Do large femoral heads reduce the risks of impingement in total hip arthroplasty with optimal and non-optimal cup positioning?

Head size in Delta ceramic-on-ceramic total hip arthroplasty: a comparative registry study

INTRODUCTION

Optimal bearing size in total hip arthroplasty (THA) has not been clearly ascertained, but large diameter ceramic balls may improve function and implant stability, with minimal concerns for wear. Delta ceramic-on-ceramic (COC) THA were stratified based on head diameter (32, 36 and 40 mm), aiming to assess: 1) survival rates, reasons for revision and hazard ratios for failure; 2) survival rates and hazard ratios for aseptic loosening, dislocation/primary instability, liner failure.

MATERIALS AND METHODS

A regional arthroplasty registry was enquired about Delta COC THA performed for primary osteoarthritis, stratified by head size. 13,161 primary cementless THAs were included in the study, with a mean follow-up of 5.7 years (range: 0-17): 3980 (30.2%) 32 mm balls, 8327 (63.3%) 36 mm heads, 854 (6.5%) 40 mm heads.

RESULTS

The three cohorts achieved similar survival rates (p = 0.99) and adjusted hazard ratios (p > 0.05). No revisions for head breakage or metallosis occurred. When revision for cup aseptic loosening was the endpoint, the survival rates of three cohorts (p = 0.08) and the adjusted hazard ratios (p > 0.05) were similar. The three cohorts achieved comparable survival rates when revision for dislocation/primary instability was the endpoint (p = 0.08). When the endpoint was revision for liner breakage, 32 mm cohort showed higher rates of revision (p = 0.01). No liner failure was detected in the 40 mm cohort.

CONCLUSIONS

32 mm, 36 mm and 40 mm provided similar 10-year survival rates in Delta COC THA. 40 mm heads emerged as safe options but did not lower the revisions for dislocations/primary instability.

LEVEL OF EVIDENCE

IV (therapeutic study).

Decreased Instability in High-Risk (Hip-Spine 2B) Patients After Modifications of Surgical Planning and Technique

BACKGROUND

Patients undergoing primary total hip arthroplasty (THA) who have spinal deformity and a stiff spine are the highest-risk group for instability. Despite the increasing use of dual-mobility cups and large femoral heads, dislocation remains a major complication after THA. Preoperative planning becomes a critical aspect of ensuring precise component positioning within a safe zone. The purpose of this study was to investigate dislocation rates over a 9-year period.

METHODS

A retrospective review of 4,731 THAs performed by 3 orthopaedic surgeons between January 2014 and March 2023 was performed. Spinopelvic measurements were conducted to determine the hip-spine classification group for each patient. Only patients classified as 2B (pelvic incidence-lumbar lordosis > 10° and Δsacral slope < 10°) were eligible. Both absolute and relative dislocation frequencies were then analyzed using time-series analysis techniques and Fisher's exact tests.

RESULTS

A total of 281 hip-spine 2B patients undergoing primary THA were eligible for analysis (57% women; mean age, range: 66 years, 23 to 87; mean body mass index, range: 28, 16 to 45). The overall dislocation rate was 4.3%. Use of femoral head sizes ≥ 40 mm increased from 4% in 2014 to 2019 to 37% in 2020 to 2023 (P < .001), while the use of dual-mobility cups decreased from 100% in 2014 to 2019 to 37% in 2020 to 2023 (P < .001). Acetabular component planning was changed from the supine plane to the standing plane in February 2020. Those changes in surgical practice were notably correlated with a significant decrease in dislocation rates from 6.8% in 2014 to 2019 to 1.5% in 2020 to 2023 (P = .03).

CONCLUSIONS

Our study demonstrates that the introduction of advanced preoperative THA planning to the standing plane, coupled with precise intraoperative technology for implant placement, can significantly reduce the risk of instability in high-risk THA patients. Notably, we observed a significant decrease in dislocation rates, which aligned with the shift in surgical practice.

LEVEL OF EVIDENCE

IV.

Total hip arthroplasty with monobloc press-fit acetabular components and large-diameter bearings for atypical acetabula is safe: a consecutive case series of 125 hips with mean follow-up of 9 years

BACKGROUND

Large-diameter head (LDH) total hip arthroplasty (THA) with a monobloc acetabular component improves hip stability. However, obtaining initial press-fit stability is quite challenging in atypical acetabula. The purpose of this study was to assess primary and secondary fixation of monobloc cups in atypical acetabula.

METHODS

In this consecutive case series, the local arthroplasty database was used to retrospectively identify patients with secondary osteoarthritis who underwent primary hip replacement with press-fit only LDH monobloc acetabular components between 2005 and 2018 and who had a minimum of 2 years of follow-up. Radiographic evaluation was performed at last follow-up, and patient-reported outcome measures (PROMs) were assessed with the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), the Forgotten Joint Score (FJS), and the Patient's Joint Perception (PJP) question.

RESULTS

One hundred and six LDH THAs and 19 hip resurfacings were included in the study. Preoperative diagnoses included hip dysplasia (36.8%), Legg-Calve-Perthes disease (32.0%), osteoarthritis with acetabular deficiency (17.6%), periacetabular osteotomy (8.0%), arthrodesis (4.0%), and osteopetrosis (1.6%). After a mean follow-up of 9.2 years, no aseptic loosening of the acetabular component was recorded nor observed on radiologic review. There were 13 (10.4%) revisions unrelated to the acetabular component fixation. The mean WOMAC and FJS scores were 9.2 and 80.9, respectively. In response to the PJP question, 49.4% of the patients perceived their hip as natural, 19.1% as an artificial joint with no restriction, 31.5% as an artificial joint with restriction, and none as a non-functional joint.

CONCLUSION

Primary press-fit fixation of monobloc acetabular components with LDH implanted in atypical acetabula led to secondary fixation in all cases with low revision and complication rates and great functional outcomes. With careful surgical technique and experience, systematic use of supplemental screw fixation is not essential in THA with atypical acetabula.

Large Femoral Heads and Select Dual-Mobility Bearings Are Associated With Reduced Instability in Contemporary Posterior Approach Total Hip Arthroplasty

BACKGROUND

Postoperative dislocation is considered the main drawback of posterior approach total hip arthroplasty (THA). Thinner highly cross-linked polyethylene and dual-mobility bearings allow maximizing femoral head diameter per a given cup size. This study evaluated dislocation rates as large femoral head bearings were introduced into a practice over an 11-year period.

METHODS

A total of 1,511 consecutive primary THAs were retrospectively reviewed. Demographics, implant sizes, femoral head-acetabular cup ratio, and dislocation status were collected from the electronic medical record. Data were evaluated using time series analysis techniques as larger femoral heads, thinner polyethylene liners, and dual-mobility bearings were introduced. The cohort was 57% women with mean age and body mass index of 62 years (range, 13 to 93) and 31 kg/m² (range, 13 to 54), respectively.

RESULTS

The overall dislocation rate was 0.98%. Use of femoral head sizes ≥ 40 millimeters increased from 4% in the years 2010 to 2016 to 51% in the years 2017 to 2021, correlating with a 50% reduction in dislocation rate from 1.4% to 0.7% (P = .279). Also, no dislocations occurred in patients who had dual-mobility bearings or ≥ 40-millimeter femoral heads (P = .007). Twelve of 14 dislocations occurred in cases with head-cup ratio < 0.7 (P = .013). Thirteen of 14 dislocations were in women (P = .005).

CONCLUSION

Maximizing the femoral head diameter per given cup size correlated with a decrease in dislocation rate in modern posterior approach THA. Furthermore, these results suggest that dual-mobility articulations should be reserved for high-risk patients or patients in whom a 40-millimeter femoral head is not possible.

LEVEL OF EVIDENCE

IV-consecutive case series; no control group.

Monobloc press-fit cups with large-diameter bearings are safe in revision total hip arthroplasty

BACKGROUND

Instability is a major cause of failure of revision total hip arthroplasty (THA) which can be avoided with the use of monobloc press-fit cups with large diameter heads (LDH).

OBJECTIVE

This consecutive case series analyses whether LDH monobloc components are a safe and clinically beneficial option for revision THA.

METHODS

This consecutive case series includes 47 revision THA with LDH monobloc acetabular cup. Acetabular bone defects were Paprosky type I (42), type IIA (2) and type IIC (3). The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Forgotten Joint Score (FJS) and the Patient's Joint Perception (PJP) scores were analysed and a radiographic evaluation for signs of implant dysfunction was performed.

RESULTS

After a mean follow-up of 4.5 years, there were 5 (10.6%) acetabular cup re-revisions: 2 loss of primary fixation and 3 instabilities. Implant survivorship at 4-years was 89.4% (95% CI: 89.3 to 89.5). Recurrent hip dislocation was reported in 1 patient (2.1%) and remains under conservative treatment. The mean WOMAC and FJS were 19.5 (16.8; 0.0 to 58.3) and 57.3 (28.9; 6.3 to 100.0), respectively. Regarding the PJP, 3 (8.8%) patients perceived their hip as natural, 8 (23.5%) as an artificial joint with no restriction, 14 (41.2%) with minor restriction and 9 (26.5%) with major restriction.

CONCLUSION

In cases of revision THA with limited bone loss, press-fit primary fixation with LDH monobloc acetabular components are valuable options that offer excellent mid-term out-comes with low re-revision and joint instability rates.

Personalized Hip Joint Replacement with Large Diameter Head: Current Concepts

Hip arthroplasty is a common procedure in elective orthopaedic surgery that has excellent outcomes. Hip replacement surgery aims to create a “forgotten” joint, i.e., a pain-free joint akin to a native articulation. To achieve such goals, hip arthroplasty must be personalised. This is achieved by restoring: the centre of rotation of the native hip; leg length equality; femoral offset; femoral orientation; soft tissue tension; joint stability with an unrestricted hip range of motion; and having appropriate stress transfer to the bone. In addition, the whole pathway should provide an uneventful and swift postoperative recovery and lifetime implant survivorship with unrestricted activities. At our institution, the preferred option is a personalized total hip arthroplasty (THA) with a large diameter head (LDH) using either monobloc or dual-mobility configuration for the acetabular component. LDH THA offers an impingement-free range of motion and a reduced risk of dislocation. The larger head-neck offset allows for a supraphysiologic range of motion (ROM). This can compensate for a patient’s abnormal spinopelvic mobility and surgical imprecision. Additionally, LDH bearing with a small clearance exerts a high suction force, which provides greater hip micro-stability. With appropriate biomechanical reconstruction, LDH THA can restore normal gait parameters. This results in unrestricted activities and higher patient satisfaction scores. We use LDH ceramic on ceramic for our patients with a life expectancy of more than 20 years and use LDH dual mobility bearings for all others.

Standard, Large-Head, Dual-Mobility, or Constrained-Liner Revision Total Hip Arthroplasty for a Diagnosis of Dislocation: An Analysis of 1,275 Revision Total Hip Replacements

BACKGROUND

Dislocation remains a leading cause of revision following primary and revision total hip arthroplasty (THA). The aim of the present study was to compare the rate of second revision THA following a major first revision for the treatment of dislocation using an implant with a standard, large head, dual-mobility, or constrained acetabular liner.

METHODS

Data were obtained from the Australian Orthopaedic Association National Joint Replacement Registry from September 1999 through December 2018. All primary THAs that had been performed for the treatment of osteoarthritis and subsequently revised for dislocation were included. All revision THA prostheses with a standard head (≤32 mm), large head (≥36 mm), dual-mobility, or constrained acetabular liner that were used for the first revision procedure were identified. The primary outcome measures were the cumulative rates of second revisions for all causes and for a subsequent diagnosis of dislocation for the 4 different constructs used in the first revision.

RESULTS

A total of 1,275 hips underwent a major first revision because of prosthesis dislocation, with 203 of these hips going on to have a second revision. The rate of all-cause second revision was significantly higher in the standard-head group compared with the constrained-acetabular-liner group (hazard ratio [HR], 1.53 [95% confidence interval (CI), 1.01 to 2.30]; p = 0.044). There was no difference in the rates of revision between other articulations. The most common cause of second revision for all implants was dislocation. There were a total of 91 second revisions for a diagnosis of dislocation. Standard heads had a higher rate of second revision compared with constrained acetabular liners (HR, 2.44 [95% CI, 1.30 to 4.60]; p = 0.005), dual-mobility implants (HR, 2.04 [95% CI, 1.03 to 4.01]; p = 0.039), and large heads (HR, 1.80 [95% CI, 1.09, 2.99]; p = 0.022). There was no difference in the rates of second revision between other articulations.

CONCLUSIONS

Surgeons have a number of options for prostheses when performing a first revision for the treatment of dislocation following a primary THA. The most common cause of a second revision is recurrent dislocation. The use of constrained acetabular liners, dual-mobility liners, and large heads (≥36 mm) are options for reducing subsequent dislocation. Standard head sizes have a higher rate of second revision for further dislocation.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

The Impingement-free, Prosthesis-specific, and Anatomy-adjusted Combined Target Zone for Component Positioning in THA Depends on Design and Implantation Parameters of both Components

BACKGROUND

Lewinnek's recommendation for orienting the cup in THA is criticized because it involves a static assessment of the safe zone and because it does not consider stem geometry. A revised concept of the safe zone should consider those factors, but to our knowledge, this has not been assessed.

QUESTIONS/PURPOSES

(1) To determine the shape, size, and location of target zones for combined cup and stem orientation for a straight stem/hemispheric cup THA to maximize the impingement-free ROM and (2) To determine whether and how these implant positions change as stem anteversion, neck-shaft angle, prosthetic head size and target range of movements are varied.

METHODS

A three-dimensional computer-assisted design model, in which design geometry was expressed in terms of parameters, of a straight stem/hemispheric cup hip prosthesis was designed, its design parameters modified systematically, and each prosthesis model was implanted virtually at predefined component orientations. Functional component orientation referencing to body planes was used: cups were abducted from 20° to 70°, and anteverted from -10° to 40°. Stems were rotated from -10° to 40° anteversion, neck-shaft angles varied from 115° to 143°, and head sizes varied from 28 to 40 mm. Hip movements up to the point of prosthetic impingement were tested, including simple flexion/extension, internal/external rotation, ab/adduction, combinations of these, and activities of daily living that were known to trigger dislocation. For each combination of parameters, the impingement-free combined target zone was determined. Maximizing the size of the combined target zone was the optimization criterion.

RESULTS

The combined target zones for impingement-free cup orientation had polygonal boundaries. Their size and position in the diagram changed with stem anteversion, neck-shaft angle, head size, and target ROM. The largest target zones were at neck-shaft angles from 125° to 127°, at stem anteversions from 10° to 20°, and at radiographic cup anteversions between 17° and 25°. Cup anteversion and stem anteversion were inverse-linearly correlated supporting the combined-anteversion concept. The range of impingement-free cup inclinations depended on head size, stem anteversion, and neck-shaft angle. For a 127°-neck-shaft angle, the lowest cup inclinations that fell within the target zone were 42° for the 28-mm and 35° for the 40-mm head. Cup anteversion and combined version depended on neck-shaft angle. For head size 32-mm cup, anteversion was 6° for a 115° neck-shaft angle and 25° for a 135°-neck-shaft angle, and combined version was 15° and 34° respectively.

CONCLUSIONS

The shape, size, and location of the combined target zones were dependent on design and implantation parameters of both components. Changing the prosthesis design or changing implantation parameters also changed the combined target zone. A maximized combined target zone was found. It is mandatory to consider both components to determine the accurate impingement-free prosthetic ROM in THA.

CLINICAL RELEVANCE

This study accurately defines the hypothetical impingement-free, design-specific component orientation in THA. Transforming it into clinical precision may be the case for navigation and/or robotics, but this is speculative, and as of now, unproven.

Kinematic alignment technique for total hip and knee arthroplasty: The personalized implant positioning surgery

Conventional techniques for hip and knee arthroplasty have led to good long-term clinical outcomes, but complications remain despite better surgical precision and improvements in implant design and quality.

Technological improvements and a better understanding of joint kinematics have facilitated the progression to ‘personalized’ implant positioning (kinematic alignment) for total hip (THA) and knee (TKA) arthroplasty, the true value of which remains to be determined.

By achieving a true knee resurfacing, the kinematic alignment (KA) technique for TKA aims at aligning the components with the physiological kinematic axes of the knee and restoring the constitutional tibio-femoral joint line frontal and axial orientation and soft-tissue laxity.

The KA technique for THA aims at restoring the native ‘combined femoro-acetabular anteversion’ and the hip’s centre of rotation, and occasionally adjusting the cup position and design based on the assessment of the individual spine-hip relation.

The key element for optimal prosthetic joint kinematics (hip or knee) is to reproduce the femoral anatomy.

The transverse acetabular ligament (TAL) is the reference landmark to adjust the cup position.

Cite this article: EFORT Open Rev 2018;3:98-105. DOI: 10.1302/2058-5241.3.170022

Otto Aufranc Award: Dual-mobility Constructs in Revision THA Reduced Dislocation, Rerevision, and Reoperation Compared With Large Femoral Heads

BACKGROUND

Dislocation is one of the most common complications after revision THA. Dual-mobility constructs and large femoral heads (ie, 40 mm) are two contemporary, nonconstrained bearing options used in revision THA to minimize the risk of dislocation; however, it is not currently established if there is a clear benefit to using dual-mobility constructs over large femoral heads in the revision setting.

QUESTIONS/PURPOSES

We sought to determine if dual-mobility constructs would provide a reduction in dislocation, rerevision for dislocation, and reoperation or other complications as compared with large femoral heads in revision THA.

METHODS

From 2011 to 2014, a series of 355 THAs underwent revision for any reason and received either a dual-mobility construct (146 THAs) or a 40-mm large femoral head (209 THAs). Indications for either construct were based on surgeon judgment; however, there is a preference to use dual-mobility constructs in patients believed to be at higher risk of dislocation. In the dual-mobility group, 20 of 146 (14%) were excluded because of loss of followup before 2 years or because they had a dual-mobility shell cemented into a preexisting acetabular component. In the large head group, 33 of 209 (16%) were lost to followup before 2 years. Followup in the dual-mobility group was 3.3 ± 0.8 years and followup in the large head group was 3.9 ± 0.9 years. Primary endpoints included dislocation, rerevisions for dislocation, and reoperations, which were determined through our institution's total joint registry and verified by individual patient chart review. Age and body mass index were not different with the numbers available between the groups, but there was a slight predominance of females in the dual-mobility group (52% [66 of 126] female) versus the 40-mm large head group (41% [72 of 176] female) (p = 0.05). Notably, 33% (41 of 126) of patients receiving the dual-mobility constructs had the index revision THA done for a diagnosis of recurrent dislocation versus 9% (17 of 176) in the 40-mm large head group. Mean effective head size in the dual-mobility group was 47 mm (range, 38-58 mm).

RESULTS

The subsequent frequency of dislocation in the dual-mobility construct group was less (3% [four of 126] dual-mobility versus 10% [17 of 176] in the 40-mm large head group; hazard ratio, 3.2 [1.1-9.4]; p = 0.03). Rerevision for dislocation in the dual-mobility construct group was less frequent (1% [one of 126] dual-mobility versus 6% [10 of 176] in the 40-mm large head group; hazard ratio, 7.1 [0.9-55.6]; p = 0.03). Reoperation for any cause in the dual-mobility construct group was less frequent (6% [eight of 126] dual-mobility versus 15% [27 of 176] in the 40-mm large head group; hazard ratio, 2.5 [1.1-5.5]; p = 0.02); there were no differences between the groups in terms of the overall percentage of complications in each group.

CONCLUSIONS

When compared with patients treated with a 40-mm large femoral head, patients undergoing revision THA who received a dual-mobility construct had a lower risk of subsequent dislocation, rerevision for dislocation, and reoperation for any reason in the first several years postoperatively. Those findings were present despite selection bias in this study to use the dual-mobility construct in patients at the highest risk for subsequent dislocation. Given the lower risk of subsequent dislocation, rerevision, and reoperation with the dual-mobility construct, some surgeons may wish to consider whether the role of dual-mobility should be judiciously expanded in contemporary revision THA.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Modularity in Total Hip Arthroplasty: Benefits, Risks, Mechanisms, Diagnosis, and Management

Modular implants are currently widely used in total hip arthroplasty because they give surgeons versatility during the operation, allow for easier revision surgery, and can be adjusted to better fit the anatomy of the specific patient. However, modular implants, specifically those that have metal-on-metal junctions, are susceptible to crevice and fretting corrosion. This can ultimately cause implant failure, inflammation, and adverse local tissue reaction, among other possible side effects. Surgeons should be aware of the possibility of implant corrosion and should follow a set of recommended guidelines to systematically diagnose and treat patients with corroded implants. Ultimately, surgeons will continue to use modular implants because of their widespread benefits. However, more research is needed to determine how to minimize corrosion and the negative side effects that have been associated with modular junctions in total hip arthroplasty. [Orthopedics. 2017; 40(6):355-366.].

The influence of spine-hip relations on total hip replacement: A systematic review

Sagittal pelvic kinematics along with spino-pelvic angular parameters have recently been studied by numerous investigators for their effect on total hip replacement (THR) clinical outcomes, but many issue of spine-hip relations (SHR) are currently unexplored. Therefore, our review aims at clarifying the following questions: is there any evidence of a relationship between articular impingement/dislocation risk in primary THR and (1) certain sagittal pelvic kinematics patterns, (2) pelvic incidence, and (3) types of SHRs? A systematic review of the existing literature utilising PubMed and Google search engines was performed in January 2017. Only clinical or computational studies published in peer-reviewed journals over the last five years in either English or French were reviewed. We identified 769 reports, of which 12 met our eligibility criteria. A review of literature shows that sagittal pelvic kinematics, but not the pelvic incidence, influences the risk of prosthetic impingement/dislocation. We found no study having assessed the relationship between this risk and the types of SHRs. Sagittal pelvic kinematics is highly variable among individuals and certain kinematic patterns substantially influences the risk of prosthetic impingement/dislocation. Recommendations for cup positioning are therefore switching from a systematic to a patient-specific approach, with the standing cup orientation Lewinneck safe zone progressively giving way to a new parameter of interest: the functional orientation of the cup. Based on a recently published classification for SHRs, We propose a new concept of "kinematically aligned THR" for the purposes of THR planning. Further studies are needed to investigate the relevance of such a classification towards the assumptions and hypothesis we have made. Level of evidence,- Level IV, systematic review of level III and IV studies.

Vitamin E-stabilized highly crosslinked polyethylenes: The role and effectiveness in total hip arthroplasty

Morphology and design of ultra-high molecular weight polyethylene (UHMWPE or simply PE) acetabular components used in total hip arthroplasty (THA) have been evolving for more than half a century. Since the late-1990s, there were two major technological innovations in PE emerged from necessity to overcome the wear-induced periprosthetic osteolysis, i.e., the development of highly crosslinked PEs (HXLPEs). There are many literature reporting that radiation crosslinked and remelted/annealed (first-generation) HXLPEs markedly reduced the incidence of osteolysis and aseptic loosening. Regardless of such clinical success in the first-generation technologies, there were some recent shifts in Japan toward the use of new second-generation HXLPEs subjected to sequential irradiation/annealing or antioxidant vitamin E (α-tocopherol) incorporation. Although the selection rate of first-generation liners still account for more than half of all the PE THAs (∼58% in 2015), the use of vitamin E-stabilized liners has been steadily growing each year since their clinical introduction in 2010. In these contexts, it is of great importance to evaluate and understand the real clinical benefits of using the new second-generation liners as compared to the first generation. This article first summarizes structural evolution and characteristic features of first-generation HXLPEs, and then provides a detailed description of second-generation antioxidant HXLPEs in regard to the role of vitamin E incorporation on their chemical and mechanical performances in THA.

[Hip dislocation after revision arthroplasty : Risk assessment and treatment strategies]

With a dislocation rate of up to 35% after revision total hip arthroplasty (THA), instability is one of the major causes why this procedure fails. Independent factors for patients at risk are age, sex, and the type of revision needed. The surgical approach, implant choice, and positioning of the components are factors that the surgeon can influence to keep the dislocation rate low. Large femoral heads or double mobility (DM) cups can increase the stability of the joint. After detailed failure analysis, targeted use of different technical innovations enhances stability in revision THA and prevents further revisions.

Large Metal Heads and Vitamin E Polyethylene Increase Frictional Torque in Total Hip Arthroplasty

PURPOSE

Trunnionosis has reemerged in modern total hip arthroplasty for reasons that remain unclear. Bearing frictional torque transmits forces to the modular head-neck interface, which may contribute to taper corrosion. The purpose of this study is to compare frictional torque of modern bearing couples in total hip arthroplasty.

METHODS

Mechanical testing based on in vivo loading conditions was used to measure frictional torque. All bearing couples were lubricated and tested at 1 Hz for more than 2000 cycles. The bearing couples tested included conventional, highly crosslinked (XLPE) and vitamin E polyethylene, CoCr, and ceramic femoral heads and dual-mobility bearings. Statistical analysis was performed using Student t test for single-variable and analysis of variance for multivariant analysis. P ≤ .05 was considered statistically significant.

RESULTS

Large CoCr metal heads (≥36 mm) substantially increased frictional torque against XLPE liners (P = .01), a finding not observed in ceramic heads. Vitamin E polyethylene substantially increased frictional torque compared with XLPE in CoCr and ceramic heads (P = .001), whereas a difference between conventional and XLPE was not observed (P = .69) with the numbers available. Dual-mobility bearing with ceramic inner head demonstrated the lowest mean frictional torque of all bearing couples.

CONCLUSION

In this simulated in vivo model, large-diameter CoCr femoral heads and vitamin E polyethylene liners are associated with increased frictional torque compared with smaller metal heads and XLPE, respectively. The increased frictional torque of vitamin E polyethylene and larger-diameter femoral heads should be considered and further studied, along with reported benefits of these modern bearing couples.

Predicting long-term wear performance of hard-on-hard bearing couples: effect of cup orientation

Wear is the major cause of implant failure, resulting in expensive revision surgeries of total hip arthroplasty. Therefore, understanding of wear mechanism and its progression is crucial to improve the physiological performance of implants. This paper presents a three-dimensional (3D) finite element (FE) wear modeling approach to estimate evolution of wear in hard-on-hard bearing components with the effect of cup abduction angle. Three bearing couples were considered, and they were PCD-on-PCD, Al2O3-on-Al2O3 and Si3N4-on-Si3N4, while the cup abduction angle varied from 35° to 70° with an increment of 5°. By adopting actual physiological hip gait loading and rotational movement for normal walking cycle in FE modeling, the contact pressure and the sliding distance were calculated to predict wear. A femoral head of 32 mm in diameter was considered, while a constant frictional contact at the inference between head and cup was used. During simulation, the geometry of cup surface was updated at a reasonable interval of gait cycles to consider the effect of wear. Wear was simulated for up to 20 million cycles which is an equivalent of 20 years of implant's life in human body. Simulation results showed that compared to other two bearing couples, the predicted linear and volumetric wear in PCD-on-PCD couple exhibited the least wear evolution for all cup angles considered. The increase in abduction angle from 35° to 70° decreases the volumetric wear by 28 % for all three bearing couples, due to the reduction in sliding distance. Steep cup angle, e.g., 70° for Al2O3 and Si3N4 bearing couples, encountered edge contact, which leads to more wear. Further, wear results were discussed and analyzed with respect to in vitro and/or clinical studies available in the literature to justify the efficacy of wear modeling.

Fabrication, Properties and Applications of Dense Hydroxyapatite: A Review

In the last five decades, there have been vast advances in the field of biomaterials, including ceramics, glasses, glass-ceramics and metal alloys. Dense and porous ceramics have been widely used for various biomedical applications. Current applications of bioceramics include bone grafts, spinal fusion, bone repairs, bone fillers, maxillofacial reconstruction, etc. Amongst the various calcium phosphate compositions, hydroxyapatite, which has a composition similar to human bone, has attracted wide interest. Much emphasis is given to tissue engineering, both in porous and dense ceramic forms. The current review focusses on the various applications of dense hydroxyapatite and other dense biomaterials on the aspects of transparency and the mechanical and electrical behavior. Prospective future applications, established along the aforesaid applications of hydroxyapatite, appear to be promising regarding bone bonding, advanced medical treatment methods, improvement of the mechanical strength of artificial bone grafts and better in vitro/in vivo methodologies to afford more particular outcomes.

Fluctuation of Cup Orientation During Press-Fit Insertion: A Possible Cause of Malpositioning

We evaluated real-time angular changes during press-fit cup insertion in 70 total hip arthroplasties. Inclination and anteversion cup angles on navigation system were recorded after each procedure of five hammer blows during cup insertion, and maximum deviated inclination (MDI) and anteversion (MDA) angles until the cup was fully seated were measured. We found 1 (1%) and 29 (41%) hips with increases and decreases in MDI of 5° or more, and 13 (19%) and 6 (8%) hips with increases and decreases in MDA of 5° or more, respectively. The MDI in men was significantly lower and the MDA for left-side surgery was significantly higher. Surgeons should pay attention to fluctuation in angular changes during cup insertion and may consider countermeasures to minimize cup malpositioning.

Ceramic-on-ceramic versus ceramic-on-polyethylene bearing surfaces in total hip arthroplasty

The choice between ceramic-on-ceramic (COC) and ceramic-on-polyethylene (COP) in primary total hip arthroplasty (THA) remains controversial. The purpose of this study was to evaluate the reliability and durability of COC vs COP bearing surfaces in THA. Based on published randomized, controlled trials (RCTs) identified in PubMed, Embase, and the Cochrane Central Register of Controlled Trials, the authors performed a meta-analysis comparing the clinical and radiographic outcomes of COC with those of COP. Two investigators independently selected the studies and extracted the data. The methodological quality of each RCT was assessed using the Physiotherapy Evidence Database (PEDro) scale. Relative risks and 95% confidence intervals from each trial were pooled using random-effects or fixed-effects models depending on the heterogeneity of the included studies. Nine RCTs involving 1575 patients (1747 hips) met the predetermined inclusion criteria. Eight of 9 included RCTs had high methodological quality. The heterogeneity was not significant, and all the results were pooled using a fixed-effects model. The results demonstrated that COC significantly increased the risks of squeaking and total implant fracture compared with COP. No significant differences with respect to revision, osteolysis and radiolucent lines, loosening, dislocation, and deep infection were observed between the COC and COP bearing surfaces. This meta-analysis resulted in no sufficient evidence to identify any clinical or radiographic advantage of COC vs COP bearing surfaces in the short- to mid-term follow-up period. Long-term follow-up is required for further evaluation.

Large diameter femoral heads: is bigger always better?

Dislocation remains among the most common complications of, and reasons for, revision of both primary and revision total hip replacements (THR). Hence, there is great interest in maximising stability to prevent this complication. Head size has been recognised to have a strong influence on the risk of dislocation post-operatively. As femoral head size increases, stability is augmented, secondary to an increase in impingement-free range of movement. Larger head sizes also greatly increase the 'jump distance' required for the head to dislocate in an appropriately positioned cup. Level-one studies support the use of larger diameter heads as they decrease the risk of dislocation following primary and revision THR. Highly cross-linked polyethylene has allowed us to increase femoral head size, without a marked increase in wear. However, the thin polyethylene liners necessary to accommodate larger heads may increase the risk of liner fracture and larger heads have also been implicated in causing soft-tissue impingement resulting in groin pain. Larger diameter heads also impart larger forces on the femoral trunnion, which may contribute to corrosion, metal release, and adverse local tissue reactions. Alternative large bearings including large ceramic heads and dual mobility bearings may mitigate some of these risks, and several of these devices have been used with clinical success.

Optimal anterior femoral offset for functional range of motion in total hip arthroplasty--a computer simulation study

PURPOSE

Compared to medial femoral offset (MFO), the role of anterior femoral offset (AFO) on range of motion (ROM) in total hip arthroplasty (THA) has not been fully examined. We therefore defined AFO as the anterior distance from the centre of the femoral head to the proximal femoral axis in the sagittal plane and determined the optimal AFO required for ROM needed for activities of daily living using a computer-simulated THA model.

METHODS

Various AFOs were obtained by changing stem anteversion (stem-AV) and stem tilt in the sagittal plane (stem-tilt) using a CT-based simulation software. The required ROM was defined as: flexion ≥ 110°, internal rotation at 90° flexion (IR) ≥ 30°, external rotation (ER) ≥ 30°, and extension ≥ 30°, and we determined AFO and MFO to satisfy required ROM.

RESULTS

AFO was positively correlated with stem-AV and anterior stem-tilt. MFO was negatively correlated with stem-AV and not influenced by stem-tilt. Flexion and IR increased with both increased AFO and MFO, whereas extension and ER decreased with increased AFO. A smoothing spline curve showed the optimal AFO and MFO for required ROM to be from 15 mm to 25 mm on average and more than 32.1 mm, respectively.

CONCLUSIONS

This is the first study to show that AFO directly influenced ROM in THA. Optimal AFO as well as MFO should be reconstructed to achieve sufficient ROM.

Stability and trunnion wear potential in large-diameter metal-on-metal total hips: a finite element analysis

BACKGROUND

Large-diameter femoral heads for metal-on-metal THA hold theoretical advantages of joint stability and low bearing surface wear. However, recent reports have indicated an unacceptably high rate of wear-associated failure with large-diameter bearings, possibly due in part to increased wear at the trunnion interface. Thus, the deleterious consequences of using large heads may outweigh their theoretical advantages.

QUESTIONS/PURPOSES

We investigated (1) to what extent femoral head size influenced stability in THA for several dislocation-prone motions; and the biomechanics of wear at the trunnion interface by considering the relationship between (2) wear potential and head size and (3) wear potential and other factors, including cup orientation, type of hip motion, and assembly/impaction load.

METHODS

Computational simulations were executed using a previously validated nonlinear contact finite element model. Stability was determined at 36 cup orientations for five distinct dislocation challenges. Wear at the trunnion interface was calculated for three separate cup orientations subjected to gait, stooping, and sit-to-stand motions. Seven head diameters were investigated: 32 to 56 mm, in 4-mm increments.

RESULTS

Stability improved with increased diameter, although diminishing benefit was seen for sizes of greater than 40 mm. By contrast, contact stress and computed wear at the trunnion interface all increased unabatedly with increasing head size. Increased impaction forces resulted in only small decreases in trunnion wear generation.

CONCLUSIONS

These data suggest that the theoretical advantages of large-diameter femoral heads have a limit. Diameters of greater than 40 mm demonstrated only modest improvement in terms of joint stability yet incurred substantial increase in wear potential at the trunnion.

CLINICAL RELEVANCE

Our model has potential to help investigators and designers of hip implants to better understand the optimization of trunnion design for long-term durability.

Large-diameter Delta ceramic-on-ceramic versus common-sized ceramic-on-polyethylene bearings in THA

The higher failure rate of total hip arthroplasty (THA) in young, active patients remains a challenge for surgeons. Recently, larger-diameter femoral heads combined with an alumina matrix composite ceramic (BIOLOX Delta; CeramTec AG, Plochingen, Germany) articulation was developed to improve implant longevity and meet patients' activity demands while reducing the risk of component-related complications. The purpose of this study was to determine whether this new device may provide advantages for young, active patients. A prospective, randomized, controlled trial was conducted on 93 patients (113 THAs) with more than 3 years of follow-up. Patients were randomly divided into a study group (51 THAs) with a 36-mm Delta ceramic-on-ceramic (COC) articulation and a control group (62 THAs) with a common-sized alumina ceramic head on polyethylene liner (COP) articulation. Clinical and radiographic results were collected to compare the outcomes and complications, including implant-related failures, osteolysis, and noises. The large-diameter Delta COC articulation provided greater range of motion improvement (6.1° more), similar Harris Hip Scores, and similar complication rates compared with the alumina COP articulation. This study suggests that in the short term, the large-diameter Delta COC articulation results in better range of motion with no higher complication rates; however, mid-term (8-10 years) or longer follow-up is necessary to determine its superiority in young, active patients.

Bone-on-bone versus hardware impingement in total hips: a biomechanical study

Dislocation remains a serious concern for total hip arthroplasty (THA). Impingement, typically between the implant femoral neck and the acetabular cup, remains the most common dislocation impetus. Wear reductions from recent bearing technology advancements have encouraged introduction of substantially increased femoral head diameters. However, there is some evidence that range of motion with larger head sizes is limited by bone-on-bone, rather than hardware, impingement. While all impingement events are of course undesirable, currently little is known biomechanically if these two impingement modes differ in terms of generation of potentially deleterious stress concentrations or with regard to dislocation resistance. Finite element (FE) analysis was therefore used to parametrically investigate the role of head diameter on the local biomechanics of bone-on-bone versus component-on-component impingement events. Of several dislocation-prone patient motion challenges considered, only squatting consistently resulted in bone-on-bone (as opposed to hardware) impingement. Implant stress concentrations arising from hardware impingement during squatting were greater than those from bony impingement, for all head sizes considered. Additionally, dislocation resistance was substantially greater for instances of bony impingement versus hardware-only impingement. These findings suggest that hardware impingement may still be a/the the predominant mode of impingement even with the use of larger femoral heads, for sub-optimally positioned cups. Additionally, the data indicate that, should impingement occur, impingements between the implant neck and cup are (1) more likely to dislocate, and (2) have a greater propensity for causing damage to the implant compared to impingement events involving bony members.

No clinical difference between large metal-on-metal total hip arthroplasty and 28-mm-head total hip arthroplasty?

PURPOSE

We aimed to test the claim of greater range of motion (ROM) with large femoral head metal-on-metal total hip arthroplasty.

METHODS

We compared 28-mm metal-on-polyethylene (MP) total hip arthroplasty with large femoral head metal-on-metal (MM) total hip arthroplasty in a randomised clinical trial. ROM one year postoperatively was determined in 50 patients. Mean head sizes were 28 mm (MP) and 48 mm (MM).

RESULTS

After one year, the large head MM group showed greater improvement in internal rotation (14 degrees) than the 28 mm group (seven degrees).There were no significant differences in the absolute values of postoperative internal rotation, external rotation, flexion, extension, abduction and abduction.

CONCLUSIONS

Absolute postoperative range of motion did not differ between the two groups. The improvement in internal rotation was greater after large femoral head metal-on-metal total hip arthroplasty. It is however questionable whether this difference is clinically relevant.

The association between the sagittal femoral stem alignment and the resulting femoral head centre in total hip arthroplasty

Adequate stem alignment is essential for the success of Total Hip Arthroplasty (THA) to avoid dislocation and impingement. One factor that has not been sufficiently investigated so far is the stem tilting in the sagittal plane, which has an influence on the position of the centre of the femoral head and thus also on prosthesis torsion. We aimed to evaluate sagittal stem position using 3D-CTs in patients with THA and to develop a mathematical-geometrical model to simulate the functional correlation between sagittal stem tilting and the influence on functional anteversion. Thirty patients with THA underwent a CT-scan. By 3D-reconstruction of the CT-data, femoral-/prosthesis-axis, torsion and sagittal tilt were determined. In accordance with the position of the femoral and prosthesis axes, the rotatory (rAV) (surgically adjusted) and functional (depending on sagittal tilt) anteversion (fAV) was measured. A three dimentional-coordinate transformation was also performed using the Euler-angles to derive a mathematical-geometrical correlation between sagittal stem tilting and corresponding influence on anteversion. The mean rAV was 8° (-11.6-26°), the fAV 18° (6.2-37°), and the difference 10° (8.8-18°). The mean degree of stem tilting was 5.2° (0.7-9°) anterior towards the femoral axis. The individually measured parameters are reflected in the mathematical-geometrical model. Depending on the extent of the sagittal deviation, a clear influence on the torsion emerges. For example, a stem implanted at a 15° anteverted angle with a sagittal tilt by two degrees towards anterior results in a fAV of 20°. A clear association between the sagittal stem alignment and the impact on the fAV was demonstrated. Hence, the rotatory anteversion intended by the surgeon may be functionally significantly different. This might pose an increased risk of dislocation or impingement. The sagittal tilt of the prosthesis should therefore be considered in the context of impingement and dislocation diagnosis. In this respect, we recommend a 3D-analysis of stem alignment.