Multiple biological and mechanical factors may be responsible for the failure of fixation in cemented total hip replacements (THRs). Although the eventual failure of THRs may appear to be biological, the initiation of the failure during early period post operation may well be mechanical. It is in this area that mechanistic analysis is of particular significance. This study builds on work by Rapperport et al, Dals-tra and Huiskes on stress analysis of implanted acetabulum, while focuses on fracture mechanics analyses of fracture of cement and of bone-cement interface. Specifically, finite element models were developed where cracks of most favourable orientations in the cement mantle were simulated. Possible crack path selections were explored. A simplified multilayer experimental model was also developed to represent the implanted acetabulum, and fatigue tests were carried out on the model. The experimental results were compared with those from the FE model. Furthermore, interfacial crack growth at bone-cement interface was simulated from the superior edge of the acetabulum, as suggested from the clinical observations. The strain energy release rates were computed for typical hip contact forces during gait and as a function of crack length. Associated phase angles were also computed to account for the materials mismatch. The results were evaluated against the interfacial fracture toughness of the bone-cement interface, measured using sandwich Brazilian disk specimens. The results show that although interfacial fracture seems to be unlikely for large phase angles where shear component is most active, the strain energy release rates are comparable with the values of the interfacial fracture toughness when mode I is predominant, suggesting interfacial fracture. The study also shows that the fracture toughness of cement is much higher than the interfacial fracture toughness of bone-cement, this may explain the reason why interfacial fracture is favoured even if the crack driving force at bone-cement interface appears to be weaker than that in the cement mantle

Objective: To examine the effect of varying the thickness of the cement mantle on the strain distribution near the bone-cement interface. Background: An insufficient cement mantle is thought to generate cement fractures near the bone-cement interface. Debonding at the bone-cement interface may accompany such fractures, and, mechanical failure of the prosthesis may follow. In this study, we aim to analyse the relationship between the cement mantle thickness and the acetabular strain distribution near the bone-cement interface. Experimental model: Four hemi-pelvic saw bones specimens were implanted with six protected precision strain gauges. All specimens were prepared to receive a 53/28 cemented polyethylene cup (Depuy Charnley Elite). Methods: We simulated hip joint force relative to the cup during normal walking for quasi-static tests on an Instron 1603 testing machine. The magnitude of the maximum and minimum principal strains, and the orientation of the maximum principal strains were calculated based on the readings of strains from a 32 channel digital acquisition system. Results: Statistically significant differences in the total strains per gait cycle (p< 0.001) have been noted at all gauge locations. In the principal load bearing quadrants, the recorded tensile strains are reduced by 50% as a result of the thicker mantle, while the transmission of compressive strain is enhanced. Conclusion: A cement mantle thickness of 5-6mm may preserve the structural integrity of the principal load bearing quadrants of the acetabulum better than a mantle thickness of 2-3mm, by minimising the acetabu-lar strains. This maybe desirable in total hip replacements for conditions such as rheumatoid arthritis and osteoporosis, where the poorer quality bone can be assisted by recruitment of a larger surface area to participate in load bearing. Keywords: Principal strains; Cement mantle; Mantle thickness; Bone-cement interface; Acetabular strains

The long-term stability of total hip replacements (THRs) critically depends on the lasting integrity of the bond between the implant and the bone. Late failure in the absence of infection is known as ‘aseptic loosening’, a process characterised by the formation and progressive thickening of a continuous layer of fibrous tissue at the interface between the prosthesis and the bone. Aseptic loosening has been identified as the most common cause for long-term instability leading to the failure of ace-tabular cups. There is clearly a need to study the failure mechanisms in the acetabular fixation if the long-term stability of THR is to be significantly improved. The bonding strength in the presence of defects is measured using interfacial fracture toughness, and this information is not available currently. In this work, interfacial fracture toughness of synthetic and bovine bone-cement interface has been studied using sandwiched Brazilian disk specimens. Experiments were carried out using a common bone cement, CMW, and polyurethane foam under selected loading angles from 0 to 25 degrees to achieve full loading conditions from tensile (mode I) to shear (mode II). Finite element analyses were carried out to obtain the solutions for strain energy release rate at a given phase angle (ratio of shear and tensile stress) associated with the experimental models. The effects of crack length on the measured interfacial fracture toughness were examined. Microscopic studies were also carried out to obtain the morphology of the fractured interfaces at selected loading angles. The results show that both polyurethane foam and bovine cancellous bone seem to produce a similar type of interfacial failure of bone-cement interface, with cement pedicles being ‘pull-out’ of the pores of the foam/ bone. Damage sustained by the cement pedicles seems to increase progressively as the increase of shear loading component. The measured values of fracture toughness are a function of crack length and phase angle, and are comparable with those published in the literature on cortical bone and cement interface. The implication of these results on the assessment of fixation in acetabular replacements is discussed, particularly in the light of results from bovine cancellous bone-cement interface

Purpose. The purpose of this study is to compare using a novel cementing technique with hydroxyapatite granules at bone-cement interface with using the 3. rd. cementing technique on the acetabular component. Patients and Methods. Between 2005 and 2007, we performed 54 primary cemented THAs using the 3. rd. generation cementing technique with hydroxyapatite granules at bone-cement interface (Group A: 21 hips) or without them (Group B: 33 hips) in 49 patients with dysplastic hip (6 males, 43 female; mean age at operation, 67 years; age range, 48–84 years). Mean follow up was 5.3 years (range, 2.3–7.1 years), with none of the patients lost to follow up. According to Crowe's classification, subluxation was Group I in 31 hips, group II in 11 hips, group III in 8 hips, and group IV in 4 hips. We used Exeter flanged cup, Exeter stem with a 22-mm diameter metal head (Stryker, Benoist Girard, France) and Simplex-P bone cement (Stryker, Limerick, Ireland) in all hips. A posterolateral approach was performed for all patients. Bone graft was performed 25 hips (block bone graft: 11 hips; impaction bone grafting with a metal mesh: 13 hips) from autogeneic femoral head. Our 3. rd. cementing technique is to make multiple 6-mm anchor holes, to clean the the host acetabular bed with pulse lavage, to dry it with hydrogen peroxide and to use Exeter balloon pressurizer and Exeter flanged cup. Results. The outcomes showed no aseptic loosening and radiological loosening at final follow up. Radiolucent line around the acetabular component was present 14% in Group A and 42% in Group B at 4 years after operation. Kaplan-Meier survivorship analysis of appearance of a radioluent line around the acetabuler component as the end point was 85.7% on group A was significant higher than 57.6% on group B at 4 years. Conclusion. Radiolucent line around cemented acetabular component in total hip arthroplasty using the 3. rd. cementing technique with hydroxyapatite granules at bone-cement interface was significant higher survivorship than them of the 3. rd. cementing technique at 4 years after operation. We suggest that improved novel cementing technique will lead to greater long-term success outcomes of the acetabular component

Retrieval studies based on revision operations at King Edwards VII Hospital reveal that, although micro-cracks develop in the cement mantle, it is the debonding between cement and bone that often defines the final failure of cemented acetabular replacements. This was illustrated at the revision surgeries by the easy removal of the acetabular cups with cement mostly attached to the cup. It is felt that a fundamental understanding of the mechanisms that initiate and propagate the interfacial failure at the bone-cement interface is the key towards solving the problem. In this work, in-vitro fatigue tests were carried out on cemented acetabular replacements using third-generation of composite pelvic bones. Standard Charnley cups were implanted using common bone cement, CMW, following the standard surgical procedures. The implanted hemi-pelvic bone model was then constrained at the sacro-iliac and pubic joints to represent the anatomic constraint conditions. Cyclic loads representing the maximum range of the hip contact force during normal walking were used and the direction of the maximum hip contact force was achieved by using angled plates. In addition to standard cup position, open cup and retroverted cup positions were also examined to assess the significance of cup orientation under fatigue loading conditions. Damage development in the reconstruction was monitored using CT scanning at regular intervals. Permanent records were collected and the sample was eventually sectioned and polished for microscopic studies. Results show excellent correlations between the results from the CT images and the microscopic studies, indicating progressive bone-cement interfacial failure in the posterior-superior quadrant. The significance of the work in the studies of ‘aseptic loosening’ will be discussed

The aim of this study is to determine whether fixation, as opposed to revision arthroplasty, can be safely used to treat reducible Vancouver B type fractures in association with a cemented collarless polished tapered femoral stem (the Exeter). This is a retrospective cohort study of 152 operatively managed consecutive unilateral Vancouver B fractures involving Exeter stems. 130 were managed with open reduction and internal fixation (ORIF) and 22 with revision arthroplasty. Radiographs were assessed and classified by 3 observers. The primary outcome measure was revision of ≥1 component. Kaplan Meier survival analysis was performed. Logistic regression was used to identify risk factors for revision following ORIF. Secondary outcomes included any reoperation, complications, blood transfusion, length of hospital stay and mortality. Fractures (B1 n=74 (49%); B2 n=50 (33%); and B3 n=28 (18%)) occurred at mean 6.7±10.4 years after primary THA (n=143) or hemiarthroplasty (n=15). Mean follow up was 6.5 ±2.6 years (3.2 to 12.1). Rates of revision and reoperation were significantly higher following revision arthroplasty compared to ORIF for B2 (p=0.001) fractures and B3 fractures (p=0.05). Five-year survival was significantly better following ORIF: 92% (86.4 to 97.4 95%CI) Vs 63% (41.7 to 83.3), p<0.001. No independent predictors of revision following ORIF were identified: fixation of B2 or B3 fractures was not associated with an increased risk of revision. Dislocation was the commonest mode of failure after revision arthroplasty. ORIF was associated with reduced blood transfusion requirement and reoperations, but there were no differences in medical complications, hospital stay or mortality between surgical groups. When the bone-cement interface was intact and the fracture was anatomically reducible, Vancouver B2 fractures around Exeter stems can be treated with fixation as opposed to revision arthroplasty. Fixation of Vancouver B3 fractures can be performed in frail elderly patients without increasing revision risk

Studies have reported stem subsidence without loosening in cemented polished tapered stems. And also, the initial radiolucency seen immediately after surgery at the bone-cement interface has decreased in some cases with polished tapered stem as time passed. The etiologies of these phenomena are not still elucidated. We made a comparative study on the relation between stem subsidence and the initial radiolucency in polished and rough surface stems. Subjects were 42 hips of 38 cases and 36 hips of 31 cases received primary THA using a Collarless Polished Tapered (CPT) stem and a polymethylmethacrylate pre-coated (VerSys Cemented Plus) stem respectively. Three x-ray films taken within 2 months, at 6 months and a year after surgery were reviewed. Stem subsidence was seen in 34 hips of 31 cases (81.0%) in the CPT group and averaged 0.72mm (range, 0–2.52mm) at a year after surgery. Decrease in the initial radiolucency was seen in 15 hips (35.7%) in the CPTgroup. Stem subsidence averaged 1.12mm (range, 0.46–2.52mm) and 0.48 mm(range, 0.00–1.91mm) in the cases with decrease in the initial radiolucency and in those without any change respectively. Stem subsidence was significantly greater in the cases with decrease in the initial radiolucency(P< 0.005). In the VerSys group, no stem subsidence was seen except in 1 case of mechanical failure with 0.65mm of subsidence. No decrease in the initial radiolucency was seen, either. It has been reported that the decrease in the radiolucency as we showed was thought a dense appearance of cancellous bone by load transfer in other polished tapered stem. In this study, stem subsidence may have caused decrease in the initial radiolucency. It has a possibility that not only a dense appearance of cancellous bone but also cement creep caused decrease in the initial radiolucency

Objective: To develop in-vitro experiments that measure the strain distributions at the bone-implant and bone-cement interface of the acetabular region under physiological loading conditions for cemented and cementless sockets. Experimental model: Four hemi-pelvic specimens of saw bones were used. Following careful placement of six protected precision strain gauges, two specimens were prepared to receive a cemented polyethylene cup (Depuy Charnley Elite 53/28). Another two specimens were prepared and implanted with un-cemented Duraloc 58/28 cups. Press-fit technique was validated by torque measurements. Background: Symptoms associated with prosthetic migration result from osteoclast induced bone resorption at the interface adjacent to bone. We aim to develop a new and more accurate method of measuring strains at this critical interface. Methods: To simulate quasi-static loading, selected variables of hip joint force relative to the cup during normal walking was used for quasi-static tests on an Instron 1603 testing machine. The magnitude and orientation of the principal strains (maximum and minimum) were calculated based on the readings of strains from a 32 channel digital acquisition system. Results: The magnitude and distribution of acetabular trabecular bone strains are dependent on the type of cup material (un-cemented/cemented) implanted. At the position of maximum load, the maximum principal strain in the un-cemented specimens was 14.4 times higher than that for the cemented specimens (T-value = −96.40, P-value = 0.007). The highest recorded tensile strains in these specimens were localised to the acetabular rim of the posterior-superior quadrant. For the cemented specimens, the maximum principal strains are highest in the dorsal acetabulum, at a location that approximates to the centre of rotation of the replaced hip joint. Shear strains in the posterior-superior quadrant of both cementless and cemented acetabuli surpass the maximum principal strains. Conclusion: In both cemented and un-cemented specimens, the maximum shear and principal strains magnitude show similar spatial and statistical distribution. As indicators of local failure prospect within the acetabulum, these strains suggest that the posterior-superior quadrant is the most likely site for load-induced micro-fractures, in both cemented and cementless acetabuli

Introduction: The use of polymethylmethacrylate (PMMA) bone cement loaded with antibiotics has become increasingly common in the treatment of infected knee and hip arthroplasties and also as prophylaxis in primary joint replacement. However bacterial resistance in antibiotics is an increasing and emerging problem. PMMA bone cements containing different antibiotics, such as gentamicin plus vancomycin may be effective in prevention and treatment of infections (particularly from MRSA and MRSE). The purpose of this study was to determine the in vitro elution characteristics of gentamicin and van-comycin when combined in acrylic cement.

Material and methods: Three groups of six cement disks were prepared. Group I (control group) contained 0.5g of gentamicin sulphate per 40-g packet of Palacos-R+G powder. Group II contained 0.5g of gentamicin sulphate and 1g of finely powdered vancomycin and Group III contained 0.5g of gentamicin sulphate and aqueous solution of vancomycin (containing 2mL water for injection and 1g vancomycin). All discs were prepared using vacuum mixing technique. Each cement disc (25mm diameter × 20mm thick) was fully immersed in a 50-mL bath of normal saline at 37o C temperature in a covered beaker. At specific sampling intervals (1, 3, 7, 15, 30, 60, 90, 120, 150, 180 days) the discs were removed and placed in fresh 50 ml bath for 24 hours. Then a 2 mL sample of each solution was taken. Samples were frozen at −60° C until they were analyzed. Gentamicin and vancomycin concentrations were measured using fluorescence polarization immunoassay.

Results: With regards to gentamicin release, high but rapidly decreasing antibiotic levels were detected within the first week, resulting in an almost steadily low concentration by the end of the first month. Cement samples eluted significantly more gentamicin (120%-20% during the first month) when powdered vancomycin (Group II) was added. The influence on the gentamicin release was significant but minor when aqueous solution of vancomycin (Group III) was added (40%-20% during the same period).

With regards to vancomycin release, high antibiotic levels were detected within the first 3 days and low concentrations after the first week. Cement samples from Group II eluted significantly more antibiotic (80%–100%) in comparison with samples from Group III during the first days.

Gentamicin and vancomycin are detectable in measurements at 150 and 180 days samples.

Conclusions: Bone cements loaded with combinations of gentamicin and vancomycin are more effective in releasing gentamicin than bone cements with gentamicin as a single drug. The presence of powdered vancomycin in cement samples has major influence on the total gen-tamicin release in comparison with cements containing aqueous solution of vancomycin.

The development of more wear resistant biomaterials and better locking mechanisms for the polyethylene into the tibial base has significantly reduced polyethylene wear as a reason for revision TKA. Aseptic loosening is now the primary cause for revision TKA. Loosening can be caused by multifactorial operative issues: 1] patient selection, 2] implant alignment, 3] cementing technique. Furthermore, aseptic loosening occurs at a consistent rate over time. Increased cement penetration is important to counter bone resorption. Increasing penetration also improves cement mantle toughness leading to better mechanical integrity of the bone-cement interface and reduces bone-cement interface stress. It is important to recognise that a cleaner and drier interface does improve bone-cement penetration. Techniques to improve the process include better cement formulations, drilling sclerotic bone, devices and implant features to increase pressurization, using negative pressure suction ports in the tibia. We have extensive experience with CarboJet, a method of CO. 2. gas jet cleaning and drying. This experience was developed during 20 years of performing TKA with NO tourniquet. Schnetler et al found that the “use of a tourniquet in TKA causes a paradoxical increase in total blood loss”. So, NO tourniquet TKA is becoming the new paradigm for knee arthroplasty in reconstructive orthopaedics. Goldstein reported that pressurised carbon dioxide jet lavage resulted in a 35% increase in cement penetration depth when used vs. use of pulsatile saline lavage alone. Meneghini used this pressurised carbon dioxide system to study the influence of NO tourniquet use in TKA. He found a significant lowering of opioid consumption postoperatively. Another important factor in increasing the cement interdigitation is the influence of lipids which significantly weakens the bond at the interfaces. If motion is allowed during cementation there is additional loss of penetration and therefore fixation. The pressurised carbon dioxide delivered by the CarboJet system actually pushes the lipid, fatty marrow up and out of the bone allowing it to be suctioned or lap dried from the interface surface. The NO tourniquet technique and the use of carbon dioxide jet gas delivery to improve the bone-cement interface in TKA will be demonstrated

Balloon kyphoplasty (BKP) is a minimally invasive surgical technique used to correct kyphosis and vertebral compression fractures. BKP uses cement to fill a void created by the inflation of a balloon in a vertebra, it can be used as an alternative to vertebroplasty to reduce cement extravasation. Issues such as poor inter digitisation of the cement and the trabecular bone can arise with the BKP method. This can be due to a compacted layer created during the procedure which can cause complications post-surgery. The primary aim of this study was to investigate alternative cement application methods which could improve the mechanical strength of the bone-cement interface. Three alternative methods were investigated, and cylindrical bone-cement specimens were created for all methods (BKP and three alternatives). An important part of this study was to replicate the compacted layer created by the inflation of the balloon tamp in BKP. Synthetic trabecular bone specimens (Sawbones®, Pacific Research Laboratories, Vashon Island, Washington, USA) were pre-loaded in compression and the resultant compacted layers were found to replicate the compacted layers found in surgery. Mechanical testing was carried out with an MTS Model 858 Bionix. ®. Servohydraulic load frame using static tensile and torsion loads. Static tests revealed that two of the three alternative methods were an improvement on BKP, with a high statistical significance in relation to the mechanical performance of the bone-cement interface (P < 0.001). This data illustrates the potential to improve the standard BKP technique, in terms of bone-cement interface performance

Polymethylmethacrylate (PMMA) bone cement is strong in compression, however it tends to fail under torsion. Sufficient pressurisation and subsequent interdigitation between cement and bone are critical for the mechanical interlock of cemented orthopaedic implants, and an irregular surface on the acetabular cup is necessary for reasonable fixation at the cup-cement interface. There is limited literature investigating discrepancies in the failure mechanisms of cemented all-polyethylene acetabular cups with and without cement spacers, under torsional loading. In vitro experimental comparison of three groups of polyethylene acetabular prosthesis (PAP) cemented into prepared sawbone hemipelvises:. * PAP without PMMA spacers maintaining an equal cement mantle circumferentially. (Group 1 n=3). * PAP without PMMA spacers cemented deliberately ‘bottoming-out’ the implant within the acetabulum. (Group 2 n=3). * PAP with PMMA spacers. (Group 3 n=3). The constructs were tested to torstional failure on a custom designed setup, and statistical analysis done by a one-way ANOVA and Tukey-Welsh test. Group 3 demonstrated superior torsional resistance with a statistically significant torque of 145Nm (SD±12Nm) at failure, compared to group 2 (109Nm, SD±7Nm) and group 1 (99Nm, SD±8Nm). Group 3 experienced failure predominantly at the bone-cement interface, in contrast, Groups 1 and 2 exhibited failure predominantly at the cup-cement interface. There was no significant difference between Group 1 and 2. Qualitative analysis of the failure mode indicates the efficient redistribution of stress throughout the cement mantle, consistent with the greater uniformity of cement. PMMA spacers increase the resistance to torsional failure at the implant-cement interface. Acetabular components without spacers (Groups 1 and 2) failed at the implant-cement interface before the cement-bone interface, at a statistically significantly lower level of torque to failure. Although the PMMA spacers may reduce cement interdigitation at the cement-bone interface the torsional forces required to fail are likely supraphysiological

The development of more wear resistant biomaterials and better locking mechanisms for the polyethylene into the tibial base has significantly reduced polyethylene wear as a reason for revision TKA. Aseptic loosening is now the primary cause for revision TKA. Loosening can be caused by multifactorial operative issues: 1] patient selection, 2] implant alignment, 3] cementing technique. Furthermore, aseptic loosening occurs at a consistent rate over time. Increased cement penetration is important to counter bone resorption. Increasing penetration also improves cement mantle toughness leading to better mechanical integrity of the bone-cement interface and reduces bone-cement interface stress. It is important to recognise that a cleaner and drier interface does improve bone-cement penetration. Techniques to improve the process include better cement formulations, drilling sclerotic bone, devices and implant features to increase pressurization, using negative pressure suction ports in the tibia. We have extensive experience with CarboJet, a method of CO2 gas jet cleaning and drying. This experience was developed during 20 years of performing TKA with NO tourniquet. Schnetler et al found that the “use of a tourniquet in TKA causes a paradoxical increase in total blood loss”. So, NO tourniquet TKA is becoming the new paradigm for knee arthroplasty in reconstructive orthopaedics. Goldstein reported that pressurised carbon dioxide jet lavage resulted in a 35% increase in cement penetration depth when used versus use of pulsatile saline lavage alone. Another important factor in increasing the cement interdigitation is the influence of lipids which significantly weakens the bond at the interfaces. If motion is allowed during cementation there is additional loss of penetration and therefore fixation. The pressurised carbon dioxide delivered by the CarboJet system actually pushes the lipid, fatty marrow up and out of the bone allowing it to be suctioned or lap dried from the interface surface. The NO tourniquet technique and the use of carbon dioxide jet gas delivery to improve the bone-cement interface in TKA will be demonstrated

Aim. The aim of this study is to evaluate if the gentamycin elution from bone cement is influenced by the timing of application of the antibiotic powder. Method. This was an experimental in vitro study that compared the elution properties of different formulation of gentamycin from a commercially available hip, knee and shoulder cement spacers. Four different experimental models were prepared. Five different spacers were prepared for each experimental mode and for each joint. We compared four different formulation of cement spacers: spacer #1, in which the spacer was prepared with a premixed bone-cement antibiotic mixture; spacer #2, in which the spacer was prepared by adding antibiotic powder to the bone cement at the time of spacer preparation; spacer #3, in which the spacer was prepared as spacer #2 but was stored for two months before starting the experiment; spacer #4, in addition to the gentamycin, other two antibiotics (tobramycin and vancomycin) were added to the bone cement. Gentamycin concentration was documented at seven intervals of time: T0 = 0h, T1 = 1h, T2 = 24h, T3 = 1W, T4 = 2W, T5 = 1M, T6 = 3M and T7 = 6M. The gentamycin elution at each interval of time was evaluated by using a T-student test. Results. Spacer #2, in which the gentamycin powder was added to the bone cement at the time of spacer preparation showed the higher gentamycin elution at each interval of time observed. In addition, Spacer #1, in which gentamycin powder was premixed with the bone cement showed a higher gentamycin elution when compared with spacer #3, in which the spacers were stored for two months to simulate the preformed spacers. Lastly, the addition of different antibiotic to the bone cement increases the gentamycin elution from the spacers (as demonstrated by spacer #4 model). Conclusions. a higher gentamycin elution was observed if spacer was prepared at the time of surgery when compared with preformed spacer. Lastly, our study confirmed the synergistic effect of adding one or more antibiotics with the aims to increase gentamycin elution

Introduction. Total hip replacement is an established surgical procedure done to alleviate hip pain due to joint diseases. However, this procedure is avoided in yonger patients with higher functional demands due to the potential for early failure. An ideal prosthesis will have have a high endurance against impact loading, with minimal micromotion at the bone cement interface, and a reduced risk of fatigue failure, with a favourable stress distribution pattern in the femur. We study the effect of varying the material properties and design element in a standard cemented total hip using Finite Element Analysis. Methods. A patient-specific 3D model of femur will be constructed from CT scan data, while a Summit® Cemented Hip System (DePuy Orthopedic) will be used to as a control for comparative evaluation. We vary the material stiffness of different parts of the prosthesis(see Fig.1) to formulate a design concept for a new total hip prosthesis design; and use Finite Element Method to predict the micromotion of the hip prosthesis at the bone cement interface, as well as the stress distribution in the the femur. Result. Validation of computational protocol was being done by comparing the principal maximum strain of the femoral cortex along the diaphysis, and the amount of deflection, with published literature, similarly, contact modelling validation was also done. Model 1–4 induced lower peak Von Mises stress in the cement, which takes a much lower value than any of the cement mechanical limits postulated. Therefore, the risk of cement failure is greatly reduced in Model 1–4. However, the effect of varying stiffness in different regions is not significant in terms of load transmission to the cement. Micromotion at the bone-cement interface was studied via two approaches: Peak micromotion at the bone cement interface; and the micromotion data at 12 Regions of Interest (ROI)s. Both results showed that model 2 and 3 are capable of reducing micromotion at bone-cement interface, in comparison with the Summit® Cemented Hip System. By comparing the Von Mises Stress distribution in the proximal femur; model 1 is found to result in a significantly reduced stress shielding effect, while model 2–4 are also favourable in comparison to the standard Summit® prosthesis in terms of stress distribution in the femur. Figure 2 shows the effects of the performance of model 1–4, presented as percentage difference from the Summit® prosthesis. Model 1 is unfavourable, despite its favourable stress distribution, because its peak and overall micromotion at the bone-cement interface is greatly increased. Conclusion. Model 2 and 3 have favourable design elements. They both have reduced micromotion at the bone-cement interface; and a favourable stress distribution in the femur. Further refining and testing of model 2 and 3 should done, as these models may provide information which may be useful in improving the performance of the current range of total hip replacement prostheses

Introduction and Objective. The surgical strategy for acetabular component revision is determined by available host bone stock. Acetabular bone deficiencies vary from cavitary or segmental defects to complete discontinuity. For segmental acetabular defects with more than 50% of the graft supporting the cup it is recommended the application of reinforcement ring or ilioischial antiprotrusio devices. Acetabular reconstruction with the use of the antiprotrusion cage (APC) and allografts represents a reliable procedure to manage severe periprosthetic deficiencies with highly successful long-term outcomes in revision arthroplasty. Objective. We present our experience, results, critical issues and technical innovations aimed at improving survival rates of antiprotrusio cages. Materials and Methods. From 2004 to 2019 we performed 69 revisions of the acetabulum using defrosted morcellized bone graft and the Burch Schneider anti-protrusion cage. The approach was direct lateral in 25 cases, direct anterior in 44. Patients were re-evaluated with standard radiography and clinical examination. Results. Eight patients died from causes not related to surgery, and two patients were not available for follow up. Five patients were reviewed for, respectively, non-osseointegration of the ring, post-traumatic loosening with rupture of the screws preceded by the appearance of supero-medial radiolucency, post-traumatic rupture of the distal flange, post-traumatic rupture of the cemented polyethylene-ceramic insert, and dislocation treated with new dual-mobility insert. Among these cases, the first three did not show macroscopic signs of osseointegration of the ring, and the only areas of stability were represented by the bone-cement contact at the holes in the ring. Although radiographic studies have shown fast remodeling of the bone graft and the implant survival range from 70% to 100% in the 10-year follow up, the actual osseointegration of the ring has yet to be clarified. To improve osseointegration of the currently available APC whose metal surface in contact with the bone is sandblasted, we combined the main features of the APC design long validated by surgical experience with the 3D-Metal Technology for high porosity of the external surface already applied to and validated with the press fit cups. The new APC design is produced with the 3D-Metal technology using Titanium alloy (Ti6Al4V ELI) that Improves fatigue resistance, primary stability and favorable environment for bone graft ingrowth. We preview the results of the first cases with short-term follow up. Conclusions. Acetabular reconstruction with impacted morcellized bone graft and APC is a current and reliable surgical technique that allows the restoration of bone loss with a high survival rate of the implant in the medium to long term. The new 3D Metal Cage is designed to offer high friction for the initial stability. The high porosity of the 3D Metal structure creates a favorable environment for bone growth, thus providing valid secondary fixation reproducing the results achieved with the 3D metal press fit cup

Objective. Cement thickness of at least 2 mm is generally associated with more favorable results for the femoral component in cemented hip arthroplasty. However, French-designed stems have shown favorable outcomes even with thin cement mantle. The biomechanical behaviors of a French stem, Charnley-Marcel-Kerboull (CMK) and cement were researched in this study. Methods. Six polished CMK stems were implanted into a composite femur, and one million times dynamic loading tests were performed. Stem subsidence and the compressive force at the bone-cement interface were measured. Tantalum ball (ball) migration in the cement was analyzed by micro CT. Results. The cement thickness of 95 % of the proximal and middle region was less than 2.5 mm. A small amount of stem subsidence was observed even with collar contact. The greatest compressive force was observed at the proximal medial region and significant positive correlation was observed between stem subsidence and compressive force. 9 of 11 balls in the medial region moved to the horizontal direction more than that of the perpendicular direction. The amount of ball movement distance in the perpendicular direction was 59 to 83% of the stem subsidence, which was thought to be slip in the cement of the stem. No cement defect and no cement breakage were seen. Conclusion. Thin cement in CMK stems produced effective hoop stress without excessive stem and cement subsidence. Polished CMK stem may work like force-closed fixation in short-term experiment. Cite this article: Y. Numata, A. Kaneuji, L. Kerboull, E. Takahashi, T. Ichiseki, K. Fukui, J. Tsujioka, N. Kawahara. Biomechanical behaviour of a French femoral component with thin cement mantle: The ‘French paradox’ may not be a paradox after all. Bone Joint Res 2018;7:485–493. DOI: 10.1302/2046-3758.77.BJR-2017-0288.R2

In clinical studies of cemented total hip arthroplasty (THA), polished stems produce less slippage at the bone-cement interface than roughened stems. Our objective is to assess the effect of stem-cement debonding on the bone-cement interface shear behaviour of hip implants using simplified axisymmetric stem-cement-aluminum models. We emulated the femoral stems using stainless steel tapered plugs with either a rough (i.e. bonded) or smooth (i.e. unbonded) surface finish. Three different taper angles (5°, 7.5°, 10°) were used for the unbonded constructs. Non-tapered and tapered (7.5°) aluminum shells were used to emulate the diaphyseal and metaphyseal segments of the femur. In all cases, the cement-aluminum interface was designed to have the same shear strength as has been reported for bone-cement interfaces (~8 MPa). The test involved applying axial compressive loading at a rate of 0.02 mm/s until failure. Six specimens were tested for each combination of the parameters. The unbonded stems sustained about twice as much load as the bonded stem, regardless of taper angle, and the metaphyseal model carried 35-50% greater loads than the diaphyseal models before shear failure or slippage. The unbonded constructs reached peak load with excessive displacement due to creep of the cement mantle while the bonded constructs failed in shear at the cement-aluminum interface. This result supports the hypothesis that the wedging forces created in the unbonded construct increase the compression forces across the aluminum-cement interface, thereby increasing its shear resistance. A finite element analysis predicted that the cement could withstand the hoop stress under these loading circumstances and this prediction was confirmed by visual inspection of the cement after each test. Our results suggest that smooth or unbonded stems should sustain less slippage and shear damage at the bone-cement interface than roughened or bonded stems due to the wedge-induced compressive stress; this increased load capacity will be particularly valuable when the condition of the bone-cement interface is suboptimal

Background. Aseptic loosening of cemented femoral stems results from migration of wear particles along the bone-cement interface, producing a foreign body reaction. After cement insertion, blood back pressure can disrupt the bone-cement interface, enabling this spread of wear particles. Our study investigates whether altering timing and speed of stem insertion can reduce this risk. Methods. We inserted mock “C-Stem” femoral components (De Puy-Synthes), using Smartset HV cement (De Puy-Synthes) into artificial femora, fitted with proximal and distal pressure transducers. Cement insertion began two, three or four minutes after mixing. Cement pressures were then allowed to settle for one minute and the stems were then inserted over durations of 25, 60 or 90 seconds. Results. Quicker insertion led to high peak pressures; however insertion over 90 seconds at 4 and 5 minutes achieved more sustained pressures above blood back pressure. Slower insertion particularly improved proximal pressurisation. Furthermore when the stem was inserted over 90 seconds at 5 minutes then the cement pressures remained high after full insertion of the stem. Conclusions. Commonly, femoral stems are inserted rapidly. Our study demonstrates that by inserting the femoral stem more slowly, cement pressure can be maintained above blood back pressure for longer. We believe that after slower stem insertion, the higher cement viscosity enables the surgeon to maintain cement pressure, via the stem, sufficient to resist blood back pressure without inadvertently over inserting the stem. This safe and simple modification of cementing technique generates higher and more sustained cement pressures. Level of evidence. 3. Disclosures. Depuy-Synthes kindly provided the equipment used in the study. None of the authors received any payment or other benefits

This paper suggests that bone-cement interlocking is superior when the cut surfaces of the bone have been prepared using pulsed lavage with saline prior to application of cement and the prostheses during total knee joint arthroplasty. The aim is to put the case forward for the inclusion of the question whether or not pulsed lavage was used on the National Joint Register questionnaire. This will then in course give guidance as to whether there is an improved outcome when pulsed lavage was used or whether it is a waste of resources. Review of the 6-month postoperative films of the total knee joint replacements of two senior surgeons was carried out in 1996. Both surgeons use the Genesis total knee system. Surgeon 1 uses pulsed lavage routinely, and surgeon 2 does not. This is the only difference in their techniques. There have been no early aseptic failures in either group at 5 years. A lucent line was consistently seen between the bone-cement interface when pulsed lavage was used. Furthermore, the depth of the cement mantle on the tibia was greater in the pulsed lavage group. We suggest that the use of pulsed lavage at the preparation of the cut bone surfaces before the application of the cement and prostheses improves the bone-cement interface. The significance of this finding is uncertain, but a case can be made for this question to be included in the National Joint Register questionnaire