Unconstrained Test Research Articles

Tibiotalar motion--effect of fibular displacement and deltoid ligament transection: in vitro study.

The purpose of this study was to quantify tibiotalar translation and rotation under various stages of fibular displacement and injury to the syndesmotic and deltoid ligaments. Ten unpaired specimens amputated below the knee were studied using an unconstrained testing apparatus. The specimens were moved through a dorsiflexing and plantarflexing arc of 55 degrees (20 degrees dorsiflexion and 35 degrees plantarflexion). Dorsiflexion of the intact lower leg was associated with an average of 4.2 degrees of external talar rotation, and plantarflexion was associated with an average of 1.4 degrees of internal talar rotation. Fibular osteotomy and displacement of the distal fibular fragment did not change the talar rotation significantly. Additional transection of the deltoid ligament, however, decreased external talar rotation significantly, to 1.4 degrees, and decreased talar internal rotation to 0.6 degrees. Talar shift was not affected in dorsiflexion or plantarflexion by fibular fracture, displacement of the distal fibular fragment, or transection of the deltoid ligament. These data may suggest that in dorsiflexion or plantarflexion, an intact lateral malleolus is not necessary for physiological talar tracking. They further suggest that in a fibular fracture with a significant injury to the deltoid ligament, healing of the ligament at its resting length is crucial to restoring physiological talar rotation.

Influence of Arthrodeses on Kinematics of the Axially Loaded Ankle Complex during Dorsiflexion/Plantarflexion

The purpose of this study was to quantify the effect of selective arthrodesis (stabilization) of the ankle, subtalar, and talonavicular joints on the rotational movement of the tibia and the calcaneus occurring with dorsiflexion/plantarflexion. Six cadaver foot-leg specimens were investigated using an unconstrained testing apparatus. Simulated ankle joint arthrodesis caused a large increase in tibial rotation and calcaneal eversion-inversion. Subtalar and talonavicular stabilization did not cause as large a rotation.

Influence of ligament transection on tibial and calcaneal rotation with loading and dorsi-plantarflexion.

The purpose of this study was to quantify the effect of sequential ligament transection (anterior talofibular, calcaneofibular, posterior talofibular, deltoid, and subtalar interosseous ligaments) on the rotational movement of the tibia and the calcaneus as associated with axial loading and dorsi-plantarflexing the foot. Eight cadaver foot-leg specimens were investigated using a unconstrained testing apparatus. As the ankle complex was axially loaded, almost the same internal rotation of the tibia and the same calcaneus eversion was found with and without the various degrees of lateral and medial ligament release; additional sectioning of the subtalar interosseous ligament tremendously increased the resulting tibial and calcaneal rotation. While tibial and calcaneal rotation from foot dorsi-plantarflexing did not alter significantly with transection of the lateral ligaments, almost no tibial and calcaneal rotation occurred after additional sectioning of the deltoid and subtalar interosseous ligament. These results indicate that, after release of the lateral ligaments, the foot becomes partially mechanically disconnected from the tibia by additional transection of the medial ligaments and even further disconnected after transection of the subtalar interosseous ligament.

In vitro kinematics of the axially loaded ankle complex in response to dorsiflexion and plantarflexion.

The rotational movements of the tibia and calcaneus that occur with dorsiflexion-plantarflexion and axial loading were studied in cadaver foot-leg specimens using an unconstrained testing apparatus. Independent of the foot flexion position, significant internal rotation of the tibia and eversion of the calcaneus were noted after the ankle complex was axially loaded. Independent of loading, 10 degrees of dorsiflexion resulted in 0.1 degrees of eversion and 2.1 degrees of internal rotation of the tibia. Conversely, 10 degrees of plantarflexion resulted in 1.6 degrees of inversion and 1.3 degrees of external rotation of the tibia. The induced rotational movements of the tibia and the calcaneus differed significantly between the specimens. These results suggest that the foot "axes" did not change by axially loading the ankle complex and they support previous reports that the ankle complex uses different axes for dorsiflexion and plantarflexion.

Biomechanical effects of transoral odontoidectomy.

The acute biomechanical effects of transoral odontoidectomy were studied by using qualitative and quantitative methods to assess atlantoaxial motion. In vitro biomechanical testing was performed on the upper cervical spines of eight baboon and five human cadaveric specimens. Using an unconstrained testing apparatus, we performed a flexibility method of testing. Physiological range loading was applied to atlantoaxial specimens, and three-dimensional motion was analyzed with stereophotogrammetry. Force-deformation relationships were delineated in intact specimens and again after surgical removal of the anterior C1 arch, odontoid process, and transverse atlantal ligament. We studied the total range of rotational and linear motions, the behavior of the neutral zone and elastic zone, the flexibility coefficients, and the instantaneous axes of rotation during flexion, extension, bilateral lateral bending, and bilateral axial rotation. Odontoidectomy produced several distinct alterations in motion and in force-deformation responses at C1-C2 that were almost identical in the baboon and human specimens. After odontoidectomy, the atlas developed significantly increased translational movements, which were most prominent in the anteroposterior direction. The total angular range of motion increased significantly during flexion, extension, and lateral bending but not during axial rotation. When the total range of motion was altered, the neutral zone was affected selectively and the elastic zone was spared. Surgery produced mobile, widely spread, unconstrained instantaneous axes of rotation that were in a constrained, fixed position in intact specimens. Clinically, transoral odontoidectomy may predispose patients to spinal instability. Even if acute spinal instability is not apparent, the patients may be susceptible to the delayed effects of the surgery because of the altered anatomy and biomechanical responses.

The effect of cryopreservation on the biomechanical behavior of bovine articular cartilage.

The short-term effect of cryopreservation on specific mechanical behaviors of bovine articular cartilage has been investigated. A flat-ended nonporous indentor was used in a nondestructive, repetitive, axisymmetric unconstrained testing system. Cyclical indentation from a fixed position to a fixed load was applied until a steady-state load-deformation relationship (limit cycle) was achieved. Indentation behaviors measured from the limit cycles of each articular cartilage specimen before and after treatment were compared. Testing was done in vitro using fresh, mature bovine radiocarpal joints. Twenty pairs of cartilage-subchondral bone cores from anatomically similar sites on contralateral joints were separated into three groups; thickness controls, dimethylsulfoxide (DMSO) controls, and cryopreserved experimental samples. Thickness controls and DMSO controls were used to examine the isolated effects of the thickness measurement and DMSO incubation techniques on articular cartilage indentation characteristics. Experimental samples were cryopreserved using DMSO, their thicknesses similarly measured and indentation behaviors examined. Following testing, histological and histochemical assessment of the specimens confirmed the nondestructive nature of the tests. Intra- and intergroup comparisons of controls and experimentals revealed no statistical differences in the mechanical behaviors measured from the limit cycle or in cartilage thickness. These results indicate that the cryopreservation protocol used did not have an effect that we could measure on these specific mechanical behaviors of articular cartilage.

Assessment of angioplasty balloon catheters: further studies

Eight millimetre diameter angioplasty balloon catheters of both the Gruntzig and Olbert types from five manufacturers have been tested in vitro to establish bursting pressures and the changes in maximum and deflated diameters following repeated inflations, both when free and within a restraining sleeve. Maximum inflated diameters were within 10% of that stated and all types of balloon except one burst at a pressure greater than the recommended value. Deflated diameters were approximately 1 mm greater than insertion diameters, which are much smaller in the Olbert type. All balloons became a little larger with each of the first few distensions, and became stiffer. The maximum diameter was reached and remained constant after 10-15 distensions. Distension within a latex sleeve did not change bursting pressures, and it is considered that results from unconstrained testing can be extrapolated to behaviour in vivo. Computer modelling and calculation of maximum stress resultants also showed that calculated longitudinal and circumferential stresses are unaffected by applied restrictions. It is concluded that balloon technology is steadily improving and it is suggested that British Standards should be established for dilatation balloon catheters. Amongst other factors these Standards should include maximum recommended inflation pressures that are at least 2 atm less than bursting pressures, whilst the stated maximum diameter should be for fully extended balloons, and should have a tolerance of more than +/- 10%.

The acquisition of parameterized grammars

In this paper, I look at some problems that arise if second language learners are assumed to acquire the L2 on the basis of unconstrained hypothesis testing, since this crucially involves the assumption of the availability of negative evidence and does not seem to be sufficiently 'fine-tuned' for the learner to acquire certain aspects of the L2 grammar. Instead, it is proposed that L2 acquisition, like L1, may involve the prior knowledge of a number of highly contrained principles of Universal Grammar which restrict the number of options available to the learner. In some cases, these principles may be subject to parametric variation, so that they do not work in identical fashion in L1 and L2, allowing for the possibility of transfer of the L1 parameter setting. Taking subjacency as a case in point, a pilot study is reported in which native speakers of French and Spanish learning English as a second language were tested for their judgements on the bounding status of S in the L2 grammar. In English S is a bounding node, whereas in French and Spanish it is not. It was found that subjects were less accurate in their judgements on the bounding status of S in English than native-speaking controls, with a number of subjects consistently transferring the L1 parameter. In most cases, subjects showed improvement with increasing level of ESL proficiency. The majority of subjects adopted a consistent position with respect to the question of the bounding status of S, suggesting that they were not indulging in unconstrained hypothesis testing.

A generalized direct search acceptable-point technique for use with descent-type multivariate algorithms

Many non-linear programming algorithms employ a univariate subprocedure to determine the step length at each multivariate iteration. In recent years much work has been directed toward the development of algorithms which will exhibit favorable convergence properties on well-behaved functions without requiring that the univariate algorithm perform a sequence of one-dimensional minimizations. In this paper a direct search method (the golden section search) is modified to search for acceptable rather than minimizing step lengths and then used as the univariate subprocedure for a generalized conjugate gradient algorithm. The resulting multivariate minimization method is tested on standard unconstrained test functions and a constrained industrial problem. The new method is found to be relatively insensitive to tuning parameters (insofar as success or failure is concerned). A comparison of the golden section acceptable-point search (GSAP) with other popular acceptable-point methods indicates that GSAP is a superior strategy for use with the conjugate directions-type algorithms and is also suitable for use with the quasi-Newton methods. The comparison are based on equivalent function evaluations required to minimize multivariate test functions.

Über die Informationsfähigkeit eines Meβgerätes

For all measurements the problem of error estimation is very important. At time there exists an arbitrariness selecting a sultable error criterion for measured values and measuring devices. This arbitrariness is removed by means of the modern information theory. Thereby the law of the a priori distribution is of high importance. As the result of stipulated considerations two distribution laws are derived for constrained and unconstrained test data from which the mean information-error of a measuring device can be computed.