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In vivo measurement of bending stiffness in fracture healing.

Hente R, Cordey J, Perren SM - Biomed Eng Online (2003)

Bottom Line: Measurement of stiffness data over time revealed a significant logarithmic increase between the third and seventh weeks, whereby the logarithmic rate of change among sheep was similar, but started from different levels.Comparative measurements showed that early individual changes between the third and fourth weeks can be used as a predictor of bending stiffness at seven weeks (r = 0.928) and at ten weeks (r = 0.710).Bending stiffness can be measured precisely, with less error in the case of pin loosening.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Regensburg, Trauma Centre Regensburg, Franz-Josef-Strauss-Allee 11, D-93042 Regensburg, Germany. reiner.hente@klinik.uni-regensburg.de

ABSTRACT

Background: Measurement of the bending stiffness a healing fracture represents a valid variable in the assessment of fracture healing. However, currently available methods typically have high measurement errors, even for mild pin loosening. Furthermore, these methods cannot provide actual values of bending stiffness, which precludes comparisons among individual fractures. Thus, even today, little information is available with regards to the fracture healing pattern with respect to actual values of bending stiffness. Our goals were, therefore: to develop a measurement device that would allow accurate and sensitive measurement of bending stiffness, even in the presence of mild pin loosening; to describe the course of healing in individual fractures; and help to evaluate whether the individual pattern of bending stiffness can be predicted at an early stage of healing.

Methods: A new measurement device has been developed to precisely measure the bending stiffness of the healing fracture by simulating four-point-bending. The system was calibrated on aluminum models and intact tibiae. The influence of pin loosening on measurement error was evaluated. The system was tested at weekly intervals in an animal experiment to determine the actual bending stiffness of the fracture. Transverse fractures were created in the right tibia of twelve sheep, and then stabilized with an external fixator. At ten weeks, bending stiffness of the tibiae were determined in a four-point-bending test device to validate the in-vivo-measurement data.

Results: In-vivo bending stiffness can be measured accurately and sensitive, even in the early phase of callus healing. Up to a bending stiffness of 10 Nm/degree, measurement error was below 3.4% for one pin loose, and below 29.3% for four pins loose, respectively. Measurement of stiffness data over time revealed a significant logarithmic increase between the third and seventh weeks, whereby the logarithmic rate of change among sheep was similar, but started from different levels. Comparative measurements showed that early individual changes between the third and fourth weeks can be used as a predictor of bending stiffness at seven weeks (r = 0.928) and at ten weeks (r = 0.710).

Conclusion: Bending stiffness can be measured precisely, with less error in the case of pin loosening. Prediction of the future healing course of the individual fracture can be assessed by changes from the third to the fourth week, with differences in stiffness levels. Therefore, the initial status of the fracture seems to have a high impact on the individual healing course.

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Calibration of the in-vivo-measurement device on aluminum model and intact tibiae. Calibration curve of the measurement device obtained from values measured on aluminum bars with interconnected modules of varying stiffness (solid line). The change in measurement (apparent stiffness, y-axis) on the effect of pin osteolysis was determined (◊: All the pins are firmly fixed, ▽: one pin loose, □: four pins loose). For bending stiffness up to 10 Nm/degree, the measurement error remains acceptably small, even under the worst condition of all pins loose. Validation of the calibration model was tested on intact tibiae (green ○). The calculated bending stiffness tends to be smaller than the actual bending stiffness (mean value 5.4%, SD ± 6.2).
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Figure 4: Calibration of the in-vivo-measurement device on aluminum model and intact tibiae. Calibration curve of the measurement device obtained from values measured on aluminum bars with interconnected modules of varying stiffness (solid line). The change in measurement (apparent stiffness, y-axis) on the effect of pin osteolysis was determined (◊: All the pins are firmly fixed, ▽: one pin loose, □: four pins loose). For bending stiffness up to 10 Nm/degree, the measurement error remains acceptably small, even under the worst condition of all pins loose. Validation of the calibration model was tested on intact tibiae (green ○). The calculated bending stiffness tends to be smaller than the actual bending stiffness (mean value 5.4%, SD ± 6.2).

Mentions: To test the effect of pin loosening, the aluminum tubes were selectively replaced with tubes where the holes of the near cortex were drilled 1 mm larger than that of the pin diameter. This created a model of mild (one loose pin) and the most severe situation of pin loosening (all four pins loose). With each model, identical calibration measurements with each interconnected module were taken, and the resulting load/deflection ratio (N/microstrain) recorded (Fig. 4).


In vivo measurement of bending stiffness in fracture healing.

Hente R, Cordey J, Perren SM - Biomed Eng Online (2003)

Calibration of the in-vivo-measurement device on aluminum model and intact tibiae. Calibration curve of the measurement device obtained from values measured on aluminum bars with interconnected modules of varying stiffness (solid line). The change in measurement (apparent stiffness, y-axis) on the effect of pin osteolysis was determined (◊: All the pins are firmly fixed, ▽: one pin loose, □: four pins loose). For bending stiffness up to 10 Nm/degree, the measurement error remains acceptably small, even under the worst condition of all pins loose. Validation of the calibration model was tested on intact tibiae (green ○). The calculated bending stiffness tends to be smaller than the actual bending stiffness (mean value 5.4%, SD ± 6.2).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC153498&req=5

Figure 4: Calibration of the in-vivo-measurement device on aluminum model and intact tibiae. Calibration curve of the measurement device obtained from values measured on aluminum bars with interconnected modules of varying stiffness (solid line). The change in measurement (apparent stiffness, y-axis) on the effect of pin osteolysis was determined (◊: All the pins are firmly fixed, ▽: one pin loose, □: four pins loose). For bending stiffness up to 10 Nm/degree, the measurement error remains acceptably small, even under the worst condition of all pins loose. Validation of the calibration model was tested on intact tibiae (green ○). The calculated bending stiffness tends to be smaller than the actual bending stiffness (mean value 5.4%, SD ± 6.2).
Mentions: To test the effect of pin loosening, the aluminum tubes were selectively replaced with tubes where the holes of the near cortex were drilled 1 mm larger than that of the pin diameter. This created a model of mild (one loose pin) and the most severe situation of pin loosening (all four pins loose). With each model, identical calibration measurements with each interconnected module were taken, and the resulting load/deflection ratio (N/microstrain) recorded (Fig. 4).

Bottom Line: Measurement of stiffness data over time revealed a significant logarithmic increase between the third and seventh weeks, whereby the logarithmic rate of change among sheep was similar, but started from different levels.Comparative measurements showed that early individual changes between the third and fourth weeks can be used as a predictor of bending stiffness at seven weeks (r = 0.928) and at ten weeks (r = 0.710).Bending stiffness can be measured precisely, with less error in the case of pin loosening.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Regensburg, Trauma Centre Regensburg, Franz-Josef-Strauss-Allee 11, D-93042 Regensburg, Germany. reiner.hente@klinik.uni-regensburg.de

ABSTRACT

Background: Measurement of the bending stiffness a healing fracture represents a valid variable in the assessment of fracture healing. However, currently available methods typically have high measurement errors, even for mild pin loosening. Furthermore, these methods cannot provide actual values of bending stiffness, which precludes comparisons among individual fractures. Thus, even today, little information is available with regards to the fracture healing pattern with respect to actual values of bending stiffness. Our goals were, therefore: to develop a measurement device that would allow accurate and sensitive measurement of bending stiffness, even in the presence of mild pin loosening; to describe the course of healing in individual fractures; and help to evaluate whether the individual pattern of bending stiffness can be predicted at an early stage of healing.

Methods: A new measurement device has been developed to precisely measure the bending stiffness of the healing fracture by simulating four-point-bending. The system was calibrated on aluminum models and intact tibiae. The influence of pin loosening on measurement error was evaluated. The system was tested at weekly intervals in an animal experiment to determine the actual bending stiffness of the fracture. Transverse fractures were created in the right tibia of twelve sheep, and then stabilized with an external fixator. At ten weeks, bending stiffness of the tibiae were determined in a four-point-bending test device to validate the in-vivo-measurement data.

Results: In-vivo bending stiffness can be measured accurately and sensitive, even in the early phase of callus healing. Up to a bending stiffness of 10 Nm/degree, measurement error was below 3.4% for one pin loose, and below 29.3% for four pins loose, respectively. Measurement of stiffness data over time revealed a significant logarithmic increase between the third and seventh weeks, whereby the logarithmic rate of change among sheep was similar, but started from different levels. Comparative measurements showed that early individual changes between the third and fourth weeks can be used as a predictor of bending stiffness at seven weeks (r = 0.928) and at ten weeks (r = 0.710).

Conclusion: Bending stiffness can be measured precisely, with less error in the case of pin loosening. Prediction of the future healing course of the individual fracture can be assessed by changes from the third to the fourth week, with differences in stiffness levels. Therefore, the initial status of the fracture seems to have a high impact on the individual healing course.

Show MeSH
Related in: MedlinePlus