INTRODUCTION. Corrosion of modular tapers is increasingly recognized as a source of adverse tissue reaction (ALTR) and revision surgery in total hip arthroplasty (THA). The incidence of corrosion and rate of revision for ALTR may differ among different types of implants. OBJECTIVE. The objective of this study was to determine if a difference exists in rate of THA revision for corrosion and ALTR with tapered broach only stems compared to ream-broach femoral stems. METHODS. We reviewed the results of 3741 primary THA performed over a 5 year period at our institution using 2 different implants by the same manufacturer, a tapered proximally coated cementless titanium stem inserted via a broach only technique (Group A) and dual tapered proximally coated cementless titanium stem inserted via a ream and broach technique (Group B). RESULTS. Of 1567 THA in group A, 964 were combined with a chrome cobalt metal head, while 603 were ceramic. Of 2174 THA in group B, 1302 were metal and 872 were ceramic. Head sizes used were similar between groups. The same polyethylene was used in all THA. At a minimum follow-up of 2 years and average follow-up of 5 years, the overall revision rate for all causes was 3.1% in group A and 1.4% in group B. There were 29 revisions for ALTR due to corrosion of the morse taper junction in group A (3.4%) and 0 in group B. Univariate and multivariate analysis indicated no relationship between revision for corrosion/ALTR and age, gender, stem size, stem offset and head size. A significant relationship was identified between revision and head length, with an increased rate of revision among longer head lengths. There were no revisions for corrosion, ALTR or unexplained pain among patients receiving ceramic heads in either group. CONCLUSION. There was a significant difference in the rate of revision for corrosion and adverse tissue reaction encountered with the use of stem A when compared to stem B. The stem geometry, taper geometry and exact metallurgy of these femoral components likely influences the incidence and severity of taper corrosion, however, more research is required to identify the exact contributions of these factors

A modular femoral head–neck junction has practical advantages in total hip replacement. Taper fretting and corrosion have so far been an infrequent cause of revision. The role of design and manufacturing variables continues to be debated. Over the past decade several changes in technology and clinical practice might result in an increase in clinically significant taper fretting and corrosion. Those factors include an increased usage of large diameter (36 mm) heads, reduced femoral neck and taper dimensions, greater variability in taper assembly with smaller incision surgery, and higher taper stresses due to increased patient weight and/or physical activity. Additional studies are needed to determine the role of taper assembly compared with design, manufacturing and other implant variables.

Cite this article: Bone Joint J 2013;95-B, Supple A:3–6.

Introduction. Several devices based upon the dual mobility (DM) concept have recently been FDA approved. However, little is available on the efficiency of current DM on THA instability prevention, and on specific complications. The aim of this retrospective study was to report on the minimal 5-year follow-up results of a cementless DM socket. Methods. Between January 2000 and June 2002, 168 primary consecutive non selected THAs were performed in 92 females and 76 males. The average age at surgery was 67.3 years. A single DM socket design was used (Tregor, Aston Medical, France) consisting of a Ti-sprayed and HA-coated CoCr shell with a highly polished inner surface articulating with a mobile intermediate polyethylene component. The opening diameter of the mobile insert was 6% smaller than that of the femoral head. In 115 hips, the modular femoral head completely covered the Morse taper, whereas a long-neck option leaved the base of the Morse taper uncovered in the remaining 53 hips. Results. At the minimum 5-year follow-up, 119 patients were still alive and had not been revised at a mean of 7.2 years (5-8.9 years), 4 hips were revised for dislocation between the femoral head and the mobile insert (intra-prosthetic dislocation) at a mean of 5.9 years, 22 patients were deceased, and 23 patients were lost to follow-up. Intra-prosthetic dislocation occurred in 4 of the 53 hips (7.5%) with an incompletely covered Morse taper, whereas no dislocation were reported in the remaining 115 hips (p = 0.009). Discussion and Conclusion. A current cementless DM socket was highly effective in the prevention of dislocation following primary THA. However, fatigue damage and wear of the mobile insert at the capturing area can lead to intra-prosthetic dislocation requiring revision. Surgeons should be aware of this specific complication and efforts should be made to avoid aggressive contact at the femoral neck to mobile insert articulation (“3. rd. articulation”)

Introduction. Large diameter metal-on-metal hip arthroplasty (LDMMTHA) provides benefits of reduced dislocation rates and low wear. The use of modular systems allows better restoration of hip biomechanics. There have been reports of modular LDMMTHAs with tapered sleeves generating excessively high metal ions, due to possible mismatch between the titanium stem and the cobalt-chrome sleeve and the dual Morse tapers involved. We evaluated metal ion levels in LDMMTHA patients with and without a cobalt-chrome (CoCr) tapered sleeve. Methods. A cross-sectional series of 91 patients with proximal porous titanium alloy stem LDMMTHA with identical design CoCr bearings, attending a 1 to 2-year review were assessed with routine clinical and radiographic examinations, hip scores and metal ion analysis. Of these 65 had a single Morse taper between monoblock CoCr heads and the stems. Twentysix had a tapered cobalt-chrome sleeve in addition, with the resultant dual taper. Mean bearing diameter was 46 mm in both groups and mean age was 58 years in the monoblocks and 66 years in the tapered sleeve group. Results. Mean Oxford Hip score is worse in the tapered group (14.7) than in the monoblocks (12.6). All patients had well-functioning hips clinically and radiologically. Median blood cobalt and chromium are higher in the tapered sleeve (2.3μg/L and 1.8 μg/L) compared to the monoblocks (1.8 μg/L and 1.1 μg/L). Urine cobalt and chromium levels in the tapered sleeve (13.8 μg/24 hr and 5.3 μg/24 hr) also are higher than those in the monoblocks (12.2 μg/24 hr and 4.5 μg/24 hr respectively). Discussion and Conclusion. The limitation of this study is that it is a cross-sectional study. The results indicate that the use of a tapered sleeve in total hip arthroplasty does lead elevation of cobalt and chromium levels and the difference is statistically significant. However these levels are not as high as the levels reported with some other hip systems which have been withdrawn and the clinical significance of the elevated levels in the present study is unknown

Introduction. The Morse taper was adapted into orthopaedics as a connecting junction in total hip replacements. The benefit of modular systems includes the adjustment of leg length, offset and the ability to remove the head for acetabular exposure during revision surgery. The design of the Morse taper facilitates the intimate contact of the conical trunnion of the femoral stem (male component), with the conical bore of the femoral head (female component). Design consideration for tapers involve physical parameters (angle, length, diameter and contact points), and manufacturing finish (surface characteristics). Orthopaedic trunnion tapers are not standardized and vary in length, taper angle and base dimension. Variations in the design and surface characteristics of the trunnion, which directly reflects on the interface at the taper junction can influence the likelihood of subsequent wear, corrosion and ultimately effect longevity of the implant. Methods and Materials. We studied 11 clean un-used commercial stems from five different companies (DePuy, Stryker, Biomet, Wright Medical, Smith and Nephew). Trunnion surface was scanned with an optical profilometer (Bruker ContourGT-I 3D Optical Microscope (Karlsruhe, Germany), an interference microscopes with the capability to analyse 3 dimensional topographical features of materials. Three measurements of each trunnion were taken on the anterior surface at the proximal, mid-point, and distal segments. Each region scan was conducted under a 20x objective with the scan length of 1000 um and a back scan of 500 um. Results. Four of the eleven hip stems demonstrated a smooth surface finish and the remaining seven had a distinct threaded surface with the Corail and the SROM surface topography shown in figure 1. All the analysed trunnion surfaces had a Sa value than Sz value (p < 0.05), indicating each trunnion surface consists of repetitive peak heights and valley depth across the scanned surface area shown in figure two. The higher Sa parameter for the threaded trunnions indicates a rougher overall surface due to a recurring threads pattern. The mean dominant thread heights of the trunnions varied from 12.91 μm on the Profemur to 3.24 μm on the SecurFit Max. The Silent, Summit and the Tri-Lock stems demonstrated a variation in thread heights on their respective surfaces. The Summit stem also demonstrated variability in the pitch of its threads which was not seen on the other threaded stems. The Silent had the widest pitch at 0.304 μm whilst the Profemur had the narrowest pitch at 0.13 μm. Conclusion. Threaded trunnion surfaces for different stems are not uniformly patterned and demonstrate variability in thread height and pitch. These differences could affect micro motion at the taper junction, influencing corrosion and fretting. The study is limited in its capacity as only one stem of each type was analysed, therefore any variation between same stem designs cannot be commented on

Despite a lack of long-term follow-up, there is an increasing trend towards using femoral heads of large diameter in total hip replacement (THR), partly because of the perceived advantage of lower rates of dislocation. However, increasing the size of the femoral head is not the only way to reduce the rate of dislocation; optimal alignment of the components and repair of the posterior capsule could achieve a similar effect. . In this prospective study of 512 cemented unilateral THRs (Male:Female 230:282) performed between 2004 and 2011, we aimed to determine the rate of dislocation in patients who received a 22 mm head on a 9/10 Morse taper through a posterior approach with capsular repair and using the transverse acetabular ligament (TAL) as a guide for the alignment of the acetabular component. The mean age of the patients at operation was 67 years (35 to 89). The mean follow-up was 2.8 years (0.5 to 6.6). Pre- and post-operative assessment included Oxford hip, Short Form-12 and modified University of California Los Angeles and Merle D’Aubigne scores. The angles of inclination and anteversion of the acetabular components were measured using radiological software. There were four dislocations (0.78%), all of which were anterior. In conclusion, THR with a 22 mm diameter head performed through a posterior approach with capsular repair and using the TAL as a guide for the alignment of the acetabular component was associated with a low rate of dislocation. Cite this article: Bone Joint J 2014;96-B:1202–6

The humeral offset has a medial-lateral and anteriorposterior dimension and can be defined as the distance of the central axis of the humeral shaft and the center of rotation of the humeral head. When using a canal filling prosthetic stem, inserted in a collinear alignment with the long axis of the humeral shaft, the placement of the humeral head within the anatomic boundaries of the humeral osteotomy surface will be dictated by how closely the prosthetic stem-humeral head offsets match that of the patient’s natural anatomic offsets. Given the fact that there are several millimetres of variation in the medial-lateral and anterior-posterior humeral offsets among the normal patient population, it follows that in many cases the prosthetic offset will not precisely match that of each patient when a canal filling medullary component is properly inserted. This mismatch in the humeral offsets can result in malposition of the humeral head within the confines of the humeral osteotomy surface when using a centred Morse taper humeral head. Iannotti and Williams have studied, using the Polhemus tracking system, the biomechanical consequences and tolerances for a malpositioned humeral head using a prosthetic reconstructed human cadaver model (JOR in press). A 4 mm or greater malposition of the humeral head, particularly in an inferior or anterior direction (most common malposition) will result in a measurable decrease in range of motion, abnormal humeral kinematics and subacromial impingement. In addition, humeral head malposition (anterior and inferior) can result in impingement of the non-articular portion of the humeral component, rotator cuff or proximal humeral metaphysis on the glenoid component. This impingement can result in abnormal glenoid component wear (type 2 wear) or premature glenoid loosening. Solutions for management of humeral head malposition include: 1.) variable stem offsets (not currently available), 2.) humeral component with an eccentric Morse taper (DePuy – Global Advantage, Tomier – Aequalis, Zimmer – Bigliani/Flatow) or an equivalent design (Stryker – Anatomica), and 3.) under-sizing and shifting the humeral stem to a centred position. The last option, best for monoblock humeral components (original Neer design), requires impaction grafting or PMMA cement to stabilise the under-sized stem in the centred position. Whatever solution is used it is important, in most cases, to select a head size which matches the normal anatomy and center it within the confines of the normal humeral osteotomy surface area

The vast majority of total hip replacements (THR) implanted today enable modularity by means of a tapered junction; based on the Morse taper design introduced for cutting tools in the 19. th. Century . 1. Morse-type tapers at the head-stem junction provide many benefits, key for a successful surgical outcome such as wider component selection and restoration of better biomechanics . 2. However, moving from mono-block to modular designs has not been without its issues. Fluid ingress and motion at the interface has led to a complex multifactorial degradation mechanism better known as fretting-corrosion . 3. Fretting-corrosion products created at the junction are commonly associated with adverse local tissue reactions . 4. . There is a wide variation in the taper junction of THR differing quite significantly from Morse's original design. Performance of the taper junction has been found to vary with different designs . 5,6. However, there is still a lack of common understanding of what design inputs makes a ‘good’ modular taper interface. The aim of this study was to better understand the links between implant design and fretting-corrosion initially focussing on the role of angular mismatch between male and female taper. A combination of experimental approaches with the aid of computational models to assist understanding has been adopted. A more descriptive understanding between taper design, engagement, motion and fretting-corrosion will be developed. Three different sample designs were created to represent the maximum range of possible angular mismatches seen in clinically available THR modular tapers (Matched: 0.020 ±0.002 °, Proximal: 0.127 ±0.016 °, Distal: −0.090 ±0.002 °). Head-stem components were assembled at 2 kN. Motion and fretting-corrosion at the interface was simulated under incremental uniaxial sinusoidal loading between 0.5–4 kN at 8 intervals of 600 cycles. The different types of motions at the interface was measured using a developed inductance circuit composed of four sensing coils, digital inductance converter chip (LDC1614, Texas Instruments, US) and microcontroller (myRIO, National Instruments, US). Fretting-corrosion was measured using potentiostatic electrochemical techniques with an over potential of +100 mV vs OCP (Ivium, NL). Complimentary finite element (FE) models were created in Ansys (Ansys 19.2, US). Under uniaxial loading, the ‘matched’ modular taper assemblies corroded most and allowed the greatest pistoning motion due to a seating action. ‘Distal’ and ‘proximal’ engaged modular tapers showed reduced corrosion and seating when compare to the ‘matched’ components. However the kinetics of corrosion and motion were interface dependent. It is hypothesized, and complimented by FEA analysis, that lower initial contact stress in the ‘matched’ modular tapers allows for greater subsidence and depassivation of the oxide layer and higher corrosion. ‘Matched’ modular tapers allowed less rotational and toggling motions compared to mismatched tapers, suggesting a reduced mismatch might perform better once the heads have seated over time. Future work involves tests conducted under a surgically relevant impaction force and physiological loading kinematics to develop this descriptive link between taper design, engagement and performance

Arthroplasty implant modularity enables the surgeon to adapt the joint replacement construct to the patient's requirements, and often facilitates revision procedures. Total shoulder arthroplasty humeral modularity exists for many implant systems. Glenoid modularity with convertibility between anatomic and reverse shoulder arthroplasty is a recent development. Glenoid modularity is very useful when reconstructing glenoid bone deficiencies, or in providing a method for reverse shoulder arthroplasty joint lateralization. The live surgery will demonstrate a bio-reverse total shoulder arthroplasty (bRTSA). The humeral component is a modular press fit stem that can accommodate either reverse or anatomic metaphyseal components. The metaphyseal components can be exchanged without removing the stem or changing the humeral height. The glenoid base has three components. The trabecular titanium peg is available in two diameters, and four lengths for each diameter. The peg is fixed to a metal base plate via Morse taper. In revision settings, these components can be easily dissociated in situ, and a coring drill inserted over a well-fixed peg allows removal with minimal bone loss. Either a polyethylene component, or glenosphere can be attached to the baseplate to complete the glenoid construct. An innovative set of instruments have been developed to reliably prepare the glenoid and humeral bone graft. While the live surgery will demonstrate the grafting technique in a bRTSA, it can also be used to reconstruct glenoid deficiencies (eg, Walch B2). Implants have been developed to solve these issues, but often do so at the expense of very limited glenoid bone stock. Bone grafting actually creates a net increase in glenoid bone stock that may improve implant durability, and decrease revision complexity. The technique is quite simple and adds approximately ten minutes to operative time. I have used this technique for 5 years with no cases of graft failure

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

Hip implant retrieval analysis is the most important source of insight into the performance of new materials and designs of hip arthroplasties. Even the most rigorous in vitro testing will not accurately simulate the behavior of implant materials and new designs of prosthetic arthroplasties. Retrieval analysis has revealed such factors as the effects of gamma-in-air sterilisation of polyethylene, fatigue failure mechanisms of polymethylmethacrylate bone cement, fretting corrosion of Morse taper junctions, third body wear effects of both hard-on-hard and hard-on-soft bearing couples, and the effects of impingement of components on the full spectrum of bearing surfaces, none of which was predicted by pre-implantation in vitro testing of these materials and combinations. The temporal sequence of the retrieval process is approximately six years from first implantation through retrieval analysis, laboratory investigation, and publication of results, and thus, in addition to rigorous clinical evaluation, represents the true development and insight cycle for new designs and materials

Acoustic emission is an uncommon but well-recognised phenomenon following total-hip arthroplasty using hard-on-hard bearing surfaces. The incidence of squeak has been reported between 1% – 10%. The squeak can be problematic enough to warrant revision surgery. Several theories have been proposed, but the cause of squeak remains unknown. Acoustic analysis shows squeak results from forced vibrations that may come from movement between the liner and shell. A potential cause for this movement is deformation of the shell during insertion. 6 cadaver hemipelvises were prepared to accept ace-tabular components. A shell was selected and pre-insertion the inner shape was measured using a profilometer. The shell was implanted and re-measured. 2x screws were then placed and the shells re-measured. The results were assessed for deformation. Deformation of the shells occurred in 5 of the 6 hemi-pelvises following insertion. The hemipelvis of the non-deformed shell fractured during insertion. Following screw insertion no further shell deformation occurred. The deformation was beyond the acceptable standards of a morse taper which may allow movement between components, and this may produce an acoustic emission. Further in-vitro testing is being conducted to see whether shell deformation allows movement producing an acoustic emission

Modular necks arrived in North America in the late 1970s. The purpose was to allow ceramic balls to be attached to metal stems. The advantages of modularity were so obvious that it was universally adopted with almost no untoward consequences. A double-taper neck was developed in Italy by the Cremascoli Company and was used extensively with few reports of problems. Recently, problems have been reported not only with double-taper necks, but also with head-neck junction tapers. Something would appear to have changed recently. Some of these changes were shortening of the taper, lengthening of the neck, version angles were increased, and head sizes bigger than 32mm were introduced. Surface finish on some of the tapers was changed and they were ridged. This produces a better fit for a ceramic ball, but facilitates crevice corrosion with a metal ball. The author used the original OTI cemented stem with a double-taper neck between 2002 and 2005. It was a cobalt chrome construct. The Cremascoli was a titanium hip. The OTI used the classic Morse taper with cogs for increased rotational resistance. One hundred forty five stems were inserted. The neck stem taper broke in two cases and dislocated in one. All of these cases had a long neck and long heads and thus produced maximum moment arm. The stem was withdrawn from the market, the taper lengthened and the strength doubled. It was reintroduced in 2007. From 2007 to 2011, the author has done 188 cases, all cemented stems. No taper problems have occurred. The conclusion is that a properly designed double taper neck does not appear to have a downside. The upside is the ability to change neck length and especially version after head insertion. Leg length and hip centering can, therefore, be fine-tuned as never before. The author continues to use this stem enthusiastically for all cemented cases

Alumina-on-alumina bearings in total hip arthroplasty (THA) were introduced about 30 years ago. Theoretically, their excellent tribological properties and low debris generation provide a solution to osteolysis. The 24-year experience of the Paris group suggests that osteolysis is no longer a problem. Any need for revision was related to mechanical failure rather than to debris, except in a few cases in which a pros-thesis that had been loose for many years resulting in metal-on-ceramic impingement. Cemented socket and screw-in ring metal-backed alumina yielded poor results. The recent improvements in alumina quality and in ceramic fixation, using cementless fully coated hydroxyapatite material, may provide a solution in active young patients. Preliminary results of the first 100 THA procedures using a cementless stem and socket and 32-mm alumina head, and alumina liner secured with a Morse taper, are very encouraging. One socket required revision because of poor initial surgery in a severe acetabular fracture. Patients ranged in age from 14 to 71 years (median 45 years)

Stem dissociation in modular revision knee replacement due to failure of the frictional lock of the Morse taper has been reported in the literature. However, the medium and long-term implications of stem dissociation are unknown, as clinical outcomes have not been reported. We report a series of 10 cases in which there was intra-operative dissociation of the tibial stem. Between 1994 and 1999, 98 patients underwent revision total knee replacement for aseptic loosening at our institution. Ten of these patients were noted to have tibial stem dissociation, apparent on the immediate post-operative radiographs. The senior author (RWP) performed all procedures and used a standardized operative technique. The Co-ordinate modular knee revision system was used in all cases. The quality of the bone was noted in all the cases intra-operatively; and was graded as 1) sound bone, 2) soft but intact, 3) soft and fractured cortex. Our study demonstrates that the tibial stem dissociation did not cause any significant detriment to the clinical outcome on minimum follow-up of six years in nine cases where the tibial metaphyseal cortical rim was intact. In one case, where the medial tibial plateau had a cortical defect, the prosthesis drifted into varus mal-alignment and the patient required a further revision for aseptic loosening. We therefore question whether long canal filling tibial stems are necessary in all revision total knee replacements particularly when the cortical rim is intact and a non-constrained poly-ethylene insert is used

Dislocations remain a significant problem, especially after revision hip surgery. Revision of components, particularly in elderly patients with co-morbidities, can be fraught with complications. The surgeon’s options are sometimes restricted, particularly when the acetabular and femoral components are well fixed. Increased head lengths are often utilised to increase tissue tension, and thus improve stability. As a niche solution we have designed a low cost modular femoral neck extender. They are manufactured from medical grade Cobalt-Chrome, conforming to ISO 200, CE mark and EN46001 standards. Available in three incremental lengths and with different connecting Morse tapers, increases in effective neck lengths of up to 49 mms can be achieved. When both the original acetabular and femoral components are well orientated, the resultant increased tissue tension imparts stability to the hip. We present a series of five patients where we have used a femoral neck extender to achieve stability of a total hip replacement. Four patients had had multiple previous dislocations. One patient was unstable at the time of revision surgery because of a high hip centre. The average age of the patients was 72 years, and the number of previous dislocations averaged four. The average follow-up after surgery was 22 months. No patients have redislocated their hips. We present our novel femoral neck extenders as an elegant and cost effective solution to convert an unstable hip to a stable hip, especially when the patient has well fixed and orientated components not in themselves requiring revision

Dislocations remain a significant problem, especially after revision hip surgery. Revision of components, particularly in elderly patients with co-morbidities, can be fraught with complications. The surgeon’s options are sometimes restricted, particularly when the acetabular and femoral components are well fixed. Increased head lengths are often utilized to increase tissue tension, and thus improve stability. As a niche solution we have designed a low cost modular femoral neck extender. They are manufactured from medical grade Cobalt-Chrome, conforming to ISO 200, CE mark and EN46001 standards. Available in 3 incremental lengths and with different connecting Morse tapers, increases in effective neck lengths of up to 49 mm can be achieved. When both the original acetabular and femoral components are well orientated, the resultant increased tissue tension imparts stability to the hip. We present a series of 5 patients where we have used a femoral neck extender to achieve stability of a total hip replacement. 4 patients had had multiple previous dislocations. 1 patient was unstable at the time of revision surgery because of a high hip centre. The average age of the patients was 72 years, and the number of previous dislocations averaged 4. The average follow-up after surgery was 22 months. No patients have redislocated their hips. We present our novel femoral neck extenders as an elegant and cost effective solution to convert an unstable hip to a stable hip, especially when the patient has well fixed and orientated components not in themselves requiring revision

Purpose: To assess the performance of a constrained liner in an unstable hip prosthesis. Materials and methods: This is a retrospective study of 66 hip prostheses implanted in 66 patients by means of the same constrained cup (Lefevre, Lepine Group, France). The cup was implanted into 15 primary prostheses and 51 revision ones in order to treat recurrent dislocations (10 cases) or to prevent dislocations (56 cases with a deficit of the periarticular musculature or mental or neuromuscular disorders). The mean age was 76.7 years, 75.7% were female, 53% were operated in the right side and the mean follow up was 30.2 months. Results: By the time the last review was made, four patients died for reasons not related to their hip surgery. One patient showed a dissociation between the femoral head and the stem at the level of the Morse taper; the head was trapped in the retentive liner and an open reduction was needed to replace the existing prosthetic head by a new one with a long neck. Another patient had a prosthetic infection that was treated by means of a two-stage replacement. Radiolucent lines were observed in de DeLee’s zone 1 in 1.5% of patients, in 3% the lines were in zone II and in 3% they were in zone. However, according to Hodgkinson’s radiographic criteria, no cups were loose. Conclusions: Although retentive cups do address hip instability, the various cases of failure that have occurred, the appearance of radiolucencies and the concerns about their long-term fixation suggest that their use should be carefully weighted

Introduction: Modular necks used during primary or revision total hip arthroplasties permit to restor the ideal femoral offset and arm of abductors muscles, to ajust leg length and to reduce impingment between the neck and the socket with good hip balancing. Material and methods: Modular necks are titanium implants manufactured with a double Morse taper: one cylindrical for the junction with the head, and one flat for the junction with the stem. They are avalaible in 2 lengths (short and long) with 6 different geometries: straight (CCD:135°), antevreted of 8° or 15°, 8° and 15° of varus (CCD: 127° and 120°), and a combination of anteverted and varus neck. 362 revision and 920 primary THA were performed with a minimal of 5 years follow-up in the Orthopaedic Department of Amiens University Hospital with modular necks. Results: 23 patients died and 11 were lost of follow-up. None rupture was deplored. Femoral offset was restored in 97% of these cases even in the revision surgery, end equalization of leg length was obtained in 98% of the patients. Residual Trendelemburg sign was noted in 37 patients, always after revision. The rate of dislocation was low with 2% because of the absence of impingment. Discussion: Because proximal femoral geometry is different for each patient and femoral offset independent from the IM canal diameter, modular neck is one easy solution to restor independent parameters. In addition, the per-operative trials permit to choose the best implant to avoid any impingment, reducing the risk of dislocation and increasing the range of motion. It’s ideal now for the use of hard bearings. Laboratory analysis have demonstrated very good resistance in assembly-distraction, deep flexion and rupture tests. No corrosion was noted and retrieved weight loss was minimal

Introduction. Modular hip replacement systems use Morse tapers as an interlocking mechanism to connect ball heads to femoral stems. Even though this interlocking mechanism generally performs successfully for decades, failures due to disassociation of the ball head from the stem are reported in the literature. Therefore, this failure mechanism of a possible loosening is usually evaluated in the course of the development of femoral stems. The disassembly force is a possible parameter to characterize the strength of the interlocking mechanism. Thus, the aim of the current study was to examine the impact of different taper parameters on the disassembly force of ceramic ball heads from titanium stem tapers by finite element studies. Materials and Methods. A 2D axisymmetric finite element model was developed to simulate the disassembly procedure. First ball head and taper were assembled with a force of 4 kN. Afterwards the system was unloaded to simulate the settlement. Disassembly was simulated displacement controlled until no more adhesion between ball head and taper occurred. Isotropic elastic material behavior was modelled for the ceramic ball head while elastic-plastic material behavior was modelled for the titanium taper. Different angular gaps (0.2°, 0.15°, 0.1°, 0.05°, 0°, −0.05°, −0.1°) and different taper topography parameters regarding groove depth (12, 15 µm), groove distance (210, 310 µm) and plateau width (1, 5, 10, 20 µm) were examined. Frictional contact between ball head and taper was modelled. Results. The topography of the taper (groove depth, distance and plateau width) within the investigated range had only a small impact on the disassembly force (Fig. 1) while the varying angular gaps had a large effect (Fig. 2). Decreasing disassembly forces were found for decreasing angular gaps. For the negative angular gaps (i.e. male taper angle > female taper angle) the forces increased. The same trends were found for the sliding distance (sliding along the tangential direction in the taper region), deformation of the grooves and contact stresses. Reciprocal behavior was found for the contacting area. Discussion. Surface topography seems to have only minor influence, while macro-geometry seems to have major impact on the disassembly force. Higher disassembly forces are associated with smaller contacting areas, higher contact stresses, larger deformations of the grooves and larger sliding distances. For a negative angular gap the maximum stresses of the ceramic component were found at the taper mouth. This could be disadvantageous since the wall thickness in this region of the ball heads decreases and critical hoop stresses could increase the risk of a fracture. The decrease in contacting areas due to the extreme angular gaps could promote corrosive effects since a larger taper area is exposed to fluid. Furthermore, the higher contact stresses and groove deformations could increase taper wear. Therefore, a general examination of possible influencing factors and cross effects on the in vivo performance have to be conducted during the development of femoral stems. Future studies will include a wear model and include 3D calculations to examine more realistic loading scenarios. To view tables/figures, please contact authors directly