Medical Engineering and Physics 37 (2015) 447–452
Contents lists available at ScienceDirect
Medical Engineering and Physics journal homepage: www.elsevier.com/locate/medengphy
Cement applicator use for hip resurfacing arthroplasty Sebastian Jaeger, Johannes S. Rieger, Beate Obermeyer, Matthias C. Klotz, J. Philippe Kretzer, Rudi G. Bitsch∗ Laboratory of Biomechanics and Implant Research, Department of Orthopaedic Surgery, University of Heidelberg, Schlierbacher Landstrasse 200a, 69118 Heidelberg, Germany
a r t i c l e
i n f o
Article history: Received 13 October 2014 Revised 4 February 2015 Accepted 16 February 2015
Keywords: Hip resurfacing arthroplasty Cementing technique Temperature Pressure Cement defect Cement applicator
a b s t r a c t We compared the manufacturer recommended cementing technique for a femoral hip resurfacing implant (BHR, S&N) to a newly designed cement applicator on 20 porous carbon foam specimens. Substantial design changes and improvements of the cement applicator were necessary: The diameter and number of the cement escaping holes at the top of the applicator were optimized for medium viscosity cement. It was necessary to add four separate air inlet holes with large diameters. The inner shape of the applicator had to be adapted to the BHR design with a circular extending chamfer in the proximal region, a parallel inner wall and a second chamfer distally. The interface temperatures showed no risk for heat necrosis using both techniques. The cement penetration depth was more uniform and significantly reduced for the applicator cementing technique (4.34 ± 1.42 mm, 6.42 ± 0.43 mm, p = 0.001). The cement-applicator showed no cement defects compared to a large defect length (0.0 ± 0.0 mm, 10.36 ± 1.10 mm, p < 0.001) with the manufacturer recommended cementing technique. The cement applicator technique appears to be effective for a homogenous cement distribution without cement defects and safe with a lower risk of polar over-penetration. © 2015 IPEM. Published by Elsevier Ltd. All rights reserved.
1. Introduction Different failure mechanisms have been documented for hip resurfacing arthroplasty [1-6]. A prospective study of 5000 Birmingham Hip Resurfacings (BHR; Smith & Nephew Orthopaedics, Warwick, United Kingdom) showed that the 56.6% of failures occurred on the femoral side [7]. A study of 98 metal-on-metal surface arthroplasty implant retrievals showed a higher cement penetration in loosened components [1]. Not only an excessive cement penetration but also inadequate and poor cementations are common causes of failure [8]. The implant design has thereby a significant influence on the cementing results and the cemented interface temperatures [9]. This showed the implant sensitivity to changes of the cementing technique [9]. There is a distinction between cement filling and cement packing techniques in the cementation of hip resurfacing implants [10-12]. Compared to cement packing techniques, the use of cement filling with different cement viscosities showed an increase in cement penetration [13]. An increased cement penetration under the femoral ∗
Corresponding author. Tel.: +49 6221 56 35405; fax: +49 6221 56 29206. E-mail address: [email protected], [email protected] (R.G. Bitsch).
http://dx.doi.org/10.1016/j.medengphy.2015.02.007 1350-4533/© 2015 IPEM. Published by Elsevier Ltd. All rights reserved.
component induces higher bone and interface temperatures, which can lead to thermal necrosis [4]. Retrieval analyses could show that the newer cement packing techniques and higher cement viscosities could be helpful in preventing over penetration of bone cement [14]. Bitsch et al. showed that a prototype of a cement applicator tool reduces cement defects and over penetration while providing a more consistent initial stability compared to a cement filling technique for the articular surface replacement (ASR; DePuy Orthopaedics) and high viscous bone cement [15]. However whether this applicator technique has comparable results with the different implant geometry of the Birmingham Hip Resurfacing (BHR; Smith & Nephew) and a medium cement viscosity is unclear. In addition, the femoral cement penetration could be influenced by many other parameters including lavage technique, bone mineral density, cementation timing, cement viscosity and the amount of cement. It takes a lot of experience to compensate for all these parameters with the different techniques available. The cement applicator was developed to optimize cement distribution on the reamed femoral head and make cementing safer, especially for beginners. The aim of the study was to compare the newly designed cement applicator with the manufacturer-recommended cementing techniques for the BHR under standardized conditions.
448
S. Jaeger et al. / Medical Engineering and Physics 37 (2015) 447–452
2. Materials and methods 2.1. Bone model We used 20 cancelated carbon foam specimens (RVC foam; ERG Materials and Aerospace, Oakland, Calif) as substitutes for human femoral heads to compare the manufacturer-recommended BHR cementing technique with a new cement-applicator. The synthetic femoral heads were double compressed with 1.2 pores per millimeter and 6% density similar to the trabecular structure of human femoral heads. The carbon foam specimens were manufactured with the geometry of the prepared and reamed femoral head of the size 48 mm. The geometry was checked prior to the test with the help of the original instruments. The specimens were filled with commercially available fat (Bechem Rhus FA 37; Carl Bechem GmbH, Hagen, Germany) to simulate bone marrow. To do this, the carbon specimens were placed with the fat filling in a fitting cylindrical syringe container. Manual pressure was applied to the syringe under visual control and the fat was pressed into the specimens. The fat filled carbon foams were irrigated with high pressure pulsed lavage (Scandimed, Biomet Merck, Sweden). The application was carried out for a period of 30 s for the top, followed by another 60 s for the chamfer and the wall, resulting in a total amount of 1125 ml of saline solution. Following the lavage, all specimens were dried with gauze sponges, as is commonly done during surgery. Bitsch et al. demonstrated that fat-filled cancelated carbon foam specimens properly emulate human femoral heads for resurfacing. The cement penetration resistance and thermal properties showed no significant difference between the carbon foam material and human femoral heads for resurfacing [16]. One important detail of the modelling with cancelated carbon foam was to adjust the surface temperature of the specimens prior to cementation. In vivo measurements showed a mean surface temperature of the femoral head after jet lavage and before cementation of 23.2 ± 0.7 °C [15]. This temperature is significantly lower than physiologic body temperature. The carbon foam specimens were slowly warmed up to body temperature using an incubator (Function Line, Heraeus Holding GmbH, Hanau, Germany). The cementation was started after a cool down of the carbon foam specimens’ surface to 23 °C.
Fig. 1. The cement penetration pressure (CPP) was measured at three different points in the implant; therefore, screw threads were integrated into the femoral component to fix the pressure probes at the top, at the chamfer, and at the wall.
2.2. Measuring temperature and pressure Cement penetration pressures (CPP) and interface temperatures were measured during both cementation and polymerization. The CPP was measured at three different points of the implant (Fig. 1). Therefore screw threads were reamed into the BHR components to fix the pressure probes (XPM5/XAM; FGP Sensors, Les Clayes sous Bios Cedex, France). Polymerization temperature at the interface was measured 5 and 15 mm under the foam surface (Fig. 2). The foam specimens were mounted in a fixture frame with an integrated port for temperature probe fixation. The temperature probes were inserted through the two port terminals (5 mm and 15 mm) into the carbon foam specimens and secured by a clamp. The stability of the temperature probes is similar to that of a K-wire. The temperature probes used were platinum resistance thermometers (Pt 100, B+B ThermoTechnik, Donaueschingen, Germany). All data were recorded in real time using custom-made data logging software (Tep_Force 1.0, Orthopeadic University Hospital, Heidelberg, Germany) and a USB data acquisition device (National Instruments-NI-BOX-DAQ-PAD-6015, National Instruments, Dublin, Ireland). 2.3. Bone cement and cement mixing The medium viscous bone cement for both investigated cementing techniques was Simplex P (Stryker GmbH & Co. KG, Duisburg,
Fig. 2. Fixation device with mounted foam specimen and ports for the temperature probes with integrated sensors. Polymerization temperatures at the interface were measured 5 and 15 mm under the foam surface. The temperature probes used were platinum resistance thermometers.
S. Jaeger et al. / Medical Engineering and Physics 37 (2015) 447–452
449
Fig. 3. This applicator consisted of an aluminum body with fixed tee-handle (A), PTFE center pin (B), and an inner liner of PTFE (C). Integrated holes at the top of the applicator are used as cement escaping holes (D) and air inlet holes which could be opened before removal of the applicator (E). The inner geometry of the applicator consists of a proximal (1) and a distal (2) circular chamfer and a parallel wall (3).
Germany). The cement was vacuum mixed with the Mixevac 3 system (Stryker, Montreux, Switzerland) at a mean room temperature of 20.58 ± 0.29 °C and a humidity of 51.78 ± 2.68%.
2.4. Cementing techniques The two different cementing techniques for the BHR were examined using standardized cement timing. Ten carbon foam specimens per group were used. For the manufacturer-recommended cementing techniques, which correspond to a cement-filling cementing technique, the femoral component of the BHR was filled with cement up to 30% of their total volume and swiveled sideways to cover the complete inner fixation surface [17]. A preliminary experiment showed that one third of the implant filled with a cement resulted in a cement mass of 11 g. We used only the BHR size 48. The quantity of cement was checked gravimetrically. For the manufacturerrecommended cementing techniques, the femoral component of the BHR was implanted between 60 and 90 s after starting the mixing process [17]. We have performed the McMinn technique (manufacturer recommendation) according to the following cementing timing. The cement was mixed for 60 s, and the implant was filled to 30% of the capacity with the cement (11 g) under gravimetric control. The implant was swiveled sideways to cover the complete inner fixation surface 80 s after the start of the mixing process and implanted in direct connection to the swivel procedure. A newly developed tool was used for the cement applicator technique, which corresponds to a highly standardized cement-packing cementing technique. Substantial design changes and improvements of the new cement applicator were necessary compared to an earlier described cement applicator prototype [15]. The diameter and number of the cement escaping holes at the top of the applicators were optimized for medium viscosity cement. It was necessary to add four separate air inlet holes with large diameters and a special locking mechanism. This required a more stable monobloc aluminum design with an inner coating instead of the three-part polytetrafluoroethyR (PTFE) prototype. The inner shape of the applicator had lene Teflon to be adapted to the inner implant geometry of the BHR with a circular extending chamfer in the proximal region and parallel distal wall. The parallel inner geometry of the distal wall was problematic since this change substantially increased the shear force and removed cement from the specimen. The parallel inner wall of the BHR respectively of the applicator can shear off the cement on the reamed bone and could inhibit adequate cement penetration. Therefore, a circular chamfer was integrated at the applicator opening (Fig. 3). As second part a center pin was used. The central pin also had a different geometry, and this made it necessary to manufacture it out of PTFE instead of aluminum (Fig. 3). The center pin was placed into the central hole at top of the carbon foam. This prevented the cementation of the BHR center pin. The center pin was also used as a guide rod for the applicator. Integrated grooves in the tee-handle allowed visualization of the center pins sliding in movement.
Fig. 4. Fixation device (A) with integrated carbon foam specimen (B) and femoral component (E) linked via custom made frame (C) to the linear motor. The cement penetration pressure was measured using the sensors (D) integrated into the femoral component.
The cementing timing of the applicator technique also includes a mixing time of 60 s for the bone cement. Compared to the manufacturer’s recommended technique, a waiting time was bided until the cement was in the doughing stage. After placing PTFE center pin into the carbon foam central hole, cement was applied at the top and at the chamfer 270 s after mixing began. There was no cement applied on the distal wall of the reamed femoral head respectively carbon foam. After 330 s, the applicator was placed on the center pin and pressed down. Holes in the top of the applicator worked as cement and air escape holes, allowing an extrusion of excess cement at the top area and preventing air inclusion. Air inlet holes were opened for the removal of the applicator to break the vacuum and adhesion between the inner PTFE liner and the cement layer (Fig. 3). The BHR was implanted after a further 60 s (390 after the start of mixing), at which time the carbon foam specimens were placed in the axial direction under the linear motor on a base plate that eliminated shear forces. The femoral components for both cementing technique groups were linked to a linear motor (ET100, Parker Hannifin GmbH & Co. KG Electromechanical Automation, Offenburg, Germany) in a custom made rack (Fig. 4). The linear motor was operated using a Compax3controller with a proportional integral derivative controller and a PC (Compax3 T40, Parker Hannifin GmbH & Co. KG Electromechanical Automation, Offenburg, Germany). The femoral components were seated with a compression force of 200 N. 2.5. Morphology After cement polymerization, the carbon foam specimens were removed from the BHR, the cement surface was examined for air entrapment or blistering and the specimens were cut into halves. For standardization of the saw cuts, a fixture frame was used. The slices were digitalized using a Copy Stand (Reprostativ, Kaiser Fototechnik GmbH & Co. KG, Buchen, Germany) and a Canon EOS 1100D (Canon EOS 1100D, Canon Deutschland GmbH, Krefeld, Germany). The digital pictures were used to analyze the cement mantle thickness, cement penetration depth, cement penetration area and cement defect length. A reference marker was used on each slice for a reliable focus and magnification. All measurements of the images were performed using the analyzed function of ImageJ (U.S. National Institute of Health). The cement layer between carbon foam surface and femoral components was defined as cement mantle thickness. Cement penetration depth was specified as maximal cement penetration into the carbon foam surface under the top area. The cement penetration area was defined as surface in the carbon foam
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S. Jaeger et al. / Medical Engineering and Physics 37 (2015) 447–452
Table 1 Details of cement penetration pressure and interface temperatures of both investigated cementing techniques. Technique
Measurement data
Ptop mean (kPa)
Ptop max (kPa)
Pcha mean (kPa)
Pcha max (kPa)
Pwall mean (kPa)
Pwall max (kPa)
Temp 5 (°C)
Temp 15 (°C)
Manufacturer recommended
Mean SD Min Max
13.65 5.72 3.65 20.94
131.49 17.87 95.18 150.38
10.47 5.01 2.38 17.26
96.84 15.95 56.09 114.37
3.17 1.23 0.85 5.31
16.88 5.79 9.07 25.94
39.97 4.10 33.50 44.59
28.69 0.83 27.67 29.84
Cementapplicator
Mean SD Min Max
44.00 20.04 5.52 77.14
131.18 54.97 13.43 199.55
30.33 8.80 16.70 43.42
108.76 31.53 55.12 156.01
4.83 2.57 0.40 8.16
13.20 7.46 1.15 25.27
36.33 6.03 29.02 47.21
27.67 1.23 26.16 30.50
p value
0.002
Contents lists available at ScienceDirect
Medical Engineering and Physics journal homepage: www.elsevier.com/locate/medengphy
Cement applicator use for hip resurfacing arthroplasty Sebastian Jaeger, Johannes S. Rieger, Beate Obermeyer, Matthias C. Klotz, J. Philippe Kretzer, Rudi G. Bitsch∗ Laboratory of Biomechanics and Implant Research, Department of Orthopaedic Surgery, University of Heidelberg, Schlierbacher Landstrasse 200a, 69118 Heidelberg, Germany
a r t i c l e
i n f o
Article history: Received 13 October 2014 Revised 4 February 2015 Accepted 16 February 2015
Keywords: Hip resurfacing arthroplasty Cementing technique Temperature Pressure Cement defect Cement applicator
a b s t r a c t We compared the manufacturer recommended cementing technique for a femoral hip resurfacing implant (BHR, S&N) to a newly designed cement applicator on 20 porous carbon foam specimens. Substantial design changes and improvements of the cement applicator were necessary: The diameter and number of the cement escaping holes at the top of the applicator were optimized for medium viscosity cement. It was necessary to add four separate air inlet holes with large diameters. The inner shape of the applicator had to be adapted to the BHR design with a circular extending chamfer in the proximal region, a parallel inner wall and a second chamfer distally. The interface temperatures showed no risk for heat necrosis using both techniques. The cement penetration depth was more uniform and significantly reduced for the applicator cementing technique (4.34 ± 1.42 mm, 6.42 ± 0.43 mm, p = 0.001). The cement-applicator showed no cement defects compared to a large defect length (0.0 ± 0.0 mm, 10.36 ± 1.10 mm, p < 0.001) with the manufacturer recommended cementing technique. The cement applicator technique appears to be effective for a homogenous cement distribution without cement defects and safe with a lower risk of polar over-penetration. © 2015 IPEM. Published by Elsevier Ltd. All rights reserved.
1. Introduction Different failure mechanisms have been documented for hip resurfacing arthroplasty [1-6]. A prospective study of 5000 Birmingham Hip Resurfacings (BHR; Smith & Nephew Orthopaedics, Warwick, United Kingdom) showed that the 56.6% of failures occurred on the femoral side [7]. A study of 98 metal-on-metal surface arthroplasty implant retrievals showed a higher cement penetration in loosened components [1]. Not only an excessive cement penetration but also inadequate and poor cementations are common causes of failure [8]. The implant design has thereby a significant influence on the cementing results and the cemented interface temperatures [9]. This showed the implant sensitivity to changes of the cementing technique [9]. There is a distinction between cement filling and cement packing techniques in the cementation of hip resurfacing implants [10-12]. Compared to cement packing techniques, the use of cement filling with different cement viscosities showed an increase in cement penetration [13]. An increased cement penetration under the femoral ∗
Corresponding author. Tel.: +49 6221 56 35405; fax: +49 6221 56 29206. E-mail address: [email protected], [email protected] (R.G. Bitsch).
http://dx.doi.org/10.1016/j.medengphy.2015.02.007 1350-4533/© 2015 IPEM. Published by Elsevier Ltd. All rights reserved.
component induces higher bone and interface temperatures, which can lead to thermal necrosis [4]. Retrieval analyses could show that the newer cement packing techniques and higher cement viscosities could be helpful in preventing over penetration of bone cement [14]. Bitsch et al. showed that a prototype of a cement applicator tool reduces cement defects and over penetration while providing a more consistent initial stability compared to a cement filling technique for the articular surface replacement (ASR; DePuy Orthopaedics) and high viscous bone cement [15]. However whether this applicator technique has comparable results with the different implant geometry of the Birmingham Hip Resurfacing (BHR; Smith & Nephew) and a medium cement viscosity is unclear. In addition, the femoral cement penetration could be influenced by many other parameters including lavage technique, bone mineral density, cementation timing, cement viscosity and the amount of cement. It takes a lot of experience to compensate for all these parameters with the different techniques available. The cement applicator was developed to optimize cement distribution on the reamed femoral head and make cementing safer, especially for beginners. The aim of the study was to compare the newly designed cement applicator with the manufacturer-recommended cementing techniques for the BHR under standardized conditions.
448
S. Jaeger et al. / Medical Engineering and Physics 37 (2015) 447–452
2. Materials and methods 2.1. Bone model We used 20 cancelated carbon foam specimens (RVC foam; ERG Materials and Aerospace, Oakland, Calif) as substitutes for human femoral heads to compare the manufacturer-recommended BHR cementing technique with a new cement-applicator. The synthetic femoral heads were double compressed with 1.2 pores per millimeter and 6% density similar to the trabecular structure of human femoral heads. The carbon foam specimens were manufactured with the geometry of the prepared and reamed femoral head of the size 48 mm. The geometry was checked prior to the test with the help of the original instruments. The specimens were filled with commercially available fat (Bechem Rhus FA 37; Carl Bechem GmbH, Hagen, Germany) to simulate bone marrow. To do this, the carbon specimens were placed with the fat filling in a fitting cylindrical syringe container. Manual pressure was applied to the syringe under visual control and the fat was pressed into the specimens. The fat filled carbon foams were irrigated with high pressure pulsed lavage (Scandimed, Biomet Merck, Sweden). The application was carried out for a period of 30 s for the top, followed by another 60 s for the chamfer and the wall, resulting in a total amount of 1125 ml of saline solution. Following the lavage, all specimens were dried with gauze sponges, as is commonly done during surgery. Bitsch et al. demonstrated that fat-filled cancelated carbon foam specimens properly emulate human femoral heads for resurfacing. The cement penetration resistance and thermal properties showed no significant difference between the carbon foam material and human femoral heads for resurfacing [16]. One important detail of the modelling with cancelated carbon foam was to adjust the surface temperature of the specimens prior to cementation. In vivo measurements showed a mean surface temperature of the femoral head after jet lavage and before cementation of 23.2 ± 0.7 °C [15]. This temperature is significantly lower than physiologic body temperature. The carbon foam specimens were slowly warmed up to body temperature using an incubator (Function Line, Heraeus Holding GmbH, Hanau, Germany). The cementation was started after a cool down of the carbon foam specimens’ surface to 23 °C.
Fig. 1. The cement penetration pressure (CPP) was measured at three different points in the implant; therefore, screw threads were integrated into the femoral component to fix the pressure probes at the top, at the chamfer, and at the wall.
2.2. Measuring temperature and pressure Cement penetration pressures (CPP) and interface temperatures were measured during both cementation and polymerization. The CPP was measured at three different points of the implant (Fig. 1). Therefore screw threads were reamed into the BHR components to fix the pressure probes (XPM5/XAM; FGP Sensors, Les Clayes sous Bios Cedex, France). Polymerization temperature at the interface was measured 5 and 15 mm under the foam surface (Fig. 2). The foam specimens were mounted in a fixture frame with an integrated port for temperature probe fixation. The temperature probes were inserted through the two port terminals (5 mm and 15 mm) into the carbon foam specimens and secured by a clamp. The stability of the temperature probes is similar to that of a K-wire. The temperature probes used were platinum resistance thermometers (Pt 100, B+B ThermoTechnik, Donaueschingen, Germany). All data were recorded in real time using custom-made data logging software (Tep_Force 1.0, Orthopeadic University Hospital, Heidelberg, Germany) and a USB data acquisition device (National Instruments-NI-BOX-DAQ-PAD-6015, National Instruments, Dublin, Ireland). 2.3. Bone cement and cement mixing The medium viscous bone cement for both investigated cementing techniques was Simplex P (Stryker GmbH & Co. KG, Duisburg,
Fig. 2. Fixation device with mounted foam specimen and ports for the temperature probes with integrated sensors. Polymerization temperatures at the interface were measured 5 and 15 mm under the foam surface. The temperature probes used were platinum resistance thermometers.
S. Jaeger et al. / Medical Engineering and Physics 37 (2015) 447–452
449
Fig. 3. This applicator consisted of an aluminum body with fixed tee-handle (A), PTFE center pin (B), and an inner liner of PTFE (C). Integrated holes at the top of the applicator are used as cement escaping holes (D) and air inlet holes which could be opened before removal of the applicator (E). The inner geometry of the applicator consists of a proximal (1) and a distal (2) circular chamfer and a parallel wall (3).
Germany). The cement was vacuum mixed with the Mixevac 3 system (Stryker, Montreux, Switzerland) at a mean room temperature of 20.58 ± 0.29 °C and a humidity of 51.78 ± 2.68%.
2.4. Cementing techniques The two different cementing techniques for the BHR were examined using standardized cement timing. Ten carbon foam specimens per group were used. For the manufacturer-recommended cementing techniques, which correspond to a cement-filling cementing technique, the femoral component of the BHR was filled with cement up to 30% of their total volume and swiveled sideways to cover the complete inner fixation surface [17]. A preliminary experiment showed that one third of the implant filled with a cement resulted in a cement mass of 11 g. We used only the BHR size 48. The quantity of cement was checked gravimetrically. For the manufacturerrecommended cementing techniques, the femoral component of the BHR was implanted between 60 and 90 s after starting the mixing process [17]. We have performed the McMinn technique (manufacturer recommendation) according to the following cementing timing. The cement was mixed for 60 s, and the implant was filled to 30% of the capacity with the cement (11 g) under gravimetric control. The implant was swiveled sideways to cover the complete inner fixation surface 80 s after the start of the mixing process and implanted in direct connection to the swivel procedure. A newly developed tool was used for the cement applicator technique, which corresponds to a highly standardized cement-packing cementing technique. Substantial design changes and improvements of the new cement applicator were necessary compared to an earlier described cement applicator prototype [15]. The diameter and number of the cement escaping holes at the top of the applicators were optimized for medium viscosity cement. It was necessary to add four separate air inlet holes with large diameters and a special locking mechanism. This required a more stable monobloc aluminum design with an inner coating instead of the three-part polytetrafluoroethyR (PTFE) prototype. The inner shape of the applicator had lene Teflon to be adapted to the inner implant geometry of the BHR with a circular extending chamfer in the proximal region and parallel distal wall. The parallel inner geometry of the distal wall was problematic since this change substantially increased the shear force and removed cement from the specimen. The parallel inner wall of the BHR respectively of the applicator can shear off the cement on the reamed bone and could inhibit adequate cement penetration. Therefore, a circular chamfer was integrated at the applicator opening (Fig. 3). As second part a center pin was used. The central pin also had a different geometry, and this made it necessary to manufacture it out of PTFE instead of aluminum (Fig. 3). The center pin was placed into the central hole at top of the carbon foam. This prevented the cementation of the BHR center pin. The center pin was also used as a guide rod for the applicator. Integrated grooves in the tee-handle allowed visualization of the center pins sliding in movement.
Fig. 4. Fixation device (A) with integrated carbon foam specimen (B) and femoral component (E) linked via custom made frame (C) to the linear motor. The cement penetration pressure was measured using the sensors (D) integrated into the femoral component.
The cementing timing of the applicator technique also includes a mixing time of 60 s for the bone cement. Compared to the manufacturer’s recommended technique, a waiting time was bided until the cement was in the doughing stage. After placing PTFE center pin into the carbon foam central hole, cement was applied at the top and at the chamfer 270 s after mixing began. There was no cement applied on the distal wall of the reamed femoral head respectively carbon foam. After 330 s, the applicator was placed on the center pin and pressed down. Holes in the top of the applicator worked as cement and air escape holes, allowing an extrusion of excess cement at the top area and preventing air inclusion. Air inlet holes were opened for the removal of the applicator to break the vacuum and adhesion between the inner PTFE liner and the cement layer (Fig. 3). The BHR was implanted after a further 60 s (390 after the start of mixing), at which time the carbon foam specimens were placed in the axial direction under the linear motor on a base plate that eliminated shear forces. The femoral components for both cementing technique groups were linked to a linear motor (ET100, Parker Hannifin GmbH & Co. KG Electromechanical Automation, Offenburg, Germany) in a custom made rack (Fig. 4). The linear motor was operated using a Compax3controller with a proportional integral derivative controller and a PC (Compax3 T40, Parker Hannifin GmbH & Co. KG Electromechanical Automation, Offenburg, Germany). The femoral components were seated with a compression force of 200 N. 2.5. Morphology After cement polymerization, the carbon foam specimens were removed from the BHR, the cement surface was examined for air entrapment or blistering and the specimens were cut into halves. For standardization of the saw cuts, a fixture frame was used. The slices were digitalized using a Copy Stand (Reprostativ, Kaiser Fototechnik GmbH & Co. KG, Buchen, Germany) and a Canon EOS 1100D (Canon EOS 1100D, Canon Deutschland GmbH, Krefeld, Germany). The digital pictures were used to analyze the cement mantle thickness, cement penetration depth, cement penetration area and cement defect length. A reference marker was used on each slice for a reliable focus and magnification. All measurements of the images were performed using the analyzed function of ImageJ (U.S. National Institute of Health). The cement layer between carbon foam surface and femoral components was defined as cement mantle thickness. Cement penetration depth was specified as maximal cement penetration into the carbon foam surface under the top area. The cement penetration area was defined as surface in the carbon foam
450
S. Jaeger et al. / Medical Engineering and Physics 37 (2015) 447–452
Table 1 Details of cement penetration pressure and interface temperatures of both investigated cementing techniques. Technique
Measurement data
Ptop mean (kPa)
Ptop max (kPa)
Pcha mean (kPa)
Pcha max (kPa)
Pwall mean (kPa)
Pwall max (kPa)
Temp 5 (°C)
Temp 15 (°C)
Manufacturer recommended
Mean SD Min Max
13.65 5.72 3.65 20.94
131.49 17.87 95.18 150.38
10.47 5.01 2.38 17.26
96.84 15.95 56.09 114.37
3.17 1.23 0.85 5.31
16.88 5.79 9.07 25.94
39.97 4.10 33.50 44.59
28.69 0.83 27.67 29.84
Cementapplicator
Mean SD Min Max
44.00 20.04 5.52 77.14
131.18 54.97 13.43 199.55
30.33 8.80 16.70 43.42
108.76 31.53 55.12 156.01
4.83 2.57 0.40 8.16
13.20 7.46 1.15 25.27
36.33 6.03 29.02 47.21
27.67 1.23 26.16 30.50
p value
0.002
