The effect of femoral component rotation on the five-year outcome of cemented mobile bearing total knee arthroplasty.

PURPOSE: Performing total knee replacement, accurate alignment and neutral rotation of the femoral component are widely believed to be crucial for the ultimate success. Contrary to absolute bone referenced alignment, using a ligament balancing technique does not automatically rotate the femoral component parallel to the transepicondylar axis. In this context we established the hypothesis that rotational alignment of the femoral component parallel to the transepicondylar axis (0° ± 3°) results in better outcome than alignment outside of this range. METHODS: We analysed 204 primary cemented mobile bearing total knee replacements five years postoperatively. Femoral component rotation was measured on axial radiographs using the condylar twist angle (CTA). Knee society score, range of motion as well as subjective rating documented outcome. RESULTS: In 96 knees the femoral component rotation was within the range 0 ± 3° (neutral rotation group), and in 108 knees the five-year postoperative rotational alignment of the femoral component was outside of this range (outlier group). Postoperative CTA showed a mean of 2.8° (±3.4°) internal rotation (IR) with a range between 6° external rotation (ER) and 15° IR (CI 95). No difference with regard to subjective and objective outcome could be detected. CONCLUSION: The present work shows that there is a large given natural variability in optimal rotational orientation, in this study between 6° ER and 15° IR, with numerous co-factors determining correct positioning of the femoral component. Further studies substantiating pre- and postoperative determinants are required to complete the understanding of resulting biomechanics in primary TKA.

Tightening force and torque of nonlocking screws in a reverse shoulder prosthesis.

BACKGROUND: Reversed shoulder arthroplasty is an accepted treatment for glenohumeral arthritis associated to rotator cuff deficiency. For most reversed shoulder prostheses, the baseplate of the glenoid component is uncemented and its primary stability is provided by a central peg and peripheral screws. Because of the importance of the primary stability for a good osteo-integration of the baseplate, the optimal fixation of the screws is crucial. In particular, the amplitude of the tightening force of the nonlocking screws is clearly associated to this stability. Since this force is unknown, it is currently not accounted for in experimental or numerical analyses. Thus, the primary goal of this work is to measure this tightening force experimentally. In addition, the tightening torque was also measured, to estimate an optimal surgical value. METHODS: An experimental setup with an instrumented baseplate was developed to measure simultaneously the tightening force, tightening torque and screwing angle, of the nonlocking screws of the Aquealis reversed prosthesis. In addition, the amount of bone volume around each screw was measured with a micro-CT. Measurements were performed on 6 human cadaveric scapulae. FINDINGS: A statistically correlated relationship (p<0.05, R=0.83) was obtained between the maximal tightening force and the bone volume. The relationship between the tightening torque and the bone volume was not statistically significant. INTERPRETATION: The experimental relationship presented in this paper can be used in numerical analyses to improve the baseplate fixation in the glenoid bone.

Recessive multiple epiphyseal dysplasia (rMED) with homozygosity for C653S mutation in the DTDST gene - phenotype, molecular diagnosis and surgical treatment of habitual dislocation of multilayered patella: case report.

BACKGROUND: Multiple epiphyseal dysplasia (MED) is one of the more common generalised skeletal dysplasias. Due to its clinical heterogeneity diagnosis may be difficult. Mutations of at least six separate genes can cause MED. Joint deformities, joint pain and gait disorders are common symptoms. CASE PRESENTATION: We report on a 27-year-old male patient suffering from clinical symptoms of autosomal recessive MED with habitual dislocation of a multilayered patella on both sides, on the surgical treatment and on short-term clinical outcome. Clinical findings were: bilateral hip and knee pain, instability of femorotibial and patellofemoral joints with habitual patella dislocation on both sides, contractures of hip, elbow and second metacarpophalangeal joints. Main radiographic findings were: bilateral dislocated multilayered patella, dysplastic medial tibial plateaus, deformity of both femoral heads and osteoarthritis of the hip joints, and deformity of both radial heads. In the molecular genetic analysis, the DTDST mutation g.1984T > A (p.C653S) was found at the homozygote state. Carrier status was confirmed in the DNA of the patient's parents. The mutation could be considered to be the reason for the patient's disease. Surgical treatment of habitual patella dislocation with medialisation of the tibial tuberosity led to an excellent clinical outcome. CONCLUSIONS: The knowledge of different phenotypes of skeletal dysplasias helps to select genes for genetic analysis. Compared to other DTDST mutations, this is a rather mild phenotype. Molecular diagnosis is important for genetic counselling and for an accurate prognosis. Even in case of a multilayered patella in MED, habitual patella dislocation could be managed successfully by medialisation of the tibial tuberosity.

Coordination pattern variability provides functional adaptations to constraints in swimming performance.

In a biophysical approach to the study of swimming performance (blending biomechanics and bioenergetics), inter-limb coordination is typically considered and analysed to improve propulsion and propelling efficiency. In this approach, 'opposition' or 'continuous' patterns of inter-limb coordination, where continuity between propulsive actions occurs, are promoted in the acquisition of expertise. Indeed a 'continuous' pattern theoretically minimizes intra-cyclic speed variations of the centre of mass. Consequently, it may also minimize the energy cost of locomotion. However, in skilled swimming performance there is a need to strike a delicate balance between inter-limb coordination pattern stability and variability, suggesting the absence of an 'ideal' pattern of coordination toward which all swimmers must converge or seek to imitate. Instead, an ecological dynamics framework advocates that there is an intertwined relationship between the specific intentions, perceptions and actions of individual swimmers, which constrains this relationship between coordination pattern stability and variability. This perspective explains how behaviours emerge from a set of interacting constraints, which each swimmer has to satisfy in order to achieve specific task performance goals and produce particular task outcomes. This overview updates understanding on inter-limb coordination in swimming to analyse the relationship between coordination variability and stability in relation to interacting constraints (related to task, environment and organism) that swimmers may encounter during training and performance.

Aerodynamic drag modeling of alpine skiers performing giant slalom turns.

PURPOSE: Aerodynamic drag plays an important role in performance for athletes practicing sports that involve high-velocity motions. In giant slalom, the skier is continuously changing his/her body posture, and this affects the energy dissipated in aerodynamic drag. It is therefore important to quantify this energy to understand the dynamic behavior of the skier. The aims of this study were to model the aerodynamic drag of alpine skiers in giant slalom simulated conditions and to apply these models in a field experiment to estimate energy dissipated through aerodynamic drag. METHODS: The aerodynamic characteristics of 15 recreational male and female skiers were measured in a wind tunnel while holding nine different skiing-specific postures. The drag and the frontal area were recorded simultaneously for each posture. Four generalized and two individualized models of the drag coefficient were built, using different sets of parameters. These models were subsequently applied in a field study designed to compare the aerodynamic energy losses between a dynamic and a compact skiing technique. RESULTS: The generalized models estimated aerodynamic drag with an accuracy of between 11.00% and 14.28%, and the individualized models estimated aerodynamic drag with an accuracy between 4.52% and 5.30%. The individualized model used for the field study showed that using a dynamic technique led to 10% more aerodynamic drag energy loss than using a compact technique. DISCUSSION: The individualized models were capable of discriminating different techniques performed by advanced skiers and seemed more accurate than the generalized models. The models presented here offer a simple yet accurate method to estimate the aerodynamic drag acting upon alpine skiers while rapidly moving through the range of positions typical to turning technique.

Effect of obesity onset on pendular energy transduction at spontaneous walking speed: Prader-Willi versus nonsyndromal obese individuals.

OBJECTIVE: To compare the mechanical external work (Wext ) and pendular energy transduction (Rstep ) at spontaneous walking speed (Ss ) in individuals with Prader-Willi syndrome (PWS) versus subjects with nonsyndromal obesity (OB) to investigate whether the early onset of obesity allows PWS subjects to adopt energy conserving gait mechanics. DESIGN AND METHODS: Wext and Rstep were computed using kinematic data acquired by an optoelectronic system and compared in 15 PWS (BMI = 39.5 ± 1.8 kg m(-2) ; 26.7 ± 1.5 year) and 15 OB (BMI = 39.3 ± 1.0 kg m(-2) ; 28.7 ± 1.9 year) adults matched for gender, age and BMI and walking at Ss . RESULTS: Ss was significantly lower in PWS (0.98 ± 0.03 m s(-1) ) than in OB (1.20 ± 0.02 m s(-1) ; P < 0.001). There were no significant differences in Wext per kilogram between groups (PWS: 0.37 ± 0.04 J kg(-1) m(-1) ; OB: 0.40 ± 0.05 J kg(-1) m(-1) ; P = 0.66) and in Rstep (PWS: 69.9 ± 2.9%; OB: 67.7 ± 2.4%; P = 0.56). However, Rstep normalized to Froude number (Rstep /Fr) was significantly greater in PWS (6.0 ± 0.6) than in OB (3.8 ± 0.2; P = 0.001). Moreover, Rstep /Fr was inversely correlated with age of obesity onset (r = -0.49; P = 0.006) and positively correlated with obesity duration (r = 0.38; P = 0.036). CONCLUSION: Individuals with PWS seem to alter their gait to improve pendular energy transduction as a result of precocious and chronic adaptation to loading.

Auditory motion affects visual biological motion processing.

The processing of biological motion is a critical, everyday task performed with remarkable efficiency by human sensory systems. Interest in this ability has focused to a large extent on biological motion processing in the visual modality (see, for example, Cutting, J. E., Moore, C., & Morrison, R. (1988). Masking the motions of human gait. Perception and Psychophysics, 44(4), 339-347). In naturalistic settings, however, it is often the case that biological motion is defined by input to more than one sensory modality. For this reason, here in a series of experiments we investigate behavioural correlates of multisensory, in particular audiovisual, integration in the processing of biological motion cues. More specifically, using a new psychophysical paradigm we investigate the effect of suprathreshold auditory motion on perceptions of visually defined biological motion. Unlike data from previous studies investigating audiovisual integration in linear motion processing [Meyer, G. F. & Wuerger, S. M. (2001). Cross-modal integration of auditory and visual motion signals. Neuroreport, 12(11), 2557-2560; Wuerger, S. M., Hofbauer, M., & Meyer, G. F. (2003). The integration of auditory and motion signals at threshold. Perception and Psychophysics, 65(8), 1188-1196; Alais, D. & Burr, D. (2004). No direction-specific bimodal facilitation for audiovisual motion detection. Cognitive Brain Research, 19, 185-194], we report the existence of direction-selective effects: relative to control (stationary) auditory conditions, auditory motion in the same direction as the visually defined biological motion target increased its detectability, whereas auditory motion in the opposite direction had the inverse effect. Our data suggest these effects do not arise through general shifts in visuo-spatial attention, but instead are a consequence of motion-sensitive, direction-tuned integration mechanisms that are, if not unique to biological visual motion, at least not common to all types of visual motion. Based on these data and evidence from neurophysiological and neuroimaging studies we discuss the neural mechanisms likely to underlie this effect.

Silencing mutant ataxin-3 rescues motor deficits and neuropathology in machado-joseph disease transgenic mice.

Machado-Joseph disease (MJD) or spinocerebellar ataxia type 3 (SCA3) is an autosomal dominantly-inherited neurodegenerative disorder caused by the over-repetition of a CAG codon in the MJD1 gene. This expansion translates into a polyglutamine tract that confers a toxic gain-of-function to the mutant protein - ataxin-3, leading to neurodegeneration in specific brain regions, with particular severity in the cerebellum. No treatment able to modify the disease progression is available. However, gene silencing by RNA interference has shown promising results. Therefore, in this study we investigated whether lentiviral-mediated allele-specific silencing of the mutant ataxin-3 gene, after disease onset, would rescue the motor behavior deficits and neuropathological features in a severely impaired transgenic mouse model of MJD. For this purpose, we injected lentiviral vectors encoding allele-specific silencing-sequences (shAtx3) into the cerebellum of diseased transgenic mice expressing the targeted C-variant of mutant ataxin-3 present in 70% of MJD patients. This variation permits to discriminate between the wild-type and mutant forms, maintaining the normal function of the wild-type allele and silencing only the mutant form. Quantitative analysis of rotarod performance, footprint and activity patterns revealed significant and robust alleviation of gait, balance (average 3-fold increase of rotarod test time), locomotor and exploratory activity impairments in shAtx3-injected mice, as compared to control ones injected with shGFP. An important improvement of neuropathology was also observed, regarding the number of intranuclear inclusions, calbindin and DARPP-32 immunoreactivity, fluorojade B and Golgi staining and molecular and granular layers thickness. These data demonstrate for the first time the efficacy of gene silencing in blocking the MJD-associated motor-behavior and neuropathological abnormalities after the onset of the disease, supporting the use of this strategy for therapy of MJD.

Neuropathological, clinical and molecular pathology in female fragile X premutation carriers with and without FXTAS.

Fragile X-associated tremor/ataxia syndrome (FXTAS) is an adult-onset neurodegenerative disorder associated with premutation alleles of the fragile X mental retardation 1 (FMR1) gene. Approximately 40% of older male premutation carriers, and a smaller proportion of females, are affected by FXTAS; due to the lower penetrance the characterization of the disorder in females is much less detailed. Core clinical features of FXTAS include intention tremor, cerebellar gait ataxia and frequently parkinsonism, autonomic dysfunction and cognitive deficits progressing to dementia in up to 50% of males. In this study, we report the clinical, molecular and neuropathological findings of eight female premutation carriers. Significantly, four of these women had dementia; of the four, three had FXTAS plus dementia. Post-mortem examination showed the presence of intranuclear inclusions in all eight cases, which included one asymptomatic premutation carrier who died from cancer. Among the four subjects with dementia, three had sufficient number of cortical amyloid plaques and neurofibrillary tangles to make Alzheimer's disease a highly likely cause of dementia and a fourth case had dementia with cortical Lewy bodies. Dementia appears to be more common than originally reported in females with FXTAS. Although further studies are required, our observation suggests that in a portion of FXTAS cases there is Alzheimer pathology and perhaps a synergistic effect on the progression of the disease may occur.

Surgical approach for total hip arthroplasty: direct lateral or posterior?

OBJECTIVE: To determine the risks of prosthesis dislocation, postoperative Trendelenburg gait, and sciatic nerve palsy after a posterior approach compared to a direct lateral approach for adult patients undergoing total hip arthroplasty (THA) for primary osteoarthritis (OA). METHODS: Medline, Embase, CINHAL, and Cochrane databases were searched until August 2003. All published trials comparing posterior and direct lateral surgical approaches to THA in adults with a diagnosis of primary hip osteoarthritis were collected. Retrieved articles were assessed independently for their methodological quality. RESULTS: Four prospective cohort studies involving 241 participants met the inclusion criteria. Regarding dislocation rate, no significant difference between posterior and direct lateral surgical approach was found (relative risk 0.35). The presence of postoperative Trendelenburg gait was not significantly different between surgical approaches. The risk of nerve palsy or injury was significantly higher with the direct lateral approach (relative risk 0.16). However, there were no significant differences when comparing this risk nerve by nerve, in particular for the sciatic nerve. Of the other outcomes considered, only the average range of internal rotation in extension of the hip was significantly higher (weighted mean difference 16 degrees ) in the posterior approach group (mean 35 degrees, SD 13 degrees ) compared to the direct lateral approach (mean 19 degrees, SD 13 degrees ). CONCLUSION: The quality and quantity of information extracted from the trials performed to date are insufficient to make a firm conclusion on the optimum choice of surgical approach for adult patients undergoing primary THA for OA.

A new approach to accurate measurement of uniaxial joint angles based on a combination of accelerometers and gyroscopes.

A new method of measuring joint angle using a combination of accelerometers and gyroscopes is presented. The method proposes a minimal sensor configuration with one sensor module mounted on each segment. The model is based on estimating the acceleration of the joint center of rotation by placing a pair of virtual sensors on the adjacent segments at the center of rotation. In the proposed technique, joint angles are found without the need for integration, so absolute angles can be obtained which are free from any source of drift. The model considers anatomical aspects and is personalized for each subject prior to each measurement. The method was validated by measuring knee flexion-extension angles of eight subjects, walking at three different speeds, and comparing the results with a reference motion measurement system. The results are very close to those of the reference system presenting very small errors (rms = 1.3, mean = 0.2, SD = 1.1 deg) and excellent correlation coefficients (0.997). The algorithm is able to provide joint angles in real-time, and ready for use in gait analysis. Technically, the system is portable, easily mountable, and can be used for long term monitoring without hindrance to natural activities.

Biomechanical characterization and in vitro mechanical injury of elderly human femoral head cartilage: comparison to adult bovine humeral head cartilage.

OBJECTIVES: In vitro mechanical injury of articular cartilage is useful to identify events associated with development of post-traumatic osteoarthritis (OA). To date, many in vitro injury models have used animal cartilage despite the greater clinical relevance of human cartilage. We aimed to characterize a new in vitro injury model using elderly human femoral head cartilage and compare its behavior to that of an existing model with adult bovine humeral head cartilage. DESIGN: Mechanical properties of human and bovine cartilage disks were characterized by elastic modulus and hydraulic permeability in radially confined axial compression, and by Young's modulus, Poisson's ratio, and direction-dependent radial strain in unconfined compression. Biochemical composition was assessed in terms of tissue water, solid, and glycosaminoglycan (GAG) contents. Responses to mechanical injury were assessed by observation of macroscopic superficial tissue cracks and histological measurements of cell viability following single injurious ramp loads at 7 or 70%/s strain rate to 3 or 14 MPa peak stress. RESULTS: Confined compression moduli and Young's moduli were greater in elderly human femoral cartilage vs adult bovine humeral cartilage whereas hydraulic permeability was less. Radial deformations of axially compressed explant disks were more anisotropic (direction-dependent) for the human cartilage. In both cartilage sources, tissue cracking and associated cell death during injurious loading was common for 14 MPa peak stress at both strain rates. CONCLUSION: Despite differences in mechanical properties, acute damage induced by injurious loading was similar in both elderly human femoral cartilage and adult bovine humeral cartilage, supporting the clinical relevance of animal-based cartilage injury models. However, inherent structural differences such as cell density may influence subsequent cell-mediated responses to injurious loading and affect the development of OA.

Relative and absolute reliability of the clinical version of the Narrow Path Walking Test (NPWT) under single and dual task conditions.

Decline in gait stability has been associated with increased fall risk in older adults. Reliable and clinically feasible methods of gait instability assessment are needed. This study evaluated the relative and absolute reliability and concurrent validity of the testing procedure of the clinical version of the Narrow Path Walking Test (NPWT) under single task (ST) and dual task (DT) conditions. Thirty independent community-dwelling older adults (65-87 years) were tested twice. Participants were instructed to walk within the 6-m narrow path without stepping out. Trial time, number of steps, trial velocity, number of step errors, and number of cognitive task errors were determined. Intraclass correlation coefficients (ICCs) were calculated as indices of agreement, and a graphic approach called "mountain plot" was applied to help interpret the direction and magnitude of disagreements between testing procedures. Smallest detectable change and smallest real difference (SRD) were computed to determine clinically relevant improvement at group and individual levels, respectively. Concurrent validity was assessed using Performance Oriented Mobility Assessment Tool (POMA) and the Short Physical Performance Battery (SPPB). Test-retest agreement (ICC1,2) varied from 0.77 to 0.92 in ST and from 0.78 to 0.92 in DT conditions, with no apparent systematic differences between testing procedures demonstrated by the mountain plot graphs. Smallest detectable change and smallest real change were small for motor task performance and larger for cognitive errors. Significant correlations were observed for trial velocity and trial time with POMA and SPPB. The present results indicate that the NPWT testing procedure is highly reliable and reproducible.

Changes in spring-mass model characteristics during repeated running sprints.

This study investigated fatigue-induced changes in spring-mass model characteristics during repeated running sprints. Sixteen active subjects performed 12 × 40 m sprints interspersed with 30 s of passive recovery. Vertical and anterior-posterior ground reaction forces were measured at 5-10 m and 30-35 m and used to determine spring-mass model characteristics. Contact (P &lt; 0.001), flight (P &lt; 0.05) and swing times (P &lt; 0.001) together with braking, push-off and total stride durations (P &lt; 0.001) lengthened across repetitions. Stride frequency (P &lt; 0.001) and push-off forces (P &lt; 0.05) decreased with fatigue, whereas stride length (P = 0.06), braking (P = 0.08) and peak vertical forces (P = 0.17) changes approached significance. Center of mass vertical displacement (P &lt; 0.001) but not leg compression (P &gt; 0.05) increased with time. As a result, vertical stiffness decreased (P &lt; 0.001) from the first to the last repetition, whereas leg stiffness changes across sprint trials were not significant (P &gt; 0.05). Changes in vertical stiffness were correlated (r &gt; 0.7; P &lt; 0.001) with changes in stride frequency. When compared to 5-10 m, most of ground reaction force-related parameters were higher (P &lt; 0.05) at 30-35 m, whereas contact time, stride frequency, vertical and leg stiffness were lower (P &lt; 0.05). Vertical stiffness deteriorates when 40 m run-based sprints are repeated, which alters impact parameters. Maintaining faster stride frequencies through retaining higher vertical stiffness is a prerequisite to improve performance during repeated sprinting.