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Biomedical subjects

I Hvid

Publications and source records attributed to I Hvid.

At least 73 records · Page 4Linked to original sources
PubMed1987

Dual-photon absorptiometry of the proximal tibia.

Dual-photon absorptiometric bone-mineral assay, penetration tests, and axial compression tests of the proximal tibial epiphyses were carried out in 18 human cadaver knees. The reproducibility of bone mineral assay was within +/- 12% (95% tolerance limits). Linear regression analysis with bone-mineral content as the independent variable showed a good correlation to the ultimate force obtained from the compression tests on the medial (r = 0.81) and the lateral (r = 0.90) condyles. The correlation between bone mineral content and an average of three condylar penetration tests was somewhat weaker (medical condyle: r = 0.65, lateral condyle: r = 0.62). It is concluded that dual-photon absorptiometric bone-mineral assay may be a suitable noninvasive alternative to bone-strength measurement and thus suitable for monitoring the changes in tibial condylar bone during follow-up studies.

Humans↗
PubMed1987

Mechanical strength of tibial trabecular bone evaluated by X-ray computed tomography.

The prospects for the use of quantitative computed tomography (QCT) for evaluation of mechanical properties of tibial trabecular bone were investigated. Computed tomography (CT) data from the proximal tibial epi- and metaphysis of six human cadaver knees were correlated with mechanical data obtained from compression tests and penetration strength measurements. In addition CT and intraoperative penetration data were compared in 20 patients. If spatial agreement between CT and mechanical measurement sites is optimized, close correlations are found between the relative linear attenuation coefficient determined by CT and the ultimate strength (r = 0.84), the yield strength (r = 0.85), the elastic modulus (r = 0.78), the ultimate energy absorption (r = 0.83), the yield energy absorption (r = 0.81), and the penetration strength (r = 0.82). It is concluded that these correlations are sufficient to make QCT a valuable tool for non-invasive evaluation of the spatial distribution of bone properties in several clinical applications.

Aged↗
PubMed1987

Stiffness behaviour of trabecular bone specimens.

Trabecular bone specimens were tested by non-destructive technique with the purpose of investigating stiffness behaviour and optimizing stiffness determination. Cylindrical specimens (n = 25) were loaded repetitively (0.1 Hz, 30 cycles) by axial compression to 50% of predicted ultimate strength and finally compressed to failure. Analyses of single compression curves showed increasing stiffness (E') until a stress level about 50% of ultimate stress followed by decreasing stiffness. Curve fit analysis of the elastic part of the compression curve showed the best fit, when a second order polynomial was used (r = 0.94, p less than 0.001). The stiffness determined non-destructively at the 25% level of ultimate strength increased significantly to the tenth loading cycle followed by a steady state. The precision of stiffness determination as an average of five consecutive measurements at steady state was E' +/- less than 5% (95% confidence limits). A reproducibility test by repetition of the test sequence after 3 h rest showed qualitatively the same stiffness behaviour. The variation of stiffness determination between the two test sequences was +/- 27% at the first loading cycle falling to +/- 12% at steady state.

Bone and Bones↗
PubMed1987

Knee arthroplasty in rheumatoid arthritis. Four- to six-year follow-up study.

A consecutive series of total condylar knee arthroplasties in patients with rheumatoid or related arthritis, with a 4-6-year follow-up period, was studied. Eighty-seven percent had an excellent or good overall result (score of 70 or more on the HSS knee rating scale). The median total score increased from 45 points before operation to 83 after operation. Sixteen complications, mostly minor, occurred in 14 patients. There were no early infections. Two prostheses were removed for deep infection, after 3 and 5 years. One patient had patellectomy for avascular necrosis. The crude prosthesis survival rate was 97%. Tibial radiolucencies were noted in 76% of cases; in 29% they were significant (2 mm or more in one or more of three zones). Two tibial components (2%) were believed to be mechanically loose, but no revisions for mechanical loosening were done. The presence of radiolucencies did not signify an inferior clinical result.

Adult↗
PubMed1987

Arthroscopic determination of patellofemoral malalignment.

Patellofemoral alignment was determinant by arthroscopy according to the degree of knee flexion at which the lateral facet, the patellar ridge, and the medial facet of the patella gained contact with the femur. The intraarticular pressure was 75 mm Hg. In 17 patients with a normal patellofemoral joint, the lateral facet aligned at a mean knee flexion of 20 degrees, the patellar ridge at 35 degrees, and the medial facet at 50 degrees. Twelve patients with patellar subluxation showed no difference in the alignment of the lateral facet, but differed significantly with regard to alignment of both the ridge and the medial facet with contact at a mean flexion of 55 degrees and 85 degrees, respectively. The median measurements in 20 patients with idiopathic anterior knee pain did not deviate significantly from the normal material. However, the dispersion was increased significantly, with eight patients having increased measurements consistent with malalignment and three having decreased measurements below the lower limit of normal alignment. Patients with idiopathic anterior knee pain apparently can be reclassified according to the arthroscopically determined alignment, which may prove important in the treatment of these patients.

Adolescent↗
PubMed1986

Bone strength measurements at the proximal tibia. Penetration tests and epiphyseal compressive strength.

Three penetration tests were obtained from corresponding locations at each condyle of 19 proximal tibiae. The patterns of condylar cancellous bone strength varied little between knees. The medial condyle was the strongest with an average medial to lateral strength ratio of 1.9, and in most knees the medial condyle was strongest centrally while the lateral condyle was strongest posteriorly. The penetration strength at 5 successive 2 mm levels beneath the resected subchondral surface also showed a constant pattern of variation. Bone strength decreased significantly at first except at the posterolateral site, then tended to level off. The reduction of strength was most pronounced in the centre of the condyles. The penetration tests were good predictors of the static compressive strength of the proximal tibia. Correlation coefficients of approximately 0.90 were obtained indicating statistically highly significant correlations (p less than or equal to 0.00001). The tests were carried out with equipment developed for in vivo measurements of cancellous bone strength during total knee replacement. The findings confirm the close relationship of these investigations to conventional compression tests.

Aged↗
PubMed1986

Subchondral bone strength in arthrosis. Cadaver studies of tibial condyles.

We measured the axial penetration strength of subchondral cancellous bone in a close, regular pattern at the tibial resection surface of five valgus and seven varus human, cadaveric knees. The strength patterns obtained were illustrated by pseudo-three-dimensional reconstructions of strength values as a function of the location on the resection surface. The varus knees had high strength values towards the medial margin of the medial condyle. Three qualitatively different strength patterns were distinguished in the valgus knees: two knees showed a near normal strength distribution with higher peak values medially; two knees with centrolateral bony attrition had high bone strength values at the center of the lateral condyle; and one knee with moderate posterolateral bony attrition showed a high strength area at the posterolateral aspect of the lateral condyle. In both types of malalignment, there was a decrease of bone strength with the depth from the resection surface.

Aged↗
PubMed1986

The vertical position of the patella estimated by four radiographic measurements.

The methods of Insall and Salvati, Blackburne and Peel, Caton and Laurin of assessing the vertical position of the patella, were applied on 200 normal knees. The indices for Insall and Salvati's, and Blackburne and Peel's methods were 1.07 +/- 0.25 and 0.78 +/- 0.19 respectively, independent of sex and flexion of the knee. The measurements for Caton's index were 0.95 +/- 0.24 and 0.88 +/- 0.22 at kneeflexions of 45 degrees and 90 degrees. Laurin's method was insufficient as it showed 50% of the patellas to be high riding. The different methods were compared. The technique of Insall and Salvati was a reliable and applicable method, and is therefore recommended for routine use.

Adult↗
PubMed1985

Trabecular bone strength patterns at the proximal tibial epiphysis.

The longitudinal compressive strength of trabecular bone from the human proximal tibial epiphysis was investigated in 12 autopsy specimens using multiple penetration tests with a small diameter indentor. Strength profiles were visualized by three-dimensional computerized reconstruction as a function of location on the resection surfaces. There were large variations of the maximal values between individuals, but the patterns obtained were remarkably uniform. The medial condyle showed the highest peak value in all but one knee with a mean medial-to-lateral peak value-ratio of 1.7. At the medial condyle the high strength area was relatively large with peak values being obtained centrally and anteriorly; the lateral condyle showed a more restricted, posteriorly localized area of high strength. Beneath the menisci, bone strength gradually decreased toward the margins of the condyles; likewise, bone strength decreased to reach very low values at the intercondylar region. There was a significant reduction of bone strength with the distance from the subchondral resection surface. This reduction was most pronounced at the high strength areas.

Biomechanical Phenomena↗
PubMed1985

Tibial plateau strength patterns in experimental modular knee replacement.

Nondestructive low-strain-rate compression tests were carried out on 12 human cadaver tibiae fitted with a metal modular resurfacing component on the medial or lateral condyle. The tests were done at 20 regularly spaced points on each plateau. The reproducibility of measurement was +/- 16% (95% tolerance limits). A statistically significant correlation was demonstrated between stiffness and ultimate force values obtained from the same points (r = 0.75, P less than 0.005). On the medial plateau the compressive stiffness of the system was maximal when load was applied to the center of the prosthesis, but declined sharply toward the medial and posterior margins. On the lateral plateau maximal stiffness values were obtained more posteriorly, and the stiffness gradients toward the periphery were less marked. Details of surgical technique and specific loading situations that may cause undesirable combinations of load and point of prosthetic component contact are discussed.

Biomechanical Phenomena↗
PubMed1985

Cancellous bone at the knee: a comparison of two methods of strength measurement.

The relation of thin-needle axial penetration tests to axial compression tests on machined specimens was examined utilizing distal femoral and proximal tibial epiphyseal cancellous bone. The penetration strength was closely related to the yield strength (r = 0.87), the ultimate strength (r = 0.86), Young's modulus (r = 0.77), the yield energy absorption (r = 0.81), and the ultimate energy absorption (r = 0.84) derived from the compression tests. Generally, femoral specimens were stronger, stiffer, and tougher than tibial specimens. Higher peak penetration strength values were obtained from the medial than from the lateral condyles. The variation of strength within compression test specimens could be expressed in terms of penetration strength; this variation differed slightly between tibial and femoral specimens, but invariably the bone deepest to the joint surface was the weakest. Accordingly, adjustments were introduced in the regression equations connecting the penetration strength to the material properties derived from the compression tests.

Aged↗
PubMed1985

Total condylar knee arthroplasty. A report of 2-year follow-up on 247 cases.

Two hundred and forty-seven consecutive total knee replacements using the Insall-Burstein standard total condylar knee system with 2 years' follow-up were studied. Of the 238 available to follow-up, two were reoperated during the period, owing to infection and traumatic loosening of a tibia component respectively. Seventy-nine patients were operated for rheumatoid arthritis and 94 for osteoarthritis. In assessment of the total therapeutic result, registration of pain, walking ability, range of motion, muscle strength, flexion deformity, valgus-varus deformities, instability, and use of walking aids were included, according to a rating system. Excellent or good results were found in 91.5%; 6.5% were fair, and 2% were poor. There were two cases of infection; one resulted in removal of the prosthesis and an arthrodesis was done. There were four suspected aseptic loosenings, three cases of transient peroneal nerve palsies, and three patients who developed reflex dystrophy.

Adult↗