Intracapsular pressure and loosening of hip prostheses. Preoperative measurements in 18 hips

Mechanically Induced Periprosthetic Osteolysis: A Systematic Review

BACKGROUND

Peri-prosthetic bone loss can result from chemical, biological, and mechanical factors. Mechanical stimulation via fluid pressure and flow at the bone-implant interface may be a significant cause. Evidence supporting mechanically induced osteolysis continues to grow, but there is no synthesis of published clinical and basic science data.

QUESTIONS/PURPOSES

We sought to review the literature on two questions: (1) What published evidence supports the concept of mechanically induced osteolysis? (2) What is the proposed mechanism of mechanically induced osteolysis, and does it differ from that of particle-induced osteolysis?

METHODS

A systematic review was performed of the PubMed and Web of Science databases. Additional relevant articles were recommended by the senior authors based on their expert opinion. Abstracts were reviewed and the manuscripts pertaining to the study questions were read in full. Studies showing support of mechanically induced osteolysis were quantified and findings summarized.

RESULTS

We identified 49 articles of experimental design supporting the hypothesis that mechanical stimulation of peri-prosthetic bone from fluid pressure and flow can induce osteolysis. While the molecular mechanisms may overlap with those implicated in particle-induced osteolysis, mechanically induced osteolysis appears to be mediated by distinct and parallel pathways.

CONCLUSIONS

The role of mechanical stimuli is increasingly recognized in the pathogenesis of peri-prosthetic osteolysis. Current research aims to elucidate the molecular mechanisms to better target therapeutic interventions.

Mechanical instability and titanium particles induce similar transcriptomic changes in a rat model for periprosthetic osteolysis and aseptic loosening

Wear debris particles released from prosthetic bearing surfaces and mechanical instability of implants are two main causes of periprosthetic osteolysis. While particle-induced loosening has been studied extensively, mechanisms through which mechanical factors lead to implant loosening have been less investigated. This study compares the transcriptional profiles associated with osteolysis in a rat model for aseptic loosening, induced by either mechanical instability or titanium particles. Rats were exposed to mechanical instability or titanium particles. After 15 min, 3, 48 or 120 h from start of the stimulation, gene expression changes in periprosthetic bone tissue was determined by microarray analysis. Microarray data were analyzed by PANTHER Gene List Analysis tool and Ingenuity Pathway Analysis (IPA). Both types of osteolytic stimulation led to gene regulation in comparison to unstimulated controls after 3, 48 or 120 h. However, when mechanical instability was compared to titanium particles, no gene showed a statistically significant difference (fold change ≥ ± 1.5 and adjusted p-value ≤ 0.05) at any time point. There was a remarkable similarity in numbers and functional classification of regulated genes. Pathway analysis showed several inflammatory pathways activated by both stimuli, including Acute Phase Response signaling, IL-6 signaling and Oncostatin M signaling. Quantitative PCR confirmed the changes in expression of key genes involved in osteolysis observed by global transcriptomics. Inflammatory mediators including interleukin (IL)-6, IL-1β, chemokine (C-C motif) ligand (CCL)2, prostaglandin-endoperoxide synthase (Ptgs)2 and leukemia inhibitory factor (LIF) showed strong upregulation, as assessed by both microarray and qPCR. By investigating genome-wide expression changes we show that, despite the different nature of mechanical implant instability and titanium particles, osteolysis seems to be induced through similar biological and signaling pathways in this rat model for aseptic loosening. Pathways associated to the innate inflammatory response appear to be a major driver for osteolysis. Our findings implicate early restriction of inflammation to be critical to prevent or mitigate osteolysis and aseptic loosening of orthopedic implants.

The implication of the osteolysis threshold and interfacial gaps on periprosthetic osteolysis in cementless total hip replacement

Osteolysis around joint replacements may develop due to migration of wear particles from the joint space into gaps between the interface bone and the implant where they can accumulate in high concentrations to cause tissue damage. Osteolysis may appear in various postoperative times and morphological shapes which can be generalized into linear and focal. However, there are no clear explanations on the causes of such variations. Patients' degree of sensitivity to polyethylene particles (osteolysis thresholds), the local particle concentration and the access route provided by the interface gaps have been described as determining factors. To study their effects, a 2D computational fluid dynamics model of the hip joint capsule in communication with an interfacial gap and the surrounding bone was employed. Particles were presented using a discrete phase model (DPM). High capsular fluid pressure was considered as the driving force for particle migration. Simulations were run for different osteolysis thresholds ranging from 5×10⁸ to 1×10¹² particle number per gram of tissue and fibrous tissue generation in osteolytic lesion due to particles was simulated for the equivalent of ten postoperative years. In patients less sensitive to polyethylene particles (higher threshold), osteolysis may be linear and occur along an interfacial gap in less than 5% of the interfacial tissue. Focal osteolysis is more likely to develop in patients with higher sensitivity to polyethylene particles at distal regions to an interfacial gaps where up to 80% of the interfacial tissue may be replaced by fibrous tissue. In these patients, signs of osteolysis may also develop earlier (third postoperative year) than those with less sensitivity who may show very minor signs even after ten years. This study shows the importance of patient sensitivity to wear particles, the role of interfacial gaps in relation to morphology and the onset of osteolysis. Consequently, it may explain the clinically observed variation in osteolysis development.

Release of zirconia nanoparticles at the metal stem-bone cement interface in implant loosening of total hip replacements

In a previous failure analysis performed on femoral components of cemented total hip replacements, we determined high volumes of abraded bone cement. Here, we describe the topography of the polished surface of polymethyl methacrylate (PMMA) bone cement containing zirconia radiopacifier, analyzed by scanning electron microscopy and vertical scanning interferometry. Zirconia spikes protruded about 300nm from the PMMA matrix, with pits of former crystal deposition measuring about 400nm in depth. We deduced that the characteristically mulberry-shaped agglomerates of zirconia crystals are ground and truncated into flat surfaces and finally torn out of the PMMA matrix. Additionally, evaluation of in vitro PMMA-on-PMMA articulation confirmed that crystal agglomerations of zirconia were exposed to grain pullout, fatigue, and abrasion. In great quantities, micron-sized PMMA wear and zirconia nanoparticles accumulate in the cement-bone interface and capsular tissues, thereby contributing to osteolysis. Dissemination of nanoparticles to distant lymph nodes and organs of storage has been reported. As sufficient information is lacking, foreign body reactions to accumulated nanosized zirconia in places of long-term storage should be investigated.

STATEMENT OF SIGNIFICANCE

The production of wear particles of PMMA bone cement in the interface to joint replacement devices, presents a local challenge. The presence of zirconia particles results in frustrated digestion attempts by macrophages, liberation of inflammatory mediators, and necrosis leading to aseptic inflammation and osteolyses. Attempts to minimize wear of articulating joints reduced the attention to the deterioration of cement cuffs. We therefore investigated polished surfaces of retrieved cuffs to demonstrate their morphology and to measure surface roughness. Industrially admixed agglomerates of the radiopacifier are abraded to micron and nano-meter sized particles. The dissemination of zirconia particles in the reticulo-endothelial system to storage organs is a possible burden. Research to replace the actual contrast media by non-particulate material deserves more attention.

Size of cup affects the anterior capsular distance in total hip arthroplasty, as measured with ultrasound

Background

Previously was found that sonography is a reliable method to measure a capsular distance in total hip arthroplasty hips. The aim of our current study was to investigate the relation between the implanted size of the cup and the anterior capsular distance, as measured with ultrasound one year after THA.

Methods

50 osteoarthritis (OA) patients operated on with total hip arthroplasty one year before were included in the study and the anterior capsular distance was measured sonographically. Patients were grouped with respect to cup size. The correlation between the implanted cup size and capsular distance was determined.

Results

The mean capsular distance in the whole group was 1.37 (SD 0.19) cm. The mean capsular distance in the group with small cups was 1.27 (SD 0.13) cm, in large cups it was 1.45 (SD 0.20) cm, p = 0.02. Spearman correlation analysis showed a statistically significant correlation between a greater capsular distance and the larger size of the cup (r = 0.5, p < 0.0001).

Conclusion

The greater capsular distance in successful THA hips is affected by cup size. We propose that this should be considered when evaluating sonography of the anterior capsular distance after THA.

Periprosthetic osteolysis after total ankle arthroplasty

BACKGROUND

Periprosthetic osteolysis in total ankle arthroplasty (TAA) is a substantial problem. We report the incidence and characteristics of periprosthetic osteolysis and its association with clinical outcomes after TAA using the HINTEGRA ankle system.

METHODS

Between May 2004 and April 2010, 126 primary TAA were performed on 115 patients. We excluded 27 ankles with a follow-up of less than 24 months; thus, 99 ankles in 90 patients with a mean follow-up of 40.8 (range, 24-89) months were included in the study. Pain and clinical outcomes were assessed using the visual analog scale and the American Orthopaedic Foot and Ankle Society score. Fluoroscopy was used for optimum visualization of the bone-implant interfaces on radiographs. Computed tomography (CT) was conducted on 25 ankles that exhibited progression of osteolysis.

RESULTS

Radiographs revealed that 37 of the 99 ankles showed radiologic evidence of osteolysis; of these, 10 demonstrated continuous progression over the study period. Helical CT scans were more accurate than radiographs for identifying and measuring periprosthetic osteolysis in TAA. None of the demographic parameters were substantially different between the 2 groups of subjects (with or without osteolysis). No major association was found between the presence of osteolysis and clinical and radiologic outcomes.

CONCLUSION

Osteolysis associated with TAA may indeed be common in the postoperative period. Although most of the osteolytic lesions observed here were relatively quiescent, these lesions raise concerns in contemporary TAA because of their incidence rate and the potential for later mechanical failure as compared to arthrodesis. Early diagnosis and careful evaluation of osteolysis may provide a clinical opportunity for limited revision surgery in ankles of impending prosthesis failure.

LEVEL OF EVIDENCE

Level IV, case series.

Osteolysis around total knee arthroplasty: a review of pathogenetic mechanisms

Aseptic loosening and other wear-related complications are some of the most frequent late reasons for revision of total knee arthroplasty (TKA). Periprosthetic osteolysis (PPOL) pre-dates aseptic loosening in many cases, indicating the clinical significance of this pathogenic mechanism. A variety of implant-, surgery- and host-related factors have been delineated to explain the development of PPOL. These factors influence the development of PPOL because of changes in mechanical stresses within the vicinity of the prosthetic device, excessive wear of the polyethylene liner, and joint fluid pressure and flow acting on the peri-implant bone. The process of aseptic loosening is initially governed by factors such as implant/limb alignment, device fixation quality and muscle coordination/strength. Later, large numbers of wear particles detached from TKA trigger and perpetuate particle disease, as highlighted by progressive growth of inflammatory/granulomatous tissue around the joint cavity. An increased accumulation of osteoclasts at the bone-implant interface, impairment of osteoblast function, mechanical stresses and increased production of joint fluid contribute to bone resorption and subsequent loosening of the implant. In addition, hypersensitivity and adverse reactions to metal debris may contribute to aseptic TKA failure, but should be determined more precisely. Patient activity level appears to be the most important factor when the long-term development of PPOL is considered. Surgical technique, implant design and material factors are the most important preventative factors, because they influence both the generation of wear debris and excessive mechanical stresses. New generations of bearing surfaces and designs for TKA should carefully address these important issues in extensive preclinical studies. Currently, there is little evidence that PPOL can be prevented by pharmacological intervention.

Emerging ideas: Instability-induced periprosthetic osteolysis is not dependent on the fibrous tissue interface

BACKGROUND

Stable initial fixation of a total joint arthroplasty implant is critical to avoid the risk of aseptic loosening and premature clinical failure. With implant motion, a fibrous tissue layer forms at the bone-implant interface, leading to implant migration and periprosthetic osteolysis. At the time of implant revision surgery, proresorptive signaling cytokines are expressed in the periimplant fibrous membrane. However, the exact role of this fibrous tissue in causing periprosthetic osteolysis attributable to instability remains unknown.

QUESTIONS/HYPOTHESES

We propose an alternative mechanism of periprosthetic osteolysis independent of the fibrous tissue layer, where pressurized fluid flow along the bone-implant interface activates mechanosensitive osteocytes in the periprosthetic bone, causing the release of proresorptive cytokines and subsequent osteoclast differentiation and osteolysis.

METHOD OF STUDY

An animal model for instability-induced osteolysis that mimics the periprosthetic bone-implant interface will be used. In this model, a fibrous tissue membrane is allowed to form in the periprosthetic zone, and pressurized fluid flow transmitted through this membrane reliably creates osteolytic lesions in the periprosthetic bone. In this study, half of the rats will have the fibrous tissue present, while the other half will not. We will determine whether the fibrous tissue membrane is essential for the release of proosteoclastic cytokines, leading to osteoclast differentiation and periprosthetic bone loss, by measuring the volume of bone resorption and presence of proresorptive cytokines at the bone-implant interface.

SIGNIFICANCE

We will determine whether the fibrous tissue membrane is crucial for osteoclastogenic signaling in the setting of periimplant osteolysis. In the future, this will allow us to test therapeutic interventions, such as specific cytokine inhibitors or alterations in implant design, which may translate into new, clinically relevant strategies to prevent osteolysis.

RANKL in the osteolysis of AES total ankle replacement implants

Peri-implant tissue reactions in failed total ankle replacement (TAR) are characterized by early developing peri-implant osteolysis. The hypothesis of the study was that this reaction is mediated by receptor activator of nuclear factor kappa B ligand (RANKL). Samples of peri-prosthetic tissues from failed TAR implants were stained for macrophages, RANKL, its receptor RANK and osteoprotegerin (OPG), and compared to control samples. The failed TAR implants were surrounded by implant capsule, synovial lining-like interface membrane or necrotic tissues. Infiltrating scavenger receptor I positive CD163(+) macrophages were frequent, in particular around necrotic soft tissues or bone sequestrate, and possibly in part formed due to ischemia and mechanical factors. In contrast, implant-derived wear debris was scanty. Still many RANK(+) macrophages were often seen in close contact with RANKL(+) mesenchymal cells, whereas OPG was mostly located at a distance in vascular endothelial cells. Foreign body giant cells were frequent. RANKL seems to stimulate locally accumulated CD163(+) RANK-expressing cells to fusion, which leads to the local formation of multinuclear foreign body giant cells (and probably of osteoclasts). Therefore, peri-implant osteolysis in early TAR implant failure seems to be caused by the RANKL-driven chronic foreign body inflammation directed against, not implant-derived particles, but against necrotic autologous tissues.

Do capsular pressure and implant motion interact to cause high pressure in the periprosthetic bone in total hip replacement?

When there is a debonding at the bone-implant interface, the difference in stiffness between the implant and the bone can result in micromotion, allowing existing gaps to open further or new gaps to be created during physiological loading. It has been suggested that periprosthetic fluid flow and high pressure may play an important role in osteolysis development in the proximity of these gaps. To explain this phenomenon, the concepts of "effective joint space" and "pumping stem" have been cited in many studies. However, there is no clear understanding of the factors causing, or contributing to, these mechanisms. It is likely that capsular pressure, gap dimensions, and micromotion of the gap during cyclic loading of an implant can play a defining role in inducing periprosthetic flow. In order to obtain a better understanding of the main influences on periprosthetic flows and the development of osteolysis, steady state and transient 2D computational fluid dynamic simulations were performed for the joint capsule of the lateral side of a stem-femur system, and a gap in communication with the capsule and the surrounding bone. It was shown that high capsular pressure may be the main driving force for high fluid pressure and flow in the bone surrounding the gap, while micromotion of only very long and narrow gaps can cause significant pressure and flow in the bone. At low capsular pressure, micromotion induced large flows in the gap region; however, the flow in the bone tissue was almost unaffected. The results also revealed the existence of high velocity spikes in the bone region at the bottom of the gap. These velocity spikes can exert excessive fluid shear stress on the bone cells and disturb the local biological balance of the surrounding interstitial fluid which can result in osteolysis development. High capsular pressure was observed to be the main cause of these velocity spikes whereas, at low capsular pressure, gap micromotion of only very long and narrow gaps generated significant velocity spikes in the bone at the bottom of the gaps.

Comparison of flanged and unflanged acetabular cup design. An experimental study using ceramic and cadaveric acetabuli

BACKGROUND AND PURPOSE

Adequate depth of cement penetration and cement mantle thickness is important for the durability of cemented cups. A flanged cup, as opposed to unflanged, has been suggested to give a more uniform cement mantle and superior cement pressurization, thus improving the depth of cement penetration. This hypothesis was tested experimentally.

MATERIALS AND METHODS

The same cup design with and without flange (both without cement spacers) was investigated regarding intraacetabular pressure, cement mantle thickness, and depth of cement penetration. With machine control, the cups were inserted into open-pore ceramic acetabular models (10 flanged, 10 unflanged) and into paired cadaver acetabuli (10 flanged, 10 unflanged) with prior pressurization of the cement.

RESULTS

No differences in intraacetabular pressures during cup insertion were found, but unflanged cups tended to migrate more towards the acetabular pole. Flanged cups resulted in thicker cement mantles because of less bottoming out, whereas no differences in cement penetration into the bone were observed.

INTERPRETATION

Flanged cups do not generate higher cementation pressure or better cement penetration than unflanged cups. A possible advantage of the flange, however, may be to protect the cup from bottoming out, and there is possibly better closure of the periphery around the cup, sealing off the cement-bone interface.

Fluid pressure and flow as a cause of bone resorption

BACKGROUND

Unstable implants in bone become surrounded by an osteolytic zone. This is seen around loose screws, for example, but may also contribute to prosthetic loosening. Previous animal studies have shown that such zones can be induced by fluctuations in fluid pressure or flow, caused by implant instability.

METHOD

To understand the roles of pressure and flow, we describe the 3-dimensional distribution of osteolytic lesions in response to fluid pressure and flow in a previously reported rat model of aseptic loosening. 50 rats had a piston inserted in the proximal tibia, designed to produce 20 local spikes in fluid pressure of a clinically relevant magnitude (700 mmHg) twice a day. The spikes lasted for about 0.3 seconds. After 2 weeks, the pressure was measured in vivo, and the osteolytic lesions induced were studied using micro-CT scans.

RESULTS

Most bone resorption occurred at pre-existing cavities within the bone in the periphery around the pressurized region, and not under the piston. This region is likely to have a higher fluid flow and less pressure than the area just beneath the piston. The velocity of fluid flow was estimated to be very high (roughly 20 mm/s).

INTERPRETATION

The localization of the resorptive lesions suggests that high-velocity fluid flow is important for bone resorption induced by instability.

Intracapsular pressure and interleukin-1beta cytokine in hips with acetabular dysplasia

BACKGROUND AND PURPOSE

Several studies have demonstrated an increased intracapsular pressure in several hip disorders such as septic arthritis, synovitis, and trauma. We therefore measured the intracapsular pressure in different positions in early dysplasic hips and its relation to the concentration of interleukin-1beta (IL- 1beta), the volume of joint fluid, and the clinical and radiographic findings before a periacetabular osteotomy.

METHODS

12 female patients (12 hips, mean age 35 (18-52)) with hip dysplasia were investigated. The intracapsular pressure was recorded and we investigated possible correlations with the Harris hip score, the Tönnis scale, radiographic findings, the volume of joint fluid, and the concentration of IL-1beta.

RESULTS

An increased intracapsular pressure was noted, especially in flexion or extension with internal rotation. We found positive correlations between the intracapsular pressure and both the volume of joint fluid and the concentration of IL-1beta.

INTERPRETATION

Increased intracapsular pressure varied with different positions, indicating the presence of synovitis resulting from early osteoarthritis in dysplastic hips. Positive correlations between the pressure and both the concentration of IL-1beta and the volume of joint fluid suggest that the inflammatory cytokines produced by the synovial membrane as a consequence of mechanical instability of the hip joint may be of importance for the initiation and/or development of osteoarthritis in dysplastic hips.

Tenascin‐C levels in pseudosynovial fluid of loose hip prostheses

OBJECTIVE

Aseptic loosening is one of the most important problems that can occur after total hip arthroplasty (THA). In this study, we analysed levels of large tenascin-C (TN-C) variants and compared them in pseudosynovial fluid from patients with aseptic loosening after THA with those in synovial fluid from patients undergoing primary THA (control).

METHODS

Pseudosynovial fluid samples (n = 24) were obtained by aspiration at the time of revision THA performed due to aseptic loosening. Synovial fluid samples (n = 12) were obtained by aspiration at the time of primary THA. Expression of TN-C splice variants was examined using immunoblotting. TN-C levels were measured using an enzyme-linked immunosorbent assay (ELISA) system that we developed previously.

RESULTS

Western blotting showed the presence of large TN-C variants in pseudosynovial fluid of artificial joints with loosening. TN-C levels were approximately three times higher in pseudosynovial fluid of loose artificial joints (median 151.9 ng/mL) than in synovial fluid controls (median 50.1 ng/mL) (p = 0.035).

CONCLUSION

Levels of TN-C including large variant subunits are elevated in pseudosynovial fluid of loose artificial joints, indicating that TN-C is a useful novel biochemical marker of loose hip prostheses.

Femoral osteolysis around the unrevised stem during isolated acetabular revision

Many surgeons treat progressive femoral osteolysis in association with a well-fixed stem with bone grafting but in uncontained proximal defects the graft could get into the joint, raising a question regarding whether the osteolysis can be treated by simple débridement without bone grafting. We investigated whether the curetted proximal osteolysis around an unrevised femoral component progressed in size and whether this lesion would have a deleterious effect on fixation of the femoral component in patients with isolated acetabular revision. We prospectively followed 21 patients (24 hips) who underwent acetabular revision and curetting of femoral osteolysis. The minimum followup was 3 years (mean, 4.3 years; range, 3-7.4 years). By the latest followup, no hips had major progression of the osteolytic defect through the followup period and none had any new osteolytic lesions. All hips were judged stable and to have well-fixed acetabular cups and femoral stems. Provided a femoral component is bone ingrown with osseointegration sufficient to provide long-term stability, the osteolytic defect is in the proximal aspect of the femur, and the defect is uncontained, simple curettage may preserve femoral implant stability and may prevent progression of osteolysis to another Gruen zone for at least 3 to 7 years.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

In vitro influence of stem surface finish and mantle conformity on pressure generation in cemented hip arthroplasty

BACKGROUND AND PURPOSE

Under physiological loads, debonded cemented femoral stems have been shown to move within their cement mantle and generate a fluid pump that may facilitate peri-prosthetic osteolysis by pressurizing fluid and circulating wear debris. The long-term physiological loading of rough and polished tapered stems in vitro has shown differences in performance, with greater interface pressures generated by the rough stems. In this study we investigated the individual effects of stem surface finish, degree of mantle wear, and mode of loading on the stem pump mechanism.

METHOD

Rough and polished stems were loaded under different regimes in artificially worn cement mantles that permitted either 2 or 5 degrees of rotational stem movement, and the interface pressures were compared.

RESULTS

The pressures generated by the rough and polished stems were similar in either type of mantle. The pattern of pressure generation in the 2-degree mantles was similar to the pressures generated by rough stems after long-term loading, but the high posterior wall pressures fell and the tip pressures increased in the 5-degree mantles. The torsional loads were principal drivers of pressure generation in all areas of the interface other than the implant tip, where axial loading predominated.

INTERPRETATION

Femoral stems with rotational instability under cyclic torsional loads generate elevated interface fluid pressures and flows independently of stem surface finish. The rough surface finish is only important in creating this instability in tapered stems.

Effects of hip joint position and intra-capsular volume on hip joint intra-capsular pressure: a human cadaveric model

BACKGROUND

Increase in hip intra-capsular pressure has been implicated in various hip pathologies, such as avascular necrosis complicating undisplaced femoral neck fracture. Our study aimed at documenting the relationship between intra-capsular volume and pressure in various hip positions.

METHODS

Fifty-two cadaveric hips were studied. An electronic pressure-monitoring catheter recorded the intra-capsular hip pressure after each instillation of 2 ml of normal saline and in six hip positions.

RESULTS

In neutral hip position, the control position for investigation, intra-capsular pressure remained unchanged when its content was below 10 ml. Thereafter, it increased exponentially. When the intra-capsular volume was 12 ml, full abduction produced a 2.1-fold increase (p = 0.028) of the intra-capsular hip joint pressure; full external rotation and full internal rotation increased the pressure by at least 4-fold (p < 0.001). Conversely, there was a 19% (p = 0.046) and 81% (p = 0.021) decrease in intra-capsular hip joint pressure with flexion of the hip joint to 90-degree and 45-degree, respectively.

CONCLUSION

Intra-capsular pressure increases with its volume, but with a wide variation with different positions. It would be appropriate to recommend that hips with haemarthrosis or effusion should be positioned in 45-degree flexion.

Once-weekly oral medication with alendronate does not prevent migration of knee prostheses: A double-blind randomized RSA study

BACKGROUND AND PURPOSE

Early migration of joint replacements is an effect of poor fixation and can predict late loosening. By reducing the bone resorption after implantation of a joint replacement, it should be possible to enhance the initial fixation of the implant. We studied the effect of once-weekly treatment with alendronate after knee replacement.

PATIENTS AND METHODS

We recruited 60 patients (60 knees) with gonarthrosis who were scheduled for a total knee replacement. They were operated on with identical implants and uncemented fixation. 30 patients were treated with a bisphosphonate (alendronate) and 30 patients underwent placebo treatment. The treatment started postoperatively and continued on a weekly basis for 6 months. The fixation of the implants was measured with repeated radiostereometry for 2 years.

RESULTS

There was no difference in migration of implants between the two groups.

CONCLUSION

With uncemented fixation of knee implants, no benefit of once-weekly treatment with alendronate, starting postoperatively, could be seen during a 2-year follow-up period.

Effect of femoral head size on polyethylene wear and synovitis after total hip arthroplasty: a sonographic and radiographic study of 39 patients

BACKGROUND AND PURPOSE

The role of synovitis and high fluid pressure in the loosening process after total hip arthroplasty has gained increasing attention. We investigated the correlation between head size, polyethylene wear, and capsular distention.

PATIENTS AND METHODS

We analyzed 39 unrevised, radiographically stable hips that had been operated with 28 or 32 mm femoral heads 10 years earlier because of osteoarthritis. We evaluated radiographic signs of loosening, linear and volumetric polyethylene wear, body mass index, activity level, and age. Sonographic examination was performed to measure capsular distance i.e. the distance between the prosthetic femoral neck and the anterior capsule.

RESULTS

Linear wear was 0.09 mm/year and 0.18 mm/year in the 28 mm and 32 mm groups, respectively (p < 0.001). The volumetric wear was 51 mm(3)/year and 136 mm(3)/year (p < 0.001) and the capsular distance was 13 mm and 17 mm, respectively (p < 0.001). There was a correlation between linear wear (r = 0.54), volumetric wear (r = 0.62), and capsular distance (p < 0.001).

INTERPRETATION

Wear was greater for the larger femoral head and was correlated to capsular distension.

High levels of substance P and CGRP in pseudosynovial fluid from patients with aseptic loosening of their hip prosthesis

BACKGROUND

Aseptic loosening is the most important complication after total hip arthroplasty (THA). The nervous system has been implicated in the etiology and pathogenesis of joint diseases.

METHODS

We compared levels of substance P (SP) and calcitonin gene-related peptide (CGRP) in pseudosynovial fluid from patients with aseptic loosening after THA with those in synovial fluid from patients undergoing primary THA for osteoarthritis, who served as controls. Levels of SP and CGRP were measured using an enzyme immunoassay.

RESULTS

We found that SP and CGRP levels were significantly higher in the pseudosynovial fluid of loose artificial joints than in the synovial fluid of controls.

INTERPRETATION

SP and CGRP may have a role in aseptic loosening.

Absence of lymphatics at the bone-implant interface: implications for periprosthetic osteolysis

BACKGROUND

Wear particles, found at the bone-implant interface surrounding a loose prosthesis, are commonly phagocytosed by macrophages. Wear particles and wear particle-containing macrophages are also found in regional lymph nodes draining arthroplasty tissues. The means by which wear particles are transported from arthroplasty tissues to lymph nodes is uncertain, as the presence or absence of lymphatic vessels in periprosthetic tissues has not been established.

METHODS

We determined immunophenotypic expression of LYVE-1 and podoplanin, two highly specific lymphatic endothelial cell markers, in the hip arthroplasty pseudocapsule surrounding the false joint and the bone-implant interface of the femoral and acetabular pseu-domembrane.

RESULTS

LYVE-1+/podoplanin+ lymphatic vessels were not identified in the pseudomembrane but were found in the pseudocapsule. Normal bone did not contain lymphatic vessels.

INTERPRETATION

Our findings suggest that the wear particles shed at the bone-implant interface are not transported to draining lymph nodes by lymphatics directly from the pseudomembrane, but via the pseudocapsule. The absence of a lymphatic clearance mechanism may contribute to accumulation of wear particles at the bone-implant interface and promote periprosthetic osteolysis through stimulation of osteoclast formation and activity.

Does bone quality predict loosening of cemented total hip replacements?

We matched 78 patients with a loose cemented Charnley Elite Plus total hip replacement (THR) by age, gender, race, prosthesis and time from surgery with 49 patients with a well-fixed stable hip replacement, to determine if poor bone quality predisposes to loosening. Clinical, radiological, biomechanical and bone mineral density indicators of bone quality were assessed.

Patients with loose replacements had more pain, were more likely to have presented with atrophic arthritis and to have a history of fragility fracture, narrower femoral cortices and lower peri-prosthetic or lumbar spine bone mineral density (all t-test, p < 0.01). They also tended to be smokers (chi-squared test, p = 0.08). Vitamin-D deficiency was common, but not significantly different between the two groups (t-test, p = 0.31)

In this series of cemented hip replacements performed between 1994 and 1998, aseptic loosening was associated with poor bone quality. Patients with a THR should be screened for osteoporosis and have regular radiological surveillance.

Lymphangiogenesis in the bone-implant interface of orthopedic implants: importance and consequence

The lymphatic system plays an essential physiological role in homeostasis, interstitial fluid composition, and immunity while impaired lymphatic function has been implicated in a number of pathological conditions, including arthritis and delayed wound healing. This study investigated lymphatic capillary growth and lymphangiogenesis pathways in the bone-implant interface from patients with aseptically loosened prosthetic joints. The newly developed lymphatic specific marker, podoplanin, has enabled the first demonstration of lymphatic capillaries in peri-prosthetic tissues (60% of cases contained podoplanin positive vessels). The pro-lymphangiogenic factor (VEGF-C) and its receptor VEGFR-3 showed high level of expression in these tissues, (often in areas of high levels of wear debris). However despite the upregulation of the lymphangiogenesis pathway by a VEGF-C/VEGFR-3-mediated mechanism, there were relatively few podoplanin positive lymphatic vessels in the bone-implant interface (3.4% of total vessels). This may have important pathological consequences in terms of perpetuating inflammation and edema by inhibiting the removal of macromolecules, cells, and interstitial fluid. The identification of lymphatic vessels with internalized polyethylene wear particles provides evidence of this route of wear debris transportation to distal sites. This paper highlights the importance of lymphatic vessels in the maintenance of local and distal inflammatory responses to prosthetic wear particles.

RSA-measured inducible micromotion and interface modeling with finite element methods

Osteolysis is the main cause of aseptic loosening and stem failure. The mechanism that leads to osteolysis is poorly understood; pressure generation caused by reversible stem micromotion may play an important role. We aimed to determine whether dynamically inducible micromotion occurs in vivo at the prosthesis-cement interface and to use these data to develop and confirm a finite element representation of this interface. Dynamically inducible micromotion was measured using radiostereometric analysis in 21 hips implanted with an Exeter stem, at 3 months and 12 months postoperatively, by changing loading from double-leg stance to single-leg stance. Dynamically inducible micromotion occurred at 3 and 12 months; similar micromotion was observed at both time points. At 3 months the head of the stem was displaced posteriorly (0.10 +/- 0.16 mm) and inferiorly (0.08 +/- 0.12 mm) on loading. A Coulomb friction nonbonded representation of the stem-cement interface was used to fit the clinically measured dynamically inducible micromotion. The final finite element model predicted gap opening and closing between the implant and the mantle. This may be a mechanism for generating pressure and distributing wear debris, which are believed to important contributors to failure.

Aseptic loosening, not only a question of wear: a review of different theories

Today, aseptic loosening is the most common cause of revision of major arthroplasties. Aseptic loosening accounts for more than two-thirds of hip revisions and almost one-half of knee revisions in Sweden. Several theories on the cause of aseptic loosening have been proposed. Most of these theories, however, are based on empiric observations, experimental animal models or anecdotal cases. In this review, we discuss the most common theories concerning aseptic loosening. It emerges from this review that aseptic loosening has a multifactorial etiology and cannot be explained by a single theory.

Cyclic hydrostatic pressure and particles increase synthesis of 1,25-dihydroxyvitamin D3 by human macrophages in vitro

1,25-Dihydroxyvitamin D(3) has a pivotal role in bone resorption and osteoclast activity. As activated macrophages are known to synthesise 1,25-dihydroxyvitamin D(3), this study examined whether pressure modulated its synthesis. Pressure and particles have been shown to increase synthesis of pro-resorptive cytokines and other factors by cultured macrophages. Human peripheral blood macrophages were isolated, cultured and exposed to pressure (similar to that found in the human joint) and/or particles. Synthesis of 1,25-dihydroxyvitamin D(3) by macrophages was assayed using high pressure liquid chromatography and in situ hybridization. Synthesis of 1,25-dihydroxyvitamin D(3) but not 24,25-dihydroxyvitamin D(3) was increased in macrophages under pressure. In situ hybridization demonstrated an increase in 1alpha-hydroxylase expression in response to pressure or particles and simultaneous exposure to both stimuli generated higher expression of 1alpha-hydroxylase. In conclusion, this is the first study to demonstrate that mechanical loading, in the form of pressure, stimulates 1,25-dihydroxyvitamin D(3) synthesis in human macrophages. These findings have implications for the in vivo situation, as they suggest that 1,25-dihydroxyvitamin D(3) could be one factor stimulating osteoclastic bone resorption in pathologies, such as arthritis or implant loosening, where intra-articular or intra-osseous pressure is raised or where wear particles interact with macrophages.

Age of donor alters the effect of cyclic hydrostatic pressure on production by human macrophages and osteoblasts of sRANKL, OPG and RANK

Background

Cyclic hydrostatic pressure within bone has been proposed both as a stimulus of aseptic implant loosening and associated bone resorption and of bone formation. We showed previously that cyclical hydrostatic pressure influenced macrophage synthesis of several factors linked to osteoclastogenesis. The osteoprotegerin/soluble receptor activator of NF-kappa β ligand /receptor activator of NF-kappa β (OPG/ RANKL/ RANK) triumvirate has been implicated in control of bone resorption under various circumstances. We studied whether cyclical pressure might affect bone turnover via effects on OPG/ sRANKL/ RANK.

Methods

In this study, cultures of human osteoblasts or macrophages (supplemented with osteoclastogenic factors) or co-cultures of macrophages and osteoblasts (from the same donor), were subjected to cyclic hydrostatic pressure. Secretion of OPG and sRANKL was assayed in the culture media and the cells were stained for RANK and osteoclast markers. Data were analysed by nonparametric statistics.

Results

In co-cultures of macrophages and osteoblasts, pressure modulated secretion of sRANKL or OPG in a variable manner. Examination of the OPG:sRANKL ratio in co cultures without pressurisation showed that the ratio was greater in donors <70 years at the time of operation (p < 0.05 Mann Whitney U) than it was in patients >70 years. However, with pressure the difference in the OPG:sRANKL ratios between young and old donors was not significant. It was striking that in some patients the OPG:sRANKL ratio increased with pressure whereas in some it decreased. The tendency was for the ratio to decrease with pressure in patients younger than 70 years, and increase in patients ≥ 70 years (Fishers exact p < 0.01).

Cultures of osteoblasts alone showed a significant increase in both sRANKL and OPG with pressure, and again there was a decrease in the ratio of OPG:RANKL. Secretion of sRANKL by cultures of macrophages alone was not modulated by pressure. Only sRANKL was assayed in this study, but transmembrane RANKL may also be important in this system. Macrophages subjected to pressure (both alone and in co-culture) stained more strongly for RANK on immunohistochemstry than non-pressurized controls and 1,25-dihydroxyvitamin D₃ (1,25 D₃) further increased this. Immunocytochemical staining also demonstrated that more cells in pressurized co-cultures exhibited osteoclast markers (tartrate-resistant acid phosphatase, vitronectin receptor and multinuclearity) than did unpressurized controls.

Conclusion

These data show that in co-cultures of osteoblasts and macrophages the ratio of OPG : sRANKL was decreased by pressure in younger patients but increased in older patients. As falls in this ratio promote bone resorption, this finding may be important in explaining the relatively high incidence of osteolysis around orthopaedic implants in young patients. The finding that secretion of OPG and sRANKL by osteoblasts in monoculture was sensitive to hydrostatic pressure, and that hydrostatic pressure stimulated the differentiation of macrophages into cells exhibiting osteoclast markers indicates that both osteoblasts and preosteoclasts are sensitive to cyclic pressure. However, the effects of pressure on cocultures were not simply additive and coculture appears useful to examine the interaction of these cell types.

These findings have implications for future therapies for aseptic loosening and for the development of tests to predict the development of this condition.

An in-vitro investigation into the cement pressurization achieved during insertion of four different femoral stems

Adequate cement pressurization during stem insertion improves the interdigitation of cement into bone. This increases the strength of the cement-bone interface, thus contributing to the reduction of the incidence of aseptic loosening, the commonest cause of revision surgery. This in-vitro study compared the cement pressurization achieved during insertion of four different stems of equivalent sizes: the Elite Plus (DePuy, UK), C-Stem (DePuy, UK), Exeter (Stryker, USA), and CPS-Plus (Plus Orthopedics, Switzerland). The maximum pressures attained at the time of stem insertion were recorded at proximal, mid and distal stem levels. The Elite Plus generated significantly higher distal pressures than the other stems. The CPS-Plus generated significantly greater proximal cement pressures than the Elite Plus, C-Stem, and Exeter prostheses. The triple taper of the C-Stem increased the cement pressurization medial to the stem. The stem shape and the presence or absence of a proximal stem centralizer affect cement pressurization. The presence of a proximal stem centralizer, a large stem volume, and a lateral-medial taper are all factors associated with increased cement pressurization during stem insertion.

Mechanisms for pumping fluid through cementless acetabular components with holes

The pumping of fluid and polyethylene wear debris from the joint space to the retroacetabular bone is implicated in the pathogenesis of osteolysis. Three possible mechanisms for this pumping: pressure gradients, diaphragm pumping, and piston pumping were studied in vitro in a laboratory model. The simulated activities of rising from a chair and climbing stairs produced high-pressure gradients and high angles of loading that could pump fluid through the apical hole to the retroacetabular bone. A noncongruent liner acted as a diaphragm pump, producing pressures 6 times higher than that seen with a congruent liner. Pistoning motion of the liner produced pressures 8 times higher than when no pistoning occurs. These pumping mechanisms could be mitigated by the use of acetabular components without holes.

An in vitro model for fluid pressurization of screw holes in metal-backed total joint components

Fluid pressure may stimulate osteolysis near screw holes in joint arthroplasty components. We developed a generalized in vitro model of a polyethylene liner and metal backing with a screw hole to investigate whether implant design factors influence local fluid pressure. We observed an order of magnitude of variation in the peak screw hole pressure (from 16.0 and 163 kPa) under clinically relevant loading conditions. Of the implant factors investigated, the surface finish of the metallic base plate had the greatest effect on peak screw hole fluid pressures; the thickness of the polyethylene liner, as well as the gap between the liner and the base plate, were also significant design variables. Our data suggest that unpolished metal base plates, thick polyethylene liners, and tight conformity between the liner and the metal base plate will all contribute to significantly reduced peak screw hole fluid pressures in joint arthroplasty.

Particle migration and gap healing around trabecular metal implants

Bone on-growth and peri-implant migration of polyethylene particles were studied in an experimental setting using trabecular metal and solid metal implants. Cylindrical implants of trabecular tantalum metal and solid titanium alloy implants with a glass bead blasted surface were inserted either in an exact surgical fit or with a peri-implant gap into a canine knee joint. We used a randomised paired design. Polyethylene particles were injected into the knee joint. In both types of surgical fit we found that the trabecular metal implants had superior bone ongrowth in comparison with solid metal implants (exact fit: 23% vs. 7% [p=0.02], peri-implant gap: 13% vs. 0% [p=0.02]. The number of peri-implant polyethylene particles was significantly reduced around the trabecular metal implants with a peri-implant gap compared with solid implants.

Expression of inflammatory cytokines, RANKL and OPG induced by titanium, cobalt-chromium and polyethylene particles

Bone resorption is regulated by cytokines such as tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1beta) and by the balance of a receptor activator of nuclear factor-kappaB ligand (RANKL) and osteoprotegerin (OPG). The aim of this study was to investigate the mechanism of particle-induced osteolysis in murine calvariae by assessing the extent of osteolysis and the expression of inflammatory cytokines, RANKL and OPG after implantation of metal and polyethylene particles. The murine calvariae implanted with Ti6Al4V, CoCr or high-density polyethylene (HDP) particles showed significantly more extensive osteolysis and elevated levels of inflammatory cytokines. The ratio between RANKL and OPG was high in the mice implanted with Ti6Al4V and HDP particles, but not in the mice implanted with CoCr particles. These observations suggested that CoCr particle-induced osteoclastogenesis may be caused directly by inflammatory cytokines rather than by the RANKL-RANK pathway. There might be different mechanisms at work in particle-induced osteolysis between Ti6Al4V, HDP and CoCr.

Pseudosynovial fluid from loosened total hip prosthesis induces osteoclast formation

Interface tissue between the bone and loosening total hip implant is acidic and highly osteolytic. It is characterized by the formation of cathepsin K positive foreign body giant cells. Similar structures to those found in the normal joint surround the artificial hip joint. Cells in synovial membrane of the artificial hip generate synovial fluid that is called pseudosynovial fluid. Interface tissue fibroblasts are able to produce receptor activator of NF-kappaB ligand (RANKL), which can induce osteoclastogenesis during the loosening process. Western blot analysis indicated that RANKL is present in the pseudosynovial fluid. Pseudosynovial fluid induced cultured peripheral blood mononuclear cells to form multinuclear TRAP positive giant cells. In the presence of osteoprotegerin, the soluble RANKL decoy receptor, the number of TRAP positive multinuclear cells was reduced to half (p < 0.05). The multinuclear cells induced with pseudosynovial fluid contained active cathepsin K protein and were capable of bone matrix resorption in vitro. The cells were shown to express osteoclast phenotype markers, such as mRNA for cathepsin K, TRAP, and calcitonin receptor. It is therefore apparent that pseudosynovial fluid from patients with aseptic loosening of total hip prosthesis contains a potent osteoclastogenic factor RANKL that further suggests a favorable environment for osteoclast formation in the peri-implant tissues. It is thus concluded that suppression of RANKL activity may be beneficial in terms of increasing the lifetime of total hip prostheses.

Effect of cyclic mechanical stretch and titanium particles on prostaglandin E2 production by human macrophages in vitro

Early implant instability has been proposed as a critical factor in the onset and progression of aseptic loosening and periprosthetic osteolysis in total joint arthroplasties. Previous in vitro studies have reported that macrophages stimulated with cyclic mechanical strain release inflammatory mediators. Little is known, however, about the response of these cells to mechanical strain with particles, which is often a component of the physical environment of the cell. We therefore studied the production of prostaglandin E(2) (PGE(2)), an important mediator in aseptic loosening and periprosthetic osteolysis in total joint arthroplasties, for human macrophages treated with mechanical stretch alone, titanium particles alone, and mechanical stretch and particles combined. A combination of mechanical stretch and titanium particles resulted in a statistically synergistic elevation of levels of PGE(2) compared with the levels found with either stretch or particles alone. Exposure of human macrophages to mechanical stretch with particles upregulated the expression of cyclooxygenase (COX)-2 mRNA but not COX-1 mRNA, this expression resulting in a 97-fold increase in PGE(2) production compared to the nonstimulated cells. The current study is the first to investigate the effects of mechanical stretch with particles on cultured macrophages and include an investigation of the time course of PGE(2) production and COX-2 mRNA expression. Our results suggest that, while mechanical strain may be one of the primary factors responsible for macrophage activation and periprosthetic osteolysis, mechanical strain with particles load may contribute significantly to the osteolytic potential of macrophages in vitro. The synergistic effect observed between mechanical stretch and particles could accelerate implant loosening and implies that reduction in either cyclic mechanical strain or wear debris load would lead to a reduction of osteolysis.

Topical, single dose bisphosphonate treatment reduced bone resorption in a rat model for prosthetic loosening

Fluid pressure, instability or particles have been suggested to cause peri-prosthetic bone resorption. High intracapsular pressures have been reported in hip joints with loose prosthetic components, and oscillating fluid pressure has been shown to cause dramatic bone resorption in animal models. Resorption can be reduced by systemic bisphosphonate treatment in rat models with oscillating fluid pressure, but this has required higher doses than needed to inhibit normal remodelling. Bisphosphonates have high affinity to bone mineral. Topical application of the drug is therefore feasible. We used a previously described rat model where oscillating fluid pressure causes bone resorption. Before pressurization, a 1 mg/ml solution of alendronate was applied onto the bone surface for 1 min, after which excess bisphosphonate was rinsed away. Bone resorption was measured on histological slides as soft tissue area at the interface. Rats treated with topical alendronate had soft tissue areas reduced by half. Topical bisphosphonate treatment before cementing a joint implant could possibly reduce the risk of later loosening.

The pumping of fluid in cementless cups with holes

Ten patients who were scheduled for revision for pelvic osteolysis were studied. All had bone-ingrown metal-backed cups with holes and polyethylene liners. Pressures were measured in the osteolytic lesion and in the hip joint while applying cyclic forces across the artificial joint. In 4 cases with lesions that were fully contained by bone, loading of the hip produced a pressure wave in the osteolytic lesion. Cyclic forces, such as those that occur in normal gait, can act on the polyethylene liner, the metal shell, and the supporting bone to pump fluid in the retroacetabular osteolytic lesion. This pumping action may contribute to the pathogenesis of osteolysis by the mechanisms of fluid pressure, fluid flow, or the transportation of wear particles.

Fate of cementless acetabular components retained during revision total hip arthroplasty

BACKGROUND

Removal of a well-fixed cementless acetabular component can result in increased operative time and postoperative morbidity. The objectives of this retrospective study were to determine whether retention of a well-fixed acetabular component at the time of isolated femoral revision was compatible with long-term socket survival.

METHODS

The records of eighty-three consecutive patients (ninety hips) in whom a well-fixed cementless socket had been retained during revision of a femoral component were reviewed. The mean age of the patients was 48.7 years at the time of the primary arthroplasty and 54.1 years at the time of femoral revision. The radiographic analysis was based on anteroposterior radiographs and was performed by a single independent reviewer. The intraoperative criterion for stability of the socket was the absence of movement at the bone-implant interface during the application of direct pressure to the edges of the socket in four quadrants with use of a metallic pusher.

RESULTS

At the time of the isolated femoral revision, no socket demonstrated a radiolucent line measuring >1 mm in any two zones and forty of the ninety hips had periacetabular osteolysis. The mean size of the osteolytic lesions was 5.71 cm(2) (range, 0.4 to 24.2 cm(2)), and twenty-eight of the forty hips underwent bone-grafting. The mean duration of follow-up was 9.7 years after the isolated femoral revision and 14.9 years after the primary arthroplasty. Five acetabular sockets were revised at a mean of 6.8 years after the femoral revision. Only one of these sockets had failed because of aseptic loosening. With revision of the acetabular component for any reason as the end point, the survival rate was 98.7% at five years and 93.5% at ten years after the femoral revision and 100% at ten years and 93.9% at fifteen years after the primary arthroplasty. No hip showed recurrence or expansion of periacetabular osteolysis. The prevalence of dislocation was 16% (fourteen of ninety).

CONCLUSIONS

Revision of a stable, cementless acetabular component solely on the basis of its duration in vivo or the presence of periacetabular osteolysis does not appear to be warranted. Retention of the socket with grafting of larger periacetabular osteolytic lesions appears to be consistent with satisfactory socket longevity.

Periprosthetic osteolysis: induction of vascular endothelial growth factor from human monocyte/macrophages by orthopaedic biomaterial particles

VEGF and VEGF receptor, Flt-1, expression was observed in periprosthetic tissues surrounding loosened total joint implants. Exposure of monocyte/macrophages to titanium particles resulted in increased VEGF expression, p44/42 MAPK activation, and VEGF-dependent macrophage chemotaxis. Increased levels of angiogenic factors, such as VEGF, may be critically important in wear debris-induced implant loosening after total joint arthroplasty.

INTRODUCTION

Periprosthetic osteolysis after total hip arthroplasty occurs in association with formation of a vascularized granulomatous tissue in response to particulate debris.

MATERIALS AND METHODS

This study examined expression of vascular endothelial growth factor (VEGF) and the VEGF receptor in 10 periprosthetic tissues from loosened prostheses and quantified effects of titanium particles on VEGF release, intracellular signaling, and VEGF-dependent chemotaxis in primary cultures of human monocyte/macrophages.

RESULTS

Double immunofluorescent staining showed that VEGF and Flt-1 co-localized with cells positive for the macrophage marker, CD11b, in the periprosthetic tissues. Monocyte/macrophages challenged with titanium particles showed a dose- and time-dependent release of VEGF ranging from 2.8- to 3.1-fold and exhibited increased expression of VEGF121 and VEGF165 mRNAs, reaching levels up to 5.0- and 8.6-fold, respectively, by 48 h (p < 0.01). Exposure of monocyte/macrophages to titanium particles upregulated phosphorylated-p44/42 mitogen-activated protein kinase (MAPK) within 30 minutes. Particle-induced activation of p44/42 MAPK and release of VEGF were dose-dependently suppressed by pretreatment of cells with PD98059, a specific inhibitor of p44/42 MAPK. Monocyte/macrophages challenged with titanium particles also showed a time-dependent activation of AP-1, a transcription factor associated with VEGF expression (p < 0.01). Supernatants from particle-challenged monocyte/macrophages increased macrophage chemotactic activity by 30%, which was significantly inhibited by anti-VEGF neutralizing antibody (p < 0.01).

CONCLUSIONS

This study suggests that induction of VEGF release from monocyte/macrophages in response to orthopaedic biomaterial wear debris may contribute to periprosthetic osteolysis and implant loosening.

A rat model for testing pharmacologic treatments of pressure-related bone loss

Fluid pressure, instability, or particles have been suggested to initiate the process leading to loosening of prosthetic implants. In a rat model where bone resorption is caused by oscillating fluid pressure, the resorptive response seems much stronger than the response that can be induced by particles or instability. Bone resorption is caused by osteoclasts. It has been suggested that the formation of osteoclasts is influenced by tumor necrosis factor-alpha, which can be blocked by etanercept. Osteoclasts can be inactivated with bisphosphonates, which bind to bone and inactivate osteoclasts when the bisphosphonate-containing bone is resorbed. Bone formation can be increased dramatically by intermittent parathyroid hormone treatment, especially at sites with high bone turnover. This might compensate for increased osteoclastic activity. Forty-two rats received a plate implant, by which fluid pressure was applied to a bone surface by compressing a soft tissue membrane. Eight rats were treated with etanercept 0.75 mg/kg/day, six rats were treated with alendronate 205 microg/kg/day, six rats received saline, and six rats were nonpressurized controls. Nine rats received intermittent parathyroid hormone treatment with nine separate controls. The area of bone resorption under the implant was evaluated by histomorphometry. Alendronate-treated rats showed less bone resorption, but etanercept, intermittent parathyroid hormone treatment, or saline did not reduce the fluid pressure-induced bone resorption. This model is a comparatively simple way of testing pharmacologic reduction of local bone resorption in vivo.

Polyethylene wear in prosthetic hips with loose components

We measured in vivo polyethylene wear of acetabular cups in 74 patients (83 hips) with Charnley total hip arthroplasties (THA), revised because of aseptic loosening of either the acetabular or femoral component. We analyzed conventional pelvic radiographs of 42 THAs before revision due to loose acetabular components alone and 41 THAs before revision due to loose femoral components alone. The THAs were revised after 10 to 26 years. The mean wear-rate in hips with a loose acetabular components was 0.3 mm/y, whereas in hips with a loose femoral components, it was 0.1 mm/y (P=.0001). The mean total linear wear, as measured on the last available radiographs before revision, was 3.4 mm and 1.5 mm, respectively (P=.0001). A significant difference in linear wear between hips with loose cups and loose stems was seen 1 year after surgery: 0.4 mm/y versus 0.3 mm/y, respectively (P=.05).

Osteolysis: a disease of access to fixation interfaces

Long-term clinical studies of total hip replacement suggest a direct relationship between bearing wear and periprosthetic osteolysis, particularly if polyethylene wear is greater than a threshold value of 0.1 mm per year. The current clinical trend to cross-linked polyethylene and hard-to-hard bearings attempts to ensure that bearing wear remains below this threshold. Fluid pressure generated in the hip during patient activity also has been implicated in the formation of periprosthetic lesions. Pressure fluctuation measured during manipulation of the hip at revision, or the identification of modular components that pump fluid during loading, suggest cyclic pressure may be a causative factor in bone resorption. Animal studies show the adverse effect of direct pressure on osteocytes. At more than 10 years followup, the low incidence of osteolytic lesions in retrospective reviews of successful cemented and cementless implant designs suggest that osteolysis is not an inevitable consequence of particle or pressure generation in the hip. If the quality of implant fixation prohibits fluid access to the surrounding bone, the rate of osteolysis is minimal. It is evident that whether the active factor in osteolysis is pressure, wear particles, or both, adverse periprosthetic effects can be minimized if access to the fixation interfaces in the hip is denied.

Effect of submicron polyethylene particles on an osseointegrated implant: an experimental study with a rabbit patello-femoral prosthesis

In a rabbit model of a weight bearing, articulating prosthetic joint we repeatedly injected submicron particles of Ultra-High-Molecular-Weight-Polyethylene (UHMWPE) produced in a hip simulator. The contralateral knee with the same prosthesis was injected with carrier (NaCl) without UHMWPE. Histomorphometrical studies on undecalcified cut and ground sections at 26 and 42 weeks involved quantifications of the entire bone to metal contact and the bone area around each implant. We found no statistically significant differences between test and control groups, and the UHMWPE debris did not induce any significant osteolysis, indicating that an osseointegrated implant with a sealed interface may not be affected by UHMWPE debris or progress to aseptic loosening.

Osteoprotegerin inhibits in vitro mouse osteoclast formation induced by joint fluid from failed total hip arthroplasty

Osteoprotegerin (OPG) is a key regulator of osteoclastogenesis. We investigated the presence of OPG and bone-resorbing cytokines, the potential of osteoclastic differentiation in joint fluid from failed total hip arthroplasty (THA), and the inhibitory effect of OPG on osteoclast formation in vitro induced by the joint fluid. The study was aimed to clarify one important step in the cascade of periprosthetic osteolysis in the process of implant loosening. OPG levels in failed THA joint fluid of 20 cases were significantly lower than osteoarthritis (OA) joint fluid of 15 cases (p < 0.001). The levels of bone-resorbing cytokines, interleukin (IL)-1beta, and IL-6 were significantly higher in failed THA joint fluid than OA fluid (p < 0.001 and p = 0.001, respectively). Marked osteoclast formation was observed in the presence of failed THA joint fluid in the mouse coculture system, when compared to OA fluid (p < 0.001). The addition of 100 ng/mL OPG to the mouse coculture system completely inhibited osteoclast formation in the presence of failed THA joint fluid (p < 0.001). The data suggest that low levels of OPG combined with higher IL-1beta and IL-6 levels represent the potential of osteoclast differentiation and its activation in failed THA joint fluid. Inhibition of osteoclastogenesis in vitro by OPG suggests that a low level of OPG with elevated bone resorbing cytokines contributes to periprosthetic osteolysis via osteolytic joint fluid, thus leading to THA prosthesis loosening.

Synergistic effect of particles and cyclic pressure on cytokine production in human monocyte/macrophages: proposed role in periprosthetic osteolysis

Macrophages, activated by particulate wear debris, are important in the process of osteolysis, which occurs during joint implant loosening. We previously found increased levels of interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor-alpha in cultured macrophages subjected to cyclical pressure of 0.138 MPa, suggesting that cyclic pressure may be another relevant cause of macrophage activation. The current study first investigated the effects of a range of cyclic pressures on cultured macrophages, including an investigation of the time course of cytokine expression. At 0.138 MPa, supernatant levels of TNF-alpha were maximal at 12 h, whereas IL-6 and IL-1beta were maximal at 24 h. All four cyclic pressure levels tested (without particles) resulted in increased production of all three cytokines relative to control. These increases were most marked at 0.069 and 0.035 MPa, and the increase in cytokine production at 0.017 MPa was not statistically significant. Further studies demonstrated that conditioned media from cyclically pressurized macrophages stimulated bone resorption in a neonatal mouse calvarial assay system. There were increased levels of calcium released from calvaria cultured in conditioned media from pressurised monocytes, and an increase in tartate-resistant acid phosphatase-positive osteoclasts was observed microscopically. As particulate wear debris is important in implant loosening, ultra high molecular weight polyethylene particles were also added to the pressurized cell cultures. The experiments compared the effect of atmospheric pressure, cyclic pressure alone, particles alone, and particles and cyclic pressure combined. A combination of ultra high molecular weight polyethylene particles and cyclic pressure at 0.017 MPa resulted in a dramatic synergistic elevation of levels of all three cytokines compared with the levels found with either pressure or particles alone. We propose that monocyte/macrophage activation by cyclic pressure plays a major role in the osteolysis seen in aseptic loosening of implants. The synergistic effect observed between particles and pressure could accelerate implant loosening, and implies that reduction in either cyclic pressure (by improving implant fixation) or wear debris load would reduce osteolysis.