Introduction. After total hip arthroplasty, dislocation is one of the most frequent serious early complications. This occurs in part due to impingement (catching and leverage of the neck-cup on the inlay/cup border). Impingement may also negatively impact long-term outcomes. Materials and Methods. A preliminary model for an optimised hip endoprosthesis system was developed to offer a mechanical solution to avoid impingement and dislocation. A computer-supported range of motion simulation using parameters of cup anteversion and inclination as well as torsion and CCD shaft angle was then performed to localise areas of anterior and posterior impingement of typical acetabular cups. Results. Through isolation of the two main trajectories of motion, and modifications with corresponding gaps to the inlay/cup areas as well as oppositional banking in the abduction/adduction plane, the combination of a snap-fit acetabular cup with reduced cup profile was the result: the “bidirectional total hip prosthesis.”. Under standardised parameters, the ranges of impingement for typical implants are not directly opposite one another (at 180°), but are found instead at an angle of 108.3°. Conclusion. Complications such as dislocation and impingement may possibly be avoided with the bidirectional total hip prosthesis. Typical implantation parameters yield an implant design with rotational asymmetry. [Fig. 1, 2]

Introduction. Total hip arthroplasty in young patients is still associated with high failure rates, especially at the acetabular side. Purpose of this study was to evaluate the long-term results of the Alloclassic cementless Zweymüller total hip prosthesis in patients younger than 50 years at the time of surgery. Methods. Between 1987 and 1994, 73 Zweymüller total hip arthroplasties with a titanium threaded cup were placed in 67 patients younger than 50 years. Mean age at surgery was 43 years (23–49 years). Patients were followed clinically with use of the HHS, revisions were determined and radiographs were analyzed. Kaplan-meier analysis was used to determine survival for different endpoints. Results. Three hips were revised for septic loosening, 3 cups for aseptic loosening and 1 hip because of periprosthetic fracture. Four patients (4 hips) died and 8 patients (9 hips) were lost to follow-up without any revision. 48 patients with 53 prostheses could be evaluated after a mean follow-up of 208 (170–253) months and the mean HHS was 90 (52–100). Cumulative survival analysis with endpoint revision for any reason was 89% (C.I. 85–93) at 17 years. With endpoint aseptic loosening, survival was 95% (C.I. 91–98) at 17 years. Conclusion. Alloclassic Zweymüller total hip arthroplasty with a titanium threaded cup showed good long-term results, even in this group of patients younger than 50 years

Introduction

Post op cup anatomical and functional orientation is a key point in THP patients regarding instability and wear. Recently literature has been focused on the consequences of the transition from standing to sitting regarding anteversion, frontal and sagittal inclination. Pelvic incidence (PI) is now considered as a key parameter for the analysis of sagittal balance and sacral slope (SS) orientation. It's influence on THP biomechanics has been suggested. Interestingly, the potential impact of this morphological angle on cup implantation during surgery and the side effects on post op functional orientation have not been studied.

Our study explores this topic from a series of standing and sitting post-op EOS images

Introduction

Revision surgery is generally recommended for recurrent dislocation following Total hip arthroplasty (THA). However, dislocation following revision THA continues to remain a problem with further dislocation rates upto 28% quoted in literature.

We present early results of one of the largest series in U.K. using dual mobility cemented acetabular cup for recurrent hip dislocation.

BACKGROUND CONTEXT

Ceramic bearings are widely used in total hip arthroplasty (THR) along with metal and polyethylene bearings. There were several studies in past few years evaluating the advantage of one over the other. The young population with high activity levels has an increased risk of wear debris production at bearing surface and subsequent implant failure. Recently, interest and use of a ceramics with high wear resistance has been growing. Early reports on ceramic on ceramic THR have demonstrated excellent clinical and radiological results.

Introduction. The metal-on-metal (MoM) total hip prosthesis is widely used. However, the adverse reactions such as pseudotumor around the total hip prosthesis are observed. This is considered the effect of the corrosion of alloy which includes metal ion release and the wear particle generation. As materials for total hip prostheses, cobalt chromium (Co-Cr) alloy is used because of the wear resistance and corrosion resistance. The passive film on the surface of alloy contributes to corrosion resistance. The passive film is removed easily with friction. Therefore, metal ion is released from bare metal. However, this removal of passive film can be restored because of oxidation reaction with neighboring environment. The modular MoM total hip prosthesis such as acetabular component-femoral head or taper junction which connect femoral head and stem have friction interfaces. The friction amplitudes must be different among these interfaces. However, how sliding amplitude affects on removal of a passive film is unclear. The main purpose of this study was to investigate the effect of the sliding amplitude of the reciplocating micromotion on removal and reformation of the passive film of Co-Cr alloy. Methods. The behavior of the passive film was observed by measuring the electric potential of the alloy. Co-Cr alloy (ASTM F75) pin specimen and common tablet specimen were immersed in simulated body fluid PBS(−) and abraded with friction testing machine. The electronic potential between the pin and the Ag/AgCl reference electrode (RE-1C, ALS, Tokyo, Japan) were measured using a high impedance electrometer (HE-104E, HOKUTO DENKO, Tokyo, Japan). The friction amplitude was chosen from 0.2–2 mm. The reciprocating cycle was 1 Hz. The load of 10 N applied on the pin by a weight. Results and discussion. The electric potential neared equilibrium before the friction, and the passive film was stable. Electric potential dropped with the onset of friction and gradually increased with the cessation of friction. The potential difference ΔV and a time constant τ of the rise in electric potential after the friction were estimated. Those ΔV and τ were used as the indicator of the passive film destruction and restoration, respectively. At the friction amplitude of 0.2 mm, ΔV was lowest among at the other amplitudes. On the other hand, τ tended to be longer (Fig. 2). It showed that the reformation of passive film was delayed. When the removal of the passive film was repeated on local area of the friction interfaces, it was presumed similar to a phenomenon of the crevice corrosion. To view tables/figures, please contact authors directly

Orthopaedic implants, such as femoral heads, sockets and stems, are manufactured with a high degree of smoothness and very low form error in order to function as low wear bearings. The surfaces are subject to both wear and damage during in vivo use. Articulating surfaces naturally wear during normal use. Aseptic loosening associated with osteolysis and release of wear particles is the main reason for revision of total hip arthroplasty (THA). Damage of femoral heads is well known to increase the wear rate at the articulating surface and is vulnerable to scratching during the maneuver of positioning the femoral component into the acetabulum component either in primary as in revision total hip arthroplasties. The findings emphasize the importance of achieving and maintaining good surface finish of the femoral head component. The author presents a very simple and “zero cost” method of preventing scratching of the femoral head of any kind of total hip prosthesis (ceramic on ceramic, ceramic on poly, metal on metal, metal on poly and even metal on ceramic) when the reduction of the femoral head prosthesis is done inside the new acetabular component with metal, ceramic liner or poly liner with metal back (where the scratching can also occur) as one of the final stages of the surgical procedure which can be crucial to the long survival of the hip prosthesis. A short one minute video on an e-poster will show how this can be done being an easy, reproducible, safe and reliable technique to prevent femoral head scratching

Backgrounds. The authors present an analysis of 30 cases of total hip prosthesis performed with minimally invasive surgical earlier compares with 30 cases of total hip prosthesis performed surgically with direct side. The intent is to demonstrate the immediate and clear advantages especially in the postoperative surgical minimally invasive front. Methods. The authors present a randomized study of thirty cases of patients undergoing surgery for osteoarthritis of the hip prosthesis with primary surgical minimally invasive front compared to a group of 30 patients undergoing surgery with direct surgical side. All patients had the same cementless implants and instruments with the same surgeon. Patients were then evaluated in four different times: before surgery, immediate postoperative, after 1 week and 4 months after surgery. Results and conclusions. The experience of the authors on the surgical front shows the immediate and clear advantages in postoperative species by saving the muscle tissues, little pain, little bleeding, more quick and easy re-education and rehabilitation

Postoperative dislocation following total hip arthroplasty (THA) remains a significant concern with a reported incidence of 1% to 10%. The risk of dislocation is multifactorial and includes both surgeon-related (i.e. implant position, component size, surgical approach) and patient-related factors (i.e. gender, age, preoperative diagnosis, neurologic disorders). While the majority of prior investigations have focused on the importance of acetabular component positioning, recent studies have shown that approximately 60% of “dislocators” following primary THA have an acceptably aligned acetabular component. Therefore, the importance of the relationship between the spine and pelvis, and its impact on functional component position has gained increased attention. Kanawade and Dorr et al. have shown patients can be categorised into having a stiff, normal, or hypermobile pelvis based on their change in pelvic tilt when moving from the standing to seated position. The degree of change in functional position of both the acetabular and femoral components is impacted by the degree of pelvic motion each patient possesses. In the “normal” pelvis, as a patient moves from the standing to seated position the pelvis typically tilts posteriorly, thus increasing the functional anteversion of the acetabular component. However, patients with lumbar degeneration or spine pathology often have a decrease in posterior pelvic tilt in the seated position, thus potentially increasing their risk of dislocation. Bedard et al. noted an 8.3% dislocation risk in patients with a spinopelvic fusion after THA vs. 2.9% in those without. There is the potential that preoperative, dynamic imaging can be used to predict the ideal component position for each individual patient undergoing THA. However, this assumes that a patient's preoperative pelvic motion will be the same following implantation of a total hip prosthesis, and that a patient's pelvic motion will remain consistent over time postoperatively. A recent study has shown that the impact of THA on pelvic motion can be highly variable, thus potentially limiting the utility of preoperative dynamic imaging in predicting a patient's ideal component position. Future investigations must focus on preoperative factors that can be used to predict postoperative pelvic motion and how pelvic motion changes over time following implantation of a total hip arthroplasty

Introduction. A 68 year old female patient underwent a left total hip replacement for primary osteoarthritis in March 2004. She was referred back by her GP 5 years as she was struggling with mobility and felt there were mice in her hip. It was squeking so loudly that it could be hear at a distance of 25 metres. There was no history of any falls or dislocation in the last 5 years. The implant used was an Exeter/ABG ceramic total hip prosthesis with Palacos cement. This ladies discomfort in her hip had been always there. She never described herself as being satisfied with the THR. However, her discomfort had worsened terribly over the last year. On examination. The slightest movement around her hip caused her severe pain. Tremendous squeaking could be heard when she was made to walk. She had significantly limb length discrepancy of 2.5cms. The radiographs revealed that she had probably broken the ceramic head as pieces could be seen around the neck area. On table. When the hip was exposed through standard lateral approach it was found that the ceramic head was intact. There was a large amount of blackish debris around the entire area and the shell of the ABG cup had a huge defect in it. It was a strartling revelation as it was initially thought that the ceramic head was broken. Revision surgery was carried out with a C stem total hip prosthesis with an orthodynamic socket. Discussion. Ceramic bearing surfaces have been introduced to reduce friction and prevent bone loss. There has been a problem with squeaky hips following ceramic implant insertion. However there has been no report of cup wear and an intact ceramic head till date in literature. To our knowledge this is the first case being reported and the images are quite startling

Introduction. Computer navigation is a highly sophisticated tool in orthopedic surgery for component placement in total hip arthroplasty (THA). In order to apply it adequately it is of upmost importance that the targets the surgeon is trying to hit are well-defined. This concept considers all four component orientations: cup inclination (cIncl) and anteversion (cAV), stem antetorsion and neck-to-shaft angle. The optimising goal in this concept is maximising the size of the cSafe-Zone. Methods. A computerised 3D- model of a total hip prosthesis was used to systematically analyse all combinations of component orientations in automatised batch runs. Component orientations were varied for cup inclination, cup anteversion, neck antetorsion and neck inclination. Results. The combined Safe-Zone outlines spaces in a 3D-diagram that show the relationship between cup inclination, cup anteversion and neck anteversion, while the neck inclination is used as a curves parameter. These spaces include all component orientation that allow the predefined iROM without prosthetic impingement. In order to compare these results to Lewinnek's recommendation cross-sections were taken at distinct neck antetorsions in 5° intervals. Conclusion. The new combined Safe-Zone (cSafe-Zone) includes all orientation parameters of both total hip components and such gives well-defined recommendations for combined positioning of both components. Ideally it can be introduced into a smart computer navigation system in order to compute in real-time the best combined orientation of both components

Introduction. The purpose of this study was to experimentally evaluate impingement and dislocation of total hip replacements while performing dynamic movements under physiological-like conditions. Therefore, a hardware-in-the-loop setup has been developed, in which a physical hip prosthesis actuated by an industrial robot interacts with an in situ-like environment mimicked by a musculoskeletal multibody simulation-model of the lower extremity. Methods. The multibody model of the musculoskeletal system comprised rigid bone segments of the lower right extremity, which were mutually linked by ideal joints, and a trunk. All bone geometries were reconstructed from a computed tomography set preserving anatomical landmarks. Inertia properties were identified based on anthropometric data and by correlating bone density to Hounsfield units. Relevant muscles were modeled as Hill-type elements, passive forces due to capsular tissue have been neglected. Motion data were captured from a healthy subject performing dislocation-associated movements and were fed to the musculoskeletal multibody model. Subsequently, the robot moved and loaded a commercially available total hip prosthesis and closed the loop by feeding the physical contact information back to the simulation model. In this manner, a comprehensive parameter study analyzing the impact of implant position and design, joint loading, soft tissue damage and bone resection was implemented. Results. The parameter study revealed a generally high dislocation risk for the seating-to-rising with adduction scenarios. Improper implant positioning or design could be compensated by adjusting prosthesis components correspondingly. Gluteal insufficiency or lower joint loading did not result in higher impingement or dislocation risk. However, severe malfunction of the artificial joint was found for proximal bone resection. Discussion. Previous testing setups ignored the impact of active muscles or relied on simplified contact mechanics. Herein, total hip replacement stability has been investigated experimentally by using a hardware-in-the-loop simulation. Thereby, several influencing factors such as implant position and design as well as soft tissue insufficiency and imbalance could be systematically evaluated with the goal to enhance joint stability

Introduction. Lewinnek's Safe-Zone gives recommendations only for cup placement in total hip arthroplasty while the orientation of the neck isn't considered. Furthermore the criteria for cup placement are not clearly defined and the ranges for cup orientation are considerably large. This study introduces new recommandations for the combined placement of both total hip components, when both, cup and stem, are considered. This defines the new dynamic combined safe-zone (cSafe-Zone) which gives clear directions for the optimal combined orientation of both components in order to maximize the intended range of movement (iROM) while reducing the risk for prosthetic impingement and dislocation. Material and Methods. The combined safe-zone outlines the area that encloses all component orientations that achieve the predefined iROM without prosthetic impingement. A computerized 3D-model of a total hip prosthesis was established that does systematically test all design parameters semi-automatically in order to identify those component positions that fulfill the predefined conditions. The analysis was carried out for straight stems, anatomic stems and short stems. The iROM is composed of basic movements like flexion/extension, internal/external rotation, ab/adduction and combination of these movements that the patient should reach and that are commonly accepted as physiologic hip movements. The orientation of the cup was varied between 20° and 70° of inclination and −10° of retro- to 40° anteversion. Stem antetorsion was tested from −10° retro- to 40°-antetorsion and CCD-angle from 110° to 150°. Head-size and head/neck ratio were additional parameters. Results. The new combined safe-zone has a dynamic location and has a polygonal outer boundary. It is smaller than Lewinnek's safe-zone. Its size and location within the cup inclination/anteversion diagram depends on the antetorsion and the CCD-angle of the stem. It can be demonstrated that a low-anteverted stem should be combined with a high-anteverted cup and vice versa, i.e. cup anteversion and stem antetorsion are linearly but inversely correlated. This is true for a straight stem as well as for anatomic and for short stems. The size of the cSafe-Zone is largest when the socket is radiographically anteverted between 20° and 25°. The neck/shaft-angle (CCD-angle) and the anatomic design do have a high impact on the preferred antetorsion of the stem. A straight 130°-CCD-stem is best implanted in about 15°+/−4degree of antetorsion while an anatomic 127°-CCD-stem can be implanted in a lower degree of antetorsion. Increasing the head/neck ratio increases the cSafe-Zone too and gives room for a lower cup inclination which increases the jumping distance. The optimal CCD-angle of a straight stem is 127°+/−3 degree. Conclusion. The new combined safe-zone (cSafe-zone) gives well-defined recommendations for cup and stem placement taking into account the dynamic interrelationship between cup and stem. In extending Lewinnek's recommendations it defines how both the cup and the stem should be oriented relative to each other and how the component's orientations are optimized in order to achieve the highest safety against prosthetic impingement while reaching the highest range of movement which is especially important for high-performance materials and in young and active patients

Several risk factors can and should be addressed during first stage or spacer implantation surgery in order to minimize complications. Technical aspects as well as practical tips and pearls to overcome common nuisances such as spacer instability or femoral and acetabular bone loss will be discussed and shown with pictures. Total joint arthroplasty (TJA) is one of the most successful procedures in orthopaedics and excellent results are expected in virtually all cases. Periprosthetic joint infection (PJI) though unusual, is one of the most frequent and challenging complications after TJA. It is the third most common cause of revision in total hip replacement, responsible for up to 15% of all cases. In the past few years several improvements have been made in the management of an infected total hip prosthesis. Nevertheless it remains a challenging problem for the orthopaedic surgeon. Although numerous studies report favourable outcomes after one-stage revision surgery, two-stage has traditionally been considered as the gold standard for management of chronic infection. Two-stage exchange consists of debridement, resection of infected implants and usually temporary placement of an antibiotic-impregnated cement spacer before reimplantation of a new prosthesis. Spacers can be classified as static or articulating. The goals of using an articulating antibiotic loaded cement spacer are two-fold: to enhance the clearance of infection by local antibiotic therapy and dead-space management while maintaining joint function during treatment thus improving the functional outcome at reimplantation. Still, hip spacer implantation is not innocuous and there are several possible complications. Going forward, one must consider not just eradicating infection but also the importance of restoring function. In this regard using a mobile spacer adds an element of physiologic motion that both increases patient comfort between stages and facilitates re-implantation surgery. Conversely, mechanical complications are one of the major consequences of this preference. Be that as it may there are ways to minimize these problems. It is the surgeon responsibility to optimize mechanical circumstances as much as possible. I would like to thank Dr. Ricardo Sousa for his help with this work

Introduction. In a recent study we evaluated the clinical and radiographic long-term results as well as the serum metal concentrations of 105 cementless primary total hip prosthesis, performed between November 1992 and May 1994 with a 28-mm high-carbide-concentration metal-on-metal articulating surfaces. Forty-one patients who had had a total of forty-four arthroplasties were available for follow-up evaluation at a minimum of seventeen years postoperatively. The median serum cobalt concentration of the patients with their hip replacement as the only source of cobalt was 0.7 µg/L (range 0.4–5.1µg/L), showing no significant difference to the previous study after a minimum of 10 years follow-up. We were investigating the systemic dissemination, which in turn, did not show more severe effects, such as carcinogenicity or renal failure. There are many complex issues associated with the analysis of metal ions, including collecting technique, analysis and reporting of the results. At the AAOS in March 2013, the Hip Society mentioned, that systemic ion levels are just one factor in the evaluation and should not be relied upon solely to determine the need for revision surgery. Furthermore, the correlation between cobalt or chromium serum, urin or synovial fluid levels and adverse local tissue reactions is incompletely understood. Patients and Methods. In our present study we evaluated the serum, urin as well as the joint aspirate metal concentrations, of cementless total hip arthroplasties with a high-carbon, metal-on-metal bearing (Metasul®) at a mean of eighteen-years follow-up. We performed a correlation analysis to evaluate the relationship between these values and to determine whether elevated serum metal concentrations are associated with elevated and local metal concentrations and with early failure of metal-on-metal articulations. Results. Spearman correlations evaluated that there was no significant relationship between the serum cobalt or chromium level and the joint aspirate cobalt (r= 0.60, p=0.15) or chromium (r=0.39, p=0.38) concentration, and the urin cobalt (r=0.21, p=0.62) or chromium (r=0.27, p=0.51) level. Additionally we evaluated a positive correlation between the local chromium concentration and the BMI (r=0.53, p= 0.21) and the cup inclination (r=0.24, p=0.64), a negative correlation between the local chrom concentration and the UCLA (r=0.25, p=0.59) and the Harris hip score (r=0.16, p= 0.73), but without a significance. Conclusion. We evaluated the regional dissemination and the local determination in the synovial fluid, which offers better information about wear and local reactions at the components level prior to the occurrence of marked adverse local tissue and therefore is the best predictor for wear related tissue reaction in MOM articulations, even in asymptomatic patients

Introduction. Total hip replacement is an established surgical procedure done to alleviate hip pain due to joint diseases. However, this procedure is avoided in yonger patients with higher functional demands due to the potential for early failure. An ideal prosthesis will have have a high endurance against impact loading, with minimal micromotion at the bone cement interface, and a reduced risk of fatigue failure, with a favourable stress distribution pattern in the femur. We study the effect of varying the material properties and design element in a standard cemented total hip using Finite Element Analysis. Methods. A patient-specific 3D model of femur will be constructed from CT scan data, while a Summit® Cemented Hip System (DePuy Orthopedic) will be used to as a control for comparative evaluation. We vary the material stiffness of different parts of the prosthesis(see Fig.1) to formulate a design concept for a new total hip prosthesis design; and use Finite Element Method to predict the micromotion of the hip prosthesis at the bone cement interface, as well as the stress distribution in the the femur. Result. Validation of computational protocol was being done by comparing the principal maximum strain of the femoral cortex along the diaphysis, and the amount of deflection, with published literature, similarly, contact modelling validation was also done. Model 1–4 induced lower peak Von Mises stress in the cement, which takes a much lower value than any of the cement mechanical limits postulated. Therefore, the risk of cement failure is greatly reduced in Model 1–4. However, the effect of varying stiffness in different regions is not significant in terms of load transmission to the cement. Micromotion at the bone-cement interface was studied via two approaches: Peak micromotion at the bone cement interface; and the micromotion data at 12 Regions of Interest (ROI)s. Both results showed that model 2 and 3 are capable of reducing micromotion at bone-cement interface, in comparison with the Summit® Cemented Hip System. By comparing the Von Mises Stress distribution in the proximal femur; model 1 is found to result in a significantly reduced stress shielding effect, while model 2–4 are also favourable in comparison to the standard Summit® prosthesis in terms of stress distribution in the femur. Figure 2 shows the effects of the performance of model 1–4, presented as percentage difference from the Summit® prosthesis. Model 1 is unfavourable, despite its favourable stress distribution, because its peak and overall micromotion at the bone-cement interface is greatly increased. Conclusion. Model 2 and 3 have favourable design elements. They both have reduced micromotion at the bone-cement interface; and a favourable stress distribution in the femur. Further refining and testing of model 2 and 3 should done, as these models may provide information which may be useful in improving the performance of the current range of total hip replacement prostheses

Introduction. Relative motion at the modular head-neck junction of hip prostheses can lead to severe surface damage through mechanically-assisted corrosion. One factor affecting the mechanical performance of modular junctions is the frictional resistance of the mating surfaces to relative motion. Low friction increasing forces normal to the head-neck interface, leading to a lower threshold for slipping during weight-bearing. Conversely, a high friction coefficient is expected to limit interface stresses but may also allow uncoupling of the interface in service. This study was performed to examine this trade-off using finite element models of the modular head-neck junction. Methods. A finite element model (FEM) of the trunnion/ head assembly of a total hip prosthesis was initially created and experimentally validated. CAD models of a stem trunnion (taper size: 12/14mm) and a prosthetic femoral head (diameter: 28mm) were discretized into elements for finite element analysis (FEA). The trunnion (Ti6Al4V) was modelled with a hexahedral mesh (33,648 elements) and the femoral head (CoCrMo) with a tetrahedral mesh (51,182 elements). A friction-based sliding contact interface was defined between the mating surfaces. The model was loaded in 2 stages: (i) an assembly load of 4000N applied along the trunnion axis, and (ii) 500N applied along the trunnion axis in combination with a torque of 10Nm. A linear static solution was set up using Siemens NX-Nastran solver. Multiple simulations were executed by modulating the frictional coefficient at the taper-bore interface from 0.05 to 0.15 in increments of 0.01, the coefficient of 0.1 serving as the control case (Swaminathan and Gilbert, 2012). Results. The vertical and tangential displacements of the nodes on the taper of the trunnion relative to the femoral head demonstrated a strong inverse dependence upon the coefficient of friction at the interface (Fig. 1). A similar trend was observed with respect to the peak interface pressure (Fig. 2). The peak von Mises stress, however, increases with increasing coefficient of friction (Fig. 2). A Fisher's R to Z correlation test was performed on each output variable to determine its correlation with coefficient of friction. The coefficient of friction correlated significantly (p<0.0001) with both tangential displacement (r = −0.990) and vertical displacement (r = −0.974). Peak von Mises stress (r = 0.995) and peak contact pressure (r = −0.984) were also found to be significantly (p<0.0001) correlated to the coefficient of friction. Discussion. A higher coefficient of friction at the taper-bore interface led to lower contact pressure and sliding at the modular junction. However, higher coefficients of friction also led to increased von Mises stresses within the bore and the trunnion increasing the risk of yielding and fatigue failure. The current results strongly indicate that factors affecting the frictional coefficient at the interface likely influence the occurrence of and severity of mechanically-assisted corrosion in THA. Significance. The results from this study will help us set tolerances for the interlocking mechanism, identifying the minimum frictional coefficient required to obtain stable implant mechanics

Introduction. Total hip arthroplasty (THA) is the most common surgery performed for complications of bipolar arthroplasty. The present study evaluated the functional results and complications associated with this surgery. Patients and Methods. Forty eight hips (48 patients) who had conversion of bipolar arthroplasty to THA between 1998 June and 2013 June, and who were followed-up for more than one year were evaluated. Twenty one hips had conversion surgery to THA using a Fitmore cup with metal-on-metal articulation (28 mm head). Six hips had surgery using the SecurFit cup and three hips, using the Lima LTO cup with ceramic-on-ceramic articulation (28 mm or 32 mm head). Eighteen hips had surgery using a large head metal-on-metal bearing: –MMC (seven hips), ACCIS (six hips) and Magnum (five hips). The average time of follow-up duration was 3.9 years (range, 1.0–11.3). There were 22 men and 26 women between the ages of 28 and 80 years (average, 68.9 years) at the time of conversion surgery. Conversion arthroplasty was performed for acetabular erosion without femoral stem loosening in 19 hips, acetabular cartilage erosion with femoral stem loosening in 13 hips, periprosthetic fracture in 12 hips, and recurrent dislocation in four hips. Results were evaluated using Harris hip score (HHS) and Western Ontario McMaster Universities Osteoarthritis Index (WOMAC) score. The radiographs were analyzed for evidence of acetabular and femoral osteolysis or loosening. The complications were evaluated. Results. The time interval between hemiarthroplasty and conversion total hip prosthesis was 6.7 years on average (range, 5 months to 12 years). Pain was the leading sign in all patients. Average HHS improved from 42 preoperatively (range, 34–67) to 86 (range, 65 – 97) postoperatively. The average total WOMAC score improved from 47 (range, 32–67) to 22 (range, 9–44) postoperatively. All the patients operated for groin pain reported significant improvement in their symptoms. Radiological evaluation showed good bony ingrowth and stability of all the femoral components. None of the acetabular component showed migration, loosening, wear, or osteolysis at last follow-up. Complications occurred in five hips. One dislocation and one recurrent dislocation were encountered in isolated acetabular revision hips; whereas one single dislocation, one recurrent dislocation, and one trochanteric nonunion occurred in the hips with revision of both components. All dislocations were occurred in hips with a femoral head size of 28 mm. Dislocations were managed by closed reduction, and none of the patients required revision for dislocation. Conclusions. Conversion THA after symptomatic bipolar arthroplasty can offer reliable pain relief and functional improvement. The perioperative complications approximate those of revision THAs

Developmental hip displasia (DHD) still presents as an important problem in our country. Latency in diagnosis and inaccurate treatment causes seconder osteoarthritis in young adults and elder patients. Variable reconstructive surgical procedures as proximal femoral and acetabular osteotomies can be performed, but the most satisfactory functional results are achieved by total hip arthroplasty (THA). In this study, we analyzed the results of the cementless total hip arthroplasties performed in coxarthrosis secondary to developmental hip displasia. Between January 2006 and October 2009, 53 patients diagnosed with hip osteoarthritis secondary to DHD, whom performed 59 total hip arthroplasties in GATA Orthopaedics and Traumatology Clinic were included in the study. 10 of the patients were male (%19), and 43 of them were female (%81). Age of the patients varied between 29 and 78 years and the mean age was 48,7. In 23 patients (%44), THA procedure was performed at the right hip and in 24 patients (%45) at the left hip. 6 patients operadted bilaterally. All patients were followed up 8–38 months (mean 20, 6 months) with clinical and radiological evaluation. The hospitalization period varied between 7–14 days, mean 8,3 days. Posterolateral incision was used at all of the patients. Totally 10 (%17) complications were observed. 5 (%8,5) of them was intraoperative and 5(%8,5) was postoperative. Patients evaluated preoperatively and postoperatively with modified Harris Hip Score. While preoperative mean Harris score was 39,1, the postoperative mean score measured as 90,3. The results were excellent in 52 cases (%88,1), and very good in 7 cases (%11,9). Appropriate implementation of cementless total hip prosthesis in patients with hip osteoarthritis secondary to DHD, who have good bone quality and surgical indicaton; clinical and radiological short term results were satisfactory

Fluid film lubricating ability of a total hip prosthesis depends on the profile accuracies including surface-roughness or the sphericity of a head or a cup. Therefore, surface polishing is important. It was, however, difficult to polish the central portion of a cup or head using the conventional rotating machine. In the present study, we developed a polishing method combining a pendulum machine and a robotic arm. The effect of the accuracy improvement by this method was evaluated by the friction measurements on some test specimens. Nine balls and a cup of Co-Cr-Mo alloy that were polished by a conventional process using a rotating machine were prepared for the prototype. The average diameter of the balls was 31.9648 mm with the sphericity of 0.0028 μm. The inside diameter of the cup was 31.9850 mm with the sphericity of 0.0044 μm. We combined a robotic arm and a pendulum apparatus to enable the further polishing. The ability of both automatic centering and change in the sliding direction was accomplished by this system. The sliding direction has been changed 180 times every ten degrees. The total distance of polishing was 120 m under vertical load of 100 N in a bath of saline solution containing abrasive grains of silicate of the diameter of 2μm. The surface roughness of the central portion of the cup, which is important area for the fluid film lubrication decreased from Ra 20.2 μm before the polishing to Ra 18.7 μm after the polishing. A pendulum type friction tester was used for the assessment of the improvement of the lubricating ability by the polishing. The measurement was run over at 10 times under the conditions of the load of 600 N in a bath of saline solution. As the result, the frictional coefficients decreased from 0.1456–0.1720 before polishing to 0.1250–0.1300 after polishing. The polishing effect was, however, observed only at the specimens that radial clearances did not exceed the value of 50 μm. The present results indicated that the surface polishing of the central portion of hip prostheses must improve the lubrication ability and the radial clearance before the finishing process should be chinked as possible