The influence of bearing surfaces on revisions due to dislocations in total hip arthroplasty

INTRODUCTION

Recurrent dislocations are still the most frequent reason for revision in total hip arthroplasty (THA). The impact of bearing surfaces on dislocations is still controversial. We hypothesized that: (1) bearing surfaces influence the revisions due to dislocations; (2) ceramic-on-ceramic reduced the revisions for dislocations in adjusted models; (3) Delta-on-Delta bearings reduced the revisions for dislocations in comparison to surfaces with cross-linked polyethylene.

MATERIALS AND METHODS

The regional arthroplasty registry was enquired about bearing surfaces and revisions for dislocations and instability. Unadjusted and adjusted rates were provided, including sex, age (<65 years or ≥65 years), head diameter (≤28 mm or >28 mm; <36 mm or ≥36 mm) as variables. 44,065 THAs were included.

RESULTS

The rate of revisions for dislocations was significantly lower in ceramic-on-ceramic and metal-on-metal bearings (unadjusted rates). After adjusting for age, sex, and head size (36 and 28 mm), hard-on-hard bearings were protective (p < 0.05): ceramic-on-ceramic had a lower risk of revisions due to dislocation than ceramic-on-polyethylene (HR 1.6, 95% CI 1.2-2.2 p = 0.0009). The rate of revisions for dislocation was similar in bearings with cross-linked polyethylene and Delta-on-Delta articulations, in unadjusted and adjusted models.

CONCLUSION

Bearings with conventional polyethylene were more predisposed to dislocations. Currently adopted bearings exerted no significant influence on revisions due to dislocations. These findings could be primarily related to wear, but due to the time distribution, soft tissue envelopes and surface tension may also play a role. Pre-clinical biomechanical evaluations and prospective matched cohort studies are required to draw definitive conclusions.

Surgical cup placement affects the heating up of total joint hip replacements

The long-term success of highly effective total hip arthroplasty (THA) is mainly restricted by aseptic loosening, which is widely associated with friction between the head and cup liner. However, knowledge of the in vivo joint friction and resulting temperature increase is limited. Employing a novel combination of in vivo and in silico technologies, we analyzed the hypothesis that the intraoperatively defined implant orientation defines the individual joint roofing, friction and its associated temperature increase. A total of 38,000 in vivo activity trials from a special group of 10 subjects with instrumented THA implants with an identical material combination were analyzed and showed a significant link between implant orientation, joint kinematics, joint roofing and friction-induced temperature increase but surprisingly not with acting joint contact force magnitude. This combined in vivo and in silico analysis revealed that cup placement in relation to the stem is key to the in vivo joint friction and heating-up of THA. Thus, intraoperative placement, and not only articulating materials, should be the focus of further improvements, especially for young and more active patients.

Association of Sex With Risk of 2-Year Revision Among Patients Undergoing Total Hip Arthroplasty

IMPORTANCE

The worldwide population is aging and includes more female individuals than male individuals, with higher rates of total hip arthroplasty (THA) among female individuals. Although research on this topic has been limited to date, several studies are currently under way.

OBJECTIVES

To evaluate the association between sex and 2-year revision after THA.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study used data from statewide databases in New York and California between October 1, 2015, and December 31, 2018. Patients 18 years or older with osteoarthritis who underwent THA and had sex recorded in the database were included in the analysis.

EXPOSURE

Total hip arthroplasty.

MAIN OUTCOMES AND MEASURES

The outcome of interest was the difference in early, all-cause revision surgery rates after primary THA between women and men. The association of sex with the revision rate was examined using Cox proportional hazards regression analysis.

RESULTS

Of 132 826 patients included in the study, 74 002 (55.7%) were women; the mean (SD) age was 65.9 (11.0) years, and the median follow-up time was 1.3 years (range, 0.0-3.0 years). The 2-year revision rate was 2.5% (95% CI, 2.4%-2.6%) among women and 2.1% (95% CI, 2.0%-2.2%) among men. After adjusting for demographic characteristics, comorbidities, and facility volume, a minimal clinically meaningful difference was observed in revision rates despite women having a higher risk of all-cause revision compared with men (hazard ratio, 1.16; 95% CI, 1.07-1.26; P < .001). The risk of revision was increased among women compared with men in the subgroup of patients who were younger than 55 years (hazard ratio, 1.47; 95% CI, 1.20-1.81; P < .001).

CONCLUSIONS AND RELEVANCE

In this cohort study, no clinically meaningful difference in all-cause revision rates after primary THA was found between men and women at 2-year follow-up. The modest difference in the risk of revision between men and women in a small subgroup of patients younger than 55 years suggests that the risk of revision in this population should be studied further.

Repeated cobalt and chromium ion measurements in patients with bilateral large-diameter head metal-on-metal ReCap-M2A-Magnum total hip replacement

Background and purpose - Whole-blood (WB) chromium (Cr) and cobalt (Co) measurements are vital in the follow-up of metal-on-metal total hip replacement (MoM THR) patients. We examined whether there is a substantial change in repeated WB, Co, and Cr levels in patients with bilateral ReCap-M2A-Magnum THR. We also specified the number of patients exceeding the safe upper limit (SUL) of WB Co and Cr in the repeated measurement.Patients and methods - We identified 141 patients with bilateral ReCap-M2A-Magnum THR operated in our institution. 61 patients had repeated WB metal ion measurements with bilateral MoM implants still in situ in the second measurement. The mean time elapsing from the first measurement (initial measurement) to the second (control measurement) was 1.9 years (SD = 0.6, range 0.2-3.5). We used earlier established SUL levels for bilateral implants by Van Der Straeten et al. (2013).Results - The median (range) Co and Cr values decreased in the repeated measurement from 2.7 (0.6-25) to 2.1 (0.5-21) and 2.6 (0.8-14) to 2.1 (0.5-18) respectively. In 13% of the patients Co levels exceeded the SUL in the initial measurement and the proportion remained constant, at 13%, in the repeated measurement. In 5% of the patients, Cr levels were above SUL in the initial measurement and an equal 5% in the control measurement.Interpretation - Repeated WB metal ion levels did not increase in patients with bilateral ReCap-M2A-Magnum THR with a mean 1.9-year measurement interval. Long-term development of WB metal ion levels is still unclear in these patients.

Mixed ceramic combinations in primary total hip arthroplasty achieved reassuring mid-to-longterm outcomes

INTRODUCTION

Ceramic-on-ceramic couplings demonstrated to be reliable bearings in primary total hip arthroplasty (THA), with long-term remarkable results. Like-on-like configurations were widely described. On the contrary, mixed material combinations from the same manufacturer, Delta-on-Forte or Forte-on-Delta, were poorly studied. In particular, it is unknown whether mixed ceramic combinations are more at risk of ceramic fractures. Thus, a registry study was conducted to investigate the long-term survival rates and reasons for revision of mixed ceramic combinations. A comparison with Delta-on-Delta couplings was also performed.

MATERIALS AND METHODS

The regional arthroplasty registry RIPO was enquired about three cohorts of ceramic bearings (head-on-liner: Delta-on-Forte, Forte-on-Delta, Delta-on-Delta). Demographics, survival rates and reasons for revision were evaluated and compared.

RESULTS

In total, 346 (1.5%) implants had a Delta-on-Forte coupling (mean follow-up: 6.4 years). In total, 1163 (5%) THAs had a Forte-on-Delta articulation (mean follow-up: 8.2 years). Delta-on-Delta surfaces were implanted in 21,874 (93.5%) hips (mean follow-up: 3.9 years). Mixed material combinations were implanted between 2003 and 2007. The survival rates of the three cohorts were similar and were higher than 95% at 10 years. In Forte-on-Delta group, four liners failed (0.3% of the implants), whereas ceramic fractures occurred in 15 cases (0.1%) in Delta-on-Delta couplings (3 heads and 12 liners). Considering ceramic fracture as endpoint, there was no significant difference between the three survival rates.

CONCLUSIONS

Mixed ceramic bearing configurations from the same manufacturer in primary THA showed mid-to-longterm dependable outcomes, not inferior to the most recent like-on-like ceramic bearings. No additional risks of ceramic fractures were evident. Thus, closer follow-ups are not required.

Prevalence of Postoperative Periprosthetic Femur Fractures Between Two Different Femoral Component Designs Used in Direct Anterior Total Hip Arthroplasty

BACKGROUND

Periprosthetic femur fractures are a well-documented complication following direct anterior uncemented total hip arthroplasty. The purpose of this study is to compare the prevalence of postoperative periprosthetic femur fractures between 2 different femoral component designs used in direct anterior total hip arthroplasty.

METHODS

Beginning in February 2015, a single fellowship-trained adult reconstruction surgeon performed 361 consecutive direct anterior total hip replacements using a flat, single-taper, wedged femoral implant. In June 2016, that same surgeon, using the exact same surgical technique and postoperative weight-bearing protocol, began using a dual-taper, hydroxyapatite-coated implant for 789 consecutive hips. The patients were carefully monitored for 3 months after surgery to identify the frequency of periprosthetic femur fractures. A Fisher's exact test was used to determine if the prevalence of periprosthetic femur fractures differed between the 2 implant designs.

RESULTS

Five of 361 (1.4%) patients sustained proximal femur fractures at an average of 19.6 days postoperatively in the first group, all demonstrating a Vancouver type B2 periprosthetic fracture and requiring femoral revision. No patients (0/789, 0%) in the second cohort sustained a postoperative, periprosthetic fracture (P = .006).

CONCLUSION

In this comparison of 2 consecutive cohorts, the dual-taper, hydroxyapatite-coated implant had a statistically significant lower postoperative periprosthetic fracture rate than a flat, single-taper, wedged design.

Understanding the uptake of new hip replacement implants in the UK: a cohort study using data from the National Joint Registry for England and Wales

OBJECTIVES

Primary: describe uptake of new implant components (femoral stem or acetabular cup/shell) for total hip replacements (THRs) in the National Joint Registry for England and Wales (NJR). Secondary: compare the characteristics of: (a) surgeons and (b) patients who used/received new rather than established components.

DESIGN

Cohort of 618 393 primary THRs performed for osteoarthritis (±other indications) by 4979 surgeons between 2008 and 2017 in England and Wales from the NJR. We described the uptake of new (first recorded use >2008, used within 5 years) stems/cups, and variation in uptake by surgeons (primary objectives). We explored surgeon-level and patient-level factors associated with use/receipt of new components with logistic regression models (secondary objectives).

OUTCOMES

Primary outcomes: total number of new cups/stems, proportion of operations using new versus established components.

SECONDARY OUTCOMES

odds of: (a) a surgeon using a new cup/stem in a calendar-year, (b) a patient receiving a new rather than established cup/stem.

RESULTS

Sixty-eight new cups and 72 new stems were used in 47 606 primary THRs (7.7%) by 2005 surgeons (40.3%) 2008-2017. Surgeons used a median of one new stem and cup (25%-75%=1-2 both, max=10 cups, max=8 stems). Surgeons performed a median total of 22 THRs (25%-75%=5-124, range=1-3938) in the period 2008-2017. Surgeons used new stems in a median of 5.0% (25%-75%=1.3%-16.1%) and new cups in a median of 9.4% (25%-75%=2.8%-26.7%) of their THRs. Patients aged <55 years old versus those 55-80 had higher odds of receiving a new rather than established stem (OR=1.83, 95% CI=1.73-1.93) and cup (OR=1.31, 95% CI=1.25-1.37). Women had lower odds of receiving a new stem (OR=0.87, 95% CI=0.84-0.90), higher odds of receiving a new cup (OR=1.06, 95% CI=1.03-1.09).

CONCLUSIONS

Large numbers of new THR components have been introduced in the NJR since 2008. 40% of surgeons have tried new components, with wide variation in how many types and frequency they have been used.

Survivorship of the Modular Femoral Revision Stem

The geriatric population represents a rapidly growing segment of society with prolonged life expectancies and more active lifestyles. Many of these patients have already undergone primary total hip arthroplasty (THA) and are presenting with aseptic loosening, polyethylene wear, osteolysis, or periprosthetic fractures. Therefore, the demand for hip revision procedures is expected to grow. Currently, there are many modular implant options available for use in complicated revision THA. Early results of modular femoral revision systems are promising for the treatment of the deficient femur in complex revision THA. The objective of this study was to evaluate component survivorship of a modular femoral revision system in revision THA. A retrospective review was conducted using electronic health records of patients who underwent revision THA performed by 1 of 3 surgeon investigators from 2010 through 2014. The authors included all patients who underwent a revision THA using a specific modular femoral revision system. The authors evaluated component survivorship and time to re-revision THA. Fifty-one revision THAs were included. Seven patients required a second revision THA (13.7%; 95% confidence interval, 4%-23%). Mean time to re-revision THA was 4.88±3.9 months. Kaplan-Meier survivorship using re-revision for any reason was 86.3% at 60 months. This study showed excellent component survivorship of the specific modular femoral revision system in revision THA. [Orthopedics. 2019; 42(5):294-298.].

Comparing In Vivo Performance of Two Highly Cross-Linked Polyethylene Thermal Treatments: Remelting vs Annealing in Acetabular Liners

BACKGROUND

The introduction of highly cross-linked polyethylene (HXLPE) acetabular liners has greatly improved the wear performance of metal-on-PE bearing surfaces used in total hip arthroplasty. Changing the sterilization environment and adding thermal treatments, such as remelting or annealing, were introduced to limit on-shelf and in vivo oxidation of cross-linked liners. This study compares the wear properties of the remelted A-CLASS (MicroPort) HXLPE liner to a sequentially annealed HXLPE.

METHODS

This retrospective study assessed linear and volumetric wear rates using Martell Hip Analysis Suite, and clinical performance through incidences of revision surgeries. A total of 80 remelted and 53 annealed liners were included in the wear analysis. All hips were reviewed for revisions.

RESULTS

There were no significant differences in steady-state linear or volumetric wear rates for remelted and annealed liners, 0.01 (-0.07 to 0.14) vs -0.01 (-0.11 to 0.1) mm/y (P = .28) and -1.03 (-30.99 to 45.43) vs -1.31 (-32.23 to 23.70) mm³/y (P = .30), respectively. Both cohorts were below the 0.1 mm/y linear wear threshold. The wear rates for patients with femoral head sizes ≥36 mm were not significantly different than those with 32 and 28 mm femoral head sizes (P = .60). Similarly, wear rates for patients with an excessively vertical acetabular component (>50°) were not significantly different than those with standard acetabular component orientations (P = .97). No hips were revised due to liner-related complications.

CONCLUSION

The wear rates of the A-CLASS remelted HXLPE acetabular liner wear rates were comparable to those of a sequentially annealed HXLPE. Further long-term studies are required to ensure acceptable resistance to fatigue and in vivo oxidation.

Femoral Stem Survivorship in Dorr Type A Femurs After Total Hip Arthroplasty Using a Cementless Tapered Wedge Stem: A Matched Comparative Study With Type B Femurs

BACKGROUND

There is a lack of understanding on relationship between the femoral geometry and outcomes of total hip arthroplasty (THA). We investigated clinical and radiographic outcomes of THA using a cementless tapered wedge stem in patients with Dorr type A proximal femoral morphology and compared with those of type B femurs at a minimum follow-up of 5 years.

METHODS

We analyzed 1089 hips (876 patients) that underwent THA using an identical cementless tapered wedge stem. We divided all femurs into 3 types (Dorr type A, B, and C). Type A and B femurs were statistically matched with age, gender, body mass index, and diagnosis by using propensity score matching. Clinical, radiographic results, and stem survivorship were compared between the matched 2 groups.

RESULTS

A total of 611 femurs (56%) were classified as type A, 427 (39%) as type B, and 51 (5%) as type C. More radiolucent lines around femoral stems were found in type A femurs (7.8%) than in type B femurs (2.5%) (P < .001). Patients with radiolucency showed worse Harris Hip Score (86.2 points) compared with those without radiolucency (93.0 points) (P < .001). The stem survivorship of type A femur (97.8%) was lower than that of type B femur (99.5%) (P = .041). The reasons for femoral revision in type A femurs were periprosthetic fracture (67%), aseptic loosening (22%), and deep infection (11%).

CONCLUSIONS

This study showed a higher rate of complications after THAs using a cementless tapered wedge stem in Dorr type A femurs than those performed in type B femurs.

Hip hemiarthroplasty for fractured neck of femur; a freedom of information study to assess national variation in implant selection and procurement

INTRODUCTION

During 2016, according to the National Hip Fracture Database (NHFD), over 65,000 patients suffered a hip fracture of which approximately half underwent hemiarthroplasty. Clear guidelines exist on the usage of proven cemented implants. The Getting It Right First Time (GIRFT) Report highlighted the financial implications of 'unwarranted variation' and stressed the importance of rationalising and standardising service provision, in particular implant usage. The primary aims of this study were to investigate the variation in hip hemiarthroplasty implant usage and associated costs. We hypothesised there to be large variation in implants used and procurement costs.

METHODS

Freedom of Information Requests (FOI) were sent to all 177 hospitals listed in the 2017 NHFD Report as treating hip fracture patients. All hospitals were asked for their most commonly used hemiarthroplasty implant and the cost of this, per patient.

RESULTS

One hundred sixty six (94%) responses were received. Eighty four (51%) provided implant name and cost, 78 (47%) provided implant name but refused costs and 4 (3%) refused to provide any details. Nineteen different prostheses were used nationally with 20 hospitals using a non-ODEP (Orthopaedic Data Evaluation Panel) 10A implant. Average total cost was £725.00 (range £71-£1378). Significant cost variation was demonstrated for the same implants; one implant was £978.19 at it's most costly and £285.59 at it's cheapest.

DISCUSSION

The aims of this study have been met. We have demonstrated huge variation in the implants used for hip hemiarthroplasty and their costs. Notwithstanding the nuances of departmental procurement processes, the financial implications for this variation are significant.

CONCLUSIONS

This article demonstrates a requirement for rationalisation of implant usage and procurement in order to potentially improve patient outcomes and provide opportunities for significant cost saving in an already overstretched health service.

Linear Wear Rates of a Highly Cross-Linked Polyethylene Hip Liner

INTRODUCTION

To help limit wear, newer polyethylene liners, such as the highly cross-linked polyethylene (HXLPE) liners, have been developed. These newer liners undergo an alternating irradiation process, resulting in a stronger, longer-lasting liner. The purpose of this study was to analyze the wear rates of patients who underwent THA and received a newer generation HXLPE acetabular insert. Specifically, we compared: 1) linear vector wear amount and 2) linear vector wear rates in patients as an overall cohort and by gender. We also assessed patient satisfaction outcomes comparing preoperative Harris Hip Scores (HHS) to seven-week, one-year, and three-year HHS scores.

MATERIALS AND METHODS

A total of 23 patients who underwent total hip arthroplasty (THA) with direct superior approach by a fellowship-trained orthopaedic surgeon at a private practice institution were analyzed after receiving institutional review board approval. Patients had a minimum two-year follow up, with the mean follow up being four years (range, three to five years). All patients received a 36-mm ceramic femoral head with an HXLPE liner. 2D radiographic polyethylene wear analysis was performed using the Martell Hip Analysis Suite (HAS; University of Chicago, Illinois), which has been previously validated in the literature. Outcomes were assessed using Harris Hip Scores.

RESULTS

A five-year linear wear rate of 0.073 mm/year (range, 0 to 0.160 mm/year) and an overall mean linear wear rate of 0.096 mm/year (range, 0 to 0.277 mm/year) were found. No significant differences in wear were seen between genders. Additionally, patients reported significantly better results at seven-weeks (83 points [range, 59 to 100 points]) and one-year (94 points [range, 85 to 100 points]) than preoperative (52 points [range, 34 to 73 points]) HSS scores (p<0.05). No patients underwent revision THA.

CONCLUSION

The results from this study highlight the benefits of using an HXLPE polyethylene liner in THA patients and further validates previously reported wear rates of HXLPE liners. After an early "wear in" period during the first year, the wear rates steadily decreased over time. This liner showed excellent early outcomes as no patients underwent revision THA. Furthermore, even as early as seven postoperative weeks, patients reported significantly better HHS scores. Future studies should track the same patient cohort over time to help develop a wear-rate prediction model.

Up to 18-Year Follow-Up Wear Analysis of a First-Generation Highly Cross-Linked Polyethylene in Primary Total Hip Arthroplasty

BACKGROUND

The advent of highly cross-linked polyethylene (HCLPE) has significantly improved total hip arthroplasty survivorship. HCLPE has been shown to improve wear properties in midterm outcomes when compared to traditional polyethylene liners; however, there is a paucity of studies evaluating long-term outcomes. In addition, there is concern that wear rates may accelerate as the implant ages. Thus, the aims of this study are to report on the longest-to-date follow-up of a specific first-generation HCLPE liner and to determine whether there is a change in the annual wear rate over time.

METHODS

Forty hips in 38 patients which were previously reported on in a midterm study were included in this long-term follow-up study. Patients in this cohort all received total hip arthroplasty between March 1999 and August 2004 using the Crossfire HCLPE liner. Annual wear rates (mm/y) were calculated for this cohort. Patients were contacted and asked about complications or revision procedures they may have had since the index procedure.

RESULTS

Clinical follow-up averaged 12.9 years with a range of 7-18 years. The average follow-up duration was 12.5 years with a range of 10-17 years. Linear wear was found to be 0.056 ± 0.036 mm/y. Osteolysis was not observed in any of the patients with greater than 10-year radiographic follow-up. Furthermore, only 1 patient required revision surgery following a mechanical fall.

CONCLUSION

Our study demonstrates the long-term wear rates associated with HCLPE liners continue to match rates published in midterm studies. Previously, we have reported that this cohort had an average annual wear rate of 0.05 mm/y over 10 years. This most recent report demonstrates a similar wear rate with up to 18-year follow-up.

Reverse hybrid total hip arthroplasty

Aims

This study aimed to evaluate implant survival of reverse hybrid total hip arthroplasty (THA) at medium-term follow-up.

Patients and Methods

A consecutive series of 1082 THAs in 982 patients with mean follow-up of 7.9 years (5 to 11.3) is presented. Mean age was 69.2 years (21 to 94). Of these, 194 (17.9%) were in patients under 60 years, 663 (61.3%) in female patients and 348 (32.2%) performed by a trainee. Head size was 28 mm in 953 hips (88.1%) or 32 mm in 129 hips (11.9%). Survival analysis was performed and subgroups compared using log rank tests.

Results

Ten-year survival (122 hips at risk) was 97.2% (95% confidence interval (CI) 95.77 to 98.11) for all-cause revision. There was no difference in survival by age (p = 0.50), gender (p = 0.78), head size (p = 0.63) or surgeon grade (p = 0.36). No acetabular components underwent revision for aseptic loosening in the entire series. Four (0.4%) aseptic stem failures occurred early at a mean of 2.5 years (0.6 to 4.8) and were associated with age under 60 years (p = 0.015). There was no difference in survival by gender (p = 0.12), head size (p = 0.43) or surgeon grade (p = 0.77) for stem revision.

Conclusion

This is the largest reported study into reverse hybrid THA and it confirms successful outcomes, irrespective of age, gender, head size and surgeon grade. Cite this article: Bone Joint J 2018;100-B:1010-17.

Contemporary Dual Mobility Head Penetration at Five Years: Concern for the Additional Convex Bearing Surface?

BACKGROUND

Dual mobility (DM) bearings are increasingly popular and second-generation designs contain highly cross-linked polyethylene. The purpose of this study is to report head penetration rates in modern DM bearings.

METHODS

A review of 63 consecutive DM bearings was performed. Radiographs were analyzed for head penetration using Martell methodology at regular postoperative intervals.

RESULTS

Thirty-four DM bearings were analyzed. Mean linear head penetration was 1.59 mm/y at 1 year, 1.07 mm/y at 2 years, and 0.27 mm/y at 5 years following an exponential regression model (R² = 0.999). Mean volumetric wear was 783 mm³/y at 1 year, 555 mm³/y at 2 years, and 104 mm³/y at 5 years following an exponential regression model (R² = 0.986).

CONCLUSION

Initial head penetration of DM bearings is larger than contemporary cross-linked polyethylene bearings; however, rates approach steady state after 2 years, analogous to traditional bearings. The larger "bedding-in" head penetration may be due to the additional convex bearing surface, creating 2 surfaces for deformation/wear.

What Is the Long-term Survival for Primary THA With Small-head Metal-on-metal Bearings?

BACKGROUND

Large-head metal-on-metal (MoM) bearing hip replacements have been shown to have a much higher rate of revision than other bearing surfaces. However, small-head (≤ 32 mm) MoM bearing surfaces have been in use for many years with several reports of satisfactory mid- to long-term survivorship. It is unclear whether the long-term survival of small-head MoM devices will continue to be satisfactory or whether the same concerns seen with the large-head MoM devices will ultimately become more prevalent.

QUESTIONS/PURPOSES

We analyzed a large national registry to ask: (1) What is the 15-year Kaplan-Meier survivorship of primary conventional THA using small-head (≤ 32 mm) MoM bearing surfaces compared with large-head MoM bearing surfaces in primary THA? (2) Is there an increased rate of revision for adverse reaction to metal debris (ARMD) in this group of patients over time?

METHODS

The Australian Orthopaedic Association National Joint Replacement Registry longitudinally maintains data on all primary and revision joint arthroplasties with nearly 100% capture. We analyzed all conventional primary THAs performed from Registry inception in September 1999 until December 31, 2015, in patients with a diagnosis of osteoarthritis and using MoM bearing surfaces ≤ 32 mm in diameter, defined as small-head MoM. The study group included 4838 primary THA with ≤ 32-mm MoM bearing surfaces. There were 2506 (51.8%) male patients and the median age of patients undergoing THA with a small-head MoM bearing surface was 64 years (range, 20-92 years of age). The outcome measure was the cumulative percent revision defined as the time to first revision using Kaplan-Meier estimates of survivorship at 15 years; reasons for revision and type of revision were also examined. We specifically investigated whether there was an increased risk of revision for ARMD in this MoM group compared with all other bearing surfaces. We compared these results with large-head MoM THAs (femoral head size > 32 mm).

RESULTS

The cumulative percent revision for small-head MoM designs at 15 years was 8.5% (95% confidence interval [CI], 7.3-9.9). The cumulative percent revision for large-head MoM at 14 years was 27.4% (95% CI, 24.8-30.2). Prostheses with a large-head MoM articulation have a higher rate of revision than small-head MoM bearing surfaces (hazard ratio after 6 years, 5.14; 95% CI, 4.1-6.5; p < 0.001). Over time, there was a gradual increase in the diagnosis of ARMD for small-head MoM and the cumulative incidence of revision for ARMD was 0.8% at 15 years.

CONCLUSIONS

Despite survival that is substantially greater than that of large-head MoM THAs, there has been a marked decrease in the use of small-head MoM designs in our registry. Although the reasons for this are likely multifactorial, the increasing incidence of revisions for ARMD among small-head MoM THAs is concerning.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Short Stems Versus Conventional Stems in Cementless Total Hip Arthroplasty: A Long-Term Registry Study

BACKGROUND

Short stems in total hip arthroplasty (THA) have recently gained increasing popularity, allowing mini-invasive exposures and bone-sparing approaches. However, long-term studies and recommendations for the routine use are not available. The aim of this report was to compare the survival rates and the reasons for revision of short stems versus conventional stems in cementless THAs, in a registry-based population.

METHODS

The Registry of Prosthetic Orthopedic Implants (RIPO) was inquired about cementless THAs performed since 2000 to 2016. The stems were divided into short (<12 cm) and conventional ones, and then, classified according to the classification by Feyen and Shimmin: short stems with neck-retaining osteotomy (group A: 1684 hips), short stems with standard osteotomy (group B: 2727 THAs), and conventional stems (group C: 57,359 cases). Demographics, survivorships, and reasons for revision were investigated and compared.

RESULTS

Short stems were preferentially implanted in younger patients and normal morphologies. Short and conventional stems showed comparable survival rates at long-term follow-up (>90% at 15 years). The rates of stem aseptic loosening, intraoperative fractures, and periprosthetic fractures were similar in the 3 groups. Group B had higher rates of revisions due to primary instability (early dislocations and impingement-related events; P < .05). Revisions due to pain were nonsignificantly higher in group B.

CONCLUSION

Short stems are reliable implants at long-term follow-up. The comparison with conventional stems showed no additional risk of premature aseptic loosening and intraoperative and periprosthetic fractures. However, the high rate of revisions due to pain and, mostly, primary instability should be investigated in clinical trials.

Short-Term Results of Ultra-Short Anatomic vs Ultra-Short Non-Anatomic Proximal Loading Uncemented Femoral Stems

BACKGROUND

Question arises as to whether rigid fixation of ultra-short anatomic or ultra-short non-anatomic proximal loading uncemented femoral stem can be obtained without diaphyseal stem fixation. The purpose of this study is to compare the short-term clinical results, radiographic results, revision and survival rates, and complication rates of ultra-short anatomic versus ultra-short non-anatomic uncemented femoral stems.

METHODS

This study consisted of 50 patients (56 hips) in the ultra-short anatomic uncemented stem group (mean age 61.4 ± 14.7 years) and 50 patients (56 hips) in the ultra-short non-anatomic uncemented stem group (mean age 59.5 ± 15.2 years). The mean follow-up was 3.4 years (range 3-4) in the ultra-short anatomic stem group and 3.5 years (range 3-4) in the ultra-short non-anatomic stem group.

RESULTS

At the final follow-up, the mean Harris hip scores (92 vs 93 points), Western Ontario and McMaster Universities Osteoarthritis scores (16 vs 15 points), University of California at Los Angeles activity scores (6.5 vs 6.8 points), the incidence of thigh pain (0% vs 4%), revision rates (0% vs 4%), aseptic loosening rate (0% vs 2%), and complication rates (2% vs 4%) were not significantly different between 2 groups.

CONCLUSION

Both ultra-short anatomic and ultra-short non-anatomic proximal loading uncemented femoral stems obtained rigid fixation without diaphyseal stem fixation in the short-term follow-up. This finding suggests that an ultra-short anatomic uncemented femoral stem can be replaced with an ultra-short non-anatomic uncemented stem to reduce inventory of the femoral stems, and consequently reduce manufacturing and delivery cost of these femoral stems.

Can Stem Version Consistently Correct Native Femoral Version Using Robotic Guidance in Total Hip Arthroplasty?

The purpose of this study is to investigate whether robotic guidance in total hip arthroplasty (THA) can consistently correct native femoral version. One hundred seventy-five consecutive patients who underwent MAKO® (Stryker, Kalamazoo, Michigan) robotic-guidance THA were included in the study. The study population had a mean age of 57.9 years and a mean body mass index (BMI) of 30.41. Forty-eight percent of the population was male and 74% of the procedures were performed through an anterior approach. Robotic guidance in THA was effective in correcting native femoral version toward a target of 15°. This can be achieved using both the anterior and posterior approach; it is not affected by BMI.

Early Experience with a Tapered Titanium Porous Plasma Sprayed Stem with Updated Design

INTRODUCTION

The Taperloc® Complete femoral stem (Zimmer Biomet, Warsaw, Indiana) builds on the widespread clinical success of the original Taperloc design used since 1982. Enhancements to the Complete design include a lowered caput-collum-diaphyseal (CCD) angle from 138° to 133° for improved offset, optimized neck taper with polished neck flats to increase range of motion, reduced distal geometry to improve proximal canal fill, and gradual off-loading that is the goal of tapered geometry. A retrospective review was conducted to assess our early experience with the updated design.

MATERIALS AND METHODS

A query of our practice's arthroplasty registry revealed 97 consented patients (103 hips) who underwent primary cementless THA performed with a Taperloc® Complete femoral component between November 2010 and March 2011. A high offset option, accomplished by a constant 7.8mm medial shift of the trunnion, was utilized in 94 hips (91%). Mean age was 61.8 years and body mass index (BMI) was 31.3 kg/m2. Underlying diagnoses were osteoarthritis in 96 (93%), four avascular necrosis, two post-traumatic arthritis, and one acute fracture.

RESULTS

Mean follow-up was 5.3 years (2-7). Harris hip scores improved from 53.6 preoperatively to 87.9 at most recent. One stem was revised for periprosthetic fracture. Other reoperations were one cup revised for iliopsoas impingement, one lateral femoral cutaneous neurectomy, and one incision and debridement for a non-healing wound. Postoperative radiographs revealed satisfactory position and alignment of components with no radiolucencies observed in all patients with no evidence of osteolysis, distal hypertrophy, or pedestal formation.

CONCLUSION

In this group, good results with a low frequency of complications and stem revision were achieved with a tapered titanium porous plasma-sprayed femoral component with updated design features. No aseptic loosening or osteolysis occurred. Radiographic findings were excellent in all hips.

Dual Mobility Acetabular Cups in Primary Total Hip Arthroplasty in Patients at High Risk for Dislocation

INTRODUCTION

Postoperative dislocation occurs in approximately 2% of primary total hip arthroplasties (THAs). Risk factors associated with dislocation include: age of 70 years or older, body mass index (BMI) of 30 kg/m2 or greater, alcohol abuse, and neuro-degenerative diseases such as multiple sclerosis or Parkinson's disease. As a result, dual-mobility articulations, which have been typically used for revision procedures, have become an increasingly popular option for these "at risk" primary THAs. Few studies have assessed their use in this complex patient population. Therefore, the purpose of this study was to assess: 1) survivorship; 2) radiographic outcomes (cup migration, progressive radiolucencies, and changes in component position); 3) Harris Hip Scores; and 4) complications of the dual-mobility articulation in the setting of primary THA for patients at high risk for dislocation.

MATERIALS AND METHODS

Five participating surgeons performed 495 primary cementless THAs between January 2011 and December 2013. During this time, four of the five surgeons used dual-mobility articulations whenever the acetabular cup size was 52 mm or greater to allow for a 28 mm head, while one surgeon used it when the cup size was less than 52 mm to allow for an effective head size of 38 mm. The remaining surgeon used it for all THAs. Of the 495 patients, 453 (92%) received dual-mobility articulations, of which, 43 patients (10%) were lost to follow-up before the two year minimum. The remaining 410 patients were further assessed to determine those who were considered high risk for dislocation (age = 70 years, BMI =30 kg/m2, had a diagnosis of alcohol abuse, or had a neuro-degenerative disorder). Two hundred forty-nine patients were included in the analysis (103 men, 146 women) who had a mean age of 66 years (range, 24 to 90 years). The mean follow-up was 3.3 years (range, 2 to 5 years). Kaplan-Meier analysis was performed to assess aseptic and all-cause acetabular cup survivorship. Radiographs were evaluated for cup migration, progressive radiolucencies, and any changes in component position. Clinical outcomes were assessed using the Harris Hip Score (HHS), and any surgery-related complications were recorded.

RESULTS

The survivorship to aseptic failure (n= 1) and all-cause (aseptic, n= 1; septic, n= 1) Kaplan-Meier acetabular component survivorships were 99.6% (95% confidence interval [CI], 99.1% to 99.9%) and 99.2% (95% CI, 98.5% to 99.9%), respectively. One hip had impingement of an anteverted cup, resulting in trunnion notching, and required revision of the cup and stem. Another hip had a deep infection, which was treated with a two-stage revision procedure. There were no dislocations in this cohort. No progressive radiolucencies or component positional changes were seen on radiographic assessment. Patients reported a mean HHS of 92.5 (range, 47 to 100 points) at final follow-up. Surgical complications included one polyethylene liner that was incompletely seated, and one loose femoral stem, which required revision of only the femoral component.

CONCLUSIONS

At short-term follow-up, dual-mobility articulations in primary THA offer survivorship, outcomes, and complications comparable to conventional THA designs in patients who are at increased risk for postoperative dislocation. Serious complications, such as polyethylene wear and intraprosthetic dislocations, have occasionally been reported with the use of these components. Therefore, future studies should be prospective, multi-center, and have longer-term follow-up to determine the true benefit of modular dual-mobility articulations in patients who are at high risk for dislocation.

Evaluation of the Effects of the Metha® Short Stem on Periprosthetic Bone Remodelling in Total Hip Arthroplasties: Results at 48 Months

INTRODUCTION

Total hip arthroplasty is one of the most performed procedures in orthopaedic surgery. Implantation of a prosthesis determines changes in the distribution of loads on the host bone, and this phenomenon, known as stress shielding, is related to the biomechanical characteristics of the implant. Usually stress shielding involves the proximal portion of the femur by reducing the mechanical strength and ability to withstand the transmitted loads. The aim of our study is to demonstrate how the use of a short hip stem reduces the stress shielding phenomenon to the proximal femur.

MATERIALS AND METHODS

The study analyzed 20 patients undergoing hip prosthesis surgery with a short stem (Metha<, B. Braun Medical, Inc., Bethlehem, Pennsylvania) at the Ist Orthopaedic Division of Pisa University (between December 2008 and January 2010). Each patient was subjected to analysis of periprosthetic bone mineral density by a bone densitometry (dual emission X-ray absorptiometry [DEXA] with the metal removal software) at 0, 6, 12, 18, 24, and 36 months, following a protocol based on the evaluation of the changes of bone density in the seven Gruen zones.

RESULTS

We recorded minimal changes in bone mineral density (BMD) at the level of the greater trochanter (-1.44%) and at the level of the calcar (-3.7%). BMD increased significantly after four years at the level of the lateral distal regions (R2 +9.6% - R3 + 12.4%) and at the level of the distal medial regions (R5 + 8.2% - R6 + 13.1%). We compared the results obtained with the literature data at 12 and 24 months with the same stem (Metha<). At 12 months follow up, we did not see a significant difference between our data and the data published in the literature. However, after 48 months of follow-up, we recorded significant differences in the curves of periprosthetic bone reabsorption at the level of the greater trochanter (Zone 1) and at the level of the calcar (Zone 7).

DISCUSSION

The data obtained from our study are in agreement with other studies in the literature, which demonstrates how the use of short stems preserves the metaphyseal bone stock at the level of the proximal femur, reducing the stress shielding phenomenon. From our data, obtained at 24 months and confirmed at 36, stress shielding seems to minimally occur at the level of the calcar. At the level of the great trochanter, we saw a good load distribution that maintained the baseline BMD; these data are in opposition to the literature data that showed a high increase of BMD at the level of the calcar (+12.9%) and a decrease at the level of the great trochanter. From the analysis of the radiographic images of our cases, and of the cases published with the same stem, these differences in load transfer encountered between the great trochanter and the calcar seems to be related to the level of the femoral neck osteotomy and the consequent stem position (varus/valgus).

CONCLUSION

We conclude that the amount of periprostetic bone reabsorption around the Metha< stem seems to be strictly related to the surgical technique and the final implant position.

Results of a Modular Femoral Revision System Before and After Taper Roller Hardening in Total Hip Arthroplasty

INTRODUCTION

Modular component options can aid in addressing complex femoral reconstructions in total hip arthroplasty (THA) by allowing for customization of version control and proximal to distal sizing. However, component breakage at the modular junction has occurred, particularly in the presence of poor bone stock. A taper roller hardening (RH) process was developed to strengthen the modular junction to reduce breakage. The purpose of this study is to review THA patients before and after taper roller hardening to compare stem survival and frequency of breakage.

MATERIALS AND METHODS

A query of our practice registry revealed 183 consented patients (202 THA) who underwent THA with a modular femoral revision component between January 1993 and September 2010. Forty THA were done before (non-RH) and 162 were done after taper roller hardening.

RESULTS

Mean follow-up was seven and 17 years in the RH and non-RH groups respectively. In the non-RH group, 15% were revised for component breakage versus 2% in the RH group. Overall, 35% non-RH versus 8% RH stems have been revised. Kaplan-Meier survival at 10 years with endpoint of stem revision for breakage revealed 84.2% ( ±6.0%) non-RH compared with 95.5% ( ±2.2%) RH (p=0.0033), and with endpoint of stem revision for any reason, 65.0% ( ±7.5%) non-RH compared with 80.3% ( ±3.7%) RH (p=0.0022).

CONCLUSIONS

Results indicate that the taper roller hardening process was successful in improving durability of a modular femoral revision system and reducing frequency of component breakage for patients who require treatment of the deficient femur in complex primary and revision THA.

Poor Acetabular Component Orientation Increases Revision Risk in Metal-on-Metal Hip Arthroplasty

BACKGROUND

The rate of and the reasons for the failure of metal-on-metal (MoM) bearings have recently been discussed in literature. The aim of this study was to evaluate the influence of acetabular cup inclination and version angles on revision risk in patients with MoM hip arthroplasty.

METHODS

We retrospectively reviewed 825 patients (976 hips) who underwent a MoM hip arthroplasty between 2000 and 2013. There were 474 men and 351 women, with a mean age of 58 (19-86) years. Acceptable cup orientation was considered to be inside the Lewinnek's safe zone.

RESULTS

The mean acetabular inclination angle was 48.9° (standard deviation, 8.1°; range, 16°-76°) and version angle 20.6° (standard deviation, 9.9°; range, -25 to 46°). The cup was found to be outside the Lewinnek's safe zone in 571 hips (58.5%). Acetabular cup revision surgery was performed in 157 hips (16.1%). The cup angles were outside Lewinnek's safe zone in 69.2% of the revised hips. The mean interobserver reliability and intraobserver repeatability of the measurements of cup inclination and version angles were excellent (intraclass correlation coefficients >0.90). The odds ratio for revision in hips outside vs inside the Lewinnek's safe zone was 1.82 (95% confidence interval, 1.26-2.62; P = .0014).

CONCLUSION

Our findings provide compelling evidence that a cup position outside the Lewinnek's safe zone is associated with increased revision risk in patients with MoM arthroplasty.

Developmental hip dysplasia treated by total hip arthroplasty using a cementless Wagner cone stem in young adult patients with a small physique

BACKGROUND

Developmental hip dysplasia (DDH) may lead to severe acetabular and femoral abnormalities that can render total hip arthroplasty (THA) challenging, especially in DDH patients with a small physique. Most conventional cemented or cementless femoral components are often difficult to implant in the narrow femoral canal and require slight version correction during surgery. The aim of this study was to present the mid-term results of THA in the treatment of DDH patients with a small physique using a cementless Wagner cone prosthesis (Zimmer®, US).

METHODS

Between January 2006 and March 2010, we retrospectively reviewed 50 patients who were treated at our center. A total of 50 patients (52 hips; 45 women, five men; mean age 32.5 years; range 27 to 38 years) who underwent THA were observed. The mean femoral medullary canal dimension at the isthmus was 7.6 mm (range 6.0 to 8.7). According to the Crowe classification, 19 hips presented dysplasia of grade I, while 33 presented dysplasia of grade II. All patients were treated with THA using a cementless Wagner cone prosthesis. Clinical and radiologic evaluations were performed on all patients.

RESULTS

The mean duration of follow-up was 7.7 years (range 5.4 to 10.5). The Harris hip score (HHS) improved from 63 ± 9 (range 55 to 70) pre-operatively to 92 ± 8 (range 88 to 100) at the last follow-up. The HHS at the most recent follow-up was excellent in 66% of patients (34 hips), good in 26% (14 hips), fair in 6% (3 hips), and poor in 2% (1 hip). Radiographic evaluation demonstrated excellent osteointegration of the implants. Stem subsidence was present in three stems, and the range of stem subsidence was 2 mm in two stems (3.9%) and 3 mm in one stem (1.9%). Femoral osteolysis was observed in nine hips (18%) in the proximal zones, and no distal osteolysis was noted. Heterotopic ossification was observed in three hips (5.8%); of these, two were classified as Brooker's grade 1, and one was classified as Brooker's grade 2 at the most recent follow-up. None of the implants were revised.

CONCLUSIONS

Based on the tapered shape and free setting of anteversion, the Wagner cone femoral stem facilitates its implantation in dysplastic hips. Therefore, this series of short stems with a smaller diameter can ensure safe implantation in narrow medullary canals, especially in young DDH patients with a small physique.

TRIAL REGISTRATION

Registration Number: ChiCTR-ORC-17011181 . Reg Date: 2017-04-19 00:44:59 Retrospective registration.