Microscopic evaluation of luting techniques for a fiber-reinforced post system

This study assessed application techniques for cementation of fiber-reinforced posts (FRPs). The treatment groups were defined by FRP luting application techniques and included 5 groups of 10 simulated teeth each: 1, application of the cement on the post using a syringe; 2, application of the cement in the canal using a syringe; 3, application of the cement in the canal and on the post using a syringe; 4, application of the cement in the canal using a syringe/Lentulo spiral instrument; and 5, application of the cement in the canal using a syringe/Lentulo spiral and on the post using a syringe. A dual-curing, automixing cement was utilized as the luting agent. For each group, the canals were endodontically prepared using tapered hand and rotary files and obturated, and then the FRPs were cemented in place. All specimens were encased in acrylic and sectioned at 2 locations, creating 4 viewing surfaces: coronal (C), middle coronal (MC), middle apical (MA), and apical (A). The surfaces were examined using a stereomicroscope and digitized computer software. The efficacy of each FRP application technique was determined in terms of percentages of cement void area by group and by surface. Group 1 exhibited a significantly (P < 0.05) greater overall percentage of cement void area than all other groups. Group 2 exhibited the smallest overall percentage of void area, although the difference was not always statistically significant. There were no statistically significant differences among the surfaces in cement void area (P > 0.05) when the areas of the different groups were combined. The most efficacious cementation method was the injection of cement into the canal space with a syringe, while the use of a Lentulo spiral instrument was found to be an unnecessary step.

Influence of instrumentation techniques and irrigating solutions on bond strength of glass fiber posts to root dentin

This study sought to evaluate how instrumentation techniques and irrigating solutions affected the bond strength of glass fiber posts. For this study, 80 human maxillary central incisors were selected. Endodontic access was obtained, root canal length was measured, and the coronal third was prepared using Gates-Glidden drills. The specimens were embedded in acrylic resin and randomly assigned to 8 groups (n = 10): manual instrumentation only (Group 1), rotary instrumentation only (Group 2), irrigation with 2.5% sodium hypochlorite (NaOCl) (Group 3), irrigation with 2% chlorhexidine (CHX) (Group 4), manual instrumentation and irrigation with 2.5% NaOCl (Group 5), manual instrumentation and irrigation with 2% CHX (Group 6), rotary instrumentation and irrigation with 2.5% NaOCl (Group 7), and rotary instrumentation and irrigation with 2% CHX (Group 8). Specimens in Groups 5-8 also received a 1 minute final rinse with ethylenediaminetetraacetic acid. Canals were filled and the specimens stored for 30 days in distilled water. The restoration material was removed down to the apical 4 mm of the root canal. The glass fiber posts were luted with resin cement and stored for 24 hours at 37°C. Specimens were subjected to a tensile strength test at a constant speed of 1.0 mm/minute and a load of 2,000 kgf. The results were analyzed by analysis of variance and Tukey's test. Irrigation with 2.5% NaOCl reduced the bond strength of fiber posts significantly (P < 0.01), while CHX showed no effect (P > 0.05). It was concluded that irrigation with 2.5% NaOCl has a negative effect on micromechanical retention of glass fiber posts, whether manual or rotary instrumentation is used.

Invention technique and clinical results of Lampang cement injection gun used in hip hemiarthroplasty

BACKGROUND

Cemented hemiarthroplasty is the common treatment of femoral neck fracture in elderly patients. The authors had invented Lampang cement gun (LCG) from a caulking gun to improve cementing technique. There was no previous study about LCG in clinical use.

OBJECTIVE

To describe invention technique and evaluate clinical result of using LCG for cemented hemiarthroplasty in elderly patients with femoral neck fracture.

MATERIAL AND METHOD

A retrospective study was conducted on 96 elderly patients who underwent cemented hemiarthroplasty (58 Austin Moore, 14 Thompson, 24 bipolar) in Lampang Hospital between October 2003 and April 2008. The femoral canal was filled with cement by using LCG Clinical outcome was assessed by Harris hip score (HHS). Radiographic quality of cementing technique was evaluated by Barrack's grading system.

RESULTS

The mean age of the patients was 76 years (range, 62-96) and follow-up period was 39 months (range, 12-66). Twenty-four patients died and five were lost to follow-up. The mean HHS in bipolar group was higher than Thompson and Austin Moore groups (83.2, 78.3 and 76.9 respectively). Excellent and good scores were found in 90.9% of bipolar hips compared with 46.7% in unipolar hips. Less than 10% of the patients had poor clinical result. Cement mantles was grade A 37.3%, B 32.8%, C 20.9% and D 9%. Probably loose was found in one grade-D hip. Two grade-D hips were removed due to infection and dislocation. One grade-C hip was revised due to periprosthetic fracture. The mortality rate at 36 months was 20.8% in unipolar and 8.3% in bipolar group.

CONCLUSION

The use of LCG for cemented hemiarthroplasties in elderly patients with femoral neck fracture provided satisfactory clinical outcome. LCG could be used to improve cementing technique and save the operative cost.

Effect of a distal centralizer on the positioning of an anatomical stem

Femoral stem centralizers were originally designed for double tapered, straight stems. In a slightly modified configuration, the PMMA centralizer is plugged in a hole in the tip of the ABG II femoral prosthesis. The purpose of this study was to determine the effect of the centralizer on the position of the anatomical ABG II stem. Thirty-nine cemented ABG II stems with a centralizer were compared with thirty-nine stems without a centralizer. We evaluated positioning of the tip of the stem according to a standard selection of criteria, using conventional AP and lateral X-ray imaging. The centralizer supplied with the ABG II was found to have no additional value in guaranteeing optimal varus-valgus positioning. If a stem was not placed neutral, generally it was placed in a slight valgus position. The number of deficient cement mantles was not influenced by the three-fin centralizer. Furthermore, the distal centralizer of the ABG II prosthesis adds a length of 27 mm to the stem, and the distal cement plug found in stems with centralizer was almost twice as long on average. The ABG II centralizer was found in this study to provide insufficient guiding of this anatomical stem and to add excessive length to the distal cement plug.

Mechanical properties of femoral cortical bone following cemented hip replacement

Femoral bone remodeling following total hip replacement is a big concern and has never been examined mechanically. In this study, six goats underwent unilateral cemented hip hemiarthroplasty with polymethyl methacrylate (PMMA) bone cement. Nine months later animals were sacrificed, and the femoral cortical bone slices at different levels were analysed using microhardness testing and microcomputed tomography (micro-CT) scanning. Implanted femurs were compared to contralateral nonimplanted femurs. Extensive bone remodeling was demonstrated at both the proximal and middle levels, but not at the distal level. Compared with the nonimplanted side, significant decreases were found in the implanted femur in cortical bone area, bone mineral density, and cortical bone hardness at the proximal level, as well as in bone mineral density and bone hardness at the middle level. However, no significant difference was observed in either variable for the distal level. In addition, similar proximal-to-distal gradient changes were revealed both in cortical bone microhardness and bone mineral density. From the mechanical point of view, the results of the present study suggested that stress shielding is an important mechanical factor associated with bone adaptation following total hip replacement.

Femoral cement pressurization in hip arthroplasty: a comparison of 3 systems

Cement pressurization is critical to achieving optimal results in cemented arthroplasty of the hip. An in vitro experiment using plastic femoral models (10 per group) was undertaken to measure the pressures developed by 3 cementing systems: the Howmedica Mark 1 (Stryker Howmedica, Limerick, Ireland) and DePuy Cemvac retrograde cementation systems (DePuy CMW, Blackpool, UK), and a novel antegrade system consisting of a 60-mL catheter-tipped syringe and a Miller proximal femoral seal (Zimmer Ltd, Swindon, UK). The mean pressure was higher for the syringe system (161.45 +/- 28.9 kPa) than the Mark 1 (103.51 +/- 22.0 kPa) or Cemvac (92.65 +/- 30.7 kPa) systems (P = .0001). In addition, fewer cement mantle defects were seen with the syringe system (1, interquartile range [IQR] 1-2) than the Mark 1 (3, IQR 2-4) or Cemvac (3, IQR 1-3) systems (P = .0256).

Cement restrictor function below the femoral isthmus

Cement restrictors rely on achieving an interference fit with the wall of the medullary canal. Depending on the design of the cement restrictor, the intramedullary fit may be compromised as the femur starts to widen distally. Three different designs of cement restrictor were identified; universal, press-fit, and expandable. We determined which design of cement restrictor could resist the greatest pressures in a closed column of cement. Additionally, we recorded leakage of cement past the restrictor. We reamed synthetic femora to recreate the normal distal flare of the femur below the femoral isthmus. After inserting the cement restrictor, low-viscosity cement was gradually pressurized using an electronically controlled pneumatic ram. We then simultaneously recorded cement pressure above the cement restrictor and displacement of the cement restrictor. There was variation in the performance of the cement restrictors. The expandable cement restrictors resisted the greatest pressures. The resorbable expandable (REX Cement Stop) and press-fit cement restrictors reliably prevented cement leakage. The press-fit and universal restrictors failed at low pressures when deployed below the isthmus. The choice of cement restrictor may need to be modified if preoperative templating indicates the restrictor will sit below the femoral isthmus.

The effect of two different types of cement restrictors on the femoral cement mantle

Cement restriction and pressurisation are helpful technical points in achieving a good cement mantle in cemented hip replacement. In this prospective study, we compared 39 cases where a Hardinge polyethylene restrictor was used and 33 cases where a bone block restrictor was used during Charnley hip replacement. The preoperative radiographs were templated, calibrated holders for the cement restrictors were used intraoperatively, keeping the distal cement height within 2-3 cm from the tip of the femoral prosthesis. Postoperative radiographs were analysed. The Harris Hip scoring system was used for clinical assessment of results. The preoperative target of having a distal cement height of 2-3 cm was achieved in only 60.6% of the bone block group and 30.6% of the Hardinge group. The difference between the two groups is statistically significant (p = 0.001). Distal migration of the restrictors more than 3 cm from the tip of the femoral prosthesis was associated with a non-homogenous cement mantle in zones 3, 4 and 5 without affecting zones 1, 2, 6 and 7. The cement mantle was adequate when the distal cement mantle remained within 2-3 cm of the tip of the femoral prosthesis.

High-viscosity cement significantly enhances uniformity of cement filling in vertebroplasty: an experimental model and study on cement leakage

STUDY DESIGN

Experimental study using a laboratory leakage model.

OBJECTIVE

To examine the working hypothesis that high-viscosity cements will spread uniformly, thus significantly reducing the risk of leakage.

SUMMARY OF BACKGROUND DATA

In vertebroplasty, forces that govern the flow of bone cement in the trabecular bone skeleton are an essential determinant of the uniformity of cement filling. Extraosseous cement leakage has been reported to be a major complication of this procedure. Leakage occurs due to the presence of a path of least resistance caused by irregularities in the trabecular bone or shell structure. Ideally, cement uniformly infiltrates the trabecular bone skeleton and does not favor specific paths. Cement viscosity is believed to affect the infiltration forces and flow during the procedure. Clinically, altering the time between cement mixing and delivery modifies the viscosity of bone cement.

METHODS

An experimental model of the leakage phenomenon of vertebroplasty was developed. A path, simulating a blood vessel, was created in the model to perturb the forces underlying cement flow and to favor leakage. Cement of varying viscosities was injected in the model, and, thereafter, the filling pattern, cement mass that has leaked, time at which leakage occurred, and injection pressure were measured.

RESULTS

A strong relationship was found between the uniformity of the filling pattern and the elapsed time from cement mixing and viscosity, respectively. Specifically, 3 distinct cement leakage patterns were observed: immediate leakage was observed when cement was injected 5-7 minutes following mixing. The cement was of a low viscosity and more than 50% of the total cement injected leaked. Moderate leakage was observed when injection occurred 7-10 minutes following mixing. Less than 10% of the cement leaked, and the viscosity was at a transient state between the low viscosity of immediate leakage and a higher viscosity, doughy cement. Cement leakage ceased completely when cement was delivered after 10 minutes. The viscosity of the cement in this case was high, and the cement was of a dough-like consistency.

CONCLUSIONS

High-viscosity cement seems to stabilize cement flow. However, the forces required for the delivery of high-viscosity cement may approach or exceed the human physical limit of injection forces. Although the working time of the cement is about 17 minutes, it may not be manually injectable with a standard syringe and cannula after 10 minutes, at which time cement leakage ceased completely.

Micromotion in cemented rotating platform total knee arthroplasty: cemented tibial stem versus hybrid fixation

INTRODUCTION

Improving the longevity and reliability of cemented total knee arthroplasty (TKA) remains a major step to achieve. It is still unclear, whether a cemented tibial stem reduces micromotion of the tibial tray and produces therefore a better initial stability or not. The higher conformity of rotating platform design and the possible rotary forces to the tibial platform may produce higher micromotion when the tibial stem remains cementless (hybrid fixation).

MATERIALS AND METHODS

An in vitro study was performed using the PFC mobile bearing tibial tray (DePuy, Warswa, IN, USA) to test the hypothesis that the addition of cement surrounding the tibial stem reduces micromotion of the tibial tray in cemented TKA with mobile bearing design. Ten tibial trays with mobile design were implanted in sawbones with a 3-mm cement mantle beneath the baseplate of the tibial tray and with or without the cemented stem. Tibial trays were loaded additionally in the ventral, lateral, medial and posterior positions with 2,500 N using the Zwick Z010 instrumentation and HBM pick up Hottinger Baldwin.

RESULTS

In this study, a significant increased mean maximum liftoff was found when only cementing the tibial baseplate (hybrid fixation), compared to the fully cemented tibial tray (P<0.02).

CONCLUSION

In conclusion, the stem of mobile bearing tibial components should be cemented to provide increased micromotion and earlier loosening.

Resin-bonded fixed partial dentures: ten-year follow-up

PURPOSE

The aim of the study was to evaluate the survival rate of resin-bonded fixed partial dentures delivered between 1993 and 2003 in the Department of Prosthodontics of the University of Turin and in several private practices.

MATERIALS AND METHODS

The analysis took into consideration the following variables: preparations, metallic alloys, metal preparation and conditioning of the inner surfaces, isolation during cementation, type of cement, kind of prostheses, number of abutments, and number of missing teeth included in the prostheses.

RESULTS

The estimated survival probability for the first debonding or failure was 85% after 5 years and 71% after 10 years.

CONCLUSIONS

The use of dental dam during cementation reduced the risk of debonding. No differences in survival rate were found for the other parameters.

A prospective comparison of cement restrictor migration in primary total hip arthroplasty

Pressurization techniques are used to improve the cement/bone interface at hip arthroplasty. Ultra-high-molecular-weight polyethylene (UHMWPE) cement restrictors leave particulate debris at insertion; biodegradable restrictors may therefore be preferable. We compared the migration behavior of 2 such cement restrictors. A prospective randomized study with 16 patients per group using either a UHMWPE or a biodegradable restrictor was performed. Comparison of intraoperative measurements and postoperative radiographs determined restrictor migration. Mean migration was 3.0 vs 0.5 cm (biodegradable vs UHMWPE, Mann-Whitney U test, P < .002); median, 2.9 vs 0.4; SD, 1.8 vs 0.4; and range, 0.6 to 6.4 vs 0 to 1.2. Our study found that the biodegradable restrictor allowed significantly more migration than the UHMWPE restrictor. Although there are theoretical advantages in avoiding UHMWPE restrictors, the current biodegradable alternative is actually inferior and its use cannot be endorsed.

A new bleeding model of the human acetabulum and a pilot comparison of 2 different cement pressurizers

In this cadaver study, we compared 2 different acetabular cement pressurizers (Exeter and Bernoski type) in paired human acetabula with simulated intraosseous bleeding. Pressure transducers were used to record intra-acetabular pressures during pressurization. Anteroposterior radiographs of the entire specimens were taken. Subsequently, standardized 3-mm-thick sections were cut through the acetabula, which were then microradiographed to evaluate cement penetration. Adequate pressurization was obtained with either pressurizer. The peak and sustained pressures obtained with the Exeter pressurizer (peak, 80 kPa; sustained, 38 kPa) tended to be higher than the pressures obtained with the Bernoski pressurizer (73 kPa; 24 kPa; P > 0.05). Accordingly, a tendency toward improved cement penetration into cancellous bone was found using the Exeter pressurizer (P >.05).

Hydrolytic stability of methacrylamide in acidic aqueous solution

In order to develop a more effective self-etching primer, with a longer lasting shelf life, we designed a self-etching primer comprised of methacrylamide, N-methacryloyl glycine, NMGly. In this study, the hydrolytic stability of the amide portion in the NMGly was examined. The difference in the hydrolytic stability between the methacrylamide and the methacrylate, 2-hydroxyethyl methacrylate, HEMA was then discussed. The addition of an acid to an aqueous solution allows for the hydrolysis of the ester portion in the methacrylate and for the production of methacrylic acid, MA and ethylene glycol, EG. From our study, the data clearly demonstrated that, if the storage duration of a commercially available self-etching primer is prolonged, then the functional methacrylates constituting the self-etching primer will be altered upon use. However, the hydrolytic stability of the amide portion in the methacrylamide, NMGly, designed as an acidic and/or hydrophilic monomer for the self-etching primer, was greater than the results achieved with the methacrylate, HEMA.

New hydraulic cements based on α-tricalcium phosphate–calcium sulfate dihydrate mixtures

Calcium sulfate dihydrate (CSD) powder was added to a cement consisting of alpha-tricalcium phosphate (alpha-TCP) and water. The changes of the physico-chemical properties of the cement were investigated as a function of the CSD amount, the phosphate concentration in the mixing solution, and the solution volume. An increase of the phosphate concentration in the mixing liquid and small additions of CSD powder strongly reduced the cement setting time. Simultaneously, the fraction of unreacted alpha-TCP powder present after 1 day of incubation increased, indicating that alpha-TCP hydrolysis was inhibited. The effects of the CSD amount and the phosphate concentration were synergetic, i.e. the effect of CSD powder was increased with an increase of the phosphate concentration and vice versa. Interestingly, none of the factors affected the cement diametral tensile strength. The present results were explained based on solubility calculations. The present study shows that the use of CSD crystals in combination with phosphate ions is an easy and interesting way to control the setting time of alpha-TCP-water mixtures, in particular, because the mechanical properties of the cement are not modified.

Microhardness of Packable Composites Used as Posts Condensed with Different Methods

The purpose of this in vitro study was to evaluate the microhardness of packable composite compacted with hand or ultrasonic pluggers in post spaces. A total of 168 extracted human anterior teeth were prepared with Gates Glidden and ParaPost drills after obturation. A primer and a dentin-bonding agent were applied to the etched surface. Half of the specimens were compacted with an ultrasonic tip and the other half with a mechanical hand compactor and all specimens were polymerized for each increment. The roots were then sectioned horizontally from 0, 2.5, 3, 3.5, 4, 4.5, and 5 mm starting from the coronal and sliced 2.5-mm long. The microhardness test was applied to each specimen. There were statistically significant differences between ultrasonically and hand-condensed groups in whole specimens (p < 0.001). There were no significant differences between groups of 0, 2.5, and 3 mm until 3.5 mm was reached. After 3.5-mm depth, there were significant differences between the groups (p < 0.001). Ultrasonic condensation of packable composites provided mechanical advantage over hand condensation in root canals measuring microhardness in different depths. However, when microhardness was measured at different depths, values decreased after the depth of 3.5 mm in both condensation groups.

Quantitative analysis of the resorption and osteoconduction process of a calcium phosphate cement and its mechanical effect for screw fixation

The clinical application of calcium phosphate cements (CPCs) composed of tetracalcium phosphate and dicalcium phosphate anhydrous has been limited because of its longer setting time, so that we developed the CPC in which the setting time was shortened to approximately 10 min. Aiming at clinical application, we evaluated the histological response in the bone quantitatively and the biomechanical effectiveness of this substance. The CPC was implanted in the rabbit femoral condyle up to 52 weeks for histological evaluation. In mechanical testing, small cancellous screws were inserted into the condyle, both with and without augmentation with the CPC, and the pull-out strength was measured. The micro-computed tomography finding demonstrated that the cross-sectional area of the implanted CPC at 24 weeks was approximately two-thirds of the initial area. The amount of newly calcified bone around the CPC was significantly greater than that of the sintered hydroxyapatite. Histologically, the new bone was formed on the surface of the implanted CPC 1 week after the implantation and resorption of the CPC was evident at 3 weeks. The pull-out strength was enhanced significantly by augmentation with the CPC and the initial strength was maintained for a 6 week period. This CPC showed good osteoconductivity and was resorbed without adverse inflammation. Using the CPC as augmentation may be capable of useful treatment options in fractures with poor bone quality.

A hybrid zinc-calcium-silicate polyalkenoate bone cement

A novel bone cement composed of sintered zinc-calcium-silicate phosphate and hybrid polyalkenoates has been developed. Synthesis and formulation of glass fillers, monomers and polymers as well as formulation of the cement were described. The effects of sintering, polymer content, glass powder/polymer liquid (P/L) ratio and comonomer on compressive strength (CS) and curing time (CT) were investigated. The effects of P/L ratio and comonomers on shrinkage as well as exotherm were also studied. Results show that the experimental cement was 61% higher in CS, 10% lower in diametral tensile strength, 35% lower in flexural strength, 62% less in exotherm, and 68% less in shrinkage, compared to conventional polymethylmethacrylate cement. With increasing polymer content and P/L ratio in the cement formulation CS of the cement increased but CT decreased. Curing time, shrinkage and exotherm of the cement decreased with increasing P/L ratio. It appears that this novel cement may be a potential candidate for orthopedic restoration if its biological performance is good and formulation is optimized.

In vitro performance of intramedullary cement restrictors in total hip arthroplasty

Contemporary cementing techniques in total hip arthroplasty include the use of a cement restrictor to occlude the intramedullary canal. As there are many different designs currently available it was the aim of our study to compare the stability of eight different systems. We investigated the displacement and the ability to occlude the femur of these cement restrictors during standardised cementing of artificial and fresh frozen femora. The maximal intramedullary pressures and the displacement of the plugs were continuously recorded and statistically evaluated. The results revealed significant differences between the tested cement restrictors. The expandable REX Cement Stop and the Exeter Plug achieved the highest stability and the least cement leakage. The more rigid designs (Palacos Plug, BUCK, Universal) in contrast showed inferior performance. Our biomechanical study emphasises the importance of cement restrictor selection, which can have a crucial influence on the fixation of a cemented total hip replacement.

Dental biomaterials and the healing of dental tissue

This paper addresses the application of new adhesive technologies to dentistry. The bonding of synthetic polymers to dentin is difficult and it has taken a long time to produce reliable methods. Success has been achieved suing a 4-methacryloyloxyethyltrimellitate anhydride/methyl methacrylate-tri-n-butyl borane system which allows the generation of a layer of hybridised dentin. This provides a pseudo-wound-healing layer that resists demineralisation and degradation, is impermeable and inhibits secondary caries and hypersensitivity.

Preliminary study of interfacial shear strength between PMMA precoated UHMWPE acetabular cup and PMMA bone cement

Followed by successful demonstration of high interfacial tensile strength in a new design of cemented all-polyethylene acetabular cup, interfacial shear strength was investigated in this study, with the use of canine-size prototypes of polymethylmethacrylate (PMMA) precoated UHMWPE acetabular cups. In addition to the PMMA precoated prototypes, three different types of controls were also prepared and tested: grooved UHMWPE cups, PMMA (bone cement) cups, and noncoated, plain UHMWPE cups. The interfacial shear strength of the precoated prototypes was 10.1 +/- 0.69 MPa (n = 6), whereas it was 24.3 +/- 0.78 MPa (n = 2) for the PMMA cup, 6.95 +/- 0.21 MPa (n = 2) for the grooved UHMWPE cup, and 0.34 +/- 0.47 MPa (n = 2) for the UHMWPE cup. These results indicate benefits of the PMMA precoating to stabilize the polyethylene acetabular cup securely when applied with bone cement in simulated clinical applications. Analysis of the failed PMMA precoated UHMWPE prototype cups suggested that the chemically induced bonds between precoated PMMA layer and bone cement played a key role in developing high shear strength. After the interfacial shear test of the PMMA precoated prototypes, major disruptions at the interface between treated UHMWPE and precoated PMMA layer were observed by scanning electron microscopy (SEM), which was a unique failure pattern, not found with other prototypes.

PMMA-based bioactive cement: effect of CaF2 on osteoconductivity and histological change with time

A new bioactive bone cement (designated GBC), which is a polymethyl methacrylate- (PMMA-) based composite consisting of bioactive glass beads as an inorganic filler and high-molecular-weight PMMA (hPMMA) as an organic matrix, has been developed. The bioactive glass beads consist of MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) glass. The purpose of the present study was to evaluate the effect of CaF(2) on osteoconductivity and to evaluate the degree of cement degradation with time. Three different types of cement were prepared. GBC(F +), which has been previously described, consisted of CaF(2)-containing bioactive glass beads and hPMMA. GBC(F -) consisted of CaF(2)-free bioactive glass beads and hPMMA. The third cement was hPMMA itself (as a reference material). These three types of cement were packed into the intramedullary canals of rat tibiae to evaluate osteoconductivity, as determined by an affinity index calculated as the length of bone in direct contact with the cement surface expressed as a percentage of the total length of the cement surface. Rats were killed at 4, 8, 25, and 52 weeks after implantation, and the affinity index was calculated for each type of cement at each time point. Histologically, new bone had formed along the surface of both GBC(F +) and GBC(F -) within 4 weeks, whereas hPMMA had little contact with bone, and an intervening soft tissue layer between bone and cement was detected. No significant difference in affinity index was found between GBC(F +) and GBC(F -) at any of the time points studied, although GBC(F -) showed higher affinity indices than GBC(F +) at 8, 25, and 52 weeks. The affinity indices for GBC(F +) and GBC(F -) were significantly higher than those for hPMMA at all time points. With GBC(F +) and GBC(F -), significant increases in the affinity indices were found as the implantation period increased, and the affinity index values at 52 weeks reached more than 70%. In hPMMA, no significant increase in affinity index was observed up to 52 weeks, and the value at 52 weeks was less than 30%. Although no significant difference in affinity index was found between GBC(F +) and GBC(F -), GBC(F -) is conclusively better than GBC(F +) because diseases such as chronic fluorosis might be caused by CaF(2)-containing glass beads. Regarding the cement degradation of both GBC(F +) and GBC(F -), the degree of the degradation at 25 weeks was the same as that at 52 weeks. Therefore, the cement degradation does not appear to proceed rapidly. Further studies are needed to better understand the degradation process.

[Air permeable diaphyseal obturators: efficacity of femoral cementing and prevention of associated cardiovascular disorders]

PURPOSE OF THE STUDY

Insertion of cement plugs into the femoral shaft has become an essential part of total hip arthroplasty procedures. The goal is to achieve secure cementing of the femoral component, but the pressure induced can cause serious problems. The purpose of this study was to determine the effect of a flexible bioabsorbable cement restrictor with decompression valves on cementing efficacy and to determine the effect of inserting the restrictor then the cement plug into the femoral shaft on respiratory functions.

MATERIAL AND METHODS

The restrictor was implanted in 108 patients undergoing first-intention total hip arthroplasty. The canal was prepared and calibrated before inserting the restrictor at a depth estimated at preoperative planning to be 10 to 20 mm below the tip of the femoral stem. The efficacy of the restrictor was assessed using radiographic criteria for the quality of the cement sheath and its position relative to the femoral stem. Oxygen saturation of arterial blood and end-expiration PCO2 were measured at first incision, at insertion of the restrictor, at insertion of the cement plug, and at insertion of the femoral stem.

RESULTS

The relative position of the restrictor was measured on postoperative x-rays at less than 20 mm in 75% of the patients, at 20-40 mm in 13% and at more than 40 mm in 12%. No cement leakage through the restrictor was identified on postoperative x-rays. The quality of the cement sheath was satisfactory in 71% of the patients (77 procedures), fair in 20% (22 procedures) and poor in 8% (9 procedures). For a first group of patients operated on under spinal anesthesia and optional oxygen delivered with a face mask, there was no significant difference in arterial blood oxygen saturation before the procedure and during the four explored operative times. Conversely, in a second group of patients who had general anesthesia without oxygen enrichment of the initial oxygen-nitrogen protoxide gas mixture, arterial blood oxygen saturation during the four operative times was statistically different from the preoperative value. The same observation was made for end-expiratory PCO2.

DISCUSSION

The retrictor's decompression valves did not allow cement leakage beyond the restrictor. The risk of restrictor migration after insertion and after the increased pressure due to cement plug insertion was not increased and was found to be less than rates reported in the literature. In the patients who had general anesthesia, blood gases showed a minimal, but significant, decrease during the operative times susceptible to induce increased intramedullary pressure. In patients who had a non-cemented acetabular insert, use of the pressure-valve cement restrictor appeared to stabilize these parameters.

Adhesive bonding of medical and implantable devices

Although there are many commercially available medical-grade adhesives, their use for new applications requires detailed investigation. It is also important that as well as the initial joint strength, durability of the bonded components during intended use, including exposure to low and high temperatures, stress, fluids and sterilisation, are investigated. Design of accelerated ageing tests, which can simulate the service environments, is critical in providing realistic durability data. Interpretation of ageing data and lifetime prediction of the joint is essential in assessing the performance of medical devices. Emergence of new types of adhesives as well as further development of precision dispensing and rapid-curing technologies offer many exciting and commercially attractive opportunities for joining medical devices.

Comparison between two clinical procedures for bonding fiber posts into a root canal: a microscopic investigation

The purpose of this study was to evaluate the influence of two brushes used as carriers of a primer-adhesive solution as to the formation of resin tags, adhesive lateral branches, and a hybrid layer when used to bond translucent fiber posts. Twenty endodontically treated teeth, extracted for periodontal reasons, were used. The samples were randomly divided into two groups of 10 samples each (Group 1: Microbrush + Scotchbond 1 + Rely X ARC resin cement; Group 2: small plastic brush + Scotchbond 1 + Rely X ARC resin cement). The adhesive system and resin cement were used strictly following manufacturers' instructions. The priming-adhesive solution of the one-bottle system was light-cured before placing the resin cement and the post. Twenty translucent fiber posts were used. After luting procedures, root samples were processed for SEM observations. The adhesive system showed a resin dentin interdiffusion zone (RDIZ), resin tag, and adhesive lateral branch formation. Microscopic examination of restored interfaces of group 1 showed a higher percentage (p < 0.05) of RDIZ than those found in samples of group 2. In group 1 samples, RDIZ morphology was well detectable and uniform in all thirds of the root canals. In group 2, RDIZ was not visible in the apical third. No statistically significant differences were found among the two groups coronally and at the middle third, but the apical third of group 1 showed significantly more resin tag formation than group 2. The characteristic reverse cone shape of resin tags was always noted in the coronal and middle third of the root canals of both groups and in the apical third of group 1. In the apical third of group 2 root canals, the resin tags showed a less uniform morphology and a shorter length than those found in the other observed thirds.

Cementless total hip arthroplasty with a tapered, rectangular titanium stem and a threaded cup: a minimum ten-year follow-up

BACKGROUND

We report the results of cementless total hip arthroplasty with a tapered, rectangular titanium stem that was introduced in 1979 and continues to be used today with only minor changes. The aim of the design is to achieve primary stability to resist rotational and axial forces through precision rasping and press-fit implantation of a tapered, rectangular femoral component.

METHODS

Between October 1986 and November 1987, 208 total hip arthroplasties with insertion of a tapered, rectangular titanium stem and a threaded cup without cement were performed in 200 consecutive patients (average age, sixty-one years; range, twenty-two to eighty-four years).

RESULTS

At the time of the latest follow-up, fifty-one patients (fifty-two hips) had died and sixteen patients had been lost to follow-up, leaving 133 patients. Twelve hips had been revised, two in patients who subsequently died, leaving 123 living patients without revision. The median follow-up time was 120.7 months. Five cups needed revision surgery because of aseptic loosening; two, because of massive polyethylene wear; one, because of posttraumatic migration; and one, because of breakage. Three femoral stems were revised: one because of malpositioning (the reoperation was done five days after implantation); one, because of infection; and the third, after multiple failed acetabular revisions. The mean Harris hip score for the patients who did not have revision was 85.4 points (range, 46 to 100 points) at the time of the latest follow-up. Four patients (3%) complained of thigh pain that was not associated with another disorder. According to the criteria of Engh et al., all femoral implants were graded as stable bone-ingrown. The probability of survival of both the femoral and the acetabular component at ten years, with any revision as the end point, was 0.92 (95% confidence interval, 0.88 to 0.97). The probability of survival of the cup was 0.93 (95% confidence interval, 0.89 to 0.97), and that of the stem was 0.99 (95% confidence interval, 0.97 to 1.00).

CONCLUSIONS

The results of arthroplasty with a tapered, rectangular titanium stem combined with a conical threaded cup inserted without cement were excellent at a minimum of ten years. Our data suggest that femoral stem fixation continues to be secure, while the threaded cup is prone to aseptic loosening.

The effects of acetabular cup temperature and duration of cement pressurization on cement porosity in a canine total hip replacement model

OBJECTIVE

To determine the effect of acetabular cup temperature and duration of cement pressurization on porosity of the acetabular cement mantel.

STUDY DESIGN

In vitro study.

METHODS

Twenty-four polyurethane foam blocks prepared for acetabular prosthetic implantation were implanted with polyethylene acetabular cups using four combinations and variations of temperature and pressure: (1) high temperature/short-term pressurization; (2) high temperature/long-term pressurization; (3) low temperature/long-term pressurization; and (4) low temperature short-term pressurization. Five 1-mm-thick slices were taken from the center of each block using a tissue processing system. The slices were scanned into a personal computer using a photo slide scanner. Imaging software was used to determine cement surface area and size, number, and distribution of pores. The quality of the cement-implant interface was subjectively evaluated. Statistical analysis of relative cement porosity was performed by a Kruskal-Wallis analysis of variance comparing the four groups individually and combining the short-term pressurization groups versus the long-term pressurization groups.

RESULTS

There were no significant differences in cement porosity between the four test groups (P =.11). There were no significant differences in porosity between the combined groups (P =.48).

CONCLUSIONS

There is no benefit in prewarming acetabular cups before implantation. There are no deleterious effects of short-term pressurization of the cement during implantation.

A technique for the removal of restoration overhangs and finishing and polishing of restoration and preparation margins

Restorations with marginal overhangs are frequently associated with localized periodontal defects. Access to overcontoured approximal margins of restorations can be difficult to obtain, however. A system featuring a multidirectional handpiece is an effective and efficient means of contouring, finishing, and polishing restoration surfaces and margins. In particular, the system facilitates access to approximal and subgingival areas for the removal of marginal excess and overhangs. This system may be a valuable addition to the practitioner's armamentarium for operative procedures.

Efficacy of a self-curing adhesive-resin cement system on luting glass-fiber posts into root canals: an SEM investigation

PURPOSE

The aim of this study was to evaluate the efficacy of a new bonding-luting system in resin tag, adhesive lateral branch, and hybrid layer formation when used in combination with an experimental fiber post.

MATERIALS AND METHODS

Thirty anterior teeth extracted for periodontal reasons were selected for this study. They were endodontically treated and randomly divided into three groups of 10 samples each: group 1 = Excite light-cured bonding agent in combination with Variolink II resin cement; group 2 = Excite dual-cured bonding agent self-activated by an experimental microbrush in combination with MultiLink resin cement; and group 3 = one-step bonding system in combination with Dual Link resin cement. In groups 1 and 3, the primer-adhesive solution was light cured before placing the resin cement and the post, whereas in group 2 the adhesive/luting materials were not light cured. Twenty FRC Postec translucent posts (groups 1 and 2) and 10 EndoAesthetic translucent fiber posts (group 3) were used. One week later, the root samples were processed for scanning electron microscopic (SEM) observations.

RESULTS

Microscopic examinations of restored interfaces from group 2 revealed a resin-dentin interdiffusion zone higher than that seen in samples from groups 1 and 3 (P < .05). At the apical and middle thirds, the samples from group 2 showed significantly more resin tags than the other two groups.

CONCLUSION

The dual-cure self-activating system showed a more uniform resin tag and resin-dentin interdiffusion zone formation along root canal walls than light-curing systems.

Retention of cast posts cemented with zinc phosphate cement using different cementing techniques

PURPOSE

This study compares the effect of different cementation techniques on the retention of cast posts and cores.

MATERIALS AND METHODS

Twenty-four extracted single rooted human teeth were used in this study. After routine preparation of the root canals, the canal space was enlarged with reamers. Direct post patterns were made with acrylic resin. Castings were fabricated using Ni-Cr-Mb alloy. Zinc phosphate cement was used as a luting agent using 4 different methods of cement introduction to the root canal space. This created 4 treatment groups consisting of 6 teeth in each group. In Group A, the cement was applied over the posts only. For the specimens in Group B, the cement was introduced into the root canals with a spiral filler and applied over the posts. In Group C, cement was injected into the root canals and then applied over the posts. Finally, for the specimens in Group D, cement was injected into the root canals and a spiral was used to spread it into the root canals, and cement was also applied over the posts. After cementation, teeth were stored in saline solution. The tensile retentive force of cast posts was evaluated using the Instron testing machine (Instron, Canton, MA).

RESULTS

The retention obtained by the 4 techniques differed significantly (p <.05). The highest tensile force to post dislodgment was observed in Group D, and the least was in Group A. Analysis of variance test revealed a highly significant difference between groups (p <.0001). According to the Fisher exact test, there was a significant increase in retention from Group A to Group D (p <.05).

CONCLUSIONS

Under the conditions of this study, the injection of cement into a root canal space followed by the use of a spiral resulted in the highest level of post retention. Retention was reduced when cement was placed using a Lentulo spiral alone (Kerr/Sybron Corp, Romulus, MI), a Jiffy tube (Teledyne Water Pik, Allegheny Teledyne Co, Fort Collins, CO) alone, or by application to the post only. J Prosthodont 2001;10:37-41.

The effect of cement restrictors on the occlusion of the humeral canal: an in vitro comparative study of 2 devices

An in vitro study investigated the efficacy of cement restrictor devices on cement containment and penetration within the humerus. Eight pairs of preserved humeri were prepared using advanced cementing technique followed by insertion of 1 of 2 cement restrictors. Low-viscosity cement was injected followed by sham humeral stem insertion. Each specimen was sectioned into transverse 10-mm slices. Slices were photographed and digitized to quantify the cement/stem and canal cross-sectional area. Cement penetration was determined from the ratio of cement area to canal area. A significant increase in cement penetration was observed among slices from distal to proximal for both restrictors (P = .02). There was no significant difference in cement penetration, leakage, or migration between restrictors. Five of the 8 specimens migrated, with means of 21.5 +/- 25.0 mm and 24.0 +/- 36.0 mm for the polyethylene and silicone restrictors. Leakage or migration resulted in a significant decrease in cement penetration with the polyethylene restrictors (P = .001). In the silicone restrictor group, migration resulted in decreased cement penetration (P = .04). When using advanced cementing techniques, intramedullary restrictors allow improved cement penetration; however, they do not ensure cement containment.

In vivo measurement of acetabular cement pressurization using a simple new design of cement pressurizer

Aseptic loosening of the acetabular component remains a limiting factor in the long-term success of total hip replacement. An instrumented pressurizer has been designed to allow the intraoperative measurement of acetabular cement pressurization, which is known to contribute to implant fixation. Average intraoperative cement pressures in 16 operations performed by 2 surgeons were 49 +/- 17 kPa (6.4 +/- 2.3 psi) and 47 +/- 17 kPa (6.2 +/- 2.2 psi), and peak pressures were 76 +/- 5 kPa (10.0 +/- 0.6 psi) and 93 +/- 15.kPa (12.2 +/- 1.9 psi), comparable to previous work in vitro. The pressurization required for optimal cement penetration into cleaned low-density cancellous bone is reported to be of the order of 35 to 50 kPa (4.6-6.6 psi) for 30 to 60 seconds, and the present data show that this is attainable in vivo using a simple device.

Comparison of fixation of the femoral component without cement and fixation with use of a bone-vacuum cementing technique for the prevention of fat embolism during total hip arthroplasty. A prospective, randomized clinical trial

BACKGROUND

Acute hypotension, hypoxemia, cardiac arrest, and sudden death are well recognized complications during total hip arthroplasty, and they have been attributed to embolization of fat and bone marrow. An increase in intramedullary pressure in the femur is the most important pathogenic factor for the development of embolic events. Intravasation of fat, bone marrow, and bone debris during the implantation of a femoral component, and the embolization of these elements through the venous system located along the linea aspera and through the metaphyseal vessels, have been demonstrated experimentally and clinically. The purpose of the present study was to compare the effects of fixation of the femoral component without cement with those of fixation with a bone-vacuum cementing technique on the severity of embolic phenomena and cardiopulmonary impairment during total hip arthroplasty. Fixation with a conventional cementing technique was also evaluated as a control.

METHODS

Sixty patients (sixty hips) were entered into a prospective, randomized clinical trial. The patients were assigned to one of three groups. Group 1 consisted of twenty patients who had the femoral component inserted without cement, Group 2 comprised twenty patients who had the component inserted with a conventional cementing technique, and Group 3 included twenty patients who had fixation with the so-called bone-vacuum cementing technique. In the hips in Group 3, a suction of -800 millibars (-80,000 pascals) was applied to a proximal drainage cannula placed along the linea aspera and a distal drainage cannula placed in the diaphysis in order to produce a vacuum in the medullary cavity of the femur during the application of cement and the insertion of the stem. Transesophageal echocardiography and hemodynamic and blood-gas analysis were performed during the operation.

RESULTS

Severe embolic events (defined as a cascade of fine echogenic particles of less than five millimeters in diameter) were observed in seventeen (85 percent) of the twenty patients during insertion of the stem with use of a conventional cementing technique but in none of the patients who had the stem inserted without cement (p < 0.05). Insertion of the femoral component with the bone-vacuum cementing technique prevented embolic phenomena in all but one patient (5 percent). Arterial oxygen saturation decreased significantly (p < 0.05) from a mean of 99.5 to 92.9 percent after insertion of the stem with a conventional cementing technique, but only slight changes were observed in the patients who had fixation of the component without cement and in those who were managed with the bone-vacuum cementing technique. Intraoperative pulmonary shunt values increased a mean of 24 percent (p < 0.05) when the femoral component was inserted with a conventional cementing technique, but with the numbers available we did not detect a significant change in those values when the component was fixed without cement or when it was inserted with use of the bone-vacuum cementing technique.

CONCLUSIONS

The present study showed that severe embolic events and intraoperative pulmonary impairment are common when a femoral component is fixed with use of a conventional cementing technique. The results clearly demonstrated a low risk of embolism during total hip arthroplasty when the femoral component was fixed without cement and when it was fixed with the bone-vacuum cementing technique. The ability of a patient to withstand an embolic event should be considered before fixation of the femoral component with use of a conventional cementing technique is planned.

Advances in the use of glass-ionomeric cement. Part 1: Experimental results and portrayal of a technique

The objective of this study was to develop a method of cement microapplication using glass-ionomeric cement. The results of an experimental study to design a microapplication method of glass-ionomeric cement (Ionocem) are presented. Typical middle ear implant materials, as well as human temporal bones and middle ear ossicles, were used to test the efficiency of this application method. Two different versions of Ionocem, low and normal viscosity, were tested under different temperatures and with several application tools. Sufficient processing time could be achieved by cooling the cement down to 4 degrees C. A subcutaneous insulin syringe with a milled-off tip proved to be cost-effective, efficient and versatile. Using this instrument, durable and secure cementation between the parts tested could be achieved. This method may be of significant importance in otologic research and microsurgical routine. In part 2, experimental animal results will follow, as the method portrayed was used to secure parts of a totally implantable middle ear hearing device.

An in vitro study of a new design of acetabular cement pressurizer

Aseptic loosening of the acetabular component remains one of the limiting factors in the long-term success of total hip arthroplasty. Cement pressurization has been shown to improve fixation. A new pressurizer has been designed that seals around the rim of the acetabulum and covers the transverse ligament notch with a flap. The results of in vitro testing of this device are presented and compared with those of pressure generated by insertion of an acetabular cup. The pressurizer allowed sustained, uniform cement pressurization. Peak pressures with the new pressurizer were 180 kPa at both the iliac region of the rim and the pole of an instrumented model acetabulum, compared with 55 kPa at the rim and 120 kPa at the pole on cup insertion. Pressures were maintained in the range of 80-90 kPa. The flap was effective in preventing cement leakage from the notch, and pressures were higher than when the flap was absent. Cup insertion alone gave only transient pressurization, substantially less near the rim of the acetabulum than at the pole. Peripheral pressurization may be significant in producing secure local fixation at the rim of the acetabulum, in particular in the region of the ilium (Charnley zone 1), where radiolucencies are most commonly observed and where stresses in the implanted acetabulum are highest. Improved rim fixation may also play a role in preventing the ingress of wear debris.

The cement mantle in femoral impaction allografting. A comparison of three systems from four centres

An analysis of the cement mantle obtained with the Exeter impaction allografting system at one centre showed that it was either deficient or absent in almost 47% of Gruen zones. We therefore examined the mantle obtained using this system at another hospital and compared the results with those from the CPT and Harris Precoat Systems at other centres. The surgical indications for the procedure and the patient details were broadly similar in all four hospitals. There was some variation in the frequency of use of cortical strut allografts, cerclage wires and wire mesh to supplement the impaction allograft. Analysis of the cement mantles showed that when uncertain Gruen zones were excluded, the incidence of zones with areas of absence or deficiency of the cement was 47% and 50%, respectively, for the two centres using the Exeter system, 21% for the CPT system and 18% for the Harris Precoat system. We measured the difference in size between the proximal allograft impactors and the definitive prosthesis for each system. The Exeter system impactors are shorter than the definitive prosthesis and taper sharply so that the cavity created is inadequate, especially distally. The CPT proximal impactors are considerably longer than the definitive prosthesis and are designed to give a mantle of approximately 2 mm medially and laterally and 1.5 mm anteriorly and posteriorly. The Harris Precoat proximal impactors allow for a mantle with a circumference of 0.75 mm in the smaller sizes and 1 mm in the larger. Many reports link the longevity of a cemented implant to the adequacy of the cement mantle. For this reason, femoral impaction systems require careful design to achieve a cement mantle which is uninterrupted in its length and adequate in its thickness. Our results suggest that some current systems require modification.

Influence of temperature and vacuum mixing on bone cement properties

To analyze the influence of varying viscosity and mixing temperature (22 degrees C and 6 degrees C) on macro- and microporosity, density, and compressive strength in vacuum mixed bone cement, high, medium, and low viscosity cement were mixed in 2 vacuum mixing systems and compared with bowl mixing at atmospheric pressure. At 22 degrees C, vacuum mixing significantly reduced void volume to less than approximately 3 per mill. The reduction was most pronounced in low viscosity cement. Microporosity also was reduced in all cements by vacuum mixing and to highest degree in low viscosity cement. At 6 degrees C the reduction of micropores was more pronounced in high viscosity cement. In medium and especially low viscosity cement, the prechilling gave an increased number of micropores. Cement density also was significantly reduced in low viscosity cement at 6 degrees C. Vacuum mixing significantly increased compressive strength by approximately 15% in all cement types (30 days). The temperature did not significantly influence compressive strength, but low viscosity cement generally was stronger when mixed at 22 degrees C. It is concluded that vacuum mixing improves cement quality. However, the temperature influences the final result; in particular, low viscosity cement should not be mixed after prechilling to 6 degrees C.

In vitro and in vivo studies of pressurization of femoral cement in total hip arthroplasty

Improvements in cementing techniques in the absence of pressurization of the cement have led to major increases in the long-term success rate of fixation of the femoral components of cemented total hip arthroplasty (THA). The strength of the cement-bone interface is strongly related to cement intrusion into the bone. The depth of cement intrusion, in turn, is correlated with the cement-intrusion pressure. Thus, adding cement pressurization to those current techniques that have already been validated may further increase the long-term durability of fixation of the femoral component of cemented THA. To assess cement pressurization in the proximal femur for THA, the authors compared in vitro the efficacy of three existing pressurization systems (the Johnson and Johnson system [New Brunswick, NJ], the Miller system [Zimmer, Warsaw, IN], and the Zimmer system [Zimmer]) in cadaver femurs using pressure transducers and evaluated their ease and optimization for clinical use. The authors then selected one (the Zimmer system) for use in studies in vivo to quantify the actual pressures achieved in the medullary canal in vivo under surgical conditions using pressure transducers placed throughout the femoral cortex. Each of the three commercially available femoral cement pressurization systems has its own advantages and disadvantages. All three systems were shown to produce average peak cement-intrusion pressures in vitro of over 21 N/cm2 (30 psi) throughout the cement mantle including, importantly, in the proximal portion of the femur.(ABSTRACT TRUNCATED AT 250 WORDS)

A new femoral cement restrictor

The authors report on the clinical trial of a new femoral cement restrictor for use during hip arthroplasty. Instrumentation and technique are described. The restrictor has three components made of high-density polyethylene that fit one inside the other and is available in small, medium, and large sizes. The advantages of this new restrictor are ease of use and secure fixation in the femoral canal when deployed. Because of its inherent strength and design, small particles do not break off during insertion. The apex of the restrictor points proximally and is cupped. This helps in centralizing the stem. It also assists in obtaining good cement pressurization as it does not distally migrate in the femoral canal when pressurization is attempted. Also, no cement escapes distally beyond it. Furthermore, should revision surgery be required, the restrictor can be easily removed without the need for windowing the femoral cortex.