Total Hip Prosthesis Research Articles

Tokophobia or post-traumatic stress disorder ? about a tunisian case

IntroductionPregnancy and delivery are considered to be an important transition stage in a woman’s life. Although this experience is emotionally rich, it varies from one person to another and each woman goes through it in her own way.Objectivesdiscuss the psychiatric outcomes after a childbirth with somatic complications.Methodscase reportResultsMrs X is a 32 years old woman, she has no particular history of illness until she gave birth to her son. He is now three and a half years old and he is an outpatient at the child and teen psychiatry department in a Tunisian hospital. After her delivery, Mrs X had several physical and psychological complications. She was hospitalized in the cardiology department for cardiomyopathy of Meadows for three weeks among it one week in the medical reanimation ward because she needed respiratory assistance. Furthermore, she suffered of left femoral head’s necrosis for which she was operated, and a total hip prosthesis replacement was done. Psychologically, Mrs X. presented a postpartum depression which resolved in its own after 9 months. Ever Since the childbirth, the patient presents symptoms concording with post-traumatic stress disorder and symptoms that may be linked to a specific phobia (fear of birthchild or tokophobia).ConclusionsIn addition to the usual health care provided to women during pregnancy and after childbirth, looking for mental health disturbances and eventually referring them for psychiatric assessment is important specially for women who have experienced traumatic events during the pregnancy or the deliveryConflict of interestNo significant relationships.

Zurich Cementless Dual Mobility Cup for Canine Total Hip Prosthesis: Implant Characteristics and Surgical Outcome in 105 Cases

AbstractDislocation after total hip arthroplasty (THA) remains a troublesome complication, and a source of frustration for the owner and the surgeon. The dislocation rate of hip prostheses in dogs is reported to range from 4 to 15%, representing the most common short-term complication. This is especially true in large and giant breed dogs, usually requiring revision surgery. With the increase in the number of THA being performed in veterinary surgery, reducing or preventing complications such as postoperative THA dislocation will be of paramount importance. The Zurich cementless dual mobility (DM) system allows impingement-free range of angulation of 80 to 132 degrees between the ceramic head and the polyether ether ketone (PEEK) cup when combined with the range of the PEEK cup in the outer metal cup. In this article, we review the use of the DM cup in THA in large and giant breed dogs, in terms of its history, biomechanics, outcomes and complications based on 105 cases.

Comparing the performance of a deep convolutional neural network with orthopedic surgeons on the identification of total hip prosthesis design from plain radiographs.

A crucial step in the preoperative planning for a revision total hip replacement (THR) surgery is the accurate identification of the failed implant design, especially if one or more well-fixed/functioning components are to be retained. Manual identification of the implant design from preoperative radiographic images can be time-consuming and inaccurate, which can ultimately lead to increased operating room time, more complex surgery, and increased healthcare costs. In this study, we present a novel approach to identifying THR femoral implants' design from plain radiographs using a convolutional neural network (CNN). We evaluated a total of 402 radiographs of nine different THR implant designs including, Accolade II (130 radiographs), Corail (89 radiographs), M/L Taper (31 radiographs), Summit (31 radiographs), Anthology (26 radiographs), Versys (26 radiographs), S-ROM (24 radiographs), Taperloc Standard Offset (24 radiographs), and Taperloc High Offset (21 radiographs). We implemented a transfer learning approach and adopted a DenseNet-201 CNN architecture by replacing the final classifier with nine fully connected neurons. Furthermore, we used saliency maps to explain the CNN decision-making process by visualizing the most important pixels in a given radiograph on the CNN's outcome. We also compared the CNN's performance with three board-certified and fellowship-trained orthopedic surgeons. The CNN achieved the same or higher performance than at least one of the surgeons in identifying eight of nine THR implant designs and underperformed all of the surgeons in identifying one THR implant design (Anthology). Overall, the CNN achieved a lower Cohen's kappa (0.78) than surgeon 1 (1.00), the same Cohen's kappa as surgeon 2 (0.78), and a slightly higher Cohen's kappa than surgeon 3 (0.76) in identifying all the nine THR implant designs. Furthermore, the saliency maps showed that the CNN generally focused on each implant's unique design features to make a decision. Regarding the time spent performing the implant identification, the CNN accomplished this task in ~0.06s per radiograph. The surgeon's identification time varied based on the method they utilized. When using their personal experience to identify the THR implant design, they spent negligible time. However, the identification time increased to an average of 8.4min (standard deviation 6.1min) per radiograph when they used another identification method (online search, consulting with the orthopedic company representative, and using image atlas), which occurred in about 17% of cases in the test subset (40 radiographs). CNNs such as the one developed in this study can be used to automatically identify the design of a failed THR femoral implant preoperatively in just a fraction of a second, saving time and in some cases improving identification accuracy.

A finite element study of fatigue load effects on total hip joint prosthesis

The main goal of this study was to perform a fatigue analysis and compare the results for different materials. A 72 years old patient was chosen and his hip radiographic/CT scan images were used to construct the geometry. We used four different material including Titanium, Titanium alloy, Cobalt-Chrome, and Stainless steel. The material characteristics of these prostheses were extracted from the literature. All models were exported to ANSYS software for mathematical analysis and the Von-Mises criteria, deformations, and the fatigue life were calculated for each material. Our findings showed that titanium prosthesis tolerated the lowest stress (i.e., 591 MPa for static, and 687 MPa for fatigue loading) and highest safety factor (i.e., 1.54). We found out that Titanium material could be used as the most appropriate one for the hip prosthesis due to lower stress concentration and longer life compared to other materials.

Measurement of the Femoral Anteversion Angle in Medium and Large Dog Breeds Using Computed Tomography.

To promote the development of an optimally functional total hip prosthesis for medium and large dog breeds, accurate measurements of the normal anatomy of the proximal femur and acetabular retroversion are essential. The aim of the current study was to obtain precise normal values of the femoral anteversion angle using computed tomography on cadavers of mature dogs with normal hip joints of both medium and large breeds. Based on the length of their femora 58 dogs were allocated either to group I: ≤195 mm or group II: >195 mm. In the study the femoral anteversion angle (FAA) was measured on each femur using multi-slice spiral computed tomography (CT). The data were processed as multi-planar and three-dimensional reconstructions using Advantage Workstation software. The CT measurements showed that the mean ± standard deviation (SD) FAA of group I was 31.34 ± 5.47° and in group II it was 31.02 ± 4.95°. There were no significant mean difference associations between the length of the femur and the femoral neck angle in either group (P > 0.05). The data suggest that a prosthesis FAA of 31 degrees would be suitable for a wide range of dog sizes.

Investigating MoP bearing wear behavior in a hip simulator with muscular properties

Metal-on-polyethylene (MoP) hip replacements with a CoCrMo alloy femoral head and an ultrahigh-molecular-weight polyethylene (UHMWPE) acetabular cup are strongly preferred due to their high clinical success. Despite this success, the wear of the bearing surfaces that causes a reduction in the prosthetic use of joint prostheses is still a baffling problem that cannot be solved. Although much research has been done on the tribological behavior of UHMWPE, there are a limited number of studies on the UHMWPE wear mechanism of all components in a hip prosthesis. This study aimed to determine the effect of all components of a total hip prosthesis on the wear behavior of UHMWPE according to three different gait cycles. The wear tests performed at the hip simulator were performed with reference to the hip joint movements and a maximum of 3000 N loads specified in ISO 14242-1. In addition to the abrasive and fatigue wear types of UHMWPE undercoat cups. It was observed that the third-body wear type, which was buried on the surface of polyethylene bearing Ti6Al4V alloy, occurred after 5 million cycles. As a result, according to wear test based on friction elements, it was determined that all hip prosthetic components play an active role in polyethylene wear due to repetitive movement and loading. Moreover, it was concluded that the wear model presented by finite-element analysis can predict the formation of wear in hip prostheses in a reasonable manner.

Mortality as a competition risk factor in the survival analysis of the results of the type of fixation of the total hip prosthesis in octogenarian patients

PurposeTotal hip replacement (THR) is challenging in octogenarians due to associated comorbidities and controversy regarding fixation type. We ask whether cemented THR is superior to uncemented THR in patients above the age of 80 years. Methods382 patients (441 hips) aged 80 years or older who underwent THR between 2004 and 2015 were analysed. A cemented THR was implanted in 196 hips (group 1), an uncemented THR with a grit-blasted stem in 121 (group 2), or with a porous-coated stem in 124 (group 3). Patients in group 1 had a higher mean age, more comorbidities and osteoporotic bone. Survival analysis was calculated using cumulative incidence function to account for the competing risk of death. ResultsMedical complications rate was similar. There were three post-operative fractures: one in group 2 and two in group 3. Competing risk analysis showed that the cumulative incidence of revision for any cause was 2.3 in group 1, 6.0 in group 2 and 4.1 in group 3 at ten years, and the cumulative incidence of revision for aseptic loosening was 1.2 in group 1, 3.7 in group 2 and 0 in group 3 at the same period. ConclusionsTHR presents an acceptable number of adverse events for octogenarian patients. Despite uncemented fixation was satisfactory, the higher peri-prosthetic fracture rate worsens results in this group.

Primer Total Kalça Protezi Uygulanmış Hastaların Peroperatif Komplikasyonları ve Postoperatif Dizilim Problemleri

INTRODUCTION: The application of hip joint arthroplasty in hip joint degenerative diseases improves joint pain. The lower elastic modulus of titanium alloy prostheses in hip prostheses than stainless steel elastic modulus ensures higher bone "bone ingrowing" in titanium alloy prostheses. However, malaligment applications during surgery shorten the life of the prosthesis. The aim of this study is to investigate post-operative alignment and to examine perioperative complications in patients undergoing total hip prosthesis. METHODS: In this study, 122 patients who underwent total hip arthroplasty for degenerative hip joint disease and elderly collum femoris fractures between 2013-2017 were evaluated. Perioperative complications in total hip prostheses and early complications of prosthesis alignment in retrospective early follow-up. RESULTS: 78 of these patients were female, 44 of them were male, the mean age was 66 years (42-87), the mean follow-up period was 27 months (6-48). Intraoperatively, femoral calcar fractures developed in 2 patients while 1.5% femoral component was placed. Malaligment was placed at an average of 6 degrees (3-9 degrees) in 9% valgus position in 11 patients. Intraoperative blood loss was observed on average 855 ml (460-1250 ml) DISCUSSION AND CONCLUSION: The results of the implants produced in our country show similar clinical and radiological results with the results stated in the literature. It is considered to be advantageous in terms of both the contribution to the country's economy and the contribution to the patient's health and being easily available.

Use of barbed suture in total hip prosthesis. Prospective randomized study

IntroductionThe correct closure of the surgical wound is an important step in the procedure of a total hip prosthesis implantation, which aims to a correct healing of the wound and minimize the risk of complications.The objective of our study is to determine if the use of a bidirectional barbed suture decreases the closing time after PTC, in the fascial and subcutaneous plane, when compared to the conventional suture polyglactin 910. The hypothesis is that there is no difference in closing time when comparing both sutures. Material and methodProspective single blind randomized study comparing 2 groups: study group with the use of bidirectional continuous barbed suture (Quill®) (Gr.Q) and a control group (Gr.V) using discontinuous polyglactin 91 suture (Vicryl®). Closure was performed in 2 planes (fascia and subcutaneous) simultaneously by 2 surgeons. The exclusion criteria were: previous surgeries on the same hip, revision surgeries, major deformities and allergies to suture components.The variables under study were: 1) fascia closure time, subcutaneous and global, 2) surgical wound infection, and 3) dehiscence. Results82 patients (39 GrQ, 43 GrV) were included. The global closing time was shorter in Gr.Q (5 min 59 s) compared to Gr.V (7.01 min); (p < 0.04). They showed differences in subcutaneous closure; Gr.Q shorter time with a 37 s difference (p = 0.048). Differences in fascial plane were not observed.Superficial infection was observed in 1 GrQ patient and 1 in GrV; 1 case of deep infection in Gr.Q (p = 0.29). One patient presented dehiscence of the wound in Gr.Q (p = 0.3). However, these differences did not show statistical significance. ConclusionsThe use of a barbed suture allows a shorter closing time compared to the conventional one. However, despite this decrease in time, no differences were found in terms of the appearance of infection or wound dehiscence.

Effectiveness of the Suprainguinal Ultrasound-Guided Block for the Management of Postoperative Pain after Application of a Total Hip Prosthesis

Objective: To assess the effectiveness of ultrasound-guided supraginguinal block (SIB) in the management of pain after total hip replacement. Material and Methods: This was a prospective, randomized, single-blind controlled study carried out in the anesthesia-intensive care unit of the Donka National Hospital in Conakry, over a period of 06 months (01/01/2020 to 30/06/2020). It concerned 32 patients: 16 patients in the “ultrasound-guided SIB” group and 16 patients in the “standard analgesia” group. Results: The pain scores assessed by the simple verbal scale and collected at the different time intervals (6H, 12H, 24H, 36H, 48H) showed mean scores 3 in the standard analgesia group (P Conclusion: Our study demonstrated that echo-guided SIB provided better analgesia compared to standard analgesia for the management of postoperative pain after total hip replacement.

About the Experimental and Virtual Analysis of Orthopedic Implant Systems for the Revision of the Hip Prosthesis with Morcellated Bone Graft and Reconstruction Net.

Introduction. Prosthesis loosening is an alteration of the function and position of a total hip prosthesis with reference to the initial surgical moment. The main mechanism unanimously accepted for aseptic prosthetic losses at the level of the cup is represented by the biological mechanism. Material and Method. Experimental and virtual, interdisciplinary tools, techniques and methods were used to determine the behavior of the hip replacement prosthesis with the morcellated graft and the reconstruction net. Performing an orthopedic assembly with a morcellated bone graft and reconstruction net. An assembly was performed on a hip joint taken from an animal (cow). The biological material and the components of the prosthesis were prepared similarly to the revision prosthesis intervention. Experimental testing of orthopedic assembly with morcellated bone graft and reconstruction net. This assembly was tested on a universal machine to determine the maximum force at which it yields. This was 1790 Kgf, i.e. 17559 N. Virtual experimental testing of the hip joint with orthopedic revision assembly with a morcellated bone graft and reconstruction net for normal gait loading. The orthopedic assembly with the morcellated graft and the reconstruction net was reconstructed in the virtual environment. Normal load was used. Results maps were obtained. Conclusions. Analyzing the results from the two tests, experimental and virtual, and important conclusions were drawn regarding this orthopedic assembly.

Balance and functional disorders in geriatric patients after total hip prosthesis removal.

One of the most difficult complications of total hip arthroplasty is an infection in the area of the implant with an incidence of 0.5% to 2.5% resulting in the most severe situation in prosthesis removal. The aim of the study was to assess postural stability and functional disorders in patients after hip prosthesis removal. A group of 15 patients after hip prosthesis removal was compared to a control group of 15 healthy persons who were age-matched without any symptoms of degenerative disorders in the lower spine and lower extremities. The static balance test was conducted on a bi-modular stabilometric platform, registering the movement of the centre of foot pressure. The functional state of the patients was assessed on the basis of the Harris Hip Score (HHS). Patients had poor functional result (HSS mean 62.29 ± 12.92 points). Obtained results of postural stability of patients showed huge difficulties maintaining stability and showed statistically significant differences in a majority of the analysed parameters. Several stability parameters showed significantly worse results in patients after hip prosthesis removal. Special attention should be paid and focused physiotherapy should be undertaken for patients with a stability disorder and functional status to prevent falls and improve functioning.

BIOMECHANICAL BEHAVIOUR OF THE TOTAL HIP PROSTHESIS SUBJECTED TO NORMAL GAIT CYCLE LOAD: IDENTIFICATION OF THE DAMAGE IN THE CEMENT MANTLE

Cement is the weakest link in the composition of total hip prosthesis in terms of mechanical properties. The knowledge of the intensity and distribution of stresses on the cement attaching the implant to the bone is of great importance for understanding the condition of the prosthesis and its failure. In this study, the finite element method is used to analyze the magnitude and the equivalent Von Mises stress distribution induced in different components of the total hip prosthesis (THP) as well as the identification of the damage induced in the cement and between two cavities located in the polymethyl methacrylate (PMMA). The crack propagation is determined and localized using the extended element method (XFEM). The results show that the fracture stress of the cement in its proximal part is very important. These stresses increase considerably with the interaction of the cavities in this binder, causing damage to the cement and the loosening of the prosthesis.

Reducing Dislocations of Antibiotic Hip Spacers via Hybrid Cement-screw Constrained Liner Fixation: A Case Series.

PurposeInfection following total hip arthroplasty is a challenging and devastating complication. In two-stage revision arthroplasty, antibiotic spacers, although efficacious, can be associated with an unacceptable rate of mechanical complications (e.g., fracture, dislocation). This series describes 15 patients with infected total hip prostheses treated with hybrid cement-screw fixation constrained liner antibiotic spacers to enhance stability and minimize mechanical complications.Materials and MethodsAll patients with an infected hip prosthesis undergoing two-stage revision arthroplasty at a single academic medical center were identified and screened for inclusion. Clinical and radiographic data including patient demographics and outcome measures were collected and retrospectively analyzed.ResultsTwo patients died of unrelated causes at an average of 6-week postoperatively. Infections in the remaining thirteen patients (100%) were successfully eradicated; all underwent uncomplicated revision arthroplasty at a mean duration of 99.5 days after the placement of the antibiotic spacer. No dislocations, fractures, or other mechanical failures of any spacer were observed in this series.ConclusionThe hybrid cement-screw fixation technique for constrained liner antibiotic spacers is a reliable and effective treatment method for eradicating prosthetic joint infections without mechanical complications.

Utilización de sutura barbada en prótesis total de cadera. Estudio prospectivo aleatorizado

IntroductionThe correct closure of the surgical wound is an important step in the procedure of a total hip prosthesis implantation (total hip arthroplasty, THA), which aims to a correct healing of the wound and minimize the risk of complications.The objective of our study is to determine if the use of a bidirectional barbed suture decreases the closing time after THA, in the fascial and subcutaneous plane, when compared to the conventional suture polyglactin 910. The hypothesis is that there is no difference in closing time when comparing both sutures. Material and methodProspective single blind randomized study comparing two groups: study group with the use of bidirectional continuous barbed suture (Quill™) (Gr. Q) and a control group (Gr. V) using discontinuous polyglactin 91 suture (Vicryl™). Closure was performed in two planes (fascial and subcutaneous) simultaneously by two surgeons. The exclusion criteria were: previous surgeries on the same hip, revision surgeries, major deformities and allergies to suture components.The variables under study were: 1) fascia closure time, subcutaneous and global; 2) surgical wound infection; and 3) dehiscence. Results82 patients (39 Gr. Q, 43 Gr. V) were included. The global closing time was shorter in Gr. Q (5 min 59 sec) compared to Gr. V (7.01 min), (p < 0.04). They showed differences in subcutaneous closure: Gr. Q shorter time with a 37 seconds difference (p = 0.048). Differences in fascial plane were not observed.Superficial infection was observed in one Gr. Q patient and another in Gr. V; one case of deep infection in Gr. Q (p = 0.29). One patient presented dehiscence of the wound in Gr. Q (p = 0.3). However, these differences did not show statistical significance. ConclusionsThe use of a barbed suture allows a shorter closing time compared to the conventional one. However, despite this decrease in time, no differences were found in terms of the appearance of infection or wound dehiscence.

Are Daily Life Activities of Patients with Proximal Femoral Tumor Resection Prosthesis as Good as those of Patients Undergoing Total Hip Prosthesis for Non-Tumor Causes?

The Barthel Index of Activities of Daily Life (ADL) is a scale used to evaluate performance in daily life activities and investigate the reason and resulting relationships in a comprehensive, non-biased manner. The aim of this study was to compare the daily life activities of patients who underwent proximal femoral tumor resection prosthesis assessed by the Barthel Index with the activities of daily living of patients with a total hip prosthesis performed for non-tumor reasons. Twenty-eight patients were included in the study. Sixteen patients underwent hip prosthesis for reasons other than tumor (femur proximal avascular necrosis, coxarthrosis, etc.) and 12 underwent wide resection and femur proximal tumor resection prosthesis due to primary malignant bone tumor or metastasis in the proximal femur. The Barthel Index was used to evaluate their life quality at 3 months. A total of 28 patients (mean age 60.9±1.4 yrs, range 19.0-84.0, 17 female and 11 male patients) were included into the study. Mean ADL score was 84.5±20.6 (5-100.0). While only one patient was totally dependent in terms of daily life activities, 8 other patients were totally independent. When the patient groups were categorized by degree of dependency according to the ADL scores, it was found that dependency states of the two surgery groups were similar in distribution (p=0.212, p=0.703, and p=1.000 respectively). Functional recovering levels were good in the patients who underwent a surgery for proximal femoral tumor resection prosthesis; there was no significant difference when we compared the functional level after total hip prosthesis applied for non-tumor reasons.

Solutions for failed osteosynthesis of the acetabulum

Osteosynthesis of the acetabulum is complex and requires very careful planning and preoperative preparation. The goal is to achieve anatomical reduction without steps or gaps in the articular surface. If it has not been possible to achieve an optimal reconstruction, one has to consider whether it makes sense to carry out reosteosynthesis or revise the fixation. The risk of infection, heterotopic ossification, avascular necrosis of the femur and cartilage damage is much higher than with the primary procedure. Often, especially in older patients, it may make more sense to achieve fracture union and to implant a total hip prosthesis in due course. In younger patients, every attempt should be made to achieve optimum anatomical reduction and this may mean consideration of reosteosynthesis after careful planning and counselling of the patient. If reosteosynthesis is considered adequate imaging including a postoperative CT is essential as part of the planning. This article looks at the possible solutions for failed osteosynthesis of the acetabulum.

Dual mobility total hip arthroplasty for the treatment of femoral neck fracture with hemiplegia

To investigate the clinical effects of dual mobility total hip prosthesis in treating femoral neck fracture patients with hemiplegia. A retrospective analysis was performed on 18 patients with femoral neck fracture combined with hemiplegia who underwent dual mobility total hip prosthesis replacement from March 2014 to December 2016. The follow up data of these patients was complete. There were 5 males and 13 females, aged 65 to 70 years old with an average of (66.50±1.38) years. The left side was involved in 12 cases, while the right side in 6 cases. There were 4 cases with Garden Ⅲ type and 14 cases with type Ⅳ. Limb muscle strength of hemiplegia were in grade Ⅳ. The posterior-lateral approach of hip joint was used in surgery for all patients. The implant position, dislocation and loosening of the prosthesis were evaluated by X-ray examination. Harris hip score and the Merle D'aubigne score were used to assess the hip function in the follow up. The operation duration was for 70-90 (81.56±7.48) min and the blood loss during the operation was for 160-200 (170.32± 12.56) ml. No blood was transfused during the operation. Postoperative incisions were healed at the first stage. The follow-up time was for 28-60(36.0±3.5) months. Harris hip score increased from 16.94±0.73 preoperatively to 96.19±1.27 at the final follow-up(P<0.05). Merle D 'Aubigne score increased from 3.96±0.06 preoperatively to 16.81±0.63 at the final follow-up(P< 0.05). No fracture or nerve or vascular injury were found during the operation. The postoperative X-ray showed that the prosthesis was in good position. No complications such as joint dislocation, dislocation of prosthesis, loosening of prosthesis, fracture around the prosthesis, pain in the front of thethigh, fracture of the self tapping screw in the ilium, and delayed infection occurred in the patients after operation. Dual mobility total hip prosthesis has the advantages of both good initial stability and low dislocation rate of the prosthesis, and the clinical application of total hip replacement in hemiplegic femoral neck fracture is satisfactory.

Alzheimer's disease and related syndromes and hospitalization: a nationwide 5-year longitudinal study.

To study the association between Alzheimer's disease and related syndromes (ADRS) and the incidence of short-stay hospitalizations from the year before (Y-1 ) to 4years after (Y1 -Y4 ) ADRS identification in the healthcare system. Among all beneficiaries of the French health insurance general scheme aged 40years or more, those with an incident ADRS in 2011, identified through long-term disease registry, hospitalization diagnoses or ADRS-specific drug delivery, were matched with beneficiaries without ADRS of the same age, gender and residence area. The annual incidence rates of all-cause hospitalizations (excluding those with a diagnosis code of ADRS) were compared between individuals with or without ADRS using incidence ratios (IRs) globally and by age, gender, deprivation index and modified Charlson score. We also studied cause-specific hospitalizations using patients' diagnoses and procedure codes. A total of 90871 subjects with and 90871 subjects without ADRS were included (mean age 79.6years, 66% females). From Y-1 to Y4 , incidence rates were significantly higher in subjects with ADRS than in those without for all-cause hospitalization [IR(Y-1 )=1.73; 95% confidence intervals, 1.71-1.75; IR(Y4 )=1.37; 95% confidence intervals, 1.35-1.39], hospitalizations forsocial reasons [IR(Y-1 )=4.28; IR(Y4 )=2.70], fall [IR(Y-1 )=5.36; IR(Y4 )=2.59], injury [IR(Y-1 )=2.71; IR(Y4 )=2.09] and infection [IR(Y-1 )=2.04; IR(Y4 )=2.07]. The inverse was observed for hospitalizations for cataract surgery [IR(Y-1 )=0.73; IR(Y4 )=0.51] or total hip prosthesis after 2years [IR(Y4 )=0.72]. Incident ADRS cases were associated with a higher incidence of hospitalization, but these subjects underwent some common non-emergency surgeries less frequently. Future studies need to assess the clinical impact of these differences.

Effect of random variation of input and various daily activities on wear in a hip joint simulator

The ISO 14242-1 standard specifies fixed, simplified, sinusoidal motion and double-peak load cycles for wear testing of total hip prostheses. In order to make the wear simulation more realistic, random variation was added for the first time to the motion and load control signals of a hip joint simulator. For this purpose and for the simulation of various daily activities, computer-controlled, servo-electric drives were mounted on a biaxial hip simulator frame and successfully introduced. Random variation did not result in a statistically significant difference in the wear factor of large diameter VEXLPE liners compared with fixed sinusoidal waveforms. However, level walking according to biomechanical literature surprisingly resulted in a 134 per cent higher, and jogging in a 57 per cent lower wear factor compared with the fixed sinusoidal waveforms. These wear phenomena were likely to be caused by a variation in the lubrication conditions and frictional heating. Simplified motion waveforms may result in an underestimation of wear in walking.