The effect of geometry and abduction angle on the stresses in cemented UHMWPE acetabular cups--finite element simulations and experimental tests

Accuracy of cup placement compared with preoperative surgeon targets in primary total hip arthroplasty using standard instrumentation and techniques: a global, multicenter study

BACKGROUND

Acetabular cup positioning in total hip arthroplasty (THA) is closely related to outcomes. The literature has suggested cup parameters defined by the Lewinnek safe zone; however, the validity of such measures is in question. Several studies have raised concerns about the benefits of using the Lewinnek safe zone as a predictor of success. In this study we elected to use prospective surgeon targets as the basis for comparison to see how successful surgeons are positioning their cup using standard instruments and techniques.

METHODS

A prospective, global, multicenter study was conducted. Cup positioning success was defined as a composite endpoint. Both cup inclination and version needed to be within 10° of the surgeon target to be considered a success. Radiographic analysis was conducted by a third-party reviewer.

RESULTS

In 170 subjects, inclination, target versus actual, was 44.8° [standard deviation (SD 0.9°)] and 43.1° (SD 7.6°), respectively (p = 0.0029). Inclination was considered successful in 84.1% of cases. Mean version, target versus actual, was 19.4° (SD 3.9°) and 27.2° (SD 5.6°), respectively (p < 0.0001). Version was considered successful in 63.4% of cases, and combined position (inclination and version) was considered successful in 53.1%.

CONCLUSION

This study shows that with traditional methods of placing the cup intraoperatively, surgeons are only accurate 53.1% of the time compared with a predicted preoperative plan. This study suggests that the inconsistency in cup positioning based on the surgeon's planned target is potentially another important variable to consider while using a mechanical guide or in freehand techniques for cup placement in THA.

TRIAL REGISTRATION

This study is registered on ClinicalTrials.gov, NCT03189303.

Wear of a Highly Cross-Linked Polyethylene Liner of the Acetabular Component Placed With Excessive Acetabular Inclination

Few studies have investigated the influence of excessive acetabular inclination during total hip arthroplasty (THA) on the wear of highly cross-linked polyethylene (HXLPE). The goal of this study was to determine whether excessive acetabular inclination during THA causes prominent wear of the HXLPE liner. We retrospectively evaluated 62 hips of 54 women and 8 men who underwent primary THA with an HXLPE liner between January 2006 and September 2011. Postoperative anteroposterior pelvic radiographs were used to measure acetabular inclination and analyze polyethylene wear. Patients were divided into the following groups: the excessive acetabular inclination group (acetabular inclination angle ≥50°; n=20) and the control group (acetabular inclination angle <50°; n=42). Clinical information and imaging findings were compared and examined between the 2 groups. Further, we evaluated the correlation between the acetabular inclination angle and the polyethylene wear rate. In all cases, mean follow-up duration was 6.3 years. The annual liner wear was 0.00446 and 0.0254 mm/y in the control and excessive acetabular inclination groups, respectively. The excessive acetabular inclination group had significantly higher polyethylene liner wear compared with the control group (P=.00991). A weak correlation was seen between acetabular inclination angle and polyethylene wear rate in all cases (Spearman's rank correlation, r=0.283, P=.0258). Excessive acetabular inclination may increase HXLPE liner wear in the long term. [Orthopedics. 2022;45(2):e96-e100.].

Radiographic results on acetabular cup placement with the SuperPath technique: a retrospective study of 756 cases

Background

The Supercapsular percutaneously assisted total hip (SuperPath) technique is a relatively new minimally invasive approach for total hip arthroplasty (THA). Good clinical outcomes related to its use are reported in the literature. Nonetheless, there are still uncertainties about its validity in terms of radiographic outcomes.

Main purpose of the study is to evaluate the effectiveness of the SuperPath in acetabular cup positioning through radiographic evaluation of acetabular inclination angle (IA) and acetabular anteversion (AA) angle within the safe zone described by Lewinnek. The leg length discrepancy (LLD), femoral offset (FO), and acetabular offset (AO) were also measured to ascertain the radiographic effectiveness of SuperPath in the acetabular cup placement.

Methods

Between January 2016 and December 2019, all SuperPath cases eligible for the study were included. They were operated by three orthopaedic surgeons with long-standing experience in THA via conventional posterolateral approach and who have performed SuperPath training fellowship. The Mann-Whitney U test was used for statistical assessments (p-value < 0.05). Means ± standard deviation (SD) of the radiographic IA and AA were calculated for each year.

Results

A retrospective analysis of 756 THAs was performed. The average percentage of IA within the Lewinnek’s safe zone was from 80 to 85%, while the average percentage of AA was from 76 to 79%. Both IA and AA showed no statistically significant difference between two consecutive years. Good results, in the ranges of normal values, were also obtained for LLD, FO and AO, with homogeneous outcomes between 1 year and the following one.

Conclusion

It is possible to achieve good radiographic values of acetabular cup orientation through the SuperPath within the Lewinnek’s safe zone. These results are similar to those reported in the literature by authors using SuperPath. Low rate (0,3%) of hip dislocations were reported. Therefore, the SuperPath technique represents a good alternative THA approach. Nevertheless, there is not a statistically significant improvement in these radiographic parameters over a four-year time.

Level of evidence

Level IV, retrospective study.

Femoral Stem Cementation in Hip Arthroplasty: The Know-How of a "Lost" Art

PURPOSE OF REVIEW

To describe the (1) indications, (2) preoperative precautions, and (3) stepwise technical details of modern femoral stem cemented fixation.

RECENT FINDINGS

Femoral stem cementation provides excellent implant longevity with a low periprosthetic fracture rate among patients with compromised bone quality or aberrant anatomy. Unfamiliarity with the details of modern cementation techniques among trainees who may lack frequent exposure to cementing femoral stems may preclude them from offering this viable option to suitable patients in later stages of their careers. As such, maximizing benefit from cemented femoral stem fixation among suitable candidates is contingent upon the meticulous use of modern cementation techniques. In addition to proper patient selection, modern cementation techniques emphasize the use of (1) pulsatile lavage of the femoral canal, (2) utilization of epinephrine-soaked swabs, (3) vacuum cement mixing, (4) retrograde cement introduction, (5) cement pressurization, and (6) the use of stem centralizers. Furthermore, identifying and optimizing the preoperative status of at-risk patients with pre-existing cardiopulmonary compromise, in addition to intraoperative vigilance, are essential for mitigating the risk of developing bone cement implantation syndrome. Further research is required to assess the utility of cemented femoral stem fixation among younger patients.

Finite Element Analysis to Probe the Influence of Acetabular Shell Design, Liner Material, and Subject Parameters on Biomechanical Response in Periprosthetic Bone

The implant stability and biomechanical response of periprosthetic bone in acetabulum around total hip joint replacement (THR) devices depend on a host of parameters, including design of articulating materials, gait cycle and subject parameters. In this study, the impact of shell design (conventional, finned, spiked, and combined design) and liner material on the biomechanical response of periprosthetic bone has been analyzed using finite element (FE) method. Two different liner materials: high density polyethylene-20% hydroxyapatite-20% alumina (HDPE-20%HA-20%Al2O3) and highly cross-linked ultrahigh molecular weight polyethylene (HC-UHMWPE) were used. The subject parameters included bone condition and bodyweight. Physiologically relevant load cases of a gait cycle were considered. The deviation of mechanical condition of the periprosthetic bone due to implantation was least for the finned shell design. No significant deviation was observed at the bone region adjacent to the spikes and the fins. This study recommends the use of the finned design, particularly for weaker bone conditions. For stronger bones, the combined design may also be recommended for higher stability. The use of HC-UHMWPE liner was found to be better for convensional shell design. However, similar biomechanical response was captured in our FE analysis for both the liner materials in case of other shell designs. Overall, the study establishes the biomechanical response of periprosthetic bone in the acetabular with preclinically tested liner materials together with new shell design for different subject conditions.

Finite element analysis of polyethylene wear in total hip replacement: A literature review

Evaluation and prediction of wear play a key role in product design and material selection of total hip replacements, because wear debris is one of the main causes of loosening and failure. Multifactorial clinical or laboratory studies are high cost and require unfeasible timeframes for implant development. Simulation using finite element methods is an efficient and inexpensive alternative to predict wear and pre-screen various parameters. This article presents a comprehensive literature review of the state-of-the-art finite element modelling techniques that have been applied to evaluate wear in polyethylene hip replacement components. A number of knowledge gaps are identified including the need to develop appropriate wear coefficients and the analysis of daily living activities.

A Fully Functional Drug-Eluting Joint Implant

Despite advances in orthopedic materials, the development of drug-eluting bone and joint implants that can sustain the delivery of the drug and maintain the necessary mechanical strength in order to withstand loading has remained elusive. Here, we demonstrate that modifying the eccentricity of drug clusters and the percolation threshold in ultrahigh molecular weight polyethylene (UHMWPE) results in maximized drug elution and in the retention of mechanical strength. The optimized UHMWPE eluted antibiotic at a higher concentration for longer than the clinical gold standard antibiotic-eluting bone cement while retaining the mechanical and wear properties of clinically used UHMWPE joint prostheses. Treatment of lapine knees infected with Staphylococcus aureus with the antibiotic-eluting UHMWPE led to complete bacterial eradication and to the absence of detectable systemic effects. We argue that the antibiotic-eluting UHMWPE joint implant is a promising candidate for clinical trials.

Fifteen-Year Comparison of Wear and Osteolysis Analysis for Cross-Linked or Conventional Polyethylene in Cementless Total Hip Arthroplasty for Hip Dysplasia-A Retrospective Cohort Study

BACKGROUND

Cross-linked polyethylene (XLPE) acetabular liners used in cementless total hip arthroplasty (THA) have demonstrated better wear resistance at 10 years compared with conventional polyethylene (CPE) liners. No clinical studies have compared XPLE to CPE liners beyond 10 years.

METHODS

We performed a 15-year retrospective cohort study on cementless THA performed in patients with developmental hip dysplasia to measure the differences in polyethylene wear rates and the presence of osteolysis. Twenty-four THAs with XLPE and 17 THAs with CPE were evaluated. The mean age of patients was 55.9 years (41-68) in the XLPE group and 54.4 years (40-67) in the CPE group. The mean follow-up period was 15.1 years (13.9-16.1) in the XLPE group and 15.2 years (14.5-16.0) in the CPE group.

RESULTS

The XLPE group had a significantly lower wear rate at 5 and 10 years compared with the CPE group; however, no significant difference was found at 15 years (XLPE group, 0.040 mm/y; CPE group, 0.034 mm/y). In addition, the incidence of osteolysis did not differ significantly between the groups. However, the incidence of excessive wear between 10 and 15 years after surgery in the XLPE group was significantly higher than that in the CPE group.

CONCLUSION

XLPE demonstrated no advantage in the wear rate or the incidence of osteolysis at 15 years, despite having superior wear resistance up to 10 years. It is concerning that the incidence of excessive wear was higher in the XLPE group between 10 and 15 years, and this finding should alert the arthroplasty community to this possible problem with the more highly cross-linked polyethylene.

Patient-specific hip geometry has greater effect on THA wear than femoral head size

In vivo linear penetration in total hip arthroplasty (THA) exhibits similar values for 28mm and 32mm femoral head diameter with considerable variations between and within the studies. It indicates factors other than femoral head diameter influence polyethylene wear. This study is intended to test the effect of patient׳s individual geometry of musculoskeletal system, acetabular cup orientation, and radius of femoral head on wear. Variation in patient׳s musculoskeletal geometry and acetabular cup placement is evaluated in two groups of patients implanted with 28mm and 32mm THA heads. Linear wear rate estimated by mathematical model is 0.165-0.185mm/year and 0.157-0.205mm/year for 28 and 32mm THA heads, respectively. Simulations show little influence femoral head size has on the estimated annual wear rate. Predicted annual linear wear depends mostly on the abduction angle of the acetabular cup and individual geometry of the musculoskeletal system of the hip, with the latter having the greatest affect on variation in linear wear rate.

The study of wear behaviors on abducted hip joint prostheses by an alternate finite element approach

An acetabular cup with larger abduction angles is able to affect the normal function of the cup seriously that may cause early failure of the total hip replacement (THR). Complexity of the finite element (FE) simulation in the wear analysis of the THR is usually concerned with the contact status, the computational effort, and the possible divergence of results, which become more difficult on THRs with larger cup abduction angles. In the study, we propose a FE approach with contact transformation that offers less computational effort. Related procedures, such as Lagrangian Multiplier, partitioned matrix inversion, detection of contact forces, continuity of contact surface, nodal area estimation, etc. are explained in this report. Through the transformed methodology, the computer round-off error is tremendously reduced and the embedded repetitive procedure can be processed precisely and quickly. Here, wear behaviors of THR with various abduction angles are investigated. The most commonly used combination, i.e., metal-on-polyethylene, is adopted in the current study where a cobalt-chromium femoral head is paired with an Ultra High Molecular Weight Polyethylene (UHMWPE) cup. In all illustrations, wear coefficients are estimated by self-averaging strategy with available experimental datum reported elsewhere. The results reveal that the THR with larger abduction angles may produce deeper depth of wear but the volume of wear presents an opposite tendency; these results are comparable with clinical and experimental reports. The current approach can be widely applied easily to fields such as the study of the wear behaviors on ante-version, impingement, and time-dependent behaviors of prostheses etc.

Quantification of clearance and creep in acetabular wear measurements

BACKGROUND

This study aimed to measure femoral head penetration before occurrence of real wear, and to quantify the portions attributable respectively to clearance and plastic deformations in various acetabular designs.

METHODS

We analyzed CT scans from 15 patients at 'day five' after total hip arthroplasty (THA). All patients received Exafit(®) femoral stems and 28 mm heads: 5 patients had cemented Durasul(®) all-PE cups, 5 patients had un-cemented Allofit(®) metal-backed cups, and 5 patients had un-cemented Stafit(®) dual-mobility cups. We also analyzed CT scans of samples of the three head-cup combinations to compare in vivo and in vitro measurements.

RESULTS

The mean femoral head penetration measured on 'day five' was lower for all-PE cups (0.196 mm) than for metal-backed cups (0.551 mm) and dual-mobility cups (0.634 mm).

CONCLUSIONS

The present study indicates that isolated measurements of femoral head penetration include 0.15-0.46 mm of radial clearance and 0.05-0.27 mm of creep, and confirms that the majority of so-called bedding-in observed in the first post-operative months is not entirely due to wear.

The investigation of nanotribology of UHMWPE in fluid using atomic force microscopy

The fundamental understanding of the nanowear behavior of ultrahigh molecular weight polyethylene (UHMWPE) at a nanometer scale needs to be achieved to provide a better understanding of the initiating wear process and the potential causes of the wear particles generation of joint replacement. A nanotribology study was performed using atomic force microscope (AFM) tips sliding against UHMWPE surfaces in both water and bovine serum lubricants. Frictional properties of the nanocontact, and the geometry and mechanical features of the resulting scratches have been quantitatively characterized using AFM lateral force and PeakForce QNM modes. The results in this work indicated that the friction force and friction coefficient were smaller in serum lubricant than that in water. A normal load of 120 nN was the transition point for the plastic deformation of the material. The plastic deformation and material accumulation evolute with the increase of applied normal loads. Material pileup formed at the edges of the scratch, but they were not symmetrical due to the asymmetrical geometry of the silicon AFM tip. The height of the material pileup on the right side was approximately 40-70% of the pileup on the left side. The information may be useful for developing strategies for surface finishing techniques, which can control and minimize the production of asymmetric asperity and the resulting pileup with particular features. Furthermore, the moduli of the pileups were much larger than that of the fresh UHMWPE, which had the moduli greater than those of the inner scratch area. This suggested that stress concentration at these points could cause the pileup to be more susceptible to further wear processes, and eventually result in detaching from the bulk material.

Generation of mineral density distribution maps from subject-specific models of mandibles - a preliminary study

BACKGROUND

Determination of the mineral content of bone and its distribution by computed tomography (CT) enables one to define the insertion points for prosthetic devices, or determine the degree of healing in cases of fracture or surgical intervention. The use of subject-specific models allows mapping of the spatial structure and the mineral content of the bone graphically and quantitatively.

METHODS

Subject-specific models and mineral density maps from pig jaws were developed using segmentation, transcription tools and finite element analysis software. This study considered six frozen heads from pigs aged 10-12 months, and phantom solutions of K(2) HPO(4) . The predicted bone mass of each jaw was compared with its respective ash mass after incineration.

RESULTS

The tridimensional maps show highest density values at the molar cusp and within the symphysis. The average percentage error relative to the mineral density maps was -18.4%. The radiation dose was reduced by a factor of eight from the recommended maximum without compromising the precision of the models.

CONCLUSIONS

The computed tridimensional mineral density maps illustrate, numerically and graphically, the spatial distribution of the density field within the mandibular bone. These maps could facilitate the location of insertion points or determine the evolution of the mineralization level of a patient's bone tissue.

The influence of acetabular inclination angle on the penetration of polyethylene and migration of the acetabular component

In this prospective study we studied the effect of the inclination angle of the acetabular component on polyethylene wear and component migration in cemented acetabular sockets using radiostereometric analysis.

A total of 120 patients received either a cemented Reflection All-Poly ultra-high-molecular-weight polyethylene or a cemented Reflection All-Poly highly cross-linked polyethylene acetabular component, combined with either cobalt–chrome or Oxinium femoral heads. Femoral head penetration and migration of the acetabular component were assessed with repeated radiostereometric analysis for two years. The inclination angle was measured on a standard post-operative anteroposterior pelvic radiograph. Linear regression analysis was used to determine the relationship between the inclination angle and femoral head penetration and migration of the acetabular component.

We found no relationship between the inclination angle and penetration of the femoral head at two years’ follow-up (p = 0.9). Similarly, our data failed to reveal any statistically significant correlation between inclination angle and migration of these cemented acetabular components (p = 0.07 to p = 0.9).

Load dispersion effects of acetabular reinforcement devices used in revision total hip arthroplasty: a simulation study using finite element analysis

Several types of acetabular reinforcement devices are used to prevent the collapse of grafted bone in revision total hip arthroplasty. However, it remains unclear how the stress is reduced by different devices. We used finite element analysis to evaluate 4 types of acetabular reinforcement devices: Kerboull-type device, Burch-Schneider anti-protrusio cage, Mueller ring, and Ganz ring. The control was a socket fixed with bone cement without any reinforcement devices. The stress distribution on the inner surface of each socket was calculated by binarization image processing. For all 4 reinforcement devices, the stress was reduced to less than one-half of that in the control. All the devices were useful for preventing the collapse of bulk bone grafts applied to load-bearing defects.

In vitro evaluation of stiffness graded artificial hip joint femur head in terms of joint stresses distributions and dimensions: finite element study

The aim of the present work is to evaluate the artificial hip joint femur head that is made of Stiffness Graded (SG) material in terms of joint stresses distributions and dimensions. In this study, 3D finite element models of femur head that is made of SG material and traditional femur heads made of Stainless Steel (SS), Cobalt Chromium alloy (Co Cr Mo) and Titanium alloy (Ti) have been developed using the ANSYS Code. The effects on the total artificial hip joint system stresses due to using the proposed SG material femur head (with low stiffness at the outer surface and high stiffness at its core) have been investigated. Also, the effects on the polymeric cup contact stresses due to the use of different sizes of femur heads, presence of metal backing shell and presence of radial clearance (gap) between cup and femur head have been investigated. The finite element results showed that using SG femur head resulted in a significant reduction in the cup contact stresses even for small femur heads compared with Ti alloy, SS and Co Cr Mo femur heads. The presence of radial clearance resulted in significant increase in the cup stresses especially for small femur heads. Finally, the presence of SS metal backing shell resulted in slight increase in the hip joint stresses especially for small femur head joints. This work analyzes successfully the usage of proposed SG material as femur head in order to reduce the predicted stresses at the total hip joint replacement due to the redistribution of strain energy in the hip prostheses. Therefore, the present results suggest that minor changes in design and geometrical parameters of the hip joint have significant consequences on the long term use of the joint and should be taken into consideration during the design of the hip joint.

Does acetabular inclination angle affect survivorship of alumina-ceramic articulations?

BACKGROUND

Reports in the literature have linked high acetabular inclination angles to increased wear of ceramic-on-ceramic bearings. However, many of these studies were only conducted in vitro and did not address the clinical relevance of such findings.

QUESTIONS/PURPOSES

We therefore determined: (1) whether the cup inclination angle influences survival or function in patients with ceramic-on-ceramic implants; (2) the incidence of radiolucencies, osteolysis, and subsidence of ceramic-on-ceramic implants; and (3) whether the survival rate higher for ceramic-on-ceramic THAs than for conventional metal-on-polyethylene THAs.

METHODS

We retrospectively reviewed 537 THAs performed in 512 prospectively followed patients having THA between October 1996 and October 2000. Eleven patients (12 hips) were lost to followup before 2 years, leaving 501 patients (525 THAs); of these, 421 were alumina ceramic-on-ceramic articulations and 104 cobalt-chromium-on-polyethylene. The mean age was 54 years. We determined acetabular cup inclination angles, Harris hip scores, Health-Status-Questionnaire-12 scores, and presence and location of any radiolucencies, osteolysis, or radiographic subsidence. We compared survival using the Kaplan-Meier method. The minimum followup was 24 months (mean, 59 months; range, 24-120 months).

RESULTS

Twenty-two of the 424 THAs (4.2%) were revised. We observed no difference in clinical or radiographic outcomes with respect to cup inclination angles. Radiographically, two loose acetabular components and two femoral components had subsided. The 5-year survival rate was slightly higher for ceramic-on-ceramic bearings (98%) than for metal-on-polyethylene (92%).

CONCLUSIONS

Although there may be a link between acetabular inclination angles and wear rates as reported by some authors, we found no differences in patient function or radiographic survivorship using alumina-on-alumina articulations.

Male gender, Charnley class C, and severity of bone defects predict the risk for aseptic loosening in the cup of ABG I hip arthroplasty

Background

We studied which factor could predict aseptic loosening in ABG I hip prosthesis with hydroxyapatite coating. Aseptic loosening and periprosthetic osteolysis are believed to be caused, at least in part, by increased polyethylene (PE) wear rate via particle disease. Based on it, increased PE wear rate should be associated with aseptic loosening regardless of the type of implant.

Methods

We analyzed data from 155 revisions of ABG I hip prostheses to examine the influence of patient, implant, surgery, and wear related factors on the rate of aseptic loosening at the site of the cup. This was calculated by stepwise logistic regression analysis. The stability of the implant and severity of bone defects were evaluated intraoperatively.

Results

We found that men (odds ratio, OR = 5.6; p = 0.004), patients with Charnley class C (OR = 6.71; p = 0.013), those having more severe acetabular bone defects (OR = 4 for each degree of severity; p = 0.002), and longer time to revision surgery (OR = 1.51 for each additional year; p = 0.012) had a greater chance of aseptic loosening of the cup. However, aseptic loosening was not directly predicted by polyethylene wear rate in our patients.

Conclusion

Severity of bone defects predicts the risk for aseptic loosening in ABG I cup. Factors potentially associated with the quality of bone bed and biomechanics of the hip might influence on the risk of aseptic loosening in this implant.