title: Do dynamic cement-on-cement knee spacers provide better function and activity during two-stage exchange?
abstract: BACKGROUND
  Implantation of an antibiotic bone cement spacer is used to treat infection of a TKA. Dynamic spacers fashioned with cement-on-cement articulating surfaces potentially facilitate patient mobility and reduce bone loss as compared with their static counterparts, while consisting of a biomaterial not traditionally used for load-bearing articulations. However, their direct impact on patient mobility and wear damage while implanted remains poorly understood.
  
  
  OBJECTIVE
  We characterized patient activity, surface damage, and porous structure of dynamic cement-on-cement spacers.
  
  
  METHODS
  We collected 22 dynamic and 14 static knee antibiotic cement spacers at revision surgeries at times ranging from 0.5 to 13 months from implantation. For these patients, we obtained demographic data and UCLA activity levels. We characterized surface damage using the Hood damage scoring method and used micro-CT analysis to observe the internal structure, cracking, and porosity of the cement.
  
  
  RESULTS
  The average UCLA score was higher for patients with dynamic spacers than for patients with static spacers, with no differences in BMI or age. Burnishing was the only prevalent damage mode on all the bearing surfaces. Micro-CT analysis revealed the internal structure of the spacers was porous and highly inhomogeneous, including heterogeneous dispersion of radiopaque material and cavity defects. The average porosity was 8% (range, 1%-29%) and more than ½ of the spacers had pores greater than 1 mm in diameter.
  
  
  CONCLUSIONS
  Our observations suggest dynamic, cement-on-cement spacers allow for increased patient activity without catastrophic failure. Despite the antibiotic loading and internal structural inhomogeneity, burnishing was the only prevalent damage mode that could be consistently classified with no evidence of fracture or delamination. The porous structure of the spacers varied highly across the surfaces without influencing the material failure.
authors.affiliation: Implant Research Center, School of Biomedical Engineering, Science, and Heath Systems, Drexel University, 3401 Market Street, Suite 300, Philadelphia, PA 19104, USA. djj25@drexel.edu
authors.forename: David J
authors.initials: DJ
authors.lastname: Jaekel
authors.forename: Judd S
authors.initials: JS
authors.lastname: Day
authors.forename: Gregg R
authors.initials: GR
authors.lastname: Klein
authors.forename: Harlan
authors.initials: H
authors.lastname: Levine
authors.forename: Javad
authors.initials: J
authors.lastname: Parvizi
authors.forename: Steven M
authors.initials: SM
authors.lastname: Kurtz
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects* / Q000295:instrumentation; D001696:Biomechanical Phenomena; D001843:Bone Cements / Q000627:therapeutic use*; D020099:Coated Materials, Biocompatible; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology / Q000601:surgery*; D007720:Knee Prosthesis / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D015143:Philadelphia; D016062:Porosity; D011474:Prosthesis Design; D011475:Prosthesis Failure; D016459:Prosthesis-Related Infections / Q000382:microbiology / Q000601:surgery*; D020127:Recovery of Function; D012086:Reoperation; D012307:Risk Factors; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D016896:Treatment Outcome; D055114:X-Ray Microtomography
chemical_list: D000900:Anti-Bacterial Agents; D001843:Bone Cements; D020099:Coated Materials, Biocompatible