What are the predictors and prevalence of pseudotumor and elevated metal ions after large-diameter metal-on-metal THA?

BACKGROUND: Soft tissue masses, or "pseudotumors," around metal-on-metal total hip arthroplasty (MoM THA) have been reported frequently; however, their prevalence remains unknown. Several risk factors, including elevated metal ion levels, have been associated with the presence of pseudotumor, although this remains controversial. QUESTIONS/PURPOSES: The goals of this study were to (1) determine the prevalence of pseudotumors after large-diameter head MoM THA; (2) identify risk factors associated with pseudotumor formation and elevated metal ion levels; and (3) determine the early failure rate of large-diameter MoM THA. METHODS: Between December 2005 and November 2012, 258 hips (215 patients) underwent large-diameter head primary MoM THA at our institution. Clinical followup was obtained in 235 hips (91%). Using an inclusion criteria of a minimum followup of 1 year, a subset of 191 hips (mean followup, 4 years; range, 1-7 years) was recruited for high-resolution ultrasound screening for the presence of pseudotumor. Whole blood cobalt and chromium ion levels, UCLA activity level, WOMAC score, patient demographics as well as surgical, implant, and radiographic data were collected. Bivariate correlations and multivariate log-linear regression models were used to compare the presence of pseudotumor and elevated metal ions with all other factors. RESULTS: Ultrasound detected a solid, cystic, or mixed mass in 20% hips (38 of 191). No correlation was found between the presence of pseudotumor and any risk factor that we examined. After controlling for confounding variables, elevated cobalt ions were correlated (p<0.001, R=0.50, R2=0.25) with smaller femoral head size, the presence of bilateral MoM THA, and female sex. Elevated chromium ions were correlated (p<0.001, R=0.59, R2=0.34) with smaller femoral head size, presence of bilateral MoM THA, and lower body mass index. The overall survival of MoM THA was 96% at a mean followup of 4.5 years (range, 2-8 years). CONCLUSIONS: With the numbers available, we found no associations between the presence of pseudotumor and the potential risk factors we analyzed, including elevated metal ion levels. Further work is needed to explain why larger femoral head sizes resulted in lower metal ion levels despite being associated with higher early failure rates in joint registry data. LEVEL OF EVIDENCE: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

A randomized controlled trial comparing Oxinium and cobalt-chrome on standard and cross-linked polyethylene.

The purpose of the investigation was to assess the clinical and radiographic outcomes in four bearing surfaces. Eighty patients (91 hips) undergoing total hip arthroplasty between 2004 and 2007 were randomized to one of four bearing surfaces: (1) cobalt-chrome (CoCr) and ultra-high molecular weight polyethylene (UHMWPE); (2) CoCr and XLPE; (3) Oxinium and UHMWPE; and (4) Oxinium and XLPE. The mean follow-up for this study was 6.8 years. There were no significant differences in clinical outcomes. The linear wear rates for the four groups were 0.241 mm/year, 0.076 mm/year, 0.238 mm/year and 0.061 mm/year respectively. HXLPE results in significantly less wear than UHMWPE. However, we found no significant reduction in wear rate by using Oxinium in place of CoCr femoral heads at early follow-up.

Rare case of acute dengue encephalitis with correlated MRI findings.

Dengue encephalitis is extremely rare, with most patients showing no significant abnormality on neuroimaging (CT/MRI). We report one of the very few documented cases of dengue encephalitis, with abnormal signal intensities on all major sequences on brain MRI.