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Biomedical subjects

S Toksvig-Larsen

Publications and source records attributed to S Toksvig-Larsen.

At least 55 records · Page 3Linked to original sources
PubMed1995

Fixation of the tibial component in knee arthroplasty after six weeks.

The fixation of cemented and uncemented PCA modular cruciform-stemmed tibial components was examined 6 weeks after operation using roentgenstereophotogrammetric analysis in 26 randomly selected patients. Physiological external forces were applied in external/internal rotation and eccentric posterior loading generated by squatting. All cases showed inducible displacement, but there were no statistically significant differences between the 2 groups in inducible displacement or in the initial migration, except for subsidence between the lying and standing position. In some, the greatest movement was found when changing from resting to standing, or during rotational stress; in others, the greatest movement was found during squatting. There was a statistical difference in subsidence on squatting which was greater in the uncemented group. The design of the cruciform stem and the use of an internally cooled saw may explain this small differences between the 2 groups.

Aged↗
PubMed1995

Heat generation and heat protection in methylmethacrylate cementation of vertebral bodies. A cadaver study evaluating different clinical possibilities of dural protection from heat during cement curing.

For metastatic disease of the spine, anterior operations on the vertebral bodies often include methylmethacrylate cementation. The cement curing process may produce high temperatures in the surroundings, as demonstrated in joint replacement surgery, and there is a risk of thermal injury to the spinal nerves. In cadavers, we studied the heat arising during curing of cement on the dural sac, and the temperature of the cement surface was measured when the vertebral body was reconstructed using acrylic cement in the same way as in tumor surgery. The temperature increase on the surface of the dural sac during polymerization was between 4 degrees and 12 degrees C, depending on the amount of protection. Only a moderate temperature elevation was measured on the surface of the dural sac, provided that the posterior cortex of the vertebra was retained together with 0.5 cm of the spongious bone or a silicone membrane.

Bone Cements↗
PubMed1995

Early migration of femoral components revised with impacted cancellous allografts and cement. A preliminary report of five patients.

We report the preliminary findings of the use of roentgen stereophotogrammetric analysis to evaluate the early migration of five femoral components after revision for mechanical loosening using impacted cancellous allograft and cement. All hips were examined at one week, four to six months and one year after surgery. All the components subsided by 0.4 to 4.9 mm during the first year. In four hips the prosthetic head was displaced 1.1 to 6.9 mm posteriorly. Fixation of the femoral components was less secure than after primary arthroplasty but the incidence and magnitude of early migration were similar to those after revision with cement alone.

Aged↗
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

Stability of the elevated fragment in tibial plateau fractures. A radiographic stereophotogrammetric study of postoperative healing.

Five cases of fracture of the lateral tibial condyle of the split-depression type were treated by elevation of the depressed fragment, bone grafting and cancellous bone screws. During the operation, tantalum markers were inserted into the depressed fragment and the tibial metaphysis for radiographic stereophotogrammetric analysis. Postoperatively a plaster cast was applied for one month and weightbearing was not allowed for 3 months. In three cases, a depression of the elevated fragment, at the most 2.8 mm, recurred during the first month after operation. This was not considered to be significant and more aggressive postoperative mobilisation may be warranted.

Adult↗
PubMed1994

Surface characteristics following tibial preparation during total knee arthroplasty.

A clinical study, where flatness of the cut surface was quantified, was performed during 26 tibial bone cuts prepared for noncemented endoprosthetic components. Using sterilized dental imprint material and measured by the Zeiss Universal Measuring Centres (UMC) 850 (Oberkochen, Germany), the characteristics of the cut surface were defined. A clinically "flat" surface was found to be uneven with a maximum roughness of 1.71 mm (range, 1.06-2.57 mm), and defined as the distance between the uppermost and lowermost points. The flatness, defined as the standard deviation of the measuring points, was 0.26 mm (range, 0.16-0.38 min). This lack of smoothness creates gaps between the bone and prosthesis that are large enough to prevent direct bone contact when using noncemented fixation. This may be one reason why bony ingrowth is found inconsistently. The surface prepared by a 2-mm thick prototype saw blade was inferior to that created by a 1-mm blade.

Aged↗
PubMed1994

Improved bone cutting using a semirotating saw. A cadaver study of the cut surface on tibial condyles.

Cut surfaces on cadaver tibial bones prepared to receive an endoprosthetic tibial component, using an oscillating and a semirotating saw, were studied. Dental imprint material was used. The imprints were measured by a Zeiss UMC 850 to define the characteristics of the cut surface. The surface was smoother using the semirotating saw than the oscillating saw, with a mean maximum roughness of 1.46 mm and 2.36 mm, respectively. The corresponding flatnesses were 0.26 mm and 0.49 mm. The primary cut surface could not be improved during second cutting trials, which showed the importance of first correctly sawing in joint replacement surgery.

Bone and Bones↗
PubMed1994

Effect of a cooled saw blade on prosthesis fixation. Randomized radiostereometry of 33 knee cases.

Tibial migration in 33 cementless total knee replacements, which were performed with a cooled saw blade vs. a conventional blade, was studied in a randomized prospective study using roentgen stereophotogrammetric analysis (radiostereometry). All cases were clinically successful after 2 years and inducible displacement was smaller in the group operated with the cooled saw blade. This group also had a tendency towards less continuous migration.

Aged↗
PubMed1993

Ingrowth of bone into pores in titanium chambers implanted in rabbits: effect of pore cross-sectional shape in the presence of dynamic shear.

The micromotion chamber consists of a titanium outer cylinder and a central core, which are pierced by a transverse 1-mm canal for tissue ingrowth. Six weeks after implantation in the proximal tibia in mature rabbits, the outer cylinder is osseointegrated; the central core can then be moved in relation to the fixed outer cylinder. Thus, the tissue growing through the pore, from the cylinder into the core, can be subjected to motion of a predetermined amplitude and frequency. In this study we investigate the influence of pore cross-sectional shape on tissue ingrowth in the canal. In six animals, the outer cylinder was pierced by a square 1-mm hole that was congruent with the square hole in the core; in five animals, the hole in the cylinder was round. The cross-sectional area of the square hole in the cylinder was about 21% greater than in a round hole. In all cases, the channel in the inner core was 1 x 1 x 5-mm quadrate. All chambers underwent 20 cycles/day of micromotion for a 3-week period. The amplitude of the micromotion was 0.5 mm. Chambers containing cylinders with a round hole demonstrated less bone ingrowth as compared to cylinders with a square hole. This observation may be due to several factors including the greater cross-sectional area of the square versus the round hole in the cylinder and the enhanced congruity provided by the square outer and inner holes, versus a round outer and square inner hole.

Animals↗
PubMed1993

Early postoperative fixation of tibial components: an in vivo roentgen stereophotogrammetric analysis.

The fixation of cemented and noncemented tibial components in 19 total knee arthroplasties was examined 3 to 10 weeks postoperatively with roentgen stereophotogrammetric analysis. Physiologic external forces were applied either in outward-inward rotation or as eccentric posterior loading generated by squatting. In one case there was no motion, while in the remaining 18 cases relative interface motion of up to 1.3 mm was found. In some cases, the largest motion was found during inward-outward rotatory stress, while in others, the largest motion was found during squatting. Posterior tilt was weakly correlated with posterior displacement of the femoral component on the tibia during squatting (r2 = 0.323, p < 0.05). For the noncemented cases, the initial fixation to bone was probably insufficient, and ingrowth of bone would not have been achieved. For the cemented cases, motion of the implant was reduced. Given the short postoperative time and the probable absence of any substantial fibrous tissue membrane, we suggest that the observed motion represented elastic deformation of the bone.

Aged↗
PubMed1993

Migration of hydroxyapatite coated femoral prostheses. A Roentgen Stereophotogrammetric study.

We allocated randomly 27 patients undergoing 28 primary uncemented total hip replacements (THR) to receive prosthetic components of similar design with either plasma-sprayed titanium alloy (Ti) coating (n = 13) or hydroxyapatite (HA) coating (n = 15). After some exclusions, 15 of the patients (15 THR; 7 with HA- and 8 with Ti-coating) were followed by roentgen stereophotogrammetric analysis at 3, 6 and 12 months to measure migration of the femoral component. Twenty-six of the patients (26 THR) were followed clinically and by conventional radiography. All the femoral components had migrated at 3 months. From 3 to 12 months, the migration of Ti-coated components continued whereas the HA-coated components had stabilised. At 12 months there was significantly less migration of the HA-coated components (p < 0.05). The maximum subsidence was 0.2 mm in both groups. The Harris hip score was equal in the two groups preoperatively but at follow-up it was better in the HA-coated group (p < 0.05) and visual analogue scale scores showed that they had less pain (p < 0.05).

Aged↗
PubMed1993

Insertion of K-wires by hammer generates less heat. A study of drilling and hammering K-wires into bone.

Laboratory tests were carried out on cadaver animal bones to evaluate the thermal effect of inserting K-wires with a pneumatic hammer as compared to drilling. The mean maximum bone temperature 0.5 mm from the K-wires was 34 (22-72) degrees C using the hammer and 54 (19-100) degrees C for drilling, 1.0 mm from the K-wire the mean maximum temperature was 31 (19-52) degrees C for hammering and 47 (17-91) degrees C for drilling. The mean time for the temperature exposure in the cases of drilling was 50 s and for hammering 41 s. The hammering device may reduce the risk of heat-induced injury.

Animals↗
PubMed1992

Temperature influence in different orthopaedic saw blades.

Laboratory tests were carried out on ox bone to evaluate the thermal effect of eight different saw blades while cutting cortical bone. These saw blades represented the usual clinical blades as well as saw blades specially manufactured in an attempt to decrease the temperature. Temperatures between 34 degrees C and 450 degrees C were registered in the saw blades. Only three measurements (of 219 tests) were below 44 degrees-47 degrees C, which is a critical limit for heat-induced bone necrosis. This test indicates that alternating saw blade design is not a way to control the temperature elevation during cutting of bone in orthopaedic procedures.

Bone and Bones↗
PubMed1992

Hyperthermia during occipito-cervical fusion with acrylic cement. Epidural thermometry in 23 cases.

In 22 patients, 23 posterior occipito-cervical fusions using acrylic cement were studied; 18 had seropositive rheumatoid arthritis and 4 traumatic atlanto-axial instability. The mean age was 60 (39-75) years. During the curing of the cement, epidural temperature measurements were performed over the cerebellum and between the foramen magnum and C1. Temperatures up to 69 degrees C were recorded. Cooling with profuse surface irrigation using normal saline solution or precooled 8 degrees C fluid did not influence the maximal temperatures recorded under the cement. Even though no gross neurological damage was noted, the epidural temperatures in occipito-cervical fusion with acrylic cement can be of sufficient degree to be hazardous; surface irrigation does not seem to be an effective way to reduce this risk.

Adult↗
PubMed1992

Intermittent micromotion inhibits bone ingrowth. Titanium implants in rabbits.

We studied the effects of micromotion on bone ingrowth into a 1-mm canal through a titanium chamber implanted in the proximal tibia of rabbits. The implant surface became "osseointegrated," but an interior core was movable, allowing the central portion of the canal to be moved in relation to the ends. Thus, the ingrowing bone in the canal had to pass an area of ad latus motion. When implanted in rabbit tibiae, the canal became filled with ingrown cancellous bone. Bone ingrowth was inhibited by 20 cycles of 0.5-mm movement applied during a 30-second period once daily. With this regimen, the canal was usually filled with vascularized fibrous tissue and significantly less bone. The micromotion chamber may enable detailed studies of the effects of different motion variables on ingrowth of bone.

Alloys↗
PubMed1991

Ten-year results of tibial osteotomy for medial gonarthrosis. The influence of overcorrection.

The results in relation to the correction achieved 1 year after surgery of a series of tibial osteotomies in 50 patients (52 knees) are presented with a total observation time of 10 years. Mean age at the time of osteotomy was 56 years. Overcorrected knees had a significantly better result after 10 years. Progress of gonarthrosis occurred in 6/34 overcorrected knees compared with 3/4 in the normo- and undercorrected group. One out of 34 overcorrected knees recurred in varus. Five knees were revised by knee arthroplasty or reosteotomy one of which was overcorrected.

Adult↗
PubMed1991

On the problem of heat generation in bone cutting. Studies on the effects on liquid cooling.

A saw blade was made from two standard oscillating blades which were fixed to each other with channels between, so that cooling fluid could be directed to the saw teeth. The blade was connected to a standard arthroscopy pump which delivered a flow of 80 ml/min through the blade. The performance of this blade was compared with that of a standard saw blade, cutting ox-bone in the laboratory. Irrigation of the standard saw blade with saline delivered by a syringe only slightly diminished the maximum temperature. Pumped irrigation was more effective but required large volumes of fluid. The heat generated by the internally cooled saw blade was negligible and the temperatures achieved (19 degrees C to 34 degrees C) fell well below the critical level for bone death (44 degrees C to 47 degrees C).

Equipment Design↗