Tribology of total hip arthroplasty prostheses: What an orthopaedic surgeon should know

Efficacy of Pericapsular Nerve Group Block for Pain Reduction and Opioid Consumption after Total Hip Arthroplasty: A Meta-Analysis of Randomized Controlled Trials

The aim of this study was to conduct a meta-analysis of randomized controlled trials (RCTs) for comparison of the effectiveness of pericapsular nerve group (PENG) block with that of other analgesic techniques for reduction of postoperative pain and consumption of opioids after total hip arthroplasty (THA). A search of records in the PubMed, Embase, and Cochrane Library, and ClinicalTrials.gov databases was conducted in order to identify studies comparing the effect of the PENG block with that of other analgesics on reduction of postoperative pain and consumption of opioids after THA. Determination of eligibility was based on the PICOS (participants, intervention, comparator, outcomes, and study design) criteria as follows: (1) Participants: patients who underwent THA. (2) Intervention: patients who received a PENG block for management of postoperative pain. (3) Comparator: patients who received other analgesics. (4) Outcomes: numerical rating scale (NRS) score and opioid consumption during different periods. (5) Study design: clinical RCTs. Five RCTs were finally included in the current meta-analysis. Significantly lower postoperative opioid consumption at 24 hours after THA was observed in the group of patients who received the PENG block compared with the control group (standard mean difference=-0.36, 95% confidence interval -0.64 to -0.08). However, no significant reduction in NRS score at 12, 24, and 48 hours after surgery and opioid consumption at 48 hours after THA was observed. The PENG block showed better results for opioid consumption at 24 hours after THA compared with other analgesics.

Analytical review on the biocompatibility of surface-treated Ti-alloys for joint replacement applications

INTRODUCTION

With the advancement of joint replacements such as total hip replacement (THR), Titanium (Ti) and its alloys are widely used as implant materials. The bearing surface of Ti improves the longevity of implants. In this perception, researchers design a Ti-alloy that increases the wear and corrosion resistance to enhance osteogenesis and mechanical stability.

AREAS COVERED

: This paper is dedicated to finding the major causes of the failure of THR. Further, this paper provides an overview of the application of metallic alloys and their influencing factors that influence biocompatibility. The most contributing part of this paper focuses on the post-treatment impact on Ti-alloys biocompatibility.

EXPERT OPINION

This paper revealed and discussed that Ti alloys' biocompatibility for orthopedic applications mainly depends on antibacterial activities that decide tissue-implant compatibility. Therefore, performing surface treatment enhances the biocompatibility of Ti alloys. It was also observed that more water contact angle (WCA) induces bacterial growth and enhances cell adhesion. In contrast, the treated surface increases the antibacterial activities at lower WCA. Surface heat treatment with sintering or micro-arc oxidation achieves suitable antibacterial or antimicrobial activities.

The Definition of Periprosthetic Osteolysis in Shoulder Arthroplasty: A Systematic Review of Grading Schemes and Criteria

BACKGROUND

Periprosthetic osteolysis is a known complication after shoulder arthroplasty that may lead to implant loosening and revision surgery. To date, there is no consensus in the shoulder arthroplasty literature regarding the definition of osteolysis or the grading criteria, thus making it difficult to quantify and compare outcomes involving this complication. The purpose of this study was to perform a systematic review of the literature to assess how periprosthetic osteolysis in shoulder arthroplasty is defined and evaluated radiographically.

METHODS

A systematic review of MEDLINE, Scopus, Cochrane, and CINAHL was performed in August 2021 for studies that provided a definition and/or grading criteria for osteolysis in shoulder arthroplasty. Only studies with a minimum of 2 years of radiographic follow-up were included.

RESULTS

Thirty-four articles met the inclusion criteria. After consolidating studies by the same primary author that included the same grading criteria, 29 studies were examined for their definition and grading criteria for osteolysis. Of these, 19 (65.5%) evaluated osteolysis surrounding the glenoid and 18 (62.1%) evaluated osteolysis surrounding the humerus. There was considerable heterogeneity in the systems used to grade periprosthetic osteolysis surrounding the glenoid, whereas humeral periprosthetic osteolysis was often categorized via visualization into binary or categorical groups (e.g., presence versus absence; mild, moderate, or severe; partial versus complete). Four studies (13.8%) provided novel measurements for assessing either glenoid or humeral osteolysis.

CONCLUSIONS

Considerable heterogeneity exists in the assessment and grading of periprosthetic osteolysis in shoulder arthroplasty. The most common grading systems were binary and used qualitative visual interpretation, making them relatively subjective and prone to bias. Quantitative measurements of osteolysis were infrequently utilized. A standardized method of assessing osteolysis would be of value to facilitate communication and research efforts.

Mode I and II Wear in Ceramic on Ceramic Total Hip Arthroplasty: A Case Report

Introduction:

Elective total hip arthroplasty (THA) is a common procedure and has been associated with favorable outcomes in both elderly and younger patients. A variety of implant and articular components exist so to allow surgeons to make a patient-specific choice with the intent of maximizing both patient outcomes and implant survival.

The utilization of ceramic bearing surfaces during THA has become increasingly prevalent, with their tribological profile conveying favorable wear and osteolysis-resistant properties. Typically, ceramic articulating components are most susceptible to failure through brittle fracture or complications such as squeaking.

Case Report:

This case describes a 68-year-old Caucasian male who underwent revision of ceramic on ceramic THA due to pain, with intraoperative analysis revealing evidence of gross Mode I acetabular ceramic component wear with a resultant Mode II wear articulation between the ceramic femoral head and acetabular liner.

Conclusion:

Wear between ceramic implants in THA is infrequently reported, and as such awareness of this uncommon phenomena as well as its potential causative factors is important when considering either primary or revision THA involving ceramic bearing components.

Comparison of a fast track protocol and standard care after hip arthroplasty in the reduction of the length of stay and the early weight-bearing resumption: study protocol for a randomized controlled trial

BACKGROUND

To date, hip arthroplasty is one of the most commonly performed surgical procedures, with growing worldwide demand. In recent decades, major progress made in terms of surgical technique, biomechanics, and tribology knowledge has contributed to improve the medical and functional management of the patient. This study aims to assess if the application of a fast track protocol, consisting of a preoperative educational intervention, adequate postoperative pain control, and intensive rehabilitation intervention, reduces the length of stay (LOS) and allows the early functional recovery compared to standard clinical practice for patients undergoing hip arthroplasty.

METHODS

The study population consists of 90 patients with primary arthrosis of the hip with an anterior indication of hip arthroplasty. The exclusion criteria are older than 70 years, a contraindication to performing spinal anesthesia, and bone mass index (BMI) greater than 32. Participants, 45 for each group, are randomly allocated to one of two arms: fast track clinical pathway or standard care protocol. During allocation, baseline parameters such as Harris Hip Score (HHS) and Western Ontario and McMaster Universities (WOMAC) index are collected. On the third postoperative day, the functional autonomy for each patient is assessed by the Iowa Level of Assistance (ILOA) scale, and it is expected the discharge for patients in the fast track group (primary outcome). On the other hand, standard care patient discharge is expected after 5-7 days after surgery. During follow-up fixed at 6 weeks and 3, 6, and 12 months, HHS and WOMAC scores are collected for each patient (secondary outcomes).

DISCUSSION

Although total hip replacement has become a widespread standardized procedure, to the authors' knowledge, only few randomized controlled trials were performed to evaluate the effectiveness of fast track pathway vs. standard care procedure in the reduction of the LOS after hip arthroplasty. It is expected that our results collected by the application of minimally invasive surgical interventions with concomitant management of perioperative pain and bleeding and early functional rehabilitation will contribute to enriching the understanding of clinical and organizational aspects linked to fast track arthroplasty.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03875976 . Registered on 15 March 2019-"retrospectively registered".

Minimum 15-year results of metasul 28-mm metal-on-metal total hip arthroplasty in patients younger than 50 years of age

Background

Some propitious mid- and long-term studies had been reported for MoM bearings; however, most studies have addressed specific patient groups rather than younger, active patients, who probably represent the most suitable population for investigations on wear and osteolysis. The purpose of this study to evaluate the long-term results of second-generation metal-on-metal cementless total hip arthroplasty (THA) in patients aged <50 years.

Methods

From December 1997 to January 2004, primary THA using a metal-on-metal bearing cementless implant was performed in 63 patients (72 hips) aged <50 years. The mean follow-up duration was 18.6 (range, 15.9–22.1) years, and the mean age at initial operation was 39 (range, 22–49) years. Clinical results, complications, survivorship, osteolysis, and aseptic loosening were evaluated.

Results

The mean Harris hip score and Western Ontario and McMaster Universities Arthritis Index scores were improved from 57.8 (range, 28–69) points and 73.4 (range, 63–94) points preoperatively to 91.7 (range, 80–100) points and 25.5 points (range, 17–38) points, respectively, at the last follow-up. Osteolysis lesions were found in 12 hips (acetabulum, 6 and femur, 6). The notching occurred on the femoral stem neck occurred in 12 hips. The mean serum cobalt and chromium concentrations were 2.3 (range, 0.2–10.6) μg/L and 1.7 (range, 0.4–8.1) μg/L, respectively, at a mean follow-up of 12.7 years in 32 patients (50.1%). The Kaplan-Meier survivorship curve analysis with revision for any reason as the endpoint revealed that 93.1% survived at 18.6 years’ follow-up.

Conclusions

Second-generation metal-on-metal cementless THA was found to produce satisfactory clinical and radiographic results with a low revision rate for osteolysis and aseptic loosening in patients aged less than 50 years.

The effect of albumin and γ-globulin on synovial fluid lubrication: Implication for knee joint replacements

Total knee arthroplasty has become a routine procedure for patients suffering from joint diseases. Although the number of operations continuously increases, a limited service-life of implants represents a persisting challenge for scientists. Understanding of lubrication may help to suitably explain tribological processes on the way to replacements that become durable well into the third decade of service. The aim of the present study is to assess the formation of protein lubricating film in the knee implant. A developed knee simulator was used to observe the contact of real femoral and transparent polymer tibial component using fluorescent microscopy. The contact was lubricated by various protein solutions with attention to the behaviour of albumin and γ-globulin. In order to suitably mimic a human synovial fluid, hyaluronic acid and phospholipids were subsequently added to the solutions. Further, the change in shape and the migration of the contact zone were studied. The results showed considerable appearance differences of the contact over the swing phase of the simplified gait cycle. Regarding film formation, a strong interaction of the various molecules of synovial fluid was observed. It was found that the thickness of the lubricating layer stabilizes within around 50 s. Throughout the contact zone, protein agglomerations were present and could be clearly visualised using the applied optical technique.

Long-term survival of hybrid total hip arthroplasty with the uncemented CLS cup, cemented Müller cobalt-chromium stem, and 28-mm Metasul™ bearings: Retrospective review of 115 hips after a minimum of 17.8 years

BACKGROUND

Hard-on-hard bearings require a meticulous implantation technique but may be associated with lower wear rates in young active patients. Among them, metal-on-metal (MoM) bearings have been blamed for specific complications including adverse reactions to metal debris and metal hypersensitivity. These complications have been chiefly reported with large-head MoM implants (except when used for hip resurfacing). Most of the published data on small-head MoM implants were obtained using uncemented stems. To our knowledge, no information on outcomes beyond 15 years is available for small-head MoM implants with cemented cobalt-nickel-chromium (Co-Ni-Cr) stems, which might increase the risk of complications. The objective of this study was to collect long-term follow-up data on patients who underwent hybrid total hip arthroplasty (THA) with 28-mm MoM Metasul™ bearings in order to assess: (1) long-term survival (based on the revision rate), (2) and the occurrence of adverse reactions to metal debris documented during revision.

HYPOTHESIS

Survival of 28-mm Metasul™ bearings used with hybrid THA is acceptable.

PATIENTS AND METHODS

A single-centre retrospective study was conducted in consecutive patients managed using 28-mm Metasul™ bearings in a press-fit cup, with a cemented Co-Ni-Cr stem. Follow-up was at least 17 years. The clinical and radiographic data were analysed. Mean age at surgery was 57.3±7.9 years (range, 29.6-75.3 years).

RESULTS

The study included 115 hips with a mean follow-up of 20.3±0.8 years (range, 17.8-21.6 years). Survival to revision for any reason was 86.10% (95% CI, 79.8-92.4%) and survival to revision for aseptic loosening was 92.6% (95% CI, 87.7-97.6). Half the specimens obtained during revision showed a macrophage reaction and a non-specific inflammatory infiltrate. No patient experienced complications specifically related to the use of Metasul™ bearings with a cemented Co-Ni-Cr stem.

DISCUSSION

Long-term survival of 28-mm MoM Metasu™ bearings was close to that of metal-on-polyethylene bearings and lower than that of ceramic-on-ceramic or small-head MoM bearings in other studies. No complications specifically related to the use of small-head MoM bearings with a cemented Co-Ni-Cr stem were recorded.

LEVEL OF EVIDENCE

IV, retrospective study.

Femoral side-only revision options for the Birmingham resurfacing arthroplasty

BACKGROUND

The Birmingham Hip Resurfacing (BHR) system (Smith and Nephew) was developed as an alternative to conventional total joint replacement for younger, more active patients. Among other complications exists the risk for femoral component failure. The only marketed revision option for such a complication involves exchange of all components for a total replacement arthroplasty. This presents as a considerable and potentially unnecessary operative burden where revision of only the femoral prosthesis would suffice. We have analysed revision options for BHR in the context of periprosthetic femoral fractures with a stable acetabular component.

METHODS

Technical details of dual mobility hip systems available in Australia were collated and analysed to assess for potential 'off label' use with an existing BHR acetabular component. These data were then compared with the custom-made Smith and Nephew dual mobility implant with respect to clearance and sizing.

RESULTS

Two dual mobility articulation modalities from two companies were identified as appropriate for potential usage with four products analysed in detail. These two demonstrated acceptable sizing and clearance measurements.

CONCLUSION

Comparison between readily available dual mobility prostheses with custom-made implants showed off label dual mobility prosthetic use to be a viable alternative for femoral-only revisions with in situ BHR. Single component revision has several advantages which include: a less complex surgical procedure, shorter operative time, decreased blood loss and the expectation of resultant lower morbidity. Furthermore, this less complex revision surgery should give comparable results to that of primary total hip arthroplasty.

A minimum 20-year outcome of 100 consecutive alumina-on-alumina arthroplasties performed by a single surgeon

BACKGROUND:

Ceramic-on-ceramic (CoC) is currently a viable bearing combination in primary total hip arthroplasty (THA) and, due to its mechanical properties, it can be used in young patients requiring a long-lasting implant. The aim of this study is to report the results of a series of CoC THAs at a minimum 20 years follow-up.

METHODS:

A retrospective study was conducted on the 1st 100 consecutive alumina-on-alumina arthroplasties performed by a single surgeon on 51 females and 40 males with an average age of 60.7 years. The mean preoperative Harris Hip Score was 35. The press-fit cup consisted of a pure titanium core with a titanium alloy mesh. Both the inlay and the head were made of dense polycrystalline surgical-grade alumina. The 32-mm femoral head was anchored on 3 different femoral components.

RESULTS:

19 patients with 22 THAs were died or lost, 2 anatomic cementless stems were revised due to sinking, 1 THA was revised for periprosthetic infection. 2 patients sustained a Vancouver B1 periprosthetic femoral fracture. None of the 78 THAs eligible for this study were revised for wear, breakage, noise of the ceramic components. None of the cups, none of the cemented stems, none of the cementless straight stems failed. HHS raised up to a mean value of 95.

CONCLUSIONS:

The present report demonstrates that CoC coupling offers minimal wear at a long-term follow-up. Further studies are needed to evaluate whether the modern ceramic composites will confirm such excellent results in total hip replacement.

Midterm results of Magnum large head metal-on-metal total hip arthroplasty

OBJECTIVES

We present the results of the prospective follow up of a sample of large head metal-metal total hip arthroplasty obtained after the safety alert regarding a higher incidence of revision of these implants.

MATERIAL AND METHODS

All patients implanted with the Recap-M2a-Magnum cup between 2008 and 2011 were included. They were prospectively reviewed recording Harris Hip Score, clinical symptoms of chromium or cobalt intoxication. Serum levels of these ions were requested as well as X-Rays and ultrasonography. An MRI was performed in the cases of positive ultrasonography.

RESULTS

Twenty-six males with a mean age of 48.54 years [32-62, SD: 7.18] were included. An anterolateral approach and Bi-Metric (7) and F-40 (19) stems were used. Cephalic diameters ranged 42-52 (mode: 46) and the mean cup inclination was 39.35° [21-59°, SD: 9.78]. During follow-up (7.3 years [5.9-9.4; SD: .78]), 3 patients (11.5%) underwent revision (2 cases aseptic loosening, 1 pseudotumour). Mean time until revision was 5.4 years [3.1-8.0; SD: 2.48]. The accumulated survival probability was 88.5% (95% CI 76.3-100%). Harris Hip Score was 94.47 [66.5-100; SD: 8.94] and the patients showed no metallic intoxication symptoms. The levels of chromium were 1.88 mcg/dl [0.6-3.9] and cobalt 1,74 mcg/dl [0.5-5,6]. One pseudotumour was found in an asymptomatic patient, and small amounts of periarticular liquid were found in 5 patients (19.2%) DISCUSSION AND CONCLUSIONS: High revision rates are still found when follow up is extended due to aseptic loosening and pseudotumour formation. MRI might not be the most adequate test to study the complications of these prostheses.

Similar Superior Patient-Reported Outcome Measures for Anterior and Posterolateral Approaches After Total Hip Arthroplasty: Postoperative Patient-Reported Outcome Measure Improvement After 3 months in 12,774 Primary Total Hip Arthroplasties Using the Anterior, Anterolateral, Straight Lateral, or Posterolateral Approach

BACKGROUND

Patient-reported outcome measures (PROMs) are used to evaluate the outcome of total hip arthroplasty (THA). We determined the effect of surgical approach on PROMs after primary THA.

METHODS

All primary THAs, with registered preoperative and 3 months postoperative PROMs were selected from the Dutch Arthroplasty Register. Based on surgical approach, 4 groups were discerned: (direct) anterior, anterolateral, direct lateral, and posterolateral approaches. The following PROMs were recorded: Hip disability and Osteoarthritis Outcome Score Physical function Short form (HOOS-PS); Oxford Hip Score; EQ-5D index score; EQ-5D thermometer; and Numeric Rating Scale measuring pain, both active and in rest. The difference between preoperative and postoperative scores was calculated (delta-PROM) and used as primary outcome measure. Multivariable linear regression analysis was performed for comparisons. Cohen's d was calculated as measure of effect size.

RESULTS

All examined 4 approaches resulted in a significant increase of PROMs after primary THA in the Netherlands (n = 12,274). The anterior and posterolateral approaches were associated with significantly more improvement in HOOS-PS scores compared with the anterolateral and direct lateral approaches. Furthermore, the posterolateral and anterior approaches showed greater improvement on Numeric Rating Scale pain scores compared with the anterolateral approach. No relevant differences in delta-PROM were seen between the anterior and posterolateral surgical approaches.

CONCLUSION

Anterior and posterolateral surgical approaches showed more improvement in self-reported physical functioning (HOOS-PS) compared with anterolateral and direct lateral approaches in patients receiving a primary THA. However, clinical differences were only small.

The effect of bearing type on the outcome of total hip arthroplasty

Background and purpose - Alternative bearing surfaces such as ceramics and highly crosslinked polyethylene (HXLPE) were developed in order to further improve implant performance of total hip arthroplasties (THAs). Whether these alternative bearing surfaces result in increased longevity is subject to debate. Patients and methods - Using the Dutch Arthroplasty Register (LROI), we identified all patients with a primary, non-metal-on-metal THA implanted in the Netherlands in the period 2007-2016 (n = 209,912). Cumulative incidence of revision was calculated to determine differences in survivorship of THAs according to bearing type: metal-on-polyethylene (MoPE), metal-on-HXLPE (MoHXLPE), ceramic-on-polyethylene (CoPE), ceramic-on-HXLPE (CoHXLPE), ceramic-on-ceramic (CoC), and oxidized-zirconium-on-(HXL)polyethylene (Ox(HXL)PE). Multivariable Cox proportional hazard regression ratios (HRs) were used for comparisons. Results - After adjustment for confounders, CoHXLPE, CoC, and Ox(HXL)PE resulted in a statistically significantly lower risk of revision compared with MoPE after 9 years follow-up (HR =0.8-0.9 respectively, compared with HR =1.0). For small (22-28 mm) femoral head THAs, lower revision rates were found for CoPE and CoHXLPE (HR =0.9). In the 36 mm femoral head subgroup, CoC-bearing THAs had a lower HR compared with MoHXLPE (HR =0.7 versus 1.0). Crude revision rates in young patients (< 60 years) for CoHXLPE, CoC, and Ox(HXL)PE (HR =0.7) were lower than MoPE (HR =1.0). However, after adjustment for case mix and confounders these differences were not statistically significant. Interpretation - We found a mid-term lower risk of revision for CoHXLPE, CoC, and Ox(HXL)PE bearings compared with traditional MoPE-bearing surfaces.

Frank Stinchfield Award: Identification of the At-risk Genotype for Development of Pseudotumors Around Metal-on-metal THAs

BACKGROUND

Once touted as the future of hip arthroplasty, metal-on-metal (MoM) bearing surfaces have fallen sharply from favor with the emergence of a strong body of evidence demonstrating unacceptably high premature implant failure rates. The previously unpredictable development of adverse local tissue reactions (ALTRs) has been a substantive contributor to this. Although the underlying pathophysiology of these so-called "pseudotumors" is now well understood, the fundamental predisposing patient risk factors have remained elusive.

QUESTIONS/PURPOSES

The aim of this research, as a clinical-genotype correlation analysis, was to identify specific alleles (genes) associated with the development of ALTRs in patients with in situ MoM THAs.

METHODS

A case-control study of patients who received a large-head, primary MoM THA between 2005 and 2008 was performed with a minimum followup of 5 years. Twenty-six patients who had undergone revision of a primary MoM THA secondary to symptomatic ALTRs were recruited. The mean timeframe from primary MoM THA to symptomatic revision was 5.5 years (range, 1-10 years). Twenty-eight control subjects were randomly selected asymptomatic patients with no evidence of ALTRs on protocol-specific screening. Baseline demographics and high-resolution genotype (human leukocyte antigen [HLA] Class II) were collected for all patients. Cohorts were similar with respect to age at the time of primary MoM THA (mean, 54.8 versus 54.9 years, p = 0.95) and serum cobalt (mean, 5.5 versus 8.5 μg/L, p = 0.09) and chromium concentrations (mean, 2.9 versus 4.2 μg/L, p = 0.27). The association between genotype and revision surgery secondary to ALTRs was determined with gender as a covariate.

RESULTS

The prevalence of the risk genotype was 30% (16 of 54) among the entire cohort. Adjusting for sex, the odds of revision were 6.1 times greater among patients with the risk genotype present than among patients without (95% confidence interval [CI], 1.5-25.4; p = 0.01). Among females, the specificity of the risk genotype was 1.0 (95% CIexact, 0.5-1.0; pexact = 0.03), and for males, it was 0.8 (95% CIexact, 0.6-0.9; pexact < 0.01).

CONCLUSIONS

The findings of this study suggest that, among patients with a primary MoM THA, allelic variation within the HLA Class II loci may be a strong, independent risk factor associated with the need for subsequent revision surgery secondary to pseudotumor formation.

CLINICAL RELEVANCE

Given the hypothesis-generating nature of this novel undertaking, confirmatory prospective clinical studies are required to further elucidate this correlation and to explore the clinical utility of targeted genetic screening in this specific population. This research may, however, represent a key missing piece in the puzzle that is metal ion-induced pseudotumor formation.

Potential presence of metals in patients treated with metal-metal coupling prostheses for hip arthroplasty at 7 and 10 years of follow-up

BACKGROUND

Beginning in 2008, metal-on-metal prostheses have been in the spotlight owing to much higher revision rates than expected. Adverse local tissue reactions have been well described in the literature as potential complications.

METHODS

Between 2012 and 2013, 13 patients with metal-on-metal total hip replacements were evaluated clinically and radiologically and with laboratory samples. The same tests were repeated between 2015 and 2016 on eight patients to assess any changes. In the laboratory assessment, we searched for chromium, cobalt, molybdenum, and nickel in blood and urine samples over 24 h.

RESULTS

Clinical assessment has shown good score in all patients except one. On a second examination, between 2015 and 2016, all patients obtained results similar to those obtained in the first assessment, except a patient, who reported a recent fall. In the radiological assessment between 2012 and 2013, results were optimal, apart from a case of aseptic mobilization. The patients reassessed 3 years after the first examination showed radiological results similar to those previously obtained, apart from a patient, who showed signals of mobilization. Metal levels found in their blood decreased in most cases after 3 years. Urine levels of nickel increased in five subjects, and chromium levels increased in four, but levels of cobalt and molybdenum decreased in four patients.

CONCLUSION

It could be hypothesized that the decreasing trend of metal ion levels is associated with a stable wear status. On the contrary, a progressive increase in metal ion levels must be considered as early proof of implant loosening.

New alternate bearing surfaces in total hip arthroplasty: A review of the current literature

As indications for total hip arthroplasty (THA) have expanded, the incidence of THA has increased among younger patients, who live longer and tend to place more strain on implants via higher activity levels. This demographical shift accentuates the importance of advancing innovation to ensure implant longevity for younger and more active patients. Future innovation, as it pertains to THA components, is likely to focus on modifying implant designs and tribology in conjunction with identification and application of newer biomaterials. By reviewing the literature for development status of various materials and novel design advancements in THA component outside of the standard highly cross-linked polyethylene, this investigation provided an update on the current and future status of design initiatives as they pertain to THA. Though the highlighted alternative bearing surfaces have shown promising in vitro and limited, yet encouraging clinical data, they lack larger and longer-term clinical trial results. Further research and innovation is warranted to identify the optimal bearing surface to most effectively accommodate for the trend of younger and more active patients undergoing THA. Implant longevity is crucial if the clinical success of THA is to be maintained.