Polyethylene wear of dual mobility cups: a comparative analysis based on patient-specific finite element modeling

Investigation of contact behavior on a model of the dual-mobility artificial hip joint for Asians in different inner liner thicknesses

BACKGROUND

The four components that make up the current dual-mobility artificial hip joint design are the femoral head, the inner liner, the outer liner as a metal cover to prevent wear, and the acetabular cup. The acetabular cup and the outer liner were constructed of 316L stainless steel. At the same time, the inner liner was made of ultra-high-molecular-weight polyethylene (UHMWPE). As this new dual-mobility artificial hip joint has not been researched extensively, more tribological research is needed to predict wear. The thickness of the inner liner is a significant component to consider when calculating the contact pressure.

AIM

To make use of finite element analysis to gain a better understanding of the contact behavior in various inner liner thicknesses on a new model of a dual-mobility artificial hip joint, with the ultimate objective of determining the inner liner thickness that was most suitable for this particular type of dual-mobility artificial hip joint.

METHODS

In this study, the size of the femoral head was compared between two diameters (28 mm and 36 mm) and eight inner liner thicknesses ranging from 5 mm to 12 mm. Using the finite element method, the contact parameters, including the maximum contact pressure and contact area, have been evaluated in light of the Hertzian contact theory. The simulation was performed statically with dissipated energy and asymmetric behavior. The types of interaction were surface-to-surface contact and normal contact behavior.

RESULTS

The maximum contact pressures in the inner liner (UHMWPE) at a head diameter of 28 mm and 36 mm are between 3.7-13.5 MPa and 2.7-10.4 MPa, respectively. The maximum von Mises of the inner liner, outer liner, and acetabular cup are 2.4-11.4 MPa, 15.7-44.3 MPa, and 3.7-12.6 MPa, respectively, for 28 mm head. Then the maximum von Mises stresses of the 36 mm head are 1.9-8.9 MPa for the inner liner, 9.9-32.8 MPa for the outer liner, and 2.6-9.9 MPa for the acetabular cup. A head with a diameter of 28 mm should have an inner liner with a thickness of 12 mm. Whereas the head diameter was 36 mm, an inner liner thickness of 8 mm was suitable.

CONCLUSION

The contact pressures and von Mises stresses generated during this research can potentially be exploited in estimating the wear of dual-mobility artificial hip joints in general. Contact pressure and von Mises stress reduce with an increasing head diameter and inner liner's thickness. Present findings would become one of the references for orthopedic surgery for choosing suitable bearing geometric parameter of hip implant.

Running-in behavior of dual-mobility cup during the gait cycle: A finite element analysis

The running-in process is considered an essential aspect of the comprehensive wear process. The phenomenon of running-in occurs during the initial stages of wear in the prosthetic hip joint. Within the field of tribology, the running-in phenomenon of the hip joint pertains to the mechanism by which the contact surfaces of the artificial hip joint components are adjusted and a suitable lubricating film is formed. During the process of hip joint running-in, there is an interaction between the metal surface of the ball and the joint cup, which results in adjustments being made until a steady state is achieved. The achievement of desirable wear existence and reliable performance of artificial hip joint components are reliant upon the tribological running-in of the hip joint. Despite the establishment of current modeling approaches, there remains a significant lack of understanding concerning running-in wear, particularly the metal-on-polyethylene (MoP) articulations in dual-mobility cups (DMC). An essential aspect to consider is the running-in phase of the dual mobility component. The present study employed finite element analysis to investigate the running-in behavior of dual mobility cups, wherein femoral head components were matched with polyethylene liners of varying thicknesses. The analysis of the running-in phase was conducted during the normal gait cycle. The results of this investigation may be utilized to design a dual-mobility prosthetic hip joint that exhibits minimal running-in wear.

Updates on Biomaterials Used in Total Hip Arthroplasty (THA)

One of the most popular and effective orthopedic surgical interventions for treating a variety of hip diseases is total hip arthroplasty. Despite being a radical procedure that involves replacing bone and cartilaginous surfaces with biomaterials, it produces excellent outcomes that significantly increase the patient's quality of life. Patient factors and surgical technique, as well as biomaterials, play a role in prosthetic survival, with aseptic loosening (one of the most common causes of total hip arthroplasty failure) being linked to the quality of biomaterials utilized. Over the years, various biomaterials have been developed to limit the amount of wear particles generated over time by friction between the prosthetic head (metal alloys or ceramic) and the insert fixed in the acetabular component (polyethylene or ceramic). An ideal biomaterial must be biocompatible, have a low coefficient of friction, be corrosion resistant, and have great mechanical power. Comprehensive knowledge regarding what causes hip arthroplasty failure, as well as improvements in biomaterial quality and surgical technique, will influence the survivability of the prosthetic implant. The purpose of this article was to assess the benefits and drawbacks of various biomaterial and friction couples used in total hip arthroplasties by reviewing the scientific literature published over the last 10 years.

No dislocation and low complication rate for a modern dual mobility cup with pre-impacted femoral head in primary hip replacement: A consecutive series of 175 hips at minimum 5-year follow-up

INTRODUCTION

Despite its excellent results in preventing dislocation, the dual mobility cup (DMC) is still struggling to be adopted by some teams due to premature wear and loosening reported on first-generation implants. Therefore, this study aimed to assess the mid-term survivorship of a modern DMC with a pre-impacted head and the radio-clinical results at a minimum follow-up of 5 years.

METHODS

This was a retrospective single-centre study performed on patients who had a primary total hip replacement for osteoarthritis in 2016. The cup was a third-generation DMC with a pre-impacted femoral head. Clinical (harris hip score (HHS)) and radiological (cup abduction, anteversion, overhang, and radiolucent lines) results were recorded, as well as complications, particularly dislocations and survivorship. A minimum of five years of follow-ups was required.

RESULTS

One hundred and seventy-five hips (167 patients) met the inclusion criteria. Five hips (2.9%, 5/175) were lost to follow-up and excluded from the postoperative analysis. The mean follow-up period was 70 ± 2.9 months [63.6-76.5]. Three cups needed revision surgery (1.8%, 3/170): one for septic loosening, and two for chronic infection. At 77 months, the global survival probability was 98.2% ± 1, and the survival probability excluding septic aetiology was 100%. There was a significant improvement in the HHS from pre-operatively (48.3 ± 6.0 [14.0-70.0]) to post-operatively (96 ± 4.5 [50-100]) (p < 0.0001). There were no postoperative dislocations recorded, nor any iliopsoas-impingement or symptomatic cam-effect.

DISCUSSION

This study showed excellent survival and good radiological and clinical results of this dual mobility cup at a mid-term follow-up. None of the patients had dislocation or any specific complication feared with dual mobility cups.

Direct Cementation of Dual Mobility Cups Into the Bony Acetabulum in Primary Total Hip Arthroplasty: Clinical and Radiographic Outcomes at a Minimum 5-Year Follow-Up

BACKGROUND

Cemented dual mobility cups (DMCs) are commonly used in combination with acetabular reinforcement devices. Indeed, according to literature, direct cementation of metal-backed acetabular components into the bony acetabulum remains controversial as this technique is potentially associated with increased rates of aseptic loosening. Therefore, this study aimed to evaluate the clinical and radiographic outcomes of DMC cemented into the bony acetabulum in primary total hip arthroplasty (THA).

METHODS

A total of 49 THA (48 patients, mean age 78 years [range, 51 to 91]) performed with direct cementation of a DMC into the bony acetabulum were prospectively included in our total joint registry and retrospectively reviewed. The clinical outcome was assessed using the Harris hip score (HHS). The radiographic outcome included measurement of component positioning and occurrence and progression of demarcation around the cemented DMC. Complications were reported with a particular attention to cemented fixation failure and aseptic loosening.

RESULTS

At a 7-year mean follow-up (range, 5 to 8), the pre-to postoperative HHS improved from 47 (range, 30 to 58) to 92 points (range, 80 to 98) (P < .01). Nonprogressive and focalized demarcations were observed in 7 THA (14%). Importantly, no progressive demarcation or DMC aseptic loosening was observed.

CONCLUSION

Direct cementation of DMC into the bony acetabulum ensured a stable fixation with no progressive demarcation or aseptic loosening at midterm follow-up. Therefore, this technique can be selectively considered in primary THA, especially in elderly or frail patients to avoid potential mechanical failure of press-fit fixation due to altered bone quality or additional morbidity related to the use of acetabular reinforcement devices.

3D-printed hemipelvic prosthesis combined with a dual mobility bearing in patients with primary malignant neoplasm involving the acetabulum: clinical outcomes and finite element analysis

BACKGROUND

Limb salvage reconstruction for pelvic tumors, especially periacetabular tumors, is challenging. We combined the use of dual mobility bearing and 3D-printed hemipelvic prosthesis to improve function and reduce the probability of complications after hemi-pelvic resection in patients with primary acetabular malignancy. The purpose of this study was to evaluate the efficacy and safety of this combination.

METHODS

Between October 2011 and May 2021, 11 patients with malignancies involving the acetabulum received hemipelvic replacement with a 3D-printed prosthesis and dual mobility bearing. Follow-up of postoperative survival, complications, and Musculoskeletal Tumor Society 93 (MSTS-93) lower limb functional scores were carried out. A finite element model of the postoperative pelvis was developed and input into the finite element analysis software. The Von Mises equivalent stress formula was used to analyze the stress distribution of each part of the pelvis under one gait cycle and the stress distribution at different angles of the hip joint.

RESULTS

By the last follow-up, 9 of the 11 patients (81.8%) were still alive, and 2 patients had local tumor recurrence. The complications including 1 deep infection and 1 dislocation of the artificial joint. Excluding 1 amputation patient, the average score of the remaining 8 patients at the last follow-up was 21.4/30 (71.3%) on the MSTS-93. In the reconstructed pelvis, stress distributions were concentrated on the junction between hemipelvic prosthesis and screw and iliac bone on the resected side, and between femoral prosthesis stem and femoral bulb, while the stress of polyethylene lining was small. Before impact, the polyethylene lining will rotate at a small angle, about 3°. The inner stress of polyethylene liner is greater than the outer stress in all conditions. The polyethylene liner has no tendency to slide out.

CONCLUSION

Pelvic tumor resection and reconstruction using 3D-printed hemipelvic prosthesis combined with dual mobility bearing was an effective treatment for pelvic tumors. Our patients achieved good early postoperative efficacy and functional recovery. The dual mobility bearing is beneficial to prevent dislocation, and the mechanical distribution and wear of the prosthesis are acceptable.

Which femoral neck for a dual mobility cup? A biomechanical evaluation

Purpose

This study aimed to evaluate polyethylene (PE) damage and wear lesions to the chamfer of mobile components under mobile and fixed femoral neck impingement at the third articulation, and to determine which femoral neck characteristics should be considered with a dual mobility cup to limit those lesions.

Methods

Two femoral neck geometries (cylindrical and quadrangular) with two surface finishing roughness (rough and polished), and two head-to-neck ratios (28- and 22.2-mm diameter femoral heads) were evaluated in a hip simulator testing. For each characteristic, six femoral necks were tested with six dual mobility cups under fixed and mobile femoral neck impingement conditions. Chamfer PE damage and volumetric wear were evaluated and compared for each femoral neck characteristic and impingement condition.

Results

Under mobile impingement condition, femoral neck characteristics did not significantly affect PE damage and wear lesions to the chamfer (p = 0.283 to 0.810). However, under fixed impingement condition, significantly higher PE damage and wear lesions to the chamfer were produced by the quadrangular geometry compared to the cylindrical geometry (p = 0.004 to 0.025). In addition, with the quadrangular geometry, rough surface finishing was demonstrated to increase volumetric wear of the chamfer (p = 0.009). No significant influence of head-to-neck ratio was observed on PE damage and wear lesions to the chamfer (p = 0.244 to 0.714).

Discussion

This biomechanical study emphasized that femoral neck characteristics are critical with dual mobility cup and tend to favor a cylindrical geometry particularly whether fixed impingement at the third articulation occurs.