Ideal femoral head size in total hip arthroplasty balances stability and volumetric wear

The impact of femoral head size on the wear evolution at contacting surfaces of total hip prostheses: A finite element analysis

Total Hip Arthroplasty has been a revolutionary technique in restoring mobility to patients with damaged hip joints. The introduction of modular components of the hip prosthesis allowed for bespoke solutions based on the requirements of the patient. The femoral stem is designed with a conical trunnion to allow for assembly of different femoral head sizes based on surgical requirements. The femoral head diameters for a metal-on-polyethylene hip prosthesis have typically ranged between 22 mm and 36 mm and are typically manufactured using Cobalt-Chromium alloy. A smaller femoral head diameter is associated with lower wear of the polyethylene, however, there is a higher risk of dislocation. In this study, a finite element model of a standard commercial hip arthroplasty prosthesis was modelled with femoral head diameters ranging from 22 mm to 36 mm to investigate the wear evolution and material loss at both contacting surfaces (acetabular cup and femoral stem trunnion). The finite element model, coupled with a validated in-house wear algorithm modelled a human walking for 10 million steps. The results have shown that as the femoral head size increased, the amount of wear on all contacting surfaces increased. As the femoral head diameter increased from 22 mm to 36 mm, the highly cross-linked polyethylene (XLPE) volumetric wear increased by 61% from 98.6 mm3 to 159.5 mm3 while the femoral head taper surface volumetric wear increased by 21% from 4.18 mm3 to 4.95 mm3. This study has provided an insight into the amount of increased wear as the femoral head size increased which can highlight the life span of these prostheses in the human body.

Large Femoral Heads With Small Acetabular Components: An Examination of 10-Year Polyethylene Wear

Highly cross-linked polyethylene (HXLPE) has improved polyethylene (PE) wear rates while decreasing osteolysis and aseptic loosening. However, concerns exist regarding the risk of mechanical failure with thin HXLPE liners in total hip arthroplasty (THA). Our purpose was to evaluate long-term outcomes and PE wear rates in primary THAs pairing large femoral heads with small acetabular components and thin HXLPE liners. We retrospectively reviewed 29 patients who underwent 33 primary THAs using large femoral heads (32 or 36 mm) with small acetabular components (48 or 50 mm) and thin HXLPE liners (3.9 or 5.9 mm) at minimum 10-year follow-up. PE liner wear was measured using a validated radiographic technique. Mean age was 66 years, 97% of the patients were women, and mean body mass index was 26.3 kg/m2. Thirty hips (90.9%) had ceramic femoral heads, and 13 hips (39%) had 36-mm femoral heads with 3.9-mm HXLPE liners. All cases used a neutral PE design. Mean linear wear rate and volumetric wear rate were 0.04 mm/year and 39.6 mm3/year, respectively, at mean 10.9-year follow-up. There were no instances of liner fracture, liner dissociation, or revision. Mean Hip disability and Osteoarthritis Outcome Score for Joint Replacement (HOOS, JR) was 92.1. In the largest long-term study of primary THAs using large femoral heads with small acetabular components and thin HXLPE liners, we found low linear and volumetric wear rates and no cases of liner mechanical failures. Thin HXLPE liners are a safe and viable option for THA surgeons. [Orthopedics. 2024;47(2):118-122.].

Risk Factors for Dislocation following Total Hip Arthroplasty in Developmental Dysplasia of the Hip: A Systematic Review and Meta-Analysis

PURPOSE

This systematic review and meta-analysis aimed to identify risk factors of dislocation after total hip arthroplasty (THA) in patients with developmental dysplasia of the hip (DDH).

METHODS

A systematic literature review was performed on 18th August 2022 using Medline, Embase, Scopus, Web of Science electronic databases, and a manual search. The study was conducted according to the PRISMA guidelines and registered with PROSPERO. Statistical analysis includes assessment of heterogeneity and data synthesis using RevMan 5.4.

RESULTS

Review of five studies including 2865 patients and 116 dislocated hips found that lower body mass index (BMI) (SMD = 0.22, p = 0.04, I2 = 0%), Crowe classification type IV versus I, II, and III (OR = 2.70, p = 0.004, I2 = 51%), higher cup inclination (SMD = 0.39 p = 0.0007, I2 = 0%), femoral head size < 28 mm (OR = 5.07, p = 0.003, I2 = 71%), lateral surgical approach (OR = 1.96, p = 0.02, I2 = 0%), and postoperative infection (OR = 6.26, p < 0.0001, I2 = 0%) were significant risk factors. However, age, gender, cup anteversion, femoral osteotomy, vertical (V-COR) centre of rotation, intraoperative fracture, preoperative and postoperative leg length discrepancy (LLD) and previous hip surgery were not found to be significant risk factors.

CONCLUSION

This study underscores importance of these risk factors in THA planning for DDH patients to reduce dislocation risk. Further research needed to understand mechanisms.

Dual-Mobility Versus Large Femoral Heads in Revision Total Hip Arthroplasty: Interim Analysis of A Randomized Controlled Trial

INTRODUCTION

This multicenter randomized controlled trial evaluated if dual-mobility bearings (DM) lower the risk of dislocation compared to large femoral heads (≥36mm) for patients undergoing revision total hip arthroplasty (THA) via a posterior approach.

METHODS

A total of 146 Patients were randomized to a DM (n=76; 46 mm median effective head size, range 36 to 59 mm) or a large femoral head (n=70; twenty-five 36 mm heads [35.7%], forty-one 40 mm heads [58.6%], and four 44mm heads [5.7%]). There were 71 single-component revisions (48.6%), 39 both-component revisions (26.7%), 24 reimplantations of THA after 2-stage revision (16.4%), seven isolated head and liner exchanges (4.8%), four conversions of hemiarthroplasty (2.7%), and one revision of a hip resurfacing (0.7%). Power analysis determined that 161 patients were required in each group to lower the dislocation rate from 8.4 to 2.2% (power=0.8, alpha=0.05).

RESULTS

At a mean of 18.2 months (range, 1.4 to 48.2), there were three dislocations in the large femoral head group compared to two in the DM cohort (4.3 vs. 2.6%; P=0.67). One patient in the large head group and none in the DM group were successfully treated with closed reduction without subsequent revision.

CONCLUSION

Interim analysis of this randomized controlled trial found no difference in the risk of dislocation between DM and large femoral heads in revision THA, although the rate of dislocation was lower than anticipated and continued follow up is needed.

Modernizing Our Understanding of Total Hip Arthroplasty in the Pediatric and Young Adult Patient: A Single-center Experience

INTRODUCTION

Pediatric hip disorders represent a broad range of pathology and remain a significant source of morbidity for children and young adults. Surgical intervention is often required for joint preservation, but when salvage is not possible, joint replacement may be indicated to eliminate pain and preserve function. Although there have been significant updates in the management of both pediatric hip disease and the field of total hip arthroplasty (THA), there is a paucity of literature reflecting advancements in the area of pediatric and young adult (PYA) arthroplasty. No study has investigated the impact of approach on outcomes after PYA THA. The purpose of this study is to describe the indications, techniques, and early outcomes of THA in the PYA population in a modern practice setting.

METHODS

We performed a retrospective descriptive analysis of all patients undergoing primary THA performed at a tertiary care children's hospital from 2004 to 2019. Ninety-three hips in 76 patients were evaluated. Demographics, intraoperative variables, postoperative pain and function ratings, and complication and revision rates were collected.

RESULTS

Eighty-five hips in 69 patients were included. Patients were aged 12 to 23 years old, with males and females represented equally (33 vs. 36, respectively). The most common cause of hip pain was avascular necrosis (AVN, 56/85, 66%), most commonly due to slipped capital femoral epiphysis (13/56, 23%) idiopathic AVN (12/56, 21%), and chemotherapy (12/56, 21%). Half of all hips had been previously operated before THA (43/85). Thirty-six procedures were performed via the posterolateral approach (36/85, 42%), 33 were performed via direct anterior approach (33/85, 39%), and 16 were performed via the lateral approach (LAT, 16/85, 19%). At final follow-up, 98% (83/85) of patients had complete resolution of pain, 82% (70/85) had no notable limp, and 95% (81/85) had returned to all activities. There were 6 complications and 1 early revision. Average Hip disability and Osteoarthritis Outcomes Score for Joint Replacement scores increased by 37 points from 56 to 93. The overall revision-free survival rate for PYA THA was 98.8% (at average 19-mo follow-up).

CONCLUSIONS

Modern PYA THA is dissimilar in indications and surgical techniques to historic cohorts, and conclusions from prior studies should not be generalized to modern practice. In our practice, PYA patients most commonly carry a diagnosis of AVN, and THA can be performed with modern cementless fixation with large cup and head sizes and ceramic-on-cross-linked polyethylene bearings utilizing any approach. Further study is required to better characterize middle-term and long-term results and patient-reported outcomes.

LEVEL OF EVIDENCE

Therapeutic Level IV-retrospective case series.

The Impact of Varying Femoral Head Length on Hip External Rotation During Posterior-approach Total Hip Arthroplasty

Background

Prior investigations of total hip arthroplasty (THA) have studied the effects of prosthetic femoral head size and stem offset on hip range of motion (ROM), impingement risk, and overall hip stability to optimize the return to activities of daily living. However, the relationship between femoral head length and hip ROM, specifically external rotation (ER), has not been evaluated. The aim of our study was to intraoperatively assess how femoral head length affects hip ROM during a posterior approach THA.

Methods

Thirty-two patients undergoing a primary elective THA through a posterior approach were prospectively included. After final femoral stem insertion, femoral head trials were performed using the targeted head length, followed by the shorter (-3.0 to -3.5 mm) and longer (+3.0 to +4.0 mm) head length configurations. At each length, hip ER was measured using an intraoperative goniometer from an imageless navigation system. ER values across the three head lengths were compared using a repeated-measures analysis of variance and paired t-tests.

Results

Varying femoral head lengths demonstrated a statically significant and reproducible effect on intraoperative ER range (analysis of variance; P < .001) in each patient. An increased femoral head length (mean 3.4 mm) significantly decreased (P < .001) ER range by 10.8 ± 3.3° while a shortened femoral head length (mean 3.5 mm) significantly increased (P < .001) the ER ROM by 6.0 ± 3.8°.

Conclusions

The results of this study demonstrate the sensitivity of hip ROM to incremental changes in femoral head length. As ER is important for activities of daily living, inadvertent lengthening should be avoided.

Major acetabular defects: outcomes of first revision total hip arthroplasty using Kerboull cross-plate with allograft and cemented dual mobility cup at a maximum follow-up of fourteen years

BACKGROUND

The use of dual mobility cups (DMC) has been shown to reduce hip instability after revision surgery. For severe acetabular bone loss, reconstruction with a Kerboull cross-plate and bone allograft would contribute to restoring native hip position and bone stock. Only two papers reported on the combination of Kerboull cross-plate with bone allograft and cemented DMC in revision total hip arthroplasty (THA).

METHODS

This is a monocentric retrospective study (28 cases) of first-time revision THA using such a construct in American Association of Orthopaedic Surgeons (AAOS) grade III and IV acetabular bone defect. Detailed demographic, clinical and radiographic results were recorded and evaluated.

RESULTS

With a mean follow-up of six ± 3.63 years, no case of instability was reported. The modified Harris Hip Score (mHHS) was 88.4 ± 10.1. No hook fracture or mechanical failure was observed. Non-progressive radiolucent lines were recorded. Osteointegration of the allografts was observed in all cases with a mean Grodet score of 7.9 ± 0.97.

CONCLUSIONS

In first revision THA, the use of a Kerboull cross-plate with allograft and a cemented DMC in AAOS grade III and IV acetabular bone defects demonstrated excellent clinical and radiological outcomes with no recorded cases of dislocation or mechanical failure.

A Comparison of Revision Rates and Dislocation After Primary Total Hip Arthroplasty with 28, 32, and 36-mm Femoral Heads and Different Cup Sizes: An Analysis of 188,591 Primary Total Hip Arthroplasties

This article was updated on August 17, 2022, because of previous errors, which were discovered after the preliminary version of the article was posted online. On page 1462, in the first sentence of the Abstract section entitled "Results," the phrase that had read "and 36-mm heads had fewer dislocations than 28-mm (HR = 0.33 [95% CI, 0.16 to 0.68]; p = 0.003), but more dislocations than 32-mm heads (HR for >2 weeks = 2.25 [95% CI, 1.13 to 4.49]; p = 0.021)" now reads "and 36-mm heads had fewer dislocations than 28-mm (HR = 0.33 [95% CI, 0.16 to 0.68]; p = 0.003) and 32-mm heads (HR for ≥2 weeks = 0.44 [95% CI, 0.22 to 0.88]; p = 0.021)." On page 1468, in the last sentence of the section entitled "Acetabular Components with a Diameter of <51 mm," the phrase that had read "and HR for ≥2 weeks = 2.25 [95% CI, 1.13 to 4.49; p = 0.021]) ( Fig. 3 )" now reads "and HR for ≥2 weeks = 0.44 [95% CI, 0.22 to 0.88; p = 0.021]) ( Fig. 3 )." Finally, on page 1466, in the upper right corner of Figure 3 , under "32mm vs 36mm," the second line that had read "2Wks+: HR=2.25 (1.13, 4.49), p=0.021" now reads "2Wks+: HR=0.44 (0.22, 0.88), p= 0.021."

Impingement in total hip arthroplasty: A geometric model

Total Hip Arthroplasty (THA) is one of the most common and successful surgical interventions. The survivorship at 10 years for the most commonly used systems is over 95%. However, the incidence of revision is usually much higher in the 0-1 year time period following the intervention. The most common reason for revision in this early time period is dislocation and subluxation, which may be defined as complete or permanent, and partial or temporary loss of contact between the bearing surfaces respectively. This study comprises the development of a geometric model of bone and an in situ total hip replacement, to predict the occurrence and location of bone and component impingement for a wide range of acetabular cup positions and for a series of frequently practiced activities of daily living. The model developed predicts that anterior-superior component impingement is associated with activities that result in posterior dislocation. The incidence may be reduced by increased cup anteversion and inclination. Posterior-inferior component impingement is associated with anterior dislocation activities. Its incidence may be reduced by decreased cup anteversion and inclination. A component impingement-free range was identified, running from when the cup was positioned with 45° inclination and 25° anteversion to 70° inclination and 15°-20° anteversion.

Trends of Femoral Neck Fracture Treatment Using Total Hip Arthroplasty: Reported From the American Joint Replacement Registry

INTRODUCTION

Total hip arthroplasty (THA) rather than hemiarthroplasty for displaced femoral neck fracture (FNF) is often chosen for younger patients who are more active and/or have underlying hip osteoarthritis. However, instability remains the primary concern of doing THA. Dual mobility (DM) has been shown to decrease this risk through a larger effective head size and greater head-to-neck ratio compared with conventional THA. The purpose of this study was to identify femoral head size and DM usage patterns for the treatment of FNF with THA in the United States using the American Joint Replacement Registry.

METHODS

A retrospective cohort study was conducted, including all primary THAs done for FNF from 2012 to 2019. THA and FNF were defined using Current Procedural Terminology or International Classification of Diseases-9 or -10 diagnosis and procedure codes. Analysis was based on patient demographics, femoral head size, and DM usage. Descriptive statistics were used using a Pearson chi-square test. All analyses were conducted using SAS version 9.4, and statistical significance was set at P < 0.05.

RESULTS

There were 18,752 THAs done by 3,242 surgeons at 789 institutions during the 8-year study period. The overall population was 66% female, and the mean age was 72.3 ± 11.8 years. The most commonly used femoral head size was 36 mm (48.5%) followed by 32 mm (24.5%), ≤28 mm (10.7%), DM (10.8%), and ≥40 mm (5.7%). A trend was observed toward decreased use of ≤28, 32, and ≥40-mm heads starting in 2016 across the years and increased use of 36-mm heads (P < 0.0001). A significant increase was observed in the usage of DM over time from 6.4% in 2012 to 16.2% in 2019 (P < 0.0001).

DISCUSSION

Most of the femoral heads used were ≥36 mm, and the use of DM increased during the study period. Additional analysis is warranted to understand how these trends will affect overall outcomes and postoperative dislocation rates.

Finite element analysis of hip implant with varying in taper neck lengths under static loading conditions

BACKGROUND AND OBJECTIVE

Total hip arthroplasty is known as one of the best advancements in orthopedics in the 20th century. Due to age or trauma hip joint has to replace by an artificial implant. After the hip arthroplasty, the patients can return to normal day-to-day activities with a normal range of motion. There are several types and designs are currently available. These designs usually depend upon the anatomy of the patients. There is a need for revision surgery due to dislocation and aseptic loosening in these joints over time in actively younger patients. Minor changes in the design stage can certainly improve the life expectancy of the implant and will also further reduce the revision rate.

METHODS

In this current work, finite element analysis is carried out by varying the neck length with a change in femoral head size for a circular-shaped stem. The effects of using a shorter neck are analyzed. A total of nine combinations are considered for analysis. Modeling is carried out in CATIA V-6 and analysis is performed in ANSYS R-19. A femoral head of 36, 40, and 44 mm and taper neck length of 18, 16, and 14 mm is considered. CoPE is considered as the material combination for all the models.

RESULTS

It was observed that the von Mises stresses in the complete implant tend to decrease with an increase in the femoral head size. Maximum 5% variation in stress values when 36 mm femoral head is compared with 44 mm. The stresses in the taper neck region tend to decrease with a decrease in the neck length. Minimum von Mises stress of 161.83 MPa was found for the complete implant and in the head-neck region, a minimum von Mises stress found 91.9 MPa.

CONCLUSIONS

Performance evaluation of hip implant under static loading conditions gives a clear idea about the behavior of implant. It was found that a decrease in the von Mises stresses with a decrease in the taper length. However, these variations won't affect much in the performance of the hip implant. Also, a reduction in taper length can significantly increase the dislocation in the implant. So it is advised to consider the optimal taper length with an increase in the femoral head size.

Recovery of activity level following total hip arthroplasty in patients less than 60 years of age

BACKGROUND

Total hip arthroplasty (THA) is a useful treatment for pain relief and functional improvement. THA indications now include younger, more active patients, with improved implant design and bearing materials. We aimed to investigate daily activity level and return to work after THA, about which limited information is available. Moreover, differences in patient background and clinical parameters including size of femoral head and surgical approach were evaluated.

METHODS

A multicentre survey was carried out in patients below 60 years, undergoing THA between 2007 and 2012, at least 1 year after surgery. Primary THA patients with osteoarthritis, avascular necrosis, rheumatoid arthritis, hip dysplasia, and no history of postoperative complications were included. The questionnaire included daily activity and occupation levels before and after surgery. University of California, Los Angeles (UCLA) activity score and occupational classification index were defined, and statistical analysis was performed.

RESULTS

The mean preoperative UCLA score in 204 patients was 4.55 which improved to 6.17 after surgery. Pre- as well as postoperative UCLA scores in males were significantly higher than that in females. No differences were observed in other parameters. Return to work rate in males was 94.4%; significantly higher than that in females (52.3%). Younger patients with large head THA were more likely to return to work.

CONCLUSIONS

Most patients showed improved activity levels. Satisfaction levels were higher in young males with large femoral head size. Patients with a higher preoperative work level are expected to have a higher return to work rate.

Wear and migration are not influenced by head size in a vitamin E-infused highly cross-linked polyethylene acetabular cup

BACKGROUND

Aseptic loosening and periprosthetic osteolysis are frequent complications in total hip arthroplasty requiring revision surgery. Highly cross-linked polyethylene (HXLPE) implants have improved wear resistance, permitting larger femoral heads. However, such implants may experience surface cracking, mechanical failure, and oxidative damage. Vitamin E-infused HXLPE (VEPE) implants were therefore developed to reduce oxidation without compromising mechanical strength. We addressed the following questions: (1) Does femoral head size affect the midterm annual polyethylene wear rates of VEPE acetabular cups? (2) Does femoral head size affect the midterm migration rates of VEPE acetabular cups? (3) Are clinical outcomes affected by femoral head size?

HYPOTHESIS

Annual wear rate, migration rate, and clinical outcomes of VEPE acetabular cups are independent of femoral head size.

PATIENTS AND METHODS

This was a prospective, multicentre, observational study of patients that underwent total hip arthroplasty. Hips were grouped according to the size of femoral head implanted (28 mm, 32 mm, and 36 mm). We determined annual wear rate and migration rate of VEPE acetabular cups using the Einzel-Bild-Röntgen-Analyse software. Clinically, we assessed the Harris Hip Score and visual analog score for pain and satisfaction.

RESULTS

We followed 253 patients (267 hips) for a mean of 55.0±20.6 months in the 28 mm, 46.2±21.4 months in the 32 mm, and 43.8±22.6 months in the 36 mm group. The annual wear rate was 0.025 mm per year from 1 year to the last follow-up and remained similar between the groups (p>0.05). Also, mean two-dimensional migration rates did not exceed 0.05 mm from 2 years to the last follow-up and remained similar between the groups (p=0.355). Finally, clinical outcomes also did not differ between the groups (p>0.05). Two patients required revision surgery.

DISCUSSION

Femoral head size did not influence midterm annual wear rate, migration rate, and clinical outcomes of VEPE acetabular cups. Furthermore, wear and cup migration rates were below the reported values leading to osteolysis and aseptic loosening. Nevertheless, studies with extended follow-up periods will be necessary to confirm these results in the long term.

LEVEL OF EVIDENCE

IV.

Recommendations for return to sports after total hip arthroplasty are becoming less restrictive as implants improve

INTRODUCTION

Total hip arthroplasty (THA) surgeries are expected to exponentially increase in the upcoming years, likely because of the overall broader indication of THAs. With these developments, an increasing number of younger (< 50 years) and active patients will receive surgical interventions, and expectations for an active lifestyle will accordingly increase. In addition, surgeons now have a growing array of techniques and implant materials to choose from. Despite these developments, evidence to provide the best standard-of-care to patients with high expectations for return to sports (RTS) is scarce and urgently needed. What recommendations do arthroplasty surgeons currently make to patients with high return to sports expectations, what factors may influence their recommendations and what surgical techniques and implant specifications are considered favorable in the treatment of patients with a more active lifestyle? This study was conducted to analyze the current recommendations, patient assessment, and patient counseling after THA to identify trends and relevant factors for surgical decision-making in patients with high-RTS expectations.

MATERIAL AND METHODS

We designed a questionnaire comprising five general items and 19 specific items that included 46 sub-items for hip arthroplasty and conducted a survey among 300 German surgeons specialized in arthroplasty at the German Arthroplasty Society (AE) to assess expert opinions, recommendations, surgical decision-making, and patient counseling for patients with high expectations for RTS after THA.

RESULTS

The majority of surgeons (81.9%) were in favor of RTS after THA. Risks associated with sports after THA were considered minimal (1%), with periprosthetic fractures ranking highest, followed by hip dislocation and polyethylene wear. Some surgical decision-making was influenced by high-RTS expectations in regard to implant fixation, stem type, femoral head diameter, and bearing-surface tribology. We observed an increasingly liberal counseling of patients for high-impact sports.

CONCLUSION

With the improvement of implants and surgical techniques, surgeons are more willing to encourage patients to adopt a more active lifestyle. However, the true long-term limitations need further investigation in future studies.

LEVEL OF EVIDENCE

5 Expert opinions.

Outcomes of total hip arthroplasty using dual-mobility cups for femoral neck fractures: a systematic review and meta-analysis

OBJECTIVES

Femoral neck fractures (FNFs), with up to 15% mortality, are prominent orthopaedic emergencies. After treating FNFs, dislocation is another challenge increasing morbidity, mortality and treatment costs substantially. The emerging dual-mobility cup (DMC) may decrease dislocation rates following total hip arthroplasty (THA) for FNFs. We performed a systematic review of literature reporting dislocation and mortality rates with DMC-THA for the treatment of FNFs.

METHODS

2 authors independently searched PubMed (MEDLINE), Google Scholar and Cochrane library for studies reporting dislocation and mortality rates for FNFs treated with DMC-THA since inception up to January 2019. Data on outcomes of interest was extracted from all studies and assessed for eligibility for a meta-analysis.

RESULTS

Out of 522 search results, 18 studies were included in the systematic review and 4 in the meta-analysis. The mean rate of dislocation following DMC-THA for FNFs was found to be 1.87% ± 2.11, with a 1-year mortality rate of 14.0% ± 10.55. Results of meta-analysis showed that dislocation and 1-year postoperative mortality rates were significantly lower for DMC-THA with a risk ratio 0.31 (95% CI, 0.16-0.59; I² = 0%, p = 0.0003) and 0.55 (0.40, 0.77; I² = 0%, p = 0.003) respectively when compared to biploar hemiathroplasty (BHA).

CONCLUSIONS

The mean dislocation and mortality rates in DMC-THA are lower than previously reported rates for THA with single cup and comparable to unipolar and bipolar hemiarthroplasty. Further research involving randomised control trials to assess differences in outcomes, longevity and cost-effectiveness needs to be conducted to make recommendations for the use of DMC in treating FNFs.

Modular dual-mobility cups using ceramic liners: an original solution for selected indications?

BACKGROUND

Dual mobility (DM) has been shown to improve stability both in primary and revision total hip arthroplasty (THA) and is increasingly used in patients at high risk of dislocation and in the treatment of THA instability. The introduction of modular liners has helped to overcome some of the limitations of monoblock DM cups. In this context, the use of a ceramic liner would avoid the conventional cobalt-chromium liner in the titanium shell, which can be problematic in some situations. The aim of this paper is to report the outcomes of a consecutive series of patients undergoing revision THA using a modular DM cup with a ceramic liner instead of the conventional metal one, and to clarify the rationale for this currently "off-label" use.

PATIENTS AND METHODS

This is a retrospective series of patients who received this new DM bearing in a single institution. Patients were followed up clinically and radiologically at 1 month, 3 months, 6 months and yearly thereafter.

RESULTS

5 patients received the ceramic liner in the study period (2014-2019). The indications were instability or high risk of dislocation in ceramic liner fracture and ARMD with soft tissue damage after MoM THA. The mean age at surgery was 74 (63-82) years, the mean follow-up was 36 (12-72) months. No dislocation occurred, and no adverse events related to the implant were recorded.

CONCLUSIONS

The use of a ceramic liner in a modular DM cup offers several advantages in selected patients, and the results of our cohort are encouraging. However, caution is needed in introducing this new bearing because knowledge is currently limited. Further studies on a larger number of patients and with longer follow-ups are needed to confirm these findings and before widespread use of the device.

Are the Wear and Osteolysis Outcomes Different between Annealed and Remelted First-Generation Highly Crosslinked Polyethylene after Long-Term Implantation?

First-generation highly crosslinked polyethylene (HXLPE) was developed to reduce polyethylene wear debris and subsequent osteolysis. Two thermal stabilization strategies were developed, annealing and remelting, to remove free radicals remaining in the polymer. Both types of HXLPEs have demonstrated better wear resistance to conventional polyethylene in hip arthroplasty. However, few studies have directly compared the mid- to long-term clinical outcomes of first-generation HXLPEs. We sought to address the following research questions: (1) is there a difference between the revision reasons for HXLPE formulations (annealed and remelted), (2) is there a difference in oxidation between annealed and remelted HXLPEs, (3) is there a difference in the linear penetration rate of annealed and remelted HXLPEs, and (4) does the formulation of first-generation HXLPEs affect the prevalence of osteolysis? A total of 129 first-generation HXLPE acetabular liners were collected in a multicenter retrieval program. These components were implanted for 5 or more years and were fabricated from annealed or remelted HXLPE. Reasons for revision, body mass index, age, sex, and activity levels were collected from medical records. Oxidation was measured at four regions of interest: bearing surface, backside surface, locking mechanism, and rim. Liner penetration was directly measured from retrievals using a micrometer. Osteolysis was reported in the operative notes by the revising surgeon and a thorough review of the operative notes and radiographs. Revision reasons included infection, instability, pain, and loosening. The annealed liners had higher oxidation indices than remelted liners. There was no difference in linear penetration rates between cohorts. There was no difference in osteolysis prevalence between cohorts. We found remelted HXLPE to be more oxidatively stable than annealed HXLPE but did not find a significant difference in the linear penetration rates or the prevalence of osteolysis. Our findings demonstrate sustained long-term wear resistance of both cohorts of HXLPE. We did not find evidence to support a long-term clinical difference between the formulations of HXLPE.

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

Using large femoral heads in total hip arthroplasty (THA) has been widely advocated to improve the function and longevity of the components. However, increasing the head size has been shown to accelerate polyethylene liner wear. Few studies have investigated the effect of other important structural parameters (such as polyethylene liner thickness, metal cup size, head-liner conformity, loading conditions, etc.) on the biomechanical functions of the THAs. In this study, an analytical model was used to evaluate the polyethylene liner wear characteristics of the THAs (defined using a biomechanical wear factor) with various structural parameters of the THAs and loading conditions. For all the THA systems examined in this study, under the same loading conditions, a larger head leads to increasing contact areas, lower contact stresses, and higher biomechanical wear factors. When the head size is fixed, a decrease in the polyethylene liner thickness or a decrease in the head-liner conformity leads to higher peak contact stresses and smaller contact areas and consequently, lower biomechanical wear factors. This study provides a parametric analysis tool for the optimal design/selection of the THA systems and for prediction of early effects of various structural parameters on the biomechanical function (such as contact stresses) and longevity (such as polyethylene liner wear) of the THA systems.

Third-Generation Medium Cross-Linked Polyethylene Demonstrates Very Low Wear in Total Hip Arthroplasty

Background

Cross-linked polyethylene (XLPE) liners have shown lower wear rates than conventional polyethylene liners in total hip arthroplasty. The primary aim of our study was to report our most recent analysis of wear rates and clinical outcomes of a third-generation XLPE liner. Secondary aims were to investigate the rate of adverse events related to mechanical failure or oxidation of this liner.

Methods

A series of 266 total hip arthroplasties using a specific XLPE liner were retrospectively reviewed. Radiographs were examined to determine linear and volumetric wear rates and presence of osteolysis. Clinical outcomes, revision rates, mechanical failures, and risk factors for accelerated polyethylene wear were additionally investigated.

Results

The mean age at the time of surgery was 65.8 years and the mean follow-up was 5.5 years. The mean linear wear rate was 0.003 mm/year and the mean volumetric wear rate was 0.42 mm³/year, and there was no evidence of osteolysis. Harris hip scores increased from 50.9 preoperatively to 96.0 at the latest follow-up. The revision rate was 0.4%, with no liner rim fractures and no liner dissociations/loosenings. Femoral head material, head size, age, body mass index, and time since implantation had no effect on wear rates.

Conclusion

Wear rates for this third-generation XLPE liner were low at mid-term follow-up, and no adverse sequelae of oxidation or deleterious mechanical properties were observed. This remained true regardless of femoral head size and material or patient age and body mass index. Further analysis will be necessary to ensure continued wear resistance, oxidative stability, and mechanical strength at long-term follow-up.

Large Diameter Head in Primary Total Hip Arthroplasty: A Systematic Review

INTRODUCTION

The literature around use of Large Diameter Heads (LDH) is abundantly available for revision Total Hip Arthroplasty (THA) but is lacking for primary uncomplicated THA. This systematic review was undertaken to synthesize data around primary THA involving LDH and analyze the associated complications (dislocation, volumetric wear, implant survivorship and functional score) along with reported effects on range of motion (ROM), patient reported outcomes and impingement rate/groin pain.

METHODS

A PRISMA compliant systematic review was done using extensive search in PubMed database, along with offline search looking for the literature published in English language between 2008 and 2018. The articles providing data on the use of large diameter heads (LDH) (36 mm or larger) on various bearing surfaces were collected. This included robust national joint registries of different countries. Narrative approach to data synthesis was used.

RESULTS

A total of 23 papers met our inclusion criteria, including six national joint registries. It was observed that LDH had significantly low dislocation rates, excellent implant survival rate as per Kaplan-Meier survivorship (> 90% at five years). Surgical approaches, except Minimally Invasive Surgery (MIS), did not increase any risk of dislocation as long as it was meticulously repaired. There was no significant improvement in any functional scores or improved ROM.

CONCLUSIONS

LDH of 32-36 mm are now commonly used in primary THA and is accepted as a popular size. The beneficial effects of a large head size are negated beyond 38 mm. The most favored size for LDH THA, therefore, is 36 mm contrary to the older literature favoring 28 mm.

The impact of polyethylene abrasion on the occurrence of periprosthetic proximal femoral fractures in patients with total hip arthroplasty

INTRODUCTION

In addition to abrasion-induced osteolysis and ensuing instabilities, the polyethylene (PE) abrasion of total hip arthroplasty (THA) inlays can also cause gait instability due to the decentralization of the hip joint. The current literature yields, as yet, insufficient findings whether these two factors are linked directly or indirectly to a higher risk for periprosthetic proximal femoral fractures (PPFF). The aim of our retrospective evaluation is to analyse the impact of PE abrasion on the pathology of PPFF in patients with THA.

MATERIAL AND METHODS

The retrospective evaluation comprises all PPFF in patients with THA in the period from 01/2010 up to 12/2016. The study group (SG) included 66 cases (n = 66). The control group (CG) was comprised of patients with asymptomatic THA (n = 66), who were treated by our outpatient department including routine check-ups and X-ray examinations. We used the matched-pair methodology to scale the period of postsurgical care of the CG to the lifetime of the implant up to PPFF in the SG. We included epidemiologic data, radiological femoral head decentralization, osteolysis (Gruen classification), instabilities, acetabular cup position, and implant properties in our analysis. For the SG, we also included intra-operative signs of abrasion.

FINDINGS

The SG showed significantly higher numbers of decentralized THA as signs of inlay erosion with 73% compared to only 41% in the CG (p > 0.001). The SG showed 1 ± 0.68 mm hip joint decentralization as to 0.5 ± 0.59 mm in the CG (p = 0.004). We found significantly more cases of osteolysis in the SG (n = 25) than in the CG (n = 13) (p = 0.003). We found no notable differences in acetabular cup inclination or anteversion as well as cup size. However, differences were significant in femoral head size (SG 32 ± 2.3 mm, CG 36 ± 2.4 mm; p = 0.042) and head material. We found more widespread use of metal femoral heads in the SG than in the CG (SG 1:1, CG 1:21; p = 0.001).

CONCLUSION

PPFF patients showed significantly higher rates of inlay erosion, resulting in femoral head decentralization and osteolysis. The higher rate of fracture is likely caused by the increasing instability of the implant fixation due to abrasion-induced osteolysis and the associated degradation of bone quality. It is conceivable that the abrasion and decentralization of the THA can also lead to gait instability, and thus, a higher proneness to falls. Gait instability can also be aggravated by increased granulation tissue and effusion due to the inlay abrasion. Although this cannot be substantiated by the investigation. In patients with decentralization of the THA and osteolysis, a radiological follow-up should be performed, and in case of gait instability (femoral head and) inlay replacements should be considered.

Uncemented cups with and without screw holes in primary THA: a Swedish Hip Arthroplasty Register study with 22,725 hips

Background and purpose - Uncemented cups in total hip arthroplasty (THA) are often augmented with additional screws to enhance their primary stability. We investigated whether there is a difference in the risk for revision between cups with screw holes and cups without screw holes. Patients and methods - We analyzed the risk for cup revision of uncemented cups registered in the Swedish Hip Arthroplasty Register (SHAR) between 2000 and 2017 with respe ct to the presence of screw holes. Only patients with primary osteoarthritis (OA) were included. 22,725 cups, including 12,354 without screw holes and 10,371 with screw holes, were evaluated. Revision rates at 2 and 10 years after the primary operation were analyzed. Results - At a median follow-up time of 3.4 years (0-18), 459 cup revisions were reported. The main reasons for cup revision during the whole observation time were infection, 52% of all cup revisions, and dislocation, 26% of all cup revisions. The survival rate with cup revision due to aseptic loosening as endpoint was 99.9% (95% CI 99.8-99.9) at 2 years for both cups with and cups without screw holes, and the survival rates at 10 years were 99.5% (CI 99.3-99.7) and 99.1% (CI 98.6-99.5), respectively. Cups without screw holes showed a decreased risk of revision due to any reason at both 2 years (adjusted hazard ratio [HR] 0.6, CI 0.5-0.8) and 10 years (HR 0.7, CI 0.5-0.9). Interpretation - We found a very low revision rate for aseptic loosening with modern, uncemented cup designs. Cups with screw holes had an increased risk of revision due to any reason in patients with primary OA.

Low dislocation rate of Saturne®/Avantage® dual-mobility THA after displaced femoral neck fracture: a cohort study of 966 hips with a minimum 1.6-year follow-up

INTRODUCTION

Dislocation is a serious and common complication and a great concern with the use of total hip arthroplasty (THA) when treating displaced femoral neck fracture (FNF). Dual-mobility (DM) THA might reduce the dislocation risk. We aim to report the dislocation and revision rate of primary DM THA in patients with displaced FNF.

MATERIALS AND METHODS

Between 2005 and 2015, 966 consecutive patients (676 women) at mean age 80.5 years (range 42-104) with displaced FNF were operated with DM articulation THA by posterolateral approach (PLA). Patient files and radiographs were evaluated for dislocations, revisions, and other complications until death of the patient or August 1st, 2017. Data were crosschecked with the National Patient Registry. Patient's mental state was tested upon admissions. Surgeon's educational level was noted and post-operative cup position was measured.

RESULTS

At minimum 1.6-year follow-up, there were 45 (4.7%) dislocations and eight (0.8%) cup revisions. The 30-day mortality was 9.2% and 533 patients (55.2%) were dead at the time of last follow-up. We observed eight intraprosthetic dislocations (IPD); six occurred in relation to closed reduction. Cementless stem fixation was associated with higher dislocation risk (p = 0.04) and higher rate of stem complications (p = 0.002). There was no significant association between cognitive impairment and dislocation (OR 2.0, 95% CI 0.96-4.34, p = 0.06).

CONCLUSION

Overall, DM THA inserted via PLA results in an acceptable dislocation risk and low revision rate in fragile, old patients with acute FNF fracture, regardless of mental status. A unique complication in DM THA is IPD, which requires an immediate open reduction surgery.

Femoral Head Penetration Rates of Second-Generation Sequentially Annealed Highly Cross-Linked Polyethylene at Minimum Five Years

BACKGROUND

Highly cross-linked polyethylene (HXLPE) liners in total hip arthroplasty (THA) have demonstrated decreased wear rates, resilience to cup orientation, and reduced osteolysis compared to conventional polyethylene. Sequential irradiation and annealing below the melting temperature is unique compared to most HXLPE which is irradiated and remelted. This study purpose is to provide minimum 5-year femoral head penetration rates of sequentially annealed HXLPE in primary THA.

METHODS

A retrospective review of a prospectively collected database identified 198 consecutive, cementless primary THAs utilizing sequentially annealed HXLPE (X3; Stryker, Mahwah, NJ). Operative technique was standardized. Radiographs were analyzed utilizing the Martell method with minimum 5-year and 1-year radiographs as baseline to minimize the initial bedding-in period.

RESULTS

Seventy-seven hips with minimum 5-year follow-up were analyzed. Mean steady state linear and volumetric head penetration rates were 0.095 mm/y and 76 mm³/y, respectively. Volumetric head penetration was significantly less for 32-mm compared to 36-mm (P = .028). In addition, less head penetration was observed for ceramic 32-mm heads at nearly half the rate compared to cobalt-chromium 36-mm heads (P ≥ .092). No correlations existed between penetration rates and age, body mass index, University of California Los Angeles Activity Level, polyethylene thickness, cup inclination, or anteversion (P ≥ .10). No radiographic osteolysis was observed.

CONCLUSION

Surprisingly, linear head penetration rates of sequentially annealed HXLPE were nearly identical to the osteolysis threshold for conventional polyethylene and greater than reports of irradiated and remelted HXLPE. Furthermore, these data corroborate reports that HXLPE is resilient to cup orientation and demographic variables. Longer term follow-up is recommended.

Have large femoral heads reduced prosthetic impingement in total hip arthroplasty?

BACKGROUND:

Prosthetic impingement is implicated in dislocation after total hip arthroplasty (THA). While use of larger diameter femoral heads reduces the incidence of dislocation, the effect of larger heads upon impingement rate is unknown. We assessed retrieved THA components for evidence of impingement to determine if large femoral heads reduced the rate of impingement in primary THA and what factors might influence impingement.

METHODS:

Liners from 97 primary THAs retrieved at revision arthroplasty were scored for evidence of impingement, defined as wear or deformation on the rim of the component. Component inclination and version were measured from anteroposterior and cross-table lateral radiographs.

RESULTS:

Independent of revision diagnosis, 77% of liners demonstrated evidence of impingement. Impingement was less prevalent and less severe as head size increased. Severe impingement was observed in 50% of the liners with 28-mm heads, 15% of liners with 32-mm heads, and 21% of liners with 36-mm heads. Regardless of head size, 76% of liners revised for instability demonstrated impingement. Decreased head-neck ratio, use of an elevated liner, increased length of implantation, and increased version were associated with increased severity of impingement.

DISCUSSION:

We showed that larger head sizes are associated with decreased incidence of impingement on retrieved acetabular liners when compared to smaller head sizes. Larger heads have reduced but not eliminated impingement, which remains a potential source of instability.

A Retrieval Analysis of Impingement in Dual-Mobility Liners

BACKGROUND

Implant-related impingement is likely a major causative factor of total hip arthroplasty (THA) instability. Dual-mobility (DM) cups can theoretically improve stability in THA, but impingement rates with DM cups are not well studied. We examined retrieved DM THA liners to determine if less evidence existed for prosthetic impingement between the neck and the polyethylene liner than historical studies from our institution on fixed-bearing THAs.

METHODS

DM components from 93 THAs were identified from 164 THAs whose DM components were revised between 2008 and 2015 through our institutional review board-approved implant retrieval program. The mean age was 63 ± 11 years, mean body mass index was 30 ± 7 kg/m², and mean length of implantation was 2.08 ± 1.89 years. Two independent graders scored each liner for the presence and severity of impingement. Radiographs were evaluated for inclination, anteversion, change in leg length, and combined offset.

RESULTS

Only 21.5% (20/93) of DM cups showed evidence of impingement compared to 77% (75/97) of fixed-bearing cups found in a previous study performed at our institution (P < .001). Of the revision components, 35.2% (5/14) demonstrated evidence of impingement compared to 19.7% (14/71) implanted in primary surgery (P = .189). In the cohort revised for instability, the rate of impingement was 35.3% (6/17); for the implants revised for any other reason, the impingement rate was 18.4% (14/77) (P = .126).

CONCLUSION

This study demonstrates that DM liners significantly reduce the rate of impingement (21.5%) when compared to fixed-bearing liners (77%).

Which is the best bearing surface for primary total hip replacement? A New Zealand Joint Registry study

INTRODUCTION

We have investigated the revision rates of all bearing surface combinations for primary total hip replacement (THR) registered on the New Zealand Joint Registry (NZJR) to determine which coupling has been the most durable and successful over the last 16 years.

METHODS

There were 106,139 primary THRs registered, resulting in 4,960 revisions for any cause. We examined all-cause revision rates, reasons for revision and performed survival analyses.

RESULTS

Ceramic-on-highly cross-linked polyethylene (CoPx) had the lowest all-cause revision rate of 0.54/100-component-years (cys) (95% confidence interval 0.48 to 0.61). This was superior to all other hard-on-soft bearing combinations in unadjusted analysis. Furthermore, the age of patients receiving CoPx was significantly lower than for metal-on-polyethylene (mean 62.9; standard deviation [SD] 10.1 vs. 69.1; SD 9.6; p<0.001). Acetabular loosening was the reason for revision in 14.5% of CoPx, compared to 33% of MoP THRs (p<0.001). Metal-on-metal bearings had the highest revision rate of 1.43/100 cys and were significantly inferior to CoPx (p<0.001). Kaplan-Meier analysis and Cox regression analyses were performed and we adjusted the analyses to control for age, femoral head size, surgical approach and fixation.

CONCLUSIONS

CoPx remained the most durable and successful coupling used in primary THR in New Zealand irrespective of age, gender or size of femoral head.

Estimating the osteolysis-free life of a total hip prosthesis depending on the linear wear rate and head size

We present a model to estimate the osteolysis-free life of total hip arthroplasty, depending on linear wear rate and femoral head size. An estimate of the radiologic osteolysis threshold was calculated, which was based on volumetric wear. The osteolysis-free life of the cup was estimated from the quotient of the osteolysis threshold and volumetric wear rate, which was calculated from the linear wear rate. The impact of the direction of linear wear was determined by sensitivity analysis. From our review, we calculated a weighted mean polyethylene volume of approximately 670 mm³ as osteolysis threshold. Osteolysis-free life of less than 20 years was estimated for linear wear rates of 50 µm/year for head sizes of 32 mm or more, or for linear wear rates of 100 µm/year for any head size. For head sizes of 36 and 40 mm with a linear wear rate of 50 µm/year, the osteolysis-free period is estimated to be only 14.10 and 11.42 years, respectively. Sensitivity analysis showed reasonably robust results. With the aim of osteolysis-free life of more than 20 years, our study presents a viable model to determine maximum possible head size for articulations. Osteolysis-free period for 36 and 40 mm head sizes are far too low for conventional polyethylenes. As the threshold wear volume for highly crosslinked polyethylene is, as of yet, unknown, more research is warranted before our model can be generalized to XLPE.

Cause of irreducible dislocation of a re-revision THR

Instability or recurrent dislocations are a common reason for revision of total hip replacements (THRs). Dual-mobility constructs can help improve stability by increasing the femoral head jump distance. These constructs are used to decrease the risk of re-revision in the setting of recurrent dislocation. This case describes an unusual case of irreducible dislocation of a re-revision THR due to intraprosthetic dislocation. The patient required open reduction and revision of this construct to a tripolar implant. This is important to appreciate from an emergency medicine point of view as repeated attempts at reduction will be fruitless and may result in a femur fracture. This particular type of dislocation is very rare. Perioperative considerations should include early referral to the orthopaedic team for reduction in theatre, and having a low threshold for open reduction. Revision options should be available when bringing a case like this to the operating theatre.

Good function and high patient satisfaction at mean 2.8 years after dual mobility THA following femoral neck fracture: a cross-sectional study of 124 patients

Aims

Our aim was to investigate function, health status and satisfaction in patients treated with primary dual mobility (DM) total hip arthroplasty (THA) after displaced femoral neck fracture (FNF).

Patients and methods

From 2005-2011, 414 consecutive FNF patients received Saturne DM THA. At a minimum of 1-year follow-up, 124 (95 women) were evaluated with Oxford Hip Score (OHS), Harris Hip Score (HHS), health-related quality of life (HRQoL) measure (EQ-5D) and two functional tests: Timed Up and Go (TUG) and Sit to Stand 10 times (STS). The FNF patients were matched 1:2 by age, sex and surgery date with patients receiving THA due to osteoarthrosis (OA group) and 1-year OHS and EQ5D were compared. FNF patients were matched by age and sex with the general population index (GPI) for EQ-5D comparison.

Results

Patient age at surgery after FNF was mean 74.8 (range 30-92) years. At mean follow-up of 2.8 (range 1.0-7.7) years, mean EQ-5D score was 0.79 (SD 0.15) in the FNF group, which was similar to the matched GPI (p = 0.4), but lower (p = 0.014) compared to the OA group. Mean OHS was 36.4 (SD 9.5) in the FNF group and 38.4 (SD 7.2) in the OA group (p = 0.18). HHS in the FNF group was 78.7 (SD 15.5). Mean TUG time was 13.5 (SD 4.9) secs, and mean STS was 37.9 (SD 15.3) secs. Eighty nine percent (n = 111) of FNF patients were satisfied with the operation result.

Conclusion

DM THA following displaced FNF provides a good functional result and quality of life in addition to high patient satisfaction.

Risk factors for conversion surgery to total hip arthroplasty of a hemiarthroplasty performed for a femoral neck fracture

INTRODUCTION

The purpose of this study was to determine risk factors for conversion to total hip arthroplasty (THA) in patients originally treated with hemiarthroplasty (HA) for displaced femoral neck fractures.

METHODS

In this case-controlled study, we identified 54 patients who were treated with HA for femoral neck fracture (FNF) who subsequently underwent conversion to THA at our institution between 2003 and 2013. We randomly selected 142 control patients who underwent HA for a displaced FNF without conversion surgery during the same time period. We compared demographic data, implant parameters, and radiographic data between the groups to identify risk factors for conversion surgery.

RESULTS

In the univariate analysis, younger age at index surgery (mean 75 vs. 80 years, p = 0.006), higher body mass index (26.1 vs. 23.7, p = 0.031), bipolar prosthesis (20% vs. 36%, p = 0.024), absence of dementia (6% vs. 23%, p = 0.01), increased leg length compared to contralateral limb (6.5 mm vs. 0.2 mm, p<0.001), and increased HA femoral head size compared to the contralateral femoral head (2.7 mm vs. 1.5 mm, p = 0.02) were associated with a significantly increased risk of conversion surgery. In the multivariate logistic regression, decreased age at index surgery, no dementia, use of a bipolar head, and increased leg length discrepancy (LLD) were associated with risk of conversion.

CONCLUSIONS

Patient characteristics, including younger age, increased BMI, and absence of dementia can lead to increased risk for conversion of HA to THA. Intraoperative considerations of head size and increase in ipsilateral LLD may increase the risk of conversion surgery. These factors should be considered by surgeons who employ HA for displaced FNFs.

Higher UHMWPE wear-rate in cementless compared with cemented cups with the Saturne® Dual-Mobility acetabular system

INTRODUCTION

Dual mobility (DM) total hip arthroplasty (THA) may reduce dislocation risk, but might increase the risk of high polyethylene (PE) wear due to double wearing surfaces.

METHODS

127 patients (97 female) with 129 hips operated with THA after displaced femoral neck fracture FNF between 2005 and 2011, were seen for a cross-sectional clinical follow-up. Acetabular components were Saturne® DM cups with 28mm chrome-cobalt heads in UHMWPE. Cementless cups (n = 73) were hydroxyapatite coated. Radiographs were obtained for analysis of cup placement, 2D polyethylene wear and wear-rate (PolyWare 3D), and further radiological evaluation. Activity measurements included Timed Up and Go test (TUG) and walking distance from Harris Hip Score (HHS).

RESULTS

At a mean follow-up of 2.83 (1.0-7.7) years the mean wear was 0.82 mm (range 0.17-4.51, SD 0.50), and the wear-rate was 0.37 mm (range 0.06-1.90, SD 0.29). Wear-rate of 0.43 mm/year (SD 0.30) in cementless cups was higher (p = 0.004) than 0.30 mm/year (SD 0.27) in cemented cups. Mean age at time of surgery was 75.1 years (range 30-95). There was no correlation between age at time of surgery and wear (p = 0.56). There was no correlation between cup inclination and wear-rate (p = 0.35). TUG was mean 13.4 seconds (range 4.5-30.1) and correlated with wear rate (p = 0.03).

CONCLUSIONS

At short term follow-up, the mean wear-rate in old and low demand patients was high, correlated to activity, and was above the generally accepted osteolysis threshold (0.1 mm/yr.). Cementless HA-coated cups had higher wear-rate than cemented cups.

Wear Rates With Large Metal and Ceramic Heads on a Second Generation Highly Cross-Linked Polyethylene at Mean 6-Year Follow-Up

BACKGROUND

Bearing surface wear and osteolysis are major factors limiting the durability of total hip arthroplasty (THA). Second generation annealed highly cross-linked polyethylene (HXLPE) and ceramics were introduced to THA for their excellent wear rates. However, there is little data comparing the wear rates of metal and ceramic heads on second generation HXLPE.

METHODS

Sixty patients who received a noncemented THA with a 32- or 36-mm delta ceramic head were matched with 60 THAs with a 32- or 36-mm metal head based on gender, head size, follow-up, and University of California, Los Angeles activity score. Linear and volumetric wear rates were measured.

RESULTS

At mean 6-year follow-up, the mean linear wear rates were 0.012 mm/y (standard deviation [SD] 0.045; 95% confidence interval [CI] 0.001-0.024) and 0.018 mm/y (SD 0.025; 95% CI 0.012-0.025) for the ceramic and metal groups, respectively (P = .724). The mean volumetric wear rates for the ceramic and metal head groups were 11.9 (SD 43.0; 95% CI 0.7-23.0) and 17.3 (SD 23.9; 95% CI 11.1-23.4), respectively. No significant differences were detectable in either the mean linear or volumetric wear rates (P = .380 and P = .398, respectively).

CONCLUSION

Second generation HXLPE had low wear rates and we were unable to detect a significant difference in wear rates with 32- or 36-mm metal and ceramic heads. We believe that this is due to the excellent tribological properties of second generation HXLPE. We continue to use ceramic as standard of care because of issues of trunnionosis with metal heads.

Third-generation pure alumina and alumina matrix composites in total hip arthroplasty: What is the evidence?

Wear, corrosion and periprosthetic osteolysis are important causes of failure in joint arthroplasty, especially in young patients.

Ceramic bearings, developed 40 years ago, are an increasingly popular choice in hip arthroplasty. New manufacturing procedures have increased the strength and reliability of ceramic materials and reduced the risk of complications.

In recent decades, ceramics made of pure alumina have continuously improved, resulting in a surgical-grade material that fulfills clinical requirements.

Despite the track record of safety and long-term results, third-generation pure alumina ceramics are being replaced in clinical practice by alumina matrix composites, which are composed of alumina and zirconium.

In this review, the characteristics of both materials are discussed, and the long-term results with third-generation alumina-on-alumina bearings and the associated complications are compared with those of other available ceramics.

Cite this article: EFORT Open Rev 2018;3:7-14. DOI: 10.1302/2058-5241.3.170034

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.].

Risk factors for conversion surgery to total hip arthroplasty of a hemiarthroplasty performed for a femoral neck fracture

INTRODUCTION

The purpose of this study was to determine risk factors for conversion to total hip arthroplasty (THA) in patients originally treated with hemiarthroplasty (HA) for displaced femoral neck fractures.

METHODS

In this case-controlled study, we identified 54 patients who were treated with HA for femoral neck fracture (FNF) who subsequently underwent conversion to THA at our institution between 2003 and 2013. We randomly selected 142 control patients who underwent HA for a displaced FNF without conversion surgery during the same time period. We compared demographic data, implant parameters, and radiographic data between the groups to identify risk factors for conversion surgery.

RESULTS

In the univariate analysis, younger age at index surgery (mean 75 vs. 80 years, p = 0.006), higher body mass index (26.1 vs. 23.7, p = 0.031), bipolar prosthesis (20% vs. 36%, p = 0.024), absence of dementia (6% vs. 23%, p = 0.01), increased leg length compared to contralateral limb (6.5 mm vs. 0.2 mm, p<0.001), and increased HA femoral head size compared to the contralateral femoral head (2.7 mm vs. 1.5 mm, p = 0.02) were associated with a significantly increased risk of conversion surgery. In the multivariate logistic regression, decreased age at index surgery, no dementia, use of a bipolar head, and increased leg length discrepancy (LLD) were associated with risk of conversion.

CONCLUSIONS

Patient characteristics, including younger age, increased BMI, and absence of dementia can lead to increased risk for conversion of HA to THA. Intraoperative considerations of head size and increase in ipsilateral LLD may increase the risk of conversion surgery. These factors should be considered by surgeons who employ HA for displaced FNFs.

Higher UHMWPE wear-rate in cementless compared with cemented cups with the Saturne® Dual-Mobility acetabular system

INTRODUCTION

Dual mobility (DM) total hip arthroplasty (THA) may reduce dislocation risk, but might increase the risk of high polyethylene (PE) wear due to double wearing surfaces.

METHODS

127 patients (97 female) with 129 hips operated with THA after displaced femoral neck fracture FNF between 2005 and 2011, were seen for a cross-sectional clinical follow-up. Acetabular components were Saturne® DM cups with 28mm chrome-cobalt heads in UHMWPE. Cementless cups (n = 73) were hydroxyapatite coated. Radiographs were obtained for analysis of cup placement, 2D polyethylene wear and wear-rate (PolyWare 3D), and further radiological evaluation. Activity measurements included Timed Up and Go test (TUG) and walking distance from Harris Hip Score (HHS).

RESULTS

At a mean follow-up of 2.83 (1.0-7.7) years the mean wear was 0.82 mm (range 0.17-4.51, SD 0.50), and the wear-rate was 0.37 mm (range 0.06-1.90, SD 0.29). Wear-rate of 0.43 mm/year (SD 0.30) in cementless cups was higher (p = 0.004) than 0.30 mm/year (SD 0.27) in cemented cups. Mean age at time of surgery was 75.1 years (range 30-95). There was no correlation between age at time of surgery and wear (p = 0.56). There was no correlation between cup inclination and wear-rate (p = 0.35). TUG was mean 13.4 seconds (range 4.5-30.1) and correlated with wear rate (p = 0.03).

CONCLUSIONS

At short term follow-up, the mean wear-rate in old and low demand patients was high, correlated to activity, and was above the generally accepted osteolysis threshold (0.1 mm/yr.). Cementless HA-coated cups had higher wear-rate than cemented cups.

Dislocation following total hip arthroplasty using dual mobility acetabular components: a systematic review

AIMS

The aim of this systematic review was to report the rate of dislocation following the use of dual mobility (DM) acetabular components in primary and revision total hip arthroplasty (THA).

MATERIALS AND METHODS

A systematic review of the literature according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines was performed. A comprehensive search of Pubmed/Medline, Cochrane Library and Embase (Scopus) was conducted for English articles between January 1974 and March 2016 using various combinations of the keywords "dual mobility", "dual-mobility", "tripolar", "double-mobility", "double mobility", "hip", "cup", "socket". The following data were extracted by two investigators independently: demographics, whether the operation was a primary or revision THA, length of follow-up, the design of the components, diameter of the femoral head, and type of fixation of the acetabular component.

RESULTS

In all, 59 articles met our inclusion criteria. These included a total of 17 908 THAs which were divided into two groups: studies dealing with DM components in primary THA and those dealing with these components in revision THA. The mean rate of dislocation was 0.9% in the primary THA group, and 3.0% in the revision THA group. The mean rate of intraprosthetic dislocation was 0.7% in primary and 1.3% in revision THAs.

CONCLUSION

Based on the current data, the use of DM acetabular components are effective in minimising the risk of instability after both primary and revision THA. This benefit must be balanced against continuing concerns about the additional modularity, and the new mode of failure of intraprosthetic dislocation. Longer term studies are needed to assess the function of these newer materials compared with previous generations. Cite this article: Bone Joint J 2017;99-B(1 Supple A):18-24.

Large-diameter total hip arthroplasty modular heads require greater assembly forces for initial stability

Objectives

Modular junctions are ubiquitous in contemporary hip arthroplasty. The head-trunnion junction is implicated in the failure of large diameter metal-on-metal (MoM) hips which are the currently the topic of one the largest legal actions in the history of orthopaedics (estimated costs are stated to exceed $4 billion). Several factors are known to influence the strength of these press-fit modular connections. However, the influence of different head sizes has not previously been investigated. The aim of the study was to establish whether the choice of head size influences the initial strength of the trunnion-head connection.

Materials and Methods

Ti-6Al-4V trunnions (n = 60) and two different sizes of cobalt-chromium (Co-Cr) heads (28 mm and 36 mm; 30 of each size) were used in the study. Three different levels of assembly force were considered: 4 kN; 5 kN; and 6 kN (n = 10 each). The strength of the press-fit connection was subsequently evaluated by measuring the pull-off force required to break the connection. The statistical differences in pull-off force were examined using a Kruskal–Wallis test and two-sample Mann–Whitney U test. Finite element and analytical models were developed to understand the reasons for the experimentally observed differences.

Results

36 mm diameter heads had significantly lower pull-off forces than 28 mm heads when impacted at 4 kN and 5 kN (p < 0.001; p < 0.001), but not at 6 kN (p = 0.21). Mean pull-off forces at 4 kN and 5 kN impaction forces were approximately 20% larger for 28 mm heads compared with 36 mm heads. Finite element and analytical models demonstrate that the differences in pull-off strength can be explained by differences in structural rigidity and the resulting interface pressures.

Conclusion

This is the first study to show that 36 mm Co-Cr heads have up to 20% lower pull-off connection strength compared with 28 mm heads for equivalent assembly forces. This effect is likely to play a role in the high failure rates of large diameter MoM hips.

Cite this article: A. R. MacLeod, N. P. T. Sullivan, M. R. Whitehouse, H. S. Gill. Large-diameter total hip arthroplasty modular heads require greater assembly forces for initial stability. Bone Joint Res 2016;5:338–346. DOI: 10.1302/2046-3758.58.BJR-2016-0044.R1.

Is There a Benefit to Head Size Greater Than 36 mm in Total Hip Arthroplasty?

This study compares the rate of dislocation and revision for instability between 36-mm and anatomic femoral heads (large diameter metal-on-metal THA, dual-mobility bearings, and hip resurfacing arthroplasty) in patients at high risk for dislocation. A total of 501 high-risk patients, over a 10-year period, were identified (282 36-mm THA, 24 dual-mobility bearings, 83 metal-on-metal arthroplasty, and 112 hip resurfacing arthroplasty). There were 13 dislocations in the 36-mm group compared to 1 in the anatomic group (4.6% vs 0.5%; P = .005). Four patients dislocated more than once in the 36-mm group (1.4% vs 0%; P = .04), and 2 patients in the 36-mm group required a revision for instability (0.7% vs 0%; P = .11). These results suggest that anatomic head sizes significantly lower the risk of dislocation in high-risk patients.

MRI Findings Associated with Recalled Modular Femoral Neck Rejuvenate and ABG Implants

MARS-MRI is suggested for the diagnosis of adverse local tissue reactions (ALTR) in patients with recalled femoral stems with modular necks, but there has been no major study looking at MARS-MRI findings in this population. A retrospective review was performed on 312 patients who received a modular neck hip implant between October 2007 and February 2012. 62% of patients had intra-articular effusions, with 27% containing debris. Extra-capsular effusions were present in 35% of hips. 54% had synovitis and 5.4% had osteolysis. Tendinopathy and tendon disruption was present in the gluteus medius (58%/12%), hamstring (56%/12%), gluteus minimus (38%/7.7%) and iliopsoas (7.1%/4.8%). Abnormal MARS-MRI findings are associated with modular neck femoral components and can suggest underlying ALTR. MARS-MRI abnormalities merit serious consideration in this population.

Dual mobility cup in revision total hip arthroplasty: dislocation rate and survival after 5 years

BACKGROUND

Dislocation is a common complication of total hip arthroplasty (THA), particularly when performed as revision surgery. Dual mobility cups (DMCs) minimize the risk of instability when implanted during primary THA. However, their usefulness and survival in revision THA remain unclear. We therefore conducted a retrospective study to assess DMC stability and survival at a minimal follow-up period of 5years after revision THA.

HYPOTHESIS

The dislocation rate associated with DMCs for revision THA is similar to that seen after primary THA.

MATERIALS AND METHODS

Cup exchange with implantation of a DMC was performed in 71 patients (74 hips) between 2000 and 2007, for the following reasons: recurrent dislocation (n=22), aseptic loosening (n=38), and infection (n=14). The DMCs were cemented in 47 cases and cementless in 27 cases. The clinical variables (Merle d'Aubigné-Postel score and Harris Hip Score) and radiological findings were collected retrospectively from the medical records and compared with those obtained at the last follow-up visit.

RESULTS

Of the 74 cases, 2 were lost to follow-up. At last follow-up, the mean Merle d'Aubigné-Postel score was 15.2 (11-18) and the mean Harris Hip Score was 80.4 (51-98). Of the 8 failures, 2 (2/72, 2.7%) were related to mechanical factors (1 case each of aseptic loosening and dislocation) and 6 were changed because of infection (recurrent infection, n=4). Mechanical failure was not linked to a specific reason for revision THA. A radiolucent line was visible in 4 cases but this finding was not associated with clinical manifestations. When failure was defined as cup revision for any non-infectious complication, 5-year implant survival was 99% (95% confidence interval, 93-100%).

DISCUSSION

Use of a DMC in revision THA was associated with a slightly higher dislocation rate (1/72, 1.4%) than in primary THA, whereas 5-year survival was comparable. Cemented DMCs were not associated with a greater risk of loosening.

CONCLUSION

DMCs are useful to decrease the risk of dislocation in revision THA performed for any reason. The low rate of loosening indicates that DMCs do not result in high stresses at the bone-implant interface.

LEVEL OF EVIDENCE

IV, retrospective study.

Do Complication Rates Differ by Gender After Metal-on-metal Hip Resurfacing Arthroplasty? A Systematic Review

BACKGROUND

Although metal-on-metal (MoM) bearing surfaces provide low rates of volumetric wear and increased stability, evidence suggests that certain MoM hip arthroplasties have high rates of complication and failure. Some evidence indicates that women have higher rates of failure compared with men; however, the orthopaedic literature as a whole has poorly reported such complications stratified by gender.

QUESTIONS/PURPOSES

This systematic review aimed to: (1) compare the rate of adverse local tissue reaction (ALTR); (2) dislocation; (3) aseptic loosening; and (4) revision between men and women undergoing primary MoM hip resurfacing arthroplasty (HRA).

METHODS

Systematic MEDLINE and EMBASE searches identified all level I to III articles published in peer-reviewed journals, reporting on the outcomes of interest, for MoM HRA. Articles were limited to those with 2-year followup that reported outcomes by gender. Ten articles met inclusion criteria. Study quality was evaluated using the Modified Coleman Methodology Score; the overall quality was poor. Heterogeneity and bias were analyzed using a Mantel-Haenszel statistical method.

RESULTS

Women demonstrated an increased odds of developing ALTR (odds ratio [OR], 5.70 [2.71-11.98]; p<0.001), dislocation (OR, 3.04 [1.2-7.5], p=0.02), aseptic loosening (OR, 3.18 [2.21-4.58], p<0.001), and revision (OR, 2.50 [2.25-2.78], p<0.001) after primary MoM HRA.

CONCLUSIONS

A systematic review of the currently available literature reveals a higher rate of complications (ALTR, dislocation, aseptic loosening, and revision) after MoM HRA in women compared with men. Although femoral head size has been frequently implicated as a prime factor in the higher rate of complication in women, further research is necessary to specifically probe this relationship. Retrospective studies of data available (eg, registry data) should be undertaken, and moving forward studies should report outcomes by gender (particularly complications).

LEVEL OF EVIDENCE

Level III, therapeutic study.

[Possibilities and limits of modern polyethylenes. With respect to the application profile]

BACKGROUND

Polyethylene is still one of the most important materials in the field of hip and knee arthroplasty. The clinical results of the last decades have helped to further develop polyethylene into a high-tech material. Progress in the development of new materials must be compared with the tried and tested ones to provide optimal and most individual patient care.

OBJECTIVES

This article gives an overview of the history and current application profile of the material ultra-high molecular weight polyethylene (UHMWPE) in hip and knee arthroplasty.

MATERIAL AND METHODS

With the aid of the current literature, new developments in the field of the material UHMWPE, also with respect to the biological activity of wear, the particular biomechanics of the knee joint as well as alternative hard-hard bearing surfaces in the hip, are represented in terms of implant safety.

RESULTS

The problems concerning polyethylene are now well recognized. The disadvantages of the material UHMWPE could be consistently reduced based on material research so that modern polyethylenes have gradually been shown in clinical trials that they can be reliably used.

CONCLUSION

Despite this the potential for improvement has still not yet been fully exploited. Any further development must be extensively tested both biomechanically and biologically before the material can be used in vivo. Long-term results are still necessary before a material can be accepted as being clinically safe.

Large-diameter metal-on-metal total hip arthroplasty: dislocation infrequent but survivorship poor

BACKGROUND

Use of large-diameter metal-on-metal (MoM) articulations in THA increased, at least in part, because of the possibility of achieving improved joint stability and excellent wear characteristics in vitro. However, there have been subsequent concerning reports with adverse reactions to metal debris (ARMD), pseudotumors, and systemic complications related to metal ions.

QUESTIONS/PURPOSES

The purpose of this study was to determine at a minimum of 2 years' followup (1) the proportion of patients who experienced a dislocation; (2) the short-term survivorship obtained with these implants; (3) the causes of failure and the proportion of patients who developed ARMD; and (4) whether there were any identifiable risk factors for revision.

METHODS

We reviewed the results of 1235 patients who underwent 1440 large-diameter MoM primary THAs at our institution using two acetabular devices from a single manufacturer with minimum 2-year followup. Large-diameter MoM devices were used in 48% (1695 of 3567) of primary THAs during the study period. We generally used these implants in younger, more active, higher-demand patients, in patients considered at higher risk of instability, and in patients with adequate bone stock to achieve stable fixation without use of screws. Clinical records and radiographs were reviewed to determine the incidence and etiology of revision. Patients whose hips were revised were compared with those not revised to identify risk factors; Kaplan-Meier survivorship analysis was performed as was multivariate analysis to account for potential confounding variables when evaluating risk factors. Minimum followup was 2 years (average, 7 years; range, 2-12 years); complete followup was available in 85% of hips (1440 of 1695).

RESULTS

Dislocation occurred in one hip overall (<1%; one of 1440). Kaplan-Meier analysis revealed survival free of component revision was 87% at 12 years (95% confidence interval, 84%-90%). The two most common indications for revision were ARMD (48%; 47 of 108 hips revised) and loosening or failure of ingrowth (31%; 34 of 108). Risk factors for component revision were younger age at surgery (relative risk [RR] 0.98 per each increased year; p=0.02), higher cup angle of inclination (RR 1.03 per each increased degree; p=0.04), and female sex (RR 1.67; p=0.03).

CONCLUSIONS

Large-diameter MoM THAs are associated with a very low dislocation rate, but failure secondary to ARMD and loosening or lack of ingrowth occur frequently. Patients with MoM THA should be encouraged to return for clinical and radiographic followup, and clinicians should maintain a low threshold to perform a systematic evaluation. Early diagnosis and appropriate treatment are recommended to prevent the damaging effects of advanced ARMD.

LEVEL OF EVIDENCE

Level IV, Therapeutic study.

Does cross-linked polyethylene decrease the revision rate of total hip arthroplasty compared with conventional polyethylene? A meta-analysis

BACKGROUND

Although cross-linked polyethylene is resistant to wear in comparison to conventional polyethylene, it remains unknown whether it can decrease the wear-related revision rate of total hip arthroplasty.

OBJECTIVES

To determine whether cross-linked polyethylene decreases the wear-related revision rate of total hip arthroplasty compared with conventional polyethylene.

DATA SOURCES

Electronic databases, including PubMed, EMBASE, and the Cochrane Central Register of Controlled Trials, were queried from inception to July 6, 2013.

STUDY SELECTION

Randomized controlled trials (RCTs) comparing cross-linked polyethylene with conventional polyethylene were included. In addition, the standard 28-mm femoral head was used, and follow-up was performed for a minimum of 5 years. The primary outcome assessed was wear-related revision. The secondary outcome measures evaluated were the incidence of osteolysis, the linear wear rate, and the linear head penetration.

DATA SYNTHESIS

The Cochrane Collaboration's tool for assessing the risk of bias was used for quality assessment. Data from eligible studies were pooled using a random effects model.

RESULTS

Eight studies involving 735 patients were included in this study. Meta-analysis showed there was no significant difference between cross-linked and conventional polyethylene group in terms of osteolysis or wear-related revision. The pooled mean differences were significantly less for the linear wear rate and linear head penetration for cross-linked polyethylene than for conventional polyethylene.

LIMITATIONS

The studies differed with respect to the cross-linked liner brands, manufacturing processes, and radiological evaluation methods. Moreover, the follow-up periods of the RCTs were not long enough.

CONCLUSIONS

The current limited evidence suggests that cross-linked polyethylene significantly reduced the radiological wear compared with conventional polyethylene at midterm follow-up periods. However, there is no evidence that cross-linked polyethylene had an advantage over conventional polyethylene in terms of reducing osteolysis or wear-related revision. Nevertheless, future long-term RCTs on this topic are needed.

KEY FINDINGS

Cross-linked polyethylene significantly reduced radiological wear but not osteolysis or wear-related revision in comparison to conventional polyethylene at midterm follow-up periods.

LEVEL OF EVIDENCE

Level I, systematic review of level I studies.

Relative head size increase using an anatomic dual mobility hip prosthesis compared to traditional hip arthroplasty: impact on hip stability

Smaller head sizes and head/cup ratios make cups smaller than 50mm and larger than 58mm, more prone to dislocation. Using computer modeling, we compared average head sizes and posterior horizontal dislocation distance (PHDD) in two 78-patient matched cohorts. Cup sizes were small (≤50mm) or large (≥58mm). The control cohort had conventional fixed bearing prostheses, while the experimental cohort had anatomical dual mobility (ADM) hip prostheses. ADM cups have larger average head sizes and PHDD than traditional fixed bearing prostheses by 11.5mm and 80% for cups ≤50mm, and 16.3mm and 90% for cups ≥58mm. Larger head sizes and increased head/cup ratio may allow the ADM prosthesis to reduce the incidence of dislocation.

Does bearing size influence metal ion levels in large-head metal-on-metal total hip arthroplasty? A comparison of three total hip systems

BACKGROUND

The purpose of the study was twofold: first, to determine whether there is a statistically significant difference in the metal ion levels among three different large-head metal-on-metal (MOM) total hip systems. The second objective was to assess whether position of the implanted prostheses, patient demographics or factors such as activity levels influence overall blood metal ion levels and whether there is a difference in the functional outcomes between the systems.

METHODS

In a cross-sectional cohort study, three different metal-on-metal total hip systems were assessed: two monoblock heads, the Durom socket (Zimmer, Warsaw, IN, USA) and the Birmingham socket (Smith and Nephew, Memphis, TN, USA), and one modular metal-on-metal total hip system (Pinnacle, Depuy Orthopedics, Warsaw, IN, USA). Fifty-four patients were recruited, with a mean age of 59.7 years and a mean follow-up time of 41 months (12 to 60). Patients were evaluated clinically, radiologically and biochemically. Statistical analysis was performed on all collected data to assess any differences between the three groups in terms of overall blood metal ion levels and also to identify whether there was any other factor within the group demographics and outcomes that could influence the mean levels of Co and Cr.

RESULTS

Although the functional outcome scores were similar in all three groups, the blood metal ion levels in the larger monoblock large heads (Durom, Birmingham sockets) were significantly raised compared with those of the Pinnacle group. In addition, the metal ion levels were not found to have a statistically significant relationship to the anteversion or abduction angles as measured on the radiographs.

CONCLUSIONS

When considering a MOM THR, the use of a monoblock large-head system leads to higher elevations in whole blood metal ions and offers no advantage over a smaller head modular system.