Effects of femoral head diameter on the predicted acetabular cup wear volume of CP-Ti and UHMWPE hip implants

Wear is a problem for metal on polymer (MOP) hip implants to perform lifetime endurance. Polymer excessive volumetric loss leads to implant failures. Attempts to solve this problem are usually initiated with tribological tests. The method is time-consuming because the sliding speed is low. There is a faster way to use a computational method to gather wear data. This research aims to investigate the numerical convergence of predicted wear volume with the finite element method (FEM). The model is a commercially pure titanium (cp Ti) and ultra-high molecular weight polyethylene (UHMWPE) MOP hip implant. A dynamic Paul physiological load was applied to the model. Volumetric loss of the polymer was calculated with a wear equation involved nonlinear contact load and contact area. The inputs of calculation are wear factor and the computational contact mechanic performed by FEM. The wear factor was obtained by performing biotribological experiments with a multidirectional pin on disc tribotest. Predicted wear volume was validated with hip simulator experimental data from the literature. Convergences were found at the mesh density of 1.38 elements/mm3. An acceptable numerical error was obtained in the model with 1 mm element size for femoral head and 0.3 mm for acetabular cup. This model was then used for the investigation of load increment effects. The result is that load increment variations do not affect wear volume and contact mechanic numerical outputs. The calculated stresses are below the UHMWPE yield stress limit. In this elastic region, the effects of strain rate caused by load increment are negligible.

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Robotic-Arm Assisted Total Hip Arthroplasty Results in Smaller Acetabular Cup Size in Relation to the Femoral Head Size: A Matched-Pair Controlled Study

Hip International ◽

10.5301/hipint.5000418 ◽

2017 ◽

Vol 27 (2) ◽

pp. 147-152 ◽

Cited By ~ 12

Author(s):

Carlos Suarez-Ahedo ◽

Chengcheng Gui ◽

Timothy J. Martin ◽

Sivashankar Chandrasekaran ◽

Parth Lodhia ◽

...

Keyword(s):

Femoral Head ◽

Head Size ◽

Robotic Arm ◽

Matched Pair ◽

Femoral Head Size ◽

Acetabular Cup ◽

Acetabular Bone ◽

Head Diameter ◽

Total Hip ◽

Femoral Head Diameter

Purpose To compare the acetabular component size relative to the patient's native femoral head size between conventional THA (CTHA) approach and robotic-arm assisted THA (RTHA) to infer which of these techniques preserved more acetabular bone. Methods Patients were included if they had primary osteoarthritis (OA) and underwent total hip replacement between June 2008 and March 2014. Patients were excluded if they had missing or rotated postoperative anteroposterior radiographs. RTHA patients were matched to a control group of CTHA patients, in terms of preoperative native femoral head size, age, gender, body mass index (BMI) and approach. Acetabular cup size relative to femoral head size was used as a surrogate for amount of bone resected. We compared the groups according to 2 measures describing acetabular cup diameter ( c) in relation to femoral head diameter ( f): (i) c-f, the difference between cup diameter and femoral head diameter and (ii) ( c-f)/ f, the same difference as a fraction of femoral head diameter. Results 57 matched pairs were included in each group. There were no significant differences between groups for demographic measures, femoral head diameter, or acetabular cup diameter (p>0.05). However, measures (i) and (ii) did differ significantly between the groups, with lower values in the RTHA group (p<0.02). Conclusions Using acetabular cup size relative to femoral head size as an approximate surrogate measure of acetabular bone resection may suggest greater preservation of bone stock using RTHA compared to CTHA. Further studies are needed to validate the relationship between acetabular cup size and bone loss in THA.

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