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THE CUP OUTER DIAMETER INFLUENCES THE CEMENT FIXATION OF CHARNLEY TOTAL HIP REPLACEMENT
S82
Presentation 1749 − Topic 10. Biotribology
THE CUP OUTER DIAMETER INFLUENCES THE CEMENT FIXATION OF CHARNLEY TOTAL HIP REPLACEMENT Xijin Hua (1), BM Wroblewski (2), Ling Wang (1), Zhongmin Jin (1,3), John Fisher (1)
1. University of Leeds, Leeds, UK; 2. Wrightington Hospital, Wigan, UK 3. Xi’an Jiaotong University, Xi’an, China
Introduction Clinical studies have shown that under similar conditions, a cup with outer diameter of 43 mm has smaller chance of aseptic loosening with increasing penetration depth compared to that of 40 mm. This is attributed to the lower friction torque with larger outer diameter of the acetabular cup. [Wroblewski, 2009]. However, no quantitative analysis has been conducted and whether other factors, such as the wear at the bearing surfaces or the mechanical actions at the bone-cement interface [Coultrup, 2010], will contribute to it should be recognized.
between the two cup designs was neglectable (less than 5%) (Figure 2a). However, the predicted maximum von Mises stress in the cement mantle near the bone-cement interface for the 40 mm outer diameter cup was higher compared with that of the 43 mm diameter component, the difference was predicted to be ~13-18% (Figure 2b). 18
10
a) 16 P (M14 er us 12 se rp 10 tc at 8 n 6 co xa 4 M2
a) P 8 (M se si 6 M n o V4 xa M
Outer diameter 40 mm
0
Methods
1
2
3
Penetration (mm)
Fully constraint at sacroiliac joint
Pelvic bone Cement mantle UHMWPE cup
Fully constraint at Pubic symphysis
Femoral head
Loading
Figure 1: The geometry and FE model of the THR
4
0
1
2
3
4
Penetration (mm)
(a) (b) Figure 2: The predicted maximum stress (MPa) as a function of penetration depth with cup outer diameter of 40 mm and 43 mm: (a) the contact stress at bearing surfaces, (b) the von Mises stress in cement mantle near the bone-cement interface
Discussion Under all conditions considered, similar tribological characteristics were predicted at the bearing surfaces between the 40 mm and 43 mm hip prostheses. This implies that wear is not the major contribution factor to the difference of aseptic loosening incidence between 40 mm and 43 mm diameter cup of Charnley THR observed clinically. It is interesting to note that the difference of predicted von Mises stress in the cement mantle at the bone-cement interface between the two cup designs (~13-18%) are comparable to the clinical findings from Wroblewski et al. [Wroblewski, 2009] who reported a difference of aseptic loosening incidence of ~20%. As recent studies have shown that high stress at the bone-cement interface would cause the failure of cement mantle and the loosening of acetabular cup [Coultrup, 2010], This implies that besides the friction torque, the difference of stress amplification in the cement mantle between the two cup designs is also responsible for the different incidence of aseptic loosening observed clinically.
Reference
Results At the same level of penetration depth, the discrepancy of the predicted contact pressure Journal of Biomechanics 45(S1)
Outer diameter 43 mm
0 0
A typical Charnley hip prosthesis with a head diameter of 22.225 mm and cup inner diameter of 22.59 mm was examined. Two cup designs with outer diameter of 40 mm and 43 mm were considered. The thickness of bone cement was selected as 2 mm. Different linear penetration depth of 1, 2, 4 mm were considered respectively. Three-dimensional finite element models were developed to simulate the position of both the head and the cup implanted into a hemi-pelvic hip joint model (Figure 1). All the materials were modelled as homogeneous, isotropic and linear elastic, except the UHMWPE which was modelled as nonlinear elastic-plastic. Frictionless contact were used at the bearing surfaces. The bone-cement and cementimplant interfaces were assumed to be fully bonded. A fixed contact force of 2500 N, 10 º medially, was applied through the center of the femoral head [Bergmann, 2001]. Nodes at the sacroiliac joint and pubic symphysis were fully constrained. The finite element models formulated were solved using ABAQUS (Version 6.9, Abaqus Inc.).
Outer diameter 40 mm
2
Outer diameter 43 mm
Wroblewski et al, JBJS [Br], 91-B: 855-858, 2009. Coultrup et al, J Orthop Res, 28: 565-570, 2010. Bergmann et al, J Biomech, 34:859-71, 2001.
ESB2012: 18th Congress of the European Society of Biomechanics
Presentation 1749 − Topic 10. Biotribology
THE CUP OUTER DIAMETER INFLUENCES THE CEMENT FIXATION OF CHARNLEY TOTAL HIP REPLACEMENT Xijin Hua (1), BM Wroblewski (2), Ling Wang (1), Zhongmin Jin (1,3), John Fisher (1)
1. University of Leeds, Leeds, UK; 2. Wrightington Hospital, Wigan, UK 3. Xi’an Jiaotong University, Xi’an, China
Introduction Clinical studies have shown that under similar conditions, a cup with outer diameter of 43 mm has smaller chance of aseptic loosening with increasing penetration depth compared to that of 40 mm. This is attributed to the lower friction torque with larger outer diameter of the acetabular cup. [Wroblewski, 2009]. However, no quantitative analysis has been conducted and whether other factors, such as the wear at the bearing surfaces or the mechanical actions at the bone-cement interface [Coultrup, 2010], will contribute to it should be recognized.
between the two cup designs was neglectable (less than 5%) (Figure 2a). However, the predicted maximum von Mises stress in the cement mantle near the bone-cement interface for the 40 mm outer diameter cup was higher compared with that of the 43 mm diameter component, the difference was predicted to be ~13-18% (Figure 2b). 18
10
a) 16 P (M14 er us 12 se rp 10 tc at 8 n 6 co xa 4 M2
a) P 8 (M se si 6 M n o V4 xa M
Outer diameter 40 mm
0
Methods
1
2
3
Penetration (mm)
Fully constraint at sacroiliac joint
Pelvic bone Cement mantle UHMWPE cup
Fully constraint at Pubic symphysis
Femoral head
Loading
Figure 1: The geometry and FE model of the THR
4
0
1
2
3
4
Penetration (mm)
(a) (b) Figure 2: The predicted maximum stress (MPa) as a function of penetration depth with cup outer diameter of 40 mm and 43 mm: (a) the contact stress at bearing surfaces, (b) the von Mises stress in cement mantle near the bone-cement interface
Discussion Under all conditions considered, similar tribological characteristics were predicted at the bearing surfaces between the 40 mm and 43 mm hip prostheses. This implies that wear is not the major contribution factor to the difference of aseptic loosening incidence between 40 mm and 43 mm diameter cup of Charnley THR observed clinically. It is interesting to note that the difference of predicted von Mises stress in the cement mantle at the bone-cement interface between the two cup designs (~13-18%) are comparable to the clinical findings from Wroblewski et al. [Wroblewski, 2009] who reported a difference of aseptic loosening incidence of ~20%. As recent studies have shown that high stress at the bone-cement interface would cause the failure of cement mantle and the loosening of acetabular cup [Coultrup, 2010], This implies that besides the friction torque, the difference of stress amplification in the cement mantle between the two cup designs is also responsible for the different incidence of aseptic loosening observed clinically.
Reference
Results At the same level of penetration depth, the discrepancy of the predicted contact pressure Journal of Biomechanics 45(S1)
Outer diameter 43 mm
0 0
A typical Charnley hip prosthesis with a head diameter of 22.225 mm and cup inner diameter of 22.59 mm was examined. Two cup designs with outer diameter of 40 mm and 43 mm were considered. The thickness of bone cement was selected as 2 mm. Different linear penetration depth of 1, 2, 4 mm were considered respectively. Three-dimensional finite element models were developed to simulate the position of both the head and the cup implanted into a hemi-pelvic hip joint model (Figure 1). All the materials were modelled as homogeneous, isotropic and linear elastic, except the UHMWPE which was modelled as nonlinear elastic-plastic. Frictionless contact were used at the bearing surfaces. The bone-cement and cementimplant interfaces were assumed to be fully bonded. A fixed contact force of 2500 N, 10 º medially, was applied through the center of the femoral head [Bergmann, 2001]. Nodes at the sacroiliac joint and pubic symphysis were fully constrained. The finite element models formulated were solved using ABAQUS (Version 6.9, Abaqus Inc.).
Outer diameter 40 mm
2
Outer diameter 43 mm
Wroblewski et al, JBJS [Br], 91-B: 855-858, 2009. Coultrup et al, J Orthop Res, 28: 565-570, 2010. Bergmann et al, J Biomech, 34:859-71, 2001.
ESB2012: 18th Congress of the European Society of Biomechanics