Background. The Kotz Modular Femoral Tibial Replacement system has been one of the most widely utilised uncemented modular systems for bone and joint reconstruction after tumour resection. We have identified a significant incidence of mechanical failure and breakage of the prosthesis. The purpose of this investigation is to review the modes of implant failure and the outcomes after prosthetic revision for a broken Kotz prosthesis. Methods. Over 20 years there were 121 distal femoral, 55 proximal tibial, 47 proximal femoral and 12 total femoral replacements performed. Results. Out of 180 currently living patients there were 27 implant fractures in 23 patients (13%) with 22 distal femoral and five proximal tibial implant failures. Mechanical failures occurred at a mean of 77 months (range 24-170). There were 21 stem fractures. Five fractured at the derotation lug and one fractured the tibial housing. Lug fracture is an unreported mode of failure of these implants. The implant design selected for revision was very much dependent on when the fractured implant was revised. Eleven patients had new KMFTR stems inserted; 4 Restoration stems (one of which was cemented), 3 GMRS stems (one of which was cemented), two total femora and one Compress (Biomet) implants have been utilised, all with custom adaptors between the stem and the KMFTR system. There were 12 complications (44%), seven infections, three implant re-fractures, one vascular insufficiency necessitating amputation and one per-prosthetic fracture. The mean pre-implant fracture and post-revision TESS scores were 80.9 (Range 54.2-98.3) and 79.1 (50-96.7). The MSTS87 pre- and post- scores were 26.8 (14-33) and 26.1 (15-33) respectively. The MSTS93 also demonstrated no differences in the pre-fracture and post-revision scores with 75.4 (50-93) and 74.8 (40-100). Conclusion. Our data illustrate that these prostheses can often be successfully revised by trephining out the broken stem and inserting new uncemented stems. Functional outcome continues to be good and is comparable to pre-revision levels, despite a 44% complication rate

Introduction. One of the major concerns in the use of modular hip prostheses is the structural failure of one or more components of the prosthesis, with total mechanical failure. In literature there are sporadic cases of breakage of the prosthetic neck in patients with high functional demand. Material and methods. In our experience we have implanted a model of modular hip prostheses in 38 patients. In 17 of these patients it was implanted a neck made of titanium alloy, while in the remaining 21 was utilised a CrCo neck. In 5 of the 17 patients with neck titanium it has been a spontaneous rupture of the neck in a time ranging from 12 to 24 months. We proceeded with the replacement of the titanium neck with similar neck made of CrCo alloy in 5 patients with failed neck, and we decided to call the remaining 12 patients with titanium neck, offering them the revision of the system. All patients accepted the revision surgery. Results. implants explanted and subject to breakage of the neck were analyzed by an independent metallurgical laboratory which has produced a document in which were found the main signs of wear which led to the deterioration of metal involved. Conclusions. The rupture of the modular hip prostheses is a possible event both because of the high functional loads required by some types of patients, that of the building materials and design of the modular components. In this study we are presented the results of the laboratory tests that allow us to pose hypotheses about the causes and failure mechanisms of modular hip prostheses

Aims. The timing of when to remove a circular frame is crucial; early removal results in refracture or deformity, while late removal increases the patient morbidity and delay in return to work. This study was designed to assess the effectiveness of a staged reloading protocol. We report the incidence of mechanical failure following both single-stage and two stage reloading protocols and analyze the associated risk factors. Methods. We identified consecutive patients from our departmental database. Both trauma and elective cases were included, of all ages, frame types, and pathologies who underwent circular frame treatment. Our protocol is either a single-stage or two-stage process implemented by defunctioning the frame, in order to progressively increase the weightbearing load through the bone, and promote full loading prior to frame removal. Before progression, through the process we monitor patients for any increase in pain and assess radiographs for deformity or refracture. Results. There were 244 frames (230 patients) included in the analyses, of which 90 were Ilizarov type frames and 154 were hexapods. There were 149 frames which underwent single-stage reloading and 95 frames which underwent a two-stage reloading protocol. Mechanical failure occurred after frame removal in 13 frames (5%), which suffered refracture. There were no cases of change in alignment. There was no difference between refracture patients who underwent single-stage or two-stage reloading protocols (p = 0.772). In all, 14 patients had failure prevented through identification with the reloading protocol. Conclusion. Our reloading protocol is a simple and effective way to confirm the timing of frame removal and minimize the rate of mechanical failure. Similar failure rates occurred between patients undergoing single-stage and two-stage reloading protocols. If the surgeon is confident with clinical and radiological assessment, it may be possible to progress directly to stage two and decrease frame time and patient morbidity. Cite this article: Bone Jt Open 2022;3(5):359–366

Introduction

Cementless acetabular fixation in total hip replacement (THA) is reliable and has been the fixation method of choice in the United States for decades. While revision for failure of osseointegration or early loosening is relatively rare, recurrent dislocation remains a leading cause of early revision. Novel acetabular implants and those offered by smaller companies often lack constrained or dual mobility liners, which may result in revision of well-fixed, well-positioned cups in cases of recurrent dislocation.

The purpose of this study was to compare outcomes of THA with three different acetabular cups with differing fixation surfaces. One hydroxyapatite (HA)-coated cup (Trident, Stryker, Kalamazoo, MI, USA) offered dual mobility or constrained liner options. The other cups were a novel highly porous cup (Restoris PST, Stryker, Kalamazoo, MI, USA), and a Calcium Phosphate (CaP)-coated cup (Trinity, Corin, Cirincester, UK), neither of which offered dual mobility or constrained options at the time of investigation. Endpoints of interest were: clinical and radiographic outcomes including evidence of osseointegration, overall reoperations, reoperations for acetabular fixation failure, and reoperations to address dislocation in which a well-positioned shell was revised due to the lack of dual mobility or constrained options.

Purpose

Two-stage re-implantation after infection of Total Knee Arthroplasty (TKA), remains the gold standard to which other forms of treatment should be compared. The primary purpose of this study was to determine the rates of failure and functional outcome of two stage revision TKA for treatment of infection comparing cemented posterior stabilized compared to constrained condylar implants.

Aim. The most frequent mechanical failure in the osteosynthesis of intertrochanteric fractures is the cut-out. Fracture pattern, reduction quality, tip-apex distance or the position of the cervico-cephalic screw are some of the factors that have been associated with higher cut-out rates. To date, it has not been established whether underlying bacterial colonization or concomitant infection may be the cause of osteosynthesis failure in proximal femur fractures (PFF). The primary objective of this study is to assess the incidence of infection in patients with cut-out after PFF osteosynthesis. Method. Retrospective cohort study on patients with cut-out after PFF osteosynthesis with endomedullary nail, from January 2007 to December 2020. Demographic data of patients (such as sex, age, ASA), fracture characteristics (pattern, laterality, causal mechanism) and initial surgery parameters were collected (time from fall to intervention, duration of surgery, intraoperative complications). Radiographic parameters were also analyzed (tip-apex distance and Chang criteria). In all cut-out cases, 5 microbiological cultures and 1 anatomopathological sample were taken and the osteosynthesis material was sent for sonication. Fracture-related infection (FRI) was diagnosed based on Metsemakers et al (2018) and McNally et al (2020) diagnostic criteria. Results. Of the 67 cut-out cases, 16 (23.9%) presented clinical, analytical or microbiological criteria of infection. Of these sixteen patients, only in 3 of them the presence of an underlying infection was suspected preoperatively. A new osteosynthesis was performed in 24 cases (35.8%) and a conversion to arthroplasty in the remaining 43 (64.2%). A comparative analysis was performed between cases with and without infection. The groups were comparable in terms of demographic data and postoperative radiological data (using Chang criteria and tip-apex distance). Patients with underlying infection had a higher rate of surgical wound complication (56.3% vs 22%, p = 0.014), higher rates of leukocytes counts (11.560 vs 7.890, p = 0.023) and time to surgery (5.88 vs 3.88 days, p = 0.072). Conclusions. One out of four osteosynthesis failure in PFF is due to underlying FRI and in almost 20% were not unsuspected before surgery. In PFF osteosynthesis failures, underlying infection should be taken into account as a possible etiological factor and thus a preoperative and intraoperative infection study should be always performed

Background. One of the major concerns of hinge knees have been reported in literature is mechanical failure. Failure in the form of component fracture (2–10%) and hinge dislocation/ failure are worrisome. In addition, higher risk of aseptic loosening with hinge knee prosthesis has been attributed to stress transfer at bone cement interface. Methods. Retrospective review of clinical and radiological results of 71 consecutive patients operated at single centre using Smiles hinge knee (Stanmore implants) between 2010 and 2014. Data was collected till the latest follow up. Mechanical failure due to any reason was considered as primary end point. Radiological evidence of aseptic loosening was considered to be one of the surrogate end points. Results. Mean age at revision knee was 65.4 years (range 42 – 84). The number of previous revisions ranged from 1 – 4. Most common indications for revision were infection (n=26) and instability (n=26). Majority of patients had rotating hinge knee (n=66). Average follow-up was 31 months (range 3 – 72). Four patients died during follow-up due to medical reasons. There were no mechanical failures of implants apart from backing out of axle due to failure of circlip in 1 patient. Asymptomatic aseptic loosening of implant on femoral side was noted in 1 patient; however, there were no peri-prosthetic fractures in this series. Three patients had re-revision for infection and one for extensor mechanism subluxation. Conclusion. To our knowledge, this is the largest series till date reporting on mechanical outcomes of hinged knee implants for complex revisions. Clip failure is of concern; however there have been no other mechanical failures. Early results are encouraging, with no symptomatic aseptic loosening of implants to report

Do we need new polyethylene? Is there a clinical problem with first generation crosslinked polyethylene (XLPE)? Are we being duped into believing that doped polyethylene will solve a problem?. Clinical failures of polyethylene bearing total hip replacements are related to wear and the mechanical properties of the polyethylene. Wear is primarily related to crosslinking. Wear failures are secondary to periprosthetic osteolysis while mechanical failure causes cracking of thin polyethylene. Use of large femoral heads that reduce dislocation may increase wear and mechanical failure in the second decade of XLPE use. There is no question that XLPE has reduced 2-dimensional (2D) head penetration, volumetric penetration and periprosthetic osteolysis with traditional 28 mm head sizes. Reported 2D penetration rates are 0.03–0.07 mm/year and clinically important polyethylene wear induced osteolysis is nonexistent. However, larger heads with the same 2D head penetration will generate more volumetric debris and could cause osteolysis. There is no question that retrieved XLPE components have low levels of oxidation at the time of explant. While this is unexpected, the levels are well below levels reported with traditional polyethylene. It remains to be seen if these levels of oxidation will cause mechanical failures. Currently available versions of polyethylene have focused on eliminating oxidation induced mechanical property reduction and not additional wear reduction. This is accomplished with Vitamin E doping or blending. While the local effects of Vitamin E polyethylene particles at the cellular level have been studied the clinical effect of these chemically new particles remains to be seen. This author believes that long term volumetric wear with large head size is a greater concern than reduced mechanical properties secondary to in-vivo oxidation. New polyethylene development needs to focus on additional wear reduction. Can we afford to pay more for a new polyethylene in a value based healthcare environment?

Two-stage treatment of chronically infected TKA is the most common form of management in North America and most parts of the world. One-stage management has pros and cons which will not be discussed in this lecture. There is great variation of techniques and timing and little data to definitively support one technique or timing approach vs. another. Most methods are based on empirical success and logic. At the time of surgery, the first step is removal of infected implants. All metallic implants and cement should be removed. The most common places to leave cement behind inadvertently include patellar lug holes, femoral lug holes, and the anterior proximal tibia behind the tibial tubercle. Formal synovectomy should be performed. The next step is typically antibiotic-impregnated spacer placement. There are pros and cons of dynamic and static spacers with no clear evidence of superiority of one vs. another. Dynamic spacers work satisfactorily with mild to moderate bone loss, but more severe bone loss is usually better treated with static spacers and a cast. Most antibiotic spacers are made of methyl methacrylate cement with addition of high-dose antibiotics. In most cases, doses of 4–8 gm of antibiotics per pack of cement are preferred. The type of dosing depends on the specific antibiotic and the type of cement used. The most common antibiotics used are vancomycin and gentamycin. When the femoral canals have been instrumented, antibiotic-impregnated cement wands are usually placed in the medullary canal, as the medullary canals have been shown to have high risk of residual bacteria being present. The resection interval may vary and there is no clear evidence of a “best” resection interval. Practically speaking, most surgeons use a resection period of 8–16 weeks depending on the type of spacer utilised. During the resection interval, serum markers (ESR and CRP) are followed periodically. One anticipates a decline or normalization of these parameters prior to second stage reimplantation procedure. There has not been a demonstrated advantage to reaspiration of the knee before reimplantation in most circumstances. At the time of reimplantation, the spacers are removed and the knee is redebrided. The key at the time of reimplantation is to obtain good implant fixation but to also balance this with the potential for manageable extraction of the implants at some later date. Good implant fixation is important because failure rates due to mechanical failure are approximately equal to those of failure due to reinfection by 10 years. It is important to remember that reinfection risk is at least 10% by ten years, and therefore extractability of implants is also important. Post-operative management typically includes IV antibiotics, followed by oral antibiotics until final intra-operative cultures are available. The results of two-stage reimplantation are reported in many series. Most show approximately 85–95% rate of successful eradication of infection in the first five years. Reinfections, often with different organisms, may occur even late after reimplantation. By ten years after surgery survival free of mechanical failure and infection in most series drops to 80% or less due to recurrent infections and mechanical failures

Aim. In patients with bone sarcoma, placing mega prostheses in the proximal tibia is associated with high rates of infection. In studies with small numbers of patients and short follow-up periods, silver-coated mega prostheses have been reported to lead to reduced infection rates. To the best of our knowledge, this study is the largest one that has compared the infection rates with titanium versus silver-coated mega prostheses in patients treated for sarcomas in the proximal tibia. Method. The infection rate in 98 patients with sarcoma or giant cell tumour in the proximal tibia who underwent placement of a titanium (n = 42) or silver-coated (n = 56) mega prosthesis. *. was assessed, along with the treatments administered for any infection. Results. As the primary end point of the study, the rates of infection were 16.7% in the titanium group and 8.9% in the silver group, resulting in 5-year prosthesis survival rates of 90% in the silver group and 84% in the titanium group. Overall, seven of 56 patients in the silver group (12.5%) developed periprosthetic infection. Two patients became infected after revision surgery due to mechanical failure of the prosthesis. In the titanium group, one patient developed a periprosthetic infection after revision surgery (which was carried out in 50% of patients) due to a mechanical prosthetic failure, leading to an overall infection rate of 19.0% (eight of 42). Overall, nine of 12 (75%) periprosthetic infections in the two groups occurred within the first 2 years postoperatively, if later revision surgery due to mechanical failure was not necessary. Whereas three of the eight patients in the titanium group (37.5%) ultimately had to undergo amputation due to infected proximal tibia replacement, these mutilating surgical procedures were necessary in the silver group in only one patient (14.3%). In the titanium group, two-stage revision surgery with a temporary antibiotic-impregnated cement spacer was ultimately successful in four of eight patients (50.0%), but this procedure was necessary in only one patient in the silver group (14.3%). Conclusions. The use of silver-coated prostheses reduced the infection rate in a relatively large and homogeneous group of patients. In addition, less aggressive treatment of infection was possible in the group with silver-coated prostheses

We retrospectively reviewed 161 revision THAs with diaphyseal fitting, mid- modular femoral components performed by ten surgeons at two academic medical centers. The average follow-up was 6.1 years. At final follow-up, 4 patients required re-revision for failure of the femoral component; 3 (2%) for aseptic loosening and 1 for mechanical failure of stem in setting of periprosthetic fracture. There were a total of 24 (14.9%) revisions for any reason, with the most common reason being septic failure (10 of 24). To our knowledge, this is the largest reported series of mid-term survivorship and complications of revision THA with mid-modular femoral components. Our results show that these stems have a low rate of aseptic loosening, subsidence, and mechanical failure

HXLPE acetabular liners were introduced to reduce wear-related complications in THA. However, post-irradiation thermal free radical stabilization can compromise mechanical properties, leave oxidation-prone residual free radicals, or both. Reports of mechanical failure of HXLPE acetabular liner rims raise concerns about thermal free radical stabilization and in vivo oxidization on implant properties. The purpose of this study is to explore the differences in the mechanical, physical and chemical properties of HXLPE acetabular liner rims after extended time in vivo between liners manufactured with different thermal free radical stabilization techniques. Remelted, single annealed and sequentially annealed retrieved HXLPE acetabular liners with in vivo times greater than 4.5 years were obtained from our implant retrieval laboratory. All retrieved liners underwent an identical sanitation and storage protocol. For mechanical testing, a total of 55 explants and 13 control liners were tested. Explant in vivo time ranged from 4.6 – 14 years and ex vivo time ranged from 0 – 11.6 years. Rim mechanical properties were tested by microindentation hardness testing using a Micromet II Vickers microhardness tester following ASTM standards. A subset of 16 explants with ex vivo time under one year along with five control liners were assessed for oxidation by FTIR, crystallinity by Raman spectroscopy, and evidence of microcracking by SEM. No significant difference in in vivo or ex vivo was found between thermal stabilization groups in either set of explants studied. In the mechanically tested explants, there was no significant correlation between in vivo time and Vickers hardness in any thermal stabilization group. A significant correlation was found between ex vivo time and hardness in remelted liners (r=.520, p = .011), but not in either annealed cohort. ANCOVA with ex vivo time as a covariate found a significant difference in hardness between the thermal free radical stabilization groups (p 0.1) was found in retrieved remelted (25%), single annealed (100%) and sequentially annealed (75%) liner rims. Crystallinity was increased in the subsurface region relative to control liners for both annealed, but not remelted, liner rims. Hardness was increased in oxidized rims for both annealed cohorts but not in the remelted cohort. Microcracking was only found along the surface of one unoxidized remelted liner rim. Mechanical properties were reduced at baseline and worsened after in vivo time for remelted HXLPE liner rims. Rim oxidation was detected in all groups. Oxidation was associated with increased crystallinity and hardness in annealed cohorts, but not remelted liners. Increased crystallinity and oxidation do not appear to be directly causing the worsened mechanical behavior of remelted HXLPE liner rims after extended in vivo time

EPRs are the treatment of choice following resection of tumours. These have been used for 39 years in our institution. There has been concern regarding the long term survival of endoprosthesis; this study investigates the fate of the reconstruction. Methods. Between 1966 and 1995, 3716 patients were seen with a suspected neoplasm and 776 patients underwent EPRs. Patients receiving growing endoprostheses were excluded from the study as they invariably require revision, leaving 667 replacements. Insufficient data was available in 6 cases, leaving 661 patients in the study group. Information was reviewed concerning the diagnosis, survival of implant and patient, subsequent surgery, complications and functional outcome. Kaplan-Meier survival analysis was used for implant survival with end points defined as revision for mechanical failure (aseptic loosening, implant fracture, instability, avascular necrosis, periprosthetic fracture, pain and stiffness) and revision for any cause (infection, local recurrence and mechanical failure). Results. Mean age at diagnosis was 34 years. Overall patient survival was 52.7% at 10 years and 45.7% at 20 years. The mean follow-up for all patients was 9 years, and for those patients who survived their original disease, the mean follow-up was 15 years. 227 (34%) patients underwent revision surgery, 75 patients for infection (33%), 36 patients for locally recurrent disease (16%) and mechanical failure in 116 patients (51%). With revision for mechanical failure as the end-point, implant survival was 75% at 10 years and 52% at 20 years. With revision any cause as an end-point implant survival was 58% at 10 years and 38% at 20 years. Overall limb salvage was maintained in 91% of patients at 10 years from reconstruction and 79% at 20 years. There was a significant difference between survival of implant between implantation sites, with the proximal humeral implant survival being the best and tibial reconstructions being the worst. The MTSS functional score was available on 151 patients, with a mean score of 25/30 (83%) at last follow-up visit. Discussion. Our results are comparable with other series of long term follow-up and justifies their continued use

Background. A first generation once annealed highly crosslinked polyethylene (HXLPE) was introduced in 1998. At 8 years it was reported to have a 78% reduction in wear compared with conventional polyethylene and no osteolysis. However, concerns regarding the long-term performance and oxidative resistance of this annealed material exist because of the presence of free radicals. Questions/purposes. We therefore addressed the following questions: (1) Does the improvement in wear observed at earlier follow-up continue out to 15 years? (2) What is the incidence of osteolysis in this group of patients?. Methods. We retrospectively reviewed 48 prospectively followed patients who had 50 hips with a once annealed HXLPE and were followed an average of 12 years (15 years maximum). Linear head penetration and cup position were measured from AP radiographs at early, 1-year, 5-year, and most recent follow-ups. There were 26 females, 22 males, with an average age of 61 years. Results. At average 12 years follow-up, annual linear wear was 0.018 mm (SD = 0.024). Average cup inclination was 50.2 degrees (SD = 5.1 range 48 to 64) and anteversion was 18.6 (SD = 8.3, range 3 to 35). No mechanical failure or osteolysis has been found on routine x-rays to date. Conclusions. At 8 year follow this once annealed material had a reported linear wear rate of 0.031mm /year. We now report, at a 12 years average 15 years maximum follow-up, a further reduction in linear wear of 0.018mm/yr. and no mechanical failures or osteolysis (Figure-1)

Introduction. Total Elbow Arthroplasty (TEA) is recognized as an effective treatment solution for patients with rheumatoid arthritis or for traumatic conditions. Current total elbow devices can be divided into linked or unlinked design. The first design usually presents a linking element (i.e. an axle) to link together the ulnar and humeral components to stabilize the joint; the second one does not present any linkage and the stability is provided by both intrinsic design constraints and the soft tissues. Convertible modular solutions allow for an intraoperative decision to link or unlink the prosthesis; the modular connections introduce however additional risks in terms of both mechanical strength and potential fatigue and fretting phenomena that may arise not only due to low demand activities loads, but also high demand (HD) ones that could be even more detrimental. The aim of this study was to assess the strength of the modular connection between the axle and the ulnar component in a novel convertible elbow prosthesis design under simulated HD and activities of daily living (ADLs) loading. Methods. A novel convertible total elbow prosthesis (LimaCorporate, IT) comprising both ulnar and humeral components that can be linked together by means of an axle, was used. Both typical ADLs and HD torques to be applied to the axle were determined based on finite element analysis (FEA); the boundary load conditions for the FEA were determined based on kinematics analysis on real patients in previous studies. The FEA resultant moment acting on the axle junction during typical ADLs (i.e. feeding with 7.2lbs weight in hand) was 3.2Nm while for HD loads (i.e. sit to stand) was 5.7 Nm. In the experimental setup, 5 axle specimens coupled with 5 ulnar bodies through a tapered connection (5 Nm assembly torque) were fixed to a torque actuator (MTS Bionix) and submerged in a saline solution (9g/l). A moment of 3.2 Nm was applied to the axle for 5M cycles through a fixture to test it under ADLs loading. After 5M cycles, the axles were analyzed with regards to fretting behavior and then re-assembled to test them against HD loading by applying 5.7 Nm for 200K cycles (corresponding to 20 years function). Results. All 5 samples withstood all 5.2M loading cycles without any mechanical failure. At the end of 5M cycles, each axle was still stable as the measured disassembly torque was 3.96 +/−0.18 Nm. Slight signs of fretting were detected on the tapered connection after 5M cycles, however they did not compromise the mechanical connection nor the stability. Discussion and Conclusions. Currently there are no reference standards that properly define protocols for biomechanical testing of elbow prostheses. In the present study, a test to mechanically assess the strength of an axle connection under both typical ADLs and HD loads was set. The connection was able to withstand the imposed conditions. In general, testing of TEA devices should include not only standard ADLs loads but also HD loads, which could be more detrimental for the long-term survivorship. For any figures or tables, please contact authors directly

Prosthetic joint infections (PJI) are caused by a variety of microorganisms but most frequently by staphylococci. The results of treatment of PJI due to organisms other than staphylococci are less known. The aim of this study is to evaluate the outcomes after streptococcal PJI. The data of 26 streptococcal (13 hip and 13 knee PJI from 24 patients) were retrieved from hospital based PJI register, and analyzed. There were 15 female and 11 male patients (mean age 66 y). Most (13) PJI were hematogenous. 15 PJI had been treated with debridement and retention (D&R) of the infected joint, 1 with permanent resection arthroplasty, 9 had two stage revision and 1 patient had one stage partial replacement. After the microbiological diagnosis was established most patients received 2–3 weeks of penicillin G or ceftriaxone followed by 2–6 months of oral amoxicillin. All patients had regular follow-ups after the procedure at least at 1 month, three months and one year. The results were classified as: PJI cure (in absence of clinical signs and symptoms of infection and with negative CRP), probable failure (in absence of clinical signs and symptoms of infection but with elevated CRP), definite failure (if a new treatment was necessary), and mechanical failure (aseptic loosening, periprosthetic fracture, quadriceps rupture). One foreign patient was lost to follow up. The mean follow up time for the rest was 60 months (from 16 to 167) months. There was probable prosthesis failure in 1 case, definite prosthesis failure in 7 cases and mechanical failure in 3 cases. The mean survival time of the failed prostheses was 28 (range from 2 to 83) months. 6 failures (40 %) occurred in group of cases that had undergone D&R, and 1 (6 %) in the two stage revision group. Among the 7 definite failures in 4 patients antibiotic treatment was empirically started after the symptoms reappeared resulting in long remission periods. Comparing to the published results of staphylococcal PJI it seems that D&R of the prosthesis for streptococcal PJI is considerably less successful. Rifampicin as a proven treatment of choice for staphylococcal infections is probably the main reason for the difference. An unexpected feature of streptococcal PJI is that definite failures are easily suppressed for long time with a short course of oral antibiotics

Introduction. HXLPE acetabular liners were introduced to reduce wear-related complications in THA. However, post-irradiation thermal free radical stabilization can compromise mechanical properties, leave oxidation-prone residual free radicals, or both. Reports of mechanical failure of HXLPE acetabular liner rims raise concerns about thermal free radical stabilization and in vivo oxidization on implant properties. The purpose of this study is to explore the differences in the mechanical, physical and chemical properties of HXLPE acetabular liner rims after extended time in vivo between liners manufactured with different thermal free radical stabilization techniques. Material and Methods. Remelted, single annealed and sequentially annealed retrieved HXLPE acetabular liners with in vivo times greater than 4.5 years were obtained from our implant retrieval laboratory. All retrieved liners underwent an identical sanitation and storage protocol. For mechanical testing, a total of 55 explants and 13 control liners were tested. Explant in vivo time ranged from 4.6 – 14.0 years and ex vivo time ranged from 0 – 11.6 years. Rim mechanical properties were tested by microindentation hardness testing using a Micromet II Vickers microhardness tester following ASTM standards. A subset of 16 explants with ex vivo time under one year along with five control liners were assessed for oxidation by FTIR, crystallinity by Raman spectroscopy, and evidence of microcracking by SEM. Results. No significant difference in in vivo or ex vivo time was found between thermal stabilization groups in either set of explants studied. In the mechanically tested explants, there was no significant correlation between in vivo time and Vickers hardness in any thermal stabilization group. A significant correlation was found between ex vivo time and hardness in remelted liners (r=.520, p=.011), but not in either annealed cohort. ANCOVA with ex vivo time as a covariate found a significant difference in hardness between the thermal free radical stabilization groups (p<.0005, η. 2. = 0.322). Post hoc analysis revealed hardness was significantly lower in the retrieved remelted group compared to both the single annealed (p=.001) and sequentially annealed (p<.0005) cohorts. Hardness was significantly higher in the retrieved remelted liners compared to controls (p=.007), with no different in either annealed cohort. Detectable subsurface oxidation (OI > 0.1) was found in retrieved remelted (25%), single annealed (100%) and sequentially annealed (75%) liner rims. Crystallinity was increased in the subsurface region relative to control liners for both annealed, but not remelted, liner rims. Hardness was increased in oxidized rims for both annealed cohorts but not in the remelted cohort. Microcracking was only found along the surface of one unoxidized remelted liner rim. Conclusion. Mechanical properties were reduced at baseline and worsened after in vivo time for remelted HXLPE liner rims. Rim oxidation was detected in all groups. Oxidation was associated with increased crystallinity and hardness in annealed cohorts, but not remelted liners. Increased crystallinity and oxidation do not appear to be directly causing the worsened mechanical behavior of remelted HXLPE liner rims after extended in vivo time. For any figures or tables, please contact authors directly

Introduction. In an effort to provide a TKA bearing material that balances resistance to wear, mechanical failure and oxidation, manufacturers introduced antioxidant polyethylene. In many designs, this is accomplished through pre-blending the polymer with the antioxidant before consolidation and radiation crosslinking. This study reports the wear performance (in terms of thickness change) of a hindered phenol (PBHP) UHMWPE from analysis of an early series of knee retrievals and explores these questions: 1) What is early-time performance of this new bearing material? 2) Is there a difference in performance between fixed and mobile bearings in this design? 3) How does quantitative surface analysis help understand performance at the insert-tray modular interface?. Methods. A series of 100 consecutive Attune™ knee inserts (DePuy Synthes, Warsaw, IN) received at revision by an IRB approved retrieval laboratory between September 2014 and March 2019 were investigated. In vivo duration was 0–52 months. Both the fixed bearing design (n=74) and the rotating platform mobile bearing design (n=26) were included. Dimensional change was determined by measurement of each insert and compared to the as-manufactured dimensions, provided by the manufacturer. The insert-tray interfaces under the loaded bearing zones were analyzed with light interferometry using an optical surface profiler (NewView™ 7300, Zygo, Middlefield, CT). Statistical analyses to explore relationships between measured variables were conducted using SPSS. Results. Mean total through-thickness change of the inserts was 0.052 mm. Mean rate of thickness change for all inserts having in vivo duration > 12 months was 0.038 mm/year (fixed bearing 0.042, mobile bearing 0.029 mm/year). The rate of thickness change for all inserts showed a decreasing trend with duration that was not statistically significant, (rho -.244, p=.094); however, the mobile bearing cohort alone showed a significant decrease in thickness change rate with duration (rho= −.659; p=.014). Surface roughness (Sa) of the distal surface of the UHMWPE inserts under the bearing areas averaged 1.24 µm (range 0.12 – 8.53) and peak-to-valley height (PV) averaged 27.1 µm (range 4 – 95). Sa and PV both showed a decreasing trend with duration in vivo in the mobile bearing inserts, but that trend did not reach statistical significance (p= 0.05 criterion). Neither Sa nor PV showed correlation with measured thickness change. Discussion. This study indicates that the rate of thickness change of a relatively new antioxidant cross-linked bearing material is very similar to other reported wear rates of crosslinked knee inserts. Lower wear rate of mobile bearing inserts compared to fixed bearings also is consistent with earlier published studies. Direct comparison between quantitative thickness change and objective, quantitative surface metrology on the same series brings new information to the arena of measuring and reporting “wear” of UHMWPE and underscores the importance of the distinction between visual damage and actual thinning of the bearing. The systematic surface analysis of the modular interfaces showing that surface roughness (Sa) and total damage feature topography (PV) trend downward with in vivo duration of mobile bearings supports the hypothesis that relative motion at that interface may ‘polish out’ the surface topography over time. For any figures or tables, please contact authors directly

355 non-cemented MOM arthroplasties, of a single surgeon, with a follow up of 3–16 years (avg. 7.5 years) were retrospectively reviewed for evidence of pseudotumor and aseptic mechanical failure. There were 186 with 28 mm heads, 126 with 34 mm heads, 47 with 38 mm heads, from a single manufacturer. There were 5 revisions of 38 mm heads for atraumatic painful “metalosis” 4–8 years after implantation (10.7%). There were 4 revisions of 34 mm heads for post-traumatic instability (dislocation) with secondary metalosis 4–7 years after implantation (3.1%). There were 2 revisions of 28 mm heads for post-traumatic instability (dislocation) with secondary metalosis 6–12 years after implantation (1.1%). There were 5 patients, all with 38 mm heads, with asymptomatic “psoas bursae” with elevated serum CR and Co levels (1.0–3.0). All of the failed THR's had acetabular components with lateral tilt <50 degrees (35–50), and anteversion angles <15 degrees (0–15). 2 of the 34 mm and both 28 mm instabilities were the consequence of injuries sustained in motor vehicle accidents. The remaining 2 instabilities with 34 mm implants were the result of mechanical falls. Particulate debris, whether secondary to polyethylene, ceramic or metal articulations has been well documented as a cause of synovitis and damage to bony and soft tissues adjacent to a THR. This debris appears to be the result of material wear and mechanical failure with use over time. Unlike native articular cartilage, these materials are incapable of self-lubrication. Therefore THR articulations are dependent upon the penetration of ambient synovial fluid to provide lubrication of the replacement surfaces. This study suggests that increase in head diameter may reduce penetration of synovial fluid between the articulating surfaces of a THR, compromising the lubrication of bearing surfaces; thereby contributing to accelerated wear and premature failure of larger MOM arthroplasties

BACKGROUND PURPOSES. dislocation is a classical complication in total hip arthroplasty (THA) revision. Cup fixation is the second concern. Since 1998 we routinely use cementless Dual mobility cup (DMC) in revision surgery. In order to know outcomes at 2 years, we followed a prospective series of 78 patients treated in our institution. Purpose is to demonstrate that DMC used in revision THA is safe as regards dislocation risk and bone fixation. MATERIAL METHODS. from January 2010 to January 2012 we collected cohort of 79 cases on 78 patients. Patients have been followed with a clinical and radio graphical standard examination. Mean delay between index surgery and revision was 12,9 years. Mean age at revision was 75,5 years. Two different types of DMC were used: standard DMC in 68 cases. In severe bone loss, a specific revision cup was used in 11 cases. RESULTS. at 2 years follow up, 65 patients have been reviewed. 5 patients are definitely lost to follow up. 8 patients deceased. One patient dislocated her hip at 1 month. Two early mechanical failures occurred. DISCUSSION. purpose of this short term follow up study is to emphasize low risk of dislocation and trustable fixation of a cementless DMC used in revision THA. THA. Instability is the leading cause of failure. In our series dislocation rate is 1,2%‥ 2 patients presented an early mechanical cup failure (2.5%). CONCLUSION. considering outcomes of this series, we may assess that in in THA revision surgery, DMC can be recommended