ABSTRACT
Nonlinear normal modes (NNMs) are widely used as a tool for developing mathematical models of nonlinear structures and understanding their dynamics. NNMs can be identified experimentally through a phase quadrature condition between the system response and the applied excitation. This paper demonstrates that this commonly used quadrature condition can give results that are significantly different from the true NNM, in particular, when the excitation applied to the system is limited to one input force, as is frequently used in practice. The system studied is a clamped-clamped cross-beam with two closely spaced modes. This paper shows that the regions where the quadrature condition is (in)accurate can be qualitatively captured by analysing transfer of energy between the modes of the system, leading to a discussion of the appropriate number of input forces and their locations across the structure.
ABSTRACT
To establish the value of quantitative radionuclide bone scanning after total knee replacement, 21 patients were scheduled for examination. Eight patients were scanned more than 1 year after surgery (group 1), and 13 within the first postsurgical year (group 2). Ratios were calculated for three regions of interest. The ratio was defined as the counts per pixel for each region of interest, normalized by dividing them by the counts per pixel of the ipsilateral femoral shaft. There was no significant difference in uptake between control subjects and patients in group 2, indicating that the test was not reliable within this time period. No statistical difference was found between the uptake scores in groups 1 and 2, demonstrating that an uninterpretable period of 1 year is perhaps too short. Using a ratio of more than three, seen more than 1 year after surgery as pathologic, a sensitivity of 100%, a specificity of 33%, and an accuracy of 75% was found. Quantitative bone scanning is a very sensitive test for detecting complications, but it is nonspecific in diagnosing loosening of total knee arthroplasties. The value of quantitative scanning presumably lies in the follow-up of patients as an objective method for the evaluation of sequential scanning. Nevertheless, radionuclide data need to be interpreted in correlation with clinical and radiologic findings.
Subject(s)
Knee Joint/diagnostic imaging , Knee Prosthesis , Evaluation Studies as Topic , Femur/diagnostic imaging , Humans , Knee Prosthesis/adverse effects , Patella/diagnostic imaging , Prosthesis Failure , Radionuclide Imaging , Technetium Tc 99m Medronate , Tibia/diagnostic imaging , Time FactorsABSTRACT
Osteoid osteoma is a benign tumor frequently situated around the knee. It should therefore be considered as a possible cause of atraumatic knee pain in young adults. The mean interval from onset of symptoms to diagnosis is 14 months. Clinical symptoms are the most reliable diagnostic factors. Block resection is the treatment of choice. A retrospective study of 10 patients is presented.
Subject(s)
Bone Neoplasms/physiopathology , Femoral Neoplasms/physiopathology , Osteoma, Osteoid/physiopathology , Pain/etiology , Adolescent , Adult , Bone Neoplasms/diagnosis , Bone Neoplasms/surgery , Diagnosis, Differential , Female , Femoral Neoplasms/diagnosis , Femoral Neoplasms/surgery , Humans , Knee , Male , Osteoma, Osteoid/diagnosis , Osteoma, Osteoid/surgeryABSTRACT
In both radiological and orthopedic journals the value of MRI for diagnosing internal derangement of the knee has been assessed recently. However, results vary widely and no study reports on the differentiation among types of ACL tears. As far as meniscal pathology is concerned, attention has been drawn by Reicher et al. (11) and Glashow et al. (5) upon the false positive tears of the posterior horn of the medial meniscus. Where most authors consider signal inversion in the posterior horn of the meniscus as a normal finding in children--due to the higher water content--the same fact in adults can be interpreted as a false positive image or a missed tear at arthroscopy (5).
Subject(s)
Anterior Cruciate Ligament/pathology , Arthroscopy , Magnetic Resonance Imaging , Menisci, Tibial/pathology , Adolescent , Adult , Anterior Cruciate Ligament Injuries , Double-Blind Method , Female , Humans , Male , Prospective Studies , Tibial Meniscus InjuriesABSTRACT
A 1 year prospective study was done to develop an accident-prone and overuse-prone profile of young athletes. A group of 185 freshman physical education students (118 males; 67 females of the same age (18.3 +/- 0.5 years) trained under the same conditions and were exposed to similar extrinsic risk factors. Using a descriptive statistical technique, an analysis of correspondence, the complex interrelation between the criterium variables (acute injuries and overuse injuries) and the predictor variables (intrinsic risk factors; physical characteristics--anthropometric data, physical fitness parameters, flexibility aspects and malalignment of the lower extremities; and psychological factors--16 personality traits) was estimated for males and females separately. Although dynamic strength seems to be an important risk factor in acute injuries, sports accidents must be seen in relation to psychological factors. However, the overuse-prone profile is mainly based on physical traits: a combination of muscle weakness, ligamentous laxity, and muscle tightness predisposes to stress injuries. In addition, these overuse effects are intensified by large body weight and length, a high explosive strength, and malalignment of the lower limbs. Nevertheless, it has to be kept in mind that psychosomatic factors play a role in how one experiences these overuse phenomena.
