Link N suppresses interleukin-1ß-induced biological effects on human osteoarthritic cartilage.

Osteoarthritis (OA) is a disease of diarthrodial joints associated with extracellular matrix proteolytic degradation under inflammatory conditions, pain and disability. Currently, there is no therapy to prevent, reverse or modulate the disease course. The present study aimed at evaluating the regenerative potential of Link N (LN) in human OA cartilage in an inflammatory milieu and determining if LN could affect pain-related behaviour in a knee OA mouse injury model. Osteo-chondro OA explants and OA chondrocytes were treated with LN in the presence of interleukin-1ß (IL-1ß) to simulate an osteoarthritic environment. Quantitative von Frey polymerase chain reaction and Western blotting were performed to determine the effect of LN on matrix protein synthesis, catabolic enzymes, cytokines and nerve growth factor expression. Partial medial meniscectomy (PMM) was performed on the knee of C57BL/6 mice and, 12 weeks post-surgery, mice were given a 5 µg intra-articular injection of LN or phosphate-buffered saline. A von Frey test was conducted over 24 h to measure the mechanical allodynia in the hind paw. LN modulated proteoglycan and collagen synthesis in human OA cartilage through inhibition of IL-1ß-induced biological effects. LN also supressed IL-1ß-induced upregulation of cartilage-degrading enzymes and inflammatory molecules in OA chondrocytes. Upon investigation of the canonical signalling pathways IL-1ß and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), LN resulted to significantly inhibit NF-κB activation in a dose-dependent manner. In addition, LN suppressed mechanical allodynia in an OA PMM mouse model. Results supported the concept that LN administration could provide therapeutic potential in OA.

Precipitants of Delirium in Older Inpatients Admitted in Surgery for Post-Fall Hip Fracture: An Observational Study.

BACKGROUND: Hip fractures precipitate several acute adverse outcomes in elderly people, thus leading to chronic adverse outcomes. OBJECTIVES: The objective of our study was to examine the clinical characteristics associated with incident delirium in community dwelling elderly individuals who have a hip fracture. DESIGN: Retrospective observational cohort study. SETTING: Data was collected from an academic tertiary hospital affiliated with McGill University. PARTICIPANTS: 114 elderly individuals who were above 65 years of age, who underwent surgery for a fractured hip. MEASUREMENTS: The main outcome variable was incident delirium, which was assessed by chart reviews of notes and observations recorded by nurses and physicians when patients were admitted post operatively to the surgical unit. Covariates included age, sex, length of stay, delay to surgery, number of medical comorbidities, number of medications and hip fracture location, and were extracted from medical records. Baseline mobility and functional status, preoperative cognitive impairment, postoperative complications, regular psychotropic medications, psychotropic medications in hospital, and location of discharge were also assessed through chart review. RESULTS: The results demonstrated that 17.5% of participants with a diagnosis of delirium had a longer length of hospitalization (p = 0.01), a lower baseline functional status (p = 0.03) and pre-operative cognitive impairment (p = 0.01). Patients receiving new psychotropic medications in hospital were more likely to have delirium (OR = 4.6, p = 0.01) which was independent of pre-operative cognitive impairment. CONCLUSION: We have shown that an association exists between psychotropic medication prescription and incident delirium in patients with hip fractures, even when adjusting for cognitive impairment. Hence, the prescription of psychotropic drugs should be judicious in these patients so as minimize the risk of adverse outcomes.

Conservative non-pharmacological treatment options are not frequently used in the management of hip osteoarthritis.

Osteoarthritis (OA) is the most frequent joint disorder in seniors. Systematic reviews suggest that conservative treatment is effective and preferred in mild-moderate cases. The objective of this study was to examine the proportion of patients receiving physiotherapy, exercise or walking aids, and to explore factors associated with their prescription. We conducted a retrospective survey of patients about to undergo total hip arthroplasty for hip osteoarthritis. Patients were asked about past prescriptions for cane use, physiotherapy and exercise. Of 161 patients (36.6% male, mean age 68.7+/-10.1 years), 76% were prescribed a cane (adherence=86.2%). The main reason for not using a cane was vanity. Of the 28.0% patients prescribed physiotherapy, 73.3% received exercises compared to only 2.6% of non-physiotherapy patients. Patients who were older or worked in manual labour were more likely to be prescribed a cane and less likely to be prescribed physiotherapy or exercises. Men were less likely than women to be prescribed all three, but only cane use was statistically significant across genders. In conclusion, physiotherapy and exercise are not commonly prescribed in patients with hip OA.

Induction of macrophage apoptosis by ceramic and polyethylene particles in vitro.

The purpose of this study was to investigate in vitro the presence of apoptotic cell death after macrophage stimulation with different ceramic (Al2O3 and ZrO2) and high density polyethylene (HDP) particles. We also analyzed the effects of particle size, concentration, and composition. The J774 mouse macrophage cell line was exposed to commercial particles of different sizes (up to 4.5 microm) and concentrations (up to 500 particles per macrophage). Fluorescence microscopy and DNA laddering were used to investigate the presence of apoptosis in cell cultures after 24 h of incubation. Fluorescence microscopy of propidium iodide stained cells showed two characteristic morphological features that occur in apoptotic cells, namely nuclear condensation and heterogeneity of stain uptake. The effect of ceramic particles on apoptotic nuclear morphology was size- and concentration-dependent and reached a plateau above 150 particles per macrophage at 1.3 microm. With regards to composition, we did not find any difference in cell morphology between Al2O3 and ZrO2. Ceramic and HDP particles induced DNA fragmentation into oligonucleosomes as evidenced by DNA laddering, another characteristic of apoptosis. The induction of DNA laddering was size- and concentration-dependent whereas particle composition (Al2O3 vs. ZrO2 and Al2O3 vs. HDP) had no effect. In conclusion, our results demonstrated that ceramic and HDP particles induce macrophage apoptotic cell death in vitro and open doors for possible modulation of debris-induced periprosthetic osteolysis.

Collagen crosslinked N-telopeptides as markers for evaluating particulate osteolysis: a preliminary study.

The purpose of this study was to determine whether a marker of bone resorption could be used noninvasively to diagnose and assess treatment of periprosthetic osteolysis. The crosslinked N-telopeptide marker of osteoclast-mediated bone resorption potentially has the sensitivity to detect periprosthetic osteolysis. Second-morning urine specimens were obtained from (a) seven age-matched controls, (b) eight patients who had a hip arthroplasty, hybrid implants at least 1 year after surgery, and no osteolysis, (c) 11 patients who had a hip arthroplasty and osteolysis, and (d) 10 patients who had a hip arthroplasty and with osteolysis before and after 6 weeks of oral Fosamax (alendronate) treatment. The Fosamax treatment consisted of one 10-mg dose per day for 6 weeks. Men and young women (less than 40 years old) were chosen for this study to avoid bone resorption enhanced after menopause as a possible confounder. An enzyme-linked immunosorbent assay technique for quantifying crosslinked N-telopeptides of type-I collagen was performed on all specimens. The patients with osteolysis had significantly elevated levels of N-telopeptide compared with the implant control group. In addition, levels of N-telopeptide were significantly lowered after Fosamax treatment. These findings indicate that a systemic bone-resorption marker (N-telopeptide) can be used to evaluate local particulate-induced osteolysis and its treatment. The study also provides clinical evidence that osteolysis is associated with increased osteoclast-mediated bone resorption and that this locally induced bone resorption can be suppressed by certain bisphosphonates (Fosamax). These insights have potential value in the understanding and clinical management of aseptic loosening.

Evidence for a humoral mechanism for enhanced osteogenesis after head injury.

The rate of fracture-healing is accelerated and abundant callus develops in patients who have a head injury and fractures. The mechanism underlying this is unclear. We studied the possibility that increased circulating growth factors or circulating factors that stimulate local release of growth factors mediate the increased osteogenesis. Samples of serum were obtained from thirty-two subjects: patients who had a head injury alone, those who had a head injury and fractures of the lower extremities, those who had only fractures, and control subjects who had neither a head injury nor a fracture. Severe head injury was defined as that producing coma of at least three days' duration. Growth-factor activity was determined by assessing the effect of serum on the incorporation of [3H]thymidine and on cell counts in primary cultures of osteoblastic cells from the calvaria of fetal rats. Samples of serum from the two groups of patients who had a head injury had higher mitogenic activity and produced a greater increase in the number of cells than did the samples from the other two groups. The mean levels of activity were not statistically different between the first two groups or between the patients who had fractures only and the control subjects. Dilution studies showed that increased mitogenic activity in the serum from the patients who had a head injury was dose-dependent. In three patients in whom it was studied, the mitogenic activity peaked approximately thirty-seven days after the head injury was sustained.

Fixation pull-out response measurement of bone screws and porous-surfaced posts.

Screws and posts are used in various implant designs to contribute to the short- and long-term fixation stability of artificial joints. This study was undertaken to measure the detailed pull-out load-displacement response of bone screws, beaded porous coated posts, and smooth-surfaced posts in both proximal tibial cancellous bone and polyurethane material under monotonic static and repetitive cyclic loadings. The effect of a number of parameters such as insertion site on the proximal tibia, rate of displacement, insertion depth, outside diameter, drill size, repetitive loading and boundary conditions were studied. Bone screws resisted significantly larger loads than posts of the same size. Smooth-surfaced posts demonstrated much larger (about twice) pull-out forces than beaded porous coated posts of the same size. The pull-out force in the proximal tibia was markedly larger at the medial region followed by the lateral region. The central region exhibited the least force. The resistance of screws and posts diminished with repetitive cyclic loads/displacements, especially when these were larger than 50% of their respective values at pull-out force evaluated under monotonic static loading conditions. The smooth-surfaced posts showed superior performance in maintaining their resistance in fatigue than did the porous coated posts and bone screws. The pull-out force was found to also depend on the pull-out material arrangement and boundary conditions. Pull-out results measured with a specific test design should not, therefore, be compared with those performed using different design configurations.

Analysis of cementless implants using interface nonlinear friction--experimental and finite element studies.

Measured interface nonlinear friction properties are used to develop models to study the short-term fixation response of smooth- and porous-surfaced posts, bone screws, and plates fixed with and without posts/screws. Experimental studies are carried out to validate the model predictions and identify the relative role of posts and screws in fixation of a plate on a polyurethane block under symmetric/eccentric axial compression loads. The idealized Coulomb's friction is also used for the sake of comparison. The incorporation of measured nonlinear, rather than the idealized Coulomb, friction is essential to compute realistic results. For plate fixation, the experimental and finite element results show that the screw fixation yields the stiffest response followed by the smooth- and then porous-coated post fixation. For example, under 1000 N eccentric axial compression, the edge of the plate opposite the loaded edge is measured to lift by 1147 +/- 72, 244 +/- 38, or 112 +/- 28 microns, respectively, for the cases with no fixation, with smooth-surfaced posts, or with screws. The corresponding models predict, respectively, values of 1538, 347, or 259 microns and also 556 microns for the plate fixed with porous coated posts. The satisfactory agreement between numerical and experimental results confirms the importance of proper interface modelling for the analysis of posts, screws, and complex fixation systems. This becomes further evident when considering cementless implants in which the bone-implant interface exhibits relatively large displacements as the maximum resistance force is reached. The developed models can be used to investigate the post-operative short-term stability of various cementless implant designs.

Cytotoxicity and macrophage cytokine release induced by ceramic and polyethylene particles in vitro.

Although the response of macrophages to polyethylene debris has been widely studied, it has never been compared with the cellular response to ceramic debris. Our aim was to investigate the cytotoxicity of ceramic particles (Al2O3 and ZrO2) and to analyse their ability to stimulate the release of inflammatory mediators compared with that of high-density polyethylene particles (HDP). We analysed the effects of particle size, concentration and composition using an in vitro model. The J774 mouse macrophage cell line was exposed to commercial particles in the phagocytosable range (up to 4.5 microns). Al2O3 was compared with ZrO2 at 0.6 micron and with HDP at 4.5 microns. Cytotoxicity tests were performed using flow cytometry and macrophage cytokine release was measured by ELISA. Cell mortality increased with the size and concentration of Al2O3 particles. When comparing Al2O3 and ZrO2 at 0.6 micron, we did not detect any significant difference at the concentrations analysed (up to 2500 particles per macrophage), and mortality remained very low (less than 10%). Release of TNF-alpha also increased with the size and concentration of Al2O3 particles, reaching 195% of control (165 pg/ml v 84 pg/ml) at 2.4 microns and 350 particles per cell (p < 0.05). Release of TNF-alpha was higher with HDP than with Al2O3 particles at 4.5 microns. However, we did not detect any significant difference in the release of TNF-alpha between Al2O3 and ZrO2 at 0.6 micron (p > 0.05). We saw no evidence of release of interleukin-1 alpha or interleukin-1 beta after exposure to ceramic or HDP particles.

Fresh osteochondral allografts for post-traumatic defects in the knee. A survivorship analysis.

Fresh osteochondral allografts were used to repair post-traumatic osteoarticular defects in 92 knees. At the time of grafting, varus or valgus deformities were corrected by upper tibial or supracondylar femoral osteotomies. A survivorship analysis was performed in which failure was defined as the need for a revision operation or the persistence of the pre-operative symptoms. There was a 75% success rate at five years, 64% at ten years and 63% at 14 years. The failure rate was higher for bipolar grafts than for unipolar and the results in patients over the age of 60 years were poor. The outcome did not depend on the sex of the patient and the results of allografts in the medial and lateral compartments of the knee were similar. Careful patient selection, correction of joint malalignment by osteotomy, and rigid fixation of the graft are all mandatory requirements for success. We recommend this method for the treatment of post-traumatic osteochondral defects in the knees of relatively young and active patients.

The irradiation effect on the initial mechanical properties of meniscal grafts.

In this study, the effect of sterilization was investigated on the mechanical properties of rabbit's meniscal grafts. The processes of freezing and irradiation were carried out and their effects upon the elastic and viscoelastic properties measured using a tensile testing machine and an indentation test. It was found that gamma irradiation, at dosages commonly used for sterilizing grafts, had a significant adverse influence on the elastic and viscous response of the grafts. Freezing led also to a small significant decrease in elastic stiffness but no change in failure strength. It is concluded that irradiation sterilization is unsuitable for clinical use and other techniques should be used whenever possible.

Fixation response of two cementless tibial implants under static and fatigue compression loading.

The short- and long-term success of tibial cementless implants depend on the initial fixation stability often provided by posts and screws. Excessive relative interface motions are known to inhibit bone ingrowth and, hence, biologic fixation. In the present study, the stability of two cementless tibial implants under static and cyclic loading was studied. An apparatus was developed to perform compression tests on tibial components fixed by screws or posts onto resurfaced tibiae. Motion transducers were placed to record liftoff and subsidence displacements. A load of 1000 N was eccentrically applied on the medial plateau via the femoral component. The response was measured under static and repetitive loading up to 4000 cycles at 1 Hz. Experimental results showed that the screw fixation yielded the stiffer response and, hence, provided greater initial stability. The tibial component fixed with posts demonstrated larger lift off displacements. Comparison of measured results of static tests before and after fatigue indicated that the load-displacement behavior was not significantly affected by the cyclic fatigue loading under 1000 N up to 4000 cycles at 1 Hz. Nevertheless, much larger permanent displacements were recorded for the post fixation systems. In contrast to screw fixation, posts fixation systems demonstrated marked deterioration under larger compression loads of approximately 2000 N.

Irradiated meniscal allotransplants of rabbits: study of the mechanical properties at six months postoperation.

In this study, the long-term effects of gamma irradiation were investigated on the indentation properties of rabbits' meniscal allotransplants. Three groups, i.e. fresh, frozen and frozen irradiated allotransplants, were studied at 6 months postoperatively. Contralateral menisci served as controls in each group. Treatment effects were assessed using three mechanical parameters, i.e. compliance to long-term creep (J(R)), compliance to rapid load (Jmu) and viscoelastic characteristic time (tau i). Comparison of the three groups showed that compliance to long-term creep of the frozen irradiated menisci was significantly reduced. This suggests that at 6 months postoperatively, the frozen irradiated allotransplants were less viscous compared to fresh or frozen transplants.

Deviations between intra-operative navigation data and post-operative weight-bearing X-rays.

Several studies have shown that computer-navigated TKA reduces the rate of outliers. Thirty-one consecutive patients were operated on by the same surgeon using a computer assisted navigation system. Data collected by the system included the final mechanical axis of the extremity (HKA angle) and the coronal angle of the tibial and femoral implants. These same values were measured using CAD software on full weight-bearing long X-rays taken 6 weeks post-surgery. Deviations were observed when X-ray measurements were compared to intra-operative data collected from the navigation system. A statistically significant difference was found in the tibial cut (1.29 degrees +/- 1.35 degrees; p < 0.0001) and in the HKA (1.59 degrees +/- 2.36 degrees; p = 0.0007). Outliers of more than 3 degrees were observed in the coronal plane of the tibial implant in 9.6% of patients, in the coronal plane of the femoral implant in 6.4% of patients, and in the HKA angle of 29% of patients. Our results indicate that the use of navigation alone is insufficient to prevent outliers beyond an acceptable range of 3 degrees .

Effect of a Type II Collagen Fragment on the Expression of Genes of the Extracellular Matrix in Cells of the Intervertebral Disc.

Knowledge of factors regulating the turnover, repair, and degeneration of the intervertebral disc (IVD) is lacking. Although type II collagen (CII) fragments accumulate in the degenerative IVD, little is known of how they affect the degenerative process. A better understanding of the cellular interactions with fragments of matrix molecules are a key factor in promoting therapies for degenerative disc diseases. In the present study, we have investigated the effect of the CII (245-270) peptide on the expression of matrix molecules, proteinases, and interleukin genes in cells of the IVD. Cells isolated from the nucleus pulposus (NP) and annulus fibrosus (AF) of adult bovine tails were cultured up to 8 days in the absence (control) or presence of the CII (245-270) peptide. RT-PCR was used to analyze the expression of the different genes. Exposure of these cells to the CII (245-270) peptide led to a transient up-regulation of the aggrecan gene in AF cells while this up-regulation was maintained for a longer time in NP cells. The fragment also enhanced a transient up-regulation of the type II collagen gene in AF cells but had no effect in NP cells. The peptide enhanced transiently the expression of matrix metalloproteinase (MMP)-1 and cathepsin K genes in both AF and NP cells whereas it increased MMP-13 expression only in NP cells. The peptide up-regulated tissue inhibitor of metalloproteinase (TIMP)-1, TIMP-2, and TIMP-3 gene expression on day 1 in AF cells but had very little effect on their expression in NP cells. Finally, the CII (245-270) peptide had no effect on IL-6 expression while IL-1alpha was not expressed in these cells. In conclusion, our results showed that the CII (245-270) peptide differentially alter the expression of genes in bovine AF and NP cells and suggest that degradation products of collagen may be involved in the regulation of IVD homeostasis.

Appropriate imaging studies and their interpretation.

Imaging studies are essential for the diagnosis and management of many of the hip disease entities dealt with in this symposium. This paper briefly touches on salient aspects of standard radiography, "special" views, arthrography, radioisotope imaging, computed tomography and magnetic resonance imaging. Orthopedic surgeons must be familiar with the correct applications and interpretation of these modalities so as to use them efficiently and economically.

Experience of total hip replacement and its effect on recovery after second hip replacement.

OBJECTIVE: To determine whether the knowledge gained through total hip replacement (THR) influences the time to recovery after a second THR. DESIGN: A retrospective study of data gathered prospectively on the recovery course of patients from their preoperative visit to 1 year after surgery. SETTING: A university teaching hospital. PATIENTS: Sixty-nine patients underwent bilateral hip replacements at the Royal Victoria Hospital, Montreal, between May 1985 and May 1992. The inclusion criteria were: (a) similar diagnoses and prostheses bilaterally, (b) time between the two THRs of less than 3 years, (c) both replacements carried out by the same surgeon and (d) attendance at the arthroplasty clinic. Forty-one patients did not fulfil the criteria for inclusion, leaving 28 patients having 56 THRs for the study. An additional 28 patients who had unilateral hip arthroplasty were randomly chosen on the basis of sex and age to act as the control group. INTERVENTION: Bilateral cementless THR. MAIN OUTCOME MEASURES: Harris hip score at one preoperative visit and postoperatively at 6 weeks, 3 months, 6 months and 1 year. RESULTS: There were no significant differences in measures of recovery between the initial and the subsequent hip replacement at any of the time intervals. Significant differences were found only between the various time periods. CONCLUSIONS: Time and not familiarity dictated progress toward recovery for patients who underwent bilateral THR with cementless prostheses. Randomized clinical trials, assessing whether time to recovery, ultimate outcome and cost-effectiveness are affected by preoperative teaching programs, are necessary to further elucidate this important issue.

Biomechanical response of the passive human knee joint under anterior-posterior forces.

OBJECTIVE: To investigate the detailed biomechanics of the passive tibiofemoral knee joints in full extension under anterior/posterior drawer forces of up to 400 N. DESIGN: A nonlinear three-dimensional finite element model of the entire human tibiofemoral joint consisting of bony structures, their articular cartilage layers, menisci, and four principal ligaments was utilized. BACKGROUND: The mechanics of the knee joint, specially under drawer forces, have extensively been investigated. Despite all these works, the detailed joint biomechanics, specially the role of boundary conditions, load transmission through menisci/articular cartilage layers, and coupling between menisci and cruciate ligaments are not yet quantified. METHODS: Nonlinear elastostatic analyses were carried out considering the tibiofemoral joint at full extension under anterior and posterior loads of up to 400 N applied either to the tibial or the femoral shaft. Cases with various boundary conditions, cruciate ligament deficiency (anterior or posterior), and total unilateral meniscectomy (medial or lateral) were analysed. RESULTS: In addition to the total primary anterior-posterior motion of about 9 mm at +/-400 N, significant coupled external tibial rotations of about 9 degrees and 10 degrees were computed under 400 N femoral posterior and anterior forces, respectively. The response was influenced by the manner of loading and boundary conditions. The anterior cruciate ligament and posterior cruciate ligament were the primary restraints to femoral posterior and anterior drawer forces, respectively. Section of either of these ligaments drastically increased the joint anterior-posterior motion. In the absence of cruciates, the collaterals became the primary restraints in both anterior-posterior forces. In this case, the tibial plateaus, specially the medial one in the anterior cruciate ligament-deficient joint, experienced much larger compressive forces. In addition to causing an increase in joint primary anterior-posterior laxity and anterior cruciate ligament forces, medial meniscectomy substantially increased coupled tibial external rotation, forces on the lateral plateau, and stresses in the articular cartilage of the lateral plateau. RELEVANCE: Our results suggest an increased role for the medial meniscus in the anterior cruciate ligament-deficient joint. Lateral meniscectomy had much smaller effects on results than the medial one. The success of any anterior cruciate ligament replacement or meniscal transplantation in the restoration of the joint stability and the protection of the articular cartilage against excessive stresses depends on the coupling between the anterior cruciate ligament and medial meniscus. Absence of any of these components would drastically influence the joint response.

Finite element analysis of human knee joint in varus-valgus.

OBJECTIVE: The overall response, load transmission, role of ligaments, and state of stress in various components under varus-valgus moments in the intact and collateral-deficient tibiofemoral joint are investigated. DESIGN: A non-linear finite element model consisting of bony structures (tibia and femur), their articular cartilage layers, medial and lateral menisci and four primary ligaments (cruciates and collaterals) is utilized. BACKGROUND: Valgus and varus stresses are among the primary mechanisms of injury to knee ligaments. Several in vitro studies have investigated the role of ligaments in resisting such loads and on the way deficiency in either collateral may affect the response. METHODS: Cartilage layers are isotropic while menisci are non-homogeneous composite. The articulation of cartilage layers with each other and with the intervening menisci and the wrapping of the medial collateral ligament around the tibial edge are treated as large displacement frictionless contact problems. The non-linear elastostatic response of the joint at full extension is computed under varus-valgus moments applied to the femur with the tibia fixed. Cases simulating deficiency in collaterals and constraint on femoral axial rotation are also studied. RESULTS: The response is non-linear with large coupled axial rotations, internal in varus and external in valgus. In intact and collateral-deficient states, the joint shows varus or valgus openings so that the articulation occurs at one plateau only, medial in varus and lateral in valgus. Large tensile forces in cruciates in collateral-cut models generate higher compression penalty on the loaded plateau. CONCLUSIONS: Collaterals are the primary load-bearing structures; their absence would substantially increase primary laxities, coupled axial rotations, forces in cruciates, and articular contact forces. Good agreement with measurements is found. RELEVANCE: Detailed knowledge of joint biomechanics is essential in the diagnosis, prevention and treatment of observed disorders. Absence of collateral ligaments increases the loads in cruciates and contact stresses transmitted through cartilage layers and menisci, and thus places the affected components at more risk, especially when varus-valgus is accompanied by other modes of loading as well.

Experimental and finite element comparison of various fixation designs in combined loads.

The short- and long-term successes of tibial cementless implants depend on the initial fixation stability often provided by posts and screws. In this work, a metallic plate was fixed to a polyurethane block with either two bone screws, two smooth-surfaced posts, or two novel smooth-surfaced posts with adjustable inclinations. For this last case, inclinations of 0, 1.5, and 3 deg were considered following insertion. A load of 1031 N was eccentrically applied on the plate at an angle of approximately 14 deg, which resulted in a 1000 N axial compressive force and a 250 N shear force. The response was measured under static and repetitive loading up to 4000 cycles at 1 Hz. The measured results demonstrate subsidence under load, lift-off on the unloaded side, and horizontal translation of the plate specially at the loaded side. Fatigue loading increased the displacements, primarily during the first 100 cycles. Comparison of various fixation systems indicated that the plate with screw fixation was the stiffest with the least subsidence and liftoff. The increase in post inclination from 0 to 3 deg stiffened the plate by diminishing the liftoff. All fixation systems demonstrated deterioration under repetitive loads. In general, the finite element predictions of the experimental fixation systems were in agreement with measurements. The finite element analyses showed that porous coated posts (modeled with nonlinear interface friction with and without coupling) generated slightly less resistance to liftoff than smooth-surfaced posts. In the presence of porous coated posts, Coulomb friction greatly overestimated the rigidity by reducing the liftoff and subsidence to levels even smaller than those predicted for the design with screw fixation. The sequence of combined load application also influenced the predicted response. Finally, the finite element model incorporating measured interface friction and pull-out responses can be used for the analysis of cementless total joint replacement systems during the post-operation period.