Mechanical torque measurement predicts load to implant cut-out: a biomechanical study investigating DHS® anchorage in femoral heads

Abstract

Introduction Bone strength plays an important role in implant anchorage. Bone mineral density (BMD) is used as surrogate parameter to quantify bone strength and to predict implant anchorage. BMD can be measured by means of quantitative computer tomography (QCT) or dual energy X-ray absorptiometry (DXA). These noninvasive methods for BMD measurement are not available pre-or intra-operatively. Instead, the surgeon could determine bone strength by direct mechanical measurement. We have evaluated mechanical torque measurement for (A) its capability to quantify local bone strength and (B) its predictive value towards load at implant cut-out. Materials and methods Our experimental study was performed using sixteen paired human cadaver proximal femurs. BMD was determined for all specimens by QCT. The torque to breakaway of the cancellous bone structure (peak torque) was measured by means of a mechanical probe at the exact position of subsequent DHS ® placement. The Wxation strength of the DHS ® achieved was assessed by cyclic loading in a stepwise protocol beginning with 1,500 N increasing 500 N every 5,000 cycles until 4,000 N. Results A highly signiWcant correlation of peak torque with BMD (QCT) was found (r = 0.902, r 2 = 0.814, P < 0.001). Peak torque correlated highly signiWcant with the load at implant cut-out (r = 0.795, P < 0.001). All specimens with a measured peak torque below 6.79 Nm failed at the Wrst load level of 1,500 N. The specimens with a peak torque above 8.63 Nm survived until the last load level of 4,000 N. Conclusion Mechanical peak torque measurement is able to quantify bone strength. In an experimental setup, peak torque identiWes those specimens that are likely to fail at low load. In clinical routine, implant migration and cut-out depend on several parameters, which are diYcult to control, such as fracture type, fracture reduction achieved, and implant position. The predictive value of peak torque towards cut-out in a clinical set-up therefore has to be carefully validated.

Assessment of the Breakaway Torque at the Posterior Pelvic Ring in Human Cadavers

“…The objective of the presented report was to provide data regarding the ideal site for screw-based fixation methods in posterior pelvic ring injuries using an objective measurement device for the resistance of trabecular bone against destruction [16][17][18]. One limitation may be that no correlation to bone mineral density (BMD) is provided since BMD can only be measured using dual energy X-ray absorptiometry (DXA) or quantitative computer tomography (QCT).…”

“…Cadavers were embalmed using the Thiel fixation method as developed by W. Thiel in 1992 and provided by the local anatomical department [15]. The method used [16][17][18] for the determination of local bone quality was based on local bone destruction. For this, the specimens were radiographically assessed prior to the measurements using CT scans aimed at detecting potential differences in the bone density, as well as deformations, fractures, neoplasms or hardware in situ at the pelvic site.…”

Prediction of Biomechanical Parameters of the Proximal Femur Using Statistical Appearance Models and Support Vector Regression

“…By using this approach one has the possibility to depict a number of different geometric and structural properties that can be used to predict biomechanical bone parameters, accurately and reliably. Although the tests were performed using images with comparably low resolution, the quantitative results in terms of the amount of correlation between real and predicted parameter values are absolutely comparable to studies that partly use higher image resolutions [7][8][9][10].…”

“…In the first setting (=setting A) the parameter "peak torque until complete breakaway" (=PTB), which was obtained using the DensiProbe tool presented in [8], should be predicted for 14 proximal femora of men and women aged between 64 and 96 years. For this purpose CT images of cadaveric femora have been used.…”

“…In [8] a tool has been developed which can be used during the surgical intervention by measuring the peak torque until complete breakaway of the cancellous bone in the femoral head. Moreover, several non invasive methods were introduced in order to predict the cut out risk using CT or x-ray images based on the calculation of Haralick texture features in CT images [9] or Minkowski functionals [10] in different regions of interest.…”