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. 2016 Dec 5;9(12):982.
doi: 10.3390/ma9120982.

An Analytical Calculation of Frictional and Bending Moments at the Head-Neck Interface of Hip Joint Implants During Different Physiological Activities

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Free PMC article

An Analytical Calculation of Frictional and Bending Moments at the Head-Neck Interface of Hip Joint Implants During Different Physiological Activities

Hamidreza Farhoudi et al. Materials (Basel). .
Free PMC article

Abstract

This study predicts the frictional moments at the head-cup interface and frictional torques and bending moments acting on the head-neck interface of a modular total hip replacement across a range of activities of daily living. The predicted moment and torque profiles are based on the kinematics of four patients and the implant characteristics of a metal-on-metal implant. Depending on the body weight and type of activity, the moments and torques had significant variations in both magnitude and direction over the activity cycles. For the nine investigated activities, the maximum magnitude of the frictional moment ranged from 2.6 to 7.1 Nm. The maximum magnitude of the torque acting on the head-neck interface ranged from 2.3 to 5.7 Nm. The bending moment acting on the head-neck interface varied from 7 to 21.6 Nm. One-leg-standing had the widest range of frictional torque on the head-neck interface (11 Nm) while normal walking had the smallest range (6.1 Nm). The widest range, together with the maximum magnitude of torque, bending moment, and frictional moment, occurred during one-leg-standing of the lightest patient. Most of the simulated activities resulted in frictional torques that were near the previously reported oxide layer depassivation threshold torque. The predicted bending moments were also found at a level believed to contribute to the oxide layer depassivation. The calculated magnitudes and directions of the moments, applied directly to the head-neck taper junction, provide realistic mechanical loading data for in vitro and computational studies on the mechanical behaviour and multi-axial fretting at the head-neck interface.

Keywords: frictional moment; head-cup interface; physical activities; total hip replacement.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Head-neck taper junction of a left hip implant and femur coordinate system. The contact force P distributed over the Hertz contact area induces a tangential frictional force during the relative motion of the head and cup. The tangential force and lever arm D produce the frictional moment Mf and its projection onto the neck direction which is the frictional torque Mn.
Figure 2
Figure 2
Contact forces in the x, y, and z axes along with flexion and abduction angles for one cycle of each activity for the average patient, data from Hip98 and Orthoload [16]: (a) slow walking; (b) normal walking; (c) fast walking; (d) stair up; (e) stair down; (f) sit-to-stand; (g) stand-to-sit; (h) one leg standing and (i) knee bending.
Figure 3
Figure 3
Components of frictional moments and bending moments for six daily activities in the neck coordinate system (xyz’): (a) Frictional moments about the x’ axis; (b) Frictional moments about the y’ axis; (c) Frictional moments about the z’ axis; (d) Bending moments about the x’ axis; (e) Bending moments about the y’ axis; and (f) Coordinate system definition.
Figure 4
Figure 4
Frictional moment (Mf) and torque at the head-neck interface (Mn) for one cycle of each activity, for the average, heaviest (H), and lightest (L) patients. In the graphs, U.T and L.T indicate the upper and lower thresholds for depassivation, respectively. (a) Slow walking; (b) normal walking; (c) fast walking; (d) stair up; (e) stair down; (f) sit-to-stand; (g) stand-to-sit; (h) one leg standing and (i) knee bending.
Figure 5
Figure 5
Frictional moment (Mf) and torque at the head–neck interface (Mn) for one cycle of normal walking, for the average patient, for different head diameters of 28, 46, and 70 mm. U.T = upper threshold for depassivation and L.T = lower threshold for depassivation.

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