Aims

Focal knee arthroplasty is an attractive alternative to knee arthroplasty for young patients because it allows preservation of a large amount of bone for potential revisions. However, the mechanical behaviour of cartilage has not yet been investigated because it is challenging to evaluate in vivo contact areas, pressure, and deformations from metal implants. Therefore, this study aimed to determine the contact pressure in the tibiofemoral joint with a focal knee arthroplasty using a finite element model.

Aims. The aim of this study was to evaluate the suitability of the tapered cone stem in total hip arthroplasty (THA) in patients with excessive femoral anteversion and after femoral osteotomy. Methods. We included patients who underwent THA using Wagner Cone due to proximal femur anatomical abnormalities between August 2014 and January 2019 at a single institution. We investigated implant survival time using the endpoint of dislocation and revision, and compared the prevalence of prosthetic impingements between the Wagner Cone, a tapered cone stem, and the Taperloc, a tapered wedge stem, through simulation. We also collected Oxford Hip Score (OHS), visual analogue scale (VAS) satisfaction, and VAS pain by postal survey in August 2023 and explored variables associated with those scores. Results. Of the 58 patients (62 hips), two (two hips) presented with dislocation or reoperation, and Kaplan-Meier analysis indicated a five-year survival rate of 96.7% (95% CI 92.4 to 100). Mean stem anteversion was 35.2° (SD 18.2°) for the Taperloc stem and 29.8° (SD 7.9°) for the Wagner Cone stem; mean reduction from Taperloc to Wagner Cone was 5.4° (SD 18.8°). Overall, 55 hips (52 patients) were simulated, and the prevalence of prosthetic impingement was lower for the Wagner Cone (5.5%, 3/55) compared with the Taperloc (20.0%, 11/55) stem, with an odds ratio of 0.20 (p = 0.038). Among the 33 respondents to the postal survey (36 hips), the mean scores were VAS pain 10.9, VAS satisfaction 86.9, and OHS 44.7. A multivariable analysis revealed that reduction of stem anteversion from Taperloc to Wagner Cone was more favourable for VAS pain (p = 0.029) and VAS satisfaction (p = 0.002). Conclusion. The mid-term survival rate for THA using the Wagner Cone stem was high, which may be supported by a reduction in prosthetic impingement. The reduction in excessive stem anteversion by using a tapered cone stem was associated with reduced pain and increased patient satisfaction. Cite this article: Bone Jt Open 2024;5(10):858–867

Aims. To explore the clinical efficacy of using two different types of articulating spacers in two-stage revision for chronic knee periprosthetic joint infection (kPJI). Methods. A retrospective cohort study of 50 chronic kPJI patients treated with two types of articulating spacers between January 2014 and March 2022 was conducted. The clinical outcomes and functional status of the different articulating spacers were compared. Overall, 17 patients were treated with prosthetic spacers (prosthetic group (PG)), and 33 patients were treated with cement spacers (cement group (CG)). The CG had a longer mean follow-up period (46.67 months (SD 26.61)) than the PG (24.82 months (SD 16.46); p = 0.001). Results. Infection was eradicated in 45 patients overall (90%). The PG had a better knee range of motion (ROM) and Knee Society Score (KSS) after the first-stage revision (p = 0.004; p = 0.002), while both groups had similar ROMs and KSSs at the last follow-up (p = 0.136; p = 0.895). The KSS in the CG was significantly better at the last follow-up (p = 0.013), while a larger percentage (10 in 17, 58.82%) of patients in the PG chose to retain the spacer (p = 0.008). Conclusion. Prosthetic spacers and cement spacers are both effective at treating chronic kPJI because they encourage infection control, and the former improved knee function status between stages. For some patients, prosthetic spacers may not require reimplantation. Cite this article: Bone Joint Res 2024;13(6):306–314

Total Hip Arthroplasty (THA) and Hip Hemiarthroplasties (HA) are successful, cost-effective procedures that improve quality of life. Dislocation is a well recognised complication with a significant health and economic burden. We aim to establish the current management practices across the United Kingdom (UK) for Prosthetic Hip Dislocations (PHD). Our definition of a PHD includes; THA, HA and revision THA. This national study builds on our regional pilot study and records one of the largest datasets of Prosthetic Hip Dislocation management within the UK. A trainee-led collaborative; the North West Orthopaedic Research Collaborative (NWORC). Conducted a retrospective audit, registered as Quality Improvement (QI) projects, collected data from 38 hospital trusts across the UK. Data was collected on patient-related factors, inpatient management, and outpatient follow up of each PHD episode between January and July 2019. Primary outcome measured definitive management, in the form of revision surgery or the consideration for this through a referral pathway. A total of 673 (THA 504, Revision THA 141, HA 28) patients were included with a total of 740 dislocation episodes. Mean age was 75.6 years with female to male ratio 2:1. The majority of PHDs were a result of a low energy mechanism (98.7%) and presented over 6 months post index procedure (80.5%). Over half (53.8%) attended with a first or second time dislocation. Only 29.9% patients received onward revision referral; whereas 70.1% followed diverse management patterns, including local non-arthroplasty and primary arthroplasty surgeon follow-ups. Revision THAs had higher rates of referral for revision (p<0.001) compared to primary THA and HA dislocations. A high number of PHDs present across the UK, with under a third receiving definitive management plans. This variation increases the economical burden to the National Health Service, highlighting the need for national guidance to manage these complex patients

Total temporomandibular joint (TMJ) replacements reduce pain and improve quality of life in patients suffering from end-stage TMJ disorders, such as osteoarthritis and trauma. Jaw kinematics measurements following TMJ arthroplasty provide a basis for evaluating implant performance and jaw function. The aim of this study is to provide the first measurements of three-dimensional kinematics of the jaw in patients following unilateral and bilateral prosthetic TMJ surgeries. Jaw motion tracking experiments were performed on 7 healthy control participants, 3 unilateral and 1 bilateral TMJ replacement patients. Custom-made mouthpieces were manufactured for each participant's mandibular and maxillary teeth, with each supporting three retroreflective markers anterior to the participant's lip line. Participants performed 15 trials each of maximum jaw opening, lateral and protrusive movements. Marker trajectories were simultaneously measured using an optoelectronic tracking system. Laser scans taken of each dental plate, together with CT scans of each patient, were used to register the plate position to each participant's jaw geometry, allowing 3D condylar motion to be quantified from the marker trajectories. The maximum mouth opening capacity of joint replacement patients was comparable to healthy controls with average incisal inferior translations of 37.5mm, 38.4mm and 33.6mm for the controls, unilateral and bilateral joint replacement patients respectively. During mouth opening the maximum anterior translation of prosthetic condyles was 2.4mm, compared to 10.6mm for controls. Prosthetic condyles had limited anterior motion compared to natural condyles, in unilateral patients this resulted in asymmetric opening and protrusive movements and the capacity to laterally move their jaw towards their pathological side only. For the bilateral patient, protrusive and lateral jaw movement capacity was minimal. Total TMJ replacement surgery facilitates normal mouth opening capacity and lateral and inferior condylar movements but limits anterior condylar motion. This study provides future direction for TMJ implant design

Aims. Computer-assisted 3D preoperative planning software has the potential to improve postoperative stability in total hip arthroplasty (THA). Commonly, preoperative protocols simulate two functional positions (standing and relaxed sitting) but do not consider other common positions that may increase postoperative impingement and possible dislocation. This study investigates the feasibility of simulating commonly encountered positions, and positions with an increased risk of impingement, to lower postoperative impingement risk in a CT-based 3D model. Methods. A robotic arm-assisted arthroplasty planning platform was used to investigate 11 patient positions. Data from 43 primary THAs were used for simulation. Sacral slope was retrieved from patient preoperative imaging, while angles of hip flexion/extension, hip external/internal rotation, and hip abduction/adduction for tested positions were derived from literature or estimated with a biomechanical model. The hip was placed in the described positions, and if impingement was detected by the software, inspection of the impingement type was performed. Results. In flexion, an overall impingement rate of 2.3% was detected for flexed-seated, squatting, forward-bending, and criss-cross-sitting positions, and 4.7% for the ankle-over-knee position. In extension, most hips (60.5%) were found to impinge at or prior to 50° of external rotation (pivoting). Many of these impingement events were due to a prominent ischium. The mean maximum external rotation prior to impingement was 45.9° (15° to 80°) and 57.9° (20° to 90°) prior to prosthetic impingement. No impingement was found in standing, sitting, crossing ankles, seiza, and downward dog. Conclusion. This study demonstrated that positions of daily living tested in a CT-based 3D model show high rates of impingement. Simulating additional positions through 3D modelling is a low-cost method of potentially improving outcomes without compromising patient safety. By incorporating CT-based 3D modelling of positions of daily living into routine preoperative protocols for THA, there is the potential to lower the risk of postoperative impingement events. Cite this article: Bone Jt Open 2023;4(6):416–423

Aims. Iliopsoas impingement occurs in 4% to 30% of patients after undergoing total hip arthroplasty (THA). Despite a relatively high incidence, there are few attempts at modelling impingement between the iliopsoas and acetabular component, and no attempts at modelling this in a representative cohort of subjects. The purpose of this study was to develop a novel computational model for quantifying the impingement between the iliopsoas and acetabular component and validate its utility in a case-controlled investigation. Methods. This was a retrospective cohort study of patients who underwent THA surgery that included 23 symptomatic patients diagnosed with iliopsoas tendonitis, and 23 patients not diagnosed with iliopsoas tendonitis. All patients received postoperative CT imaging, postoperative standing radiography, and had minimum six months’ follow-up. 3D models of each patient’s prosthetic and bony anatomy were generated, landmarked, and simulated in a novel iliopsoas impingement detection model in supine and standing pelvic positions. Logistic regression models were implemented to determine if the probability of pain could be significantly predicted. Receiver operating characteristic curves were generated to determine the model’s sensitivity, specificity, and area under the curve (AUC). Results. Highly significant differences between the symptomatic and asymptomatic cohorts were observed for iliopsoas impingement. Logistic regression models determined that the impingement values significantly predicted the probability of groin pain. The simulation had a sensitivity of 74%, specificity of 100%, and an AUC of 0.86. Conclusion. We developed a computational model that can quantify iliopsoas impingement and verified its accuracy in a case-controlled investigation. This tool has the potential to be used preoperatively, to guide decisions about optimal cup placement, and postoperatively, to assist in the diagnosis of iliopsoas tendonitis. Cite this article: Bone Jt Open 2023;4(1):3–12

This technical choice constitutes an effective solution for all those cases where, due to the infective damage, the radical surgical debridement needed or in presence of a septic pseudoarthrosis, there is a relevant loss of bone stock in the proximal femur. As a treatment for these specific clinical patterns oncological prosthetic implants can be used, to overcome the amount of bone loss. Sometimes acetabular prosthetic implantation, or reimplantation, is also needed because of its septic mobilization, otherwise a bicentric endoprosthesis can be implanted. The main issue for the surgeon is the gluteal muscular deficiency, caused often by the loss of the great trochanter, a severe condition often worsened by the damage on muscles and soft tissues given by previous surgical procedures and debridements. The offset itself, really often not sufficient for the limited amount of sizes and lengths of the oncological designed prosthetic implants, represent a key issue of this treatment with a high luxation risk, with a higher rate in those cases when an arthroprosthesis has been performed. In this article are described 4 cases, all four treated with a two-stage surgical approach and a definitive oncological prosthetic system to overcome the severe bone loss of the proximal femur. The cases are examined about the surgical indication to this prosthetic choice, the postoperative period with the related complications (1 case of recurrent luxation) and with a minimum follow up of 6 months (maximum 36 months). In all the cases at the follow up the infection is solved. At the end the specific rehabilitation program for the range of motion and the muscular strength regain, that we developed in our Operative Unit is described; in this program we occasionally used for the immediate post surgery period a jointed hip brace. The length of the rehabilitation could not be standard, but should be customized and variations of the program could be done during the follow up. In the immediate post-surgical period the rehabilitative goals are maintaining the correct posture in bed and regaining the passive articular range of motion. In the longer period the main goals are regain strength of the gluteal muscles, proprioception and gait, even if claudication (Trendelemburg), hyposthenia a recurrent dislocation can be let. The weight bearing is allowed usually at the eight week after surgery, but only after clinical and x-ray evaluation

Aims. Over time, the locking mechanism of Modular Universal Tumour and Revision System (MUTARS) knee arthroplasties changed from polyethylene (PE) to polyether-ether-ketone Optima (PEEK) and metal-on-metal (MoM) in an attempt to reduce the risk of mechanical failure. In this study, we aimed to assess the cumulative incidence of locking mechanism revision for symptomatic instability by type of material, and assess potential associated risk factors. Methods. The MUTARS Orthopaedic Registry Europe was used for a retrospective review of 316 patients (54% male (n = 170), median age 44 years (IQR 23 to 61)) who underwent a MUTARS knee arthroplasty for oncological indications between December 1995 and January 2023. The minimum follow-up was 12 months, and the median follow-up was 7.9 years (IQR 3.3 to 13.0). A competing risk model was used to estimate the cumulative incidence of first locking mechanism revision with death and revision for any other reason as competing events. Possible risk factors were assessed employing a univariate cause-specific hazards regression model. Results. Symptomatic instability of the hinge or locking mechanism due to wear (n = 20) or breakage (n = 14) occurred in 34 patients (11%): 9% of PE (n = 4/45), 20% of PEEK (n = 9/44), and 9% of MoM locking mechanisms (n = 21/227). The cumulative incidences of revision for instability due to wear or locking mechanism breakage at two, five, and ten years were 0%, 5% (95% CI 1 to 15), and 5% (95% CI 1 to 15) for PE, 5% (95% CI 1 to 14), 14% (95% CI 5 to 26), and 16% (95% CI 7 to 29) for PEEK, and 0%, 3% (95% CI 1 to 6), and 10% (95% CI 5 to 16) for MoM. With PE as the reference category, the cause-specific hazard ratio for PEEK and MoM were 3.6 (95% CI 1.1 to 11.9; p = 0.036) and 3.2 (95% CI 1.1 to 9.5; p = 0.043), respectively. Age, BMI, resection length, and extra-articular resections were not associated with the time to locking mechanism revision. Conclusion. Alterations in prosthetic materials have not decreased the revision risk for locking mechanism failure. Besides locking mechanism material, no other patient- or prosthesis-related risk factors for locking mechanism failure were identified. Improvement of the locking mechanism is warranted since revision exposes patients to the risk of serious secondary complications. Cite this article: Bone Joint J 2025;107-B(2):239–245

Total Hip Replacements (THR) and Hip Hemiarthroplasties (HA) are both successful and common orthopaedic procedures. Dislocation is a well-recognised complication carrying significant morbidity and, in some cases, increased mortality risks. We define prosthetic hip dislocations (PHDs) to include both THRs and HAs. Prosthetic Hip Dislocations (PHDs) are a common acute admission yet there are no published guidelines or consensus on management following reduction. A retrospective audit was undertaken by the North West Orthopaedic Research Collaborative (NWORC) between January 2019 and July 2019. A questionnaire was used to capture the management of each dislocation episode presenting to 11 Hospital trusts. The study was registered as a Quality Improvement (QI) project at each site. Data regarding the surgical management physiotherapy input, ongoing care and further management plans were recorded. A total of 183 patients with 229 dislocations were submitted for initial analysis (171 THRs, 10 HAs, 2 PFRs). Female to male ratio was 2:1 with mean age of 76.7 years. Average time to first dislocation was 8.1 years. 61.1% were first or second time dislocators and 38.9% presented with 3 or more dislocations. Initial reductions were predominantly attempted in theatre (96.5%, n=221) with only 3.5% (n=8) attempted in the emergency department. In theatre 89% (n=201) were reduced closed. There was no plan for revision surgery in 70.6% cases with no difference seen between patients with >=3 dislocations and <=2 dislocations. Of the patients with a revision plan, 71% of these were performed or planned locally. The high number of patients with 3 or more dislocations and the lack of plans for definitive interventions in the majority of cases highlights the significant variation in the management of this complex group of patients. This variation in the quality of care increases the burden on the National Health Service through repeat hospital episodes. We aim to roll out this study nationally to assess regional variations and ultimately make the case for national guidance on the management of prosthetic hip dislocations

Introduction. Instability continues to be the number one reason for revision in primary total hip arthroplasty (THA). Commonly, impingement precedes dislocation, inducing a levering out the prosthetic head from the liner. Impingement can be prosthetic, bony or soft tissue, depending on component positioning and anatomy. The aim of this virtual study was to investigate whether bony or prosthetic impingement occurred first in well positioned THAs, with the hip placed in deep flexion and hyperextension. Methods. Twenty-three patients requiring THA were planned for a TriFit/Trinity ceramic-on-poly cementless construct using the OPS. TM. dynamic planning software (Corin, UK). The cups were sized to best fit the anatomy, medialised to sit on the acetabular fossa and orientated at 45° inclination and 25° anteversion when standing. Femoral components and head lengths were then positioned to reproduce the native anteversion and match the contralateral leg length and offset. The planned constructs were flexed and internally rotated until anterior impingement occurred in deep flexion [Fig. 1]. The type (bony or prosthetic), and location, of impingement was then recorded. Similarly, the hips were extended and externally rotated until posterior impingement occurred, and the type and location of impingement recorded [Fig. 2]. Patients with minimal pre-operative osteophyte were selected as a best-case scenario for bony impingement. Results. 6/23 (26%) patients were planned with only a 32mm articulation (<50mm cup size), with the remaining 17 patients all planned with both 32mm and 36mm articulations (≥50mm cup size). Anterior impingement was 26% prosthetic and 74% bony with the 32mm articulations, and 100% bony with the 36mm articulations. Bony impingement in deep flexion was exclusively anterior neck on anterior inferior iliac spine. Posterior impingement was 57% prosthetic and 43% bony with the 32mm articulations, and 41% prosthetic and 59% bony with the 36mm articulations. Bony impingement in hyperextension was exclusively lesser trochanter (LT) on ischium. Of the patients planned with both 32mm and 36mm articulations, there was a 14% increase in prosthetic impingement when a 32mm head was planned (35% and 21% respectively). Discussion. Impingement in THA usually precedes dislocation and should be avoided with appropriate component positioning. We found that in hyperextension, prosthetic and bony impingement were equally common. In deep flexion, impingement was almost exclusively bony. Further studies should investigate the effects of stem version, cup orientation, liner design, cup depth, native offset and retained osteophytes on the type of impingement in THA. For any figures or tables, please contact the authors directly

Aim. metagenomic next-generation sequencing (mNGS) has shown to be a useful method for pathogen detection in prosthetic joint infections (PJI). The technique promises to minimize the PJIs without the known causative agent. Our study aimed to compare diagnostic accuracies of cultures and mNGS. Method. In this study, a meta-analysis following PRISMA recommendations was performed. PubMed and OVID Medline databases were used for article search. The studies using mNGS whole-genome sequencing method and the ones where PJI diagnosis was based on one of the currently recognized criteria were included. Studies were excluded if they comprised less than twenty cases, the ones with insufficient data for the analyses (true positive, true negative, false positive and false negative values for both mNGS and culture results) and publications with strong duplication bias. Univariate metanalysis using a random-effect model has been performed in R studio with a “meta” package. Pooled sensitivity and pooled specificity were calculated. Results. Seven studies with a total of 822 cases were included in the meta-analysis, 476 cases defined as PJI and 346 controls. Two studies used IDSA (Infectious Diseases Society of America) diagnostic criteria and the Illumina HiSeq 2500 platform for sequencing and five studies used MSIS (MusculoSkeletal Infection society). Four of those used the BGISEQ-500 sequencing platform. For one study there was no data available. Studies were performed on prosthetic hip and knee joints. Through meta-analysis, it was observed that mNGS technique is more sensitive than cultures with 90% (CI 79%– 95%) and 74% (CI 68%-79%) respectively (p=0.006). The specificity between methods was similar, for mNGS reaching 94% (CI 89%-96%) and for cultures 97% (CI 90%-99%) (p=0.285). In the PJI group, 117 new possible pathogens that were not isolated by microbiological culture were detected by the mNGS, most frequently anaerobes and coagulase-negative staphylococci both in 20/117 (17.1%) cases. Fourteen new organisms were detected in the control group and were mostly regarded as contaminants. Conclusions. Metagenomic sequencing has shown to be more sensitive than microbiological cultures in pathogen detection and thus has a great potential to improve the diagnosis and treatment of PJI. More studies on different prosthetic joints and comparing different diagnostic criteria for PJI would be needed to better understand the true diagnostic power of this method

Aim. As the populations of patients who have multiple prosthetic joints increase these years, the fate of a single joint periprosthetic joint infection in these patients is still unknown. Risk factors leading to a subsequent infection in another prosthetic joint are unclear. Our goal is to identify the risk factors of developing a subsequent infection in another prosthetic joint and describe the organism profile to the second prosthetic infection. Method. We performed a retrospective cohort study of all PJI cases underwent surgical intervention at our institute, a tertiary care referral center over 11 years, during January 2006 to December 2016. We identified 96 patients with periprosthetic joint infection who had another prosthetic joint in place at the time of presentation. The comorbidity, number of prosthetic joints, date and type of each arthroplasty, times of recurrent infection at each prosthetic joint with subsequent debridement or 2-stage resection arthroplasty, organisms from every infection episode, the outcome of each periprosthetic joint infection in these patients were analyzed. Results. During January 2006 to May 2017, we retrospective collected 294 PJI cases (159 hips, 135 knees) in our institute. Patients with single prosthetic joint were excluded and finally 96 patients were included. Of the 96 patients, 19 (19.79%) developed a periprosthetic joint infection in a second joint. The type of organism was the same as the first infection in 12 (63.16%) of 19 patients. The time to developing a second infection averaged 2.16 years (range, 0–9.3 years). The risk factors leading to a subsequent infection in another prosthetic joint are albumin level (< 3.5 mg/dl), long-term steroid usage (> 5mg/day, > 3 months), history of necrotizing fasciitis, history of invasive dental procedure (> Grade IV procedure), 3-stage resection arthroplasty or more, and PJI caused by vacomycin-resistent enterococcus (VRE). Conclusions. A PJI might predispose patients to subsequent PJI in another prosthesis. Patients and surgeons must be aware of the risk factors contribute to this devastating complication. Most organisms in the second PJI are identical to the first one, and we believe the bacteremia may be the pathogenesis, but need further proved. The preventive policy may be needed in the future for this population who has multiple prosthetic joints

Aims. To determine if primary cemented acetabular component geometry (long posterior wall (LPW), hooded, or offset reorientating) influences the risk of revision total hip arthroplasty (THA) for instability or loosening. Methods. The National Joint Registry (NJR) dataset was analyzed for primary THAs performed between 2003 and 2017. A cohort of 224,874 cemented acetabular components were included. The effect of acetabular component geometry on the risk of revision for instability or for loosening was investigated using log-binomial regression adjusting for age, sex, American Society of Anesthesiologists grade, indication, side, institution type, operating surgeon grade, surgical approach, polyethylene crosslinking, and prosthetic head size. A competing risk survival analysis was performed with the competing risks being revision for other indications or death. Results. The distribution of acetabular component geometries was: LPW 81.2%; hooded 18.7%; and offset reorientating 0.1%. There were 3,313 (1.5%) revision THAs performed, of which 815 (0.4%) were for instability and 838 (0.4%) were for loosening. Compared to the LPW group, the adjusted subhazard ratio of revision for instability in the hooded group was 2.31 (p < 0.001) and 4.12 (p = 0.047) in the offset reorientating group. Likewise, the subhazard ratio of revision for loosening was 2.65 (p < 0.001) in the hooded group and 13.61 (p < 0.001) in the offset reorientating group. A time-varying subhazard ratio of revision for instability (hooded vs LPW) was found, being greatest within the first three months. Conclusion. This registry-based study confirms a significantly higher risk of revision after cemented THA for instability and for loosening when a hooded or offset reorientating acetabular component is used, compared to a LPW component. Further research is required to clarify if certain patients benefit from the use of hooded or offset reorientating components, but we recommend caution when using such components in routine clinical practice. Cite this article: Bone Joint J 2021;103-B(11):1669–1677

Introduction. The prevalence of the various patterns of spinopelvic abnormalities that increase the risk for prosthetic impingement is unknown. While prior surgery or lumbar fusion are recognized as a risk factors for postoperative dislocation, many patients presenting for THA do not have obvious radiographic abnormalities. The purpose of this study is to determine the prevalence of large posterior pelvic tilt (PPT) when standing, stiff lumbar-spine (SLL) and spino-pelvic sagittal imbalance (SSI) in patients undergoing primary THA. Methods. A consecutive series of 1592 patients (56% female) over 2 years underwent functional analysis of spinopelvic mobility using CT, standing, and flexed seated lateral radiographs as part of pre-operative THA planning. The average age was 65 (20–93). We investigated the prevalence of these 3 validated spinopelvic parameters known to increase the risk for impingent and correlated them to the patient's age and gender using Chi squared analysis. Finally, the risk of flexion and extension impingement was modeled for each patient at a default supine cup orientation (DSCO) of 40°/20° (±5°). Results. Overall, 221 hips (14%) had at least 1 risk factor for impingement, while 64 (4%) had 2, and 18 (1 %) had all 3 risk factors. The most common risk factor was large PPT (10%) followed by SLL (4%) and SSI (4%). Female gender was not associated with increased spinopelvic abnormalities (p = 0.64), but age > 75 years increased the likelihood of at least having 1 risk factor (p<0.01) (Table-1). Placing the cup within the DSCO resulted in observed prosthetic impingement in 792 patients (50%) (Fig-1). 158 hips (20%) had at least 1 risk factor, while 56 (7%) had 2, and 16 (2 %) had all 3 risk factors for impingement. Posterior pelvic tilt was associated with extension impingement risk, while SLL and SSI increased flexion impingement risk. Conclusion. Spinopelvic risk factors that increase impingement risk are not infrequent in THA patients. We observed 50% prosthetic impingement when a single target for acetabular orientation target was applied. For any figures, tables, or references, please contact the authors directly

Objectives. Preclinical data showed poly(methyl methacrylate) (PMMA) loaded with microsilver to be effective against a variety of bacteria. The purpose of this study was to assess patient safety of PMMA spacers with microsilver in prosthetic hip infections in a prospective cohort study. Methods. A total of 12 patients with prosthetic hip infections were included for a three-stage revision procedure. All patients received either a gentamicin-PMMA spacer (80 g to 160 g PMMA depending on hip joint dimension) with additional loading of 1% (w/w) of microsilver (0.8 g to 1.6 g per spacer) at surgery 1 followed by a gentamicin-PMMA spacer without microsilver at surgery 2 or vice versa. Implantation of the revision prosthesis was carried out at surgery 3. Results. In total, 11 of the 12 patients completed the study. No argyria or considerable differences in laboratory parameters were detected. Silver blood concentrations were below or around the detection limit of 1 ppb in ten of the 11 patients. A maximum of 5.6 ppb at 48 hours after implantation of the silver spacer, which is below the recommended maximum level of 10 ppb, was found in one patient. No silver was detected in the urine. Drainage fluids showed concentrations between 16.1 ppb and 23.3 ppb at 12 hours after implantation of the silver spacers, and between 16.8 ppb to 25.1 ppb at 48 hours after implantation. Pathohistological assessment of the periprosthetic membrane did not reveal any differences between the two groups. Conclusion. Microsilver-loaded gentamicin-PMMA spacers showed good biocompatibility and the broad antimicrobial activity warrants further clinical research to assess its effectivity in reducing infection rates in prosthetic joint infection. Cite this article: V. Alt, M. Rupp, K. Lemberger, T. Bechert, T. Konradt, P. Steinrücke, R. Schnettler, S. Söder, R. Ascherl. Safety assessment of microsilver-loaded poly(methyl methacrylate) (PMMA) cement spacers in patients with prosthetic hip infections: Results of a prospective cohort study. Bone Joint Res 2019;8:387–396. DOI: 10.1302/2046-3758.88.BJR-2018-0270.R1

Background. The current use of a spherical prosthetic humeral head in total shoulder arthroplasty results in an imprecise restoration of the native geometry and improper placement of the center of rotation, maintained in a constant position, in comparison to the native head and regardless of glenoid component conformity. A radially-mismatched spherical head to allow gleno-humeral translation is a trade-off that decreases the contact area on the glenoid component, which may cause glenoid component wear. This finding suggests that the use of a non-spherical head with a more conforming glenoid component may reduce the risk of glenoid component wear by allowing gleno-humeral translation while increasing the contact area. A non-spherical prosthetic head more accurately replicates the head shape, rotational range of motion and gleno-humeral joint kinematics than a spherical prosthetic head, compared with the native humeral head. The combination of inversion of the bearing materials with the non-spherical configuration of the humeral head may thus decrease polyethylene wear. Aim of the present study is to evaluate in vitro wear behaviour of an all-polyethylene elliptical humeral head component against a metallic glenoid component in an anatomic configuration. Material and methods. The prosthetic components tested are from the Mirai. ®. Modular Shoulder System by Permedica S.p.A.. The prosthetic bearing components were tested in their anatomic configuration: the humeral head rubbing against the glenoid inlay, assembled over the glenoid base-plate. The glenoid insert is made of Ti6Al4V alloy coated with TiNbN. The glenoid insert, as the glenoid base-plate have the same shape which reproduce the native shape of the glenoid. Moreover, the glenoid insert has a concave articular surface described by two different radii on orthogonal planes. The vitamin E-blended UHMWPE humeral head is not spherical but elliptic-shaped with an articular surface described by two different profiles in sagittal and coronal plane. The component sizes combination tested have the greatest radial mismatches allowed between humeral head and glenoid insert. The test was performed up to 2.5 million of cycles applying a constant axial load of 756 N. Results. After 2.500.000 cycles the mean mass loss from the humeral head was 0.68 mg. The mean wear rate of the humeral head was 0.28 mg/Mc (SD 0.45 mg/Mc). The surface of the humeral heads showed an elliptical worn area with matt and polished areas with scratching. The surface of the TiNbN-coated glenoid insert counterparts did not show wear signs. Conclusion. The tested prosthetic humeral head has a non-spherical shape with an elliptical base and 2 different radii on sagittal and coronal plane. Also the tested glenoid insert has 2 different radii on sagittal and coronal planes. This components geometry leads to a radial mismatch between head and glenoid on sagittal and coronal planes. A different kinematics, allowing gleno-humeral translation while increasing the contact area, radial mismatch in different planes and the inversion of bearing materials may have a role in reducing component wear and may explain the extremely low wear rate found in the present study

Introduction. Roentgen stereophotogrammetric analysis (RSA) is currently the gold standard to measure early prosthetic migration which can predict aseptic loosening. However, RSA has some limitations such as the need for perioperative placed markers and exposure to X-radiation during follow up. Therefore, this study evaluates if low field MRI could be an alternative for RSA. Low field MRI was chosen because it is less hampered by metal artifacts of the prosthesis than high field MRI. Methods. 3D models of both the tibial component of a total knee prosthesis (Genesis II, Smith and Nephew) and the porcine tibia were made. The tibial component was implanted in the tibial bone. Consequently, 17 acquisitions with the low field MRI scanner (Esaote G-scan 0.25T) in transverse direction with a 2D PD weighted metal artifact reducing sequence PD-XMAR (TE/TR 10/1020ms, slice thickness 3mm, FOV 180×180×120 mm³, matrix size 224×224) were made. The first five acquisitions were made without repositioning the cadaver, the second twelve after slightly repositioning the cadaver within limits that are expected to be encountered in a clinical setting. Hence, in these 17 acquisitions no prosthetic-bone motions were induced. The scans were segmented and registered with Mimics. Virtual translation and rotation of the prosthesis with respect to the bone between two scans were calculated using a Procrustes algorithm. The first five scans without repositioning were used to calculate the measurement error, the following twelve to calculate the precision of low field MRI to measure prosthetic migration. Results were expressed as the maximum total point motion, mean error and 95% CI and expressed in boxplots. Results. The error of the method to measure the prosthetic position without repositioning has a mean translation between 0.09 and 0.22mm with a 95%CI between 0.30 and 0.46mm. The mean rotation was between 0.02° and 0.11° with a 95%CI between 0.18° and 0.32° with a MTPM of 0.45mm. The precision of low field MRI to measure migration with repositioning has a mean translation between 0.02 and 0.12mm with a 95%CI between 1.16mm and 1.86mm. The mean rotation was between 0.01° and 0.15° with a 95%CI between 1.78° and 3.26° with a MTPM of 2.35mm. The overall registration error was largest in the distal-proximal direction. Discussion. At the moment the low field MRI technique is not as accurate as this gold standard RSA. The accuracy of RSA varies between 0.05 and 0.5 mm for translation and 0.15 ° to 1.15 ° for rotation (95% confidence intervals). However, results are comparable with markerless RSA studies. The largest measurement error was found in the distal-proximal direction, which can be explained by the through-plane resolution of 3 mm, which is larger than the in-plane resolution of 0.8×0.8 mm². Future research should focus on improving resolution in the distal-proximal direction which would improve the precision. Moreover, an actual migration study should be performed to proof the true value of this low field MRI base markerless and X-radiation free alternative to measure prosthetic migration

Introduction. Debridement, antibiotics, and implant retention (DAIR) for acute prosthetic hip infection is a popular low morbidity option despite less than optimal success rates. We theorized that the delay between DAIR and explantation in failed cases may complicate eradication due to biofilm maturation and entrenchment of bacteria in periprosthetic bone. We ask, what are the results of two-stage reimplantation after a failed DAIR versus an initial two-stage procedure?. Methods. 114 patients were treated with 2-stage exchange for periprosthetic hip infection. 65 were treated initially with a 2-stage exchange, while 49 underwent an antecedent DAIR prior to a 2-stage exchange. Patients were classified according to MSIS host criteria. Failure was defined as return to the OR for infection, a draining sinus, or systemic infection. Results. Treatment failure occurred in 42.9% (21 of 49) of patients treated with an antecedent DAIR. In contrast, treatment failure occurred in only 12.3% (8 of 65) of initial 2-stage procedures (p< 0.001). Relative Risk of return to the OR after a 2-stage reimplantation with an antecedent DAIR compared to initial resection was 4.52 (95% CI 1.71, 11.9). MSIS host grading was similar between groups and did not influence the rate of failure. The DAIR cohort had increased hospitalization length and greater number of operative procedures (p< 0.001). Conclusion. We have shown that if irrigation and debridement fails to treat acute prosthetic hip infection, subsequent attempts at two-stage reimplantation may be compromised. Additionally, in the antecedent DAIR group, the average number of infection-related procedures (5) was nearly twice that of those initially resected (2.7). This by nature implies a significantly greater burden to the patient and cost to the healthcare system

Aim. Prompt recognition and identification of the causative microorganism in acute septic arthritis of native and prosthetic joints is vital to increase the chances of successful treatment. The aim of this study was to independently assess the diagnostic accuracy of the multiplex BIOFIRE® Joint Infection (JI) Panel (investigational use only) in synovial fluid for rapid diagnosis. Method. Synovial fluid samples were prospectively collected at the University Medical Center Groningen from patients who had a clinical suspicion of a native septic arthritis, early acute (post-operative, within 3 months after arthroplasty) periprosthetic joint infection (PJI) or late acute (hematogenous) PJI. JI Panel results were compared to culture-based methods as reference standard. Results. A total of 45 samples were analyzed. The BIOFIRE JI Panel showed a high specificity (100%, 95% CI 73 – 100) and positive predictive value (100%, 95% CI 79 – 100) in all patient categories. Sensitivity and negative predictive value were 83% (95% CI 36 – 99) and 88% (95% CI 47 – 99) respectively for patients with a clinical suspicion of native septic arthritis (n=12), 77% (95% CI: 46 – 94) and 63% (95% CI: 26 – 90) for patients with a clinical suspicion of a late acute PJI (n=14), and 27% (95% CI 7 – 61) and 27% (95% CI: 7 – 61) for patients with a clinical suspicion of an early acute PJI (n=19). Conclusions. The results of this pilot study indicate a clear clinical benefit of the BIOFIRE JI Panel in patients with a suspected native septic arthritis and late acute (hematogenous) PJI, but a low clinical benefit in patients with an early acute (post-operative) PJI due to the absence of low-grade microorganisms in the panel