Gap Balancing vs. Measured Resection Technique in Total Knee Arthroplasty

A goal of total knee arthroplasty is to obtain symmetric and balanced flexion and extension gaps. Controversy exists regarding the best surgical technique to utilize to obtain gap balance. Some favor the use of a measured resection technique in which bone landmarks, such as the transepicondylar, the anterior-posterior, or the posterior condylar axes are used to determine proper femoral component rotation and subsequent gap balance. Others favor a gap balancing technique in which the femoral component is positioned parallel to the resected proximal tibia with each collateral ligament equally tensioned to obtain a rectangular flexion gap. Two scientific studies have been performed comparing the two surgical techniques. The first utilized computer navigation and demonstrated a balanced and rectangular flexion gap was obtained much more frequently with use of a gap balanced technique. The second utilized in vivo video fluoroscopy and demonstrated a much high incidence of femoral condylar lift-off (instability) when a measured resection technique was used. In summary, the authors believe gap balancing techniques provide superior gap balance and function following total knee arthroplasty.     

Relationship Between Ligament Forces and Contact Forces in Balancing at Total Knee Surgery

BackgroundSpacer blocks, tensors, or instrumented tibial trials are current methods of balancing the knee during surgery but there are no current techniques for measuring ligament forces. Our goal was to study the relationship between the collateral ligament forces and the condylar contact forces to determine whether there was equivalence.MethodsA test rig was constructed modeling an artificial knee joint with collateral ligaments. The ligament forces as well as the lateral and medial tibial contact forces were measured during flexion for different positions of the femoral component on the femur, producing a set of forces for the simulated conditions. A regression analysis was used to study the correlation between the ligament and contact forces.ResultsThe combined medial and lateral ligament and contact forces showed a linear relation with a correlation coefficient of 0.98. For the medial and lateral sides separately, the correlations were 0.85 and 0.88, respectively, with more than 80% of points within a ±25% deviation from the linear relations. This deviation from the linear correlation is linked to differences in medial-lateral femoral-tibial contact point locations at different flexion angles.ConclusionWithin balancing accuracies generally achieved at surgery, the collateral ligament forces were linearly correlated to the condylar contact forces. These forces can also be equally correlated to the distraction forces as well as the moments at which condylar liftoff would occur from varus-valgus moments. This indicated a unification of the different balancing parameters, and hence such quantitative methods can be used interchangeably.     

Gap velocity measurements of a blood pump model

This paper presents the velocity measurements in the gap between the impeller and the pump casing of a 5:1 enlarged centrifugal blood pump model at operating condition. Both the radial and tangential velocity at the gap were measured. It was found that there was no cross flow in both the radial and tangential velocity distributions at the seven radial locations. This implies that the 0.2 mm gap in the prototype should be the optimal clearance of the pump. The vector plot of the resultant velocity showed that the double volute design of the pump, especially the splitter plate that started at theta; = 180 degrees, has created a washout mechanism in the clearance gap; that is, a sector of flow ranging from theta; = 100 degrees to theta; = 190 degrees has directed strongly toward the eye while the rest of the flow in the gap is in a tangential direction. It is important that the blood should flow out of the gap through the eye instead of continuing to circulate in the clearance gap. This explains why the pump has minimum hemolysis and thrombus formation and is able to function with nominal efficiency as compared to other centrifugal pumps.     

Differential Dose-dependent Effects of α-, β-Carotenes and Lycopene on Gap-junctional Intercellular Communication in Rat Liver in vivo

In order to examine the relevance of alteration of gap-junctional intercellular communication (GJIC) to chemopreventive activity against carcinogenesis, the effects of α and β -carotene as well as lycopene, typical chemopreventive carotenoids, on cell coupling via gap junctions in rat liver in vivo were studied using a direct functional dye-transfer technique. We found that all three test compounds given at a dose of 50 mg/kg-body weight (b.w.) daily, 5 times by gavage, inhibited GJIC, while similar treatment with 5 mg/kg b.w. caused enhancement, especially in the β-carotene and lycopene-treated groups. At the dose level of 0.5 mg/kg b.w., the three compounds had no effect. The findings show that all three agents differentially modulate GJIC depending on the dose, with beneficial effects on cell communication only detected at the one dose. The result suggests that determination of the dose of chemicals to be used is crucial for human intervention studies.     

Characterization of gap junctions between osteoblast-like cells in culture

Summary The structure of gap junctions in osteoblast-like cells (OBs) and the connexins (cx) that build up these structures were characterized by ultrastructural, immunocytochemical, and molecular techniques. Ultrastructural studies revealed numerous gap junctions which were mostly located on processes of neighboring cells. Immunofluorescence labeling using two different antibodies (specific to mouse live cx26 and cx32 and to a peptide-specific rat heart gap junction protein cx43) gave evidence that in OBs, gap junctions consist mainly of cx43. The presence of cx43 in cultured OB was also confirmed by Western blot analysis. Dye-coupling with Lucifer yellow led to a staining of up to 30 neighboring cells. Parallel intracellular recordings showed that membrane potential amplitude changes (4–5 mV) are typically related to those in the coupled cells. Thus, there is morphological and functional evidence for intercellular communication between OB in culture. OBs in culture express the same connexins as observed in vivo and may serve as a model to investigate electrophysiological events in response to different stimulation signals.     

A Comparison of Flow Field Structures of Two Tri-Leaflet Polymeric Heart Valves

Polymeric heart valves have the potential to reduce thrombogenic complications associated with current mechanical valves and overcome fatigue-related problems experienced by bioprosthetic valves. In this in vitro study, the velocity fields inside and downstream of two different prototype tri-lealfet polymeric heart valves were studied. Experiments were conducted on two 23 mm prototype polymeric valves, provided by AorTech Europe, having open or closed commissure designs and leaflet thickness of 120 and 80 m, respectively. A two-dimensional LDV system was used to measure the velocity fields in the vicinity of the two valves under simulated physiological conditions. Both commissural design and leaflet thickness were found to affect the flow characteristics. In particular, very high levels of Reynolds shear stress of 13,000 dynes/cm² were found in the leakage flow of the open commisure design. Maximum leakage velocities in the open and closed designs were 3.6 m/s and 0.5 m/s respectively; the peak forward flow velocities were 2.0 m/s and 2.6 m/s, respectively. In both valve designs, shear stress levels exceeding 4,000 dyne/cm² were observed at the trailing edge of the leaflets and in the leakage and central orifice jets during peak systole. Additionally, regions of low velocity flow conducive to thrombus formation were observed in diastole. The flow structures measured in these experiments are consistent with the location of thrombus formation observed in preliminary animal experiments.     

Quinine, a blocker of neuronal cx36 channels, suppresses seizure activity in rat neocortex in vivo

PURPOSE: The selective contribution of neuronal gap junction (GJ) communication via connexin 36 (Cx36) channels to epileptogenesis and to the maintenance and propagation of seizures was investigated in both the primary focus and the mirror focus by using pharmacologic approaches with the 4-aminopyridine in vivo epilepsy model. METHODS: ECoG recording was performed on anesthetized adult rats, in which either quinine, a selective blocker of Cx36, or the broad-spectrum GJ blockers carbenoxolone and octanol were applied locally, before the induction or at already active epileptic foci. RESULTS: The blockade of Cx36 channels by quinine before the induction of epileptiform activity slightly reduced the epileptogenesis. When quinine was applied after 25-30 repetitions of seizures, a new discharge pattern appeared with frequencies >15 Hz at the initiation of seizures. In spite of the increased number of seizures, the summated ictal activity decreased, because of the significant reduction in the duration of the seizures. The amplitudes of the seizure discharges of all the patterns decreased, with the exception of those with frequencies of 11-12 Hz. The blockade of Cx36 channels and the global blockade of the GJ channels resulted in qualitatively different modifications in ictogenesis. CONCLUSIONS: The blockade of Cx36 channels at the already active epileptic focus has an anticonvulsive effect and modifies the manifestation of the 1- to 18-Hz seizure discharges. Our findings indicate that the GJ communication via Cx36 channels is differently involved in the synchronization of the activities of the networks generating seizure discharges with different frequencies. Additionally, we conclude that both neuronal and glial GJ communication contribute to the manifestation and propagation of seizures in the adult rat neocortex.     

Modulation of muscarinic facilitation of epileptiform discharges in immature rat neocortex

We examined the cholinergic effects on epileptiform discharge generation in immature (postnatal days 10-20) rat neocortex. Evoked and spontaneous field potentials were recorded from the deep layers of neocortical slices during GABA(A) receptor blockade by bicuculline methiodide (BMI, 50 microM). The anticholinesterase eserine (10 microM) as well as the ACh-analog carbamylcholine chloride (CCh, 25 microM) decreased the amplitude and duration of evoked field potentials and in parallel, increased significantly the rate of occurrence of spontaneous discharges. These effects were reversed by the muscarinic antagonist atropine (2.5 microM, n = 20), but not by the nicotinic receptor antagonist hexamethonium (50 microM, n = 3). The M1 subtype-selective muscarinic antagonist pirenzepine (1 microM, n = 12) blocked spontaneous discharges in 8/12 slices, while muscarinic antagonists of the M2 (AFDX 116 n = 4), M3 (4-DAMP n = 4) and M4 (gallamine n = 5, tropicamide n = 6) type, all at 1 microM, only reduced their frequency. CCh-induced spontaneous discharges were blocked by the combination of the glutamate receptor antagonists AP5 and CNQX (both at 10 microM; n = 11). Gap junction blockers abolished them (halothane, n = 7) or reduced their frequency by 65% (carbenoxolone, n = 8). Inhibiting Ca2+ release from intracellular stores by dantrolene (100 microM, n = 5) or thapsigargin (1 microM, n = 5) also depressed their frequencies by 55-65%. By contrast, their rates were not altered by perfusion with high Ca2+ (7 mM; n = 6) medium, a manipulation suppressing polysynaptic connections. These findings demonstrate that activation of muscarinic receptors, notably of the M1 type, in immature rat neocortex facilitates the generation of glutamatergic epileptiform discharges. These discharges are strongly inhibited by gap junction blockers, and are also partly mediated by the, presumably muscarinic receptor-dependent, mobilization of intracellular calcium.     

A decay of gap junctions associated with ganglion cell differentiation during retinal regeneration of the adult newt

Changes in the gap junctional coupling and maturation of voltage-activated Na(+) currents during regeneration of newt retinas were examined by whole-cell patch-clamping in slice preparations. Progenitor cells in regenerating retinas did not exhibit Na(+) currents but showed prominent electrical and tracer couplings. Cells identified by LY-fills were typically slender. Na(+) currents were detected in premature ganglion cells with round somata in the 'intermediate-II' regenerating retina. No electrical and tracer couplings were observed between these cells. Mature ganglion cells did not exhibit electrical coupling, but showed tracer coupling. On average, the maximum Na(+) current amplitude recorded from premature ganglion cells was roughly 2.5-fold smaller than that of mature ganglion cells. In addition, the activation threshold of the Na(+) current was nearly 11 mV more positive than that of mature cells. We provide morphological and physiological evidence showing that loss of gap junctions between progenitor cells is associated with ganglion cell differentiation during retinal regeneration and that new gap junctions are recreated between mature ganglion cells. Also we provide evidence suggesting that the loss of gap junctions correlates with the appearance of voltage-activated Na(+) currents in ganglion cells.     

Freeze fracture aspects of the spiral limbus

Summary Replicas of the freeze fractured spiral limbus are studied in chinchillas. Zonulae occludentes are demonstrated between the interdental cells and the inner sulcus cells; gap junctions are described connecting interdental cells and inner sulcus cells to one another and they are found between the perilymphatic cells in the spiral limbus.