Survival at 11 to 21 years for 779 Metasul® metal-on-metal total hip arthroplasties

Quantification and severity grading of femoral vessel compression by adverse reactions to metal debris in metal-on-metal total hip arthroplasty

INTRODUCTION

Metal-on-metal (MoM) total hip arthroplasty (THA) may cause adverse reactions to metal debris (ARMD). ARMD causing femoral vessel compression with serious complications has been described in case reports, but the rate of compression by ARMD is not known. This study aims to investigate the rate, and quantify the severity, of femoral vessel compression in MoM hips with ARMD lesions.

METHODS

Patients under surveillance for MoM THA investigated with MRI were studied. In patients with confirmed ARMD, femoral artery (FA) and vein (FV) diameters were measured at the point of maximal compression and compared to contralateral vessels. The primary outcome measure was presence or absence of compression. Cases were then classified by compression ratios. Secondary outcome measures were rates of deep vein thrombosis, revision surgery and time to ARMD from index procedure.

RESULTS

MRI scans for 436 patients with MoM THA were screened. Of these, 211/436 (48.4%) showed evidence of ARMD. Measurements were obtained on 133/211 (63.0%) patients. The FV was compressed in 102/133 (76.7%) and FA in 58/133 (43.6%), while 31/133 (23.3%) patients had no compression. In FVs, 42 demonstrated mild compression, 39 moderate and 21 severe. In FAs, none were severely compressed, 6 were moderate and 52 showed mild compression. There were 3 DVT cases, 2 in patients with moderate FV compression and 1 in patients without FV compression. Revision rates were highest in patients with severe FV compression (14/21, 66.7%). The mean time for MRI-diagnosed ARMD from index procedure was 8 years and 1 month (range 11 months-14.5 years).

CONCLUSIONS

Extra-luminal compression of the femoral vessels was found in >75% of patients with ARMD. Although it is not clear whether revision for femoral vessel compression is required, quantification of FV compression may be useful for surgeons and radiologists considering revision for ARMD.

Cobalt ions induce metabolic stress in synovial fibroblasts and secretion of cytokines/chemokines that may be diagnostic markers for adverse local tissue reactions to hip implants

Adverse local tissue reactions (ALTRs) are a prominent cause of hip implant failure. ALTRs are characterized by aseptic necrosis and leukocyte infiltration of synovial tissue. The prevalence of ALTRs in hips with failing metal implants, with highest rates occurring in patients with metal-on-metal articulations, suggests a role for CoCrMo corrosion in ALTR formation. Although hypersensitivity reactions are the most accepted etiology, the precise cellular mechanism driving ALTR pathogenesis remains enigmatic. Here we show that cobalt ions released by failing hip implants induce mitochondrial stress and cytokine secretion by synovial fibroblasts: the presumptive initiators of ALTR pathogenesis. We found that in-vitro treatment of synovial fibroblasts with cobalt, but not chromium, generated gene expression changes indicative of hypoxia and mitophagy responses also observed in ALTRs biopsies. Inflammatory factors secreted by cobalt-exposed synovial fibroblasts were among those most concentrated in ALTR synovial fluid. Furthermore, both conditioned media from cobalt-exposed synovial fibroblasts, and synovial fluid from ALTRs patients, elicit endothelial activation and monocyte migration. Finally, we identify the IL16/CTACK ratio in synovial fluid as a possible diagnostic marker of ALTRs. Our results provide evidence suggesting that metal ions induce cell stress in synovial fibroblasts that promote an inflammatory response consistent with initiating ALTR formation. STATEMENT OF SIGNIFICANCE: We demonstrate that the cytotoxic effects of cobalt ions on the synovial cells (fibroblast) is sufficient to trigger inflammation on hip joints with metal implants. Cobalt ions affect mitochondrial function, leading to the auto phagocytosis of mitochondria and trigger a hypoxic response. The cell's hypoxic response includes secretion of cytokines that are capable of trigger inflammation by activating blood vessels and enhancing leukocyte migration. Among the secreted cytokines is IL-16, which is highly concentrated in the synovial fluid of the patients with adverse local tissue reactions and could be use as diagnostic marker. In conclusion we define the cells of the hip joint as key players in triggering the adverse reactions to hip implants and providing biomarkers for early diagnosis of adverse reactions to hip implants.