Comparison of Landing Variables between Countermovement Jump Landings and Drop Vertical Jump Landings from Equal Heights

The countermovement jump (CMJ) and drop vertical jump (DVJ) are often used as a measurement of physical ability or performance potential, while analysis of landing can provide crucial information regarding injury risk. In theory, similar landing strategies should be employed when CMJ jump height and DVJ drop height are controlled, yet we know of no studies have investigated this possibility. PURPOSE: to examine and compare landing characteristics between CMJ and DVJ when flight height is controlled. METHODS: Forty (20 males; 20 females; 22.5 ± 4.3 years, 1.7 ± 0.1 m, 73.2 ± 13.3 kg) recreationally active individuals performed three CMJ and three DVJ trials, each from the same height which was controlled using a Vertec. Vertical ground reaction force (VGRF) data was obtained from a portable force platform. Landing momentum, landing time, and peak vGRF were obtained from the processed vGRF data using a custom analysis program. Variables were compared between jumps (CMJ, DVJ) using paired samples t-tests (α = 0.05). Cohen’s d is used to supplement statistical outcomes by demonstrating the magnitude of mean differences. RESULTS: Landing momentum was 4.8% greater during DVJ than during CMJ and the difference was small (DVJ = -193.6 ± 52.2, CMJ = -184.4 ± 52.5; P=0.049, d = 0.4), indicating slightly greater landing heights during DVJ. Landing time during DVJ was 52% shorter than the CMJ landing time and the difference was very large (DVJ = 0.4 ± 0.2, CMJ = 0.7 ± 0.2; P\u3c0.001, d =1.7), while DVJ peak impact force was 14.7% less than CMJ peak impact force and the difference was moderate (DVJ = 3.5 ± 1.0; CMJ = 4.1 ± 0.7; P=0.002, d = 0.6). CONCLUSION: While the significant difference in landing momentum was not random, the magnitude of mean difference was small, indicating relatively similar landing momentum between jumps. Thus, the present study shows that, even when controlling jump height between the CMJ and DVJ, the tasks do not have similar landing demands, defined by momentum, time, nor peak impact force. Due to the differences observed, the CMJ and DVJ should not be used interchangeably or as a comparison between one another when examining these specific landing variables. Finally, the DVJ might expose performers to lesser overuse injury risks related to impact forces

Lithic Morphological Organization: Gahagan Bifaces from Texas and Louisiana

This study is focused upon an analysis of Gahagan biface morphology and enlists the three largest samples of these bifaces, to include that of the type site (Gahagan Mound) as well as the Mounds Plantation and George C. Davis sites. Results indicate a significant difference in Gahagan biface morphology at the Mounds Plantation site when compared with Gahagan bifaces from the Gahagan Mound and George C. Davis sites. A test of morphological integration indicates that the bifaces are significantly integrated, meaning that those traits used to characterize their shape (blade and base) vary in a coordinated manner. Tests for allometry and asymmetry were not significant. Results confirm that Gahagan biface production at Mounds Plantation differs significantly when compared with industries at Gahagan Mound and George C. Davis. Results augment previous inquiries, and provide additional evidence for a north-south divide based upon the morphology associated with communities of practice for Gahagan bifaces. When viewed in concert with similar shifts in Hickory Fine Engraved and Smithport Plain bottle morphology, multiple lines of evidence lend support to an increasingly robust argument for two previously unrecognized and morphologically-unique Caddo communities of practice

Material Loss at the Head Taper Junction of the Metal-on-Metal Pinnacle Total Hip Replacement

Introduction The ASR XL (DePuy) total hip replacement (THR) is a notable example of a modern metal-on-metal (MOM) implant design that has demonstrated unacceptable survival rates, leading to its recall by the manufacturer; national joint registries have reported revision rates at 7 years of 40% when paired with the Corail stem [1]. The ASR XL THR has a considerably greater risk of revision than the ASR resurfacing hip, which used the same bearing design. This suggests that material loss at the head-stem junction may be responsible for the greater percentage of THR failures observed in this design. The Pinnacle MOM-THR (DePuy) however used the same Corail stem as the ASR XL THR but demonstrated better clinical results, with revision rates of less than 10% at 7 years [1]. The ASR XL and MOM Pinnacle are two designs that have been widely used in hip replacement surgery. The reasons for the differences in the failure rates of the two designs are not fully understood. Comparing the mechanisms of failure of both hips will help surgeons understand whether patients with MOM Pinnacle hips will experience the same types of problems as with those seen with the ASR XL. The aims of this retrieval study were to investigate the significance of differences between the ASR XL and MOM Pinnacle in relation to: (1) pre-revision whole blood Co/Cr ratios, (2) visual evidence of taper corrosion, (3) volumetric material loss at the bearing surfaces and (4) volumetric material loss at the taper surfaces. Methods This study involved a series of failed MOM hips consisting of the ASR XL (n=30) and Pinnacle (n=30), all that had been used with a Corail stem. The bearing material in each design was cobalt-chromium and the Corail stem is of a cementless titanium 12/14 design. The ASR XL and Pinnacle had a median head diameter of 47mm (39-55) and 36mm (36-40) respectively, and a median time to revision of 38.5 months (12-74) and 55 months (14-86) respectively. Pre-revision whole blood metal ion levels were collected for each Table 1 summarises patient and implant data for the hips in this study. The female taper surfaces of all 60 heads were examined macroscopically and microscopically to assess the severity of corrosion. Each surface was graded with a score of between 1 (no corrosion) and 4 (severe corrosion) using a well-published scoring system, which has been shown to be statistically reliable. A Zeiss Prismo (Carl Zeiss Ltd, Rugby, UK) coordinate measuring machine (CMM) was used to determine the volume of material loss at the cup and head bearing surfaces. Up to 300,000 data points were collected using a 2mm ruby stylus that was translated along 400 polar scan lines on the surface. The raw data was used to map regions of material loss by comparing with the unworn geometry of the bearing. A Talyrond 365 (Hobson, Leicester, UK) roundness measuring machine was used to measure the volumetric material loss at each of the head taper surfaces. Published protocols were used to take a series of 180 vertical traces along the taper surface using a 5μm diamond stylus; worn and unworn regions were mapped and used to calculate material loss. Neither the volumetric measurement data nor corrosion scores were normally distributed. Therefore non-parametric tests were performed to assess the statistical significance of differences between the two designs in relation to the parameters under investigation in this study. Results Both the whole blood Co ion levels and the Co/Cr ratios, Figure 1, of the ASR XL hips were significantly greater than the Pinnacles (p<0.05). There was no significant difference between the whole blood Cr ion levels between the two designs (p=0.0542). 18 of the ASR XL hips presented evidence of edge wearing of the cup, compared with 14 Pinnacle hips; this difference was not significant (p=0.438). The length of the stem trunnion contact engagement length with the taper was approximated as being 10.5mm for both designs. The median time to revision of the ASR XL hips was significantly less than the Pinnacle hips (p<0.01). There was visual evidence of corrosion in 93% (n=28) and 90% (n=27) of head tapers for the ASR XLs and Pinnacles respectively. Moderate to severe corrosion was observed in 67% (n=20) of ASR XLs compared to 60% (n=18) of Pinnacles. There was however no statistically significant difference between the scores of the two groups (p=0.927). Figure 2 presents the distribution of material loss rates for the bearing and taper surfaces of the two designs in this study. The median total bearing surface (combined cup and head) rate of material loss for the ASR XL and Pinnacle hips was 4.45mm3/year (0.32-22.85) and 4.03mm3/year (0.87-62.12) respectively. There was no significant difference between the two groups (p=0.928). The median material loss rate at the taper surfaces of the ASR XL and Pinnacle hips was 0.62mm3/year (0-4.20) and 0.30mm3/year (0-3.12); this difference was not significant (p=0.198). Discussion The work of this study presents comparisons of retrieval findings between the ASR XL and Pinnacle MOM-THRs; these hip designs were two of the most commonly implanted in patients worldwide. The significantly greater whole blood Co/Cr ratios found in the ASR XL group compared to the Pinnacle group are of interest. It is speculated that a Co/Cr ratio of greater than 1 may be an indicator of corrosion of an implant whereby more Cr ions are retained on the surface, whilst comparatively more Co ions are released into the blood. In the current study we found wear rates at the bearing surfaces of both designs to be comparable, suggesting that the significantly greater Co/Cr ratios in the ASR XL hips must be due to greater corrosion at the taper junction than the Pinnacles. Although the ASR XL hips had been implanted for a significantly shorter period of time, our visual assessment of the corrosion of the taper junctions found that corrosion scores were comparable between the two designs; indeed, a marginally greater number of ASR XL tapers had evidence of moderate to severe corrosion. This finding, coupled with the elevated Co/Cr ratios suggests that the ASR XL design is more susceptible to corrosion at the taper junction than the Pinnacle hip. We found that the median rate of material loss at the ASR XL taper was over twice that of the Pinnacle taper. Whilst not statistically significant, this difference may be due to a greater risk of corrosion at this interface in the ASR XL design. The differences in material loss and corrosion that were observed at the taper junctions may be explained by considering the larger head sizes of the ASR XL hips in comparison to the Pinnacles. It has previously been shown that increasing head size is correlated with greater visual evidence of corrosion and that increased frictional torque along the taper junction due a larger head diameter can increase the risk of fretting-corrosion. It is suggested therefore that the combination of the larger head sizes of the ASR XLs coupled with the comparatively short, rough surface of the Corail trunnion results in a cumulative effect leading to greater corrosion at the taper junction. Significance The results of the study suggest that the combination of (1) increased frictional torque in the larger ASR XLs and (2) the rough Corail trunnion surface, results in greater corrosion at the taper junction in comparison to the Pinnacle hips; this helps to explain the higher risk of revision in this hip design

Identifying The Pattern of Material Loss at the Head-Neck Junction Wear Helps Determine the Mechanism of Failure of Metal on Metal Total Hip Replacements

Material loss at the Head-Neck junction accounts for a third of the total volume material loss in contemporary metal-on-metal total hip replacements. It is speculated that the material loss is the result of corrosion and mechanical wear (fretting). High volumes of material loss have been reported, especially from the head taper. There is only one report on characterizing the pattern of material loss and this was in a very small number of cases (n=5). Our aim was to identify the different material loss patterns at the head taper and their corresponding mechanisms We retrospectively analysed a series of retrieved Large Head Metal on Metal Total Hip Replacements (155 cups, 155 femoral heads and 4 stems). We measured material loss on the bearing surfaces and the head-neck junction using well-published metrology methods. Furthermore we collected patient (age, gender and time of primary/revision operations), pre-revision (cobalt and chromium blood metal ion, oxford hip score, cup orientation and implant position) implant (cup and head size, manufacturer and corrosion severity) data. Finally we used surface analysis techniques (microscopy and spectroscopy) to identify fretting, imprinting and the material composition of debris. We devised a novel four-group classification and two blinded engineers classified the material loss patterns using wear maps derived from the metrology analysis We observed four distinct patterns of taper surface material loss at our retrieval centre and we set out to characterize these types and relate them to patient, implant and clinical variables. The four groups of material loss patterns were defined as: (1) Low wear (n= 63), (2) Open-end band (n=32), (3) Stripped material loss (n=54) and (4) Coup-Countercoup (n=6) (Figure). The Interobserver Reliability Kappa score was 0.78 (p<0.001) indicating substantial agreement between the two examiners. Analysis of variables between the groups identified significantly different head sizes (highest: Group 2, p=0.000), corrosion severity (highest: Group 2, p=0.004) and time to revision (highest: Group 3, p=0.040). We identified four different material loss patterns each with its own mechanism. Corrosion was identified as the principal mechanism in Groups 1 and 3. Group 1 head-neck junctions are thought to have a better seal with less fluid ingress in the junction. Group 3 head-neck junctions are attacked by corrosion either circumferentially, or unilaterally, along the whole engagement length. Mechanically assisted corrosion was the principal mechanism in Group 2. The higher friction torque opens up the open-end part of the junction and the ingressing fluid accelerates the corrosion. Extensive fretting was also observed under the scanning electron microscope. Intra-operative surgical damage was identified as the principal mechanism in Group 4, with only 6 components. The patterns and the mechanisms of material loss at the head-neck junction contribute to the understanding of large head metal-on-metal hip replacements. As a result, better implants can be designed in the future. Clinically, these findings suggest that head size and head taper-trunnion fit are the main factors that determine the longevity of the head-neck junction. On the other hand, patients selection does not influence the integrity of the junction

Recent Decisions

Comments on recent decisions by John A. Vuono, Robert D. LeMense, Louis G. Basso, Harry D. Snyder, Jr., Wilbur L. Pollard, and Paul R. Jackiwicz

Views from the coalface: chemo-sensors, sensor networks and the semantic sensor web

Currently millions of sensors are being deployed in sensor networks across the world. These networks generate vast quantities of heterogeneous data across various levels of spatial and temporal granularity. Sensors range from single-point in situ sensors to remote satellite sensors which can cover the globe. The semantic sensor web in principle should allow for the unification of the web with the real-word. In this position paper, we discuss the major challenges to this unification from the perspective of sensor developers (especially chemo-sensors) and integrating sensors data in real-world deployments. These challenges include: (1) identifying the quality of the data; (2) heterogeneity of data sources and data transport methods; (3) integrating data streams from different sources and modalities (esp. contextual information), and (4) pushing intelligence to the sensor level

Dancers Exhibit Different Organizations of Muscular Effort in the Dominant versus Non-Dominant Limb during the Impact Phase of the Grand Jeté

Overuse musculoskeletal injuries of the hip, knee, and ankle are prevalent in dancers. Differences in muscular effort between the dominant and non-dominant limbs may increase musculoskeletal injury risk during dance movements involving a jump followed by a high-impact unilateral landing. PURPOSE: To investigate potential differences in lower extremity muscular effort (i.e., joint angular work) between the dominant and non-dominant limbs during the landing phase of a grand jeté movement in dancers. METHODS: Collegiate dancers consisting of eight women (19 ± 1 y; 54.7 ± 6.9 kg; 1.7 ± 0.1 m) and two men (21 ± 1 y; 70.6 ± 8.9 kg; 1.8 ± 0.01 m) performed three trials of the grand jeté movement on each leg (6 total trials) while kinematic and kinetic data were collected using a 12-camera motion capture system (200 Hz) and a force platform (1000 Hz). Paired-samples t-tests (α = 0.05) were conducted to compare the dominant and non-dominant limbs for the following variables of interest: total lower limb work (absolute sum of the angular work performed about the hip, knee, and ankle joints) and the corresponding percent contributions of the hip, knee, and ankle joints during the loading (time between ground contact and peak vertical ground reaction force [GRF]) and attenuation (time between peak vertical GRF and the end of downward center of mass motion) phases of landing. Effect sizes (ES) were calculated to supplement statistical probabilities and provide the magnitude of the mean differences. RESULTS: Total lower limb work was not significantly different between the dominant and non-dominant limbs during the loading phase and the mean difference was small (p = 0.062; ES = 0.40). However, the difference between limbs for the percent contribution of the knee musculature during the loading phase was large despite not being statistically significant (p = 0.076; ES = 0.89), with greater contributions occurring during landings on the non-dominant limb (49.0 ± 14.8%) versus the dominant limb (36.7 ± 12.9%). No other differences were detected during either phase of landing. CONCLUSION: Dancers appear to utilize limb-specific energy absorption strategies during the landing portion of the grand jeté, with greater muscular efforts about the knee joint in the non-dominant limb during the time when greatest external stress is experienced. As such, dancers may be at greater risk for developing overuse injuries or chronic ailments (e.g., patellofemoral pain syndrome) in the non-dominant limb

Cellular uptake and anticancer activity of carboxylated gallium corroles

We report derivatives of gallium(III) tris(pentafluorophenyl)corrole, 1 [Ga(tpfc)], with either sulfonic (2) or carboxylic acids (3, 4) as macrocyclic ring substituents: the aminocaproate derivative, 3 [Ga(ACtpfc)], demonstrated high cytotoxic activity against all NCI60 cell lines derived from nine tumor types and confirmed very high toxicity against melanoma cells, specifically the LOX IMVI and SK-MEL-28 cell lines. The toxicities of 1, 2, 3, and 4 [Ga(3-ctpfc)] toward prostate (DU-145), melanoma (SK-MEL-28), breast (MDA-MB-231), and ovarian (OVCAR-3) cancer cells revealed a dependence on the ring substituent: IC_(50) values ranged from 4.8 to >200 µM; and they correlated with the rates of uptake, extent of intracellular accumulation, and lipophilicity. Carboxylated corroles 3 and 4, which exhibited about 10-fold lower IC_(50) values (> 3 > 2 >> 1 (intracellular accumulation of gallium corroles was fastest in melanoma cells). We conclude that carboxylated gallium corroles are promising chemotherapeutics with the advantage that they also can be used for tumor imaging

Comments on Maki v. Frelk--Comparative v.Contributory Negligence: Should the Court or Legislature Decide?

Believing that the holdings and opinions in the case of Maki v. Frelkare significant legal developments, the Vanderbilt Law Review has solicited comments on these decisions, which it is now pleased to publish. These comments by six distinguished torts teachers and writers bear on the relative merits of comparative and contributory negligence, but more importantly, they discuss whether the judicial or legislative method is most appropriate for adoption of a rule of comparative negligence. It is hoped that these comments will be used as a sound basis for action, whether the problem arises before the courts or legislatures