Biomedical subjects

P Benum

Publications and source records attributed to P Benum.

At least 19 recordsLinked to original sources

PubMed2004

Impacted bone stiffness measured during construction of morsellised bone samples.

Impacted morsellised bone is widely used for filling bone deficiencies during revision of total hip arthroplasties. However, the physical properties and mechanical behaviour of this bone material are still not well understood. In this study we recorded the increase of stiffness in pellets of morsellised bone during their construction. The construction of bone pellets was measured stroke-by-stroke to ascertain optimal stiffness. We have derived an impact-constrained module of elasticity, which represents the dynamic resistance in the granulated bone mass to impaction. Drop level of the impaction slap hammer increases constrained bone stiffness during impaction and load. However, increasing the number of impaction strokes at the highest drop level does not improve stiffness properties; no significant increase in stiffness was achieved after five strokes on each layer of morsellised bone.

Absorptiometry, Photon↗

PubMed2001

Changes in proximal femoral strain after insertion of uncemented standard and customised femoral stems. An experimental study in human femora.

We have compared the changes in the pattern of the principal strains in the proximal femur after insertion of eight uncemented anatomical stems and eight customised stems in human cadaver femora. During testing we aimed to reproduce the physiological loads on the proximal femur and to simulate single-leg stance and stair-climbing. The strains in the intact femora were measured and there were no significant differences in principal tensile and compressive strains in the left and right femora of each pair. The two types of femoral stem were then inserted randomly into the left or right femora and the cortical strains were again measured. Both induced significant stress shielding in the proximal part of the metaphysis, but the deviation from the physiological strains was most pronounced after insertion of the anatomical stems. The principal compressive strain at the calcar was reduced by 90% for the anatomical stems and 67% for the customised stems. Medially, at the level of the lesser trochanter, the corresponding figures were 59% and 21%. The anatomical stems induced more stress concentration on the anterior aspect of the femur than did the customised stems. They also increased the hoop strains in the proximomedial femur. Our study shows a consistently more physiological pattern of strain in the proximal femur after insertion of customised stems compared with standard, anatomical stems.

Aged↗

PubMed2000

Cancellous bone as an antibiotic carrier.

We compared the release characteristics of antibiotics from in vivo and in vitro processed morselized cancellous bone. The bone was impregnated with 7 antibiotics and compressed into a wire-mesh cylinder. In vitro, the bone was processed by daily transfer of the cylinder with its contents into test tubes with broth. The amount of antibiotic eluted from the bone was measured after 1, 3 and 7 days. In vivo, the cylinder was implanted intramuscularly in the interscapular region in rats. After 1, 3 and 7 days, the cylinder was removed and the amount of antibiotic eluted in broth was measured. The results showed that morselized cancellous bone can act as a carrier of antibiotics in vitro and in vivo. The elution profiles of netilmicin-, vancomycin-, clindamycin- and rifampicin-impregnated cancellous bone processed in vitro and in vivo were similar.

Animals↗

PubMed1999

[Testing of a standard referral form in Sør-Trøndelag].

January 1st 1998 Norwegian health authorities introduced a standard referral form to be used for all referrals to specialists. The form had been developed by a working group in the Norwegian Board of Health. The group also was responsible for testing out the form. One test was performed by use of a medical audit method in Sør-Trøndelag County in September 1997. The evaluation from the specialists who received the referrals was positive with regard to the information needed for appraisal of the referral. The general practitioners who participated had a more varied evaluation; in 90% of the cases the form was evaluated as good or serviceable, but only in 30% of the cases was it considered an improvement. At the closing workshop the participating doctors had many proposals for changes and improvements of the form. The most important conclusion of the pilot study is that efforts to improve communication between doctors must be closely linked to developments in computer software for medical practice.

Adult↗

PubMed1999

Determination of Hounsfield value for CT-based design of custom femoral stems.

Ct and advanced computer-aided design techniques offer the means for designing customised femoral stems. Our aim was to determine the Hounsfield (HU) value of the bone at the corticocancellous interface, as part of the criteria for the design algorithm. We obtained transverse CT images from eight human cadaver femora. The proximal femoral canal was rasped until contact with dense cortical bone was achieved. The femora were cut into several sections corresponding to the slice positions of the CT images. After obtaining a computerised image of the anatomical sections using a scanner, the inner cortical contour was outlined and transferred to the corresponding CT image. The pixels beneath this contour represent the CT density of the bone remaining after surgical rasping. Contours were generated automatically at nine HU levels from 300 to 1100 and the mean distance between the transferred contour and each of the HU-generated contours was computed. The contour generated along the 600-HU pixels was closest to the inner cortical contour of the rasped femur and therefore 600 HU seem to be the CT density of the corticocancellous interface in the proximal part of cadaver femora. Generally, femoral bone with a CT density beyond 600 HU is not removable by conventional reamers. Thus, we recommend the 600 HU threshold as one of several criteria for the design of custom femoral implants from CT data.

Adult↗

PubMed1997

In vivo measurements show tensile axial strain in the proximal lateral aspect of the human femur.

Two conflicting theories exist concerning the stress pattern for the proximal lateral aspect of the human femur. According to the classic theory of Pauwels, a bending moment on the femur leads to compression medially and to tension laterally. The alternative theory is that muscle forces contribute to a moment-free loading of the femur, with both the medial and lateral cortices subjected to compression. To examine these theories, we measured the strain at the external surface of the proximal lateral aspect of the femur of two female patients undergoing surgery for "snapping hip syndrome." During the surgical procedure, a strain-gauge rosette was bonded to the lateral aspect of the femur and the cortical strains were monitored while the patient performed a series of activities. In both patients, principle tensile strain increased significantly during one-legged stance, walking, and stair climbing as compared with that during two-legged stance. During each loading situation, the principal tensile strain was aligned within 22 degrees to the longitudinal femoral axis. Dynamic strain measurements consistently revealed tensile axial strain at the lateral aspect of the femur during each activity. The present study supports the classic bending theory of Pauwels and demonstrates that the proximal lateral aspect of the femur is subjected to tension during the stance phase of gait.

Adult↗

PubMed1996

A prospective, randomized study of three operations for acute rupture of the anterior cruciate ligament. Five-year follow-up of one hundred and thirty-one patients.

A five-year, prospective, randomized follow-up study was done to compare three methods for repair of a rupture of the anterior cruciate ligament of the knee; acute primary repair (Group 1), acute repair with a synthetic ligament-augmentation device (Group 2), and acute repair augmented with an autologous bone-patellar ligament-bone graft (Group 3). One hundred and fifty patients who had an acute rupture of the anterior cruciate ligament were randomized to one of the three repair groups, with fifty patients in each group. The patients were between sixteen and fifty years old (mean, twenty-nine years old). All patients had the operation within ten days after the injury. The rehabilitation protocol was identical for each group. The patients were evaluated prospectively at one, two, and five years with use of the Tegner scoring system for level of activity and the scoring system of Lysholm and Gillquist for function, and the stability of the knee was assessed with clinical examination and with use of the KT-1000 arthrometer. One hundred and thirty-one patients completed the study and ten other patients were known to have had a failure of the procedure, a 94 percent rate of follow-up. All three groups had a lower level of activity at the five-year follow-up evaluation than they had had before the injury. The patients who had had augmentation with a patellar-ligament graft had a significantly higher mean level of activity at two years than those who had had non-augmented repair with (p = 0.002) and those who had had repair with a synthetic ligament-augmentation device (p = 0.01). They also had a significantly higher mean level of function at two years than those who had had non-augmented repair (p = 0.0001) and those who had had repair with a synthetic ligament-augmentation device (p = 0.03) and a significant higher mean level of function at five years than those who had had non-augmented repair (p = 0.004). The ability to attain full extension improved significantly in all three groups during the five-year follow-up period; the highest gains occurred in the group that had had augmentation with a patellar-ligament graft. Rotatory and anterior instability progressively increased during the follow-up period for all three groups. At one, two, and five years, the knees that had had repair with a patellar-ligament graft were significantly more stable than those that had had non-augmented repair and those that had had repair with a ligament-augmentation device (p < 0.0001 to p = 0.03). The findings of this study reinforce the conclusions of our two-year follow-up report that a non-augmented primary repair should not be performed, a repair with a ligament-augmentation device has an unacceptably high rate of failure (more than one-third of the patients), and a repair that is augmented with the patellar ligament has the best outcome.

Adolescent↗

PubMed1995

Extraarticular transposition of the patellar tendon for anterolateral instability of the knee. Poor results in 52 patients after 5-14-year follow-up.

Several extraarticular surgical procedures have been proposed to eliminate the anterolateral rotatory instability of an anterior cruciate-deficient knee. We examined the outcome in 52 patients with an extraarticular transposition of the lateral third of the patellar tendon to the lateral femoral condyle. The mean follow-up time was 9 years. The evaluation was based on the patients' subjective assessment, the Tegner activity level score, range of motion, Lysholm functional score, assessment of knee instability using manual testing as well as arthrometer measurements, and weight-bearing radiographs. At follow-up, 37 patients stated that they had good-to-excellent knee function. The mean Tegner score dropped from a preinjury level of 7 to 5.43 patients had a good-to-excellent Lysholm score. 20 patients had a positive Lachman sign of grade 2 or 3, and 23 patients had a side-to-side difference of more than 3 mm as measured by an arthrometer. 17 had a positive pivot shift sign. 12 patients had meniscal resections performed after the primary operation, and 27 had radiographic evidence of arthrosis. Although the outcome of this technique is equivalent to or better than results reported for other extraarticular procedures, the recurrence rate of symptomatic instability and the deterioration of subjective knee function are too high.

Adolescent↗

PubMed1993

Muscle function after plated and nailed femoral shaft fractures.

We studied retrospectively 14 patients who had been nailed and 12 patients who had been plated for femoral shaft fractures respectively 37 and 67 months previously. Isokinetic thigh muscle function measurements showed quadriceps strength to be fully restored in nailed patients, while there was a moderate persisting median deficit among plated patients. There was a similar moderate deficit in flexion strength for both groups. Strength restoration did not correlate with age at fracture or fracture level in the femur. It did, however, correlate strongly with the interval between fracture and study for flexion strength among nailed patients. It may be that this parameter also is eventually normalized in nailed patients.

Adolescent↗

PubMed1993

Incapacity for work in elective orthopaedic surgery: a study of occurrence and the probability of returning to work after treatment.

STUDY OBJECTIVE: The extent to which patients undergoing elective surgery for orthopaedic disorders were incapacitated for work while they were on the waiting list and whether they were able to return to work after surgery were studied. DESIGN: This was a prospective cohort study of patients admitted to hospital for elective orthopaedic surgery. Main outcome measures were occurrence of sickness certification during the waiting time, and whether those incapacitated for work at the time of surgery returned to work during the first year after treatment. Multivariate logistic regression was used to estimate adjusted odds ratios for factors influencing return to work. SETTING: Orthopaedic department in charge of all elective orthopaedic surgery in a population of 197,354 persons in central Norway. SUBJECTS: All 2803 patients admitted to hospital for chronic orthopaedic disorders in the defined population between 1 September 1988 and 31 August 1990 were included in the study. MAIN RESULTS: Of the 1333 patients who were employed, 42% had been certified sick due to the orthopaedic disorder for some period of the waiting time. Sickness benefits from the national insurance scheme (paid from the 15th day of sickness certification) had been received by 33% and were received by 29% at the time of surgery. Of 380 patients incapacitated for work at the time of surgery, 53% returned to work within the first year after surgery. Using those treated within one month of being placed on the waiting list as the reference group, the adjusted odds ratios for not returning to work during the first year after surgery were 9.2 (p < 0.0001) for those who waited more than a year for surgery, 6.2 (p = 0.002) for those waiting nine to 12 months, and 4.9 (p = 0.02) for those waiting for six to nine months. CONCLUSIONS: A high proportion of these patients were incapacitated for work, 53% of those incapacitated returned to work within the first year after surgery. The probability of returning to work after surgery is strongly influenced by the length of time on the waiting list. Waiting for more than one year, compared with immediate treatment, was associated with an adjusted odds ratio of 9.2 for not returning to work.

Absenteeism↗

PubMed1991

[Waiting time for treatment in hospital. How can we measure and regulate the waiting time?].

We discuss different measures of waiting time, as well as the factors that influence the waiting time, the number of patients accumulated on the waiting list, the inflow of patients to the list, the number of patients removed from the list without treatment, and the number of patients removed from the list as treated. We describe a method for continuous registration and surveillance of these factors, and of the waiting time for treated and waiting patients. We also present a mathematical model to describe the relation between these factors. This model has proved to be a useful tool in predicting waiting time and in estimating the treatment capacity required to reach defined goals for waiting time.

Hospital Administration↗

PubMed1991

Leg-length discrepancy measured by ultrasonography.

Leg-length discrepancy was determined by real-time ultrasonography (ultrasound) in 45 patients, and the measurements were compared with those of erect-posture radiography. A special device for holding and moving the ultrasound transducer was constructed, and the leg length was measured as the highest level of the femoral head in the standing position. The correlation coefficient r between ultrasound and radiography was 0.94, the mean difference was -1.9 mm, and the limits of agreement (mean +/- 2 SD) were -9.1 to 5.3 mm. The mean difference between examiners 1 and 2 was 1.7 mm, and the 95 percent confidence interval was +/- 7 mm. We conclude that leg-length discrepancy can be reliably determined by ultrasound, although the accuracy is less than that obtained by radiographic methods. Because ultrasound is not limited by radiation hazards, our technique can be used for clinical screening.

Adolescent↗

PubMed1990

Anterolateral rotatory instability of the knee. Cadaver study of extraarticular patellar-tendon transposition.

A cadaver knee-testing system was used to analyze the effect of an extraarticular reconstruction for anterolateral rotatory instability in which the lateral one third of the patellar tendon with a patellar bone block was transposed to the lateral femoral condyle. Ligament and reconstruction tendon forces were measured using buckle transducers, and joint motion was measured using an instrumented spatial linkage as 90 N anteriorly directed tibial loads were applied to seven knee specimens at 0 degree, 30 degrees, 60 degrees, and 90 degrees of flexion by a pneumatic load apparatus. This was done for each knee with first an intact, then an excised anterior cruciate ligament, and finally the extraarticular reconstruction. Forces in the transposed graft exhibited an isotonic pattern over the flexion range, unlike the intact anterior cruciate ligament, which was more highly loaded in extension than in flexion. The transposition of the patellar tendon led to external rotation of the tibia in both unloaded and anterior load conditions throughout flexion. Collateral ligament forces increased with anterior cruciate ligament excision, with the force in the medial ligament remaining higher than normal with the reconstruction, while the lateral forces became lower than normal.

Biomechanical Phenomena↗

PubMed1990

Pelvic inclination and spatial orientation of the acetabulum. A radiographic, computed tomographic and clinical investigation.

In a study of 40 young adults the pelvic inclination measured by a specially constructed inclinometer was found to be the same in the supine and standing positions when related to the horizontal and frontal planes, respectively. Consequently supine CT measurements of the hip are also representative of corresponding standing angles. The variations of the acetabular anterversion and the sector angles on CT of the hips in 5 adult corpses were measured by angulating the gantry in increments of 5 degrees to +/- 20 degrees. An approximate linear relationship was found for all parameters, the acetabular anteversion varied 0.5 degree with 1 degree pelvic rotation, and the sector angles 0.7 degree. A theoretic mathematical model for the variation of the acetabular anteversion outside the measured range employing a sine curve is introduced.

Acetabulum↗

PubMed1989

[Treatment and rehabilitation of anterior cruciate ligament injuries in Norway. A comparison with the Anterior Cruciate Ligament Study Group].

The method of treatment for ruptures of the anterior cruciate ligament range from nonoperative treatment through direct repair to complicated augmentation. The Anterior Cruciate Ligament (ACL) Study Group, consisting of orthopaedic surgeons from USA, Canada, Australia, Sweden, Austria and Switzerland, summarized its thoughts on treatment and rehabilitation in a recent paper. A survey has been carried out on Norwegian treatment practice and compared with the practice of the Anterior Cruciate Ligament Study Group. This paper describes the difference in treatment between the two groups of surgeons and reviews the methods of rehabilitation used for acute tears of the Anterior Cruciate Ligament Study Group. The majority of Norwegian surgeons in this study use primary repair with no augmentation, while surgeons in the Anterior Cruciate Ligament Study Group use augmentation methods allowing early mobilization and return to preinjury activities. 88% of the Norwegian surgeons prescribed a cast for six weeks after surgery, while only 15% of the surgeons in the Anterior Cruciate Ligament Study Group prescribe immobilization for more than four weeks. In the rehabilitation protocol the Anterior Cruciate Ligament Study Group emphasizes strength training of the hamstring in order to protect the Anterior Cruciate Ligament, at the same time preventing dynamic exercises of the quadriceps for the last 30 degrees of extension so as to prevent strain on the Anterior Cruciate Ligament. This policy was shared by less than 50% of the Norwegian surgeons.

Humans↗

PubMed1989

Advancement of the tibial tuberosity for patellar pain. A 5-year follow-up.

During the period 1978-1984, 38 patients aged 23-55 years were treated for patellofemoral pain by the Maquet procedure. The mean postoperative observation time was 5(3-9) years. Thirty-three of the 38 patients were available for follow-up including functional and activity scoring, clinical examination, and Cybex II dynamometer muscle-strength measurement. Ten patients improved, 17 were unchanged, and 6 were worse. Characteristic for the improved group was Grades III and IV chondromalacia - mainly involving the lateral facet - whereas the group with no improvement or deterioration exhibited a low-grade chondromalacia, chiefly affecting the medial patellar facet.

Adult↗

PubMed1989

Primary suture of the anterior cruciate ligament. A 6-year follow-up of 74 cases.

Seventy-four consecutive patients were reviewed 6 (3-9) years after primary suture according to Palmer of a fresh rupture of the anterior cruciate ligament. Three fourths had excellent or good function as evaluated by the Lysholm score. The pivot shift test was trace-positive in one fifth and 2+ or 3+ in one quarter, and the Lachman test was 2+ or higher in one third. Tibial anterior instability was present in 23 knees. Radiographically, 15 knees had signs of arthrosis, 4 of which severe. Our 0.25 failure rate suggests that other procedures should be considered in the treatment of acute rupture of the anterior cruciate ligament.

Adolescent↗

PubMed1989

Early postoperative weight-bearing and muscle activity in patients who have a fracture of the ankle.

Fifty-six patients who had a displaced fracture of the ankle necessitating surgical fixation were randomly assigned to one of three postoperative treatment regimens: no plaster cast or weight-bearing, and active exercises of the ankle; a non-weight-bearing plaster cast; or a plaster walking cast for the first six postoperative weeks. At follow-up with a duration of as much as two years, there were no consistent differences in the clinical results between the three groups. The time lost from work and the proportion of excellent and good clinical results were also uninfluenced by the postoperative regimen. No adverse effects could be detected as a result of the patient's having walked before the syndesmosis screw had been removed. It was concluded that none of the three postoperative regimens has any advantage over the others in a patient who has a stable osteosynthesis of a fracture of the ankle.

Adult↗