More Is Not Merrier: Increasing Numbers of All-Inside Implants Do Not Correlate with Higher Odds of Revision Surgery.

The purpose of this study was to evaluate the relationship between the number of all-inside meniscal repair implants placed and the risk of repair failure. We hypothesized that the use of higher numbers of all-inside meniscus repair implants would be associated with increased failure risk. A retrospective chart review identified 351 patients who underwent all-inside meniscus repair between 2006 and 2013 by a sports medicine fellowship-trained orthopaedic surgeon at a single institution. Patient demographics (age, body mass index [BMI], sex) and surgical data (number of implants used, concomitant anterior cruciate ligament reconstruction [cACLR], and tear type/size/location) were recorded. Patients who received repairs in both menisci or who had follow-up < 1-year postoperatively were excluded. Repair failure was identified through chart review or patient interviews defined as a revision surgery on the index knee such as partial meniscectomy, total knee arthroplasty, meniscus transplant, or repeat repair. Logistic regression modeling was utilized to evaluate the relationship between the number of implants used and repair failure. A total of 227 all-inside meniscus repairs were included with a mean follow-up of 5.0 ± 3.0 years following surgery. Repair failure was noted in 68 knees (30.3%)-in 28.1% of knees with fewer than four implants and in 35.8% of knees with four or more implants (p = 0.31). No significant increase in failure was observed with increasing number of all-inside medial (odds ratio [OR]: 1.15; 95% confidence interval [CI]: 0.79-1.7; p = 0.46) or lateral (OR: 0.86; 95% CI: 0.47-1.57; p = 0.63) implants after controlling for patient age, BMI, cACLR, tear type, or size. Tears of the lateral meniscus located in the red-white and white-white zones had lower odds of failure (OR: 0.14; 95% CI: 0.02-0.88; p = 0.036) than tears within the red-red zone, and patients with cACLR had lower odds of repair failure (OR: 0.40; 95% CI: 0.18-0.86, p = 0.024) than those without. The number of all-inside implants placed during meniscus tear repair did not affect the likelihood of repair failure leading to reoperation after controlling for BMI, age, tear type, size, location, and cACLR. LEVEL OF EVIDENCE: III.

The physiology of Venezillo arizonicus: water balance and the cuticular water barrier.

This study investigated the water balance physiology of Venezillo arizonicus, a land isopod endemic to the Southwest Desert Ecoregion of North America. Evaporative water losses were measured in two ways: gravimetric in dry air, and by perfusing animals with dry air in a respirometry chamber and monitoring downstream relative humidity (RH). The respective mean loss flux estimates were 0.140 and 0.177 µg h-1 cm-2 Pa-1, lower than other N. American Oniscidea described to date (≥0.491 µg h-1 cm-2 Pa-1). Humidity monitoring revealed intermittent sharp peaks in RH, attributed to the release of maxillary urine. Whole-animal flux increased as a function of temperature, with a critical temperature (Tc) between 38 and 42 °C identifiable by a clear Arrhenius break point. Hexane-rinsed whole animals yielded straight-chain, saturated hydrocarbons (C21-C33). The surface density of extracted alkanes (0.64 µg cm-2) was somewhat higher than previously determined values for mesic species, although modest compared to insects and arachnids. Dehydrated animals exposed to high RH (>88%) demonstrated active water vapor absorption (WVA) like other Crinocheta, with an extrapolated uptake threshold of approximately 85% RH (Aw = 0.85), the lowest value reported for Oniscidea. The maximum uptake flux increased linearly as a function of ambient RH. Mass-specific uptake in 100% RH was 49% d-1, similar to values determined previously for Armadillidium vulgare and Porcellio scaber. The low WVA threshold of V. arizonicus, and the species' low permeability, are consistent with its known range in the arid desert southwest and the desiccation stress of its typical aeolian sand and seasonal wash habitats.

Water vapor absorption allows for volume expansion during molting in Armadillidiumvulgare and Porcelliodilatatus (Crustacea, Isopoda, Oniscidea).

Arthropods require periodic molting in order to grow which presents a number of challenges to terrestrial taxa. Following ecdysis, the pliant new cuticle is susceptible to buckling under gravity and requires elevated hydrostatic pressure for support. Terrestrial species also require a mechanism of volume expansion and stretching of the integument prior to sclerotization, a need that is readily met in aquatic arthropods by drinking. Options for land arthropods include drinking of dew, swallowing of air, or using muscular contractions to inflate air sacs in tracheate taxa. In this study we tested the hypothesis that crinochete terrestrial isopods (Isopoda: Oniscidea: Crinocheta) exploit their capacity for active water vapor absorption (WVA) to increase volume during molting. Two crinochete species, Armadillidiumvulgare and Porcelliodilatatus, were studied and compared with the non-absorbing species Ligidiumlapetum (Oniscidea: Ligiamorpha). Pre-molting animals were identified by sternal CaCO3 deposits and exposed to 100% or 97% relative humidity (RH). Mass-changes were monitored by daily weighing and the timing of the posterior and anterior ecdyses was used to categorize time (days premolt and days post-molt) over the molt cycle. In each treatment RH, A.vulgare and P.dilatatus showed a progressive mass increase from 5 days premolt until the posterior or anterior ecdysis, followed abruptly by period of mass-loss lasting 3-4 days post-molt. The fact that the initial mass-gain is seen in 97 % RH, a humidity below the water activity of the hemolymph, confirms the role of WVA. Similarly, since the post-molt mass-loss is seen in 100 % RH, this must be due to active expulsion of water, possibly via maxillary urine. Concurrent changes in hemolymph osmolality were monitored in a separate batch of A.vulgare and show sustained osmolality during premolt and an abrupt decrease between the anterior and posterior ecdysis. These patterns indicate a mobilization of sequestered electrolytes during premolt, and a loss of electrolytes during the post-molt mass-loss, amounting to approximately 8.6 % of total hemolymph solutes. WVA, in conjunction with pulses of elevated hemolymph pressure, provides an efficient mechanism of pre-molt volume expansion prior to and during the biphasic molt in these species. Premolt Ligidiumlapetum exposed to same treatments failed to molt successfully and no premolt animals survived to day 3 (72 h) even in 100 % RH. The apparent dependence of this species on liquid water for successful molting could explain its obligatory association with riparian fringe habitats.

Exceptional running and turning performance in a mite.

The Southern California endemic mite Paratarsotomus macropalpis was filmed in the field on a concrete substrate and in the lab to analyze stride frequency, gait and running speed under different temperature conditions and during turning. At ground temperatures ranging from 45 to 60 °C, mites ran at a mean relative speed of 192.4 ± 2.1 body lengths (BL) s(-1), exceeding the highest previously documented value for a land animal by 12.5%. Stride frequencies were also exceptionally high (up to 135 Hz), and increased with substrate temperature. Juveniles exhibited higher relative speeds than adults and possess proportionally longer legs, which allow for greater relative stride lengths. Although mites accelerated and decelerated rapidly during straight running (7.2 ± 1.2 and -10.1 ± 2.1 m s(-2), respectively), the forces involved were comparable to those found in other animals. Paratarsotomus macropalpis employs an alternating tetrapod gait during steady running. Shallow turns were accomplished by a simple asymmetry in stride length. During tight turns, mites pivoted around the tarsus of the inside third leg (L3), which thus behaved like a grappling hook. Pivot turns were characterized by a 42% decrease in turning radius and a 40% increase in angular velocity compared with non-pivot turns. The joint angle amplitudes of the inner L2 and L3 were negligible during a pivot turn. While exceptional, running speeds in P. macropalpis approximate values predicted from inter-specific scaling relationships.

Exceptional thermal tolerance and water resistance in the mite Paratarsotomus macropalpis (Erythracaridae) challenge prevailing explanations of physiological limits.

Physiological performance and tolerance limits in metazoans have been widely studied and have informed our understanding of processes such as extreme heat and cold tolerance, and resistance to water loss. Because of scaling considerations, very small arthropods with extreme microclimatic niches provide promising extremophiles for testing predictive physiological models. Corollaries of small size include rapid heating and cooling (small thermal time constants) and high mass-specific metabolic and water exchange rates. This study examined thermal tolerance and water loss in the erythracarid mite Paratarsotomus macropalpis (Banks, 1916), a species that forages on the ground surface of the coastal sage scrub habitat of Southern California, USA. Unlike most surface-active diurnal arthropods, P. macropalpis remains active during the hottest parts of the day in midsummer. We measured water-loss gravimetrically and estimated the critical thermal maximum (CTmax) by exposing animals to a given temperature for 1h and then increasing temperature sequentially. The standardized water flux of 4.4ngh(-1)cm(-2)Pa(-1), averaged for temperatures between 22 and 40°C, is among the lowest values reported in the literature. The CTmax of 59.4°C is, to our knowledge, the highest metazoan value reported for chronic (1-h) exposure, and closely matches maximum field substrate temperatures during animal activity. The extraordinary physiological performance seen in P. macropalpis likely reflects extreme selection resulting from its small size and resultant high mass-specific water loss rate and low thermal time-constant. Nevertheless, the high water resistance attained with a very thin lipid barrier, and the mite's exceptional thermal tolerance, challenge existing theories seeking to explain physiological limits.

Discontinuous ammonia excretion and glutamine storage in littoral Oniscidea (Crustacea: Isopoda): testing tidal and circadian models.

A key evolutionary development facilitating land colonization in terrestrial isopods (Isopoda: Oniscidea) is the intermittent liberation of waste nitrogen as volatile ammonia. Intermittent ammonia release exploits glutamine (Gln) as an intermediary nitrogen store. Here, we explore the relationship between temporal patterns of ammonia release and Gln accumulation in three littoral oniscideans from Southern California. Results are interpreted in terms of water availability, habitat, activity patterns, and ancestry. A two-way experimental design was used to test whether ammonia excretion and Gln accumulation follow a tidal or diel periodicity. Ammonia excretion was studied in the laboratory using chambers with or without available seawater and using an acid trap to collect volatile ammonia. Ligia occidentalis releases ammonia directly into seawater and accumulates Gln during low tide (48.9 ± 6.5 µmol g⁻¹ at low tide, 24.1 ± 3.0 µmol g⁻¹ at high tide), indicating that excretion is tidally constrained. Alloniscus perconvexus and Tylos punctatus can excrete ammonia directly into seawater or utilize volatilization. Both species burrow in sand by day and show a diel excretory pattern, accumulating Gln nocturnally (31.8 ± 2.7 µmol g⁻¹ at dawn and 21.8 ± 2.3 µmol g⁻¹ at dusk for A. perconvexus; 85.7 ± 15.1 µmol g⁻¹ at dawn and 25.4 ± 2.9 µmol g⁻¹ at dusk for T. punctatus) and liberating ammonia diurnally. Glutaminase shows higher activity in terrestrial (0.54-0.86 U g⁻¹) compared to intertidal (0.25-0.31 U g⁻¹) species, consistent with the need to generate high PNH3 for volatilization. The predominant isoform in Armadillidium vulgare is phosphate dependent and maleate independent; phosphate is a plausible regulator in vivo.

Kinematic evidence for superfast locomotory muscle in two species of teneriffiid mites.

Locomotory muscles typically operate over a narrow range of contraction frequencies, characterized by the predominant fiber types and functional roles. The highest documented frequencies in the synchronous sound-producing muscles of insects (550 Hz) and toadfish (200 Hz) far exceed the contraction frequencies observed in weight-bearing locomotory muscles, which have maximum documented frequencies below 15-30 Hz. Laws of scaling, however, predict that smaller arthropods may employ stride frequencies exceeding this range. In this study we measured running speed and stride frequency in two undescribed species of teneriffiid mites from the coastal sage scrub of southern California. Relative speeds of both species [129-133 body lengths (BL)s(-1)] are among the fastest documented for any animal. Measured stride frequencies for both species far exceed those documented for any weight-bearing locomotory muscle, with measured values for one species ranging from 93 Hz at 25 degrees C to 111 Hz at 45 degrees C. Stride frequencies either closely approximate or, for one species, exceed predicted values based on an interspecific scaling of frequency and animal mass. Consequently, while the ultra-high frequencies of these muscles must depend on appropriately scaled kinetics of the calcium transient and contraction-relaxation cycle, these do not appear to limit the operating frequencies during running. The predicted low muscle forces operating at these very high frequencies evidently suffice for locomotion, probably because of the larger relative muscle force generated by smaller animals.

Postprandial energy expenditure in whole-food and processed-food meals: implications for daily energy expenditure.

BACKGROUND: Empirical evidence has shown that rising obesity rates closely parallel the increased consumption of processed foods (PF) consumption in USA. Differences in postprandial thermogenic responses to a whole-food (WF) meal vs. a PF meal may be a key factor in explaining obesity trends, but currently there is limited research exploring this potential link. OBJECTIVE: The goal was to determine if a particular PF meal has a greater thermodynamic efficiency than a comparable WF meal, thereby conferring a greater net-energy intake. DESIGN: Subjective satiation scores and postprandial energy expenditure were measured for 5-6 h after isoenergetic meals were ingested. The meals were either 'whole' or 'processed' cheese sandwiches; multi-grain bread and cheddar cheese were deemed whole, while white bread and processed cheese product were considered processed. Meals were comparable in terms of protein (15-20%), carbohydrate (40-50%), and fat (33-39%) composition. Subjects were healthy women (n=12) and men (n=5) studied in a crossover design. RESULTS: There were no significant differences in satiety ratings after the two meals. Average energy expenditure for the WF meal (137+/-14.1 kcal, 19.9% of meal energy) was significantly larger than for the PF meal (73.1+/-10.2 kcal, 10.7% of meal energy). CONCLUSION: Ingestion of the particular PF meal tested in this study decreases postprandial energy expenditure by nearly 50% compared with the isoenergetic WF meal. This reduction in daily energy expenditure has potential implications for diets comprised heavily of PFs and their associations with obesity.

In vivo ion fluxes across the eggs of Armadillidium vulgare (Oniscidea: Isopoda): the role of the dorsal organ.

The thin-walled, lecithotrophic eggs of land isopods (suborder Oniscidea) are brooded in a fluid-filled maternal marsupium until a few days following the second embryonic molt. Eggs of Armadillidium vulgare possess a well-developed dorsal organ underlying a broad silver-staining saddle on the vitelline membrane. Based on its chloride permeability and known transport functions in planktotrophic crustaceans, we hypothesized that the dorsal organ functions in passive or active ion movements. To study this, we employed the automated scanning electrode technique with self-referencing ion-selective microelectrodes to measure ion fluxes across the dorsal organ and adjacent egg poles. Stage 1 (chorionated) eggs revealed only small ion fluxes, indicating low permeability. Early stage 2 eggs--between the first embryonic molt and blastokinesis--showed evidence for active uptake of Ca(2+) and Cl(-) and possibly Na(+) against low bathing concentrations, and uptake fluxes were predominantly localized over the dorsal organ. Late stage 2 eggs revealed no capacity for ion uptake, consistent with the atrophy of the dorsal organ at blastokinesis, but high ion permeability. In all stages, the silver-staining saddle showed a sustained outward proton flux indicating that it is the primary site for metabolic acid/CO(2) excretion. The emerging picture is that the embryo dorsal organ in A. vulgare serves important functions in ion regulation, calcium provisioning, and acid excretion.

Respiratory physiology of the Oniscidea: aerobic capacity and the significance of pleopodal lungs.

The radiation of the terrestrial isopods (sub-order Oniscidea) has been accompanied by evolution of pleopodal lungs in the sections Tylida and Crinocheta. To understand the significance of such lungs for aerobic respiration, comparative studies were conducted using 6 species. Ligia occidentalis, lacking lungs, behaved as a metabolic conformer in reduced PO(2), and showed decreased V(.-)O(2) in low humidity and following dehydration. In species possessing lungs, metabolism was insensitive to dehydration. However, lung development did not show a clear relationship to metabolic regulation: Porcellio dilatatus was a metabolic conformer while Tylos punctatus and Armadillidium vulgare were efficient regulators. The metabolic conformers did not accumulate lactate during moderate hypoxia (10% O(2)), indicating that reduced V(.-)O(2) is not compensated with anaerobic glycolysis. In contrast, Alloniscus perconvexus, a littoral species with limited metabolic regulation, showed the largest lactate accumulation during hypoxia and also possessed the highest tissue LDH activity. It is hypothesized that these are adaptations to periodic hypoxia in sand burrows and the high metabolic cost of burrowing. Differences in lactate accumulation during immersion were curious, with the largest increases occurring in L. occidentalis and A. perconvexus that tolerate prolonged immersion in seawater. Possible functions of this lactate accumulation may include modulation of hemocyanin oxygen affinity.

Water vapour absorption in the penicillate millipede Polyxenus lagurus (Diplopoda: Penicillata: Polyxenida): microcalorimetric analysis of uptake kinetics.

The aberrant millipedes of the order Polyxenida are minute animals that inhabit xeric microclimates of bark and rock faces. The lichens and algae that provide their main food substrates tolerate extensive dehydration, effectively eliminating a liquid water source during periods of drought. In this study, we used microcalorimetry to test whether Polyxenus lagurus (L.) exploits active water vapour absorption (WVA) for water replenishment. Individual animals were pre-desiccated to 10-20% mass-loss and heat fluxes then monitored using a TAM 2277 microcalorimeter. The calorimetric cell was exposed to an air stream increasing progressively in humidity from 84% to 96%. WVA was distinguishable as large exothermic fluxes seen in > or = 86% RH. Owing to very small and opposing heat fluxes from metabolism and passive water loss, the measured flux provided a good measure of water uptake. WVA showed an uptake threshold of 85% RH and linear sorption kinetics until >94% RH, when uptake became asymptotic. Uptake was rapid, and would allow recovery from 20% dehydration (by mass) in little over 5 h. The uptake flux scales proportional, variant mass (0.61), suggesting an area-limited mechanism. Polyxenus possesses a cryptonephric system, analogous to that of tenebrionid beetle larvae. Measurements of water absorption and desorption from faecal pellets voided in different humidities gave an estimated rectal humidity of 85.5%. The close congruence between this value and the WVA threshold provides evidence for a cryptonephric uptake mechanism derived independently from that of tenebrionids. Polyxenus represents the first documented example of WVA in the myriapod classes.

Metabolic changes associated with active water vapour absorption in the mealworm Tenebrio molitor L. (Coleoptera, Tenebrionidae): a microcalorimetric study.

Water vapour absorption (WVA) is an important mechanism for water gain in several xeric insects. Theoretical calculations indicate that the energetic cost of WVA should be small (5-10% of standard metabolic rate) assuming realistic efficiencies. In this study we explored the relationship between WVA, metabolic heat flux (HFmet.) and CO2 release in larvae of Tenebrio molitor using microcalorimetry. By comparing metabolic heat flux with the catabolic rate estimated from VCO2 , we were able to differentiate anabolic and catabolic rates prior to and during WVA, while simultaneously monitoring water exchange. Three to four hours before the onset of WVA, larvae showed clear increases in HFmet. and catabolic flux, and a simultaneous decrease in anabolic flux. Following the onset of WVA, HFmet. decreased again until indistinguishable from control (non-absorbing) values. Possible factors contributing to the "preparatory phase" are discussed, including mobilization of Malpighian tubule transporters and muscular activity in the rectum. Absorbing larvae reduced the water activity of the calorimetric cell to 0.906, agreeing with gravimetric estimates of the critical equilibrium activity. Periods of movement during WVA coincided with decreased uptake fluxes, consistent with the animal's hydrostatic skeleton and the need to close the anus to generate pressure increases in the haemocoel.

Diel variation in ammonia excretion, glutamine levels, and hydration status in two species of terrestrial isopods.

Terrestrial isopods (suborder Oniscidea) excrete most nitrogen diurnally as volatile ammonia, and ammonia-loaded animals accumulate nonessential amino acids, which may constitute the major nocturnal nitrogen pool. This study explored the relationship between ammonia excretion, glutamine storage/mobilization, and water balance, in two sympatric species Ligidium lapetum (section Diplocheta), a hygric species; and Armadillidium vulgare (Section Crinocheta), a xeric species capable of water-vapor absorption (WVA). Ammonia excretion (12-h), tissue glutamine levels, and water contents were measured following field collection of animals at dusk and dawn. In both species, diurnal ammonia excretion exceeded nocturnal excretion four- to fivefold while glutamine levels increased four- to sevenfold during the night. Most glutamine was accumulated in the somatic tissues ("body wall"). While data support the role of glutamine in nocturnal nitrogen storage, potential nitrogen mobilization from glutamine breakdown (162 micromol g(-1) in A. vulgare) exceeds measured ammonia excretion (2.5 micromol g(-1)) over 60-fold. This may serve to generate the high hemolymph ammonia concentrations (and high P(NH3)) seen during volatilization. The energetic cost of ammonia volatilization is discussed in the light of these findings. Mean water contents were similar at dusk and dawn in both species, indicating that diel cycles of water depletion and replenishment were not occurring.