Wear in alumina-on-alumina ceramic total hip replacements: a retrieval analysis of edge loading

Contemporary, non-navigation, cup orientation techniques improve accuracy and eliminate differences seen between the anterior and posterior approach in THA

BACKGROUND

This study aimed to: (1) Determine the ability to achieve the surgeons' desired cup orientation, without navigation, using contemporary measures with the anterior- (AA) and posterior- approaches (PA); and (2) assess whether surgical approach is associated with cup orientation accuracy, as previously reported, when contemporary measures are used.

METHODS

A prospective, 2-centre, multi-surgeon study of 400 THAs (200 AA; 200 PA) was performed. Intraoperative radiographs were obtained with the AA. A digital inclinometer and 3-point pelvic support were used with the PA. With the PA, intraoperative cup inclination at impaction was recorded. Radiographic inclination/anteversion (RI/RA) was measured from intraoperative radiographs (AA-only) and from postoperative radiographs for all cases. Optimum inclination/anteversion was defined as 40°/20° (±10°). The difference between intra- and postoperative orientations allowed for determination of the difference in pelvic position at impaction.

RESULTS

Optimum RI and RA were achieved in 91.3% (n = 365) and 92% (n = 368) of cases respectively. Optimum cup orientation was detected in 84% of cases (n = 336). There was equivalent ability to achieve cup orientation between approaches (AA: 82.5% vs. PA: 85.5%; p = 0.41). The use of an inclinometer in the PA was associated with a smaller variability of inclination at implantation (10° vs. 14°) and counteracted the greater difference in pelvic position (4.4° vs. 2.1°) seen with the PA.

CONCLUSIONS

Over 80% of cases can have optimum orientation without navigation, using simple, cheap contemporary measures. Such measures eliminate differences between approaches, related to patient position. Narrower implantation angles will further reduce variability in cup orientation achieved.

FEM wear prediction of ceramic hip replacement bearings under dynamic edge loading conditions

Hard-on-Hard hip implants, specifically ceramic tribo-pair, have produced the highest in-vivo wear resistance, biocompatibility, superior corrosion resistance, and high fracture toughness. However, this ceramic tribo-pair suffers from edge loading, sharply increasing wear and accelerating early implant failures due to micro-separation. Even though in-vitro studies have tested the occurrence of wear due to dynamic edge loading, the Finite Element Method (FEM) gives the advantage of accurately estimating the wear, minimizing the experimental time and cost. A new fundamental FEM model is developed to predict wear for ceramic hip replacement bearings under dynamic edge loading conditions for a fixed separation and fixed inclination angle. The model is directly validated with the existing hip simulator data up to 3 million cycles in terms of wear depth, wear scar and volumetric wear rate. The results from the model show that the accuracy in wear prediction was more than 98% for the wear depth and volumetric wear rate for the dynamic edge loading condition. A stripe wear scar is captured, depicting the edge loading conditions. The developed model from this study can predict wear under pure standard and dynamic edge loading conditions.

Functional Femoral Anteversion: Axial Rotation of the Femur and its Implications for Stem Version Targets in Total Hip Arthroplasty

Background

Acetabular and femoral component positioning are important considerations in reducing adverse outcomes after total hip arthroplasty (THA). Previous assessments of femoral anteversion examined anatomic femoral anteversion (AFA) referenced to anatomic landmarks. However, this does not provide a functional understanding of the femur's relationship to the hip. We investigate a new measurement, functional femoral anteversion (FFA), and sought to measure its variability across a large sample of patients undergoing THA.

Methods

A total of 1008 consecutive patients underwent THA surgery between September 2019 and July 2021. All patients were measured for supine and standing functional femoral rotation (FFR), AFA, and FFA.

Results

The mean standing FFA was 13.2° ± 12.2° (-27.8° to 52.3°). The mean change in FFR from supine to standing was -2.2° ± 11.8° (-43.0° to 41.9°). Of all, 161 (16%) patients had standing FFA version greater than 25°. Four hundred sixty (46%) patients had standing FFR (internal or external) greater than 10°. One hundred twenty-three (12%) patients exhibited an increase in external rotation from supine to standing of greater than 10°. A moderate, negative linear relationship was observed between AFA and standing external femoral rotation (P <<.001, R = -0.46), indicating people may externally rotate their femur as AFA decreases with age.

Conclusions

Functional alignment of the femur in patients requiring THA is understudied. It is now understood that the femur, like the pelvis, can rotate substantially between functional positions. Enhancing our understanding of FFA and FFR may improve both acetabular and femoral component positioning.

An Atypical Adverse Local Tissue Reaction After Ceramic-on-Ceramic Primary Total Hip Arthroplasty

Adverse local tissue reaction is an uncommon but frequently described complication after total hip arthroplasty (THA). It is most often associated with metal-on-metal hips and less frequently with metal-on-polyethylene implants as part of a mechanically assisted crevice corrosion process. In this report, we describe a rare case of an atypical adverse local tissue reaction in a patient with a ceramic-on-ceramic THA. Abrasive backside liner wear from a prominent screw head, failure of the liner locking mechanism, and liner fragmentation secondary to component-component impingement created an atypical mass and fluid collection leading to THA failure. This case demonstrates the importance of appropriate cup-liner positioning, thorough workup of pain after THA, and the ability of ceramic debris to cause an associated, atypical adverse local tissue reaction.

A Modeling Study of a Patient-specific Safe Zone for THA: Calculation, Validation, and Key Factors Based on Standing and Sitting Sagittal Pelvic Tilt

BACKGROUND

Lumbar-pelvic stiffness and sagittal imbalance have been reported to increase the risk of dislocation and wear after THA. One potential way to approach this concern is by identifying patient-specific safe zones for THA components based on the standing and sitting sagittal pelvic tilt. However, there is no algorithm to integrate the standing and sitting pelvic tilt into the surgical plan of component orientations.

QUESTIONS/PURPOSES

We established a new mathematical algorithm for determining a patient-specific safe zone for THA by integrating the impingement-free ROM requirements of standing and sitting while preventing edge loading while standing. We aimed to determine (1) the accuracy of this new method for predicting the impingement-free ROM for a given component orientation, (2) the sensitivity and specificity of detecting an impingement-free acetabular cup position for standing and sitting, and (3) the influences of key factors including pelvic tilt while standing and pelvic tilt while sitting and implant parameters on patient-specific safe zones.

METHODS

A strategy for calculating the intersection of standing and sitting impingement-free safe zones and the zone of a standing radiographic inclination of ≤ 45° was used to develop patient-specific safe zones. We conducted a computer simulation study including the pelvis and THA prosthesis to answer the three study questions. We enrolled 10 patients who underwent robot-assisted THA for avascular necrosis of the femoral head (mean age 49 ± 19 years; five were women) from October 2019 to December 2019. We used a prosthesis model with a conical stem neck and a non-hooded liner, with the femoral head diameter ranging between 28 mm and 40 mm, and the corresponding head-neck ratio ranging between 2.33 and 3.33. We tested 1680 movements for the accuracy of impingement-free ROM (Question 1), and 80 marginal points and 120 non-marginal points of the comprehensive impingement-free safe zone, which combines the standing and sitting postures (Question 2). For Question 3, we explored the influences of standing and sitting pelvic tilt, femoral head diameter, and ROM criteria on the size of the patient-specific safe zone.

RESULTS

With the simulation method as a reference for detecting impingement, the mean absolute error (arithmetic mean of all the absolute errors) of the calculated impingement-free ROM was 1.4° ± 2.3°, and the limit of agreement of errors was between -3.6° and 3.7°. The sensitivity of detecting a safe cup orientation within the comprehensive impingement-free safe zone for a given ROM criterion was 98.9% (95% CI 93.6% to 99.9%), and specificity was 97.1% (95% CI 91.0% to 99.2%). There were no impingement-free safe zones for 29% (pelvic tilt combinations without an impingement-free safe zone and all tested combinations) and no patient-specific safe zones for 46% (pelvic tilt combinations without a patient-specific safe zone and all tested combinations) of the tested combinations of standing and sitting pelvic tilt. The patient-specific safe zone was sensitive to changes in standing and sitting pelvic tilt, femoral head diameter, stem version, and ROM criteria. Stem anteversions beyond 10° to 20° dramatically reduced the size of the patient-specific safe zone to 0 within a change of 10° to 20°.

CONCLUSION

The patient-specific safe zone algorithm can be an accurate method for determining the optimal orientation for acetabular cups and femoral stems in THA. The patient-specific safe zone is sensitive to changes in standing and sitting pelvic tilt, stem version, ROM criteria, and the femoral head diameter. A narrow zone of 10° to 20° for stem anteversion is recommended to maximize the size of the patient-specific safe zone.

CLINICAL RELEVANCE

This study suggests the potential of a mathematical algorithm to optimize the orientation of THA components and illustrates how key parameters affect the patient-specific safe zone.

Capsular ligaments provide a passive stabilizing force to protect the hip against edge loading

AIMS

In the native hip, the hip capsular ligaments tighten at the limits of range of hip motion and may provide a passive stabilizing force to protect the hip against edge loading. In this study we quantified the stabilizing force vectors generated by capsular ligaments at extreme range of motion (ROM), and examined their ability to prevent edge loading.

METHODS

Torque-rotation curves were obtained from nine cadaveric hips to define the rotational restraint contributions of the capsular ligaments in 36 positions. A ligament model was developed to determine the line-of-action and effective moment arms of the medial/lateral iliofemoral, ischiofemoral, and pubofemoral ligaments in all positions. The functioning ligament forces and stiffness were determined at 5 Nm rotational restraint. In each position, the contribution of engaged capsular ligaments to the joint reaction force was used to evaluate the net force vector generated by the capsule.

RESULTS

The medial and lateral arms of the iliofemoral ligament generated the highest inbound force vector in positions combining extension and adduction providing anterior stability. The ischiofemoral ligament generated the highest inbound force in flexion with adduction and internal rotation (FADIR), reducing the risk of posterior dislocation. In this position the hip joint reaction force moved 0.8° inbound per Nm of internal capsular restraint, preventing edge loading.

CONCLUSION

The capsular ligaments contribute to keep the joint force vector inbound from the edge of the acetabulum at extreme ROM. Preservation and appropriate tensioning of these structures following any type of hip surgery may be crucial to minimizing complications related to joint instability. Cite this article: Bone Joint Res 2021;10(9):594-601.

The Effect of a Degenerative Spine and Adverse Pelvic Mobility on Prosthetic Impingement in Patients Undergoing Total Hip Arthroplasty

BACKGROUND

Despite the placement of acetabular components in the traditional "safe-zone", dislocations and all parts of the instability spectrum, including impingement, continue to be an issue. Recent research has established the importance of a degenerative spine and adverse pelvic mobility on functional acetabular orientation. The purpose of this study is to quantify the clinical consequences of a degenerative spine and adverse pelvic mobility on prosthetic impingement in patients undergoing total hip arthroplasty.

METHODS

Between January 2018 and December 2019, a series of 1592 patients undergoing total hip arthroplasty had functional lateral radiographs and a computed tomography scan taken. Two spinal parameters and 2 pelvic mobility parameters were investigated for their association with impingement. Each patient was evaluated for anterior and posterior impingement, at all orientations within a traditional supine safe zone and a patient-specific functional safe zone.

RESULTS

Patients with limited lumbar flexion (stiff spine), higher pelvic incidence-lumbar lordosis mismatch (sagittal imbalance), and more anterior pelvic mobility from stand to flexed-seated, exhibit increased anterior impingement. Patients with larger posterior pelvic mobility from supine-to-stand exhibited increased posterior impingement. Impingement was reduced 3-fold when the target cup orientation was tailored to a patient's functional safe zone rather than a generic target. Six percent of patients showed unavoidable impingement even with an optimized functional cup orientation.

CONCLUSION

Our results support growing evidence that patients with a degenerative spine and adverse pelvic mobility are likely to have unfavorable functional cup orientations, resulting in prosthetic impingement. Preoperative functional radiographic screening is recommended to assess the likelihood of a patient experiencing impingement due to their unique spinopelvic mobility.

Treatment of Recurrent Dislocation after Total Hip Arthroplasty Using Advanced Imaging and Three-Dimensional Modeling Techniques: A Case Series

BACKGROUND

Surgical treatment options for addressing recurrent dislocation after total hip arthroplasty (THA) vary. Identifying impingement mechanisms in an unstable THA may be beneficial in determining appropriate treatment.

QUESTIONS/PURPOSES

We sought to assess the effectiveness of developing pre-operative plans for treating hip instability after THA. We used advanced imaging and three-dimensional modeling techniques to perform impingement analyses in patients with unstable THA.

METHODS

We evaluated a series of eight patients who would require revision THA to treat recurrent dislocation. Using a pre-operative algorithmic approach, we built patient-specific models and evaluated hip range of motion with computed tomographic scanning and biplanar radiography. This information was used to determine a surgical treatment plan that was then executed intra-operatively. Patients were followed for 2 years to determine whether they experienced another hip dislocation following treatment.

RESULTS

Pre-operative kinematic modeling showed four of the eight patients had limited hip range of motion during flexion and internal rotation; a prominent anterior inferior iliac spine (AIIS) was found to limit hip range of motion in some of these cases. In the other four patients, range of motion was acceptable, suggesting soft-tissue causes of dislocation. No patients in this series experienced dislocation after undergoing revision THA.

CONCLUSION

Advanced modeling techniques may be useful for identifying the impingement mechanisms responsible for instability after THA. Once variables contributing to limited hip range of motion are identified, surgeons can develop treatment plans to improve patient outcomes. Resecting a hypertrophic AIIS may improve hip range of motion and may be an important consideration for hip surgeons when revising unstable THAs.

Wear measurements with use of radiostereometric analysis in total hip arthroplasty with obscured femoral head

Radiostereometric analysis (RSA) has evolved as gold standard in the evaluation of wear and especially as regards novel hip implant materials. However, several cup shell materials and articulation types used in total hip arthroplasty (THA) cannot be studied due to poor radiographic visibility of the femoral head (FH). We addressed this problem with use of a point transfer function in the RSA software to indirectly measure FH translations with use of stem markers. In a base examination, the stem marker segment and cup center, as an approximation for the FH center position, were mathematically coupled. Thereafter, in subsequent examinations, we used the point transfer function to calculate FH positions from stem marker positions. To determine the variance of the difference of directly and indirectly measured FH positions, four stem marker configurations were studied in THAs with radiographically visible FHs. For the axis with least variance we also compared directly and indirectly measured translation up to 7 years. Finally, we applied the method in a ceramic-on-ceramic (COC) articulation and measured proximal translation up to 7 years and also estimated precision. Vertical translations had the smallest variation between measured and calculated FH position. Directly and indirectly measured vertical FH translation correlated well but indirect measurements had increased variance. Proximal steady-state penetration rate in uncemented COC THA was -0.003 (SD 0.021) mm/year with 99% precision along the vertical axis measuring 0.34 mm. The point transfer function can be used to measure proximal FH penetration, but with less precision than direct RSA.

A Preoperative Analytical Model for Patient-Specific Impingement Analysis in Total Hip Arthroplasty

Prosthetic impingement is important to consider during total hip arthroplasty planning to minimise the risk of joint instability. Modelling impingement preoperatively can assist in defining the required component alignment for each individual. We developed an analytical impingement model utilising a combination of mathematical calculations and an automated computational simulation to determine the risk of prosthetic impingement. The model assesses cup inclination and anteversion angles that are associated with prosthetic impingement using patient-specific inputs, such as stem anteversion, planned implant types, and target Range of Motion (ROM). The analysed results are presented as a range of cup inclination and anteversion angles over which a colour map indicates an impingement-free safe zone in green and impingement risk zones in red. A validation of the model demonstrates accuracy within +/- 1.4° of cup inclination and anteversion. The study further investigated the impact of changes in stem anteversion, femoral head size, and head offset on prosthetic impingement, as an example of the application of the model.

Component positioning and ceramic damage in cementless ceramic-on-ceramic total hip arthroplasty

BACKGROUND

In ceramic-on-ceramic (CoC) total hip arthroplasty (THA), component positioning demonstrated to influence the bearing damage: however the connection between angles and clinical outcomes at long-term follow-ups is currently lacking. Aims of this study were: the computer tomography (CT) assessment of component positioning in CoC THAs; the correlation analysis between positioning and ceramic damage; the identification of safe zones.

METHODS

91 consecutive post-operative CT scans including two types of CoC implants, with a mean follow-up of 12 ± 4.4 years, were evaluated. III generation (74.2%) and IV generation (25.8%) CoC surfaces were included. The angle measurements (cup abduction, anteversion, cup tilt, stem antetorsion, sacral slope) were automated using a CT-based software. The combined anteversion was assessed as well as the cup-neck position at -15°, 0°, 45° and 90° of flexion. Ceramic damage was diagnosed using synovial fluid analyses and radiological criteria.

RESULTS

63.7% of THAs was inside the cup abduction target 30°-45° and 68.1% was inside the cup anteversion target 5°-25°. 19 patients (20.9%) showed signs of ceramic damage. High cup abduction and high cup-neck 45° minimum angle (which stood for high abduction and extreme combined version) significantly correlated with ceramic damage. No demographical features apart III generation ceramic bearings influenced the results. No safe zones could be detected.

CONCLUSIONS

In CoC THA, no safe zones can be described. However it is important to avoid cup inclination over 45° and a combination of steep cup and extreme combined version.

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.

Pelvic positioning in the supine position leads to more consistent orientation of the acetabular component after total hip arthroplasty

Aims

This study aims to: determine the difference in pelvic position that occurs between surgery and radiographic, supine, postoperative assessment; examine how the difference in pelvic position influences subsequent component orientation; and establish whether differences in pelvic position, and thereafter component orientation, exist between total hip arthroplasties (THAs) performed in the supine versus the lateral decubitus positions.

Patients and Methods

The intra- and postoperative anteroposterior pelvic radiographs of 321 THAs were included; 167 were performed with the patient supine using the anterior approach and 154 were performed with the patient in the lateral decubitus using the posterior approach. The inclination and anteversion of the acetabular component was measured and the difference (Δ) between the intra- and postoperative radiographs was determined. The target zone was inclination/anteversion of 40°/20° (± 10°). Changes in the tilt, rotation, and obliquity of the pelvis on the intra- and postoperative radiographs were calculated from Δinclination/anteversion using the Levenberg–Marquardt algorithm.

Results

The mean postoperative inclination/anteversion was 40° (± 8°)/23° (± 9°) with Δinclination and/or Δanteversion > ± 10° in 74 (21%). Intraoperatively, the pelvis was anteriorly tilted by a mean of 4° (± 10°), internally rotated by a mean of 1° (± 10°) and adducted by a mean of 1° (± 5°). Having Δinclination and/or Δanteversion > ± 10° was associated with a 3.5 odds ratio of having the acetabular component outside the target zone. A greater proportion of THAs that were undertaken with the patient in the lateral decubitus position had Δinclination and/or Δanteversion > ± 10° (35.3%, 54/153) compared with those in the supine position (4.8%, 8/167; p < 0.001). A greater number of acetabular components were within the target zone in THAs undertaken with the patient in the supine position (72%, 120/167), compared with those in the lateral decubitus position (44%, 67/153; p < 0.001). Intraoperatively, the pelvis was more anteriorly tilted (p < 0.001) and more internally rotated (p = 0.04) when the patient was in the lateral decubitus position.

Conclusion

The pelvic position is more reliable when the patient is in the supine position, leading to more consistent orientation of the acetabular component. Significant differences in pelvic tilt and rotation are seen with the patient in the lateral decubitus position. Cite this article: Bone Joint J 2018;100-B:1280–8.

Increase in Benign Squeaking Rate at Five-Year Follow-Up: Results of a Large Diameter Ceramic-on-Ceramic Bearing in Total Hip Arthroplasty

BACKGROUND

Squeaking is an on-going complication with a variable incidence of 0.5%-20.7%. The mechanism of squeaking has not been understood completely and is most likely multifactorial in nature. Previously, we have reported on a squeaking rate of 7.3% at 2 years. Our current results show a substantial increase in the squeaking incidence from 7.3% to 17.4% with the DeltaMotion articulation at the 5-year follow-up.

METHODS

Two hundred six total hip arthroplasties with a large ceramic-on-ceramic bearing were performed on 195 patients by 2 senior authors. The minimum duration of follow-up was 5 years (range 5-6.2).

RESULTS

The mean Harris Hip Score remained stable at 91.7 at 5 years compared to 92 after 2 years. However, we observed an increase in the squeaking rate from 7.3% after 2 years to 17.4% after 5 years. As in previous studies, we did not find significant differences between the silent and squeaking group in relation to age, height, weight, and femoral head diameter. In contrast, others reported no significant differences regarding range of motion and gender between the silent and the squeaking hip group at 2 years of follow-up, whereas at 5 years, the squeaking group showed a significantly higher combined range of motion and a higher relative risk of squeaking in women compared to the silent group.

CONCLUSION

While large diameter ceramic bearings may produce squeaking, especially in female patients, our mid-term clinical results of a large ceramic-on-ceramic bearing in total hip arthroplasty are encouraging. Nevertheless, long-term follow-up is recommended.

A comparison of two different navigated hip replacement techniques on leg length discrepancy

We hypothesised that a femoral array placed into bone or an external (pinless) reference marker made no difference to leg length discrepancy in patients undergoing navigated total hip arthroplasty. Consecutive patients undergoing navigated total hip arthroplasty. 162 patients. No statistical difference between preoperative leg length discrepancy (p = 0.524). Mean intraoperative change was 3.7 mm and 4.6 mm (p = 0.262). The mean change in leg length measure post operatively was 4.2 mm and 4.1 mm (p = 0.656). No significant difference in leg length discrepancy between a pinless reference markers and a femoral array placed into the bone.

A Minimum Ten Years of Follow-Up of Alumina Head on Delta Liner Total Hip Arthroplasty

BACKGROUND

In the early days when delta ceramics were developed, there was a period of using delta ceramic liner and alumina ceramic head. Therefore, the purpose of this study is to investigate the clinical and radiological outcomes of total hip arthroplasty using delta ceramic liner on alumina ceramic head after a minimum of 10 years of follow-up and to evaluate problems of early delta ceramic liner.

METHODS

Alumina on delta cementless total hip arthroplasty was performed in 92 hips (85 patients) from August 2005 to March 2007 at our hospital. Bilateral total hip arthroplasty were performed in 7 patients, 30 patients on the left side and 48 patients on the right side. Preoperative diagnosis was osteonecrosis of the femoral head in 34 hips (37%), degenerative arthritis in 31 hips (33.7%), femur neck fracture in 21 hips (22.8%), and rheumatoid arthritis in 6 hips (6.5%). All surgeries were carried out with anterolateral approach. For the clinical evaluation, Harris hip score (HHS), pain, and range of motion were assessed. Radiographs were reviewed by the authors to search for any signs of osteolysis, loosening of implants, and heterotopic ossification.

RESULTS

HHS was compared between preoperative and final follow-ups. The mean HHS improved from preoperative 58.3 points (range 27-76) to 92.7 points (range 78-98) on the final follow-up (P = .02). The mean range of hip motion at the final follow-up was flexion 116.9°, adduction 23.8°, abduction 34.6°, internal rotation 16.3°, and external rotation 39.2°. As for the postoperative pain, 1 patient complained of inguinal pain and 4 patients complained of thigh pain. Because of trauma, 3 cases of dislocation were observed in all cases. There are 3 cases with dislocation and 2 cases were treated with conservative treatment without recurrence, but 1 case was required for surgical treatment due to eccentric rim wear of delta liner. The aseptic loosening of acetabular cup and femoral stem was each 1 hip.

CONCLUSION

Alumina head-on-delta liner cementless THA, using a large femoral head 32-36 mm in diameter, demonstrated satisfactory clinical and radiological results in the minimum 10 years of follow-up. Eccentric rim wear can occur even in delta ceramic liners that are known to have high strength, and this can lead to dislocation which can, in turn, increase the possibility of linear fracture.

The effect of seated pelvic tilt on posterior edge-loading in total hip arthroplasty: A finite element investigation

Edge-loading of a ceramic-on-ceramic total hip replacement can lead to reproducible squeaking and revision. A patient’s functional acetabular cup orientation, driven by their pelvic tilt, has been shown to be a significant factor in squeaking during hip flexion. The aim of this study was to investigate the effect of seated pelvic tilt on the contact mechanics at the ceramic bearing surface. A finite element model of a ceramic-on-ceramic total hip replacement was created. The cup was orientated at 40° inclination and 15° anteversion relative to the anterior pelvic plane. The stem was flexed 90° to replicate sitting in a chair. The model was loaded using data from in vivo measurements taken during a sit-to-stand activity. The pelvis was modelled in seven different sagittal positions, ranging from −30° to 30° of pelvic tilt, where a positive value denotes anterior pelvic tilt. Three different head sizes were investigated: 32, 36 and 40 mm. The maximum contact pressure and contact patch to rim distance were determined for each of the 21 simulations. Edge-loading (contact patch to rim distance < 0 mm) occurred with all head sizes when seated pelvic tilt was ≥10° and induced a large increase in contact pressure on the liner, with a maximum pressure exceeding 500 MPa. Edge-loading initiated at seated pelvic tilts of 7°, 9° and 5° for the 32, 36 and 40 mm heads, respectively. Patients with anterior pelvic tilts in the seated position are susceptible to posterior edge-loading. As the position of the pelvis when seated is patient specific, cup orientation should be adjusted on an individual basis to minimise edge-loading.

Zirconia phase transformation in retrieved, wear simulated, and artificially aged ceramic femoral heads

Zirconia in Zirconia toughened alumina ceramic hip replacements exists in an unstable state and can transform in response to stress giving the material improved fracture toughness. Phase transformation also occurs under hydrothermal conditions such as exist in vivo. To predict the hydrothermal aging that will occur in vivo accelerated aging procedures have been used, but validation of these models requires the study of retrieved hip joints. Here 26 retrievals are analysed to determine the degree of phase transformation in vivo. These were compared with virgin heads, heads that had undergone the accelerated aging process and heads wear tested to 5 million cycles in a hip simulator. Monoclinic content and surface roughness were measured using Raman spectroscopy and white light interferometry respectively. The monoclinic content for retrieved heads was 28.5% ± 7.8, greater than twice that in virgin, aged, or wear tested heads and did not have a significant correlation with time, contrary to the predictions of the hydrothermal aging model. The surface roughness for retrieved heads in the unworn area was not significantly different to that in virgin, aged, or unworn areas of wear tested heads. However in worn areas of the retrieved heads, the surface roughness was higher than observed in wear simulator testing. These results indicate that current testing methodologies do not fully capture the operational conditions of the material and the real performance of future new materials may not be adequately predicted by current pre-clinical testing methods. © 2017 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society 35:2781-2789, 2017.

Changes in spinopelvic indices after hip arthroplasty and its influence on acetabular component orientation

OBJECTIVE

To evaluate spinopelvic changes after hip arthroplasty in standing and ready-to-rise positions.

METHODS

We compared pelvic tilt, sacral slope, cobb's angle, and hip flexion on pre and postoperative spinopelvic radiographs.

RESULTS

Standing: All postoperative indices were similar to preoperative ones except sacral slope (mean difference:1.6°, p = 0.046). Ready-to-rise: All postoperative indices were similar to preoperative ones except pelvic tilt which was significantly greater postoperatively (mean difference: 5.1°, p = 0.017). Fifteen patients showed >10° increase in pelvic tilt postoperatively.

CONCLUSION

Changes in pelvic tilt in ready-to-rise position can predispose to posterior edge loading, edge wear, and dislocation; especially with inadequate cup anteversion.

Inflammatory pseudotumor after ceramic-on-ceramic total hip arthroplasty

We present a unique case of a symptomatic adverse local tissue reaction in a patient with a ceramic-on-ceramic total hip bearing surface. To our knowledge, this pathological finding has not yet been described in a ceramic-on-ceramic articulation without a cobalt-chromium alloy trunnion or modular neck component as a source of metal wear. We conclude that despite its mechanical mostly benign wear characteristics, ceramic wear debris is not entirely inert and may lead to the development of adverse local tissue reaction.

Variation in functional pelvic tilt in patients undergoing total hip arthroplasty

Aims

The pelvis rotates in the sagittal plane during daily activities. These rotations have a direct effect on the functional orientation of the acetabulum. The aim of this study was to quantify changes in pelvic tilt between different functional positions.

Patients and Methods

Pre-operatively, pelvic tilt was measured in 1517 patients undergoing total hip arthroplasty (THA) in three functional positions – supine, standing and flexed seated (the moment when patients initiate rising from a seated position). Supine pelvic tilt was measured from CT scans, standing and flexed seated pelvic tilts were measured from standardised lateral radiographs. Anterior pelvic tilt was assigned a positive value.

Results

The mean pelvic tilt was 4.2° (-20.5° to 24.5°), -1.3° (-30.2° to 27.9°) and 0.6° (-42.0° to 41.3°) in the three positions, respectively. The mean sagittal pelvic rotation from supine to standing was -5.5° (-21.8° to 8.4°), from supine to flexed seated was -3.7° (-48.3° to 38.6°) and from standing to flexed seated was 1.8° (-51.8° to 39.5°). In 259 patients (17%), the extent of sagittal pelvic rotation could lead to functional malorientation of the acetabular component. Factoring in an intra-operative delivery error of ± 5° extends this risk to 51% of patients.

Conclusion

Planning and measurement of the intended position of the acetabular component in the supine position may fail to predict clinically significant changes in its orientation during functional activities, as a consequence of individual pelvic kinematics. Optimal orientation is patient-specific and requires an evaluation of functional pelvic tilt pre-operatively. Cite this article: Bone Joint J 2017;99-B:184–91.

High prevalence of noise following Delta ceramic-on-ceramic total hip arthroplasty

Aims

We evaluated the short-term functional outcome and prevalence of bearing-specific generation of audible noise in 301 patients (336 hips) operated on with fourth generation (Delta) medium diameter head, ceramic-on-ceramic (CoC) total hip arthroplasties (THAs).

Patients and Methods

There were 191 female (63%) and 110 male patients (37%) with a mean age of 61 years (29 to 78) and mean follow-up of 2.1 years (1.3 to 3.4). Patients completed three questionnaires: Oxford Hip Score (OHS), Research and Development 36-item health survey (RAND-36) and a noise-specific symptom questionnaire. Plain radiographs were also analysed. A total of three hips (0.9%) were revised.

Results

There were 52 patients (54 hips, 17%) who reported noise, and in 25 (48%) of them the noise was frequently heard. In the multiple regression analysis, the only independent risk factor for noise was a specific THA brand, with a threefold increased risk (95% confidence intervals 1.39 to 6.45, p = 0.005) of noise compared with the reference THA brand. Patients with noisy hips had lower median OHS (43 versus 46.5, p = 0.002) and their physical functioning (p = 0.021) subscale in RAND-36 was reduced.

Conclusion

Noise was surprisingly common in this population. Cite this article: Bone Joint J 2017;99-B:44–50.

Patient-specific instrumentation improves the accuracy of acetabular component placement in total hip arthroplasty

Aims

Accurate placement of the acetabular component during total hip arthroplasty (THA) is an important factor in the success of the procedure. However, the reported accuracy varies greatly and is dependent upon whether free hand or navigated techniques are used. The aim of this study was to assess the accuracy of an instrument system that incorporates 3D printed, patient-specific guides designed to optimise the placement of the acetabular component.

Patients and Methods

A total of 100 consecutive patients were prospectively enrolled and the accuracy of placement of the acetabular component was measured using post-operative CT scans.

Results

The mean absolute deviation from the planned inclination and anteversion was 3.9° (0.0° to 13.6°) and 3.6° (0.0° to 12.9°), respectively. In 91% of cases the planned target of +/-10° was achieved for both inclination and anteversion.

Conclusion

Accurate placement of the acetabular component can be achieved using patient-specific guides and is superior to free hand techniques and comparable to navigated and robotic techniques. Cite this article: Bone Joint J 2016;98-B:1342–6.

Functional orientation of the acetabular component in ceramic-on-ceramic total hip arthroplasty and its relevance to squeaking

Aims

Long-term clinical outcomes for ceramic-on-ceramic (CoC) bearings are encouraging. However, there is a risk of squeaking. Guidelines for the orientation of the acetabular component are defined from static imaging, but the position of the pelvis and thus the acetabular component during activities associated with edge-loading are likely to be very different from those measured when the patient is supine. We assessed the functional orientation of the acetabular component.

Patients and Methods

A total of 18 patients with reproducible squeaking in their CoC hips during deep flexion were investigated with a control group of 36 non-squeaking CoC hips. The two groups were matched for the type of implant, the orientation of the acetabular component when supine, the size of the femoral head, ligament laxity, maximum hip flexion and body mass index.

Results

The mean functional anteversion of the acetabular component at the point when patients initiated rising from a seated position was significantly less in the squeaking group than in the control group, 8.1° (-10.5° to 36.0°) and 21.1° (-1.9° to 38.4°) respectively (p = 0.002).

Conclusion

The functional orientation of the acetabular component during activities associated with posterior edge-loading are different from those measured when supine due to patient-specific pelvic kinematics. Individuals with a large anterior pelvic tilt during deep flexion might be more susceptible to posterior edge-loading and squeaking as a consequence of a significant decrease in the functional anteversion of the acetabular component. Cite this article: Bone Joint J 2016;98-B:910–16.

Gait alterations can reduce the risk of edge loading

Following metal-on-metal hip arthroplasty, edge loading (i.e., loading near the edge of a prosthesis cup) can increase wear and lead to early revision. The position and coverage angle of the prosthesis cup influence the risk of edge loading. This study investigates the effect of altered gait patterns, more specific hip, and pelvis kinematics, on the orientation of hip contact force and the consequent risk of antero-superior edge loading using muscle driven simulations of gait. With a cup orientation of 25° anteversion and 50° inclination and a coverage angle of 168°, many gait patterns presented risk of edge loading. Specifically at terminal double support, 189 out of 405 gait patterns indicated a risk of edge loading. At this time instant, the high hip contact forces and the proximity of the hip contact force to the edge of the cup indicated the likelihood of the occurrence of edge loading. Although the cup position contributed most to edge loading, altering kinematics considerably influenced the risk of edge loading. Increased hip abduction, resulting in decreasing hip contact force magnitude, and decreased hip extension, resulting in decreased risk on edge loading, are gait strategies that could prevent edge loading. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1069-1076, 2016.

Detailed inspection of metal implants

Detailed visual inspection of metal hips is the first step in retrieval analysis. In this study a systematic visual inspection protocol was developed to quantify bearing surface changes and their associations with material loss was investigated. Simple and multiple linear regression models found that moderate surface scratching, discolouration, haziness and the size of visible wear scars were all significantly associated with material loss (R2 = 5%-73%, p<0.05). Visual inspection is not a substitute for measurement of material loss but an understanding of bearing surface changes may offer unique clues as to the mechanisms of failure of retrieved hips.

Review on squeaking hips

Squeaking is a well-recognized complication for hard-on-hard bearings. The nature of squeaking is not yet completely understood however it is considered a multifactorial phenomenon. Patient, implant, and surgical factors play a role in squeaking. It is believed that mechanisms damaging the fluid film lubrication in which these bearings function optimally have a critical role. Such mechanisms include edge loading, stripe wear, impingement, third body particles and ceramic fracture. The resonance of metallic parts can produce noise in the human audible range hence the implant metallurgic composition and design may play a role. Implant positioning can facilitate impingement and edge loading enhancing the occurrence of squeaking. The recent introduction of large heads (> 36 mm) 4^th generation ceramic-on-ceramic bearing may accentuate the conditions facilitating noise formation; however the current literature is insufficient. Clinically, squeaking may manifest in extreme hip positions or during normal gait cycle however it is rarely associated with pain. Evaluations of patients with squeaking include clinical and radiographic assessments. Computer tomography is recommended as it can better reveal ceramic breakage and implant malposition. The treatments for most squeaking patients include reassurance and activity modification. However for some, noise can be a problem, requiring further surgical intervention. In the occurrence of ceramic fracture, implant failure, extreme components malposition, instability and impingement, surgery should be advised. This review will aim to discuss the current literature regarding squeaking.

The envelope of passive motion allowed by the capsular ligaments of the hip

Laboratory data indicate the hip capsular ligaments prevent excessive range of motion, may protect the joint against adverse edge loading and contribute to synovial fluid replenishment at the cartilage surfaces of the joint. However, their repair after joint preserving or arthroplasty surgery is not routine. In order to restore their biomechanical function after hip surgery, the positions of the hip at which the ligaments engage together with their tensions when they engage is required. Nine cadaveric left hips without pathology were skeletonised except for the hip joint capsule and mounted in a six-degrees-of-freedom testing rig. A 5 N m torque was applied to all rotational degrees-of-freedom separately to quantify the passive restraint envelope throughout the available range of motion with the hip functionally loaded. The capsular ligaments allowed the hip to internally/externally rotate with a large range of un-resisted rotation (up to 50±10°) in mid-flexion and mid-ab/adduction but this was reduced towards the limits of flexion/extension and ab/adduction such that there was a near-zero slack region in some positions (p<0.014). The slack region was not symmetrical; the mid-slack point was found with internal rotation in extension and external rotation in flexion (p<0.001). The torsional stiffness of the capsular ligamentous restraint averaged 0.8±0.3 N m/° and was greater in positions where there were large slack regions. These data provide a target for restoration of normal capsular ligament tensions after joint preserving hip surgery. Ligament repair is technically demanding, particularly for arthroscopic procedures, but failing to restore their function may increase the risk of osteoarthritic degeneration.

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.

Wear testing of total hip replacements under severe conditions

Controlled wear testing of total hip replacements in hip joint simulators is a well-established and powerful method, giving an extensive prediction of the long-term clinical performance. To understand the wear behavior of a bearing and its limits under in vivo conditions, testing scenarios should be designed as physiologically as possible. Currently, the ISO standard protocol 14242 is the most common preclinical testing procedure for total hip replacements, based on a simplified gait cycle for normal walking conditions. However, in recent years, wear patterns have increasingly been observed on retrievals that cannot be replicated by the current standard. The purpose of this study is to review the severe testing conditions that enable the generation of clinically relevant wear rates and phenomena. These conditions include changes in loading and activity, third-body wear, surface topography, edge wear and the role of aging of the bearing materials.

The capsular ligaments provide more hip rotational restraint than the acetabular labrum and the ligamentum teres : an experimental study

In this in vitro study of the hip joint we examined which soft tissues act as primary and secondary passive rotational restraints when the hip joint is functionally loaded. A total of nine cadaveric left hips were mounted in a testing rig that allowed the application of forces, torques and rotations in all six degrees of freedom. The hip was rotated throughout a complete range of movement (ROM) and the contributions of the iliofemoral (medial and lateral arms), pubofemoral and ischiofemoral ligaments and the ligamentum teres to rotational restraint was determined by resecting a ligament and measuring the reduced torque required to achieve the same angular position as before resection. The contribution from the acetabular labrum was also measured. Each of the capsular ligaments acted as the primary hip rotation restraint somewhere within the complete ROM, and the ligamentum teres acted as a secondary restraint in high flexion, adduction and external rotation. The iliofemoral lateral arm and the ischiofemoral ligaments were primary restraints in two-thirds of the positions tested. Appreciation of the importance of these structures in preventing excessive hip rotation and subsequent impingement/instability may be relevant for surgeons undertaking both hip joint preserving surgery and hip arthroplasty.

Cite this article: Bone Joint J 2015; 97-B:484–91.

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.

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

BACKGROUND

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

OBJECTIVES

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSION

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

The result of revision total hip arthroplasty in patients with metallosis following a catastrophic failure of a polyethylene liner

BACKGROUND

Wear cannot be completely prevented after total hip arthroplasty. If severe polyethylene (PE) liner wear develops, the so-called catastrophic failure occurs and metallosis develops. We postulated that longevity of the new implant may be affected after revision surgery for metallosis following a catastrophic failure of a PE liner due to the substantial amount of PE wear particles and infiltration of the metal particles in this catastrophic condition.

METHODS

Twenty-three hips of 23 patients were identified because they showed metallosis during revision total hip arthroplasties performed in Seoul National University Hospital between January 1996 and August 2004. They were followed for at least 6.5 years after the index revision total hip arthroplasty. The clinical and radiological results of revision total hip arthroplasties in these patients were evaluated.

RESULTS

The median Harris hip score increased from 60 points before revision total hip arthroplasties to 90 points at the final follow-up. Osteolysis was detected at an average of 9.3 years after revision total hip arthroplasties in 13 hips and acetabular cup loosening at average 9.8 years after revision total hip arthroplasties in 9 hips. With radiographic evidence of osteolysis and loosening as the end points, the 15-year survival rates were 28.2% and 56.0%, respectively.

CONCLUSIONS

The survival rate of revision total hip arthroplasty in patients with metallosis following a catastrophic failure of a PE liner was low.

Squeaking in large diameter ceramic-on-ceramic bearings in total hip arthroplasty

We analyzed the results of 206 consecutive total hip arthroplasties performed using large diameter ceramic-on-ceramic bearings. At an average follow-up of 28months, the mean Harris Hip Score improved from 54 to 92. Fifteen (7.3%) hips were noted to squeak. There was no significant difference between silent and squeaking hips with regards to age, weight, height, BMI, range of movement, femoral head diameter, leg length, and offset or center of rotation. No correlation was present between incidence of squeaking and increasing cup inclination and anteversion. 5.2% of cups orientated within Lewinnek's safe zone squeaked. No hips required revision for squeaking. While large diameter ceramic bearings may produce squeaking, our early results of surgery using large head ceramic bearings are encouraging. However, long-term follow-up is required.

A new method of registration in navigated hip arthroplasty without the need to register the anterior pelvic plane

A prospective clinical study of 50 patients was conducted to validate a new method of imageless computer navigated hip arthroplasty. The new method enables the surgeon to acquire all registration points with the patient positioned and draped in lateral decubitus position. The final component orientation was measured from post-operative CT scans. The mean error in component position was -1.1° (SD 3.1°) for inclination and 0.9° (SD 4.3°) for anteversion. This compared favourably with the error of -1.8° (SD 1.8°) for inclination and -4.8° (SD 2.7°) for anteversion when using the traditional APP registration. Results show that one can expect the acetabular component to be within a safe zone of ±10° in 99.8% for inclination and 97.7% for anteversion when using the new lateral registration method. Level of Evidence Level II, Prognostic study.

Cup position alone does not predict risk of dislocation after hip arthroplasty

We used a large prospective institutional registry to determine if there is a 'safe zone' that exists for acetabular component position within which the risk of hip dislocation is low and if other patient and implant factors affect the risk of hip dislocation. Patients who reported a dislocation event within six months after hip arthroplasty surgery were identified, and acetabular component position was measured with anteroposterior radiographs. The frequency of dislocation was 2.1% (147 of 7040 patients). No significant difference was found in the number of dislocated hips among the radiographic zones (±5°,±10°,±15° boundaries). Dislocators <50 years old were less active preoperatively than nondislocators (P=0.006). Acetabular component position alone is not protective against instability.

Ceramic femoral component fracture in total knee arthroplasty: an analysis using fractography, fourier-transform infrared microscopy, contact radiography and histology

Ceramic components in total knee arthroplasty (TKA) are evolving. We analyze the first case of BIOLOX delta ceramic femoral component fracture. A longitudinal midline fracture in the patellar groove was present, with an intact cement mantle and no bony defects. Fractographic analysis with laser scanning microscopy and white light interferometry showed no evidence of arrest lines, hackles, wake hackles, material flaws, fatigue or crack propagation. Analysis of periprosthetic tissues with Fourier-transform infrared (FT-IR) microscopy, contact radiography, histology, and subsequent digestion and high-speed centrifugation did not show ceramic debris. A macrophage-dominated response was present around polyethylene debris. We conclude that ceramic femoral component failure in this case was related to a traumatic event. Further research is needed to determine the suitability of ceramic components in TKA.

Risk of impingement and third-body abrasion with 28-mm metal-on-metal bearings

BACKGROUND

Concerns have been raised about the sequelae of metal-on-metal (MoM) bearings in total hip arthroplasty (THA). However, retrieval studies, which offer the best insight into the clinically relevant mechanisms of MoM wear, have followed predictable trends to date such as indicting cobalt-chromium (CoCr) metallurgy, cup design, high conformity between the head and cup, "steep cups," "microseparation," and "edge wear."

QUESTIONS/PURPOSES

We wished to evaluate a set of retrieved 28-mm MoM THA for signs of (1) cup-to-stem impingement; (2) normal wear pattern and concomitant stripe damage on femoral heads that would signify adverse wear mechanics; and (3) well-defined evidence of third-body scratches on bearings that would indicate large abrasive particles had circulated the joint space.

METHODS

Ten 28-mm MOM retrievals were selected on the basis that femoral stems were included. Revision surgeries at 3 to 8 years were for pain, osteolysis, and cup loosening. CoCr stems and the MoM bearings were produced by one vendor and Ti6Al4V stems by a second vendor. All but two cases had been fixed with bone cement. We looked for patterns of normal wear and impingement signs on femoral necks and cup rims. We looked for adverse wear defined as stripe damage that was visually apparent on each bearing. Wear patterns were examined microscopically to determine the nature of abrasions and signs of metal transfer. Graphical models recreated femoral neck and cup designs to precisely correlate impingement sites on femoral necks to cup positions and head stripe patterns.

RESULTS

The evidence revealed that all CoCr cup liners had impinged on either anterior or posterior facets of femoral necks. Liner impingement at the most proximal neck notch occurred with the head well located and impingement at the distal notch occurred with the head rotated 5 mm out of the cup. The hip gained 20° motion by such a subluxation maneuver with this THA design. All heads had stripe wear, the basal and polar stripes coinciding with cup impingement sites. Analysis of stripe damage revealed 40 to 100-μm wide scratches created by large particles ploughing across bearing surfaces. The association of stripe wear with evidence of neck notching implicated impingement as the root cause, the outcome being the aggressive third-body wear.

CONCLUSIONS

We found consistent evidence of impingement, abnormal stripe damage, and evidence of third-body abrasive wear in a small sample of one type of 28-mm MoM design. Impingement models demonstrated that 28-mm heads could lever 20° out of the liners. Although other studies continue to show good success with 28-mm MoM bearings, their use has been discontinued at La Pitie Hospital.

The current state of bearing surfaces in total hip replacement

We reviewed the literature on the currently available choices of bearing surface in total hip replacement (THR). We present a detailed description of the properties of articulating surfaces review the understanding of the advantages and disadvantages of existing bearing couples. Recent technological developments in the field of polyethylene and ceramics have altered the risk of fracture and the rate of wear, although the use of metal-on-metal bearings has largely fallen out of favour, owing to concerns about reactions to metal debris. As expected, all bearing surface combinations have advantages and disadvantages. A patient-based approach is recommended, balancing the risks of different options against an individual’s functional demands.

Cite this article: Bone Joint J 2014;96-B:147–56.

Squeaking: Current knowledge and how to avoid it

This review aims to update the reader with current thinking and research related to the well documented phenomenon of squeaking hip arthroplasties. The etiology of squeaking is multifactorial and still not well understood. We aim to share our own experience and views on the combination of factors we believe increases the likelihood of squeaking, along with mechanisms by which the sound may be generated. Recent published findings from other groups are summarized along with an appropriate management algorithm we recommend for this cohort of patients.

A fatigue assessment technique for modular and pre-stressed orthopaedic implants

Orthopaedic implants experience large cyclic loads, and pre-clinical analysis is conducted to ensure they can withstand millions of loading cycles. Acetabular cup developments aim to reduce wall thickness to conserve bone, and this produces high pre-stress in modular implants. As part of an implant development process, we propose a technique for preclinical fatigue strength assessment of modular implants which accounts for this mean stress, stress concentrating features and material processing. A modular cup's stress distributions were predicted computationally, under assembly and in vivo loads, and its cyclic residual stress and stress amplitude were calculated. For verification against damage initiation in low-cycle-fatigue (LCF), the peak stress was compared to the material's yield strength. For verification against failure in high-cycle-fatigue (HCF) each element's reserve factor was calculated using the conservative Soderberg infinite life criterion. Results demonstrated the importance of accounting for mean stress. The cup was predicted to experience high cyclic mean stress with low magnitude stress amplitude: a low cyclic load ratio (Rl=0.1) produced a high cyclic stress ratio (Rs=0.80). Furthermore the locations of highest cyclic mean stress and stress amplitude did not coincide. The minimum predicted reserve factor Nf was 1.96 (HCF) and 2.08 (LCF). If mean stress were neglected or if the stress ratio were assumed to equal the load ratio, the reserve factor would be considerably lower, potentially leading to over-engineering, reducing bone conservation. Fatigue strength evaluation is only one step in a broader development process, which should involve a series of verifications with the full range of normal and traumatic physiological loading scenarios, with representative boundary conditions and a representative environment. This study presents and justifies a fatigue analysis methodology which could be applied in early stage development to a variety of modular and pre-stressed prosthesis concepts, and is particularly relevant as implant development aims to maximise modularity and bone conservation.

Functional acetabular component position with supine total hip replacement

Orientation of the acetabular component influences wear, range of movement and the incidence of dislocation after total hip replacement (THR). During surgery, such orientation is often referenced to the anterior pelvic plane (APP), but APP inclination relative to the coronal plane (pelvic tilt) varies substantially between individuals. In contrast, the change in pelvic tilt from supine to standing (dPT) is small for nearly all individuals. Therefore, in THR performed with the patient supine and the patient’s coronal plane parallel to the operating table, we propose that freehand placement of the acetabular component placement is reliable and reflects standing (functional) cup position. We examined this hypothesis in 56 hips in 56 patients (19 men) with a mean age of 61 years (29 to 80) using three-dimensional CT pelvic reconstructions and standing lateral pelvic radiographs. We found a low variability of acetabular component placement, with 46 implants (82%) placed within a combined range of 30° to 50° inclination and 5° to 25° anteversion. Changing from the supine to the standing position (analysed in 47 patients) was associated with an anteversion change < 10° in 45 patients (96%). dPT was < 10° in 41 patients (87%). In conclusion, supine THR appears to provide reliable freehand acetabular component placement. In most patients a small reclination of the pelvis going from supine to standing causes a small increase in anteversion of the acetabular component.

Cite this article: Bone Joint J 2013;95-B:1326–31.

Hip abduction can prevent posterior edge loading of hip replacements

Edge loading causes clinical problems for hard-on-hard hip replacements, and edge loading wear scars are present on the majority of retrieved components. We asked the question: are the lines of action of hip joint muscles such that edge loading can occur in a well-designed, well-positioned acetabular cup? A musculoskeletal model, based on cadaveric lower limb geometry, was used to calculate for each muscle, in every position within the complete range of motion, whether its contraction would safely pull the femoral head into the cup or contribute to edge loading. The results show that all the muscles that insert into the distal femur, patella, or tibia could cause edge loading of a well-positioned cup when the hip is in deep flexion. Patients frequently use distally inserting muscles for movements requiring deep hip flexion, such as sit-to-stand. Importantly, the results, which are supported by in vivo data and clinical findings, also show that risk of edge loading is dramatically reduced by combining deep hip flexion with hip abduction. Patients, including those with sub-optimally positioned cups, may be able to reduce the prevalence of edge loading by rising from chairs or stooping with the hip abducted.

Periprosthetic tissues from third generation alumina-on-alumina total hip arthroplasties

The histological features of periprosthetic tissues are related to the bioreactivity of particles generated by the prosthesis. This study analyzed synovial-like pseudocapsules collected from 21 patients with alumina ceramic-on-ceramic hip arthroplasties and correlated histological features with wear of the ceramic bearings, duration of implantation and clinical factors such as neck-to-rim impingement. A histopathological classification system was developed for this purpose. The pseudocapsules were viable, with few foreign body type giant cells and occasional lymphocytes. This differs from tissues in polyethylene containing hip arthroplasties which often have extensive foreign body type inflammatory changes or from metal-on-metal hip arthroplasties in which extensive necrosis is common. Soft-tissue inflammation was not associated with failure of the hip arthroplasties, and may be clinically insignificant in alumina-on-alumina total hip arthroplasties.

The incidence of noise generation arising from the large-diameter Delta Motion ceramic total hip bearing

Noise generation has been reported with ceramic-on-ceramic articulations in total hip replacement (THR). This study evaluated 208 consecutive Delta Motion THRs at a mean follow-up of 21 months (12 to 35). There were 141 women and 67 men with a mean age of 59 years (22 to 84). Patients were reviewed clinically and radiologically, and the incidence of noise was determined using a newly described assessment method. Noise production was examined against range of movement, ligamentous laxity, patient-reported outcome scores, activity level and orientation of the acetabular component. There were 143 silent hips (69%), 22 (11%) with noises other than squeaking, 17 (8%) with unreproducible squeaking and 26 (13%) with reproducible squeaking. Hips with reproducible squeaking had a greater mean range of movement (p < 0.001) and mean ligament laxity (p = 0.004), smaller median head size (p = 0.01) and decreased mean acetabular component inclination (p = 0.02) and anteversion angle (p = 0.02) compared with the other groups. There was no relationship between squeaking and age (p = 0.13), height (p = 0.263), weight (p = 0.333), body mass index (p = 0.643), gender (p = 0.07) or patient outcome score (p = 0.422). There were no revisions during follow-up. Despite the surprisingly high incidence of squeaking, all patients remain satisfied with their hip replacement.