Risk factors for accelerated polyethylene wear and osteolysis in ABG I total hip arthroplasty

Body morphometry did not affect the accuracy of a second-generation, miniature imageless navigation system for total hip arthroplasty (THA) using a posterior approach

Introduction

Some modern imageless navigation platforms for total hip arthroplasty (THA) rely on virtual frontal and sagittal planes determined with the patient in the lateral decubitus position. Body morphometry that changes with gender, body mass index, and other demographic factors may affect accuracy in patient positioning and consequently, navigation accuracy. The objective of this study was to analyze the influence of patient factors on the intraoperative accuracy of a second-generation imageless computer-assisted surgery platform.

Methods

325 consecutive patients undergoing posterior approach, navigated THA arthroplasty for primary osteoarthritis by a single surgeon were retrospectively reviewed. An optic-based imageless navigation system referenced off a generic sagittal and coronal plane was used to determine acetabular inclination and anteversion. Acetabular accuracy was determined by assessing differences between intraoperative values and those obtained from measuring standardized 6-week follow-up radiographs. The effect of age, gender, BMI, race, ethnicity, and laterality on acetabular accuracy was assessed via t-tests, Pearson correlation and ANOVA.

Results

Gender had a significant impact on raw inclination accuracy (females and males had an average error of 1.41° and -1.03°, respectively - p < 0.001). There was a weak correlation between acetabular accuracy and patient age and BMI as a continuous variable (both absolute γ < 0.2). No difference was found between acetabular accuracy and BMI groups.

Conclusion

This second-generation imageless computer assisted device provided accurate cup positioning regardless of patient's BMI. Gender was the only factor impacting inclination accuracy.

How the hip-spine relationship influences total hip arthroplasty

INTRODUCTION

Motion in the spine, pelvis and hips which make up the spinopelvic femoral complex (SPFC) implies mechanical relationships that help maintain trunk balance and optimize hip functionThe aim of this study was to understand the physiology of the SPFC and evaluate the dysfunctions of the SPFC and their implications for total hip arthroplasty considering the hip-spine relationship.

METHODS

A review of relevant and comprehensive studies on this subject is reported in order to highlight a pathophysiology that integrates the description of the evaluations of the spine-pelvic and hip parameters and recommendations for the kinematic planning of the THA procedure. The primary objective was to determine which type of hip-spine relationship has the highest risk for THA complications and to become proficient in selecting the priority surgical intervention when both the hip and spine are affected. Finally, this review attempted to assist hip surgeons with surgical technique, tools, implant selection, and goals of planning a THA that requires personalized kinematic alignment. Determine the influence of THA on these kinematics and the effect of stiffness of the lumbopelvic complex on the risk of THA failure.

RESULTS

When a person sits, the pelvis goes into retroversion and the acetabulum opens forward. This frees the femoral head and neck to allow hip flexion. The opposite - pelvic anteversion - occurs when a person stands. When pelvic mobility is limited, the hip must increase its range of motion to accommodate these posture changes. Disturbances in spinal and pelvic kinematics lead to abnormal hip function, which may contribute to complications following total hip arthroplasty (THA).

CONCLUSION

A precise evaluation of the parameters governing the SPFC must be taken into account in order to best optimize the placement and choice of THA implants.

LEVEL OF EVIDENCE

IV.

CT-based, robotic-arm assisted total hip arthroplasty (Mako) through anterior approach provides improved cup placement accuracy but no difference in clinical outcomes when compared to conventional technique

BACKGROUND

With the restoration of the natural hip biomechanics, a successful total hip arthroplasty (THA) and long-term survival is pursued. Although robotic THA (rTHA) has been developed to increase accuracy of implant positioning, leg lengths and offsets, discussions about its radiological and clinical advantages over conventional THA (cTHA) continues.

OBJECTIVE

The aim of this study was to compare clinical and radiological outcomes of robotic and conventional THA.

METHODS

This retrospective study compares functional and radiological outcomes of 82 rTHA with a matched group of 82 cTHA in terms of age, sex, body mass index and preoperative functional scores. The minimum follow up was 12 months for all patients. Functional outcomes were Harris Hip Score (HHS) and the Western Ontario and McMaster University Osteoarthritis index (WOMAC) evaluated pre- and postoperatively. Radiological evaluations included position of cup placement according to Lewinnek and Callanan safe zones, Canal Fill Ratio (CFR), Leg Length Discrepancy (LLD), Lateral offset (LO) and Femoral Component Alignment (FCA). Complications were also evaluated.

RESULTS

In the rTHA group, 91.5% (75 out of 82) of the acetabular cups were positioned within the safe zone whereas it was 63.4% (52 out of 82) for the cTHA group (p< 0.001). According to Callanan, they were 84.1% and 50%, respectively (p< 0.001). Between the groups, no statistically significant difference was found in CFR, LLD, HO, FCA, AI, AA, WOMAC, HHS and major complication rates.

CONCLUSION

rTHA is superior to cTHA in terms of accuracy and reproducibility of the cup placement, however no apparent clinical benefit was found in short term follow.

A review of robotic-assisted total hip arthroplasty

Total hip arthroplasty (THA) is a successful surgical method for hip replacement but still poses challenges and risks. Robotic-assisted THA (rTHA) using new generation robotic systems has emerged to improve surgical precision and outcomes. The purpose of this paper is to review the literature on rTHA, with a focus on its advantages, such as individualized preoperative planning, intraoperative assistance, and improved accuracy in implantation, especially in complex cases. Additionally, it aims to explore the disadvantages associated with the use of rTHA, including high costs, the learning curve, and prolonged operation time compared to manual THA (mTHA), which are critical drawbacks that require careful consideration and efforts for minimization. Some financial analyses suggest that rTHA may offer cost-effectiveness and reduced postoperative costs compared to mTHA. While technological advancements are expected to reduce technical complications, there are still debates surrounding long-term outcomes. Practical limitations, such as limited availability and accessibility, also warrant attention. Although the development of rTHA shows promise, it is still in its early stages, necessitating critical evaluation and further research to ensure optimal patient benefits.

Metal-on-crosslinked polyethylene in total hip arthroplasty - an excellent combination at fifteen to twenty years of follow-up

PURPOSE

Cross-linked polyethylene (PE) has been used with great clinical success in total hip arthroplasty (THA) since its debut in the late 1990's. However, reports regarding this bearing couple near the end of its second decade of service are still scant. The aim of this study was to first determine the long term clinical and radiological results and second Investigate what factors affect wear rates using a metal-on-crosslinked PE bearing articulation.

METHODS

55 THAs using a single brand of cross-linked liner, cementless cup and 28 mm hip ball were performed in 44 patients. Age, sex, Charlson Comorbidity Index (CCI) and need for revision surgery were recorded. Linear and volumetric wear was determined using the Martell method.

RESULTS

Mean age at operation was 51.2 (29-73 ± 12.1) years. Mean duration of follow-up was 16.9 years (range 15.0-20.1 ± 1.1 years). Osteolysis was not present in the latest follow-up radiographs. Median linear and volumetric wear rate was 0.038 mm/year (95% CI 0.032-0.047) and 7.115mm3/year (95% CI 6.92-17.25) respectively. Acetabular component position was not found to be related to both linear and volumetric wear. No significant difference was found in the linear and volumetric wear rates of thinner and thicker liners (8 mm or below and > 8 mm) (p = 0.849 and p = 0.64 respectively).

CONCLUSION

Metal-on-crosslinked PE is associated with low linear and volumetric wear rates which has virtually obviated osteolysis and has translated to excellent survivorship even at long term follow up. In-vivo oxidation does not appear to be of clinical concern at this point.

Cup positioning and its effect on polyethylene wear of vitamin E- and non-vitamin E-supplemented liners in total hip arthroplasty: radiographic outcome at 5-year follow-up

BACKGROUND

Aseptic loosening remains a challenging problem after total hip arthroplasty. Accurate cup placement and supplementation of antioxidants in acetabular liners might reduce material failure rates. The aim of this study is to assess the effect of the cup position on the wear behaviour of UHMWPE-XE and UHMWPE-X liners in vivo using virtual radiographs.

METHODS

We conducted a prospective, randomized, controlled, multicenter trial. Clinical data of 372 probands were analyzed. Anteroposterior pelvic X-rays of 324 patients immediately postoperatively and after 1 and 5 years were evaluated by the RayMatch® analysis software regarding cup position and wear behaviour.

RESULTS

Mean cup anteversion was 20.3° (± 7.4) and inclination was 41.9° (± 7.0) postoperatively. 62.3% of all patients had an anteversion and inclination within the Lewinnek safe zone. Anterior and anterolateral approaches led to significantly higher cup anteversion compared to lateral approaches (27.3° ± 5.5; 20.9° ± 7.2; 17.5° ± 6.6; p < 0.001 and p = 0.001, respectively). Mean anteversion increased to 24.6° (± 8.0) after 1 year (p < 0.001). Only one revision occurred because of implant dislocation. Wear rates from UHMWPE-X and UHMWPE-XE did not differ significantly. Anteversion angles ≥ 25° correlated to increased polyethylene wear (23.7 µm/year ± 12.8 vs. 31.1 µm/year ± 22.8, p = 0.012) and this was amplified when inclination angles were ≥ 50° (23.6 µm/year ± 12.8 vs. 38.0 µm/year ± 22.7, p = 0.062).

CONCLUSION

Anterior approaches lead to the highest inaccuracy of cup placement, but cup positioning outside the Lewinnek safe zone does not necessarily cause higher dislocation rates. Moreover, mean anteversion increased by approximately four degrees within the first year after operation, which is expected to be functional due to a regularization of pelvic tilt after intervention. Mid-term wear rates of UHMWPE-X and UHMWPE-XE liners are comparable, but steep cup positions lead to significantly increased polyethylene wear. In summary, a re-evaluation of target zones for intraoperative cup positioning might be considered. In the long-term reduced oxidative embrittlement could lead to superior wear behaviour of vitamin E-blended liners.

Does obesity affect acetabular cup position, spinopelvic function and sagittal spinal alignment? A prospective investigation with standing and sitting assessment of primary hip arthroplasty patients

Background

Total hip arthroplasty (THA) instability is influenced by acetabular component positioning, spinopelvic function and sagittal spinal alignment. Obesity is considered as a risk factor of THA instability, but the causal relationship remains unknown. This study aimed to investigate the influence of BMI on (1) spinopelvic function (lumbar flexibility, pelvic mobility and hip motion), (2) sagittal spinal alignment pre- and postoperatively and (3) acetabular cup position postoperatively in primary THA patients in a prospective setting.

Methods

One hundred ninety patients receiving primary total hip arthroplasty were enrolled in a prospective cohort study and retrospectively analysed. All patients received stereoradiography (EOS) in standing and relaxed sitting position pre-and postoperatively. C7-sagittal vertical axis (C7-SVA), lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), anterior plane pelvic tilt (APPT), and pelvic femoral angle (PFA) were assessed. Key parameters of the spinopelvic function were defined as lumbar flexibility (∆ LL = LL_standing − LL_sitting), pelvic mobility (∆ PT = PT_standing − PT_sitting) and hip motion (∆ PFA = PFA_standing − PFA_sitting). Pelvic mobility was further defined based on ∆ PT as stiff, normal and hypermobile (∆ PT < 10°; 10°–30°; > 30°). The patients were stratified to BMI according to WHO definition: normal BMI ≥ 18.5–24.9 kg/m² (n = 68), overweight ≥ 25.0–29.9 kg/m² (n = 81) and obese ≥ 30–39.9 kg/m² (n = 41). Post-hoc analysis according to Hochberg's GT2 was applied to determine differences between BMI groups.

Results

Standing cup inclination was significant higher in the obese group compared to the normal BMI group (45.3° vs. 40.1°; p = 0.015) whereas standing cup anteversion was significantly decreased (22.0° vs. 25.3°; p = 0.011). There were no significant differences for spinopelvic function key parameter lumbar flexibility (∆ LL), pelvic mobility (∆ PT) and hip motion (∆ PFA) in relation to BMI stratified groups. The obese group demonstrated significant enhanced pelvic retroversion compared to the normal BMI group (APPT − 1.8° vs. 2.4°; p = 0.028). The preoperative proportion of stiff pelvic mobility was decreased in the obese group (12.2%) compared to normal (25.0%) and overweight (27.2%) groups. Spinal sagittal alignment in C7-SVA and PI-LL mismatch demonstrated significantly greater imbalance in the obese group compared to the normal BMI group (68.6 mm vs. 42.6 mm, p = 0.002 and 7.7° vs. 1.2°, p = 0.032, respectively) The proportion of patients with imbalanced C7-SVA was higher in the obese (58.5%) than in the normal BMI group (44.1%).

Conclusions

The significantly increased spinal sagittal imbalance with altered pelvic mechanics is a potential cause for the reported increased risk of THA dislocations in obese patients. Consequently, the increased spinal sagittal imbalance in combination with normal pelvic mobility need to be taken into account when performing THA in obese patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-021-02716-8.

Femoral head penetration in Vitamin-E polyethylene liner versus conventional liners in total hip arthroplasty: systematic review and meta-analysis of randomised control trials

BACKGROUND

Debate encompasses the use of Vitamin E Polyethylene or conventional Polyethylene liner in primary hip arthroplasty. Does the Inclusion of Vitamin E in PE give adequate protection from oxidation and maintains lower rates of wear?

PATIENTS AND METHODS

We performed this study following the Preferred Reporting Items for Systematic Reviews and Meta-analyses Statement (PRISMA) and the Cochrane Handbook for systematic reviews and meta-analysis. Studies were included from any region, written in any language. We had only the randomised control trials comparing the femoral head penetration between Vitamin-E diffused highly cross-linked polyethylene (VEPE) liner and conventional liners in primary total hip arthroplasty.

RESULTS

We included 10 studies in this meta-analysis. We conducted them using Review Manager V.5.0. We computed the risk ratio to measure the treatment effect, considering the heterogeneity. We used Random-effect models. VEPE had insignificant marginal advantages for FHP within three months post-operative. Additionally, VEPE showed significantly less FHP after two and five years. After one year, it showed significantly less FHP with the VEPE group versus the UHMWPE cohort and a non-significant difference between the VEPE and XLPE group.

CONCLUSIONS

In terms of FHP, this metanalysis shows less FHP for the VEPE than conventional PE. A longer follow-up period is required to evaluate whether the oxidation protection gained by Vitamin E results in lower wear rates, less osteolysis, and aseptic loosening compared to the conventional PE in the long term.

Wear Risk Prevention and Reduction in Total Hip Arthroplasty. A Personalized Study Comparing Cement and Cementless Fixation Techniques Employing Finite Element Analysis

The wear rate on Total Hip Arthroplasty (THA) entails a heavy burden for patients. This becomes more relevant with increased wear risk and its consequences such as osteolysis. In addition, osteolysis has been described in cemented and uncemented acetabular implants, and nowadays, controversy remains as to whether or not to cement the acetabular component. A personalized theoretical study was carried out to investigate which parameters have an influence on wear risk and to determine the best fixation method. Liner wear risk was assessed for two different types of fixation (cemented vs uncemented) through Finite Elements Analysis (FEA). The intraoperative variables used to determine the wear risk (cervical-diaphyseal angle, Center of Rotation positioning -COR-, head material, head size, and liner thickness) are vital parameters in surgical planning. Two types of tridimensional liner models of Ultra High Molecular Weight Polyethene (UHMWPE) were simulated through finite element analysis (FEA-over 216 cases were the core of this research). A significant relationship was found between the cervical-diaphyseal angle and wear risk (p < 0.0001), especially in valgus morphology. The acetabular fixation technique (p < 0.0001) and liner thickness (p < 0.0001) showed a significant relationship with wear risk. According to our study, using a cemented fixation with a thick liner in the right center of rotation appears to be the proper stratagy for preventing polyethylene liner wear.

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.

Short-term Clinical Outcomes of Robotic-Arm Assisted Total Hip Arthroplasty: A Pair-Matched Controlled Study

Advances have made robotic assistance a viable option in total hip arthroplasty (THA). However, the clinical outcomes of this procedure relative to manual THA are limited in the literature. This study compared robotic-arm assisted (RAA) THA and manual THA at minimum 2-year follow-up. Data were collected prospectively on all THAs performed from July 2011 to January 2015. Patients were included if they underwent RAA primary THA for idiopathic osteo-arthritis and had minimum follow-up of 2 years. The following patient-reported outcomes were compared: Harris Hip Score (HHS), Forgotten Joint Score (FJS-12), visual analog scale (VAS) pain score, and satisfaction. Postoperative radio-graphs were analyzed for cup inclination, cup version, leg-length discrepancy, and global offset. Robotic-arm assisted THA patients were matched 1:1 with manual THA patients for age, sex, body mass index, and surgical approach. Each study group included 85 patients. There were no significant differences in the demographic factors between the groups. Both HHS and FJS-12 were significantly higher in the RAA group at minimum 2-year follow-up. The VAS score was lower in the RAA group, but this difference was not statistically significant. A significantly higher proportion of patients were in the Lewinnek and Callanan safe zones for cup orientation. There was no difference between the groups in patient satisfaction. Robotic-arm assisted THA yielded improved short-term patient outcomes compared with manual THA and higher likelihood of cup placement in the safe zones. No differences were found regarding VAS scores, patient satisfaction, complication rates, or subsequent revisions between groups. [Orthopedics. 2021;44(2):e236-e242.].

Trends and patient factors associated with technology-assisted total hip arthroplasty in the United States from 2005 to 2014

Background

Technology-assisted total hip arthroplasty (TA-THA) using either computer-assisted navigation or robotic assistance has become increasingly more popular. The purpose of this study was to examine the trends and patient factors associated with TA-THA.

Methods

This is a retrospective review utilizing the National Inpatient Sample, a large national database incorporating inpatient hospitalization information. International Classification of Diseases, 9th Revision codes were used to identify patients with hip osteoarthritis who underwent primary total hip arthroplasty (THA). Patients were then separated into those who underwent TA-THA or conventional THA. Outcomes of interest included annual TA-THA utilization; patient and hospital characteristics associated with TA-THA; and trends for length of stay (LOS), cost, and discharge to home.

Results

From 2005 to 2014, a total of 2,588,304 patients with hip osteoarthritis who underwent THA were identified in the National Inpatient Sample database. Of those, 39,700 (1.5%) underwent TA-THA. The number of TA-THA procedures increased from 178 (0.1% of all THA) in 2005 to 10,045 (3.0% of all THA) in 2014, which represented a 30-fold increase in incidence (P-trend <.0001). TA-THA was associated with Hispanic race, higher patient income, and the Western region of the United States. During the study period, there was a trend toward decreased LOS and increased discharge to home for both TA-THA and conventional THA. TA-THA was associated with higher inpatient cost.

Conclusion

TA-THA is being increasingly used in the United States and is associated with specific patient factors. However, the value of TA-THA compared to conventional THA remains unclear and should be assessed with future research.

Level of Evidence

III (retrospective cohort study).

Current topics in robotic-assisted total hip arthroplasty: a review

Total hip arthroplasty (THA) is among the most successful procedures of modern medicine, yet failures and complications continue to occur, leaving room for improvement. Robotics is a cutting-edge technology that tries to improve joint arthroplasty surgery. There is some evidence that shows that robotic-assisted THA improves implant positioning, but less is known about its effect on clinical outcomes or the rate of complications. This article reviews the literature on robotic-assisted THA to elucidate the history, advantages, disadvantages, and current clinical understanding of this procedure.

Isolated acetabular revision with femoral stem retention using computed tomography-based navigation

BACKGROUND

In isolated acetabular revision surgery, surgeons must place the cup at an appropriate angle with various retained stem anteversion angles to prevent postoperative dislocation. For accurate acetabular cup position, various navigation systems have been used. Nevertheless, no publications have reported combined cup and stem anteversion and dislocation rates after isolated acetabular revision, especially comparing the use of navigation with manual implantation. Therefore we performed a retrospective comparative study to answer the following questions: (1) What is the combined anteversion after isolated acetabular revision with computed tomography-based navigation? (2) Does navigation improve the accuracy of cup angle and combined anteversion, (3) reduce dislocation rate, and (4) reduce operative time?

HYPOTHESIS

A navigation system makes combined anteversion near the target angle in isolated acetabular revision.

PATIENTS AND METHODS

We conducted a retrospective study of 32 hips in 24 patients who underwent isolated acetabular revision total hip arthroplasty using computed tomography-based navigation system. The control group comprised 8 hips in 8 patients who underwent the same procedure without navigation.

RESULTS

In the navigation group, average Widmer's combined anteversion was 39.0°±8.7° (range, 25.3°-56.6°). Cup positions were 40.3°±2.9° (range, 29.0°-49.0°) for radiographic abduction angle, 24.3°±8.0° (range, 4.6°-42.6°) for radiographic anteversion. In the control group, Widmer's combined anteversion was 47.2°±15.1° (range, 27.0°-74.3°, p=0.048). The average cup positions for radiographic abduction angle and anteversion were 36.7°±8.9° (range, 24.5°-54.9°) and 29.1°±7.3° (range, 17.2°-38.8°), respectively (p>0.05). Widmer's combined anteversion deviated from the target angle by a smaller amount in the navigation group than in the control group: errors in measurement of Widmer's combined anteversion were 7.2°±5.1° (range, 0.74°-19.6°) in the navigation group and 13.9°±11.1° (range, 3.6°-37.3°) in the control group (p=0.135). Postoperative dislocation occurred in none of the 32 hips (0%) in the navigation group and in one of the 8 hips (12.5%) in the control group (p=0.2).

DISCUSSION

Using the navigation system, combined anteversion is made near the target angle in isolated acetabular revision surgery and more accurately than manual implantation. These results should be considered as preliminary since this is a limited cohort, but it brings new knowledge in navigation considering the very limited number of series using of navigation in isolated cup revision of total hip arthroplasty. In addition this is the first study to investigate combined cup and stem anteversion in isolated acetabular revision. The use of CT-scan is helpful to diagnose error in stem anteversion and to adapt the orientation of the new cup.

LEVEL OF EVIDENCE

III, Retrospective case control study.

Which one is more affected by navigation-assisted cup positioning in total hip arthroplasty: Anteversion or inclination? A retrospective matched-pair cohort study in Asian physique

INTRODUCTION

The purpose of this study was to compare acetabular cup positioning using an imageless navigation-assisted total hip arthroplasty (THA) to a case-matched control group using the conventional technique in Asian physique.

METHODS

Case matching controlled study using retrospectively collected data for THAs was done. Matching criteria were gender, age ± 5 years, and body mass index ± 5 kg/m². Thirty patients who had navigation THAs were manually matched to a conventional group of 30 patients. After measuring anteversion and inclination on 3-D CT, final cup anteversion was calculated using the mathematical formula (anteversion = arctan [tan (anatomic anteversion) × sin (inclination)]).

RESULTS

No significant difference was observed between mean inclination ( p = 0.420), anteversion ( p = 0.697), and the mean deviation from 15° for anteversion ( p = 0.649). However, there was a statistical significant difference for mean deviation from 40° for inclination ( p = 0.027). There was a significant difference in the percentage of correctly placed acetabular cup in safe zones with inclination ( p = 0.039).

CONCLUSIONS

Although soft tissue overlying the pubic tubercle interfered with registration of the bony landmark and thereby induced inaccuracy of anteversion angles in the navigation group, the use of imageless navigation-assisted technique increases the placement within the safe zone for inclination and enhances the accuracy and the precision of inclination of the acetabular cup relative to the conventional THA rather than anteversion. This finding may be due to the effect of the patient's physique on the anterior pelvic plane (APP)-based reference system of imageless navigation.

Ten- to Sixteen-Year Follow-Up of Highly Cross-Linked Polyethylene in Total Hip Arthroplasty: What Factors Affect Wear?

BACKGROUND

Increase in acetabular cup abduction in total hip arthroplasty (THA) using conventional polyethylene is associated with greater linear wear. Whether this relationship holds true for highly crosslinked liners, particularly with long-term follow-up, is still controversial. The effect of liner thickness on wear of highly cross-linked liners also remains to be clarified.This study sought to determine (1) the long-term clinical and radiological performance of highly cross-linked polyethylene in THA and (2) the effect of acetabular component positioning, polyethylene thickness, and patient demographics on wear.

METHODS

Ninety-three THAs using a 28-mm hip ball, single brand of highly cross-linked polyethylene liner, and cementless cup were performed in 87 patients. Clinical outcomes were evaluated using the Harris Hip Score and need for revision surgery. Linear and volumetric wear, presence of osteolysis, and cup abduction angle were assessed.

RESULTS

The mean age at operation was 51.4 years. The mean duration of follow-up was 12.7 years (10-16 years). Patients aged >50 years had higher rates of linear wear than those aged <50 years (P = .015). Positive correlation was found between cup abduction angle (P = .014) and cup version (P = .035) with a linear wear rate. Thinner liners (≤7 mm) had similar rates of linear and volumetric wear as thicker liners (≥8 mm) (P = .447).

CONCLUSION

This is the only study to demonstrate a positive significant relationship between cup abduction angle and version with linear wear rate in THA with at least 10 years of follow-up. Liner thickness was not found to affect wear rates.

Accuracy and Precision of Acetabular Component Placement With Imageless Navigation in Obese Patients

BACKGROUND

Obesity is a risk factor for acetabular component malposition when total hip arthroplasty is performed with manual techniques. The utility of imageless navigation in obese patients remains unknown. This study compared the accuracy and precision of imageless navigation for component orientation between obese and nonobese patients.

METHODS

A total of 459 total hip arthroplasties performed for osteoarthritis using imageless navigation were reviewed from a single surgeon's institutional review board-approved database. Einzel-Bild-Roentgen Analyse determined component orientation on 6-week postoperative anteroposterior radiographs. Mean orientation error (accuracy) and precision were compared between obese (body mass index ≥ 30 kg/m²) and nonobese patients. Regression analysis evaluated the influence of obesity on component position.

RESULTS

The difference in mean inclination and anteversion between obese and nonobese groups was 1.1° (43.0° ± 3.5°; range, 35.8°-57.8° vs 41.9° ± 4.4°; range, 33.0°-57.1° and 24.9° ± 6.3°; range, 14.2°-44.3° vs 23.8° ± 6.6°; range, 7.0°-38.6°, respectively). Inclination precision was better for nonobese patients. No difference in inclination accuracy or anteversion accuracy or precision was detected between groups. And 83% of components were placed within the target range. There was no relationship between obesity (dichotomized) and component placement outside the target ranges for inclination, anteversion, or both. As a continuous variable, increased body mass index correlated with higher odds of inclination outside the target zone (odds ratio, 1.06; P = .001).

CONCLUSION

Using imageless navigation, inclination orientation was less precise for obese patients, but the observed difference is likely not clinically relevant. Accurate superficial registration of landmarks in obese patients is achievable, and the use of imageless navigation similarly improves acetabular component positioning in obese and nonobese patients.

LEVEL OF EVIDENCE

Therapeutic Level IV.

Patient positioning and cup orientation during total hip arthroplasty: assessment of current UK practice

INTRODUCTION:

Acetabular cup orientation during total hip arthroplasty (THA) remains a challenge. This is influenced by patient positioning during surgery and the method used to orientate the acetabular cup. The aim of this study was to assess current UK practice for patient positioning and cup orientation, particularly with respect to patient supports and techniques used to achieve target version and inclination.

METHODS:

A literature review and pilot study were initially conducted to develop the questionnaire, which was completed by British Hip Society members ( n = 183). As the majority of THA surgical procedures within the UK are performed with the patient in lateral decubitus, orthopaedic surgeons who operated with the patient in the supine position were excluded ( n = 18); a further 6% were incomplete and also excluded ( n = 11).

RESULTS:

Of those who operated in lateral decubitus, 76.6% ( n = 118/154) used the posterior approach. Only 31% ( n = 47/154) considered their supports to be completely rigid. More than 35% ( n = 55/154) were unhappy with the supports that they presently use. The most common methods for controlling operative inclination and version were a mechanical alignment guide (MAG; n = 78/154; 50.6%) and the transverse acetabular ligament (TAL; n = 82/154; 53.2%); 31.2% (48/154) used a freehand technique to control operative inclination.

CONCLUSION:

Limited studies have been conducted whereby patient supports have been analysed and key design principles outlined. With 35.7% of the orthopaedic surgeons surveyed having issues with their current supports, a greater awareness of essential characteristics for patient supports is required.

Radiostereometric Analysis Permits In Vivo Measurement of Very Small Levels of Wear in TKA

BACKGROUND

Revision of TKA as a result of polyethylene wear is decreasing, but long-term wear performance of polyethylene is still a topic of interest to surgeons and device manufacturers seeking to improve longevity. Measuring wear of modern, wear-resistant implants has been described using radiostereometric analysis (RSA). Performing in vivo measurements would establish whether implant retrieval studies are representative of wear in well-performing knees.

QUESTIONS/PURPOSES

For a single knee implant system, we sought to determine (1) the linear wear rate using RSA; (2) the association between demographic factors and wear rate; and (3) the association between limb alignment and wear rate.

METHODS

A total of 49 patients with a minimum followup of 10 years (median, 12 years; range, 10-20 years) were retrospectively selected. During the examined period, 4082 TKAs were performed of which 2085 were the implant examined in this study. There were 71 of these patients who met the criteria including an available full-leg radiograph postoperatively, and 34 of these patients returned for examination along with 15 additional from a separate RSA study that also met the criteria. All patients received a posterior-stabilized, cobalt-chromium-on-conventional polyethylene total knee implant from a single implant system, which was the most commonly used at our institution at the time. Patients underwent standing RSA examinations from 0° to 120° of flexion at a single time point without the use of marker beads. Linear wear rates (including creep) were measured based on intersections between the femoral component and tibial insert models. Associations between wear and patient age at surgery, sex, height, weight, body mass index, tibial insert size, and limb alignment were examined.

RESULTS

Using the maximum linear wear rate from any flexion angle, the lateral rate was 0.047 mm/year (interquartile range [IQR], 0.034-0.066 mm/year) and the medial rate was 0.052 mm/year (IQR, 0.040-0.069 mm/year). Using the median of the linear wear rates across all flexion angles, the lateral rate was 0.027 mm/year (IQR, 0.017-0.046 mm/year) and the medial rate was 0.038 mm/year (IQR, 0.022-0.054 mm/year). This rate for males was 0.049 mm/year medially (IQR, 0.042-0.077 mm/year) and 0.032 mm/year laterally (IQR, 0.026-0.059 mm/year), and for females was 0.027 mm/year medially (0.016-0.039 mm/year) and 0.020 mm/year laterally (IQR, 0.013-0.032 mm/year). The wear rate for males was greater medially (difference = 0.022 mm/year, p < 0.001) and laterally (difference = 0.012 mm/year, p = 0.008). There were associations between greater wear and increasing height (ρ = 0.48, p < 0.001 medially and ρ = 0.30, p = 0.04 laterally), decreasing body mass index (ρ = -0.31, p = 0.03 medially), and greater implant size (ρ = 0.34, p = 0.02 medially). Increasingly varus leg alignment was associated with greater medial wear (ρ = 0.33, p = 0.02).

CONCLUSIONS

Greater wear rates were associated with demographic factors and leg alignment. Further RSA wear studies of other modern implant systems would provide complementary information to retrieval studies and valuable data on wear resistance.

CLINICAL RELEVANCE

Good wear resistance was demonstrated by well-performing implants in patients at long-term followup with wear magnitudes in agreement with reported values from retrieval studies.

Clinical and radiological evaluation of post total hip arthroplasty patients with acetabulum defect

BACKGROUND

Total Hip Arthroplasty (THA) is one of many therapies given to hip joint injury patients. The main indication for THA in elderly patients is degenerative diseases of the joints. One of the difficulties encountered in this THA procedure is to overcome the acetabulum deficiency, with Paprosky Classification. This study aims to evaluate patients with acetabulum defect that have undergone THA at Dr. Soetomo Hospital in 2014-2016.

METHODS

This was an observational retrospective study with descriptive analysis. The sample amount was 20 patients, from 80 patients who had THA procedure. Patients were evaluated based on the wear from acetabulum, migration from a cup, the presence of bone loss, heterotopic ossification, and also clinical condition based on Harris Hip Score. The presented results were analyzed by using Kruskal-Wallis on SPSS 19.0 for Windows Program.

RESULTS

Hypothesis testing was performed on THA patients based on acetabulum defect type I, II, and III in one, two, and three years after surgery respectively. Massin Score resulted no differences with p = 0.156, p = 0.574, and p = 0223. Bone Loss Classification resulted no differences with p = 0.296, p = 0.287, and p = 0223. No difference on Wear Rate with p = 0.072, p = 0.110, and p = 0.325. There was no difference of Harris Hip Score with p = 0.320, p = 0.082, and p = 0.472.

CONCLUSION

There were no significant differences in radiological evaluation of the Migration Rate, Heterotopic Ossification or Bone Loss, Wear Rate, and on clinical evaluation of Harris Hip Score in all three groups of evaluated acetabulum defects.

Risk factors for increased sagittal pelvic motion causing unfavourable orientation of the acetabular component in patients undergoing total hip arthroplasty

Aims

It is important to consider sagittal pelvic rotation when introducing the acetabular component at total hip arthroplasty (THA). The purpose of this study was to identify patients who are at risk of unfavourable pelvic mobility, which could result in poor outcomes after THA.

Patients and Methods

A consecutive series of 4042 patients undergoing THA had lateral functional radiographs and a low-dose CT scan to measure supine pelvic tilt, pelvic incidence, standing pelvic tilt, flexed-seated pelvic tilt, standing lumbar lordotic angle, flexed-seated lumbar lordotic angle, and lumbar flexion. Changes in pelvic tilt from supine-to-standing positions and supine-to-flexed-seated positions were determined. A change in pelvic tilt of 13° between positions was deemed unfavourable as it alters functional anteversion by 10° and effectively places the acetabular component outside the safe zone of orientation.

Results

For both men and women, the degree of lumbar flexion was a significant predictor of risk in hip flexion (p < 0.0001) with increased odds of unfavourable pelvic mobility in those with lumbar flexion of < 20° (men, odds ratio (OR) 6.74, 95% confidence interval (CI) 3.83 to 11.89; women, OR 2.97, 95% CI 1.87 to 4.71). In women, age and standing pelvic tilt were significant predictors of risk in hip extension (p = 0.0082 and p < 0.0001, respectively). The risk of unfavourable pelvic mobility was higher in those aged > 75 years (OR 2.28, 95% CI 1.56 to 3.32) and those with standing pelvic tilt of < -10° for extension risk (OR 7.10, 95% CI 4.10 to 10.29). In men, only standing pelvic tilt was significant (p < 0.0001) for hip extension with an increased risk of unfavourable pelvic mobility (OR 8.68, 95% CI 5.19 to 14.51).

Conclusion

Patients found to have unfavourable pelvic mobility had limited lumbar flexion and more posterior standing pelvic tilt in both men and women, as well as increasing age in women. We recommend that patients undergo preoperative functional radiographic screening to determine specific parameters that can affect the functional orientation of the acetabular component. Cite this article: Bone Joint J 2018;100-B:845–52.

Delay of total hip arthroplasty to advanced stage worsens post-operative hip motion in patients with femoral head osteonecrosis

PURPOSE

Osteonecrosis of the femoral head (ONFH) is commonly detected in young patients and most surgeons tend to delay total hip arthroplasty (THA) until the end stage of the disease. We hypothesised that post-operative range of motion (ROM) of the hip as well as baseline ROM at the time of surgery decreases with the disease progression. The purpose of this study was to determine whether patients, who were operated at an advanced stage, have pre- and post-operative hip ROM similar to ROM of patients, who were operated at earlier stages.

METHODS

Eight hundred and fifty patients (850 hips) treated with THA for ONFH were classified according to pre-operative stages of Association Research Circulation Osseous (ARCO). Fifty-six patients were operated at stage 2, 458 at stage 3, and 336 at stage 4. Pre-operative and one year post-operative ROM was compared among the stages.

RESULTS

Pre-operative sum of hip ROM decreased with the progression of ARCO stage (P < 0.001) and correlated with the post-operative sum of hip ROM (correlation coefficient 0.661). Although hip ROM improved after THA in all stages, post-operative ROM in patients with lower pre-operative ROM did not improve to the same level as in those with a higher pre-operative ROM (P < 0.001).

CONCLUSIONS

The progression of ONFH negatively affected post-operative hip ROM as well as baseline hip ROM at the time of THA. Surgeons should consider a delay of THA negatively affects the hip ROM after the arthroplasty, when they determine the treatment modality for ONFH patients.

Hip malformation is a very common finding in young patients scheduled for total hip arthroplasty

INTRODUCTION

In Denmark, 20% of all registered total hip arthroplasties (THA) from 1995 to 2014 has been patients younger than 60 years with primary idiopathic osteoarthritis (OA). It is speculated that hip malformations may be a major contributor to early OA development. It has been shown that hip malformation may compromise implant position and, therefore, identifying and knowing the incidence of malformations is important. Our aim was to assess the prevalence and type of hip malformations in a cohort of younger patients undergoing THA.

MATERIALS AND METHODS

In this prospective two center cohort study, 95 consecutive patients (106 hips) met the inclusion criteria. One observer performed radiographic measurements for malformations and radiographic OA. Inter- and intraobserver variability was assessed.

RESULTS

From 95 patients (male n = 52 and female n = 43) age ranged from 35 to 59 years and prevalences of hip malformations were; CAM-deformity 50.9 and 25.5%, coxa profunda 33 and 27.4%, acetabular retroversion 33 and 29.2%, and acetabular dysplasia 10.4 and 3.8%. All patients showed minimum of one malformation. Prevalences of Tönnis grade 0-1 were 22.6% and 2-3 were 77.4%.

CONCLUSION

All patients showed malformations, especially high prevalences were found for CAM-deformity, coxa profunda and acetabular retroversion. Identifying these malformations is fairly simple and recognizing the high prevalence may help surgeons avoid pitfalls during implant positioning in THA surgery. Further, focus on hip malformations may facilitate correct referral to joint-preserving surgery before OA develops.

A simple method of measuring the wear of explanted acetabular component inserts

Objectives

The determination of the volumetric polyethylene wear on explanted material requires complicated equipment, which is not available in many research institutions. Our aim in this study was to present and validate a method that only requires a set of polyetheretherketone balls and a laboratory balance to determine wear.

Methods

The insert to be measured was placed on a balance, and a ball of the appropriate diameter was inserted. The cavity remaining between the ball and insert caused by wear was filled with contrast medium and the weight of the contrast medium was recorded. The volume was calculated from the known density of the liquid. The precision, inter- and intraobserver reliability, were determined by four investigators on four days using nine inserts with specified wear (0.094 ml to 1.626 ml), and the intra-class correlation coefficient was calculated. The feasibility of using this method in routine clinical practice and the time required for measurement were tested on 84 explanted inserts by one investigator.

Results

In order to get the mean for all investigators and determinations, the deviation between the measured and specified wear was -0.08 ml (sd 0.12; -0.21 to 0.11). The interobserver reliability was 0.989 ml (95% confidence interval (CI) 0.964 to 0.997) and the intraobserver reliability was 0.941 for observer 1 (95% CI 0.846 to 0.985), 0.983 for observer 2 (95% CI 0.956 to 0.995), 0.939 for observer 3 (95% CI 0.855 to 0.984), and 0.934 for observer 4 (95% CI 0.790 to 0.984). The mean time required to examine the samples was two minutes (sd 2; 1 to 5).

Conclusion

The method presented here was shown to be sufficiently precise for many settings and is a cost-effective and quick method of determining the volumetric wear of explanted acetabular components. However, the measurement of wear for scientific purposes will probably continue to involve more accurate and dedicated laboratory equipment.

Cite this article: L. Krakow, A. Klockow, E. Roehner, S. Brodt, H. Eijer, J. Bossert, G. Matziolis. A simple method of measuring the wear of explanted acetabular component inserts. Bone Joint Res 2017;6:530–534. DOI: 10.1302/2046-3758.69.BJR-2016-0249.R1

Technology in Arthroplasty: Are We Improving Value?

PURPOSE OF REVIEW

Total joint arthroplasty is regarded as a highly successful procedure. Patient outcomes and implant longevity, however, are related to proper alignment and position of the prostehses. In an attempt to reduce outliers and improve accuracy and precision of component position, navigation and robotics have been introduced. These technologies, however, come at a price. The goals of this review are to evaluate these technologies in total joint arthroplasty and determine if they add value.

RECENT FINDINGS

Recent studies have demonstrated that navigation and robotics in total joint arthroplasty can decrease outliers while improving accuracy in component positioning. While some studies have demonstrated improved patient reported outcomes, not all studies have shown this to be true. Most studies cite increased cost of equipment and longer operating room times as the major downsides of the technologies at present. Long-term studies are just becoming available and are promising, as some studies have shown decreased revision rates when navigation is used. Finally, there are relatively few studies evaluating the direct cost and value of these technologies. Navigation and robotics have been shown to improve component position in total joint arthroplasty, which can improve patient outcomes and implant longevity. These technologies offer a promising future for total joint arthroplasty.

Patient Obesity Influences Pelvic Lift During Cup Insertion in Total Hip Arthroplasty Through a Lateral Transgluteal Approach in Supine Position

BACKGROUND

Movement of the pelvis during implantation of total hip arthroplasty (THA) has a major influence on the positioning of the acetabular cup. Strong traction caused by retractors leads to iatrogenic pelvic lift and can thus be partly responsible for cup malpositioning. The objective of this study was to investigate such factors that influence pelvic lift.

METHODS

The dynamic movement of the pelvis was measured during implantation of THA in 67 patients. This was done by measuring the acceleration using the SensorLog app on a smartphone.

RESULTS

At its maximum, the pelvis was lifted by an average of 6.7°. When impacting the press-fit cup, the surgical side was raised by 4.4° compared with the time of skin incision. This lift at the time of cup implantation correlates significantly with the body mass index and the patient's abdominal and pelvic circumference.

CONCLUSION

Every surgeon performing THA must be aware of the pelvic lift during an operation. Especially in patients with a high body mass index, a large abdominal circumference, or a large pelvic circumference, there is an increased risk of malpositioning of the acetabular cup. When impacting the cup, we recommend releasing the traction of the retractor, so that the pelvis can tilt back into its natural position, and thus, the anticipated cup positioning can be implemented as exactly as possible.

The mechanical effects of cup inclination and anteversion angle on the bearing surface

BACKGROUND

Regarding the cup setting in total hip arthroplasty, range of motion and prevention of dislocation are important. From past reports, the wear of the bearing surface may affect long-term results. This study evaluated the stress applied to the bearing surface by the combined use of the three-dimensional rigid spring model and the finite-element analysis.

METHODS

For contact pressure distribution of the bearing surface, interference analysis was performed using a three-dimensional rigid body spring model. Furthermore, stress was applied to the inner surface of the cup installed in the bone so that the same stress distribution obtained from the interference analysis was achieved. The finite-element analysis was then performed at each condition, which changed the inclination and anteversion angles of the cup to examine the relationship of maximum equivalent stress.

RESULTS AND DISCUSSION

The maximum equivalent stresses on the bearing surface under the condition with fixation of an anteversion angle of 0° were 0.78, 0.85, and 1.15 MPa at inclination angles of 25°, 40°, and 55°, respectively. The stress value at 55° was approximately 1.5 times greater than that at 25°. The maximum equivalent stresses on the bearing surface under the condition with fixation of an inclination angle of 40° were 0.85, 0.9, and 1.02 MPa at anteversion angles of 0°, 15°, and 30°, respectively. The stress value at 30° was approximately 1.2 times greater than that at 0°. This study suggests that large inclination and anteversion angles may enhance the stress on the bearing surface and affect long-term results.

Effect of Acetabular Position on Polyethylene Liner Wear Measured Using Simultaneous Biplanar Acquisition

BACKGROUND

Studies that have previously examined the relationship between acetabular component inclination angle and polyethylene wear have shown increased wear of conventional polyethylene with high inclination angles. To date, there are no long-term in vivo studies examining the correlation between cup position and polyethylene wear with highly crosslinked polyethylene.

METHODS

An institutional arthroplasty database was used to identify patients who had metal-on-highly crosslinked polyethylene primary total hip arthroplasty using the same component design with a minimum follow-up of 10 years. A modified radiostereometric analysis examination setup was utilized, recreating standard anteroposterior and cross-table lateral examinations in a single stereo radiostereometric analysis acquisition. The same radiographs were used to measure inclination angle and anteversion.

RESULTS

A total of 43 hips were included for analysis in this study. Average follow-up was 12.3 ± 1.2 years. The average linear wear rate was calculated to be 0.066 ± 0.066 mm/y. Inclination angle was not correlated with polyethylene wear rate (P = .82). Anteversion was also not correlated with polyethylene wear rate (P = .11).

CONCLUSION

At long-term follow-up of >10 years, highly crosslinked polyethylene has a very low wear rate. This excellent tribology is independent of acetabular position. The low wear rate highlights the excellent results of metal on highly crosslinked polyethylene, and supports its use in total hip arthroplasty.

Patient-Specific Orthopaedic Implants

Patient-specific orthopaedic implants are emerging as a clinically promising treatment option for a growing number of conditions to better match an individual's anatomy. Patient-specific implant (PSI) technology aims to reduce overall procedural costs, minimize surgical time, and maximize patient outcomes by achieving better biomechanical implant fit. With this commercially-available technology, computed tomography or magnetic resonance images can be used in conjunction with specialized computer programs to create preoperative patient-specific surgical plans and to develop custom cutting guides from 3-D reconstructed images of patient anatomy. Surgeons can then place these temporary guides or "jigs" during the procedure, allowing them to better recreate the exact resections of the computer-generated surgical plan. Over the past decade, patient-specific implants have seen increased use in orthopaedics and they have been widely indicated in total knee arthroplasty, total hip arthroplasty, and corrective osteotomies. Patient-specific implants have also been explored for use in total shoulder arthroplasty and spinal surgery. Despite their increasing popularity, significant support for PSI use in orthopaedics has been lacking in the literature and it is currently uncertain whether the theoretical biomechanical advantages of patient-specific orthopaedic implants carry true advantages in surgical outcomes when compared to standard procedures. The purpose of this review was to assess the current status of patient-specific orthopaedic implants, to explore their future direction, and to summarize any comparative published studies that measure definitive surgical characteristics of patient-specific orthopaedic implant use such as patient outcomes, biomechanical implant alignment, surgical cost, patient blood loss, or patient recovery.

Are CT Scans a Satisfactory Substitute for the Follow-Up of RSA Migration Studies of Uncemented Cups? A Comparison of RSA Double Examinations and CT Datasets of 46 Total Hip Arthroplasties

As part of the 14-year follow-up of a prospectively randomized radiostereometry (RSA) study on uncemented cup fixation, two pairs of stereo radiographs and a CT scan of 46 hips were compared. Tantalum beads, inserted during the primary operation, were detected in the CT volume and the stereo radiographs and used to produce datasets of 3D coordinates. The limit of agreement between the combined CT and RSA datasets was calculated in the same way as the precision of the double RSA examination. The precision of RSA corresponding to the 99% confidence interval was 1.36°, 1.36°, and 0.60° for X-, Y-, and Z-rotation and 0.40, 0.17, and 0.37 mm for X-, Y-, and Z-translation. The limit of agreement between CT and RSA was 1.51°, 2.17°, and 1.05° for rotation and 0.59, 0.56, and 0.74 mm for translation. The differences between CT and RSA are close to the described normal 99% confidence interval for precision in RSA: 0.3° to 2° for rotation and 0.15 to 0.6 mm for translation. We conclude that measurements using CT and RSA are comparable and that CT can be used for migration studies for longitudinal evaluations of patients with RSA markers.

Cheating the Acetabular Component Horizontally in Total Hip Arthroplasty

To avoid inadvertent vertical positioning of the acetabular component during total hip arthroplasty (THA), the authors routinely "cheat" component abduction an additional 10° horizontal (goal=30°). This likely increases the incidence of components placed into abduction of less than 30°, the clinical consequences of which are not well studied. The purpose of this study was to determine the clinical and radiographic outcomes in patients undergoing THA with acetabular components positioned in less than 30° of abduction as compared with those with components positioned between 30° and 50°. A retrospective review was performed of consecutive patients undergoing primary THA with horizontally cheated acetabular component position performed by a single surgeon. Patients were grouped into cohorts with either component abduction less than 30° or between 30° and 50°. Demographic data, operative data, and complications were recorded. Harris Hip Scores (HHS) and radiographic analysis were obtained from preoperative and most recent clinic visits. Between September 2004 and September 2010, 320 consecutive THA procedures were performed. A total of 149 hips had component abduction less than 30° (mean, 25.8°; range, 15.7°-29.4°). No components had greater than 50° of abduction. At an average 37-month follow-up, no significant difference in HHS was found between the 2 cohorts (P=.137). The horizontal cohort had no dislocations, component loosening, or osteolysis. By cheating the acetabular component more horizontal, an excessively vertical position was avoided. Component abduction less than 30° yielded equivalent clinical outcomes to component abduction between 30° and 50°. [Orthopedics. 2016; 39(6):e1092-e1096.].

Quality of outcome data in total hip arthroplasty: comparison of registry data and worldwide non-registry studies from 5 decades

PURPOSE

This systematic review assessed evidence on outcome (revision rate for all reasons) following hip arthroplasty from its beginning 5 decades ago.

METHODS

We evaluated all studies from all current hip implants since their market introduction in 1962 regarding "revision rate per 100 observed component years". Data were compared with arthroplasty registries.

RESULTS

A total of 54 different hip implants were included: for 81% (44 of 54) data is either absent or poor; for 30% (16 of 54) not a single publication could be found. For 52% (28 of 54) less than 100 revisions for all reasons are published in non-registry studies. The remaining 10 implants (19%) comprise 92638 primary implants with 4473 revisions. Control group were the same implants with 111658 primary cases and 3029 revisions from arthroplasty registries. A systematic developer bias as in knee arthroplasty could not be found but several independent authors were found to significantly bias the literature. The overall revision rates per 100 observed component years from non-registry studies (and joint registries) are 0.4 (0.5) for stems, 0.7 (0.7) for cups and 1.4 (2.1) for resurfacing systems.

CONCLUSIONS

For 81% of all hip implants assessed limited evidence exists from non-registry studies regarding outcome (revision rate) even 5 decades after market introduction. For the remaining 19% of implants no systematic developer bias could be found but several individual authors significantly biased results of single implants. We therefore ask for a more active publication of new implants.

Morbidly Obese Patients Undergoing Reduced Cup Anteversion Through a Direct Lateral Approach

BACKGROUND

The presence of obesity negatively affects the results after total hip arthroplasty. The influence of morbid obesity on cup positioning is investigated.

METHODS

A retrospective analysis of radiographs from 790 patients in 2013 and 2014 was performed. The correlation of cup inclination and anteversion with body mass index (BMI) was analyzed. Three groups were formed: 139 patients with normal weight (BMI of <25 kg/m(2)), 566 patients with moderate obesity (BMI between 25 and 34 kg/m(2)), and 85 patients with morbid obesity (BMI of ≥35 kg/m(2)).

RESULTS

Cup anteversion significantly correlated with BMI (R = -0.127, p < 0.001) and patient age (R = 0.115, p = 0.001). This corresponded with a reduction of anteversion by 3.4° (p < 0.001) in the morbidly obese group compared with the normal-weight group. Cup inclination was not influenced by BMI or patient age.

CONCLUSIONS

The precision of cup positioning declines with increasing obesity. In addition, significantly reduced anteversion is found in younger patients. We assume that this is due to iatrogenically changed pelvic tilt resulting from increased pressure exerted on the dorsal and ventral acetabular rim retractors.

LEVEL OF EVIDENCE

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

Acetabular Dysplasia and Surgical Approaches Other Than Direct Anterior Increases Risk for Malpositioning of the Acetabular Component in Total Hip Arthroplasty

BACKGROUND

Persistent acetabular dysplasia (AD) after periacetabular osteotomy has been hypothesized to increase the risk for malpositioning of the acetabular component. In this study, we investigate whether AD is an independent risk factor for cup malpositioning during primary total hip arthroplasty (THA).

METHODS

Patient demographics, surgical approach, presence of AD assessed using the lateral center-edge angle, and acetabular cup positioning determined using Martell Hip Analysis Suite were investigated in 836 primary THA patients enrolled in a prospective multicenter study.

RESULTS

We found that presence of AD, defined as the lateral center-edge angle of <25°, is an independent risk factor for malpositioning of the acetabular component during primary THA. Surgical approach other than direct anterior was also independently associated with malpositioned cups.

CONCLUSIONS

Surgeons should therefore take special care during placement of the acetabular component in patients with AD.

The Impact of Lumbar Spine Disease and Deformity on Total Hip Arthroplasty Outcomes

Concurrent spine and hip disease is common. Spinal deformities can restrict lumbar range of motion and lumbar lordosis, leading to pelvic obliquity and increased pelvic tilt. A comprehensive preoperative workup and component templating ensure appropriate compensation for altered pelvic parameters for implantation of components according to functional positioning. Pelvic obliquity from scoliosis must be measured to calculate appropriate leg length. Cup positioning should be templated on standing radiograph to limit impingement from cup malposition. In spinal deformity, the optimal position of the cup that accommodates pelvic parameters and limits impingement may lie outside the classic parameters of the safe zone.

Surgical Modification of the Murine Calvaria Osteolysis Model

The murine calvaria model has been adopted for evaluation of osteolysis and inflammation induced by polyethylene (PE) or metal wear debris. However, this model suffers from several complications. The purpose of our study is to introduce a surgical modification with lower complication rates, thus providing more accurate results. Forty C57/BL6 mice were divided into two groups, both receiving polyethylene particles. Surgical modifications were performed in group 1, and group 2 underwent traditional surgeries. The incidence of fluid leakage was recorded on the operative day. Curst formation, wound dehiscence, and bone exposure were recorded on day 7. Histological osteolysis was demonstrated by HE staining of tissue slices. Micro-CT was used for quantifying evaluation of osteolysis in two groups. Intraoperative fluid leakage was significantly reduced in group 1. Postoperative crust formation, wound dehiscence, and bone exposure were also significantly decreased in group 1. HE staining results revealed obvious osteolysis in group 1 and more obvious osteolysis in group 2. Bone volume fraction (BVF) was (0.32 ± 0.03) in group 1 compared to group 2 (0.24 ± 0.05). Bone mineral density (BMD) was (1.11 ± 0.03) in group 1 compared to group 2 (1.01 ± 0.02). Surgical modifications provide a reliable way for establishment of the murine calvaria osteolysis model.

The difference between the radiographic and the operative angle of inclination of the acetabular component in total hip arthroplasty: use of a digital protractor and the circumference of the hip to improve orientation

A high radiographic inclination angle (RI) contributes to accelerated wear and has been associated with dislocation after total hip arthroplasty (THA). With freehand positioning of the acetabular component there is a lack of accuracy, with a trend towards a high radiographic inclination angle. The aim of this study was to investigate whether the use of a digital protractor to measure the operative inclination angle (OI) could improve the positioning of the acetabular component in relation to a 'safe zone'. We measured the radiographic inclination angles of 200 consecutive uncemented primary THAs. In the first 100 the component was introduced freehand and in the second 100 a digital protractor was used to measure the operative inclination angle. The mean difference between the operative and the radiographic inclination angles (∆RI-OI) in the second cohort was 12.3° (3.8° to 19.8°). There was a strong correlation between the circumference of the hip and ∆RI-OI. The number of RI outliers was significantly reduced in the protractor group (p = 0.002). Adjusting the OI, using a digital protractor and taking into account the circumference of the patient's hip, improves the RI significantly (p < 0.001) and does not require additional operating time.

Pelvic tilt in patients undergoing total hip arthroplasty: when does it matter?

Pelvic tilt (PT) affects the functional anteversion and inclination of acetabular components in total hip arthroplasty (THA). One-hundred and thirty-eight consecutive patients who underwent unilateral primary THA were reviewed. Most cases had some degree of pre-operative PT, with 17% having greater than 10° of PT on standing pre-operative radiographs. There was no significant change in PT following THA. A computer model of a hemispheric acetabular component implanted in a range of anatomic positions in a pelvis with varying PT was created to determine the effects of PT on functional anteversion and inclination. Based on the study results, tilt-adjustment of the acetabular component position based on standing pre-operative imaging will likely improve functional component position in most patients undergoing THA.

Influence of clinical and radiological variables on the extent and distribution of periprosthetic osteolysis in total hip arthroplasty with a hydroxyapatite-coated multiple-hole acetabular component: a magnetic resonance imaging study

Polyethylene wear-induced osteolysis constitutes the most severe long-term complication of total hip arthroplasties (THA). Our aim was to assess through MRI the severity and growth pattern of osteolysis, as well as the influence clinical-radiographic variables exert. We analyzed 75 THA with an average evolution time of 13.67years. The implant was a titanium alloy, non-cemented, multiple-hole model with hydroxyapatite coating. Osteolysis was found with a peripheral pattern in 48 and a central pattern in 6; in 52 cases it was continuous, and in 4, isolated. Out of 118 screws, 20 exhibited lysis. There was a proportional correlation between osteolysis severity and wear rate with age, physical activity and acetabular abduction, as well as an association between said variables and peripheral and continuous patterns.

Utilization rates of hip arthroplasty in OECD countries

BACKGROUND

Hip arthroplasty and revision surgery is growing exponentially in OECD countries, but rates vary between countries.

METHODS

We extracted economic data and utilization rates data about hip arthroplasty done in OECD countries between 1990 and 2011. Absolute number of implantations and compound annual growth rates were computed per 100,000 population and for patients aged 65 years old and over and for patients aged 64 years and younger.

RESULTS

In the majority of OECD countries, there has been a significant increase in the utilization of total hip arthroplasty in the last 10 years, but rates vary to a great extent: In the United States, Switzerland, and Germany the utilization rate exceeds 200/100,000 population whereas in Spain and Mexico rates are 102 and 8, respectively. There is a strong correlation between gross domestic product (GDP) and health care expenditures per capita with utilization rate. Utilization rates in all age groups have continued to rise up to present day. A seven fold higher growth rate was seen in patients aged 64 years and younger as compared to older patients.

CONCLUSION

We observed a 38-fold variation in the utilization of hip arthroplasty among OECD countries, correlating with GDP and health care expenditures. Over recent years, there has been an increase in the utilization rate in most countries. This was particularly evident in the younger patients. Due to increasing life expectancy and the disproportionally high use of arthroplasty in younger patients we expect an exponential increase of revision rate in the future.

Comparison of acetabular shell position using patient specific instruments vs. standard surgical instruments: a randomized clinical trial

Total hip arthroplasty (THA) survivorship relies largely upon appropriate acetabular cup placement. The purpose of this prospective randomized controlled trial was to determine whether the use of a preoperative 3D planning software in combination with patient specific instrumentation (PSI) results in improved cup placement compared with traditional techniques. Thirty-six THA patients were randomized into standard (STD) or PSI technique. Standard approach was completed using traditional techniques, while PSI cases were planned and customized surgical instruments were manufactured. Postoperative CT scans were used to compare planned to actual results. Differences found between planned and actual anteversion were -0.2° ± 6.9° (PSI) and -6.9°±8.9° (STD) (P = 0.018). Use of 3D preoperative planning along with PSIs resulted in significantly greater anteversion accuracy than traditional planning and instrumentation.

Excessive polyethylene wear and acetabular bone defects from standard use of a hooded acetabular insert in total hip arthroplasty

PURPOSE

In total hip arthroplasty (THA) the use of a polyethylene (PE) insert with a hooded rim can be considered to reduce dislocation risks. This benefit has to be balanced against the potential introduction of impingement of the femoral component on this rim. We present a case series of early acetabular revisions for excessive PE wear and acetabular bone defects from overuse of such a hooded rim insert.

MATERIAL AND METHODS

Twenty-eight patients with 34 consecutive early acetabular revisions were evaluated on failure mechanism. One type of implant was used in all cases. Standard pelvic radiographs and pre-operative CT scans were used to quantify PE wear, implant positioning and acetabular bone defects.

RESULTS

An acetabular revision with impaction grafting was performed in all cases with a mean cup survival of ten years (range 1.3-19.3). No concurrent stem revisions were necessary. Overall implant positioning was adequate with a mean cup inclination of 45° (range 39-57) and anteversion of 25° (range eight to 45). The mean PE wear was 0.24 mm/year (range 0.00-1.17). The mean acetabular bone defect on pelvic CT scans was calculated as 352 mm² (range zero to 1107) and 369 mm² (range zero to 1300) in the coronal and transversal planes, respectively. A hooded acetabular insert was retrieved in all cases and profound PE wear, typically from the posterior hooded rim, was encountered.

CONCLUSION

The use of hooded acetabular inserts may be considered to improve implant stability intra-operatively. This case series clearly presents that together with these devices, component impingement with concordant complications such as accelerated PE wear may be introduced. Standard use of these stabilizing inserts should thus be avoided.

Comparison of robotic-assisted and conventional acetabular cup placement in THA: a matched-pair controlled study

BACKGROUND

Improper acetabular component orientation in THA has been associated with increased dislocation rates, component impingement, bearing surface wear, and a greater likelihood of revision. Therefore, any reasonable steps to improve acetabular component orientation should be considered and explored.

QUESTIONS/PURPOSES

We therefore sought to compare THA with a robotic-assisted posterior approach with manual alignment techniques through a posterior approach, using a matched-pair controlled study design, to assess whether the use of the robot made it more likely for the acetabular cup to be positioned in the safe zones described by Lewinnek et al. and Callanan et al.

METHODS

Between September 2008 and September 2012, 160 THAs were performed by the senior surgeon. Sixty-two patients (38.8%) underwent THA using a conventional posterior approach, 69 (43.1%) underwent robotic-assisted THA using the posterior approach, and 29 (18.1%) underwent radiographic-guided anterior-approach THAs. From September 2008 to June 2011, all patients were offered anterior or posterior approaches regardless of BMI and anatomy. Since introduction of the robot in June 2011, all THAs were performed using the robotic technique through the posterior approach, unless a patient specifically requested otherwise. The radiographic cup positioning of the robotic-assisted THAs was compared with a matched-pair control group of conventional THAs performed by the same surgeon through the same posterior approach. The safe zone (inclination, 30°-50°; anteversion, 5°-25°) described by Lewinnek et al. and the modified safe zone (inclination, 30°-45°; anteversion, 5°-25°) of Callanan et al. were used for cup placement assessment. Matching criteria were gender, age ± 5 years, and (BMI) ± 7 units. After exclusions, a total of 50 THAs were included in each group. Strong interobserver and intraobserver correlations were found for all radiographic measurements (r > 0.82; p < 0.001).

RESULTS

One hundred percent (50/50) of the robotic-assisted THAs were within the safe zone described by Lewinnek et al. compared with 80% (40/50) of the conventional THAs (p = 0.001). Ninety-two percent (46/50) of robotic-assisted THAs were within the modified safe zone described by Callanan et al. compared with 62% (31/50) of conventional THAs p (p = 0.001). The odds ratios for an implanted cup out of the safe zones of Lewinnek et al. and Callanan et al. were zero and 0.142, respectively (95% CI, 0.044, 0.457).

CONCLUSIONS

Use of the robot allowed for improvement in placement of the cup in both safe zones, an important parameter that plays a significant role in long-term success of THA. However, whether the radiographic improvements we observed will translate into clinical benefits for patients-such as reductions in component impingement, acetabular wear, and prosthetic dislocations, or in terms of improved longevity-remains unproven.

Accuracy of acetabular component position in hip arthroplasty

BACKGROUND

Acetabular component malposition is linked to higher bearing surface wear and component instability. Outcomes following total hip arthroplasty and surface replacement arthroplasty depend on multiple surgeon and patient-dependent factors. The purpose of this study was to examine the frequency in which acetabular components are placed within a predetermined target range.

METHODS

We evaluated postoperative anteroposterior pelvic radiographs for every consecutive primary total hip arthroplasty and surface replacement arthroplasty completed from 2004 to 2009 at a single institution. Acetabular component abduction and anteversion angles were determined using Martell Hip Analysis Suite software. We defined target ranges for abduction and anteversion for both total hip arthroplasty (30° to 55° and 5° to 35°, respectively) and surface replacement arthroplasty (30° to 50° and 5° to 25°, respectively). Surgeon and patient-related factors were analyzed for risk associated with placing the acetabular component outside the target range.

RESULTS

Of the 1549 total hip arthroplasties, 1435 components (93%) met our abduction target, 1472 (95%) met our anteversion target, and 1363 (88%) simultaneously met both targets. Of the 263 surface replacement arthroplasties, 233 components (89%) met our abduction target, 247 (94%) met our anteversion target, and 220 (84%) simultaneously met both targets. When previously published target ranges of abduction (30° to 45°) and anteversion (5° to 25°) angles were used, only 665 total hip replacements (43%) met the abduction target, 1325 (86%) met the anteversion target, and 584 (38%) simultaneously met both targets. Of the surface replacement arthroplasties, 181 (69%) met the abduction target, 247 (94%) met the anteversion target, and 172 (65%) simultaneously met both targets. Low-volume surgeons were 2.16 times more likely to miss target component position compared with high-volume surgeons (p = 0.002). The odds of missing the target increased by ≥ 0.2 for every 5 kg/m2 increase in body mass index. Minimally invasive approaches, diagnosis, years of surgical experience, femoral head size, and age of the patient did not affect component position.

CONCLUSIONS

Increased odds of component malposition were found with lower-volume surgeons and higher body mass index. No other variables had a significant effect on component placement.

LEVEL OF EVIDENCE

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

Are morbidly obese patients undergoing total hip arthroplasty at an increased risk for component malpositioning?

Acetabular cup positioning is a critical factor in determining adverse clinical outcomes in THA. This evaluation was performed to determine if morbid obesity (BMI ≥35kg/m(2)) is a contributing risk factor to cup malpositioning. Two groups of patients were obtained from a local arthroplasty registry and match-controlled for gender, age, and diagnosis (n=211 morbidly obese; n=211 normal). Intraoperative data and postoperative AP pelvis and cross-table lateral radiographs were obtained for each patient. The Martell Hip Analysis Suite was used to calculate cup positioning (successful positioning defined as 30°-45° of abduction, and 5°-25° of anteversion), as well as varus-valgus alignment of the femoral stem. There was a significant correlation between morbid obesity with respect to underanteversion; using multivariate analysis, there was a trend toward a combined underanteversion/overabduction of the acetabular cup. Of all variables considered, high BMI was the most significant risk factor leading to malpositioning.