The effect of structural parameters of total hip arthroplasty on polyethylene liner wear behavior: A theoretical model analysis

Moving fluoroscopy-based analysis of THA kinematics during unrestricted activities of daily living

Introduction: Knowledge of the accurate in-vivo kinematics of total hip arthroplasty (THA) during activities of daily living can potentially improve the in-vitro or computational wear and impingement prediction of hip implants. Fluoroscopy- based techniques provide more accurate kinematics compared to skin marker-based motion capture, which is affected by the soft tissue artefact. To date, stationary fluoroscopic machines allowed the measurement of only restricted movements, or only a portion of the whole motion cycle. Methods: In this study, a moving fluoroscopic robot was used to measure the hip joint motion of 15 THA subjects during whole cycles of unrestricted activities of daily living, i.e., overground gait, stair descent, chair rise and putting on socks. Results: The retrieved hip joint motions differed from the standard patterns applied for wear testing, demonstrating that current pre-clinical wear testing procedures do not reflect the experienced in-vivo daily motions of THA. Discussion: The measured patient-specific kinematics may be used as input to in vitro and computational simulations, in order to investigate how individual motion patterns affect the predicted wear or impingement.

The midcortical-line is more reliable than the T-line in predicting stem anteversion in patients with developmental hip dysplasia after total hip arthroplasty

Background

Precise preoperative planning improves postoperative outcomes in total hip arthroplasty (THA), especially in developmental dysplasia of the hip (DDH) cases. Previous studies used the T-line and midcortical-line as preoperative landmarks to predict postoperative stem anteversion (PSA). However, the most reliable landmark in predicting PSA in DDH patients remains unclear. To find the most reliable measurement to predict the PSA in DDH patients, this study compared the midcortical-line and T-line at different femoral neck levels.

Methods

Pre- and postoperative Computed Tomography (CT) scans of 28 hips in 21 DDH patients who received THA were obtained for three-dimensional femoral models. The preoperative CT scan was used to measure the anteversion of the midcortical-line on the axial cross-sectional plane images (AM-CT), the anteversion of the midcortical-line from 3D models (AM-3D), and the T-line from 3D models (AT-3D) at simulated osteotomy planes at 5 and 10 mm heights proximal to the base of the lesser trochanter. The correlation between the preoperative femoral anteversion (AM-CT, AM-3D, AT-3D) and the PSA was assessed to evaluate the prediction accuracy.

Results

The correlations between the AM-CT and the PSA were 0.86 (mean difference (MD) = 1.9°) and 0.92 (MD = −3.0°) at 5 and 10 mm heights, respectively. The correlation between the AM-3D and the PSA were 0.71 (MD = −11.6°) and 0.61 (MD = −12.9°) at 5 and 10 mm heights. The AT-3D was significantly greater (MD = 15.4°) than the PSA (p-value <0.01) at 5 mm cutting height, and the correlation between the AT-3D and the PSA was 0.57 (MD = 7.8°) at 10 mm cutting height.

Conclusions

The AM-CT at the 10 mm height had the strongest correlation with the PSA and was more reliable in predicting the PSA when compared with the AM-3D and the AT-3D in DDH patients.

To what extent could the acetabular liner thickness be reduced yet remaining tribologically acceptable in metal-on-vitamin E-diffused crosslinked polyethylene hip arthroplasty?

The aim of the present study was to evaluate how much reduction in acetabular liner thickness could be tribologically acceptable in metal-on-vitamin-E diffused highly crosslinked ultra-high molecular weight polyethylene (Vit-E XLPE) bearings for total hip arthroplasty. We tested thick- (10.3 mm), moderate- (6.3 mm), and thin- (4.3 mm) Vit-E XLPE liners coupled with 28-mm cobalt-chromium femoral heads on a hip simulator to 5 million cycles, and peak contact stress was predicted based on mathematical modeling. Wear damage was also evaluated in terms of surface topology and morphology. Wear simulation demonstrated that the 2-4 mm thickness reduction (6.3 → 4.3 mm and 10.3 → 6.3 mm) did not significantly affect the wear rate for Vit-E XLPE liner, whereas 6-mm reduction (10.3 → 4.3 mm) significantly increased liner wear (by 309%) and head roughness (by 415%). This effect was attributed to a contact stress increase (by 24-41%). However, the wear rates for all thicknesses tested were much lower than those previously reported for thicker non-crosslinked materials. The original crystalline morphology was maintained in all liners after wear. Our results suggest that the 2-4 mm thickness reduction may be tribologically acceptable in Vit-E XLPE liners. However, more severe and longer term simulations are necessary to determine a minimum acceptable thickness.

A review of advances in tribology in 2020–2021

Around 1,000 peer-reviewed papers were selected from 3,450 articles published during 2020–2021, and reviewed as the representative advances in tribology research worldwide. The survey highlights the development in lubrication, wear and surface engineering, biotribology, high temperature tribology, and computational tribology, providing a show window of the achievements of recent fundamental and application researches in the field of tribology.

Outcomes of Ceramic Composite in Total Hip Replacement Bearings: A Single-Center Series

Despite the fact that total hip replacement is one of the most successful surgical procedures for treatment of a variety of end-stage hip diseases, the process of osteolysis and implant loosening remains a significant problem, especially in young and high-demand patients. More than 40 years ago, ceramic bearings were introduced due to their mechanical advantage in order to obtain a reduction in wear debris, and due to the conviction that it was possible to minimize friction and wear owing to their mechanical hardness, high chemical stability, surface lubrication by fluids and low friction coefficient. Together with excellent mechanical properties, ceramics have a biological inertness: eventual ceramic debris will lead to a reactive response with a high predominance of fibrocystic cells, rather than macrophagic cells, and absence of giant cells, which is ideal from a biological perspective. As a consequence, they will not trigger the granulomatous reaction necessary to induce periprosthetic osteolysis, and this clearly appears to be of great clinical relevance. In recent years, tribology in manufacturing ceramic components has progressed with significant improvements, owing to the development of the latest generation of ceramic composites that allow for an increased material density and reduced grain size. Currently, ceramic-on-ceramic bearings are considered the attractive counterparts of ceramic- or metal-on-polyethylene ones for patients with a long life expectancy. The aim of this paper is to report the results of total hip replacements performed with a ceramic-on-ceramic articulation made from a ceramic composite in a single center, focusing on its usefulness in specific preoperative diagnosis.

Analysis of the Risk of Wear on Cemented and Uncemented Polyethylene Liners According to Different Variables in Hip Arthroplasty

Wear debris in total hip arthroplasty is one of the main causes of loosening and failure, and the optimal acetabular fixation for primary total hip arthroplasty is still controversial because there is no significant difference between cemented and uncemented types for long-term clinical and functional outcome. To assess and predict, from a theoretical viewpoint, the risk of wear with two types of polyethylene liners, cemented and uncemented, a simulation using the finite element (FE) method was carried out. The risk of wear was analyzed according to different variables: the polyethylene acetabular component’s position with respect to the center of rotation of the hip; the thickness of the polyethylene insert; the material of the femoral head; and the relationship of the cervical–diaphyseal morphology of the proximal end of the femur to the restoration of the femoral offset. In all 72 simulations studied, a difference was observed in favour of a cemented solution with respect to the risk of wear. With regard to the other variables, the acetabular fixation, the thickness of the polyethylene, and the acetabular component positioning were statistically significant. The highest values for the risk of wear corresponded to a smaller thickness (5.3 mm), and super-lateral positioning at 25 mm reached the highest value of the von Mises stress. According to our results, for the reconstruction of the acetabular side, a cemented insert with a thickness of at least 5 mm should be used at the center of rotation.

Total hip arthroplasty for dysplastic coxarthrosis using a cementless Wagner Cone stem

Background

Total hip arthroplasty (THA) is currently the best surgical option for hip osteoarthritis secondary to developmental hip dysplasia (DDH); it may be extremely challenging, because of the hypoplasic proximal metaphysis, pathological anteversion, and excessive cervico-diaphyseal angle of the neck at the femoral side. The purpose of this retrospective study was to evaluate the long-term survival and clinical and radiological results of Conus uncemented stems, implanted in patients affected by hip osteoarthritis with Crowe not-type IV secondary to DDH.

Material and methods

We identified 100 consecutive THAs performed for DDH in 63 women and 24 men, with an average age of 53 years in a single center. Thirteen patients underwent bilateral hip replacement. The patients’ mean body mass index was 29.8 kg/m² (range 27.1–35.6 kg/m²). The main indications for surgery were severe hip pain and considerable functional impairment: the preoperative Harris Hip Score was 29.5 on average (range 22–61). Radiologically, 8 hips were classified as Crowe I, 43 hips as Crowe II, and 49 hips as Crowe III. In all cases, we implanted the Wagner femoral cone prosthesis using the direct lateral approach; in the attempt to reestablish native hip biomechanics, 66 stems were 135° and 34 were 125°.

Results

The mean follow-up of the study was 11.7 years (range 2.2–21.8 years). Harris Hip Score increased to a mean value of 71.5 points (range 52–93 points). Radiographic evaluation demonstrated osteointegration of the implant with stable bone growth observed at the stem–endosteum interface; signs of bone readaptation and thinning of the femoral calcar were present in nine hips. None of the patients underwent revision for septic or aseptic loosening of the stem; none sustained a periprosthetic fracture.

Conclusions

This study confirms the theoretical advantages that suggest the choice of the Wagner cone when technical difficulties during prosthetic surgery are expected owing to abnormal proximal femoral anatomy.

Level of evidence

Level IV, retrospective case study