Improved acetabular pressurization gives better cement penetration: in vivo measurements during total hip arthroplasty

The addition of a flange does not improve the pressure generated during cemented acetabular cup implantation

Flanged acetabular cups were developed with the rationale that, at insertion, they would increase the pressure of the cement and improve penetration of cement into the acetabular bone. Various studies have been inconclusive regarding their effectiveness. In this work, we aimed to eliminate all confounding factors and measure the pressures generated during acetabular pressurization and cup implantation using a simplified steel acetabulum, high precision pressure transducers, proper surgical techniques and two acetabular cups, identical apart from the addition of a flange to one. It was found that the flanged acetabular component did not significantly increase the pressure in the acetabulum and in some cases reduced the pressures generated when compared to an unflanged cup. The addition of a flange did not reduce the pressure differential between the pole and the rim of the acetabulum, nor did it have a significant effect on pressure lost over the cup implantation period. It was concluded that flanged acetabular cups provide no significant improvement in the pressures generated in the acetabulum during acetabular cup implantation. It is hypothesized that the flange may be seen as a design feature intended to slow the insertion of the cup into the cement, thus requiring the surgeon to apply a larger load in order to correctly position the acetabular cup; in this way larger pressure will be generated.

Does vacuum mixing affect diameter shrinkage of a PMMA cement mantle during in vitro cemented acetabulum implantation?

Radiolucent lines on immediate postoperative cemented acetabular component radiographs between the PMMA bone cement mantle and bone are an indicator of an increased risk of early loosening. The cause of these lines has yet to be identified. Thermal and chemical necrosis, fluid interposition and cement shrinkage have all been suggested in the literature. The aim of the study reported here was to take an engineering approach - eliminating confounding variables present during surgery - to quantify the size of the interstice created by cement shrinkage when a 50 mm diameter flanged acetabular cup is implanted in a model acetabulum with a 52 mm hemispherical bore under controlled conditions using vacuum and non-vacuum mixed cement. Irrespective of the mixing method used, a significant interstice was created between the bone cement and the mock acetabulum. When the cement was mixed under vacuum the interstice created between the mock acetabulum and the cement mantle was 0.60 mm ± 0.09 mm; when the cement was mixed under non-vacuum conditions the interstice created was 0.39 mm ± 0.15 mm. Possible explanations for radiolucent lines are discussed.

What is the Optimum Pattern of Pressurisation to Gain Maximum Penetration of Methylmethacrylate Cement into the Reamed Acetabulum?

Introduction

The cemented polyethylene cup has remained the standard acetabular implant for 50 years although there has been little research into cementing techniques. In the past, cement was previously inserted by sequential manual pressurisation (thumbing) but this technique was prone to contamination of the cement leading to weakening of fixation. In recent times, third-generation techniques using sealed pressurisation with rim preparation have been espoused with similar results. We were interested in establishing whether repeated cycles of compression of cement allowing adequate time for relaxation increases its depth of penetration, and the optimum period of relaxation required to achieve this goal.

Method

A single mix of polymethylmethacrylate cement at dough stage was inserted into a model of the reamed acetabulum. Cyclical pressurisation of the cement with 50 N followed nine different patterns to simulate thumbing, constant pressure, and the application of a sealed and unsealed acetabular cup implant.

Results

A constant load was as effective as all variations of repeated cycles of load and relaxation except for 50 N pressure applied for four seconds with four second intervals. A four second interval of relaxation achieved significantly more penetration than five or three seconds.

Following two minutes of constant pressure, the application of a sealed or unsealed thrust of the plunger had no effect on cement penetration.

Conclusion

This study suggests that optimal polymethylmethacrylate cement penetration into the acetabulum occurs with cycled application of load for four seconds followed by four seconds of relaxation. The subsequent pressurisation with either a flanged or unflanged acetabular implant does not appear to improve cement penetration.

Bone cement usage modalities at a multi-site university hospital centre

BACKGROUND

Although cements are widely used during arthroplasty procedures, few recommendations exist regarding their optimal usage modalities, which, nevertheless, govern the long-term surgical outcomes. No detailed information is available on how cements are used in French hospitals. The objectives of this questionnaire survey among surgeons working at a multi-site university hospital in France were to describe practices, determine whether these varied with surgeon experience, and look for differences compared to recommendations.

HYPOTHESIS

Cementing techniques vary widely among surgeons at a university hospital.

MATERIAL AND METHODS

A questionnaire was sent to the five orthopaedic departments of our university hospital to collect data on the surgeons (age, sex, years of experience), their practice (type of implants used, annual number of arthroplasties with each arthroplasty type and each indication, and proportion of cemented arthroplasties), the type of cement used, and the cementing technique.

RESULTS

Of the 34 surgeons, 21 completed the questionnaire, 20 males and 1 female with a mean age of 41 years (range, 31-59 years) and a mean of 11 years (range, 1-29 years) of experience. High-viscosity antibiotic-loaded cement was preferred by 20 (95%) surgeons, notably for knee arthroplasties, of which the median annual numbers were 55 (range, 0-218) and 8 (range, 1-40) for primary and revision cemented procedures, respectively. Various cementing techniques in ambient air were used: 12/21 (57%) surgeons used pulsed lavage to prepare the bone before cementation and 18/21 (86%) applied the cement to both the bone cuts and the implant. Of the 18 surgeons who performed knee arthroplasties, 12 used pulsed lavage, including 9 of the 11 surgeons with more than 5 years of experience and only 3 of the 7 less experienced surgeons. Similarly, of the 12 surgeons who used pulsed lavage for cemented arthroplasties, 11 were among the 12 surgeons who performed more than 15 cemented arthroplasties annually and 1 was among the 6 who performed fewer cemented arthroplasties.

DISCUSSION

Cementing techniques varied widely, reflecting the dearth of recommendations and controversial results of published studies. In our centre, the use of pulsed lavage to improve bone preparation and cement application to both the bone and the implant should be promoted, as both techniques are universally advocated. Our study demonstrates the need to provide surgeons with opportunities to exchange their experiences about the other aspects of cementing in order to harmonise practices and to optimise the use of cement.

LEVEL OF EVIDENCE

IV, questionnaire survey.

Comparison of two pressurisers for cementation of the proximal femur

PURPOSE

To compare pressures generated by 2 different cement pressurisers at various locations in the proximal femur.

METHODS

Two groups of 5 synthetic femurs were used, and 6 pressure sensors were placed in the femur at 20-mm intervals proximally to distally. Cement was filled into the femoral canal retrogradely using a cement gun with either the half-moon pressuriser or the femoral canal pressuriser. Maximum pressures and pressure time integrals (cumulative pressure over time) of the 2 pressurisers were compared.

RESULTS

At all sensors, the half-moon pressuriser produced higher maximum pressures and pressure time integrals than the femoral canal pressuriser, but the difference was significant only at sensor 1 (proximal femur). This may result in reduced cement interdigitation in the proximal femur.

CONCLUSION

The half-moon pressuriser produced higher maximum cementation pressures and pressure time integrals than the femoral canal pressuriser in the proximal femur region, which is critical for rotational stability of the implant and prevention of implant fracture.

Pressurisation leads to better cement penetration into the glenoid bone: a cadaveric study

The aim of this study was to compare a third-generation cementing procedure for glenoid components with a new technique for cement pressurisation. In 20 pairs of scapulae, 20 keeled and 20 pegged glenoid components were implanted using either a third-generation cementing technique (group 1) or a new pressuriser (group 2). Cement penetration was measured by three-dimensional (3D) analysis of micro-CT scans. The mean 3D depth of penetration of the cement was significantly greater in group 2 (p < 0.001). The mean thickness of the cement mantle for keeled glenoids was 2.50 mm (2.0 to 3.3) in group 1 and 5.18 mm (4.4 to 6.1) in group 2, and for pegged glenoids it was 1.72 mm (0.9 to 2.3) in group 1 and 5.63 mm (3.6 to 6.4) in group 2. A cement mantle < 2 mm was detected less frequently in group 2 (p < 0.001). Using the cement pressuriser the proportion of cement mantles < 2 mm was significantly reduced compared with the third-generation cementing technique.

Modified femoral pressuriser generates a longer lasting high pressure during cement pressurisation

Background

The strength of the cement-bone interface in hip arthroplasty is strongly related to cement penetration into the bone. A modified femoral pressuriser has been investigated, designed for closer fitting into the femoral opening to generate higher and more constant cement pressure compared to a commercial (conventional) design.

Methods

Femoral cementation was performed in 10 Sawbones^® models, five using the modified pressuriser and five using a current commercial pressuriser as a control. Pressure during the cementation was recorded at the proximal and distal regions of the femoral implant. The peak pressure and the pressure-time curves were analysed by student's t-test and Two way ANOVA.

Results

The modified pressuriser showed significantly and substantially longer durations at higher cementation pressures and slightly, although not statistically, higher peak pressures compared to the conventional pressuriser. The modified pressuriser also produced more controlled cement leakage.

Conclusion

The modified pressuriser generates longer higher pressure durations in the femoral model. This design modification may enhance cement penetration into cancellous bone and could improve femoral cementation.

The effect of the Rim Cutter on cement pressurization and penetration on cemented acetabular fixation in total hip arthroplasty: an in vitro study

The Rim Cutter (Stryker Orthopedics, Mahwah, New Jersey) is a tool designed to cut a ledge inside the rim of the acetabulum, onto which a precisely trimmed, cemented, flanged cup can be fitted. The aim was to investigate the effect of the Rim Cutter on the intra-acetabular cement mantle pressure and the depth of cement penetration during cup insertion. The study had two parts. In the first part, hemi-pelvis models were fitted with pressure sensors. Pressure in the acetabulum was measured on insertion of a conventional cemented flanged cup with and without the use of a Rim Cutter to prepare the rim of the acetabulum. The second part assessed cement penetration when the same cups were inserted into a foam shell model. The shell was mounted in a jig and had holes drilled in it; the distance that cement penetrated into the holes was measured. A significant increase in cement pressure at the apex (p = 0.04) and the rim (p = 0.004) is seen when the Rim Cutter is used. Cement penetration in the Rim Cutter group was significantly increased at the rim of the acetabulum (p = 0.003). Insertion of a flanged cup after the acetabulum is prepared with the Rim Cutter leads to a significant increase in cement pressure and penetration during cup insertion in vitro when compared with conventional flanged cups.

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

BACKGROUND AND PURPOSE

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

MATERIALS AND METHODS

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

RESULTS

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

INTERPRETATION

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

Comparison of two methods of fatigue testing bone cement

Two different methods have been used to fatigue test four bone cements. Each method has been used previously, but the results have not been compared. The ISO 527-based method tests a minimum of 10 samples over a single stress range in tension only and uses Weibull analysis to calculate the median number of cycles to failure and the Weibull modulus. The ASTM F2118 test regime uses fewer specimens at various stress levels tested in fully reversed tension-compression, and generates a stress vs. number of cycles to failure (S-N) or Wöhler curve. Data from specimens with pores greater than 1mm across is rejected. The ISO 527-based test while quicker to perform, provides only tensile fatigue data, but the material tested includes pores, thus the cement is closer to cement in clinical application. The ASTM regime uses tension and compression loading and multiple stress levels, thus is closer to physiological loading, but excludes specimens with defects obviously greater than 1mm, so is less representative of cement in vivo. The fatigue lives between the cements were up to a factor 15 different for the single stress level tension only tests, while they were only a factor of 2 different in the fully reversed tension-compression testing. The ISO 527-based results are more sensitive to surface flaws, thus the differences found using ASTM F2118 are more indicative of differences in the fatigue lives. However, ISO 527-based tests are quicker, so are useful for initial screening.

Does use of a "rim cutter" improve quality of cementation of the acetabular component of cemented exeter total hip arthroplasty?

A randomized controlled trial was performed to assess the effect of a rim cutter device on cement mantles in modern elective total hip arthroplasty using a flanged acetabular component. Forty patients were randomized to a rim cutter (21) or control (19) group. A statistically significant improvement in cement penetration was demonstrated in zone 1 (10.1 vs 8.6 mm, P = .023), and in cement mantle thickness in zones 2 and 3 (7.8 and 6.7 mm vs 5.7 and 5.4 mm [P < .001 and P = .017]), with a reduced incidence of bottoming out of the socket (1/21 vs 8/19 [P = .007]). Cement mantle thicknesses greater than 8 mm were achieved more consistently in the rim cutter group (30% vs 2%). This technique improves cement penetration and mantle thickness in a reliable manner.

Prosthesis survival after total hip arthroplasty--does surgical approach matter? Analysis of 19,304 Charnley and 6,002 Exeter primary total hip arthroplasties reported to the Norwegian Arthroplasty Register

BACKGROUND AND PURPOSE

Controversies still exist about whether there is any effect of operative approach on survival of hip prostheses. We compared long-term survival of primary total hip arthroplasties in a well-defined study population from a national prospective population-based registry with regard to the three most commonly used surgical approaches.

METHODS

We assessed prosthesis survival according to surgical approach (the lateral with or without trochanteric osteotomy, and the posterolateral) for 19,304 Charnley and 6,002 Exeter total hip arthroplasties performed from 1987 to 2004.

RESULTS

For Charnley total hip arthroplasties, lateral approach with trochanteric osteotomy had a lower probability of revision than lateral approach without trochanteric osteotomy (RR=0.6, 95% CI: 0.5-0.8). The lower revision rate was due to fewer revisions for aseptic loosening and dislocation. The differences had declined in the latest time period (1995-2004). We observed no differences between lateral approach without trochanteric osteotomy and posterolateral approach, except that there were more revisions due to dislocation in the posterolateral approach group (RR=1.9, 95%CI: 1.1-3.2). No statistically significant differences were observed for Exeter total hip arthroplasties.

INTERPRETATION

For Charnley prostheses, the lateral approach with trochanteric osteotomy gave a reduced revision risk compared to the other approaches, which was due to fewer revisions for dislocation, and in the first time period also fewer revisions due to aseptic loosening.

The influence of initial pressurization and cup introduction time on the depth of cement penetration in an acetabular model

BACKGROUND

Acetabular cementation during total hip arthroplasty is considered difficult mainly due to the appearance and anatomy of the acetabulum. Improved cementation technique has been shown to improve the longevity of acetabular components.

METHOD

We designed a ceramic model to investigate the effect of varying the initial cement pressurization and cup introduction times on the depth of cement penetration. 4 groups were prepared, 2 of which involved varying initial cement pressurization and cup introduction times. Group 3 involved initial cement pressurization with no cup introduction, while group 4 involved cup introduction with no prior cement pressurization.

RESULTS AND INTERPRETATION

Most cement penetration occurred in the early pressurization phase, and we conclude that a relatively early and longer cement pressurization time and late cup introduction are positive factors for increased cement penetration in the acetabulum model.

Cement pressurisation in the acetabulum

Cement pressurisation is an important step in total hip arthroplasty that determines the long-term integration at the cement-bone interface. Our aim was to evaluate the performance of a new pressuriser designed by us against the standard existing pressurisers in an in vitro experimental set-up using two parameters: cement penetration and cement pressurisation. A polypropylene cup model was designed to represent the acetabulum. DePuy's T-handle, Exeter and our own plunger type pressuriser were each tested for cement pressurisation in this acetabular model. Cement penetration and pressures were measured. The cement intrusion into the capillaries with the DePuy pressuriser was found to vary between 2 and 8 mm (mean: 5 mm at the pole and 4.6 mm at the rim), with the Exeter pressuriser it varied between 3 and 9 mm (mean: 5.8 mm at the pole and 7.8 mm at the rim) and with the plunger type pressuriser it varied between 4 and 6 mm (mean 5.2 mm at the pole and 4.8 mm at the rim). The peak pressure achieved with the DePuy pressuriser was 60 kPa whereas it was 70 kPa with the plunger type pressuriser. The mean penetration with the plunger type pressuriser was found to be better than the other types. The penetration was found to be more uniform with equal penetration at the rim as well as at the pole.

A comparison of structural and mechanical properties in cancellous bone from the femoral head and acetabulum

Mechanical interlock obtained by penetration of bone cement into cancellous bone is critical to the success of cemented total hip replacement (THR). Although acetabular component loosening is an important mode of THR failure, the properties of acetabular cancellous bone relevant to cement penetration are not well characterized. Bone biopsies (9mm diameter, 10mm long) were taken from the articular surfaces of the acetabulum and femoral head during total hip replacement. After mechanical and chemical defatting the two groups of bone specimens were characterized using flow measurement, mechanical testing and finally serial sectioning and three-dimensional computer reconstruction. The mean permeabilities of the acetabular group (1.064 × 10−10 m2) and femoral group (1.155x 10−10m2) were calculated from the flow measurements, which used saline solution and a static pressure of 9.8 kPa. The mean Young's modulus, measured non-destructively, was 47.4 MPa for the femoral group and 116.4MPa for the acetabular group. Three-dimensional computer reconstruction of the specimens showed no significant differences in connectivity and porosity between the groups. Results obtained using femoral head cancellous bone to investigate bone cement penetration and fixation are directly relevant to fixation in the acetabulum.

Migration of the acetabular component: effect of cement pressurization and significance of early radiolucency: a randomized 5-year study using radiostereometry

BACKGROUND

Cementing technique is a crucial factor in prosthesis fixation. No randomized studies have been published, however, comparing the outcome of conventional fingerpacking with the outcome of pressurization of the cement prior to cup insertion.

PATIENTS AND METHODS

We randomized 50 THAs to either fingerpacking or sequential pressurization (including individual pressurization of each anchorage hole) and followed the patients with RSA for 5 years. The penetration of cement into the anchorage holes was measured on digital radiographs. Postoperative radiolucent lines around the cup were correlated to later RSA results. For clinical evaluation, we used SF-36 and HHS.

RESULTS

The pressurized group of THAs was more stable regarding changes in inclination. We found no other difference in the migratory behavior. The cement penetration into the anchorage holes was deeper with the pressurization technique than with fingerpacking. For the whole group taken together, there was a strong relation between the presence of radiolucent lines as measured on the postoperative radiograph and later migration observed by RSA at 2 and 5 years.

INTERPRETATION

Pressurization of the cement produced better cement penetration and increased the cup stability in terms of changes in inclination. Early findings of radiolucent lines can predict later unfavorable cup migration.

Acrylic bone cements: clinical developments and current status: Scandinavia

This article focuses on bone cement, the cementing technique used, and their influence on aseptic loosening and infection of acrylic and joint implants--Scandinavian view.