Systematic Biomechanical Analysis of Prerequisites for Reliable Intraoperative Bonding of Polymethylmethacrylate Bone Cement in Preexisting Cement in Revision Arthroplasty

Systematic Biomechanical Analysis of Prerequisites for Reliable Intraoperative Bonding of Polymethylmethacrylate Bone Cement in Preexisting Cement in Revision Arthroplasty

Orthopedics
Feature Article 
Systematic Biomechanical Analysis of Prerequisites for Reliable Intraoperative Bonding of Polymethylmethacrylate Bone Cement in Preexisting Cement in Revision Arthroplasty
Dominik Kaiser, MD; Nora Zimmerli, MSc; Rebecca Hartmann, MD; Elias Bachmann, MSc; Klaus-Dieter Kühn, PhD; Dominik C. Meyer, MD
Orthopedics.
Abstract
Abstract
Removal of a stable cement mantle may be invasive and time consuming and may result in unnecessary damage to bone and surrounding soft tissue. The goal of this study was to investigate the feasibility of the use of polymethylmethacrylate cement on preexisting cement as well as to explore the prerequisites for practical clinical use under standardized laboratory conditions. The strength of the cement–cement interface was evaluated with a 4-point bending to failure test, according to International Organization for Standardization 5833, as well as standardized shear strength, according to American Society for Testing and Materials D732. Various intraoperative cleaning agents were tested to remove simulated contamination with bone marrow. Contamination of the cement–cement interface with bone marrow decreases bending strength, modulus, and shear strength. Removal of the bone marrow with a degreasing agent significantly increases bending strength as well as bending modulus and can increase shear strength up to 9% compared with use of a nondegreasing agent. The cement–cement interface may reach up to 85% of bending strength, 92% of bending modulus, and comparable shear strength compared with a uniform cement block. Meticulous removal of fatty contaminant is important. Use of a degreasing agent further increases the stability of the cement–cement interface. With these precautions, it is safe to assume that the combined molecular and mechanical interlock is sufficient for most clinical applications and will not represent the weakest link in prosthetic revision. [Orthopedics. 2021;44(x):xx–xx.]
Full Text
Abstract
Removal of a stable cement mantle may be invasive and time consuming and may result in unnecessary damage to bone and surrounding soft tissue. The goal of this study was to investigate the feasibility of the use of polymethylmethacrylate cement on preexisting cement as well as to explore the prerequisites for practical clinical use under standardized laboratory conditions. The strength of the cement–cement interface was evaluated with a 4-point bending to failure test, according to International Organization for Standardization 5833, as well as standardized shear strength, according to American Society for Testing and Materials D732. Various intraoperative cleaning agents were tested to remove simulated contamination with bone marrow. Contamination of the cement–cement interface with bone marrow decreases bending strength, modulus, and shear strength. Removal of the bone marrow with a degreasing agent significantly increases bending strength as well as bending modulus and can increase shear strength up to 9% compared with use of a nondegreasing agent. The cement–cement interface may reach up to 85% of bending strength, 92% of bending modulus, and comparable shear strength compared with a uniform cement block. Meticulous removal of fatty contaminant is important. Use of a degreasing agent further increases the stability of the cement–cement interface. With these precautions, it is safe to assume that the combined molecular and mechanical interlock is sufficient for most clinical applications and will not represent the weakest link in prosthetic revision. [Orthopedics. 2021;44(x):xx–xx.]
Acrylic bone cement is the most commonly used nonmetallic implant material in orthopedics, especially for stable fixation of endoprostheses. 1–5 As the population ages, the number of revision surgeries of cemented endoprostheses continues to increase. 6 Often a surgeon is confronted with a stable cement mantle around the prosthesis that must be explanted for other reasons, for example, to convert an anatomic shoulder prosthesis to a reverse shoulder prosthesis or to remove a femoral component for revision of a loose cup, recurrent dislocation secondary to component malposition, or debonding of the femoral component within an intact cement mantle. 7 Complete removal of polymethylmethacrylate cement from the bone may be invasive and can cause major damage to the bone and surrounding soft tissue. 8,9 In such a situation without infection, it appears far more attractive to leave all or part of the stable cement mantle in place and to cement a smaller shaft into the cement in place. However, the cement-in-cement interface has not been studied fully, 10 and there is uncertainty under what conditions this practice is acceptable. Several reports support this strategy, whereas others advise against this procedure because of the potential for a poor mechanical bond between the old and new implanted cement, particularly if there is contamination with blood or bone marrow. 8,9,11–21 Additionally, the roughness of the cement surface, 22 the post-cure duration, 15 and the porosity of the cement 23 can affect mechanical quality. No systematic statistical data are available on the appropriate treatment of intraoperatively contaminated cement to achieve acceptable bonding strength with newly implanted cement.
Because of the massive number of surgical procedures involving revision of cemented prostheses and the invasiveness of removing solidly implanted cement, the authors recognized the need to specify the requirements for preparing and preserving a stable cement mantle.
The goal of this study was to investigate the cement-in-cement interface in a laboratory setting by determining bending strength and bending modulus, according to the International Organization for Standardization (ISO), 24 in a 4-point bending test, and determining shear strength, according to the American Society for Testing and Materials (ASTM), 25 in a standardized shear test. The authors sought to identify the effect of surface roughness and contamination with porcine bone marrow with different methods of subsequent mechanical and chemical cleaning.
Materials and Methods
Cement Preparation
Palacos R (Heraeus Medical GmbH) acrylic bone cement was used in this study. The doughy mass was used to fill specific molding templates. Preparation time for the cement until application was less than 4 minutes. 12
Specimen Fabrication
Specimen Fabrication for 4-Point Bending Tests. Uniform rectangular specimens that were 90.0 mm long, 10.0 mm wide, and 3.3 mm high were produced and post-cured for 24 hours at 23 °C in a dry environment. 26 The first 6 specimens underwent no further treatment and were used as the control group. The next batches of specimens were cut in half with a band saw and further treated as described later.
Specimen Fabrication for Shear Tests. For the shear specimens, hollow cement cylinders with outer diameter of 50.8 mm, inner diameter of 25.0 mm, and height of 40.0 mm were prepared by filling premixed cement in a custom-made polyoxymethylene mold with a centrally placed casting rod. 15 After a curing time of at least 15 minutes, the hollow cement cylinders were removed and the surface treatments were applied to the inner cylinder surface as described later.
Surface Treatments. For specimen group p40, the surface was treated with sandpaper with grain size of 40 to establish a rough surface, rinsed with Ringer's solution, and wiped with gauze to remove residue.
For specimen group p400, the surface was treated in the same way as described for specimen group p40, but with sandpaper with grain size of 400.
For specimen group p40+brush, the surface was treated in the same way as described for specimen group p40 and also brushed with a surgical brush (Medi-Scrub; Rovers Medical Devices).
For specimen group bone marrow, the surface was treated in the same way as described for specimen group p40 and then contaminated with porcine bone marrow to simulate realistic contamination.
For specimen group Ringer, the surface was treated in the same way as described for specimen group bone marrow, thoroughly cleaned 3 times for 3 seconds each with a surgical brush soaked in Ringer's solution, and rinsed with Ringer's solution.
For specimen group H202, the surface was treated in the same way as described for specimen group Ringer, with the brush soaked in 3% hydrogen peroxide solution, and then rinsed with Ringer's solution.
For specimen group ethanol, the surface was treated in the same way as described for specimen group Ringer, with the brush soaked in Softasept N (B Braun), a solution containing 654.3 mg ethanol and 83.0 mg/1 mL isopropanol, and then rinsed with Ringer's solution.
For specimen group soap, the surface was treated in the same way as described for specimen group Ringer, with the brush soaked in Lifosan Soft soap (B Braun), and then rinsed with Ringer's solution.
For specimen group control, a uniform block of acrylic bone cement was used without further treatment.
Mechanical Testing
Four-Point Bending Tests According to ISO 5833 (2002). The treated specimen halves were reinserted into the casting mold. The other half of the casting mold was filled with fresh acrylic bone cement, according to the protocol described earlier. After curing for at least 15 minutes, the specimens were removed from the casting mold and stored for 24 hours at 23 °C.
Shear Tests According to ASTM D732 (1993). The treated cylinders were reinserted into the mold, and fresh cement was placed into the cavity where the casting rod had been located previously, resulting in solid cylinders. After 15 minutes of curing, the solid cylinders were removed from the mold, and an 11-mm–diameter drill hole was placed centrally with a bench drill. The cylinders were then cut into 5-mm–thick slices.
Four-Point Bending Tests According to ISO 5833. The 4-point bending test was performed with a Universal material testing machine (Zwick 1456; Zwick GmbH) mounted with a 20-kN load cell (K-Series; Gassmann Theiss Messtechnik GmbH) in a laboratory setting. The 4-point testing rig had a 25-mm load span and a 75-mm support span, which deviates from the norm (20-mm load span, 60-mm support span) (Figure 1A ). The tests were performed with a constant crosshead speed of 5.00 mm/min until failure occurred. After failure occurred, the fracture site was examined for irregularities. The bending modulus was calculated according to the method of Kuehn et al. 26
Figure 1:
Four-point bending test setup to test bending strength and modulus of the cement–cement interface (A). Shear test setup to test shear strength of the cement–cement interface (B). Both tests were performed with a Universal material testing machine (Zwick 1456; Zwick GmbH).
Shear Tests According to ASTM D732. Shear testing was performed with the same machine, and 6 samples per group were tested. Before testing, the thickness of each specimen was measured. Subsequently, the disks were rigidly mounted on the punch and positioned in the support fixture before the specimens were loaded with a crosshead speed of 1.27 mm/min (Figure 1B ). Shear strength of each specimen was determined by dividing the load required to shear the specimen by the product of the thickness of the specimen and the circumference of the punch, according to the applied standard.
For an additional laboratory test, the authors combined 2 rectangular Palacos R specimens. One specimen was approximately 15 years old, and the other specimen had been freshly prepared. The fresh cement was set within a mold on the long side of the old specimen. The mechanical stability of the bond was tested manually.
Statistical Analysis
Statistical analysis was performed with one-way analysis of variance and Tukey's multiple comparisons test for bending strength, bending modulus, and shear strength. Differences were considered statistically significant at P

Images Powered by Shutterstock