Limits...
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.

Show MeSH

Related in: MedlinePlus

Calculated measurement error in case of one pin loose. The calculated absolute and relative measurement errors obtained from the aluminum calibration model increases with higher bending stiffness. If actual bending stiffness is below 10 Nm/degree, the measurement error is below 3.4%. The observed non-continuous increase of measurement error in the lower part of the curve is related to small variations of the calculated curve-fit model, and not to systemic changes.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC153498&req=5

Figure 5: Calculated measurement error in case of one pin loose. The calculated absolute and relative measurement errors obtained from the aluminum calibration model increases with higher bending stiffness. If actual bending stiffness is below 10 Nm/degree, the measurement error is below 3.4%. The observed non-continuous increase of measurement error in the lower part of the curve is related to small variations of the calculated curve-fit model, and not to systemic changes.

Mentions: Generally, in case of pin loosening, the apparent measured values are lower with increasing bending stiffness of the fracture. Analysis of the measurement error calculated from the fitted curves was found to be in the range of 0 to 16.5% for one pin loose (Fig. 5) and the range of 0 to 51.4% for four pins loose (Fig. 6. In the range of lower values of bending stiffness, representing the early phase of healing up to 10 Nm/degree, measurement error was below 3.4% for one pin loose and below 29.3% for four pins loose.


In vivo measurement of bending stiffness in fracture healing.

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

Calculated measurement error in case of one pin loose. The calculated absolute and relative measurement errors obtained from the aluminum calibration model increases with higher bending stiffness. If actual bending stiffness is below 10 Nm/degree, the measurement error is below 3.4%. The observed non-continuous increase of measurement error in the lower part of the curve is related to small variations of the calculated curve-fit model, and not to systemic changes.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 5: Calculated measurement error in case of one pin loose. The calculated absolute and relative measurement errors obtained from the aluminum calibration model increases with higher bending stiffness. If actual bending stiffness is below 10 Nm/degree, the measurement error is below 3.4%. The observed non-continuous increase of measurement error in the lower part of the curve is related to small variations of the calculated curve-fit model, and not to systemic changes.
Mentions: Generally, in case of pin loosening, the apparent measured values are lower with increasing bending stiffness of the fracture. Analysis of the measurement error calculated from the fitted curves was found to be in the range of 0 to 16.5% for one pin loose (Fig. 5) and the range of 0 to 51.4% for four pins loose (Fig. 6. In the range of lower values of bending stiffness, representing the early phase of healing up to 10 Nm/degree, measurement error was below 3.4% for one pin loose and below 29.3% for four pins loose.

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