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1.  Failed Metal-on-Metal Hip Arthroplasties: A Spectrum of Clinical Presentations and Operative Findings 
Background
A number of recent reports have described novel failure mechanisms of metal-on-metal bearings in total and resurfacing hip arthroplasty. Hip arthroplasties with metal-on-metal articulations are also subject to the traditional methods of failure seen with different bearing couples. There is currently little information in the literature to help guide timely clinical evaluation and management of these patients.
Questions/purposes
We therefore describe the (1) clinical presentations; (2) reasons for failure; (3) operative findings; and (4) histologic findings in patients with failed metal-on-metal hip arthroplasties.
Methods
We retrospectively identified all 37 patients (37 hips) with metal on metal total hip or resurfacing arthroplasties who underwent revision over the past 3 years at our institution. Relevant clinical, radiographic, laboratory, intraoperative, and histopathologic findings were analyzed for all patients.
Results
Of the 37 patients, 10 were revised for presumed hypersensitivity specific to the metal-on-metal articulation. This group included eight patients with tissue histology confirming chronic inflammation with lymphocytic infiltration, eight with aseptic loosening of a monoblock screwless uncemented acetabular component, two with iliopsoas impingement associated with a large-diameter femoral head, and three with femoral neck fracture after resurfacing arthroplasty; the remainder of the patients were revised for infection, instability, component malposition, and periprosthetic fracture.
Conclusions
Increased awareness of the modes of failure will bring to light the potential complications particular to metal-on-metal articulations while placing these complications into the context of failures associated with all hip arthroplasties. This novel clinical information should be valuable for the practicing surgeon faced with this patient population.
Level of Evidence
Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-010-1419-0
PMCID: PMC2919884  PMID: 20559767
2.  Differential effects of biologic vs bisphosphonate inhibition of wear debris-induced osteolysis assessed by longitudinal micro-CT 
Summary
Aseptic loosening secondary to periprosthetic osteolysis remains a serious orthopaedic problem and the greatest limitation of total joint replacement. This process is caused by wear debris-induced osteoclastic bone resorption, for which effective small molecule (bisphosphonates, BPs) and biologic (RANK antagonists) drugs have been developed. While BPs have proven to be effective in preventing metabolic bone loss in non-inflammatory conditions such as osteoporosis, they do not have the same efficacy in the setting of inflammatory bone loss such as that observed in periprosthetic osteolysis. Since this difference has been attributed to the anti-apoptotic inflammatory signals that protect osteoclasts from BP-induce apoptosis, but not RANK antagonists, we tested the hypothesis that osteoprotegerin (OPG) is more effective in preventing wear debris-induced osteolysis than zoledronic acid (ZA) or alendronate (Aln) in the murine calvaria model. Based on the shortcomings of previous animal studies that focused on 2D imaging and histology endpoints, and the emergence of quantitative 3D-CT, we developed in vivo micro-CT methods for the murine calvaria model to more rigorously test our hypothesis and correlate the osteolysis results with traditional histology. Although this approach proved to be incompatible with titanium (Ti) particles, due to metal artifact, we were able to demonstrate a 3.2-fold increase in osteolytic volume over 10 days induced by ultra high molecular weight polyethylene (PE) particles vs. sham controls (0.49 +/− 0.23mm3 vs. 0.15 +/− 0.067mm3; p<0.01). While OPG and high dose ZA completely inhibited this PE-induced osteolysis (p<0.001), pharmacological doses of ZA and Aln were less effective but still reached statistical significance (p<0.05). Traditional histomorphometry of the sagital suture area of calvaria from both Ti and PE treated mice confirmed the remarkable suppression of resorption by OPG (p<0.001) vs. the lack of effect by physiological BPs. The differences in drug effects on osteolysis were largely explained by the significant difference in osteoclast numbers observed between OPG vs. BPs in both Ti and PE treated calvaria; and linear regression analyses that demonstrated a highly significant correlation between osteolysis volume and sagittal suture area vs. osteoclast numbers (p<0.001). Taken together our results demonstrate the sensitivity and utility of in vivo 3D-CT to detect the effects of BPs on wear debris-induced osteolysis that could not be observed by histology alone; and that the greater suppression of bone resorption observed with OPG treatment vs. BPs is due to its ability to dramatically reduce osteoclast numbers in the presence of inflammatory signals.
doi:10.1002/jor.20620
PMCID: PMC2742224  PMID: 18404739
Aseptic Loosening; wear debris; osteolysis; osteoprotegerin (OPG); bisphosphonate (BP); 3D-micro-CT

Results 1-2 (2)