Joint stability characteristics of the ankle complex after lateral ligamentous injury, part I: a laboratory comparison using arthrometric measurement

CONTEXT

The mechanical property of stiffness may be important to investigating how lateral ankle ligament injury affects the behavior of the viscoelastic properties of the ankle complex. A better understanding of injury effects on tissue elastic characteristics in relation to joint laxity could be obtained from cadaveric study.

OBJECTIVE

To biomechanically determine the laxity and stiffness characteristics of the cadaver ankle complex before and after simulated injury to the anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL) during anterior drawer and inversion loading.

DESIGN

Cross-sectional study.

SETTING

University research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Seven fresh-frozen cadaver ankle specimens.

INTERVENTION(S)

All ankles underwent loading before and after simulated lateral ankle injury using an ankle arthrometer.

MAIN OUTCOME MEASURE(S)

The dependent variables were anterior displacement, anterior end-range stiffness, inversion rotation, and inversion end-range stiffness.

RESULTS

Isolated ATFL and combined ATFL and CFL sectioning resulted in increased anterior displacement but not end-range stiffness when compared with the intact ankle. With inversion loading, combined ATFL and CFL sectioning resulted in increased range of motion and decreased end-range stiffness when compared with the intact and ATFL-sectioned ankles.

CONCLUSIONS

The absence of change in anterior end-range stiffness between the intact and ligament-deficient ankles indicated bony and other soft tissues functioned to maintain stiffness after pathologic joint displacement, whereas inversion loading of the CFL-deficient ankle after pathologic joint displacement indicated the ankle complex was less stiff when supported only by the secondary joint structures.

Joint stability characteristics of the ankle complex in female athletes with histories of lateral ankle sprain, part II: clinical experience using arthrometric measurement

CONTEXT

This is part II of a 2-part series discussing stability characteristics of the ankle complex. In part I, we used a cadaver model to examine the effects of sectioning the lateral ankle ligaments on anterior and inversion motion and stiffness of the ankle complex. In part II, we wanted to build on and apply these findings to the clinical assessment of ankle-complex motion and stiffness in a group of athletes with a history of unilateral ankle sprain.

OBJECTIVE

To examine ankle-complex motion and stiffness in a group of athletes with reported history of lateral ankle sprain.

DESIGN

Cross-sectional study.

SETTING

University research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Twenty-five female college athletes (age = 19.4 ± 1.4 years, height = 170.2 ± 7.4 cm, mass = 67.3 ± 10.0 kg) with histories of unilateral ankle sprain.

INTERVENTION(S)

All ankles underwent loading with an ankle arthrometer. Ankles were tested bilaterally.

MAIN OUTCOME MEASURE(S)

The dependent variables were anterior displacement, anterior end-range stiffness, inversion rotation, and inversion end-range stiffness.

RESULTS

Anterior displacement of the ankle complex did not differ between the uninjured and sprained ankles (P = .37), whereas ankle-complex rotation was greater for the sprained ankles (P = .03). The sprained ankles had less anterior and inversion end-range stiffness than the uninjured ankles (P < .01).

CONCLUSIONS

Changes in ankle-complex laxity and end-range stiffness were detected in ankles with histories of sprain. These results indicate the presence of altered mechanical characteristics in the soft tissues of the sprained ankles.

Development of agro-environmental scenarios to support pesticide risk assessment in Europe

This paper describes work carried out within the EU-funded FOOTPRINT project to characterize the diversity of European agricultural and environmental conditions with respect to parameters which most influence the environmental fate of pesticides. Pan-European datasets for soils, climate, land cover and cropping were intersected, using GIS, to identify the full range of unique combinations of climate, soil and crop types which characterize European agriculture. The resulting FOOTPRINT European agro-environmental dataset constitutes a large number of polygons (approximately 1,700,000) with attribute data files for i) area fractions of annual crops related to each arable-type polygon (as an indicator of its probability of occurrence); and, ii) area fractions of each soil type in each polygon (as an indicator of its probability of occurrence). A total of 25,044 unique combinations of climate zones, agricultural land cover classes, administrative units and soil map units were identified. The same soil/crop combinations occur in many polygons which have the same climate while the fractions of the soils and arable crops are different. The number of unique combinations of climate, soil and agricultural land cover class is therefore only 7961. 26-year daily meteorological data, soil profile characteristics and crop management features were associated with each unique combination. The agro-environmental scenarios developed can be used to underpin the parameterization of environmental fate models for pesticides and should also have relevance for other agricultural pollutants. The implications for the improvement and further development of risk assessment procedures for pesticides are discussed.

Developing climatic scenarios for pesticide fate modelling in Europe

A climatic classification for Europe suitable for pesticide fate modelling was constructed using a 3-stage process involving the identification of key climatic variables, the extraction of the dominant modes of spatial variability in those variables and the use of k-means clustering to identify regions with similar climates. The procedure identified 16 coherent zones that reflect the variability of climate across Europe whilst maintaining a manageable number of zones for subsequent modelling studies. An analysis of basic climatic parameters for each zone demonstrates the success of the scheme in identifying distinct climatic regions. Objective criteria were used to identify one representative 26-year daily meteorological series from a European dataset for each zone. The representativeness of each series was then verified against the zonal classifications. These new FOOTPRINT climate zones provide a state-of-the-art objective classification of European climate complete with representative daily data that are suitable for use in pesticide fate modelling.

The relationships between instrumented measurements of ankle and knee ligamentous laxity and generalized joint laxity

AIM

The purpose of this study was to evaluate whether lower extremity joint laxity is a function of a particular joint and/or a generalizable characteristic (trait) of the person. Validated instrumented measurements of ankle and knee joint-specific laxity in the same individual were correlated to determine whether a relationship exists. In addition, ankle and knee joint-specific laxity were correlated with generalized joint laxity using the modified Beighton mobility index.

METHODS

Fifty-seven male and female athletes were studied. We examined dominant ankle laxity using an ankle arthrometer and dominate knee anterior laxity using the KT 2000. The dominant ankle was loaded in anteroposterior (AP) drawer and inversion-eversion (I-E) rotation. Laxity was measured as total AP displacement (millimeters) after +/-125 N of applied force and total I-E rotation (degrees) was measured after +/-4 N x m of applied torque. The dominant knee was loaded with an anterior drawer and laxity (millimeters) was measured after manual maximum displacement.

RESULTS

Non-significant correlations were observed among the test variables for generalized joint laxity (0.21 to 0.37; P>0.05) and instrumented ankle and knee joint laxity (0.19 to 0.21; P>0.05). When examined by gender, no statistically significant correlations (0.05 to 0.40; P>0.05) were found for either generalized laxity or instrumented ankle and knee joint laxity.

CONCLUSIONS

These results imply that ankle and knee joint laxity are joint-specific and not generalizable.

Using a linked soil model emulator and unsaturated zone leaching model to account for preferential flow when assessing the spatially distributed risk of pesticide leaching to groundwater in England and Wales

Although macropore flow is recognized as an important process for the transport of pesticides through a wide range of soils, none of the existing spatially distributed methods for assessing the risk of pesticide leaching to groundwater account for this phenomenon. The present paper presents a spatially distributed modelling system for predicting pesticide losses to groundwater through micro- and macropore flow paths. The system combines a meta version of the mechanistic, dual porosity, preferential flow pesticide leaching model MACRO (the MACRO emulator), which describes pesticide transport and attenuation in the soil zone, to an attenuation factor leaching model for the unsaturated zone. The development of the emulator was based on the results of over 4000 MACRO model simulations. Model runs describe pesticide leaching for the range of soil types, climate regimes, pesticide properties and application patterns in England and Wales. Linking the MACRO emulator to existing spatial databases of soil, climate and compound-specific loads allowed the prediction of the concentration of pesticide leaching from the base of the soil profile (at 1 m depth) for a wide range of pesticides. Attenuation and retardation of the pesticide during transit through the unsaturated zone to the watertable was simulated using the substrate attenuation factor model AQUAT. The MACRO emulator simulated pesticide loss in 10 of 12 lysimeter soil-pesticide combinations, for which pesticide leaching was shown to occur and also successfully predicted no loss from 3 soil-pesticide combinations. Although the qualitative aspect of leaching was satisfactorily predicted, actual pesticide concentrations in leachate were relatively poorly predicted. At the national scale, the linked MACRO emulator/AQUAT system was found to predict the relative order of, and realistic regional patterns of, pesticide leaching for atrazine, isoproturon, chlorotoluron and lindane. The methodology provides a first-step assessment of the potential for pesticide leaching to groundwater in England and Wales. Further research is required to improve the modelling concept proposed. The system can be used to refine regional groundwater monitoring system designs and sampling strategies and improve the cost-effectiveness of the measures needed to achieve 'good status' of groundwater quality as required by the Water Framework Directive.

Sparse matrix approximation method for an active optical control system

We develop a sparse matrix approximation method to decompose a wave front into a basis set of actuator influence functions for an active optical system consisting of a deformable mirror and a segmented primary mirror. The wave front used is constructed by Zernike polynomials to simulate the output of a phase-retrieval algorithm. Results of a Monte Carlo simulation of the optical control loop are compared with the standard, nonsparse approach in terms of accuracy and precision, as well as computational speed and memory. The sparse matrix approximation method can yield more than a 50-fold increase in the speed and a 20-fold reduction in matrix size and a commensurate decrease in required memory, with less than 10% degradation in solution accuracy. Our method is also shown to be better than when elements are selected for the sparse matrix on a magnitude basis alone. We show that the method developed is a viable alternative to use of the full control matrix in a phase-retrieval-based active optical control system.

The strength of a cement acetabular locking mechanism

To minimize the morbidity associated with revision of a well-fixed acetabular shell, some surgeons advocate cementing a polyethylene liner into the shell when a liner exchange is not possible. So far the strength of this cement locking mechanism has been measured on only a few specimens. The purpose of this study is to correct that oversight by measuring the push-out and lever-out strengths of an acetabular polyethylene liner cemented into a porous-coated shell. We cemented acetabular liners into porous-coated acetabular shells using first-generation cementing techniques. Each of 30 specimens was tested for its push-out or lever-out strength. The results suggest that the strength of a cemented polyethylene liner locking mechanism is similar to that of an uncemented acetabular shell.

Aspartyl beta -hydroxylase (Asph) and an evolutionarily conserved isoform of Asph missing the catalytic domain share exons with junctin

The mouse aspartyl beta-hydroxylase gene (Asph, BAH) has been cloned and characterized. The mouse BAH gene spans 200 kilobase pairs of genomic DNA and contains 24 exons. Of three major BAH-related transcripts, the two largest (6,629 and 4,419 base pairs) encode full-length protein and differ only in the use of alternative polyadenylation signals. The smallest BAH-related transcript (2,789 base pairs) uses an alternative 3' terminal exon, resulting in a protein lacking a catalytic domain. Evolutionary conservation of this noncatalytic isoform of BAH (humbug) is demonstrated in mouse, man, and Drosophila. Monoclonal antibody reagents were generated, epitope-mapped, and used to definitively correlate RNA bands on Northern blots with protein species on Western blots. The gene for mouse junctin, a calsequestrin-binding protein, was cloned and characterized and shown to be encoded from the same locus. When expressed in heart tissue, BAH/humbug preferably use the first exon and often the fourth exon of junctin while preserving the reading frame. Thus, three individual genes share common exons and open reading frames and use separate promoters to achieve differential expression, splicing, and function in a variety of tissues. This unusual form of exon sharing suggests that the functions of junctin, BAH, and humbug may be linked.

Pesticides in rainfall in Europe

Papers and published reports investigating the presence of pesticides in rainfall in Europe were reviewed. Approximately half of the compounds that were analysed for were detected. For those detected, most concentrations were below about 100 ng/l, but larger concentrations, up to a few thousand nanograms per litre, were detected occasionally at most monitoring sites. The most frequently detected compounds were lindane (gamma-HCH) and its isomer (alpha-HCH), which were detected on 90-100% of sampling occasions at most of the sites where they were monitored. For compounds developed more recently, detection was usually limited to the spraying season. A classification of pesticides according to their deposition pattern is proposed.

Change in meniscal strain with anterior cruciate ligament injury and after reconstruction

Meniscal injury has been well documented in association with injury to the anterior cruciate ligament. The purpose of this study was to evaluate the effect of anterior cruciate ligament transection and reconstruction on meniscal strain. Four differential variable reluctance transducer strain gauges were placed in the medial and lateral menisci of nine cadaveric knees. Each specimen was mounted to a six-degree-of-freedom knee testing device. Testing was conducted with the knee fully extended and at 45 degrees and 90 degrees of flexion, both with and without applied axial load. At each angle of flexion, an anterior and posterior tibial load was applied. Next, the anterior cruciate ligament was transected and the testing sequence was repeated. Finally, the ligament was reconstructed using a central one-third patellar tendon graft and the testing sequence was repeated. The results demonstrated statistically significant increases in meniscal strain in ligament-transected knees compared with intact specimens. A reduction in meniscal strain to a level similar to that detected in the ligament-intact knees was observed after anterior cruciate ligament reconstruction. These results have important clinical implications regarding the potentially deleterious effect of the anterior cruciate ligament-deficient knee on meniscal strain and the potential benefit of anterior cruciate ligament reconstruction.

Possible role of valvular serotonin 5-HT(2B) receptors in the cardiopathy associated with fenfluramine

Dexfenfluramine was approved in the United States for long-term use as an appetite suppressant until it was reported to be associated with valvular heart disease. The valvular changes (myofibroblast proliferation) are histopathologically indistinguishable from those observed in carcinoid disease or after long-term exposure to 5-hydroxytryptamine (5-HT)(2)-preferring ergot drugs (ergotamine, methysergide). 5-HT(2) receptor stimulation is known to cause fibroblast mitogenesis, which could contribute to this lesion. To elucidate the mechanism of "fen-phen"-associated valvular lesions, we examined the interaction of fenfluramine and its metabolite norfenfluramine with 5-HT(2) receptor subtypes and examined the expression of these receptors in human and porcine heart valves. Fenfluramine binds weakly to 5-HT(2A), 5-HT(2B), and 5-HT(2C) receptors. In contrast, norfenfluramine exhibited high affinity for 5-HT(2B) and 5-HT(2C) receptors and more moderate affinity for 5-HT(2A) receptors. In cells expressing recombinant 5-HT(2B) receptors, norfenfluramine potently stimulated the hydrolysis of inositol phosphates, increased intracellular Ca(2+), and activated the mitogen-activated protein kinase cascade, the latter of which has been linked to mitogenic actions of the 5-HT(2B) receptor. The level of 5-HT(2B) and 5-HT(2A) receptor transcripts in heart valves was at least 300-fold higher than the levels of 5-HT(2C) receptor transcript, which were barely detectable. We propose that preferential stimulation of valvular 5-HT(2B) receptors by norfenfluramine, ergot drugs, or 5-HT released from carcinoid tumors (with or without accompanying 5-HT(2A) receptor activation) may contribute to valvular fibroplasia in humans.

Instrumented measurement of anteroposterior and inversion-eversion laxity of the normal ankle joint complex

Manual examination is the most common method for the evaluation of ankle anteroposterior (AP) and inversion-eversion (I-E) laxity. Objective assessment data of normal ankle laxity must be provided before comparison with an injured ankle can be made. The purpose of this study was to compare AP translation and I-E rotation at three force loads between dominant and nondominant ankles and to assess the test-retest reliability of a portable arthrometer in obtaining these measurements. The arthrometer consists of a frame that is fixed to the foot, a pad that is attached to the tibia, and a load-measuring handle that is attached to the foot plate through which the load is applied. A six-degrees-of-freedom spatial kinematic linkage system is connected between the tibial pad and the foot frame to measure motion. Instrumented measurement testing of total AP displacement and I-E rotation of both ankles was performed in 41 subjects (21 men and 20 women; mean age, 23.8 +/- 4.4 years). Subjects had no history of ankle injury. Subjects were tested in the supine position while lying on a table with the knee secured in extension and the foot positioned at 0 degrees of flexion. Laxity was measured from total AP displacement (millimeters) during loading to 125 N of AP force and from total I-E rotation (degrees of range of motion) during loading to 4000 N-mm. Reliability was evaluated by calculating intraclass correlation coefficients (2,1) at 75 N, 100 N, and 125 N of AP force and at 2000, 3000, and 4000 N-mm torque loads. Mean differences for displacement and rotation between the dominant and nondominant ankles at each of the force and torque loads were analyzed by dependent t-tests. For both the dominant and nondominant ankles, respectively, the reliability coefficients at each of the force loads for AP displacement (range, 0.82-0.89) and I-E rotation (range, 0.86-0.97) were high. The t-test analyses showed no significant differences (P > or = 0.05) for total AP displacement or I-E rotation between the dominant and nondominant ankles at any of the force loads. The results are clinically useful in providing information about the reliability of measures at different AP and I-E force loads using a portable ankle ligament arthrometer.

Cloning and characterization of ADAMTS11, an aggrecanase from the ADAMTS family

Aggrecan is responsible for the mechanical properties of cartilage. One of the earliest changes observed in arthritis is the depletion of cartilage aggrecan due to increased proteolytic cleavage within the interglobular domain. Two major sites of cleavage have been identified in this region at Asn(341)-Phe(342) and Glu(373)-Ala(374). While several matrix metalloproteinases have been shown to cleave at Asn(341)-Phe(342), an as yet unidentified protein termed "aggrecanase" is responsible for cleavage at Glu(373)-Ala(374) and is hypothesized to play a pivotal role in cartilage damage. We have identified and cloned a novel disintegrin metalloproteinase with thrombospondin motifs that possesses aggrecanase activity, ADAMTS11 (aggrecanase-2), which has extensive homology to ADAMTS4 (aggrecanase-1) and the inflammation-associated gene ADAMTS1. ADAMTS11 possesses a number of conserved domains that have been shown to play a role in integrin binding, cell-cell interactions, and extracellular matrix binding. We have expressed recombinant human ADAMTS11 in insect cells and shown that it cleaves aggrecan at the Glu(373)-Ala(374) site, with the cleavage pattern and inhibitor profile being indistinguishable from that observed with native aggrecanase. A comparison of the structure and expression patterns of ADAMTS11, ADAMTS4, and ADAMTS1 is also described. Our findings will facilitate the study of the mechanisms of cartilage degradation and provide targets to search for effective inhibitors of cartilage depletion in arthritic disease.

Purification and cloning of aggrecanase-1: a member of the ADAMTS family of proteins

We purified, cloned, and expressed aggrecanase, a protease that is thought to be responsible for the degradation of cartilage aggrecan in arthritic diseases. Aggrecanase-1 [a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4)] is a member of the ADAMTS protein family that cleaves aggrecan at the glutamic acid-373-alanine-374 bond. The identification of this protease provides a specific target for the development of therapeutics to prevent cartilage degradation in arthritis.

Hubble Space Telescope Faint Object Camera calculated point-spread functions

A set of observed noisy Hubble Space Telescope Faint Object Camera point-spread functions is used to recover the combined Hubble and Faint Object Camera wave-front error. The low-spatial-frequency wave-front error is parameterized in terms of a set of 32 annular Zernike polynomials. The midlevel and higher spatial frequencies are parameterized in terms of set of 891 polar-Fourier polynomials. The parameterized wave-front error is used to generate accurate calculated point-spread functions, both pre- and post-COSTAR (corrective optics space telescope axial replacement), suitable for image restoration at arbitrary wavelengths. We describe the phase-retrieval-based recovery process and the phase parameterization. Resultant calculated precorrection and postcorrection point-spread functions are shown along with an estimate of both pre- and post-COSTAR spherical aberration.

Analysis of a biodegradable composite for bone healing

A degradable L-PLA/calcium carbonate composite made of interconnecting phases was examined. This structure was used both to slow the degradation rate and to reduce the brittleness of the ceramic. Both in vitro and in vivo degradation studies were performed. Samples were incubated in buffered saline or placed in the dorsum of rats for 0, 1, or 4 weeks. Mechanical testing was performed on both groups, volume fraction of each component was determined for in vitro samples, and histology was performed on in vivo samples. Failure load, tensile strength, and elastic modulus significantly decreased during the 1st week for both groups. Continued decreases were seen at 4 weeks for in vitro samples but not for in vivo. Failure strain and tensile strength decreased only for in vitro specimens. PLA fraction significantly decreased during the 1st week and then stabilized. Histology showed that tissue ingrowth occurred at 4 weeks. The decrease in mechanical properties was probably a result of the decreased PLA fraction. The stabilization and even a slight increase in tensile strength and failure strain in the in vivo samples was probably due to the tissue ingrowth forming an implant-tissue composite.

Biomechanical comparison of reconstruction techniques in simulated lateral ankle ligament injury

Eighteen intact ankles were loaded with inversion-eversion and anterior-posterior forces, and motions of the talus and calcaneus were measured. Ankles were tested in neutral, 15 degrees of dorsiflexion, and 15 degrees of plantar flexion. The anterior talofibular ligament was then sectioned and testing was repeated. In half the specimens the calcaneofibular ligament was also sectioned followed by repeat testing. The Evans, Watson-Jones, and Chrisman-Snook procedures were performed on each ankle and testing was repeated. With inversion-eversion loading, only the Chrisman-Snook reconstruction resulted in a significantly more stable ankle joint complex than in the anterior talofibular ligament cut ankles. All three reconstructions increased ankle stability over the anterior talofibular and calcaneofibular ligament cut state. With anterior-posterior loading, all reconstructions resulted in a significantly more stable ankle joint complex than the anterior talofibular ligament cut ankles. The Evans and Chrisman-Snook procedures resulted in more stability than the anterior talofibular and calcaneofibular ligament cut ankles. There was no difference in subtalar joint motion with inversion-eversion loading among ankles with the anterior talofibular ligament cut and those with any of the reconstructions. For the anterior talofibular and calcaneofibular ligament cut ankles, subtalar joint motion was similar to that in intact ankles after each reconstruction. All three reconstructions resulted in ankles with significantly less subtalar joint motion with anterior-posterior loading than ankles with the anterior talofibular ligament cut or with the anterior talofibular and calcaneofibular ligaments cut. The Chrisman-Snook procedure resulted in ankles with significantly less motion than intact ankles.

Simulated lateral ankle ligamentous injury. Change in ankle stability

The effect of simulated ankle ligamentous injury on ankle-subtalar joint complex laxity was studied. Thirty-six intact ankles were loaded in inversion-eversion and anterior-posterior directions. Motions of the talus and calcaneus were measured with respect to the tibia. Ankles were tested at neutral, 15 degrees of dorsiflexion, and 15 degrees of plantar flexion. In all the specimens the anterior talofibular ligament was sectioned and then the calcaneofibular ligament was sectioned; testing was then repeated. With sectioning of the anterior talofibular ligament, motion increased primarily in dorsiflexion with both anterior-posterior and inversion-eversion loading. This increase was primarily caused by a large increase in subtalar motion. Additional sectioning of the calcaneofibular ligament produced little change in ankle subtalar joint motion except in dorsiflexion. Clinically, these findings show that if an anterior-posterior drawer test shows less laxity in dorsiflexion than in neutral and greater laxity than the contralateral asymptomatic side, then an isolated anterior talofibular ligamentous tear exists. Similarly, laxity in 15 degrees of dorsiflexion and in neutral suggests calcaneofibular ligament disruption. During inversion-eversion loading, the increase in ankle-subtalar joint complex rotation with calcaneofibular ligament sectioning occurred primarily in the ankle joint, implying that the calcaneofibular ligament constrains the talus through the calcaneus. Therefore, a talar tilt on stress radiographs demonstrates a torn calcaneofibular ligament.

A six-degree-of-freedom test system for the study of joint mechanics and ligament forces

A joint testing system was designed to transmit a specified motion or force to a joint in all six degrees of freedom (d.o.f.) using a spatial linkage system for position feedback. The precise reproducibility of position provided by this method of position feedback allows determination of in situ ligament forces for external joint loadings. Load on the structure of interest is calculated from six d.o.f. load cell output after the loaded position is reproduced with all other structures removed. In a test of this system, measured loads showed good agreement with applied loads.

Biomechanical analysis of patellar tendon allografts as a function of donor age

We evaluated the biomechanical properties of patellar tendon allografts from donors aged 18 to 55 years. Bone-patellar tendon-bone complexes were harvested from acceptable donors and processed. Fat and soft tissue were removed, and the tendons were sectioned lengthwise leaving the central third. Area measurements were taken, and mechanical testing was performed. Specimens were pulled to failure at a rate of 10% of the initial length per second. The force at failure, tensile stress, modulus of elasticity, and percent elongation were determined for each specimen. There was no significant correlation (P > 0.05) between age and any of the mechanical properties. Load at failure ranged from 2110 to 4650 N, with a mean of 3424 N. Regression analysis showed slightly decreasing tensile stress with increasing age, but the correlation was not significant. It appears that patellar tendon allografts from donors up to age 55 have similar mechanical properties.

Initial stability of porous coated acetabular implants. The effect of screw placement, screw tightness, defect type, and oversize implants

The effects of screw location, screw tightness, acetabular bony defects, and implant size on the initial stability of porous coated acetabular implants was studied in vitro using 12 fresh frozen cadaver pelves. The fixation of porous coated acetabular implants was compared following fixation with either rim or center screws. Implants were tested first under axial and torsional stress. Then, either a peripheral or central bony defect was created in the acetabulum and testing was repeated in a similar fashion. Rim screws were noted to significantly improve the initial fixation of implants in intact acetabula and in acetabula with central bony defects. It was also shown that the tightness of the screws is an important factor affecting the strength of fixation. Although bony defects compromise the fixation of implants, specimens with central defects were very stable, particularly when tested with axial load. Acetabula with peripheral defects lost significant stability. The use of larger implants in acetabula with bony defects was shown to increase bony coverage and the overall implant stability.

A biomechanical evaluation of an intramedullary fixation device for intertrochanteric fractures

The strength and stability of an intramedullary device when used to fix intertrochanteric fractures were determined and compared with the dynamic hip screw (DHS). A standard four-part osteotomy was created in eight paired fresh frozen human cadaver femurs. The intramedullary fixation device and a DHS were implanted in each pair member, and mechanical testing was performed. Micromotion was measured during cyclic loading to determine implant stability, and then the specimens were loaded to failure. The intramedullary fixation device had significantly greater stability in cyclic loading than the DHS and required more than twice the force for failure. For patients with osteoporosis, this device may be a useful alternative to standard sliding nail systems.

Tensile properties of the human femur-anterior cruciate ligament-tibia complex. The effects of specimen age and orientation

The structural properties of 27 pairs of human cadaver knees were evaluated. Specimens were equally divided into three groups of nine pairs each based on age: younger (22 to 35 years), middle (40 to 50 years), and older (60 to 97 years). Anterior-posterior displacement tests with the intact knee at 30 degrees and 90 degrees of flexion revealed a significant effect of knee flexion angle, but not of specimen age. Tensile tests of the femur-ACL-tibia complex were performed at 30 degrees of knee flexion with the ACL aligned vertically along the direction of applied tensile load. One knee from each pair was oriented anatomically (anatomical orientation), and the contralateral knee was oriented with the tibia aligned vertically (tibial orientation). Structural properties of the femur-ACL-tibia complex, as represented by the linear stiffness, ultimate load, and energy absorbed, were found to decrease significantly with specimen age and were also found to have higher values in specimens tested in the anatomical orientation. In the younger specimens, linear stiffness (242 +/- 28 N/mm) and ultimate load (2160 +/- 157 N) values found when the femur-ACL-tibia complex was tested in the anatomical orientation were higher than those reported previously in the literature. These values provide new baseline data for the design and selection of grafts for ACL replacement in an attempt to reproduce normal knee kinematics.

The effects of knee motion and external loading on the length of the anterior cruciate ligament (ACL): a kinematic study

A six-degrees-of-freedom mechanical linkage device was designed and used to study the unconstrained motion of ten intact human cadaver knees. The knees were subjected to externally applied varus and valgus (V-V) moments up to 14 N-m as well as anterior and posterior (A-P) loads up to 100 N. Tests were done at four knee flexion angles; 0, 30, 45, and 90 deg. Significant coupled axial tibial rotation was found, up to 21.0 deg for V-V loading (at 90 deg of flexion) and 14.2 deg for A-P loading (at 45 deg of flexion). Subsequently, the knees were dissected and the locations of the insertion sites to the femur and tibia for the anteromedial (AM), posterolateral (PL), and intermediate (IM) portions of the ACL were identified. The distances between the insertion sites for all external loading conditions were calculated. In the case when the external load was zero, the AM portion of the ACL lengthened with knee flexion, while the PL portion shortened and the intermediate (IM) portion did not change in length. With the application of 14 N-m valgus moment, the PL and IM portions of the ACL lengthened significantly more than the AM portion (p less than 0.001). With the application of 100 N anterior load, the AM portion lengthened slightly less than the PL portion, which lengthened slightly less than the IM portion (p less than 0.005). In general, the amount of lengthening of the three portions of the ACL during valgus and anterior loading was observed to increase with knee flexion angle (p less than 0.001).

A new device to measure the structural properties of the femur-anterior cruciate ligament-tibia complex

Previous studies of biomechanical properties of femur-anterior cruciate ligament-tibia complex (FATC) utilized a wide variety of testing methodologies, particularly with respect to ligament orientation relative to loading direction. A new device was designed and built to test the anterior-posterior displacement of the intact porcine knee at 30 and 90 deg of flexion, as well as the tensile properties of the FATC at any loading direction and flexion angle. Tensile tests were performed with the knees at 30 and 90 deg of flexion with the loading direction along either the axis of the tibia (tibial axis) or the axis of the anterior cruciate ligament (ligament axis). The results showed that the stiffness, ultimate load and energy absorbed were all significantly increased when the FATC was tested along the ligament axis. This study demonstrates the importance of alignment in the evaluation of the biomechanical characteristics of the femur-ACL-tibia complex.

Use of patellar tendon autograft for anterior cruciate ligament reconstruction in the rabbit: a long-term histologic and biomechanical study

To assess the degree of success of anterior cruciate ligament (ACL) replacement using the patellar tendon (PT) autograft, 29 New Zealand white rabbits underwent ACL reconstruction using a medial one-third PT autograft. The femur-ligament-tibia complexes were evaluated at 0, 6, 30, and 52 weeks postoperatively for gross and histologic appearances and tensile load to failure properties. Grossly, the autografts did not resemble the control ACLs. Histologically, the autografts progressed from being hypercellular with a random collagen fiber bundle organization to having a near normal cellularity with a more parallel collagen fiber bundle pattern. Anteroposterior knee laxity was more than two times that of the control knees 52 weeks after reconstruction. Biomechanically, the PT autografts plateaued at 30 weeks postoperatively. The ultimate load and stiffness were 15 +/- 5% and 24 +/- 6% of the control ACLs, respectively. At 52 weeks, the appearance of the PT autograft had some general histologic similarities as compared with the native ACL. However, these similarities did not extend to the functional properties of the autograft.

HCO emission from H II-molecular cloud interface regions

A survey of well-known molecular clouds in the four strongest HCO NK-,K+ = 1(01)-0(00) hyperfine transitions has been carried out to determine the prevalence of HCO and to study its chemistry. HCO emission was observed in seven molecular clouds. Three of these, NGC 2264, W49, and NGC 7538, were not previously known sources of HCO. In addition, NGC 2024 and Sgr B2 were mapped and shown to have extensive HCO emission. The survey results show the HCO abundance to be enhanced in H II-molecular cloud interface regions and support a correlation between C+ and HCO emission. The strength of the HCO emission in NGC 2024 is interpreted in terms of this enhancement and the source structure and proximity to Earth.

Sustained pressurization of polymethylmethacrylate: a comparison of low- and moderate-viscosity bone cements

There is at present great uncertainty relating to the fixation of joint implants. The deficiencies of acrylic bone cement are well documented, but the limitations of cementless fixation are as yet imcompletely identified. The purpose of this study was to investigate the potential of sustained external pressurization to improve the mechanical characteristics of conventional acrylic bone cement. The effect of serially increasing sustained pressurization of two commerically available acrylic bone cements (Simplex-P and LVC) was evaluated in human cadaver femora. A new method for determination of the shear strength of the bone-cement interface in place of the traditional pushout tests was used. In this model, there was a significant increase in the bone-cement interfacial shear strength with increasing pressure, but no difference in the shear strength was found between the two cements. At all pressure levels, the shear strength of the cement was greater than that previously reported. Increased cement penetration into the cortical bone was demonstrated with increasing pressure and low-viscosity cement, but the extent of cement penetration did not correlate with the shear strength of the bone-cement interface.

Treatment of the medial collateral ligament injury. I: The importance of anterior cruciate ligament on the varus-valgus knee laxity

The purpose of this study was to explain the functional roles of the medial collateral ligament (MCL) and the ACL and how they affect the kinematics of the knee joint after isolated MCL injury. Varus-valgus joint laxity was quantitatively measured using a device which allowed various degrees of freedom (DOF) of joint motion during application of a varus-valgus bending moment to the canine knee joint. When the knee motion was limited to 3 DOF (varus-valgus rotation, proximal-distal, and medial-lateral translation), valgus laxity increased significantly (171%) after sectioning the MCL. Thus, the MCL was the primary restraint to the valgus bending moment in the 3 DOF mode. However, the effect of sectioning the MCL on valgus laxity became minimal (21% increase) when the DOF of knee motion was increased to 5 (by adding axial tibial rotation and anterior-posterior translation). In this situation, external and internal tibial axial rotation were coupled with the varus and valgus rotation of the knee joint, respectively, and the ACL also functioned to restrain the varus-valgus rotation. The results of this study suggest that under normal knee joint motion, the functional deficit of the MCL in valgus rotation was compensated for by the remaining structures, especially by the ACL.

Effects of knee flexion on the structural properties of the rabbit femur-anterior cruciate ligament-tibia complex (FATC)

Many studies have been conducted to determine the biomechanical properties of the anterior cruciate ligament (ACL). The method of holding the femur-ACL-tibia complex (FATC) test specimen, the strain rate applied, the angle of knee flexion and the direction of the applied loads have an important effect on the outcome. It is felt that the tensile properties and strength of the ligament should be measured by applying the tensile force along the axis of the ligament. A versatile clamp was designed to accomplish this purpose. Fifty-seven rabbit knee specimens were tested at angles of flexion of 0 degrees, 30 degrees or 90 degrees. In addition, a comparative study of 25 pairs of rabbit legs were performed, whereby loading was either along the ligament or along the tibial axis. Cyclic hysteresis, ultimate load, energy absorbed, and stiffness were determined. The ultimate load values for the FATC decreased with increased knee flexion for those loaded along the tibial axis, while no such change was detected for FATC tested along the ligament axis. Other structural properties measured followed similar trends. It is concluded that the structural properties of the rabbit FATC change minimally with knee flexion (from 0 to 90 degrees) when loaded along the ligament axis, but decrease significantly with knee flexion when loaded along the axis of the tibia. Therefore, the data obtained in this field of study can be compared only if the direction of loading with respect to the ACL is similar.

Cement composite delivery system

Several new and innovative techniques have recently been introduced that purport to increase the strength of polymethyl methacrylate bone cement. One of these concepts is the use of carbon and polymer fibers to form a cement composite. Bone cement composites usually 1% fiber, are very difficult to use clinically. The composite is very sticky and viscous, which precludes effective hand packing or the use of conventional delivery systems. A new delivery system for very viscous materials is presented and examples of in vitro application are shown.

Cyclic axial loading of spinal implants

The performance characteristics of Harrington distraction rods were evaluated and compared with paired wired L-rods when subjected to cyclic axial compression loading. Twelve fresh frozen swine spines with intact facet joints and anterior and posterior ligamentous complexes were instrumented and tested in a specially designed pneumatic testing device. Nine spines were displaced 2.54 cm over 10,000 cycles at a pressure of 10.3-13.8 kN/m2 (15-20 psi). Four spines were mounted in an Instron machine (Instron Engineering Corp., Canton, MA). Load displacement curves were determined for each spine without instrumentation, with Harrington distraction rod and with paired wired L-rods. Results of this cyclic axial compression testing showed that the Harrington distraction rod allowed 0.5 cm shortening in contrast to the L-rods that permitted 1.5 cm of axial displacement. Friction movement and metallic debris were noted between the sublaminal wires and the L-rods. The Luque Instrumented spine showed greater coronal plane displacement than the Harrington instrumented spines. Displacements in the sagittal plane were greater with the Harrington than Luque instrumented spines. Rotation changes in the sagittal plane were greater with the Harrington than Luque instrumented spines. Load displacement curves done on four spines indicated a wide range of applied load, 356 N (80 lbs) to 712 N (160 lbs) being necessary to displace the spines 2.54 cm. The clinician should be aware that the Luque system does not resist imposed axial compression loading in the axial and coronal planes as well as the Harrington distraction rod.(ABSTRACT TRUNCATED AT 250 WORDS)

Probing the presently tenuous link between comets and the origin of life

A unique set of millimeter-wave experiments for future cometary space missions is discussed. These experiments could yield answers to many basic questions about the presently undetermined nature of cometary nuclei and inner comae. This same set of experiments, designed to do fundamental cometary research, could simultaneously provide information on whether the accepted biological requirements necessary for the development of life are met in comets.