Aims

Removal of infected components and culture-directed antibiotics are important for the successful treatment of chronic periprosthetic joint infection (PJI). However, as many as 27% of chronic PJI patients yield negative culture results. Although culture negativity has been thought of as a contraindication to one-stage revision, data supporting this assertion are limited. The aim of our study was to report on the clinical outcomes for one-stage and two-stage exchange arthroplasty performed in patients with chronic culture-negative PJI.

Aims

The complex relationship between acetabular component position and spinopelvic mobility in patients following total hip arthroplasty (THA) renders it difficult to optimize acetabular component positioning. Mobility of the normal lumbar spine during postural changes results in alterations in pelvic tilt (PT) to maintain the sagittal balance in each posture and, as a consequence, markedly changes the functional component anteversion (FCA). This study aimed to investigate the in vivo association of lumbar degenerative disc disease (DDD) with the PT angle and with FCA during postural changes in THA patients.

Aims

The removal of the cruciate ligaments in total knee arthroplasty (TKA) has been suggested as a potential contributing factor to patient dissatisfaction, due to alteration of the in vivo biomechanics of the knee. Bicruciate retaining (BCR) TKA allows the preservation of the cruciate ligaments, thus offering the potential to reproduce healthy kinematics. The aim of this study was to compare in vivo kinematics between the operated and contralateral knee in patients who have undergone TKA with a contemporary BCR design.

Background

Adverse local tissue reactions (ALTR) in metal-on-polyethylene (MoP) total hip arthroplasty (THA) with head-neck taper corrosion is likely to be multifactorial involving implant and patient factors. However, there is a paucity of clinical data on implant parameters as predisposing factors in MoP head-neck taper corrosion. The aim of this study was to identify any potential implant factors associated with failed MoP THA due to head-neck taper corrosion.

Introduction

Inability to reproduce 6-degrees of freedom (6DOF) kinematics, abnormal “paradoxical” anterior femoral translation and loss of normal medial pivot rotation are challenges associated with contemporary posterior cruciate retaining and posterior stabilized total knee arthroplasty (TKA). The removal of the anterior and/or both cruciate ligaments in CR/PS TKA, leading to significant kinematic alteration of the knee joint, has been suggested as one of the potential contributory factors in patients remaining dissatisfied after TKA. Bi-cruciate retaining (BCR) TKA designs allow preservation of both anterior and posterior cruciate ligaments with the potential to replicate normal knee joint kinematics. Physically demanding tasks such as sit-to-stand (STS), and deep lunging may be more sensitive tools for investigating preserved kinematic abnormalities following TKA. This study aims to compare in-vivo kinematics between the operated and the contralateral non-operated knee in patients with contemporary BCR TKA design.

Dual mobility (DM) cups are designed to improve stability, however have been associated with increased risk of impingement that can ultimately result in intraprosthetic dislocation. It is speculated that the femoral neck plays a role in their performance. We investigated the effect of neck topography on the wear of new-generation liners.

This was a retrieval study involving 70 DM cups implanted with liners made of highly crosslinked polyethylene and paired with two neck types: either highly polished (n=35) or rough necks (n=35). The median time of implantation was 30 months.

The rim edge of all inserts was investigated by two examiners for evidence of contact with the femoral neck, presenting as deformation of the polyethylene. A high precision roundness machine and micro-CT scans of the components were used to measure the size of the deformations observed.

28 of the 35 (80%) DM liners paired with rougher necks had evidence of neck impingement resulting in a raised lip, whilst 8 out of 35 (23%) liners paired with smooth necks had a raised lip; this difference was significant (p<0.0001). The repeatability and the inter-observer reproducibility of the deformation scores was found to be substantial κ >0.70. The height of the raised rims of the DM cups paired with rough necks had a median (range) of 139 µm (72–255), whilst had a median (range) of 52 µm (45–90) with smooth necks, the difference between the groups was significant (p<0.0001).

Liner rim deformation resulting from contact with the femoral neck likely begins during early in-vivo function.

Rough necks can increase the damage on the polyethylene rim in dual-mobility bearing, which may lead to loss of the retentive power of these components over time.

Dual-taper implants provide surgeons with options to optimise patients' anatomy intraoperatively but are at risk of early revision due to adverse tissue reactions to corrosion debris. Risk factors for failure and linkage with symptoms however are not fully understood. We related retrieval findings to clinical and implant variables.

This study involved 88 failed dual-taper implants with TMZF femoral stems and cobalt-chromium necks, revised for pain, elevated Co (median = 7.3μg/L) and Cr (median = 2.15μg/L) ions levels and fluid collection on MRI.

Stem-neck surfaces were assessed for: 1) severity of corrosion using a published visual method and 2) severity of material lost and location of damage with a roundness-measuring machine. Five traces were taken on each round section of the taper surface at 45° increments to compute the relative depth of damage. The total area of these traces provided a measure of surface damage for comparative purposes.

The stem-neck taper junctions were severely corroded; the deepest areas of damage were on the inferior-proximal and superior-distal part of the necks, compatible with cantilever bending. Elemental analysis revealed chromium rich deposits indicative of corrosion processes and metal transfer from the stem to the neck.

There was a positive correlation between the severity of damage and time of implantation (p<0.0001). Co and Cr levels in the blood were also strongly correlated (p<0.0001, p=0.0002). No other implant or patient variables were linked.

The stem-neck junction was severely corroded in all cases. The severity and location of the areas of surface damage did not link with implant or patient characteristics in this big cohort suggesting that the design and material combination is the predominant source of failure in these designs.

Dual-taper hips are severely corroded at the stem-neck junction; this appears to be due to the use of a TMZF alloy stem paired with CoCrMo necks.

Objectives

The use of ceramic femoral heads in total hip arthroplasty (THA) has increased due to their proven low bearing wear characteristics. Ceramic femoral heads are also thought to reduce wear and corrosion at the head-stem junction with titanium (Ti) stems when compared with metal heads. We sought to evaluate taper damage of ceramic compared with metal heads when paired with cobalt chromium (CoCr) alloy stems in a single stem design.

Introduction

An equal knee joint height during flexion and extension is of critical importance in optimizing soft-tissue balancing following total knee arthroplasty (TKA). However, there is a paucity of data regarding the in-vivo knee joint height behavior. This study evaluated in-vivo heights and anterior-posterior (AP) translations of the medial and lateral femoral condyles before and after a cruciate-retaining (CR)-TKA using two flexion axes: surgical transepicondylar axis (sTEA) and geometric center axis (GCA).

The contemporary metal-on-metal (MoM) bearings were reintroduced due to their lower volumetric wear rates in comparison to conventional metal-on-polyethylene bearings. This has the potential to substantially reduce wear-induced osteolysis as the major cause of failure and greater implant stability with the use of large femoral heads. It has been estimated that since 1996 more than 1,000,000 MoM articular couples have been implanted worldwide. However, with increasing clinical experience, the national joint registries have recently reported the failure rate of THA with MoM bearings to be 2–3 fold higher than contemporary THA with non-metal-on-metal bearings. Moreover, adverse periprosthetic tissue reactions have emerged as an important reason for failure in MoM patients.

A painful MoM hip arthroplasty has various intrinsic and extrinsic causes. As in all painful THA, a thorough clinical history, a detailed physical examination, as well as radiographic and laboratory tests are essential to delineate potential cause(s) of pain in patients with MoM hip arthroplasty. While specialised tests such as metal ion analysis are useful modalities for assessing MoM hip arthroplasty, over-reliance on any single investigative tool in the clinical decision-making process should be avoided. There should be a low threshold to perform a systematic evaluation of patients with MoM hip arthroplasty as early recognition and diagnosis will facilitate the initiation of appropriate treatment prior to significant adverse biological reactions. A systematic risk stratification recommendation, for multiple modes of failure including adverse local tissue reactions, based on the currently available evidence will be presented to optimise management.

Since the advent of total hip arthroplasty (THA), there have been many changes in implant design that have been implemented in an effort to improve the outcome of the procedure and enhance the surgeon's ability to reproducibly perform the procedure. Some of these design features have not stood the test of time. However, the introduction of femoral stem head/neck modularity made possible by the Morse taper has now been a mainstay design feature for over two decades. Modularity at the head-neck junction facilitates intraoperative adjustments. ‘Dual Taper’ modular stems in total hip arthroplasty have interchangeable modular necks with additional modularity at the neck and stem junction. This ‘dual taper’ modular femoral stem design facilitates adjustments of the leg length, the femoral neck version and the offset independent of femoral fixation. This has the potential advantage of optimizing hip biomechanical parameters by accurately reproducing the center of rotation of the hip.

More recently, however, there is increasing concern regarding the occurrence of adverse local tissue reactions in patients with taper corrosion, which is emerging as an important reason for failure requiring revision surgery. Although adverse tissue reactions or ‘pseudotumor’ were initially described as a complication of metal-on-metal (MoM) bearings, the presence of pseudotumor in patients with taper corrosion is thought to result from corrosion at the neck-stem taper junction, secondary to reciprocating movement at the modular junction leading to fretting corrosion in a process described as mechanically assisted crevice corrosion (MACC). Therefore, the focus of this presentation is to summarise clinical challenges in diagnosis and treatment of patients with adverse tissue reactions due to taper corrosion and review up-to-date evidence.

Introduction

Dual-mobility bearings increase the stable range of motion of total hip arthroplasty (THA) but are limited by the mechanical effects of a large diameter metal on polyethylene bearing which may cause high rates of wear from the surfaces of the polyethylene bearing and the head-stem taper. Improved polyethylene (PE) has reduced concern over bearing wear but the effects on the taper junction are unknown.

We aimed to better understand the effect of dual mobility bearings on fretting-corrosion damage to the taper junction by comparison to standard bearings.

Measurements of shoulder kinematics during activities of daily living (ADL) can be used to evaluate patient function before and after treatment and help define device testing conditions. However, due to the difficulties of making 3D motion measurements outside of laboratory conditions, there are few reports of measured shoulder 3D kinematics during ADL. The purpose of this study was to demonstrate the feasibility of using wearable inertial measurement units (IMUs) to track shoulder joint angles.

A nonrandom sample of 5 subjects with normal shoulders was selected based on occupation. The occupations were: dental hygienist, primary school teacher, mechanical project engineer, administrative assistant, and retail associate. Subjects wore two OPAL IMUs (APDM, Portland OR) as shown in Figure 1 on the sternum and on the upper arm for approximately 4 hours while at their workplace performing their normal work place activities and then up to 4 hours while off-work.

Orientation angles from IMUs have traditionally been estimated by integrating gyroscope data and calculating inclination angles relative to gravity with accelerometers. A significant problem is that inaccuracies inherent in the measurements can degrade accuracy. In this study, we used an Unscented Kalman Filter (UKF) with IMU output to track shoulder angles. The UKF mitigates the effect of random drift by incorporating domain knowledge about the shoulder normal range of motion, and the gyroscope and accelerometer characteristics into the state-space models. Initially, in the horizontal plane, without gravity measurements from the accelerometer to aid the gyroscope data, there were unacceptable errors in transverse rotation. To mitigate this error, additional constraints were applied to model gyroscope drift and a zero velocity update strategy was included. These additions decreased tracker errors in heading by 63%. The resulting accuracy with the modified tracker in all motion planes was about 2° (Figure 2).

Subjects commented that the IMUs were well tolerated and did not interfere with their ability to perform tasks in a normal manner. The overall averaged 95th percentile angles (Figure 3) were: flexion 128.8°, adduction 128.4°, and external rotation 69.5°. These peaks angles are similar to other investigator's reports using laboratory simulations of ADL tasks measured with optical and electromagnetic technologies, though this study's observations did show 17% greater extension and 40% greater adduction. Additionally, in these observations, occurrences of maximal internal rotation were rare compared to maximal external rotation and when maximum external rotation did occur, it was in combination with an average flexion angle of 103°. Finally, by performing a Fourier transform of the arm angles and using the 50th percentile frequency the number of arm cycles in a 10 year period was calculated at over 600,000 cycles.

Application of the UKF with the additional drift correction made substantial improvements in shoulder tracking performance and this feasibility data suggests that IMUs with the UKF are suitable for extended use outside of laboratory settings. The motion data collected provides a novel description of arm motion during ADLs including estimating the cycle count of the upper arm at more than 600,000 cycles over 10 years.

Aims

There are many guidelines that help direct the management of patients with metal-on-metal (MOM) hip arthroplasties. We have undertaken a study to compare the management of patients with MOM hip arthroplasties in different countries.

Introduction

Osteolysis caused by wear of the ultrahigh molecular weight polyethylene (UHMWPE) often leads to failure. Cross-linking improves wear, but also produces residual free radicals that decrease oxidative stability. In vitro studies have shown that the anti-oxidative properties of vitamin E UHMWPE stabilize free radicals while retaining the physical and chemical properties of UHMWPE. The porous surface of the Regenerex™ shell was developed for improved bone in-growth fixation. The increased porosity of the Regenerex™ shell promotes early bony in-growth with the goal of greater long-term stability. The purpose of this study was to evaluate vitamin E infused polyethylene (VEPE) wear and stability of acetabular and femoral components using RSA.

Combined acetabular and femoral anteversion (CA) of the hip following total hip arthroplasty (THA) is critical to the hip function and longevity of the components. However, no study has been reported on the accuracy in restoration of CA of the hip after operation using robotic assistance and conventional free-hand techniques. The purpose of this study was to evaluate if using robotic assistance in THA can better restore native CA than a free-hand technique.

Twenty three unilateral THA patients participated in this study. Twelve of them underwent a robotic-arm assisted THA (RIO® Robotic Arm Interactive Orthopedic System, Stryker Mako., Fort Lauderdale, FL, USA) and eleven received a free-hand THA. Subject specific 3D models of both implanted and non-implanted hips were reconstructed using post-operative CT scans. The anteversion and inclination of the native acetabulum and implanted cup were measured and compared. To determine the differences of the femoral anteversion between sides, the non-implanted native femur was mirrored and aligned with the remaining femur of the implanted side using an iterative closest point algorithm. The angle between the native femoral neck axis and the prosthesis neck axis in transverse plane was measured as the change in femoral anteversion following THA. The sum of the changes of the acetabular and femoral anteversion was defined as the change of CA after THA. A Wilcoxon signed rank test was performed to test if the anteversion of the navigation and free-hand THAs were different from the contralateral native hips (α = 0.05).

The acetabular anteversion were 22.0°±7.4°, 35.9°±6.5° and 32.6°±22.6° for the native hips, robotic assisted THAs and free-hand THAs, respectively, and the corresponding values of the acetabular inclinations were 52.0°±2.9°, 35.4°±4.4° and 43.1°±7.1°. The acetabular anteversion was increased by 12.2°±11.1° (p=0.005) and 12.5°±20.0° (p=0.102) for the robotic assisted and the free-hand THAs. The femoral anteversion was increased by 6.3°±10.5° (p=0.077) and 11.0°±13.4° (p=0.014) for the robotic assisted and free-hand THAs, respectively. The CA were significantly increased by 18.5°±11.7° (p<0.001) and 23.5°±26.5° (p=0.019) for the robotic assisted and the free-hand THAs. The changes of the CA of the free-hand THAs varied in a larger range than those of the robotic assisted THAs.

This study is the first to evaluate the changes in acetabular and femoral anteversions of the hips after robotic assisted and free-hand THAs using the contralateral native hip as a control. The results demonstrate that both the navigation and free-hand THAs significantly increased the CA compared to the contralateral native hips, but the changes of the robotic assisted THAs (18.5°±11.7°) were smaller and varied less than those of the free-hand THAs (23.5°±26.5°). These data suggest that the robotic assisted THA can better restore the native hip CAs with higher repeatability than the free-hand technique. Further studies are needed to investigate the effects of the hip anteversion changes on the in-vivo function of the hip and the long-term outcomes in THA patients.

Introduction:

Acetabular cup position is an important factor in successful total hip arthroplasty (THA). Optimal cup placement requires surgeons to possess an accurate perception of pelvic orientation during cup impaction, however, varying pelvic anatomy and limited visual cues in the surgical field may interfere with this process. The purpose of this study was to evaluate the utility of an inertial measurement unit (IMU) in monitoring pelvic position during THA.

Due to technology advancement, many studies have reported on in-vivo human knee kinematics recently (Dannis, 2005; Moro-oka, 2008; Tashman, 2003; Koo, 2008). This abstract summarized the joint kinematics during three motions usually seen in our daily living, i.e. gait, step-up (stair ascending) and single-legged lunge that was measured using a combined dual-fluoroscopic imaging system and MRI based modeling technique (Li, 2008). Cartilage contacts or condylar motion using transepicondylar axis (TEA)/geometric center axis (GCA) were used to describe the motion characters of the knee during these motions.

In the treadmill gait, the movement of the medial femoral condyle along the anteroposterior direction was significantly greater than that of the lateral femoral condyle during the stance phase using either TEA (9.7 ± 0.7 mm vs. 4.0 ± 1.7 mm, respectively; p < 0.01; Fig. 1A) or GCA (17.4 ± 2.0 mm vs. 7.4 ± 6.1 mm, respectively; p < 0.01; Fig. 1B). A “lateral-pivoting” of the knee was observed (Kozanek, 2009).

In the step-up motion, both medial and lateral contact points moved anteriorly on the tibial articular surfaces along the step-up motion path. The contact points on the medial and lateral tibial plateau moved anteriorly (13.5 ± 3.2 mm vs. 10.7 ± 5.0 mm, respectively; p > 0.05; Fig. 2A) with knee extension. Using the TEA (Fig. 2B), the femoral condylar motions presented a similar pattern as the contact points; nonetheless, using the GCA (Fig. 2C), the femoral condylar motion pattern was dramatically different. The medial condyle moved anteriorly, while the lateral condyle shifted posteriorly. However, none of them showed a significant pivoting phenomenon (Li, 2013).

In the single-legged lunge, both medial and lateral contact points moved similarly before 120° of knee flexion, but the lateral contact moved posteriorly and significantly more than the medial compartment in high flexion (1.9 ± 2.1 mm vs. 4.8 ± 2 mm, respectively; p < 0.05). The single-legged lunge didn't show a single motion pattern (Fig. 3) (Qi, 2013).

These data provide baseline knowledge for the understanding of normal physiological function of the knee during gait, step-up and lunge activities. The findings of these studies demonstrated that knee joint kinematics is activity-dependent and indicated that the knee joint motions could not be described using a single motion character such as “medial-pivoting” that has recently been popularized in total knee arthroplasty design areas.

Introduction

Acetabular cup positioning has been linked to dislocation and increased bearing surface wear. A previous study found correlations between patient and surgical factors and acetabular component position. The purpose of this study was to determine if acetabular cup positioning improves when surgeons receive feedback on their performance.

Introduction

Metal-on-metal (MoM) hip resurfacing arthroplasty is a popular choice for young and active patients. However, there are concerns recently regarding soft tissue masses or pseudotumours. The appearance of these complications is thought to be related blood metal ion levels. The level of metal ions in blood is thought to be the result of MoM wear. In the present study the contribution of acetabulum orientation to stress distribution was investigated.

Objectives

Pseudotumours (abnormal peri-prosthetic soft-tissue reactions) following metal-on-metal hip resurfacing arthroplasty (MoMHRA) have been associated with elevated metal ion levels, suggesting that excessive wear may occur due to edge-loading of these MoM implants. This study aimed to quantify in vivo edge-loading in MoMHRA patients with and without pseudotumours during functional activities.

Introduction: Edge-loading, a phenomenon whereby the femoral component comes into contact with the edge of the acetabular component, has been suggested to increase wear in metal-on-metal hip resurfacing arthroplasty (MoMHRA). Pseudotumours (soft-tissue mass relating to the hip joint) have been associated with elevated serum and hip aspirate metal ion levels. This study aimed to investigate in vivo edge-loading in MoMHRA patients with pseudotumours by quantifying dynamic loci of the hip joint segment force relative to the acetabular component during functional activities.

Materials and Methods: A total of 21 MoMHRA patients (30 hips) in two groups were investigated in this Ethics approved study:

6 patients with pseudo-tumours detected using ultrasound/MRI;

Three-dimensional lower limb motion analysis (12 camera Vicon System) was performed to estimate hip joint segment force during walking, chair-rising and stair-climbing. CT scans were used to determine each patient’s specific hip joint centre and acetabular component orientation. Edge-loading was defined to occur when a hip joint segment force vector/ cup intersection was located within 10% of the cup radius from the edge of the cup. Serum cobalt and chromium levels were analysed using Inductively-Coupled Plasma Spectrometer.

Results: Edge-loading in the pseudotumour group occurred with significantly (p=0.02) longer (4-fold increase) duration as well as greater magnitude (7-fold increase) of force, compared to the non-pseudotumour group. The duration and force of the edge-loading were activity-dependent, with proportionally greater difference observed during stair climbing. The acetabular cup orientation values in the pseudotumour group were found within the safe zone of Lewinnek in one third of the hips with the remaining two thirds outside the safe zone. The presence of pseudotumour was associated with:

significantly higher median serum cobalt levels: 14.3ug/l (range 10.6–64.1) vs. 1.9ug/l (range 1.2–5.0), p< 0.001;

Discussion: Edge-loading in MoMHRA patients with pseudotumours occurred in vivo with significantly longer duration and greater magnitude of force impulse compared to the patients with a well functioning MoMHRA during activities of daily living. This suggests that edge-loading may be an important mechanism that leads to localised high wear, with subsequent elevation of metal ion levels in MoMHRA patients with pseudotumours. Although the acetabular component malposition, such as increase in both inclination and anteversion angles, appears to be an important factor in edge-loading, the aetiology of edge-loading is likely to be multi-factorial.

Introduction: 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 in vivo wear of implants revised for pseudotumours and a control group of implants revised for other reasons of failure.

Methods: A total of 30 contemporary MoMHRA implants in two groups were investigated in this Institutional Review Board approved study:

8 MoMHRA implants revised due to pseudotumour;

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.

Results: In comparison with the non-pseudotumour implant group, the pseudotumour implant group was associated with:

significantly higher median linear wear rate of the femoral component: 8.1um/year (range 2.75–25.4um/year) vs. 1.79um/year (range 0.82–4.15um/year), p=0.002; and

Similarly, differences were also measured in absolute wear values. The median absolute linear wear was significantly higher in the pseudotumour implant group:

21.05um (range 2.74–164.80um) vs. 4.44um (range 1.50–8.80um) for the femoral component, p=0.005; and

Wear on the acetabular cup components in the pseudotumour group always involved the edge, indicating edge-loading of the bearing. In contrast, edge-loading was observed in only one acetabular component in the non-pseudotumour group of implants. The deepest wear was observed well within the bearing surface for the rest of the non-pseudotumour group. The difference in the incidence of edge-loading between the two groups was statistically significant (Fisher’s exact test, p=0.03).

Discussion: 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 provides the first direct evidence to confirm that pseudotumour is associated with increased wear at the MoM articulation. Furthermore, edge-loading with the loss of fluid film lubrication may be the dominant wear generation mechanism in patients with pseudotumour.

Introduction: Metal-on-metal hip resurfacing arthroplasty (MoMHRA) has gained popularity as an alternative to THR for younger patients with osteoarthritis. A growing concern has been the association of MoMHRA with the development of inflammatory pseudotumours (IP), especially in women. These have been linked to metal-on-metal wear, which can be related to metal ion concentrations. Although cup orientation has been shown to influence wear, the optimum cup position has not been clearly defined. We have identified an optimal cup orientation to minimise IP risk, based on a case controlled study, for inclination/anteversion within ±10° of 40°/20°. Our aim was to see if this optimal position results in lower metal ions, and to identify the boundary of an optimal placement zone for low wear.

Methods: A cohort of 104 patients (60M: 44F) with unilateral MoMHRA was included in this study. Blood tests were obtained at a mean follow up of 3.9 years (range 1.7–7 years) and serum Co and Cr ion levels were measured (ICPMS). High metal ion concentrations were defined as Co> 4.1ppb and Cr> 5.2ppb. Radiographic cup inclination and anteversion were measured using EBRA. The differences in ion levels between different cup orientation zones were investigated. Three orientation zones were defined centered on the target orientation of 40°/20°: Z1 within ±5°, Z2 outside ±5°/within ±10° and Z3: within ±10°.

Results: There was a wide range of cup placements; mean inclination/anteversion were 46.3°(21.5°–64.6°)/15°(2.7°–35.6°). Cr levels, but not Co, were higher in female patients (p=0.002) and those with small femoral components (< 50mm, p =0.03).

For the whole cohort, there was no significant difference in ion levels (Cr: p=0.092. Co=0.075) between cups positioned within Z3 (n=58) versus those outside (n=46 mean). Male patients with cups within Z3 (n=27) had lower ion levels in comparison to those outside Z3, which were significantly lower for Co (p=0.049) but not Cr (p=0.084). Female patients had similar levels within and out of Z3 for both ions (Cr: p=0.83, Co: p=0.84). However, patients with cups within Z1 (n=13) had significantly lower Co (p=0.005) and Cr (p=0.001) than those outside Z1 (n=95). Interestingly, Co levels were significantly lower in Z1 (n=13) in comparison to Z2 (n=33) (p=0.048) but Cr levels were not different (p=0.06).

Discussion: MoMHRA cups placed with ±5° of the ideal position of 40°/20°gave rise to significantly lower metal ions indicating lower wear within this narrow zone, in both sexes. This safe zone, could be extended to ±10° for male patients only. Gender specific factors, such as pelvic anatomy and joint flexibility, could be responsible for the narrower ‘safe’ zone seen in females. The narrower safe zone coupled with smaller components implanted are factors contributing to higher ion levels and hence the increased incidence of IP seen in females.

Introduction: The development of Inflammatory Pseudotumour (IP) is a recognised complication following Metal on Metal Hip Resurfacing Arthroplasty (MoMHRA), thought to occur secondary to wear and elevated ion levels. Studies have shown that acetabular component orientation influences the wear of metal-on-metal hip replacement bearings. The aims of this study were to investigate the significance of cup orientation in the development of IP, and to identify a ‘safe-zone’ for cup placement with lower-risk for IP development.

Methods: Twenty six patients (n=27 hips) with IP confirmed radiologically, intra-operatively and histologically were matched for sex, age, pre-operative diagnosis, component size and follow-up with a cohort of asymptomatic MoMHRA patients (Control n=58). Radiographic acetabular anteversion and inclination were measured using EBRA. We calculated the distance in degree space of each acetabular component from the optimum position of 40° inclination and 20° anteversion, recommended by the designers, and thus compared acetabular component position between the two groups. Three different zones were tested as possibly optimum for acetabular placement. These were Lewinneck’s Zone (LZ) (inclination/anteversion; 30–50°/5–25°), and two zones defined by ±5° (Zone 1) or ± 10° (Zone 2) about the suggested target of 40°/20°. An optimal placement zone was determined based on a significant difference in IP incidence between components in the zone versus those outside.

Results: There was a wide range in cup orientations; mean inclination and anteversion were similar in the two groups: IP 47.5° (10.1°–80.6°)/14.1° (4.1°–33.6°) Vs Control 46.1° (28.8°–59.8°)/15.6° (4.3°–32.9°). Acetabular components in the IP group were significantly further away from the optimum position of 40°/20° in comparison to the controls (p=0.023). There was no difference in IP incidence between cups positioned within (IP:13/27, Control:35/58) or out of LZ (p=0.09) and within (IP: 2/27, Control: 10/58) or out of Zone 1 (p=0.156). Cups placed in Zone 2 (IP:6/27, Control:27/58) had significantly lower IP incidence versus those outside this zone (p=0.01). The odd’s ratio of developing IP when the cup is positioned out-of Zone 2 was 3.7.

Discussion: This study highlights the importance of ace-tabular component orientation in IP development. On the whole, patients with pseudotumour had acetabular components that were further away from the optimum position in comparison to the controls. However, a small number of IP patients had well-placed components implying that additional factors, possibly patient and/or gender specific, are involved in the development of pseudotumour. Furthermore, we defined an optimum, ‘safe-zone’ of ±10° around the cup position of 40°/20°. Patients with acetabular components outside this safe zone have an increased risk of IP development.

Introduction: Symptomatic abnormal soft-tissue masses relating to the hip joint, such as those described as pseudotumours, are being increasingly reported following metal-on-metal hip resurfacing arthroplasty (MoMHRA). These were found to be locally destructive, requiring revision surgery in a high proportion (75%) of patients. Lymphocyte infiltrations seen in pseudotumours were similar to aseptic lymphocyte vascular associated lesion (ALVAL), which is thought to represent a T-lymphocyte-mediated delayed type hypersensitivity. Therefore, a delayed hypersensitivity reaction to nickel (Ni), chromium (Cr) or cobalt (Co) has been suggested to play a role in pseudotumour aetiology. In patients with bilateral MoMHRA who presented with symptoms on one side, subsequent scans have demonstrated pseudotumours both on the symptomatic and asymptomatic side. Thus, there are concerns that there may be an appreciable number of asymptomatic pseudotumours that surgeons are unaware of and these may eventually become symptomatic.

Aim: The aims of this study were:

to determine the prevalence of asymptomatic pseudotumours after MoMHRA; and

Methods: A total of 201 MoMHRA implanted hips in 158 patients (97 male, 61 female) with a mean age of 56 years (range 33–73 years) were evaluated. The mean follow-up was 61 months (range 13–88 months). Resurfacing devices implanted included 128 Birmingham Hip Resurfacing, 66 Conserve Plus and seven ReCap. The control groups included additional 20 patients, 10 male and 10 female (a mean age 68 years, range 57–80 years) with metal-on-polyethylene total hip arthroplasty and a further 22 age-matched patients (a mean age 55 years) without any metal implants. Ultrasound was used as the initial imaging modality and MRI was used to assess the extent of the identified masses. Patients with a soft-tissue mass had ultrasound-guided aspiration or core biopsy performed. Venous blood samples were collected in all patients for serum cobalt and chromium ion levels analysis using Inductively-Coupled Plasma Mass Spectrometer and lymphocyte transformation tests (LTT). The Oxford Hip Score (OHS) was used to measure the functional outcomes of patients. Acetabular component abduction angle was measured from standardised anteroposterior pelvis radiographs.

Results: Prevalence – Pseudotumours were found in 7 patients (6 female and 1 male). The overall prevalence of asymptomatic pseudotumours was 4%, with a relatively very high (30%) prevalence in females with bilateral implants. Histological examinations showed extensive necrosis of connective tissue, in which there were scattered aggregates of metal particles and a diffuse lymphocyte infiltrate.

Metal Ion Levels – The presence of pseudotumour was associated with significantly higher median serum cobalt levels (9.2mg/L vs. 1.9mg/L, p< 0.001), chromium levels (12.0mg/L vs. 2.1mg/L, p< 0.001), hip aspirate cobalt levels (1182 mg/L vs. 86.2mg/L, p=0.003), and aspirate chromium levels (883mg/L vs. 114.8mg/ L, p=0.006), as well as with inferior functional scores (OHS 41 vs. 47 p< 0.001). There was no significant difference in acetabular cup inclination angle (p=0.51). Lymphocyte Reactivity: A higher incidence and level of enhanced lymphocyte reactivity to Ni (p=0.001), but not to Co or Cr (the principal elements in the CoCr alloy used in metal-on-metal hip resurfacing implants), was found in patients with MoMHRA compared to the patients without MoM implants. However, lymphocyte reactivity to Co, Cr and Ni did not significantly differ in patients with pseudotumours compared to those patients without pseudotumours.

Conclusion: The prevalence of asymptomatic pseudotumours in females was high, especially in females with bilateral MoMHRA implants (30%). The patients with ‘asymptomatic’ pseudotumours were in fact mildly symptomatic. Lymphocyte reactivity to Co, Cr and Ni did not differ in patients with pseudotumour compared to those patients without pseudotumours, suggesting that systemic hypersensitivity type IV reactions, mediated by lymphocyte reactivity to these metals, is not the dominant mechanism in pathogenesis of the soft tissue pseudotumours. Furthermore, pseudotumours were not detected in those patients who had normal levels of cobalt and chromium ions. This suggests that pseudotumours do not occur if MoM articulations are well functioning. Therefore, pseudotumours are likely to be a biological consequence of the large amount of metal debris generated in vivo due to excessive wear.

Despite the satisfactory short-term implant survivor-ship, there is an increasing concern that the metal-on-metal hip resurfacing arthroplasty (MoMHRA) release large amount of very small wear particles and metal ions. The periprosthetic soft-tissue masses such as pseudotumours are being increasingly reported. These were found be locally destructive, requiring revision surgery in most patients. It has been suggested that either an immune reaction or cytotoxic effect of chromium(Cr) or cobalt(Co) may play a role in its aetiology. However, the effect of the phagocytosis of implant-associated metal nanoparticles on macrophages has not been elucidated. The aim of this study was to investigate the in vitro viability and proliferative response of murine macrophages to clinically relevant metal nanoparticles and ions.

Materials and Methods: The RAW 264.7 murine macrophage cell line was cultured in MEM at a seeding density of 10E5 cells/cm2. Culture was set up in the presence of either:(1) negative control: medium alone;(2)Cobalt sulphate heptahyrate and chromium chloride hexahydrate (Sigma) at concentrations of 1uM, 10uM, 100uM;(3)Metal nanoparticles sized 30–35nm (American Elements) of cobalt, chromium and titanium at concentrations from 10E7 to 10E14 particles/ml.

At the end of day 1 and 4, two methods were used to quantify cell proliferation and viability. The AlamarBlue assay(Invitrogen) incorporates a fluorimetric growth indicator and the fluorescence signal correlates with metabolic activity of the cells. LIVE/DEAD stain kit(Molecular Probes) contains two fluorescent dyes to stain living cells green and dead cells red. The viability was calculated by the number of live cells divided by total cell numbers. Inter-group comparisons were performed using one-way ANOVA with Tukey post hoc test. Differences at p< 0.05 were considered to be significant.

Results: Compared with control, Alamar blue assay showed inhibition of cell proliferation in all three metal particles (p< 0.05). The Live/Dead staining showed Co nanoparticles were cytotoxic to most of cells Day 1 and Day 4 at 10E11/mL. At 10E13/mL, the Cr group showed cytotoxicity at day 4 (p< 0.05). There was no difference between Ti and control group. The Co2+ and Cr3+ ions led to inhibition to cell proliferation. At 10uM concentration, Co2+ caused a dramatic decrease in cell number. Live/Dead staining showed that Co2+ were toxic to cells (p< 0.05). Cr3+ group showed cytotoxicity at Day 4 (p< 0.05).

Discussion: This study demonstrates that Co and Cr nanoparticles and ions have dose-dependent proliferation and cytotoxic effects on the macrophages in vitro. The cytotoxicity occurred at the high concentration range that is found in the hip aspirates of MoMHRA patients with pseudotumours. This suggests the formation of pseudotumour may be the local sequelae of cytotoxicity due to increased production of metal wear nanoparticles.

Recently, a series of locally destructive soft tissue pseudotumour has been reported in patients following metal-on-metal hip resurfacing arthroplasty (MoMHRA), requiring revision surgery in a high percentage of patients. Based on the histological evidence of lymphocytic infiltration, a delayed hypersensitivity reaction to nickel (Ni), chromium (Cr) or cobalt (Co) has been suggested to play a role in its aetiology. The aim of this study was to investigate the incidence and level of hypersensitivity reaction to metals in patients with pseudotumour.

Materials and Methods: 25 patients were investigated in this Ethics approved study:

Group 1: MoMHRA patients with pseudotumours, detected on the ultrasound and confirmed with MRI (n=6, 5 F:1 M, mean age 53 years);

Lymphocyte transformation tests (LTT) were used to measure lymphocyte proliferation responses to metals. Peripheral blood mononuclear cells were isolated from heparinized blood samples using standard Ficoll–Hypaque® (Pharmacia). The PBMC were cultured at a cell density of 106 cells/mL. Culture was set up in the presence of either:

medium alone;

After 5 days of culture, cells were pulsed with [3H]-thymidine and proliferation was assessed by scintillation counting. The stimulation index (SI) was calculated by the ratio of mean counts per minute of stimulated to unstimulated cultures. A SI value of greater than 2.0 was interpreted as a positive result.

Results: A clinical history of metal allergy was reported in 2/6 in Group 1, 2/13 in Group 2, and none in Group 3. In pseudotumour group, the incidence of reactivity to Ni, Co and Cr was 60%, 17% and 0%, respectively. Within Group 2, the reactivity to Ni, Co and Cr was 69%, 8% and 15%, respectively. One control subject had reactivity to Ni. Inter-group comparisons of mean SI values (Kruskal-Wallis non-parametric analysis of variance) showed no significant differences (p> 0.05).

Discussion: The incidence of enhanced lymphocyte response to metals in patients with MoMHRA was more common than the control group. However, in comparison with non-pseudotumour patients, there was no significant difference in the incidence or the level of lymphocyte reactivity in patients with pseudotumour. We conclude that patients with MoMHRA have an enhanced lymphocyte response to metal ions, reflecting exposure and immune reactivity. However, patients with pseudotumours have a similar proliferative response to those without pseudotumours, which suggests that type IV hypersensitivity may not be the cause of the pseudotumours.

Tribological studies of hip arthroplasty suggest that larger diameter metal-on-metal (MOM) articulations would produce less wear than smaller diameter articulations. Other advantages using these large femoral heads implants include better stability with lower dislocation rates and improved range of motion. The aim of the present study was to compare chromium (Cr), cobalt (Co) and titanium (Ti) ion concentrations up to 1-year after implantation of different large diameter MOM total hip arthroplasty (THA).

Methods: Cr, Co and Ti concentrations were measured using a high resolution mass spectrometer (HR-ICP-MS) by an independent laboratory in 110 patients, randomized to receive a large metal-on-metal articulation unce-mented Ti THA from one of the following companies: Zimmer, Smith & Nephew, Biomet or Depuy. Samples of whole blood were collected pre-operatively, and postoperatively at six months and one year.

Summary of Results: At 6 months, whole blood cobalt levels were: (table removed)

Statistical group comparison revealed significant difference for Cr (p=0.006), Co (p=0.047) and Ti (p=< 0.001). With Biomet implants presenting the best results for Cr and Co and Zimmer the highest Ti level.

Discussion: Different implant factors may influence measured metal ion level in whole blood: articular surface wear and implant passive corrosion. Bearing wear may be related to its diameter, quality of the surface finish, component sphericity, radial clearance, manufacturing process (forged vs cast metal) and metal carbon content. Biomet articulation seems to present the best factors selection. Passive corrosion of exposed metallic surfaces is represented by the elevated Ti levels found in all tested systems (Ti was not part of the bearing surfaces). The plasma sprayed acetabular component surface of the Zimmer’s component seems to be responsible for the significant difference in Ti versus the other implants.

Introduction: Metal on metal Hip Resurfacing Arthroplasty (MoMHRA) has gained popularity due to its perceived advantages of bone conservation and relative ease of revision to a conventional THR if it fails. This retrospective study is aimed at assessing the functional outcome of failed MoMHRA revised to THR and comparing it with a matched cohort of primary THRs.

Method: Since 1999 we have revised 53 MoMHRA to THR. The reasons for revision were femoral neck fracture (Group A, n=21), pseudotumour (Group B, n=16) and other causes (Group C, n=16: loosening, avascular necrosis and infection). Average follow-up was 3 years months (1.2–7.3). These revisions were compared with 106 primary THRs which were age, gender and follow-up matched with the revision group in a ratio of 2:1.

Results: The mean Oxford Hip Score (OHS) was 20.1 (12–51) for group A, 39.1 (14– 56) for group B, 22.8 (12–39) for group C and 17.8 (12–45) for primary THR group. In group A, there were three infections requiring further revisions. In group B, there were three recurrent dislocations, three patients with femoral nerve palsy and one femoral artery stenosis. In group C, there were no complications. The differences in clinical and functional outcome between group B and the remaining groups as well as the difference in the outcome between group B and control group were statistically significant (p < 0.05).

Conclusions: THR for failed MoMHRA was associated with significantly more complications, operation time and need for blood transfusion for the pseudotumour group. In addition, the revisions secondary to pseudotumour also had significantly worse functional outcome when compared to other MoMHRA revisions or primary THR.

Introduction: Despite the satisfactory short-term implant survivorship of MoM hip resurfacing arthroplasty, symptomatic abnormal periprosthetic soft-tissue masses relating to the hip joint, ‘pseudotumours’, are being increasingly reported. These were found be locally destructive, requiring revision surgery in 75% of patients. Asymptomatic pseudotumours have not been previously investigated.

Methods: The aims were: (1) to investigate the prevalence of asymptomatic pseudotumours; and (2) to investigate their potential association with the level of metal ions. A total of 160 hips in 123 patients with a mean age 56 years (range 33–73) were evaluated at a mean follow-up of 61 months (range 13–88). Radiographs and OHS were assessed. Patients with a cystic or solid mass detected on the ultrasound/MRI had an aspiration or biopsy performed. Cobalt and chromium levels were analysed using Inductively-Coupled Plasma Spectrometer.

Results: Pseudotumours were found in 6 patients (5F: 1M). In 80% of bilateral cases, it was found in both sides. Histological examination showed extensive necrosis and diffuse lymphocyte infiltration. The presence of pseudotumour was associated with higher serum cobalt (9.2 μg/L vs. 1.9μg/L, p< 0.001) and chromium levels (12.0μg/L vs. 2.1μg/L, p< 0.001); higher hip aspirate cobalt (1182 μg/L vs. 86.2μg/L, p=0.003) and chromium levels (883μg/L vs. 114.8μg/L, p=0.006); and with inferior OHS (23 vs. 14 p=0.08).

Discussion: The prevalence of asymptomatic pseudotumour (5%) was higher than previously reported for the symptomatic pseudotumours (1%). There was a sixfold elevation of serum and a twelve-fold elevation of hip aspirate levels of cobalt and chromium in patients with pseudotumours. This suggests that pseudotumours may be a biological consequence of the large amount of metal debris generated in vivo. The association between pseudotumour and elevated metal ion levels might theoretically be explained by either systemic hypersensitivity responses to metal ions or local cytotoxic effects due to a high level of metal ions.

The presence of pseudotumours, which are soft-tissue masses relating to the hip, after metal-on-metal hip resurfacing arthroplasty has been associated with elevated levels of metal ions in serum, suggesting that pseudotumours occur when there is increased wear. We aimed to quantify the wear in vivo of implants revised for pseudotumours (eight) and of a control group of implants (22) revised for other reasons of failure.

We found that the implant group with pseudotumours had a significantly higher rate of median linear wear of the femoral component at 8.1 μm/year (2.75 to 25.4) than the 1.79 μm/year (0.82 to 4.15; p = 0.002) of the non-pseudotumour group. For the acetabular component a significantly higher rate of median linear wear of 7.36 μm/year (1.61 to 24.9) was observed in the pseudotumour group compared with 1.28 μm/year (0.81 to 3.33, p = 0.001) in the other group. Wear of the acetabular component in the pseudotumour group always involved the edge of the implant, indicating that edge-loading had occurred.

Our findings are the first direct evidence that pseudotumour is associated with increased wear at the metal-on-metal articulation. Furthermore, edge-loading with the loss of fluid-film lubrication may be an important mechanism of generation of wear in patients with a pseudotumour.

We evaluated 3 cases of ceramic-on-ceramic THA in that the evidence of the impingement between the metal neck and the ceramic liner was found.

Between July 2007 and January 2008, impingement between the metal and the ceramic liner was found in 3 cases of ceramic-on-ceramic THA during re-operation. The re-operation was performed 3–6 years after the primary surgery because of ceramic head fracture, deep infection and cup loosening. All patients frequently sat on the floor in tailor fashion but did not have any sound in the hip after THA.

In all cases, V-shaped indented wear scar was found on the postero-superior aspect of the metal neck. Two ceramic liners could be retrieved. Both showed black staining in the postero-superior portion of the rim. The outer edge of the bearing surface of the retrieved acetabular liners was evaluated with SEM. The black stained area of the acetabular liner rim was found to be roughened. A micro-crack propagating into the deep portion of the ceramic liner was observed in one liner.

Our observations suggest that impingement between the ceramic liner and the metal neck can cause crack formation leading to ceramic liner failure in vivo.

Metal-on-metal hip resurfacing is commonly performed for osteoarthritis in young active patients. We have observed cystic or solid masses, which we have called inflammatory pseudotumours, arising around these devices. They may cause soft-tissue destruction with severe symptoms and a poor outcome after revision surgery. The aim of this study was to determine the incidence of and risk factors for pseudotumours that are serious enough to require revision surgery.

Since 1999, 1419 metal-on-metal hip resurfacings have been implanted by our group in 1224 patients; 1.8% of the patients had a revision for pseudotumour. In this series the Kaplan-Meier cumulative revision rate for pseudotumour increased progressively with time. At eight years, in all patients, it was 4% (95% confidence interval (CI) 2.2 to 5.8). Factors significantly associated with an increase in revision rate were female gender (p < 0.001), age under 40 (p = 0.003), small components (p = 0.003), and dysplasia (p = 0.019), whereas implant type was not (p = 0.156). These factors were inter-related, however, and on fitting a Cox proportional hazard model only gender (p = 0.002) and age (p = 0.024) had a significant independent influence on revision rate; size nearly reached significance (p = 0.08). Subdividing the cohort according to significant factors, we found that the revision rate for pseudotumours in men was 0.5% (95% CI 0 to 1.1) at eight years wheras in women over 40 years old it was 6% (95% CI 2.3 to 10.1) at eight years and in women under 40 years it was 13.1% at six years (95% CI 0 to 27) (p < 0.001).

We recommend that resurfacings are undertaken with caution in women, particularly those under 40 years of age but they remain a good option in young men. Further work is required to understand the aetiology of pseudotumours so that this complication can be avoided.

Inflammatory pseudotumours occasionally occur after metal-on-metal hip resurfacing and often lead to revision. Our aim was to determine the severity of this complication by assessing the outcome of revision in these circumstances and by comparing this with the outcome of other metal-on-metal hip resurfacing revisions as well as that of matched primary total hip replacements.

We identified 53 hips which had undergone metal-on-metal hip resurfacing and required revision at a mean of 1.59 years (0.01 to 6.69) after operation. Of these, 16 were revised for pseudotumours, 21 for fracture and 16 for other reasons. These were matched by age, gender and diagnosis with 103 patients undergoing primary total hip replacement with the Exeter implant.

At a mean follow-up of three years (0.8 to 7.2) the outcome of metal-on-metal hip resurfacing revision for pseudotumour was poor with a mean Oxford hip score of 20.9 (sd 9.3) and was significantly worse (p < 0.001) than the outcome for fracture with a mean Oxford hip score of 40.2 (sd 9.2) or that for other causes with a mean Oxford hip score of 37.8 (sd 9.4). The clinical outcome of revision for pseudotumour was also significantly worse (p < 0.001) than the outcome of matched primary total hip replacements. By contrast, the outcome for fracture and other causes was not significantly different from that of matched primary total hip replacements (p = 0.065). After revision for pseudotumour there were three cases of recurrent dislocation, three of palsy of the femoral nerve, one of stenosis of the femoral artery and two of loosening of the component. Five hips required further revision. In three of these there was evidence of recurrent pseudotumour, and one is currently awaiting further revision. The incidence of major complications after revision for pseudotumour (50%) was significantly higher (p = 0.018) than that after revision for other causes (14%).

The outcome of revision for pseudotumour is poor and consideration should be given to early revision to limit the extent of the soft-tissue destruction. The outcome of resurfacing revision for other causes is good.

Patella infera can cause knee pain and lead to patellofemoral osteoarthritis. Treatment is usually unsatisfactory. We describe a case of severe patella infera after operative treatment for fracture of the patella. We used Ilizarov external fixation and gradual lengthening of the patellar tendon. The patellar height was restored and the patient’s symptoms were much improved.

Introduction: Spondylolysis is amongst the commonest causes of low back pain in the athletic child. We observed increased uptake in the pedicles of the affected segment and a triangular pattern of uptake in the sagittal projection of tomographic studies of fractures of the pars interarticularis. The hypothesis that these observations were specific for fractures of the pars interarticularis was tested in a variety of spinal disorders.

Methods:. A retrospective study of 25 young athletes with a variety of spinal disorders was undertaken (17males, 8 females; average age 13.5 years [range: nine to16 years]). The patients were referred from a specialised sports clinic. Back pain was present for an average of four months (Range six weeks to 11 months). All children had planar and tomographic scintigraphic bone scans with special reconstruction. The diagnosis was confirmed by radiological studies and/or response to treatment.

Results:. All 15 children with spondylolysis had evidence of increased uptake in the ipsilateral (12/15) or contra-lateral pedicle (3/15). None of the cases of muscle insertion injury, facet joint or disc disease demonstrated this pattern. A triangular shaped pattern of uptake was only seen in the sagittal view of the tomographic studies in patients with fractures of the pars interarticularis.

Conclusion:. We have described two unique features of spondylolysis that add to the confidence with which the scintigraphic diagnosis may be made.