Introduction. Ultra-high molecular weight polyethylene (UHMWPE) is the sole polymeric material currently used for weight- bearing surfaces in total joint replacement. However, the wear of UHMWPE in the human body after total joint replacement causes serious clinical and biomechanical reactions. Therefore, the wear phenomenon of UHMWPE is now recognized as one of the major factors restricting the longevity of artificial joints. In order to minimize the wear of UHMWPE and to improve the longevity of artificial joints, it is necessary to clarify the factors influencing the wear mechanism of UHMWPE. Materials and Methods. In a previous study (Cho et al., 2016), it was found that roundness (out-of-roundness) of the retrieved UHMWPE acetabular cup liner [Figure 1(a)] had a tendency to increase with increasing roundness of the retrieved metal femoral head [Figure 1(b)]. It appears that roundness of the femoral head contributes to increase of wear of the polyethylene liners. We focused on the roundness of femoral head as a factor influencing the wear of polyethylene liner in hip prosthesis. In this study, further roundness measurements for 5 retrieved metal femoral heads were performed by using a coordinate measuring machine. The elasto-plastic contact analyses between femoral head and polyethylene liner using the finite element method (FEM) were also performed in order to investigate the influence of femoral head roundness on the mechanical state and wear of polyethylene liner in hip prosthesis. Results. The range of roundness of the 5 retrieved metal femoral heads measured in this study was 14.50∼44.70 µm. Two examples of the results of FEM contact analyses are shown in Figure 2. Figure 2(a) is the results of the repeated contact analysis between femoral head and polyethylene liner under constant axial loading of 1000 N. Figure 2(b) is the results of the repeated contact analysis between femoral head and polyethylene liner under hip joint loading during normal gait. These figures show the distribution of the contact stress (von Mises equivalent stress) in the polyethylene liner. The graph in Figure 3 shows the changes in the maximum contact stress in the polyethylene liner with the flexion/extension angle of femoral head. Discussion and Conclusions. As the results of a series of the FEM contact analyses, it was found that repeated high contact stresses which exceed the yield stress of UHMWPE caused by roundness of the metal femoral head occurred in the polyethylene liner as shown in Figures 2 and 3. It was also found that the magnitude and amplitude of the repeated contact stresses had a tendency to increase with increasing roundness of the femoral head and axial loading applied to the femoral head. The results of this analytical study suggest that the roundness (out-of- roundness) of the femoral head is associated with accelerating and/or increasing wear of the UHMWPE acetabular cup liner in a hip prosthesis after total hip replacement. For any figures or tables, please contact authors directly

Introduction. Ultra-high molecular weight polyethylene (UHMWPE) is the sole polymeric material currently used for weight- bearing surfaces in total joint replacement. However, the wear of UHMWPE and the polyethylene wear debris generated in the human body after total joint replacement cause serious clinical and biomechanical reactions. Therefore, the wear phenomenon of UHMWPE in total joint replacement is now recognized as one of the major factors restricting the longevity of these implants. In order to minimize the wear of UHMWPE and to improve the longevity of artificial joints, it is necessary to clarify the factors influencing the wear mechanism of UHMWPE. Materials and Methods. The wear and/or failure characteristics of 33 retrieved UHMWPE acetabular cup liners of hip prostheses were examined in this study. The retrieved liners had an average in vivo duration of 193.8 months (75 to 290 months). Several examples of the retrieved liners are shown in Figure 1. The elasto-plastic contact analyses between metal femoral neck and polyethylene liner and between metal femoral head and polyethylene liner using the finite element method (FEM) were also performed in order to investigate the factors influencing the wear and/or failure mechanism of the polyethylene liner in hip prosthesis. Results. In the examination of the retrieved polyethylene liners, the generation of component impingement was observed in 24 cases of the 33 retrieved liners (72.7%) as shown in Figures 1(a) and (b). In addition, the generation of cold flow into the screw holes in the metal acetabular cup was observed in 27 cases of the 33 retrieved liners (81.8%) as shown in Figures 1(c) and (d). Several examples of the results of the FEM contact analyses are shown in Figure 2. In the simulation of the component impingement, it was found that high contact stresses which exceed the yield stress of UHMWPE and considerable plastic strains occurred in the rim of the polyethylene liner as shown in Figures 2(a) and (b). In the simulation of the cold flow, it was found that the stress concentration near the edge of screw hole has significant influence on the states of contact stresses and plastic strains in the surface and undersurface (backside) of the polyethylene liner as shown in Figures 2(c) and (d). Discussion and Conclusions. In this study, we focused on the impingement between the metal femoral neck and the polyethylene liner and the cold flow into the screw holes on the backside of the polyethylene liner as the factors influencing the wear and/or failure of the UHMWPE acetabular cup liner in hip prosthesis. The results of these retrieval and analytical studies confirmed that the component impingement and the cold flow into the screw holes contribute to increase of wear and/or failure of the polyethylene liner. Therefore, it is necessary to improve resistance to the component impingement and the cold flow in order to decrease the wear and/or failure of the UHMWPE acetabular cup liner and to increase the longevity of hip prosthesis. For any figures or tables, please contact authors directly

Introduction. Ultra-high molecular weight polyethylene (UHMWPE) is the sole polymeric material currently used for weight- bearing surfaces in total joint replacement. However, the wear of UHMWPE in knee and hip prostheses after total joint replacement is one of the major restriction factors on the longevity of these implants. In order to minimize the wear of UHMWPE and to improve the longevity of artificial joints, it is necessary to clarify the factors influencing the wear of UHMWPE. A number of studies have investigated the factors influencing the wear of UHMWPE acetabular cup liner in hip prosthesis. Most of these studies, however, have focused on the main articulating surfaces between the femoral head and the polyethylene liner. Materials and Methods. In a previous study (Cho et al., 2016), the generations of cold flow into the screw holes in the metal acetabular cup were observed on the backside of the retrieved UHMWPE acetabular cup liners as shown in Figure 1. We focused on the screw holes in the metal acetabular cup (Figure 2) as a factor influencing the wear behavior of polyethylene liner in hip prosthesis. In this study, computer simulations of the generation of cold flow into the screw holes were performed using the finite element method (FEM) in order to investigate the influence of the screw holes in the metal acetabular cup on the mechanical state and wear behavior of polyethylene liner in hip prosthesis. Results. An example of the results of the FEM simulations performed in this study is shown in Figure 3. In the region which the cold flow into the screw holes occurred, it was found that locally high contact stresses which exceed the yield stress of UHMWPE and considerable plastic strains were generated throughout the overall thickness between the backside and top surface of the polyethylene liners. On the contrary, in the case of the polyethylene liner combined with the metal acetabular cup without screw hole, although the regions of high contact stress and high plastic strain had a tendency to be limited around contact surface compared with those of the combination with screw holes, the values of contact stress and plastic strain were lower than the combination with screw holes. Discussion and Conclusions. The results of this study suggest that the cold flow generated by the existence of the screw holes in the metal acetabular cup of hip prosthesis reduces the wear resistance of the UHMWPE acetabular cup liner. It would appear that the cold flow into the screw holes contributes to structural weakening of the UHMWPE and reduction of the polyethylene thickness, thus increase of internal stresses and plastic strains in and around the regions of cold flow. Therefore, it is required that improvement of the screw holes in the metal acetabular cup and/or improvement of fixation method of the metal acetabular cup to a pelvis in order to enhance the wear resistance of the polyethylene liner. For any figures or tables, please contact authors directly

The accurate differentiation of aseptic loosening from periprosthetic infection in the painful hip prosthesis is a major clinical challenge. FDG-PET imaging has shown great promise in various clinical settings for detection of infection. This prospective study was designed to determine the efficacy of FDG-PET imaging in the assessment of patients with painful hip prosthesis. One hundred and thirteen patients with 127 painful hip prostheses were evaluated by FDG-PET. Approximately 60 minutes after the intravenous administration of FDG images of the lower extremities were acquired using a dedicated PET machine. FDG-PET images were interpreted by experienced nuclear medicine physicians. Images were considered positive for infection if PET demonstrated increased FDG activity at the bone-prosthesis interface of the femoral component of the prosthesis. Surgical findings, histopathology, and clinical follow-up served as the “gold standard”. FDG-PET was positive for infection in 35 hips and negative in 92 hips. Among 35 positive PET studies, 28 were proven to be infected by surgical and histopathology findings as well as follow-up tests. Of 92 hip prostheses with negative FDG-PET findings, 87 were proven to be aseptic. The sensitivity, specificity, positive and negative predictive values for FDG-PET were 0.85 (28/33), 0.93 (87/94), 0.80 (28/35), and 0.95 (87/92), respectively. The overall accuracy of FDG-PET in this clinical setting was 90.5% (115/127). The results demonstrate that FDG-PET is a highly accurate diagnostic test for differentiating infected from non-infected painful hip prosthesis. Therefore, FDG-PET imaging is considered the study of choice in the evaluation of patients with suspected hip prosthesis infection

Background: Revision total hip replacement is challenging when there is severe proximal bone loss. The Kent hip femoral prosthesis – a distally locked femoral stem – was designed to overcome this difficulty, however no study to date has assessed its durability. Methods: We independently reviewed the results of 105 Kent Hip Prostheses used at one hospital between 1987 and 2000. The indication for revision was aseptic loosening in 64, periprosthetic fracture in 19, septic loosening in 4, and severe bony deformity in 14. In the remaining 4 cases, a Kent hip prosthesis was inserted in the presence of metastatic tumour in the proximal femur to enable mobilisation. A functional evaluation of these patients using the Oxford Hip Score and a survival analysis of the stems was performed. Results: The mean duration of follow-up was 5.3 years (range 20 months to 15 years). The mean time to full weight bearing following surgery was 4 days and mean hospital stay was 13 days. Almost all patients experienced substantial improvement in hip related pain and disability (as measured by the Oxford Hip Score). 12 stems required further revision. Taking removal of the stem for any cause as the end point, cumulative survival at 15 years was 88%. Conclusions: Cumulative survival rates for the Kent hip femoral prosthesis compare favourably with other revision stems used where there is severe proximal bone loss. It enables early full weight bearing and hospital discharge, resulting in a low post-operative medical complication rate. However the need for continuing follow-up remains, since the rate of complications such as locking screw fracture, aseptic loosening, and periprosthetic fracture, may increase in the future

The Huckstep ( Bbraun Medical) interlocking hip prosthesis has been used in the Sheffield Lower Limb Arthroplasty Unit in cases of complex primary and revision hip arthroplasty since 1996. We reviewed the outcomes in cases performed prior to October 2001. Eighty cases were identified. Of these, eight died within one year of surgery, four of which were in the peri operative period. A further thirteen were lost to follow up in the first year due to medical deterioration, move from area or refusal to attend. The remaining 57 patients had a mean time to follow up of 34 months (12–81m). As a primary prosthesis the Huckstep was used to allow corrective osteotomy. In revision cases it was employed to bypass periprosthetic fractures and fragile proximal femoral bone, in cases requiring extended trochanteric osteotomy to facilitate cement removal, and to enable use of bulk proximal femoral allograft. The use of the Huckstep was planned pre operatively in 67 cases and as a salvage option in 13.The design of the implant allowed a stable construct without the need for bone cement which could interpose and prevent bone healing or graft incorporation. It avoids problems incurred in pressurising cement or impaction grafting against fragile bone. Complications included infection requiring further surgery (5), dislocation (5), periprosthetic fracture (2), screw breakage (4), and mechanical failure (2). Eleven patients required further revision surgery. The apparently high complication rate reflects the complex nature of the surgery and the high degree of co morbidity in the elderly patient group. In conclusion, we have found the Huckstep hip prosthesis to be a useful option in cases of complex hip surgery. Whilst the long term outcome is as yet unknown, our short term results show it to have allowed healing of fractures, osteotomy sites and cortical defects, allograft incorporation and replenishing of bone stock, hence facilitating further arthroplasty surgery

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

Fracture of the femur in association with total hip arthroplasty is a challenging complication that has been well described. A variety of surgical treatment options have been reported. We present our experience of the Kent hip prosthesis in the management of periprosthetic femoral fractures. We reviewed all patients (46) who had a Kent hip inserted for a periprosthetic femoral fracture. This group consisted of 16 males and 30 females of average age 73 years (43–96 years) at the time of fracture. Follow up ranged from 2 to 85 months (average, 4 years). In 26 cases the primary prosthesis was a Charnley stem. Of the remaining cases the primary prostheses were as follows: 6 Austin Moore prostheses, 5 Howse, 4 Custom, 1 Exeter, 1 DHS, 1 Richards and 1 Thompson stem. There were 6 intraoperative fractures. Of the postoperative fractures forty-four were associated with a traumatic event. Time to fracture varied from 3 weeks to 20 years (average, 8 years). Prior to fracture 42 patients were living in their own home and 24 patients were mobile unaided. Twenty patients had pain prior to their fracture. The majority of patients were deemed ASA grade II or III. Thirty fractures were Johanssen type II, 14 type I, and 2 type III. At the time of surgery, 32 patients had a loose stem and/or cup. Operating time was on average 143 minutes (range, 65–235 minutes) and intraoperative transfusion requirements ranged from 0–7 units of packed red cells (average, 3 units). Duration of hospital stay was on average 23 days (range, 7–77 days). Two patients developed superficial wound infections, six patients dislocated their prosthesis and one patient developed a chronic wound sinus. In 34 cases fracture union was complete at latest review. Three patients required revision surgery for stem breakage and in 10 cases there was evidence of screw breakage. At latest review, of the 31 patients that could be contacted 18 are still resident in their own homes. Twenty-six patients require the use of a walking aid (most commonly one stick). Ten patients have ongoing pain in relation to their operated hip. In conclusion, we feel that the Kent hip prosthesis is a useful surgical option in the one-stage management of periprosthetic femoral fractures

We report the result of 46 patients (30 female, 16 male) with periprosthetic femoral fractures who underwent insertion of the Kent Hip Prosthesis. Average age was 73 years (range 43–96years) and follow-up ranged from one to seven years (average, 4 years). The primary implants involved were as follows: Charnley (26), Austin Moore (6), Howse (5), Custom (4), Exeter (1), DHS (1), Thompson (1) and Richards (1). Average time to fracture from insertion of the primary implant ranged from 3 weeks to 20 years (average, 8 years). Forty cases were post-primary implant fractures (38 traumatic, 2 atraumatic) and 6 occurred intraoperatively. Using the Johanssen classification there were 12 type I, 30 type II and two type III fractures. Of the 46 cases, prior to fracture, 42 were living in their own home, 24 were mobile unaided and 20 had thigh and/or groin pain. Thirty-two had a loose stem and/or cup assessed at the time of surgery. Operating time was on average 143 mins (65–235mins). At latest follow-up, 43 were living in their own home, 5 were walking unaided and 10 had ongoing pain. In 34 cases complete union was achieved. There were no cases on non-union. Three patients required revision surgery for broken stems. Three patients sustained wound infections and there were six posterior dislocations. All of the complications were treated satisfactorily. We conclude that the Kent Hip Prosthesis is a useful option in the management of periprosthetic femoral fractures

Introduction. This study reports outcomes of 35 revisions of a recalled metal-on-metal (MOM) monoblock prosthesis performed by a single surgeon. Methods. We prospectively collected data on all patients who underwent revision of a recalled metal-on-metal monoblock prosthesis between 2010 and 2015. Average follow-up was 2.5 years post-revision and 6.9 years post-primary procedure. We evaluated the cohort for age, BMI, gender, existence of medical comorbidities, and post-op complications. We compared pre and post-revision cup abduction angles, anteversion angles, combined angles, cup sizes, and Harris Hip Scores. Cobalt and chromium levels were followed throughout the study period for each patient. Results. Thirty-one patients underwent 35 revisions surgeries for pain, high metal ions, infection, aseptic loosening, failure of ingrowth, leg length discrepancy and/or pseudotumor. Two of these revisions were subsequently re-revised – one for continued pain and one for failure involving multiple dislocations, breakage of screws, and acetabular fracture. The survival rate for our revisions to date is 94.3%. Female patients comprised a majority of revisions (54%) despite comprising a minority (28%) of primary hip replacements using the studied prosthesis. Revised patients were an average of 51.8 years of age with a BMI of 31.07. Demographics are included on Table 1. There were five post-operative complications, including 2 infections, 2 dislocations, and one DVT. Cups were revised from a mean abduction angle of 47.5° in primary hips to 42.3° in revisions. Cups were revised from a mean of 53.4 to 57.8. Cobalt and chromium levels were followed in all patients and showed significant decrease after revision (Graph 1). Cobalt levels decreased from an average of 33.7 to 13.1 ng/mL while Chromium levels decreased from an average of 12.4 to 9.2 ng/mL. Harris Hip Scores increased significantly after revision (45.8 to 72.1). Conclusion. This study presents 35 revisions of a recalled monoblock hip prosthesis performed by a single surgeon at our institution from 2010 to 2015. To our knowledge, this is the largest single-surgeon study reported in the literature. Acetabular cups were revised to a lower average abduction angle. Patients have had significant improvements in Harris Hip Scores and significant decreases in Cobalt and Chromium levels after revisions. Our revision survival rate to date is 94.3% at an average of 2.5 years (range 2 weeks – 4.3 years). To view tables/figures, please contact authors directly

Previous scientific studies have highlighted how coupling is an important element affecting total hip arthroplasty's survival.

This study aims to evaluate whether metal-on-metal (MOM) coupling could be a statistically significant risk factor.

The data from the regional joint registry (Registro dell'Impiantologia Protesica Ortopedica, RIPO) was used for analysis. The data collection accuracy of this registry was 97.2% in 2017.

We retrospective evaluate all MOM total hip arthroplasties (THAs) implanted in our department between January 01st 2000 and December 31st 2011. We used a control group composed by all other prosthesis implanted in our Department in the same time lapse.

We registered 660 MOM THAs. Mean age of patients was 66.9 years. 603 patients have a >36mm head, while 78 a <36 mm one. Neck modularity was present in half of patients. 676 implants were cementless. We registered 69 revisions, especially due to aseptic mobilization (16 THAs), implant breakage (9 THAs) and periprosthetic fracture (6 THAs).

The MOM THAs overall Kaplan-Meier survival rate was 87.2 at 15 years, and the difference between MOM THAs and other implants two curves is statistically significant (p<0.05). Male sex is a significant risk factors. Further evaluations are in progress to establish the presence of any additional risk factors. We think weight and/or BMI may be included in this category.

Our study confirms the data currently present in the literature regarding a lower survival of metal-on-metal hip prostheses.

The male sex is a statistically significant risk factor (p<0.05), while age, head size and modularity of the prosthetic neck are not statistically significant (p>0.05).

Any new finds will be presented at the congress venue.

Nine cases of acetabular erosion following insertion of the Monk "hard top" hip prosthesis for subcapital fractures are presented. All of these patients had significant symptoms and represented 5% of the total group. In our experience acetabular erosion has proved to be a significant complication of the Monk "hard top" prosthesis

Elderly patients with a high mortality risk for revision surgery are severely handicapped by a loosened hip prosthesis. Loosening is mainly caused by particle-induced osteolysis leading to the formation of a synovium-like interface tissue. As an alternative to revision surgery we have investigated the possibility of removing the tissue using a gene therapy approach and thereafter stabilizing the prosthesis with percutaneous cement injection. First we demonstrated that transduction of interface cells with a gene coding for E.coli nitroreductase (NTR) resulted in a 60-fold increase in sensitivity to the prodrug CB1954 that is converted to a toxic metabolite by NTR. Given these in-vitro data, we explored if intra-articular administration of this adenoviral vector encoding NTR followed by the prodrug was able to kill sufficient tissue in-vivo to allow refixation of the prosthesis by cement. We report the first three patients from a phase 1 study of 12 patients with a loosened hip who are experiencing debilitating pain and have significant comorbidity. On day 1 the vector is injected into the hip joint and on day 3 the prodrug is injected. On day 10 three holes are drilled in the femur and one in the acetabulum. Biopsies are taken from the periprosthetic space and low viscosity cement (Osteopal, Biomet Merck, Sjöbo, Sweden) is injected under fluoroscopic guidance. The first three patients have been included in the study and five more are planned for treatment before June 2005. The patients are females of 86, 72, and 79 years old. There were no adverse effects from vector injection (3x10 exp 9 particles). Six hours after prodrug injection the patients experienced nausea, (WHO grade 1) a commonly reported reaction to this prodrug. There was vomiting in two patients. Hip pain increased, but this was anticipated as this therapy will increase prosthesis loosening. 16 ml of cement was subsequently injected into the periprosthetic space in the first patient and 18 ml in the second. The patients were ambulated the day after surgery. The first two patients have a follow-up of twelve and six weeks. There was no pain in the hip. The maximum walking distance had increased from 5 to 30 meters in the first patient. The current study is the first to use in vivo intra-articular adenoviral mediated gene transfer in a clinical setting. Our preliminary results suggest that gene therapy and cement injection for hip prosthesis refixation is clinically feasible

We report the clinical and operative details of seven cases of fracture of the femoral stem of the Ring TiMESH cementless hip prosthesis (two were cemented and five uncemented). Six fractures occurred in the proximal one-third of the stem and one at mid-stem. The failures are attributed mainly to two defects in stem design, the narrowness of the anteroposterior dimensions and the depth of the recess for the titanium mesh pads. Great difficulty was experienced in removing the osseo-integrated distal fragments of the broken stems

Aims: The authors report oncological and functional results after 15 acetabular reconstructions, followed tumor resection, with an original technique using homo-lateral proximal femoral autograft and total hip prosthesis. Material and method: The modiþed Musculoskeletal Tumor Society Score (MSTS) and the Toronto Extremity Salvage Score (TESS) were used for functional analysis. Functional results were available for only 10 patients who presented with a minimal of 2 years follow-up. Results: Fifteen consecutive patients, 9 men and 6 women with a median age of 50 years, were managed in our department for acetabular bone malignant tumor. The tumors involved the zones II in 5 patients, the zones II and III in 5 patients. The tumors included 10 chon-drosarcomas, 1 malignant þbrous histiocytoma, 1 radio-induced sarcoma, 1 myeloma and 2 metastasis. The mean follow-up was 31 months (Range, 12 to 50 months). Local recurrence occurred in 1 case and metastases in 3 cases. Three patients died of tumoral disease and one of intercurrent disease. Eight complications were observed: aseptic failure (n=1), obturator nerve damage (n=1), deep infection (n=4), skin necrosis (n=2), pros-thesis dislocations (n=1) and deep venous thrombosis (n=1). Five revision were performed. The mean MTS was 72% (range, 40 to 96%) and the mean TESS was 82.5% (range, 56 to 86%). Fusion occurred in all reconstructions and all patients recovered an active hip abduction and ßexion. Discussion: This original technique, using an autograft and a standard total hip prosthesis, is available for zone II and III acetabular reconstructions

A 70-year-old man with an uncemented metal-on-polyethylene total hip prosthesis underwent revision arthroplasty 33 months later because of pain, swelling and recurrent dislocation. There appeared to be corrosion and metal release from the prosthetic head, resulting in pseudotumour formation and severe local soft-tissue destruction. The corrosion occurred at the junction between the titanium-molybdenum-zirconium-iron taper and the cobalt-chrome-molybdenum head, but the mechanism was unproven

Radiographs are often used to determine the varus/ valgus alignment of the prosthesis in relation to the long axis of femur. This is usually considered to be one of the important parameters in predicting early mechanical failure of the total hip replacement. The measurements made by the University of Dundee X-Ray Analysis Software and skilled manual operators of the varus and valgus angulations of hip prosthesis in relation to the femoral shaft were compared for inter and intra-observer reliability. The manual measurements were carried out on the same randomly selected digitised images of 78 postoperative X-rays by two independent observers and by the same analysis software twice. The results of the study showed a very high agreement between the readings of the two methods (the largest difference was 0.6 degrees) and two observers (the largest difference being 0.08 degrees) indicating excellent intra and inter observer reliability. The lowest correlation was 0.82 and this was between software reading 1 of observer 1 and software reading 1 of observer 2. The highest correlation of 0.99 was between software reading 1 and software reading 2 for the same observer. The software analysed the x-rays with precision and accuracy and was much faster than manual measurement. A further benefit of the computerised method is an unskilled operator can be trained in 15 minutes to use the software

Because we encountered a high failure rate of the acetabular component of the uncemented, hydroxy-apatite coated, Omnifit total hip prosthesis (Osteonics corporation, Allendale, NJ, USA), we conducted a retrospective study of 418 consecutive total hip arthroplasties with a mean follow up of 60 months. The results of 418 hydroxy-apatite coated, uncemented Omnifit total hip arthroplasties, conducted between 1989 and 1996 were evaluated. Two different acetabulum cups were used: 145 screwcups with one central screwhole, and 273 press fit (PF) cups with several screwholes. The internal geometry of these cups and the fixation of the polyethylene insert in the metal cups were identical. In 339 arthroplasties a 32-mm femur-head was used, in 79 a 28-mm head. Patients’ records and x-rays were evaluated for clinical findings, polyethylene (PE) wear, acetabular and femoral osteolysis and findings during revision surgery. Revision surgery was performed in 73 patients, mainly because of symptomatic acetabular osteolysis (79%). Mean PE wear was 0.16 mm/year (0.19 mm in PF cups, 0.11 mm in screwcups). Acetabular osteolysis was found to be present in178 hips (70 screwcups and 108 PF cups). In both cupdesigns the osteolysis was mainly found around the screwholes of the metal cups. During revision surgery these osteolytic defects were a lot larger than suggested by x-ray imaging. In 22.6% of the hips osteolysis was also present in the proximal femur. Kaplan-Meier survival analysis showed, after 6 year follow up, a better survival for of the screwcup (96%, confidence interval 93–99%) than the PF cup (66%, 95%CI 56–77%). We hypothesized that this specific combination of metal cup and polyethylene insert -possibly due to an insufficient fitting- is responsible for the migration of polythylene wear particles through the screwholes in the metal cup, causing acetabular osteolysis and neces-satating revision surgery. For this reason we abandonned the use of this type of uncemented acetabular component

Introduction: One of the primary complications in total hip and knee arthroplasty is infection. One of the major risk factors for deep periprosthetic infection is wound infection. This alone is associated with a substantial morbidity-increase which, in turn, increases hospital admittance time and therefore adds significant costs to the healthcare system. The aim of this study is to determine whether contamination of instruments used during primary insertion of a prosthesis, can be considered an early indicator for the occurrence of prolonged wound discharge. Early antibiotic treatment could then prevent this and decrease hospital admittance time and costs to the health care system. Material and Methods: During 121 procedures, swabs were taken from the first unused broach at the beginning and at the end of the procedure. Removed material from the bone (acetabulum and femur in the hip joint; femur and tibia in case of the knee joint) was tested for contamination as well. During 50 procedures a control swab was taken. The patients on the ward were also monitored to find out whether prolonged wound discharge occurred and to see after how many days the patients were discharged. Results: In 46 cases (38%) at least one culture showed microbial growth. In the other 75, there was no growth at all. If one of the cultures is positive, there is a 52% risk of prolonged wound discharge. Ifall cultures are negative, this risk is reduced to 13% (Chi-square: PO.001). Patients with a positive peroperative culture have to remain in the hospital for an additional 2.4 days (T-test: P-0.001). Conclusion: Peroperative culturing during primary insertion of a knee or hip prosthesis, provides a reliable tool to predict postoperative duration of wound discharge and hospital-admittance time

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