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Orthopaedic Proceedings
Vol. 100-B, Issue SUPP_6 | Pages 59 - 59
1 Apr 2018
Clarke I Bowsher J Savisaar C Donaldson T
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Metal-on-metal (MOM) and ceramic-on-metal (COM) studies in total hip arthroplasty (THA) documented adverse wear termed “edge loading”. Laboratory simulations necessitated cups steeply inclined to produce edge- loading, whereby cup rims could attenuate the normal wear patterns. Size of cup wear-pattern was therefore key in defining edge-loading. From prior simulator studies (‘Anatomic’ test: ISO-14242), we could demonstrate a linear relationship between size of cup wear-patterns and MOM diameters, cup wear-areas decreasing from 18% to 8%. However, retrieval studies (COM/ MOM) showed cup wear-patterns in vivo were much larger, typically covering 50–55% cup surfaces (Clarke 2013: Koper 2015). In prior MOM Anatomic simulator study (head oscillating, cup fixed), we noted areas worn on 60mm heads and cups averaging 1,668mm2 and 442mm2, respectively (Bowsher 2009). Thus, ratio ×3.77 described distributed area worn on heads relative to focal area worn in cups. In the orbital simulator, the only way to achieve larger cup wear areas was to reverse the component positions, i.e. cups oscillating, heads fixed. The overall goal for this project was to develop an understanding of how such edge-loading affected adverse-wear performance of THA in simulators. 60mm MOM (DJO, Austin TX) were chosen comparable to our prior study (Bowsher 2009) and cups were mounted inverted (oscillating) under fixed heads. Adaptors were machined to incline cup faces at 17o and 27o and, with the simulator's +/−23° motion, they experienced 40oand 50o cyclic peak oscillations, respectively. The orbital simulator was identical to that of prior study as was the test protocol (Bowsher 2009). Wear patterns on components were assessed visually and microscopically, taped and colored red to aid photography. The 40° and 50° tests produced circular cup wear patterns that came progressively closer to the rims without actually producing edge-loading, creating average wear area of 1,663mm2. These proved identical to wear areas on heads (orbiting) in prior Anatomic test (1,668mm2). Using the hemispherical-area datum of 5,655mm2 for 60mm MOM, our test produced cup wear patterns with desired 29.4% coverage. The value of ISTA conferences is that by definition these bring new arthroplasty ideas and technologies to the forefront. The international guideline for simulators (ISO-14242) has proven useful for standard ‘Anatomic’ cup tests that do not require edge-loading conditions. However, ours is the 1st simulator study to; (i) predict the size of THA wear patterns, (ii) show that ratio of head: cup wear-areas average ×3.8 in favor of mobile component, and (iii) demonstrated cups can be run Inverted to produce more clinically-relevant wear patterns that in edge- loading studies. The new learning experience was that studies of edge-loading in THA cups need to consider the ‘Inverted’ test in order to simulate clinically relevant tribo-mechanical parameters. Compared to Anatomic test, the Inverted-cup test has the advantage of (iv) producing larger cup wear areas, (v) clinically-relevant attenuation of wear patterns at cup rim, and (vi) intermittent edge-loading (instead of constant loading) judged likely to apply to a larger patient population at risk


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXI | Pages 25 - 25
1 May 2012
Y-M. K S. G D. S A. K P. M H.S. G D M
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Pseudotumours (soft-tissue masses relating to the hip joint) following metal-on-metal hip resurfacing arthroplasty (MoMHRA) have been associated with elevated serum and hip aspirate metal ion levels, suggesting that pseudotumours occur when there is increased wear. This study aimed to quantify the wear of implants revised for pseudotumours and a control group of implants revised for other reasons of failure. A total of 30 contemporary MoMHRA implants in two groups were investigated: (1) 8 MoMHRA implants revised due to pseudotumour; (2) 22 MoMHRA implants revised due to other reasons of failure. The linear wear of retrieved implants was measured using a Taylor-Hobson Roundness machine. The average linear wear rate was defined as the maximum linear wear depth divided by the duration of the implant in vivo. In comparison with the non-pseudotumour implant group, the pseudotumour implant group was associated with: (1) significantly higher median linear wear rate of the femoral component: 8.1 um/year (range 2.75-25.4 um/year) vs. 1.97 um/year (range 0.82-13.00 um/year), p=0.002; and (2) significantly higher median linear wear rate of the acetabular component: 7.36 um/year (range 1.61-24.9 um/year) vs. 1.28 um/year (range 0.18-3.33 um/year), p=0.001. Wear on the acetabular cup components in the pseudotumour group always involved the edge, indicating edge-loading of the bearing. Significantly greater linear wear rates of the MoMHRA implants revised due to pseudotumour support the in vivo elevated metal ion concentrations in patients with pseudotumours. This study is the first to confirm that pseudotumour occurs when there is increased wear at the MoM articulation. Furthermore, edge-loading may be the dominant wear generation mechanism in patients with pseudotumour


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_9 | Pages 132 - 132
1 May 2016
Pierrepont J Feyen H Baré J Young D Miles B Shimmin A
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Introduction. Acetabular cup orientation has been shown to be a factor in edge-loading of a ceramic-on-ceramic THR bearing. Currently all recommended guidelines for cup orientation are defined from static measurements with the patient positioned supine. The objectives of this study are to investigate functional cup orientation and the incidence of edge-loading in ceramic hips using commercially available, dynamic musculoskeletal modelling software that simulates each patient performing activities associated with edge-loading. Methodology. Eighteen patients with reproducible squeaking in their ceramic-on-ceramic total hip arthroplasties were recruited from a previous study investigating the incidence of noise in large-diameter ceramic bearings. All 18 patients had a Delta Motion acetabular component, with head sizes ranging from 40 – 48mm. All had a reproducible squeak during a deep flexion activity. A control group of thirty-six patients with Delta Motion bearings who had never experienced a squeak were recruited from the silent cohort of the same original study. They were matched to the squeaking group for implant type, acetabular cup orientation, ligament laxity, maximum hip flexion and BMI. All 54 patients were modelled performing two functional activities using the Optimized Ortho Postoperative Kinematics Simulation software. The software uses standard medical imaging to produce a patient-specific rigid body dynamics analysis of the subject performing a sit-to-stand task and a step-up with the contralateral leg, Fig 1. The software calculates the dynamic force at the replaced hip throughout the two activities and plots the bearing contact patch, using a Hertzian contact algorithm, as it traces across the articulating surface, Fig 2. As all the squeaking hips did so during deep flexion, the minimum posterior Contact Patch to Rim Distance (CPRD) can then be determined by calculating the smallest distance between the edge of the contact patch and the true rim of the ceramic liner, Fig 2. A negative posterior CPRD indicates posterior edge-loading. Results. The mean CPRD was significantly less in the squeaking group than the control group, −2.5mm and 2.9mm respectively, (p < 0.001), Fig 3. The mean pelvic tilt in the flexed seated position was 12.6° (range −13.5° to 30.3°) for the squeaking group and 5.1° (−9.8° to 26.4°) for the control group. Consequently, the mean functional cup anteversion at seat-off was significantly less in the squeaking group than the control group, 8.1° (−10.5° to 36.0°) and 21.1° (−1.9° to 38.4°) respectively (p < 0.001), Fig 3. There were 67% (12) of patients in the squeaking group that showed posterior edge-loading in the simulation compared to only 28% (10) in the control group that exhibited posterior edge-loading in the simulation. Conclusions. Acetabular cup orientation during activities associated with edge-loading are likely very different from those measured when supine. Patients with large anterior pelvic tilts during deep flexion activities might be more susceptible to posterior edge-loading and squeaking in ceramic-on-ceramic bearings, as a consequence of a significant decrease in cup anteversion. If these patients can be identified preoperatively, cup orientation and bearing choice could be customised accordingly to accommodate these individual motion patterns


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_4 | Pages 7 - 7
1 Feb 2017
Haider H Weisenburger J Garvin K
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Wear testing of THR has chaperoned generations of improved UHMWPE bearings into wide clinical use. However, previous in vitro testing failed to screen many metal-on-metal hips which failed. This talk tours hip wear testing and associated standards, giving an assortment of THR wear test results from the author's laboratory as examples. Two international hip wear-simulator standards are used: ISO-14242-1 (anatomic configuration) and ISO-14242-3 (orbital-bearing). Both prescribe 5 million (MC) force-motion cycles involving cross-shear synchronized with compression simulating walking gate of ideally aligned THRs. ISO-14242-1 imposes flexion (flex), abduction-adduction (ad-ab) and internal-external (IE) rotations independently and simultaneously. An orbital-bearing simulator more simply rotates either a tilted femoral head or acetabular component, switching from flexion-dominated to ad-ab-dominated phases in each cycle with some IE. In the latter, the acetabular component is typically placed below the femoral head to accentuate abrasive conditions, trapping third-body-wear debris. Wear is measured (ISO-14242-2) gravimetrically (or volumetrically in some hard-on-hard bearings). Wear-rate ranges from negligible to >80mg/MC beyond what causes osteolysis. This mode-1 adhesive wear can therefore “discriminate” to screen hip designs-materials in average conditions. Stair-climbing, sitting, squatting and other activities may cause THR edge-loading and even impingement with smaller head-to-neck ratios or coverage angle, naturally worse in metal-on metal hips. Deformation of thin acetabular components during surgical impaction may cause elevated friction or metal-metal contact, shedding more metal-ions and accelerating failure. Surgical misalignments in inclination angle, version and tilt can make this worse, even during modest activities in hard-on-hard bearings. Abrasive particulate debris from bone or bone-cement, hydroxyapatite, neck-impingement, normal wear, or corrosion can compound the above. Such debris can scratch the femoral head surface, or embed in the UHMWPE liner compromising the wear of even metal-on-plastic hips. Much of the belated standardization activity for higher demand hip testing is in response to the metal-metal failures. ASTM F3047M is a recent non-prescriptive guide for what more rigorous testing can generally be done. Third-body particulate can be intentionally introduced or random scratching of the femoral component surface in extra abrasion testing. Also, the compressive load can be increased, more frequent start-stops to disrupt lubrication, and steepening acetabular shell-liner angles to reduce contact area and cause edge-loading, made harsher when combined with version misalignment. Transient separation can occur between head and liner during the swing phase in a lax THR joint with low coverage angle and misalignments; the separated head impacts the liner rim when reseating. An edge-loading ISO test is currently being discussed where (so-called) “microseparation” to a known distance is directly imposed by a lateral spring force in a hip simulator. Friction testing of a THR in a pendulum-like setup undergoing flexion or abduction swings is being discussed in the ASTM, and so have multi-dimensional THR friction measurements during a long-term wear test simultaneously measuring and separating friction of three rotational (flex, ad-ab, and IE) axes. THR wear test methods continue to evolve to address more challenges such as novel duo-mobility THR designs, where UHMWPE bearings cannot be removed for gravimetric wear measurements


Orthopaedic Proceedings
Vol. 100-B, Issue SUPP_6 | Pages 38 - 38
1 Apr 2018
LaCour M Ta M Sharma A Komistek R
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Background. In vivo fluoroscopic studies have proven that femoral head sliding and separation from within the acetabular cup during gait frequently occur for subjects implanted with a total hip arthroplasty. It is hypothesized that these atypical kinematic patterns are due to component malalignments that yield uncharacteristically higher forces on the hip joint that are not present in the native hip. This in vivo joint instability can lead to edge loading, increased stresses, and premature wear on the acetabular component. Objective. The objective of this study was to use forward solution mathematical modeling to theoretically analyze the causes and effects of hip joint instability and edge loading during both swing and stance phase of gait. Methods. The model used for this study simulates the quadriceps muscles, hamstring muscles, gluteus muscles, iliopsoas group, tensor fasciae latae, and an adductor muscle group. Other soft tissues include the patellar ligament and the ischiofemoral, iliofemoral, and pubofemoral hip capsular ligaments. The model was previously validated using telemetric implants and fluoroscopic results from existing implant designs. The model was used to simulate theoretical surgeries where various surgical alignments were implemented and to determine the hip joint stability. Parameters of interest in this study are joint instability and femoral head sliding within the acetabular cup, along with contact area, contact forces, contact stresses, and ligament tension. Results. During swing phase, it was determined that femoral head pistoning is caused by hip capsule laxity resulting from improperly positioned components and reduced joint tension. At the point of maximum velocity of the foot (approximately halfway through), the momentum of the lower leg becomes too great for a lax capsule to properly constrain the hip, leading to the femoral component pistoning outwards. This pistoning motion, leading to separation, is coupled with a decrease in contact area and an impulse-like spike in contact stress (Figure 1). During stance phase, it was determined that femoral head sliding within the acetabular cup is caused by the proprioceptive notion that the human hip wants to rotate about its native, anatomical center. Thus, component shifting yields abnormal forces and torques on the joint, leading to the femoral component sliding within the cup. This phenomenon of sliding yields acetabular edge-loading on the supero-lateral aspect of the cup (Figure 2). It is also clear that joint sliding yields a decreased contact area, in this case over half of the stable contact area, corresponding to a predicted increase in contact stress, in this case over double (Figure 2). Discussion. From our current analysis, the causes and effects of hip joint instability are clearly demonstrated. The increased stress that accompanies the pistoning/impulse loading scenarios during swing phase and the supero-lateral edge-loading scenarios during stance phase provide clear explanations for premature component wear on the cup, and thus the importance of proper alignment of the THA components is essential for a maximum THA lifetime. For any figures or tables, please contact authors directly


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_3 | Pages 38 - 38
1 Jan 2016
Miki H
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In total hip arthroplasty (THA), acetabular cup orientation is critical for avoiding edge-loading and implant-implant impingement, which may lead to serious complications such as dislocation, mechanical loosening, accelerated wear, or implant breakage. Many studies recommended to place the acetabular cup radiographically at an inclination of <50° to avoid edge-loading. Simultaneously, larger prosthetic ROMs than the patients’ ROM during daily activities are needed to minimize impingement related complications. Several three-dimensional computer simulation studies have been done for optimal cup orientation to avoid prosthetic impingement within possible hip ROMs in the late 1990s. However, the reference angles in the directions of flexion, extension, external rotation and internal rotation at 90 ° flexion as possible hip ROMs have not been consistent in previous simulation studies. Thus, different reference angles of hip ROMs resulted in different optimal cup orientation. Therefore, to give accurate information about the reference hip ROM, we measured passive hip ROMs intraoperatively using a navigation system in 91 patients. Pelvic and femoral coordinate systems referred a functional pelvic plane in the supine position and a retrocondylar plane, respectively. The neutral position of the hip ROM was defined as the position in which corresponding axes of the pelvic and femoral coordinate systems were parallel. Maximum flexion, extension, external rotation and abduction were 120°, 36 °, 43 ° and 55 °, respectively. Moreover, we investigated the hip ROM during five traditional Japanese hip positions which required large hip flexion and internal rotation angles in five healthy female volunteers by a 3D image matching technique using an open-configuration MRI. Maximum flexion was 122 ° and maximum internal rotation was 40 ° at more than 90 ° of flexion position. Therefore, we recommended using 120 ° for flexion, 40 ° for extension, 40 ° for external rotation and 40 ° for internal rotation at 90 ° flexion as the reference ROM when calculating an optimum cup orientation. We calculated radiographic cup anteversion, when radiographic cup inclination was 40 °, without prosthesis impingement in the reference hip ROMs using computer aided design models of prosthesis, which included a cementless CentPillar stem with a head 32mm in diameter and cementless Trident cup with a flat liner. The results showed the optimal cup target zone existed when the stem anteversion was between 20 ° and 45 °. The size of the target zone was widest when the stem anteversion was 30 °, and then it was plus or minus 5 ° of inclination and anteversion from the center of the zone. To eliminate outliers of cup orientation form the target zone, a computer assisted system such as navigation is recommended


Orthopaedic Proceedings
Vol. 101-B, Issue SUPP_4 | Pages 40 - 40
1 Apr 2019
Vigdorchik J Cizmic Z Elbuluk A Jerabek SA Paprosky W Sculco PK Meere P Schwarzkopf R Mayman DJ
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Introduction. Computer-assisted hip navigation offers the potential for more accurate placement of hip components, which is important in avoiding dislocation, impingement, and edge-loading. The purpose of this study was to determine if the use of computer-assisted hip navigation reduced the rate of dislocation in patients undergoing revision THA. Methods and Materials. We retrospectively reviewed 72 patients who underwent computer-navigated revision THA [Fig. 1] between January 2015 and December 2016. Demographic variables, indication for revision, type of procedure, and postoperative complications were collected for all patients. Clinical follow-up was performed at 3 months, 1 year, and 2 years. Dislocations were defined as any episode that required closed or open reduction or a revision arthroplasty. Data are presented as percentages and was analyzed using appropriate comparative statistical tests (z-tests and independent samples t- tests). Results. All 72 patients (48% female; 52% male) were included in the final analysis [Fig. 2]. Mean age of patients undergoing revision THA was 70.4 ± 11.2 years. Mean BMI was 26.4 ± 5.2 kg/m. 2. The most common indications for revision THA were instability (31%), aseptic loosening (29%), osteolysis/eccentric wear (18%), infection (11%), and miscellaneous (11%). During revision procedure, polyethylene component was most commonly changed (46%), followed by femoral head (39%), and acetabular component (15%). At 3 months, 1 year, and final follow-up, there were no dislocations among all study patients (0%). Compared to preoperative dislocation values, there was a significant reduction in the rate of dislocation with the use of computer-assisted hip navigation (31% vs. 0%; p<0.05). Discussion. Our study demonstrates a significant reduction in the rate of dislocation following revision THA with the use of computer navigation. Although the cause of postoperative dislocation is often multifactorial, the use of computer-assisted surgery may help to curtail femoral and acetabular malalignment in revision THA


Orthopaedic Proceedings
Vol. 100-B, Issue SUPP_5 | Pages 54 - 54
1 Apr 2018
Pierrepont J Ellis A Walter L Marel E Bare J Solomon M McMahon S Shimmin A
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Introduction. The pelvis moves in the sagittal plane during functional activity. These movements can have a detrimental effect on functional cup orientation. The authors previously reported that 17% of total hip replacement (THR) patients have excessive pelvic rotation preoperatively. This increased pelvic rotation could be a risk factor for instability and edge-loading in both flexion and/or extension. The aim of this study was to investigate how gender, age and lumbar spine stiffness affects the number of patients at risk of excessive sagittal pelvic rotation. Method. Pre-operatively, 3428 patients had their pelvic tilt (PT) and lumbar lordotic angle (LLA) measured in three positions; supine, standing and flexed-seated, as part of routine planning for THR. The pelvic rotation from supine-to-standing and from supine-to-seated was determined from the difference in pelvic tilt measurements between positions. Lumbar flexion was determined as the difference between LLA standing and LLA when flexed-seated. Patients were stratified into groups based upon age, gender and lumbar flexion. The percentage of patients in each group with excessive pelvic rotation, defined by rotation ≥13° in a detrimental direction, was determined. Results. Posterior pelvic rotation from supine-to-stand increased with age and decreasing lumbar flexion. This was more pronounced in females. Similarly, anterior pelvic rotation from supine-to-seated increased with age and decreasing lumbar flexion. This was more pronounced in males. Notably, 30% of elderly females had excessive pelvic rotation. Furthermore, 38% of patients with lumbar flexion <20° had excessive pelvic rotation. Conclusions. Excessive pelvic rotation was more common in older patients and in patients with limited lumbar flexion. This might be a factor in the increased dislocation rate in the elderly population. A more stable articulation might be a consideration in patients with limited lumbar flexion (<20°). This constitutes 5% of the THR population. The large range of pelvic rotation in each group supports individual analysis on all patients undergoing THR


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_9 | Pages 30 - 30
1 May 2016
Pierrepont J Walter L Miles B Marel E Baré J Solomon M McMahon S Shimmin A
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Introduction. The pelvis is not a static structure. It rotates in the sagittal plane depending upon the activity being performed. These dynamic changes in pelvic tilt have a substantial effect on the functional orientation of the acetabulum. The aim of this study was to quantify the changes in sagittal pelvic position between three functional postures. Methodology. Pre-operatively, 90 total hip replacement patients had their pelvic tilt measured in 3 functional positions – standing, supine and flexed seated (posture at “seat-off” from a standard chair), Fig 1. Lateral radiographs were used to define the pelvic tilt in the standing and flexed seated positions. Pelvic tilt was defined as the angle between a vertical reference line and the anterior pelvic plane (defined by the line joining both anterior superior iliac spines and the pubic symphysis). In the supine position pelvic tilt was defined as the angle between a horizontal reference line and the anterior pelvic plane. Supine pelvic tilt was measured from computed tomography, Fig 2. Results. The mean standing pelvic tilt was −2.1° ± 7.4°, with a range of −15.2° – 15.3°. Mean supine pelvic tilt was 4.1° ± 5.5°, with a range of −9.7° – 17.9°. Mean pelvic tilt in the flexed seated position was −1.8° ± 14.1°, with a range of −31.8° – 29.1°, Fig 3. The mean absolute change from supine to stand, and stand to flexed seated was 6.9° ± 4.1° and 11.9° ± 7.9° respectively. 86.6% of patients had a more anteriorly tilted pelvis when supine than standing. 52.2% of patients had a more anteriorly tilted pelvis when seated than standing. Conclusions. The position of the pelvis in the sagittal plane changes significantly between functional activities. The extent of change is specific to each patient. Planning and measurement of cup placement in the supine position can lead to large discrepancies in orientation during more functionally relevant postures. As a result of the functional changes in pelvic position, cup orientations during dislocation and edge-loading events are likely to be significantly different to that measured from standard CT and radiographs. Optimal cup orientation is likely patient-specific and requires an evaluation of functional pelvic dynamics to pre-operatively determine the target angles


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_6 | Pages 18 - 18
1 Mar 2017
Stratton-Powell A Tipper J Williams S Redmond A Brockett C
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Introduction. Total ankle replacement (TAR) is less successful than other joint replacements with a 77% survivorship at 10 years. Predominant indications for revision include: Insert dislocation, soft tissue impingement and pain/stiffness. Insert edge-loading may be both a product and cause of these indications and was reported to affect 22% of patients with the, now withdrawn from market, Ankle Evolutive System (AES) TAR (Transysteme, Nimes, France). Compressive forces up to seven times body weight over a relatively small contact area (∼6.0 to 9.2 cm. 2. ), in combination with multi-directional motion potentially causes significant polyethylene wear and deformation in mobile-bearing TAR designs. Direct methods of measuring component volume (e.g. pycnometer) use Archimedes' principle but cannot identify spatial changes in volume or form indicative of wear/deformation. Quantitative methods for surface analysis bridge this limitation and may advance methods for analysing the edge loading phenomena in TAR. Aim. Determine the frequency of edge loading in a cohort of explanted total ankle replacements and compare the quantitative surface characteristics using a novel explant analysis method. Methods. Thirty-two AES TAR devices were implanted and retrieved by the same surgeon (UK Health Research Authority approval: 09/H1307/60). Mean implantation time was 7.8 years (1.5 to 12.1 range). Pain and/or loosening were the primary indications for revision. An Alicona Infinite microscope measured the entire superior surface of each insert (10× mag; 1.76µm lateral resolution). Abbott-Firestone curves were produced per insert to quantify the deviation of the insert surface from flat. Peak material volume (Vmp), core material volume (Vmc), core void volume (Vvc) and dale void volume (Vvv) were measured. Edge loading was identified visually by a depressed area in the insert surface indicative of articulation with the edge of the tibial component. Inserts were identified as either edge-loaded or not edge-loaded and the above analyses compared. Results. Seventeen inserts (53%) showed edge loading. Peak material volume (Vmp) was significantly increased for the edge loaded inserts 5.64 ± 5.42µm compared to the normal inserts 1.29 ± 0.954µm (Independent T-Test, P=0.005). No difference was found for the other volume parameters (Figure 2). A progressive change in insert form, beginning at the edges of the superior insert surface, was evident (Figure 1). Machining marks identified at the centre of several components supported this observation. Discussion. Insert edge loading affected 53% of TAR explants. The volume parameters showed a statistically significant inflection of material at the inserts' edge for the affected ankles. Spatial changes to insert form progressed over time in-vivo. Machining marks at the centre of several inserts remained which indicated the deformation/wear process commenced at the periphery of the insert. Normal ranges of volume change/redistribution are not established for TAR devices and the implications of insert form change are not yet understood. However, edge-loaded components composed over half of this cohort, which reflects the conflict between design simplicity and kinematic complexity. For any figures or tables, please contact authors directly (see Info & Metrics tab above).


Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_22 | Pages 26 - 26
1 May 2013
Su E
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Surface replacement of the hip has become established as an alternative treatment to total hip replacement in the younger, active, male patient. By the very nature of preserving the femoral head and neck, there may be failures due to femoral neck fracture and femoral component loosening. Additionally, revisions of hip resurfacing for acetabular loosening may be necessary. Other scientific papers have described problems that may arise as a result of the metal-on-metal bearing either due to excess metal production or an immunologic-mediated reaction to the metal debris. Grammatopolous et al. describe poor results of revisions of surface replacements due to massive tissue destruction at the time of revision surgery, persistent pain, and swelling. In my experience with hip resurfacing, this complication is extremely rare. In my series of 925 resurfacings with a minimum of 2 year follow up, 12 revisions (1.3%) have been performed. Of these revisions, only 3 (0.3%) were for complications related to the metal-on-metal bearing; 2 for edge-loading and excess metal production, and 1 for metal hypersensitivity. None of the revision cases have had abductor destruction, or nerve/vascular involvement. Reconstruction of the joint was carried out with standard and revision components; post-operative function of these patients has been comparable to that of a primary total hip replacement. With careful monitoring of the post-operative resurfacing patient, problems can be identified early and surface replacement conversion can be performed with excellent results


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_3 | Pages 20 - 20
1 Jan 2016
Marel E Walter L Solomon M Shimmin A Pierrepont J
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Malorientation of the acetabular cup in Total Hip replacement (THR) may contribute to premature failure of the joint through instability (impingement, subluxation or dislocation), runaway wear in metal-metal bearings when the edge of the contact patch encroaches on the edge of the bearing surface, squeaking of ceramic-ceramic bearings and excess wear of polyethylene bearing surfaces leading to osteolysis. However as component malorientation often only occurs in functional positions it has been difficult to demonstrate and often is unremarkable on standard (usually supine) pelvic radiographs. The effects of spinal pathology as well as hip pathology can cause large rotations of the pelvis in the sagittal plane, again usually not recognized on standard pelvic views. While Posterior pelvic rotation with sitting increases the functional arc of the hip and is protective of a THR in regards to both edge loading and risk of dislocation, conversely Anterior rotation with sitting is potentially hazardous. We developed a protocol using three functional positions – standing, supine and flexed seated (posture at “seat-off” from a standard chair). Lateral radiographs were used to define the pelvic tilt in the standing and flexed seated positions. Pelvic tilt was defined as the angle between a vertical reference line and the anterior pelvic plane. Supine pelvic tilt was measured from computed tomography. Proprietary software (Optimized Ortho, Sydney) based on Rigid Body Dynamics then modelled the patients’ dynamics through their functional range producing a patient-specific simulation which also calculates the magnitude and direction of the dynamic force at the hip and traces the contact area between prosthetic head/liner onto a polar plot of the articulating surface. Given prosthesis specific information edge-loading can then be predicted based on the measured distance of the edge of the contact patch to the edge of the acetabular bearing. Results and conclusions. The position of the pelvis in the sagittal plane changes significantly between functional activities. The extent of change is specific to each patient. Spinal pathology can be an insidious “driver” of pelvic rotation, in some cases causing sagittal plane spinal imbalance or changes in orientation of previously well oriented acetabular components. Squeaking of ceramic on ceramic bearings appears to be multi factorial, usually involving some damage to the bearing but also usually occurring in the presence of anterior or posterior edge loading. Often these components will appear well oriented on standard views [Fig 1]. Runaway wear in hip resurfacing or large head metal-metal THR may be caused by poor component design or manufacture or component malorientation. Again we have seen multiple cases where no such malorientation can be seen on standard pelvic radiographs but functional studies demonstrate edge loading which is likely to be the cause of failure [Fig 2]. Clinical examples of all of these will be shown


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_2 | Pages 12 - 12
1 Jan 2016
Liu F Gross TP
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Dysplasia has long been identified as a high-risk group for total hip replacement(THR). The underlying causes include younger age, underlying joint deformity, and greater tissue laxity. A higher failure rate has also been identified for hip resurfacing arthroplasty (HRA) in these patients. Many experts have advised avoiding HRA in these patients, although comparative studies are not available. We do not practice patient selection, because THR has not been proven any more reliable for these patients. Instead, we have taken the approach of studying the causes of failure and finding methods to improve the results of HRA in dysplasia patients. We have identified three primary failure modes for the young women who typically have dysplasia: failure of initial acetabular ingrowth (FAI), adverse wear related failure (AWRF), and early femoral failure (EFF: femoral neck fracture and head collapse). Improvements in technique to address all of these failure modes were in place by 2008: acetabular components with supplemental fixation for severe deformities (trispike), guidelines and intraoperative x-ray techniques to eliminate malpositioned acetabular components resulting in edge-loading, uncemented femoral fixation and a bone management protocol that has eliminated early femoral failure. Group I includes 142 cases done before 2008 and Group II includes 168 cases with minimum 2-year follow-up done after this date. Two-year failure rates improved from 5% (8/142) to 0.6% (1/168) and 5-year Kaplan-Meier survivorship improved from 93% to 99%. In Group II we have had only one failure (femoral neck fracture) in 168 dysplasia cases with 2–5 year follow-up. There have been no failures of acetabular ingrowth, no AWRF, no femoral head collapse, no failures of femoral ingrowth, no femoral loosenings, no dislocations and no nerve palsies. All acetabular components placed since 2008 meet our published RAIL (relative acetabular inclination limit) guidelines, which we have shown to be 99% reliable in avoiding high on levels and AWRF. Both groups were 70% female. With a mean bearing size 48mm (high-risk for HRA). There was also no differences in DEXA scan T score, BMI, ASA score, length of incision (4 inches) HHS, or patients participating in impact sports (UCLA activity score 9&10). In Group II the mean age was 3 years greater (52), the mean operative time was 20 minutes shorter (96 minutes), estimated blood loss was 120 ml less (140ml) and the mean hospital stay was one day shorter (2 days) probably reflective of greater experience in this single surgeon series. We have demonstrated that with sufficient surgeon experience and properly designed implants, hip resurfacing can be performed with a failure rate that is lower than most reports on THR for this disorder


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_3 | Pages 19 - 19
1 Jan 2016
Marel E Walter L Solomon M Shimmin A Pierrepont J
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Achieving optimal acetabular cup orientation in Total Hip Replacement (THR) remains one of the most difficult challenges in THR surgery (AAOR 2013) but very little has been added to useful understanding since Lewinnek published recommendations in 1978. This is largely due to difficulties of analysis in functional positions. The pelvis is not a static reference but rotates especially in the sagittal plane depending upon the activity being performed. These dynamic changes in pelvic rotation have a substantial effect on the functional orientation of the acetabulum, not appreciated on standard radiographs [Fig1]. Studies of groups of individuals have found the mean pelvic rotation in the sagittal plane is small but large individual variations commonly occur. Posterior rotation, with sitting, increases the functional arc of the hip and is protective of a THR in regards to both edge loading and risk of dislocation. Conversely Anterior rotation, with sitting, is potentially hazardous. We developed a protocol using three functional positions – standing, supine and flexed seated (posture at “seat-off” from a standard chair). Lateral radiographs were used to define the pelvic tilt in the standing and flexed seated positions. Pelvic tilt was defined as the angle between a vertical reference line and the anterior pelvic plane (defined by the line joining both anterior superior iliac spines and the pubic symphysis). In the supine position pelvic tilt was defined as the angle between a horizontal reference line and the anterior pelvic plane. Supine pelvic tilt was measured from computed tomography. Proprietary software (Optimized Ortho, Sydney) based on Rigid Body Dynamics then modelled the patients’ dynamics through their functional range producing a patient-specific simulation which also calculates the magnitude and direction of the dynamic force at the hip and traces the contact area between prosthetic head/liner onto a polar plot of the articulating surface, Fig 2. Given prosthesis specific information edge-loading can then be predicted based on the measured distance of the contact patch to the edge of the acetabular liner. Delivery of desired orientation at surgery is facilitated by use of a solid 3D printed model of the acetabulum along with a patient specific guide which fits the model and the intra-operative acetabulum (with cartilage but not osteophytes removed) - an incorporated laser pointer then marks a reference point for the reamer and cup inserter to replicate the chosen orientation. Results and conclusions. The position of the pelvis in the sagittal plane changes significantly between functional activities. The extent of change is specific to each patient. Spinal pathology is a potent “driver” of pelvic sagittal rotation, usually unrecognised on standard radiographs. Pre-operative patient assessment can identify potential orientation problems and even suitability for hard on hard bearings. Optimal cup orientation is likely patient-specific and requires an evaluation of functional pelvic dynamics to pre-operatively determine the target angles. Post-operatively this technique can identify patient and implant factors likely to be causing edge loading leading to early failure in metal on metal bearings or squeaking in ceramic on ceramic bearings


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXVIII | Pages 183 - 183
1 Sep 2012
Amin A Sproule JA Chin T Daniels TR Younger AS Boyd G Glazebrook M
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Purpose. Total Ankle Replacement (TAR) is increasingly being offered to patients as an alternative to arthrodesis for the operative management of debilitating end-stage ankle arthritis. The Mobility Total Ankle System is a third-generation design consisting of a three component, cementless, unconstrained, mobile-bearing prosthesis. This study reports the early results of a multi-centre prospective study of the Mobility prosthesis. This is the first such report by independent researchers. Method. The senior authors implanted 86 consecutive Mobility prostheses. The underlying diagnosis was primary OA in 24 ankles, secondary OA in 47 ankles and inflammatory arthritis in 15 ankles. There were 41 males (Mean age 67 / Range 51–87) and 44 females (Mean age 60 / Range 29–72). The mean BMI was 28 (Range 22–36) for males, and 28 (Range 20–39) for females. Previous ankle operations were performed in 24 patients, 22 of which were for fracture fixation. Ankles were classified according to the COFAS end-stage ankle arthritis classification system. Coronal plane deformity was quantified pre-operatively. Clinical outcome was assessed using the AOFAS hindfoot score. Radiological assessment was performed from weight-bearing radiographs, documenting post-operative alignment, osseous integration, edge-loading and heterotopic bone formation. The mean follow-up time was 40 months (Range 30–60). Survival analysis was calculated according to the Kaplan-Meier method. Failure was defined as exchange of any component of the TAR, arthrodesis or amputation. Results. Type 1 ankle arthritis was demonstrated in 54 ankles (63%). No patient had pre-operative coronal plane angulation > 20. In 30 ankles (35%), the pre-operative coronal alignment was neutral, and in 32 ankles (37%), the deformity was < 10. The mean AOFAS hindfoot score improved from 37.4 (Range 12–59) pre-operatively to 77.9 (Range 51–100) post-operatively. 78 (90%) of prosthetic components were implanted within 5 of the optimal position. Bone-implant interface abnormalities were identified in 16 ankles (18%). In total, 5 TARs required revision, 4 for aseptic loosening and one for component malpositioning. There was one conversion to arthrodesis, and one BKA for CRPS. 30 simultaneous procedures were performed in 28 patients. The most common was gastrocnemius recession. There were 8 re-operations, most commonly for impingement due to peri-articular ossifications. Delayed wound healing occurred in 3 patients, and there was one case of deep infection. There were 5 patients that sustained fractures of the medial malleolus: 2 were intra-operative, and underwent internal fixation. There are 6 patients being investigated for ongoing pain. The 2-year survival was 96.4% (95% CI 89.4–99.1) and 3-year survival was 91.7% (95% CI 83.3–96.3). Conclusion. Although early results of the Mobility TAR are encouraging for independent researchers, they do not match those reported by designer surgeons. Most patients achieve good pain relief and improved function post-operatively


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXV | Pages 26 - 26
1 Jun 2012
Su E Chotai P
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Introduction. Alumina Ceramic liners are increasingly used in patients undergoing Total Hip Replacement (THR). The rate of fracture of ceramic liner is decreasing with improved manufacturing techniques from 1. st. to 3. rd. generation alumina-ceramic liners. We report the first case of a fracture of a modern, 4. th. generation alumina bearing ceramic liner, which incorporates a metal sheath to help avoid fracture. Our case is a 60 years old female presenting two years and three months after a bilateral total hip replacement using Stryker Trident cup, securfit stem and alumina on alumina bearing ceramic liner. Ceramic liners are commonly used, especially in young patients because of their excellent biocompatibility, low wear rate and superior tribology. Although fracture of ceramic liner is a less common complication of modern total hip arthroplasty, it is a major concern with the use of ceramic on ceramic THR, the reason being brittleness of ceramic. Cases of 3. rd. generation ceramic liner fracture have been reported which might be associated with impingement due to excessive anteversion of the socket in Asian patients who habitually squat. Habitual squatting, sitting cross legged and kneeling were not characteristic of this case. Methods. The patient presented with complains of mechanical grinding in left hip. She also reported a past history of clicking sound from left hip on extension of left hip and long stride gait. There was no history of trauma or fall. On examination she had a nonantalgic gait and left hip had audible and palpable crepitations. The range of motion on left hip was intact with no subluxation. Right hip was symptom free and examination did not detect any abnormalities. Evaluation & Results. Radiographs of left hip revealed eccentric positioning of the head [Fig. 1] within the socket and excessive anteversion of the socket, which likely caused edge-loading in extension, leading to catastrophic failure in form of fracture of ceramic liner on left hip. She was treated with revision surgery using polyethylene liner with metal head. Intra-operative findings confirmed the ceramic liner fracture [Fig. 2] and revealed impingement of the metal neck against the metal rim of the liner. Discussion & Conclusion. Although ceramic on ceramic hips have excellent wear properties, it is subject to fracture due to its brittle nature. This can lead to catastrophic failure with edge loading. In this case, the alumina-ceramic liner fractured; despite of being surrounded by a metal rim to prevent fracture. It fractured at the anterior edge, which is where it was loaded in extension. We believe that careful attention must be paid not only to inclination, but version of the socket, so as to avoid this complication. Other factors which might lead to such complication are obesity, high activity level, improper manufacturing teachniques for ceramic liners and entrapment and impingement of a micromm sized foreign body between ceramic liner and prosthetic head which initiates wear


Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_15 | Pages 30 - 30
1 Mar 2013
Yoon J Duff ML Johnson A Takamura K Ebramzadeh E Campbell P Amstutz HC
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It has been suggested that metal ion levels are indicative of in vivo bearing performance of metal-on-metal hip replacements. A cobalt or Chromium level of 7μg/L or higher is proposed to be indicative of a bearing malfunction and the need for clinical intervention. Component design, size, acetabular orientation, patient gender and activity level have been suggested as factors leading to accelerated wear and elevated metal ions. The contact patch to rim (CPR) distance is a calculation that describes the distance from the point where a theoretical joint reaction force intersects the cup to the acetabular rim for a patient in standing position, dependent on the coverage, size, and orientation of the acetabular component. It has been suggested that CPR distance determines the hip joint susceptibility to edge loading, and the risk for increased wear and high ion levels (Langton et al JBJS Br 91: 2009). This study examined the effects of patient activity, gender, and CPR distance on serum metal ion concentrations in a series of patients treated with one type of metal on metal hip resurfacing arthroplasty (MMHRA) performed by one surgeon. 182 patients (73 females and 109 males)with a unilateral Conserve Plus (WMT, TN USA) MMHRA and had who had provided blood for metal ion analysis data from December 2000 to June 2011 were retrospectively studied. Only measurements made more than 12 months after surgery were included in order to exclude hips that had yet to reach steady-state wear. For patients with multiple draws, the most recent qualifying draw was used. Activity level was assessed by the UCLA activity score. The mean age was 51.5 years (20.0 to 77.5 years). The mean follow-up time for the last blood draw was 70 months (range, 12 to 165). Serum cobalt (CoS) and chromium (CrS) levels were analyzed using inductively coupled plasma mass spectrometry in a specialized trace element lab. Using acetabular abduction and anteversion measured by EBRA, component size, and reported coverage angle of the acetabular component, the CPR distance was calculated as previously described. Multiple logistic regression was performed to identify significant relationships between high metal ion levels (7 μg/L or greater) and gender, activity and CPR distance. The median CoS level for the entire cohort was 1.13 μg/L (range, 0.15 to 175.30), and the median CrS level was 1.49 μg/L (range, 0.06 to 88.70). The average CPR distance was 13.8 mm (range, 3.2 to 22.1). There was a significant association between low CPR values and CoS and CrS. There was a 37-fold increase in the risk of CoS >7μg/L (p=0.005) and 11-fold increase in the risk of CrS > 7μg/L (p=0.003) when CPR distance was 10 mm or less. No associations were shown for gender and UCLA activity scores. CPR distance was found to be a reliable predictor of ion levels > 7μg/L and appears to be a useful indicator to evaluate the multi-factorial process of edge-loading and wear. Patients with a low CPR distance should be monitored for increased metal ion levels