken from Sprague-Dawley rats of various ages and streptozotocin-diabetic rats. In nondiabetic rats, the sum of HbA1c and other minor glycated hemoglobins separated by the HPLC method is close to the total glycated hemoglobin obtained by affinity chromatography for each age group of animals. In diabetic rats, the glycated hemoglobins measured by whatever method show a linear increase during the first 3 weeks following streptozotocin administration, with the difference that glycated hemoglobin values obtained by affinity chromatography are markedly higher than those obtained by HPLC technique. Interestingly, a comparative determination of glycated hemoglobin in diabetic patients gives the same results with both methods. Therefore, it appears that in the rat, unlike man, at high glucose concentrations glycation occurs preferentially at the amino groups of hemoglobin components, which are not separated by the HPLC method. Our results indicate that while affinity chromatography should be used to detect the total extent of hemoglobin glycosylation in diabetic rats, the utilization of rapid and automatized HPLC procedures can be a very convenient alternative for the determination of glycated hemoglobin in both euglycemic and hyperglycemic rats.

[Serum lactate-dehydrogenase isoenzymes in HIV positive children. A longitudinal study]

The impairment of humoral immunity with rapid turn-over of cellular B clones in children with HIV infection is known as well as the conduct of LDH isoenzymes in B cell lymphoproliferative diseases like Burkitt's lymphoma. Therefore, serum lactate-dehydrogenase activity (LD, EC 1.1.1.27) and its isoenzymes have been evaluated twice (within 12 months) in 11 children with HIV infection with respect to a control group (30 subjects). Furthermore, the relationship between those and other clinical and immunologic parameters (total lymphocytes, CD4/CD8, immunoglobulins, classification according to the Atlanta CDC 1987) has been studied. HIV infected children have shown a significant decrease in LD1 rates, which was directly correlated to CD4/CD8 values. After the follow-up, this correlation became even more significant. Thus, these findings may suggest the usefulness of LDH isoenzymes evaluation as a marker of disease activity in children with HIV infection.

Intracellular ADP modulates the Ca2+ release-activated Ca2+ current in a temperature- and Ca2+-dependent Way

The rat basophilic cell line RBL-1 is known to express high levels of the Ca2+ current activated by store depletion, known as Ca2+ release-activated Ca2+ current (ICRAC), the main Ca2+ influx pathway so far identified in nonexcitable cells. We show here that, as reported in other cell types, metabolic drugs strongly inhibit the Ca2+ influx operated by store depletion in RBL-1 cells also. We have tested the hypothesis that intracellular adenine and/or guanine nucleotide levels act as coupling factors between ICRAC and cell metabolism. Using the whole cell configuration of the patch-clamp technique, we demonstrate that addition of ADP to the intracellular solution significantly reduces ICRAC induced by inositol 1,4,5-trisphosphate. This phenomenon differs from other regulatory pathways of ICRAC, since it is highly temperature-dependent, is observable only in the presence of low intracellular Ca2+ buffering capacity, and requires a cytosolic factor(s) which is rapidly lost during cell dialysis. Moreover, the inhibition is specific for ADP and is partially mimicked by ADPbetaS and AMP, but not by GDP or GTP.

Modulation of Ca2+ influx dependent on store depletion by intracellular adenine-guanine nucleotide levels

The effects of a number of metabolic inhibitors on the influx of Ca2+ activated by stimulation of receptors coupled to inositol 1,4,5-trisphosphate generation or by depletion of intracellular Ca2+ stores with thapsigargin were investigated in four different cell types: Ehrlich ascites tumor cells, Jurkat and HeLa cell lines, and rat hepatocytes. Independently of their chemical structure and site of inhibition, all of these metabolic poisons markedly inhibited Ca2+ influx without significantly affecting Ca2+ release. This inhibition was not due to membrane potential depolarization or to alteration in cytosolic pH but appeared correlated to a drop in the cellular concentration of ATP. The decreases in cellular [ATP] were paralleled by decreases in [GTP] and by increases in [ADP] and [GDP]. The reduction in ATP level necessary to drastically reduce Ca2+ influx was quite small, e.g. a 50% inhibition for a 5% reduction in [ATP], thus within the range of fluctuation presumably occurring under physiological conditions. We suggest that changes in the adenine or guanine nucleotide concentrations may represent an important modulatory mechanism of Ca2+ influx activated by store depletion.

Receptor-activated Ca2+ influx: how many mechanisms for how many channels?

Receptors that are coupled to the production of inositol (1,4,5)-trisphosphate cause an increase in cytosolic free Ca2+ concentration as a consequence of both Ca2+ mobilization from intracellular stores and Ca2+ influx through the plasma membrane. Although this latter phenomenon appears attributable to the activation of a number of Ca(2+)-permeable channels, the channels that are controlled by the Ca2+ content of the intracellular stores have recently received much attention. In this review, Cristina Fasolato, Barbara Innocenti and Tullio Pozzan summarize the characteristics of this Ca(2+)-influx pathway and discuss the hypotheses about its mechanism of activation and its relationship with other receptor-activated Ca2+ channels.

ATP-dependent ionic permeability on nuclear envelope in in situ nuclei of Xenopus oocytes

The nuclear envelope represents a structural and functional barrier between cytoplasm and nucleoplasm. Small molecules and solutes passively cross the nuclear envelope, whereas the transport of large proteins and RNA requires metabolic energy. Using in situ Xenopus oocyte nuclei, we characterized ATP-dependent ionic permeabilities on the external surface of the envelope. The presence, but not necessarily the hydrolysis, of ATP is crucial to maintaining the channels in an open state. Localization of the ionic channels is still unclear. From morphologic and current kinetics data, we suggest a relation between the ionic channels and the nuclear pores. We try, in this way, to explain the apparent contradiction between the presence of ion-selective channels in parallel with large aqueous pores on the nuclear envelope. Under this hypothesis, variations in the metabolic energy content of the cytoplasm would induce nucleocytoplasmic passive exchanges. The distribution and movement of charged particles across the nuclear envelope may influence many cytoplasmic functions. Regulation of the current by ATP could play an important role in hormonal stimulation, divalent ion permeation into the nucleus, and cell cycle mechanisms.

[Lactate dehydrogenase isoenzymes in HIV-positive children]

Considering that in the HIV infection there is a precocious deterioration of humoral immunity with rapid turn-over of cellular B clones, we have evaluated the conduct of serum lactate-dehydrogenase activity (LD, EC 1.1.1.27) and its isoenzymes in 21 children born from HIV-positive mother respect to a control group (30 subjects). Furthermore we have checked the existence of a probable correlation between those and other clinical and immunologic parameters (total lymphocytes, CD4/CD8, immunoglobulins, classification according to the Atlanta CDC). In seropositive children we saw, respect to those evolved towards P3 stage, a significantly raising of LD4 (also vs. control group) for likely pulmonary parenchyma's damage, LD3 for B immature lymphocytes' increase and a reduction of LD1 (also vs. control group) for mature clones' decrement. Furthermore in seropositive subjects there was the existence of a direct correlation between LD1 and CD4/CD8 values. As such, the evaluation of LD isoenzymes can establish an useful element in the clinical monitoring of seropositive children.

Multicentre evaluation of a biphasic culture system for recovery of mycobacteria from clinical specimens

A new biphasic system (MB Check, Roche) for isolation of mycobacteria from clinical specimens was evaluated by eight different microbiological laboratories in comparison with methods routinely used in the respective laboratories. Altogether 1125 clinical specimens were processed; pretreatment, if performed, was by a variety of methods. Mycobacteria were recovered from 167 specimens with the biphasic system and 165 specimens with the other methods. The average time required for isolation of Mycobacterium tuberculosis was 22.6 days with the biphasic system and 24.7 days with egg-based media; for other mycobacterial species it was 23.5 versus 20.8 days. The inclusion of a chocolate agar section in the biphasic system facilitated the early detection of contaminants, while the NAP-containing section appeared unable to differentiate Mycobacterium tuberculosis from other mycobacterial species. The biphasic system, which enables recovery of mycobacteria in small laboratories without specialized equipment, is more practical than conventional methods and at least as sensitive.

Identification of a nucleo-cytoplasmic ionic pathway by osmotic shock in isolated mouse liver nuclei

The observation that the nuclear envelope outer membrane contains ion channels raises the question of whether these conductances communicate between the cytosol and the nuclear envelope cisternae or between the cytosol and the cytoplasm. Failure to detect large, nonselective holes using the patch-clamp technique has led to the speculation that ion channels and nuclear pores are in fact the same. In this paper we present evidence that the ionic channel, recorded in isolated liver nuclei with the patch-clamp configuration of "nucleus-attached," spans the double membrane of the envelope, providing a direct contact between nucleoplasm and cytoplasm.