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P Herberts

Publications and source records attributed to P Herberts.

At least 19 recordsLinked to original sources
PubMed1995

Voluntary redistribution of muscle activity in human shoulder muscles.

Four shoulder muscles (the supraspinatus, the infraspinatus, the anterior and middle portion of the deltoid, and the descending part of the trapezius) were examined with electromyography in abducted arm positions. By using feedback techniques, we found that the subjects could reduce the EMG activity voluntarily by 22-47% in the trapezius muscle while keeping different static postures. This was not true for any other muscle investigated. When the trapezius activity was reduced there was a tendency towards an increase of EMG activity in some other shoulder muscles, particularly the infraspinatus. The findings may be related to relaxation from an initial overstabilization of the shoulder, or redistribution of load among synergists. It is suggested that the possibility of reducing trapezius activity may be of ergonomic significance. It is also noted that EMG trapezius activity may not serve as a universal descriptor of total muscular load in the shoulder.

Adult↗
PubMed1995

Accuracy of migration analysis in hip arthroplasty. Digitized and conventional radiography, compared to radiostereometry in 51 patients.

We assessed the accuracy of migration measurements on conventional and digitized radiographs of total hip arthroplasties by comparing the results with radiostereometry (RSA). 4 stem and 3 acetabular designs were studied. 2 of the stem designs and 1 cup design were uncemented. 180 manual and 202 digitized measurements were done on 120 conventional radiographic examinations. The readings on digitized radiographs did not differ from the manual measurements on the same radiographs. A comparison of the measurements from plain radiographs and with RSA of the femoral stems revealed an accuracy (absolute mean + 2 SD) of between 3.9 and 12.3 mm, depending on the choice of landmarks. The greatest accuracy was obtained by using tantalum markers inserted into the greater or the lesser trochanter and the shoulder of the stem. The most medial point of the lesser trochanter proved to be the best bony landmark. Measurements, including both the center of the femoral head and the greater trochanter, were associated with poor accuracy. The accuracy as regards horizontal cup migration varied from 4.4 to 6.5 mm and the accuracy as regards vertical migration varied between 4.4 and 6.3 mm. The intraobserver error (2 SD) ranged from 1.6 mm to 5.6 mm, The corresponding figures for the inter-observer error were 2.6 mm and 6.6 mm, respectively. One of the cemented cup designs was associated with inferior accuracy. Stem design did not affect the accuracy.

Bias↗
PubMed1995

Roentgen stereophotogrammetric analysis as a predictor of mechanical loosening of knee prostheses.

The tibial components in 143 patients with total knee replacements performed before 1988 were assessed for micromotion using roentgen stereophotogrammetric analysis (RSA) over a period of 13 years. The fixation of the prostheses remained clinically sound in all cases, although revision had been required for other reasons in seven. In a second group taken from all cases with RSA available on our full database to 1990, 15 tibial components had been followed by RSA from the insertion until, 1 to 11 years after the initial arthroplasty, they were revised for mechanical loosening of the tibial component; 12 of these comprised all the loosenings in the base group, thus making a total of 155 consecutive cases, while an additional three were inserted after the base material had been compiled. The mean migration in the first group was about 1 mm at one year, but subsequent migration was slower, reaching a mean of about 1.5 mm after ten years. About one-third migrated continuously throughout follow-up, while two-thirds ceased to migrate after one to two years. In the revision group, 14 components had migrated continuously and at one year significantly more than those in the first group. One revision case lacked the crucial one-year follow-up and could not be classified. These findings suggest that mechanical loosening begins early in the postoperative period. Clinical symptoms which necessitate revision, seen at this stage in 20% of abnormally migrating tibial components, may not appear until up to ten years after the operation.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1994

Bone response to hydroxyapatite-coated and commercially pure titanium implants in the human arthritic knee.

Rough and smooth commercially pure (c.p.) titanium implants and hydroxyapatite-coated (HA-C) implants were inserted in arthritic human knees and left in situ in order to compare the response of bone to these three implants. Radiographic examination alone could not determine if bone apposition had occurred. After 3 and 6 months, histomorphometric analyses of undecalcified sections, 10 microns thick, revealed a statistical significance in the amount of bone apposition to rough-surfaced and HA-C implants as compared with smooth uncoated implants. Most of the rough-surfaced c.p. titanium implants and the HA-C implants had achieved bone apposition on the order of 50%. No statistically significant differences in apposition were seen between the rough-surfaced and HA-C implants. The smooth c.p. titanium implants were mostly encapsulated in fibrous tissue.

Arthritis↗
PubMed1994

Long-term results of Charnley arthroplasty. A 12-16-year follow-up study.

A retrospective, long-term study was initiated to analyze clinical function, failures, and radiographic status in 95 Charnley low-friction arthroplasties performed during 1973-1977. Only patients with primary osteoarthrosis were included, and no patients were lost during the follow-up period. At the follow-up evaluation, 39 patients (41 hips) were deceased. Ten hips were revised (including 3 of the deceased patients), leaving 47 hips available for follow-up evaluation. Four patients (5 hips) were interviewed by telephone, and the remaining 42 hips were examined by the authors. With a mean follow-up period of 14 years, many of the patients had excellent pain relief with a mean Harris hip score for pain of 42 points (maximum, 44 points). Ninety-four percent of the patients were satisfied with their results. The survivorship for all 95 hips was 92% at 10 years and 83% at 16 years. Follow-up radiographs revealed that three (7%) of the femoral components were definitively loose, but only two (5%) of the acetabular components were probably loose. Forty-three percent of the hips had signs of polyethylene wear of the cup. The clinical and radiographic outcome is, in spite of an early cementing technique, very good in this long-term follow-up study.

Aged↗
PubMed1994

A multicenter 10-year study of cemented revision total hip arthroplasty in patients younger than 55 years old. A follow-up report.

In 1988, the authors reported the results of 67 cemented revision total hip arthroplasties performed for aseptic loosening in patients younger than 55 years old. Both components were cemented at both the primary operation and revision. With an average follow-up period of 4 years, 14 hips (21%) required a second revision arthroplasty. Eight hips in this study group were revised using the Christiansen prosthesis, which is known to have a high failure rate and is, consequently, not in use anymore. Therefore, these eight hips have been excluded from this extended follow-up study. The authors were able to follow the remaining 59 hips for an average of 10 years (range, 8-13 years). In all, 49 hips (83%) were rerevised or radiographically loose or painful. Nevertheless, 75% of the patients, rerevisions included, were satisfied with the final result. There was an increase in bone loss at the final follow-up visit compared to the initial revision, reducing the prerequisites for a good result if further revision surgery was to be performed. After 10 years, survivorship analysis depicted a 48% survival rate when rerevision for aseptic loosening was considered a failure. The survival rate was 65% for the cup and 61% for the stem. The authors conclude that there is an increased failure rate with longer follow-up periods for cemented, revision total hip arthroplasties in young and active patients, and therefore, these patients must be followed indefinitely. The long-term results in this study provide an opportunity for valid comparisons of more sophisticated surgical techniques.

Adult↗
PubMed1994

Micromotion of femoral stems in total hip arthroplasty. A randomized study of cemented, hydroxyapatite-coated, and porous-coated stems with roentgen stereophotogrammetric analysis.

The fixation of the femoral stem in a total hip arthroplasty was studied in sixty patients (sixty-four hips) with use of roentgen stereophotogrammetric analysis. The hips were randomly stratified on the basis of the age, sex, and weight of the patient; the roentgenographic quality of the bone; and the reason for the operation (primary or secondary osteoarthrosis). The hips were then randomly assigned to one of three types of fixation of the femoral component: insertion with cement, hydroxyapatite coating, or porous coating. Examinations with roentgen stereophotogrammetry were done as long as two years after the operation. Micromotion of the prostheses was evaluated in terms of subsidence or proximal migration and rotations and translations of the proximal-lateral (shoulder) and distal (tip) parts of the prostheses. The clinical results at the two-year follow-up evaluation did not differ significantly between the groups with regard to the Harris hip score or the pain score (p > 0.05 for both; Wilcoxon rank-sum test). There were small or no differences in rotations and micromotions of the shoulder and the tip of the prostheses. Increased subsidence of 0.1 to 0.2 millimeter was recorded for the cemented and the porous-coated prostheses (p = 0.002 and p = 0.02, respectively; Wilcoxon rank-sum test). Thus, proximal hydroxyapatite coating seems to enhance the early fixation of the stem. Conventional roentgenography revealed an increased number of radiodense lines surrounding the porous-coated prostheses. Distal hypertrophy of the femoral cortex was found mainly around the hydroxyapatite-coated prostheses. Proximal resorption of bone and heterotopic ossification occurred to approximately the same extent regardless of the type of fixation used.

Adult↗
PubMed1993

Prognosis of total hip replacement in Sweden. Follow-up of 92,675 operations performed 1978-1990.

A prospective, national multi-center study of all reoperations after total hip replacement (THR) was started by the Swedish Orthopedic Association in 1979. The material comprises all THR performed in Sweden, presently more than 10,000 yearly or 130 THR per 100,000 inhabitants; uncemented implants have been used in less than 2 percent. The main reasons for revision have been aseptic loosening 79 percent, infection 10 percent, technical error 6 percent, and dislocation 2 percent. The cumulative rate of revision for deep infection has dropped from 0.9 percent to < 0.5 percent for implants inserted 1979 and 1983, respectively. With the Charnley prosthesis as the gold, standard the performance of other prostheses was analyzed. Improved cementation techniques and anti-infection measures have continuously reduced the revision risk. The register demonstrates that the average orthopedic surgeon cannot match the results achieved by experts. However, the vast majority of THR, worldwide, are not performed by experts. Quality-assurance in this sector of orthopedics demands a continuous analysis of the outcome of these operations.

Aged↗
PubMed1992

Proximally cemented versus uncemented Freeman-Samuelson knee arthroplasty. A prospective randomised study.

We studied the effect of a layer of cement placed under the tibial component of Freeman-Samuelson total knee prostheses with a metal back and an 80 mm intramedullary stem, using roentgen stereophotogrammetry to measure the migration of the tibial component during one year in 13 uncemented and 16 cemented knees. The addition of cement produced a significant reduction in migration at one year, from a mean of 1.5 mm to one of 0.5 mm (p less than 0.01), including a significant reduction in pure subsidence. One year postoperatively the clinical results were similar between the groups, but, at three years, one uncemented knee had required revision.

Adult↗
PubMed1992

Cemented revision hip arthroplasty. A multicenter 5-9-year study of 204 first revisions for loosening.

In a prospective study of total hip replacements in Sweden, the epidemiology of all the reoperations has been documented since 1979. From this nationwide register, the results of initial revision arthroplasty for aseptic loosening were evaluated in a well-described patient population, aged 55 to 70 years at the time of revision. Totally, 202 patients (204 hips) were available for clinical and radiographic analysis. The average follow-up time was 7 years. A re-revision or radiographically loose components occurred in 38 percent of the hips. The survival rate, with re-revision as the end point, was 75 percent at 8 years. We concluded that the initial revision on still active patients, using previous cementing techniques, provided poor results with a high risk of mechanical loosening and re-revisions. The results of this study, obtained in a well-described patient population, can be contemplated as a baseline that provides an opportunity for valid comparisons of new techniques.

Aged↗
PubMed1991

Intramuscular pressure and electromyography in four shoulder muscles.

Estimations of shoulder muscle load are important in biomechanic and ergonomic research. We have studied shoulder muscle load in the trapezius (six subjects), deltoid (six subjects), infraspinatus (eight subjects), and supraspinatus (seven subjects) muscles with simultaneous intramuscular pressure (IMP) and intramuscular bipolar electromyography (EMG) recordings. For imposition of shoulder muscle load, the arm was positioned in abduction or flexion with different hand loads (0, 1, or 2 kg), or isometric force registrations were performed. The microcapillary infusion technique was used for IMP recordings. The IMP in the supra- and infraspinatus muscles were high compared with the trapezius and deltoid muscles in abducted arm positions. In all test situations, IMP and EMG gave a similar description of local muscle load. IMP at maximal voluntary contraction was highest in the supraspinatus and infraspinatus muscles. Both IMP and EMG in all four muscles showed an almost linear correlation to recorded isometric external force. The difference in IMP between shoulder muscles in the same arm position may be due to muscle anatomy, muscle function, and compliance of surrounding tissues. Because a high IMP may impede muscle blood flow, our findings may possibly explain the physiological stress on the rotator cuff muscles as compared with the deltoid and trapezius muscles in work with elevated arms.

Biomechanical Phenomena↗
PubMed1991

Biomechanical model of the human shoulder joint--II. The shoulder rhythm.

A method to investigate the rhythm of the human shoulder, i.e. the interplay between the motion of constituent parts of the shoulder, has been devised and tested. The method is based upon numerical evaluation of low dose roentgenstereophotogrammetric motion pictures of subjects equipped with radiation dense implantations in the bones. Evaluation of the method shows that it may be used in determining motion patterns and that the employed interpolation techniques can be used to simulate motions not actually performed in the laboratory. The shoulder rhythm has been previously poorly investigated and quantified results published pertain to one plane only. Our results on motion patterns correlate with previous investigations. With this method, we show that the absolute position of the bones varies significantly between individuals while the relative displacement of the bones during motion exhibit similarities. In particular the results show that, under normal conditions, the individual rhythm is very stable and insensitive to small hand-loads.

Acromion↗
PubMed1991

The effect of arm support on supraspinatus muscle load during simulated assembly work and welding.

The effect of arm support, by a suspension device, on muscle load in the supraspinatus muscle was evaluated with simultaneous intramuscular pressure measurement and electromyography (EMG) in nine healthy subjects. Two work situations, a low load assembly type of work, and welding with a higher shoulder muscle load, were simulated in the laboratory. Each subject performed three work-cycles of each type, with and without arm support. Arm suspension reduced supraspinatus muscle load in both work situations with reduction in pressure of 34% and 22% respectively, and reduction in normalized EMG of 20% and 17% respectively. The reduction of muscle load was significant, but in the welding situation with arm-suspension 10-15 N, average muscle pressure was still high enough to reduce muscle blood flow. The interpretation of the importance of this load reduction for the development of work-related shoulder pain is problematic.

Adult↗
PubMed1990

The effect of a stem on the tibial component of knee arthroplasty. A roentgen stereophotogrammetric study of uncemented tibial components in the Freeman-Samuelson knee arthroplasty.

We studied the effect of a metal tray with an intramedullary stem on the micromotion of the tibial component in total knee arthroplasty. Of 32 uncemented Freeman-Samuelson knee arthroplasties performed in London and Gothenburg, nine had a metal backing and stem added to the tibial component. Micromotion of the tibial components, expressed as migration and inducible displacement, was analysed using roentgen stereophotogrammetric analysis up to two years follow-up. The addition of a metal back and a 110 mm stem to the standard polyethylene component significantly reduced both migration over two years and inducible displacement.

Adult↗