This study presents an unusual recurrent case of pigmented villonodular synovitis (PVNS) around a ceramic-on-metal (COM) hip retrieved at 9-years. PVNS literature relates to metal-polyethylene and ceramic-ceramic bearings. Amstutz reported 2 cases with MOM resurfacing and Xiaomei reported PVNS recurring at 14 years with metal-on-polyethylene THA. Friedman reported on PVNS recurrence in a ceramic THA. Ours may be the first reported case of recurrent PVNS of a ceramic-on-metal articulation.

This young female patient (now 38-years of age) had a total hip replacement in 2006 for PVNS in her left hip. In her initial work-up, this case was presumed to be a pseudotumor problem, typical of those related to CoCr debris with high metal-ion concentrations. She had an CoCr stem (AML), 36mm Biolox-delta head (Ceramtec), and a Pinnacle acetabular cup with CoCr liner (Ultramet, Depuy J&J). This patient had no concerns regarding subluxation, dislocation or squeaking. Three years ago she complained of mild to moderate groin and thigh pain in her left hip. This worsened in the past year. She noticed increased swelling now with an asymmetry to her right hip. She went to the emergency room in Dec-2014 and was referred to a plastic surgeon. In our consult we reviewed MARS-MRI and CT-scans that demonstrated multiple mass lesions surrounding the hip. Laboratory results presented Co=0.7, Cr=0.3 ESR=38 and Crp=0.3.

At revision surgery, the joint fluid was hemorrhagic/bloody with hemosiderin staining the soft tissues. Multiple large 4–5×5cm nodules were present in anterior aspect of the hip as well as multiple nodules surrounding posterior capsule and sciatic nerve. Pathology demonstrated a very cellular matrix with hemosiderin-stained tissue and multiple giant cells, which was judged consistent with PVNS. The trunnion showed no fretting, no contamination and no discoloration. The superior neck showed impingement due to low-inclination cup. There was minimal evidence of metal-debris staining the tissues. There was a large metallic-like stripe across the ceramic head.

This is a particularly interesting case and may be the first reported recurrent PVNS around a ceramic-on-metal bearing (COM). Data is scant regarding clinical results of COM bearings and here we have a nine-year result in a young and active female patient. She was believed to have a metalosis-related pseudotumor yet her metal-ion levels were not alarmingly high and there was no particular evidence of implant damage or gross wear products. In addition, the CoCr trunnion appeared pristine. Our work-up continues with analyses of wear and histopath-evidence. This case may demonstrate the need for a broadening of the differential diagnosis when dealing with hip failures.

The treatment of patients with osteoarthritis of the knee and associated extra-articular deformity of the leg is challenging. Current teaching recognises two possible approaches: (1) a total knee replacement (TKR) with intra-articular bone resections to correct the malalignment or (2) an extra-articular osteotomy to correct the malalignment together with a TKR (either simultaneously or staged).

However, a number of these patients only have unicompartmental knee osteoarthritis and, in the absence of an extra-articular deformity would be ideal candidates for joint preserving surgery such as unicompartmental knee replacement (UKR) given its superior functional outcome and lower cost relative to a TKR [1).

We report four cases of medial unicondylar knee replacement, with a simultaneous extra-articular osteotomy to correct deformity, using novel 3D printed patient-specific guides (Embody, UK) (see Figure 1). The procedure was successful in all four patients, and there were no complications. A mean increase in the Oxford knee score of 9.5, and in the EQ5D VAS of 15 was observed.

To our knowledge this is the first report of combined osteotomy and unicompartmental knee replacement for the treatment of extra-articular deformity and knee osteoarthritis. This technically challenging procedure is made possible by a novel 3D printed patient-specific guide which controls osteotomy position, degree of deformity correction (multi-plane if required), and orientates the saw-cuts for the unicompartmental prosthesis according to the corrected leg alignment.

Using 3D printed surgical guides to perform operations not previously possible represents a paradigm shift in knee surgery. We suggest that this joint preserving approach should be considered the preferred treatment option for suitable patients.

Use of “CPR” distance has proven clinical utility in stratifying risks of “steep cups” in MOM failures.[1, 4] The CPR indice has been defined as distance between point of intersection of the hip reaction force (Fig. 1: vector-R in contact patch) and closest point on the inner cup rim.[4] However, the CPR indice has limitations. It assumes that, (1) the hip load-vector (R) will be angled 10°-medial in all patients, (2) the contact patch will be same size in all patients, and (3) the contact patch will be invariant with increasing MOM diameter. In contrast it is known from retrieval studies that larger MOM bearings created much larger wear patches.[3] Furthermore, the size of cup wear-patches in MOM bearings can now be estimated with some certainty using simulator wear data.[2] Our objective was to develop an algorithm that would predict (i) contact-patch size for all cup designs and diameters, (ii) determine actual margin of safety (Fig. 1: MOS) for different laterally-inclined cups, and (iii) predict critical test angles for “steep” cup studies in hip simulators.

The ‘CPR-distance’ (Fig. 1) is subtended by the CPA angle, but the true margin of safety is the distance from edge of wear patch to cup rim, indicated here by MOS angle. In this algorithm the wear-patch size (CAP angle) is a key parameter, as derived from MOM wear data (Fig. 2). The CAP angles decrease with increasing MOM diameter, as defined by strong linear trend (R=0.998). The key 2nd parameter is cup inclination angle that juxtaposes the wear-pattern to the cup rim (CCI). For hemispherical cups the critical inclination is given by CCI = 90 – CAP/2, where articulation angle ABA = 180o. The cup bearing-surface is typically reduced < 180o(sub-hemispherical profile, instrumentation groove, rim bevel, etc). These effects are grouped under ‘rim-detail’, as defined by RD = (180-ABA)/2 (Fig. 1). Thus critical inclination any cup is given by CCI = 90o – (CAP/2) – RD = (ABA – CAP)/2. The margin-of-safety (Fig. 1) is then represented by the equation MOS = 100 – (CIA + CAP/2 + RD).

Applicability of the new algorithm can be visualized with a 48mm MOM (cup ABA=160o) run in a standard simulator test (Fig. 3). The algorithm predicts that with cup at 40o inclination there is good margin of safety (11.8o), representing a 5mm distance. This would become much reduced at CIA = 50o, while true edge-wear appears at the 60o test inclination (Fig. 3. EW = −8.2o). For clinical comparison with ‘CPR-distances’, the algorithm shows that positioning the wear patch 10o-medial (Figs. 1, 3) has margin of safety averaging 11.5 mm (MOS) less than was predicted by the CPR indice. While CPR has shown clinical utility, it is believed that compensating for actual size of cup wear-patterns provides a more realistic risk assessment for different MOM diameters in different cup positions. Thus the new algorithm permits accurate depiction of cup wear-patterns for use in both clinical and simulator studies.

Introduction

Patient Specific Instrumentation (PSI) has the potential to allow surgeons to perform procedures more accurately, at lower cost and faster than conventional instrumentation. However, studies using PSI have failed to convincingly demonstrate any of these benefits clinically. The influence of guide design on the accuracy of placement of PSI has received no attention within the literature.

Our experience has suggested that surgeons gain greater benefit from PSI when undertaking procedures they are less familiar with. Lateral unicompartmental knee replacement (UKR) is relatively infrequently performed and may be an example of an operation for which PSI would be of benefit. We aimed to investigate the impact on accuracy of PSI with respect to the area of contact, the nature of the contact (smooth or studded guide surfaces) and the effect of increasing the number of contact points in different planes.

Metal-on-metal retrieval studies indicated that MOM wear-rates could rise as high as 60–70mm3/year in short-term failures (Morlock, 2008). In contrast, some MOM and ceramic-on-ceramic (COC) devices of 1970's era performed admirably over 2–3 decades (Schmalzreid, 1996; Shishido, 2003). While technology has aided analysis of short-term MOM and COC failures (Morlock 2008; Lord 2011), information on successful THA remains scant. Lack of long-term data creates difficulties in setting benchmarks for simulator studies and establishing guidelines for use in standards. In this study we compared clinical and wear histories for a 30-year MOM and a 32-year COC to establish such long-term, wear-rates.

The McKeeTM retrieval was cemented and made 100% of CoCr alloy (Fig. 1a). This patient had a right femoral fracture at 47 years of age, treated by internal-fixation, which failed. Her revision with a Judet implant also failed, leaving her right hip as a Girdlestone. At the age of 68, she had a McKee THA implanted in left hip, and used it until almost 98 years of age (Campbell, 2003). The COC case was a press-fit AutophorTM THA, head and cup made of alumina ceramic, with the only metal being the CoCr stem (Fig. 1c). This was implanted in a female patient 17-years of age active in sports (water-skiing). This modular THA was revised 32-years later due to hip pain from cup migration. Wear on these implants was identified by stereomicroscopy and stained red for photography (Fig. 1). Cup-to-neck impingement was denoted by circumferential neck notching, roughness was assessed by interferometry, and wear determined by CMM (Lord, 2011).

McKee head wear covered 1092mm2 area (Figs. 1a, 2: hemi-area ratio 58%). There was no stripe wear and head roughness was 36nm (Ra). Cup wear covered an area of 1790mm2 (hemi-area 63%). Circumferential damage was noted on the supero-posterior femoral neck with scuff marks also on posterior collar (Fig. 2c). Head and cup wear amounted to 37.7 and 25.2mm3, respectively. Total MOM wear was 62.9mm3, indicating a wear-rate of 2.1mm3/year.

Ceramic head wear consisted of two circular patterns (Fig. 1c), the major one of area 1790mm2 (hemi-area 79%). No wear stripes were identified. Non-worn and extensively worn surfaces had roughness (Ra) 17nm and 123nm, respectively. The cup showed 360o circumferential arc of rim wear with a small, non-wear zone inferiorly (Fig. 1c). Gray metallic transfer was evident, EDS revealing Co and Cr (Fig. 3a). Head and cup wear volumes were 77.2 and 54mm3, respectively. Total COC wear amounted to 131.2mm3 indicating a wear-rate of 4.1mm3/year.

These two THA functioned successfully over 3 decades. The McKee retrieval had minor signs of impingement but no adverse “stripe wear”. This MOM performed satisfactorily due to good positioning and patient's advanced age (68 to 98Yrs of age). The COC patient was 17 years of age at index surgery and active. The ceramic cup showed 360o of edge wear, CoCr transfer and a COC wear-rate double that of the MOM retrieval. Thus the high ceramic wear-resistance protected this youthful patient.

The purpose of this study was to determine the survivorship for a MOM implant series performed by a single community surgeon followed using a practical clinical model. A retrospective cohort of 104 primary MOM THA procedures (94 patients) were all performed by one surgeon at three local hospitals now with 10–13 years follow-up. Sixteen patients are deceased and 16 patients have been lost to follow-up. In the remaining 62 patients, 8 are bilateral providing a total of 70 THA for study. The clinical follow-up model included: hip scores, X-rays, ultrasound, and metal ion concentrations (Co, Cr, Ti). Due to the diversity of patient location, a variety of clinical labs were utilized for metal ions. Statistical methods included Kaplan-Meier survival curve and One-way ANOVA. Hip scores were available for 70 THA and of these 61 had a hip score (HHS) above 80 (87%). X-rays were available for 49 hips and of these 38 (78%) had lateral/version angles in the safe zone (Fig 1: inclination ≤ 55 and anteversion ≤ 35). Thirty-eight ultrasound exams were performed and of these three yielded fluid collections (8%). Metal ion concentrations were documented in 39 of 62 patients (63%, either serum or whole blood). Six outliers were identified with high concentrations of metal ions (Fig 2); Co 0.3–143.9 ppb (median 3.6), Cr 0.2–200.3 ppb (median 2.2) and Ti 2-110 ppb (median 54). Six patients were revised by the original surgeon. Three of six with elevated ions were documented as wear problems and the other three were revised for infection, femur fracture and metal-ion sensitivity. The survivorship of 92.5% at 10 years (Fig. 3) may be partly due to the exclusive use of antero-lateral approach performed by one surgeon with 78% of cups well placed and the MOM design used exclusively.

Explanations for “bearing” noise in ceramic-on-ceramic hips (COC) included stripe-wear formation and loss of lubrication leading to higher friction. However clinical and retrieval studies have clearly documented stripe wear in patients that did not have squeaking. Seldom highlighted has been the risk of metal-on-metal or metal-on-ceramic impingement present in total hip arthroplasty (THA) with metal and ceramic cup designs. The limitation in THA positioning studies has been (i) reliance on 2-dimensional radiographic images and (ii) patients lying supine on the examination table, thus not imaged in squeaking positions. We collected eleven squeaking COC cases for an EOS 3D-imaging functional study. Hip positions were documented in each patient's functional ‘squeaking’ posture using standard and 3-D EOS images for sitting, rising from a chair, hip extension in striding, and single-legged stance.

EOS imaging documented for the 1st time that postural dysfunctions with potential impingements were demonstrable for each squeaking case. The 1st major insight in this study came from a female patient who complained of squeaking while walking in flat-soled shoes (Figs. 1a, b). She found that when wearing high-heeled shoes her hip stopped squeaking (Figs. 1c, d). Her lateral EOS view in standing position with heeled shoes revealed that the femoral stem had approximately 3o less hyper-extension compared to flat shoes (Figs. 1b, d, arrows #1,3). The three-dimensional ‘sky-view’ EOS reconstruction of pelvis and femurs (Fig. 2) showed that her femur was also more internally rotated when she wore heels. These subtle shifts in position changed her COC hip from one of squeaking to non-squeaking. A squeaking male patient observed similar postural effects while walking up his boat ramp but not going down the ramp. In both cases, the squeaking was a consequence of cup impinging on a metal femoral neck. Thus the primary cause of squeaking appeared to be hip impingement, i.e. repetitive subluxations that patients generally were not aware of. Another case is representative of situations due to atypical and subtle cup/stem mal-adjustments (Fig. 3); frontal pelvic-tilt, thoracolumbar scoliosis, with 1cm of femur lengthening and a significant increase of offset are observed. Also evident was the femoral-neck retroversion in both standing and sitting. Squeaking occurred when modification of the functional neck orientation occured in one-legged stance (Fig. 3c) or when climbing a stair (Fig. 3d).

It was apparent in our EOS studies that patient functionality controlled whether squeaking occurred or not. Thus the new data indicated COC squeaking was a three-fold consequence of component positioning, spine and pelvic adaptions, and variations in patient posture. One limitation here is that our conclusions are based on a small sample of patients and may not be applicable to all. A consequence of such repetitive impingement can be cup rim damage and neck-notching, with release of metal debris. It is well documented that retrieved ceramic bearings are frequently stained black. Thus hip squeaking may likely result from (i) impingement and secondarily (ii) due to ingress of metal particles, and then (iii) producing a failure of lubrication.

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Retrieval studies of metal-on-metal (MOM) resurfaced hips revealed cup “edge wear” as a common failure mechanism [Morlock-2008]. Retrieval analysis of total hip arthroplasty (THA) also demonstrated extensive rim wear (Fig. 1: 190–220o arcs), typically across the superior cup [Clarke-2013]. Such wear patterns have not been demonstrated in hip simulator studies. The simulator “steep cup” models typically had motion arcs (flexion, etc.) input via the femoral head [Leslie-2008, Angadji-2009]. With fixed-inclination cups this produces constant loading of cup rim against the head (Fig. 2a). This is unlikely to be the physiological norm, unless patients walk constantly on the rims of mal-positioned cups. More likely the patients produce edge-wear intermittently due to functional and postural variations. Therefore a novel simulator model is proposed in which the cup undergoes edge-wear intermittently at one extreme of flexion (Fig. 2a). Our study objective using this new simulator model (Fig. 2a, b) was to (i) demonstrate MOM wear-rates and wear patches as a function of these dynamic-inclinations (40 o, 50 o, 70o), and (ii) compare the simulator data to MOM retrievals (Fig. 1).

Two simulator studies were run, both using 60mm MOM. Four bearings were run to 1-million cycles (1Mc) with cups peaking at 40 and 50° dynamic-inclinations, thus providing control data with no edge-wear. In 2nd study, 4 MOM were run with cups given a dynamic-inclination of 70° to produce edge-wear effects. In study-2 currently at 2.5Mc duration, the femoral heads showed the two classical wear phases with run-in at 1.7mm³/Mc and steady-state at 0.084mm³/Mc (Fig. 3a). Wear-rate for cups at 2.34mm³/Mc was 40% higher than heads and continued to rise linearly with time (Fig. 3a). At 2.5Mc, cup wear averaged ×5.7 greater than heads and resulting wear-patterns extended 85°−225° around cup rim (Fig. 3b: average 151°). In study-1, wear patches in cups with 40° dynamic-inclination approached within 12.4mm of the cup rim as denoted by circumferential grooves. This margin-of-safety (MOS) represented a 24°angle. The cup wear-patch averaged area of 1,760mm2. With cups run at 70o dynamic-inclination, the wear patches were transferred an additional 30o towards the rim thereby representing a 6° transfer across the rim.

This is the 1st wear study to use the new dynamic-inclination test mode to better simulate cup function in vivo. It was particularly satisfying to see the similarity in wear-patterns between retrieval (Fig. 1) and simulator cups (Fig. 3b). It is also the 1st study to monitor sites and magnitudes of cup wear areas and to purposely produce “edge wear”. The cups with 40° and 50° dynamic-inclinations had large margins of safety. With 70° dynamic-inclination the margin of safety was lost - effectively there was a 6° transfer of the wear patch across the cup rim. Even this apparently small effect at one location in each gait cycle sufficiently perturbed MOM performance that wear increased by an order of magnitude. Notably this was all cup wear and not by femoral head participation. The study continues but at 2.5Mc duration the cups revealed 5-fold greater wear than heads.

Introduction

Opening wedge high tibial osteotomy is an attractive surgical option for physically active patients with early osteoarthritis and varus malalignment. Unfortunately use of this surgical technique is frequently accompanied by an unintended increase in the posterior tibial slope, resulting in anterior tibial translation, and consequent altered knee kinematics and cartilage loading(1).

To address this unintended consequence, it has been recommended that the relative opening of the anteromedial and posterolateral corners of the osteotomy are calculated pre-operatively using trigonometry (1). This calculation assumes that the saw-cut is made parallel to the native posterior slope; yet given the current reliance on 2D images and the ‘surgeon's eye’ to guide the saw-cut, this assumption is questionable.

The aim of this study was to explore how accurately the native posterior tibial slope is reproduced with a traditional freehand osteotomy saw-cut, and whether novel 3D printed patient-specific guides improve this accuracy.

The knee joint displays a wide spectrum of laxity, from inherently tight to excessively lax even within the normal, uninjured population. The assessment of AP knee laxity in the clinical setting is performed by manual passive tests such as the Lachman test. Non-invasive assessment based on image free navigation has been clinically validated and used to quantify mechanical alignment and coronal knee laxity in early flexion. When used on cadavers the system demonstrated good AP laxity results with flexion up to 40°. This study aimed to validate the repeatability of the assessment of antero-posterior (AP) knee joint laxity using a non-invasive image free navigation system in normal, healthy subjects.

Twenty-five healthy volunteers were recruited and examined in a single centre. AP translation was measured using a non-invasive navigation system (PhysioPilot) consisting of an infrared camera, externally mounted optical trackers and computer software. Each of the volunteers had both legs examined by a single examiner twice (two registrations). The Lachman test was performed through flexion in increments of 15°. Coefficients of Repeatability (CR) and Interclass Correlation Coefficients (ICC) were used to validate AP translation. The acceptable limits of agreement for this project were set at 3mm for antero-posterior tibial translation.

The most reliable and repeatable AP translation assessments were at 30° and 45°, demonstrating good reliability (ICC 0.82, 0.82) and good repeatability (CR 2.5, 2.9). The AP translation assessment at 0°, 15°, 75° and 90° demonstrated moderate reliability (ICC ≤ 0.75), and poor repeatability (CR ≥3.0mm).

The non-invasive system was able to reliably and consistently measure AP knee translation between 30° and 45° flexion, the clinically relevant range for this assessment. This system could therefore be used to quantify abnormal knee laxity and improve the assessment of knee instability and ligamentous injuries in a clinic setting.

Purpose:

To evaluate if adding clonidine to a standard nerve root block containing local anaesthetic and steroid improved the outcome of patients with severe lumbar nerve root pain secondary to MRI proven lumbar disc prolapse.

Introduction

Over 40-years the dominant form of implant fixation has been bone cement (PMMA). However the presence of circulating PMMA debris represents a 3rd-body wear mechanism for metal-on-polyethylene (MPE). Wear studies using PMMA slurries represent tests of clinical relevance (Table 1). Cup designs now use many varieties of highly-crosslinked polyethylene (HXPE) of improved wear resistance. However there appears to be no adverse wear studies of vitamin-E blended cups.1–4 The addition of vitamin E as an anti-oxidant is the currently preferred method to preserve mechanical properties and ageing resistance of HXPE. Therefore the present study examined the response of vitamin-E blended liners to PMMA abrasion combined with CoCr and ceramic heads. The hip simulator wear study was run in two phases to compare wear with, (i) clean lubricants and (ii) PMMA slurries.

Metal-on-metal (MOM) retrieval studies have demonstrated that CoCr bearings used in total hip arthroplasty (THA) and resurfacing (RSA) featured stripe wear damage on heads, likely created by rim impact with CoCr cups.^1-3 Such subluxation damage may release quantities of large CoCr particles that would provoke aggressive 3^rd-body wear. With RSA, the natural femoral neck reduces the head-neck ratio but avoids risk of metal-to-metal impingement (Fig. 1).⁴ For this study, twelve retrieved RSA were compared to 12 THA (Table 1), evaluating, (i) patterns of habitual wear, (ii) stripe-wear damage and (iii) 3^rd-body abrasive scratches. Considering RSA have head/neck ratios much lower than large-diameter THA, any impingement damage should be uniquely positioned on the heads.

Twelve RSA and THA retrievals were selected with respect to similar diameter range and vendors with follow-up ranging typically 1–6 years (Table 1). Patterns of habitual wear were mapped to determine position in vivo. Stripe damage was mapped at three sites: polar, equatorial and basal. Wear patterns were examined using SEM and white light interferometry (WLI). Graphical models characterized the complex geometry of the natural femoral neck in coronal and sagittal planes and provided RSA head-neck ratios.⁴

Normal area patterns of habitual wear were similar on RSA and THA bearings. The wear patterns showing cup rim-breakout proved larger for RSA cups than THA. Polar stripes presented in juxtaposition to the polar axis in both RSA and THA (Fig. 1). As anticipated, basal stripes on RSA occurred at steeper cup-impingement angles (CIA) than THA. The micro-topography of stripe damage was similar on both RSA and THA heads. Some scratches were illustrative of 3^rd-body wear featuring raised lips, punctuated terminuses, and crater-like depressions (Fig. 2).

Neck narrowing observed following RSA procedures may be a consequence of impingement and subluxation due to the small head-neck ratios. However, lacking a metal femoral neck, such RSA impingement would not result in metal debris being released. Nevertheless it has been suggested that cup-to-head impingement produced large CoCr particles and also cup “edge wear” as the head orbits the cup rim.⁴ Our study showed that impingement had occurred as evidenced by the polar stripes and 3^rd-body wear by large hard particles as evidenced by the wide scratches with raised lips. We can therefore agree with the prior study, that 2-body and 3rd-body wear mechanisms were present in both RSA and THA retrievals.

Introduction

Hip simulators proved to be valuable, pre-clinical tests for assessing wear. Preferred implant positioning has been with cup mounted above head, i.e. ‘Anatomical’ (Figs. 1a-c) ^1,2 while the ‘Inverted’ test (cup below head) was typically preferred in debris studies (Figs. 1d-f).^3,4 In an Anatomical study, wear patterns on cups and heads averaged 442 and 1668 mm² area, respectively, representing 8% and 30% of available hemi-surface (Table 1), i.e. the head pattern was ×3.8 times larger than cup. This concept of wear patterns is illustrated well in the ‘pin-on-disk’ test (Fig. 1) in which the oscillating pin has the ‘contained’ wear area (CWP) and the large wear track on the disk is the ‘distributed’ pattern (DWP). Hip simulators also create CWP and DWP patterns, site dependant on whether Anatomical (Fig. 1a-c) or ‘Inverted’ (Fig. 1d-f) test. However there is scant foundation as to clinical merits of either test mode. Retrieval studies of MOM bearings have indicated that cups have the larger wear patterns, i.e. contrary to simulator tests running Anatomical cups (Table 1).⁵ Therefore we compared Anatomical and Inverted cup modes using 38mm and 40mm MOM in two 5-million cycle simulator studies.

Introduction

Looking for optimal solutions to wear risks evident in total hip arthroplasty (THA), silicon nitride ceramic bearings (Si₃N₄) are noted for demanding high-temperature applications such as diesel engines and aerospace bearings. As high-strength ceramic for orthopedic applications, Si₃N₄ offers improved fracture toughness and fracture strength over contemporary aluminas (Al₂O₃). Our pilot studies of Si₃N₄ in 28mm diameter THA showed promising results at ISTA meeting of 2007.¹ In this simulator study, we compared the wear resistance of 40mm to 28mm diameter Si₃N₄ bearings.

The 28mm and 40mm bearings (Fig. 1) were fabricated from Si₃N₄ powder (Amedica Inc, Salt Lake City, UT).¹ Wear tests run were run at 3kN peak load in an orbital hip simulator (SWM, Monrovia, CA) and. The lubricant was standard bovine serum (Hyclone: diluted to 17 mg/ml protein concentration). Wear was measured by gravimetric method and wear-rates calculated by linear regression. SEM and interferometic microscopic was performed at 3.5-million cycles (3.5Mc) to 12Mc.

The simulator was run to 3.5Mc duration with no consistent weight-loss trends. The bearings could show either small positive or negative weight fluctuations in an unpredictable manner (Fig. 2). Surface analysis showed protein layers up to 3μm thick, furrowed due to abrasion by small particles (Fig. 3). The low ceramic wear was camouflaged by protein contaminants alternatively forming and shedding. From 3.5 to 12.8Mc duration we experimented with various detergents and wash-procedures, all to no avail. Protein coatings were also more prevalent on 44 mm heads, likely due to frictional heating by the larger diameter effect. Selected heads were washed with a mild acid solution - the cumulative effect appeared to be removal of some protein layers, but not in a predictable manner.

The Si₃N₄ ceramic is used in demanding industrial applications and it is therefore unfortunate that we are yet not able to quantify the actual wear performance of Si₃N₄/ Si₃N₄ bearings (COC). The contaminating protein layers combined with low-wearing silicon nitride obscured the actual wear data. This has also been a problem in prior studies with alumina and zirconia bearings. Considerable challenges still stand in the way of the optimal biomaterials choices that will result in reduced risk of failure while providing extended lifetimes. Thus important issues remain unsolved and call for innovative solutions. Searching for a more effective ‘wear-measurement’ remedy, we noted that abrasive slurries of bone cement (PMMA) used in contemporary simulator studies were effective in promoting adverse wear in polyethylene bearings. These investigations also revealed that PMMA debris did not damage CoCr heads^2,3, alumina heads^4,5 or diffusion-hardened zirconia heads (ZrDH).⁶ We can therefore speculate at this ISTA meeting of 2014 that future ceramic wear tests should incorporate PMMA slurries. Here a new hypothesis can be formulated, that PMMA particulates will provide a continual and beneficial removal of contaminating proteins from the ceramic surfaces (see Fig. 3) and thereby aid definition of low-wearing COC bearings such as Si₃N₄.

The application of non-oxide ceramics such as silicon nitride presented here may become a viable alternative for THA designs of next decade.

Introduction

The assessment of leg length is essential for planning the correction of deformities and for the compensation of length discrepancy, especially after hip or knee arthroplasty. CT scan measures the “anatomical” lengths but does not evaluate the “functional” length experienced by the patients in standing position. Functional length integrates frontal orientation, flexion or hyperextension. EOS system provides simultaneously AP and lateral measures in standing position and thus provides anatomical and functional evaluations of the lower limb lengths.

The objective of this study was to measure 2D and 3D anatomical and functional lengths, to verify whether these measures are different and to evaluate the parameters significantly influencing these potential differences

A 35-year-old female (age 35Yrs) had primary MOM total hip arthroplasty (THA) in 2008. At 8 months this patient postoperatively developed headaches, memory loss, vertigo, and aura-like symptoms that progressed to seizures. At 18 months review, she complained of progressive hip pain, a popping sensation and crepitus with joint motion. This patient weighed 284lbs with BMI of 38.5. Radiographs revealed the cup had 55° inclination, 39° anteversion (Fig. 1). Metal ion concentrations were high (blood: Co=126 mcg/L, Cr= 64mcg/L). Revision was performed in November 2010 A dark, serous fluid was observed, along with synovitis. The implants were well fixed and the femoral head could not be removed; thus the stem was removed by femoral osteotomy. With the head fused on this femoral stem, for the 1^st time it was possible to precisely determine the habitual patterns of MOM wear relative to her in-vivo function. We investigated (1) size and location of wear patterns and (2) signs of cup-stem impingement to help explain her symptoms developed over 32 months follow-up.

The retrieved MOM was a Magnum™ with head diameter 50mm and 50×56mm cup (Biomet). This was mounted on a Taperloc™ lateralized porous-coated stem. Components were examined visually and wear damage mapped by stereo-microscopy, interferometry, CMM, SEM, and EDS. Main-wear zone (MWZ) areas were calculated using standard spherical equations¹ and centroidal vectors determined.

The head-cup mismatch was 427um with the cup revealing a form factor of 228um. The cup showed wear area of 1275mm² that extended up to the cup rim over 150°arc. The cup rim was worn thin over a 90° arc with loss of cup bevel. The head showed an elliptical wear area of 2200mm² located centrally on the superior-medial surface (ellipsoidal ratio ×1.2). Compared to the hemispherical surface (50mm: hemi-area = 3927mm²), the worn area represented hemi-area ratio of 56%. The centroidal vectors measured 8° anterior and 24° superior to the head's polar axis (Fig. 2). Stripe wear damage revealed multiple impingement sites. SEM and EDS revealed stripes were contaminated by metal transfer from the stainless-steel instruments used at revision. The main impingement position was identified (Fig. 3) indicating the site of repetitive subluxations whereby the subluxing head thinned the cup, i.e. “edge wear”.

Cup and head wear patterns corresponded well, reinforcing our definition of the MWZ locations in vivo. The femoral MWZ was centrally located superiorly and medially with respect to the polar axis of the femoral neck and head. The noted impingement position indicated this patient had experienced repetitive subclinical subluxations (RSS).² The taper inside the fused head may also have been a contributory factor that we cannot ignore. Nevertheless her excessive cup thinning was likely a result of a steep cup and considerable anteversion allowing the femoral head to sublux over the cup rim, thus thinning the cup and wearing the rim bevel, and producing MOM wear debris.

Introduction

Coronal misalignment of the lower limbs is closely related to the onset and progression of osteoarthritis. In cases of severe genu varus or valgus, evaluating this alignment can assist in choosing specific surgical strategies. Furthermore, restoring satisfactory alignment after total knee replacement promotes longevity of the implant and better functional results. Knee coronal alignment is typically evaluated with the Hip-Knee-Ankle (HKA) angle. It is generally measured on standing AP long-leg radiographs (LLR). However, patient positioning influences the accuracy of this 2D measurement. A new 3D method to measure coronal lower limb alignment using low-dose EOS images has recently been developed and validated. The goal of this study was to evaluate the relevance of this technique when determining knee coronal alignment in a referral population, and more specifically to evaluate how the HKA angle measured with this 3D method differs from conventional 2D methods.

Introduction

One unpredictable clinical risk with THA may be impingement of a metal cup rim against a metal femoral-neck, with concomitant release of metal particles. Our objective was to determine if metal debris could be one trigger for catastrophic MOM wear.

Introduction

Surgical site infection (SSI) remains a concern following total hip arthroplasty (THA). We aimed to identify risk factors for post-operative SSI in THA.