The natural history of inflammatory pseudotumors in asymptomatic patients after metal-on-metal hip arthroplasty

Abstract

Background: Although pseudotumors have been reported in 32% of asymptomatic metal-on-metal hips, the natural history of asymptomatic pseudotumors is unknown. Questions/purposes: The purpose of this study was to assess changes over time in asymptomatic pseudotumors and the effect of revision on pseudotumor mass. Methods: Followup ultrasound was performed a mean of 25.8 months (range, 21-31 months) after the detection of 15 pseudotumors and five isolated fluid collections in a cohort of 20 asymptomatic patients (13 metal-on-metal, three metal-on-polyethylene, and four hip resurfacings) [42]. Changes in pseudotumors and fluid collections size and nature, and serum ion levels were determined. Results: Among the 15 nonrevised patients, pseudotumors increased in size in six (four solid and two cystic) of 10 patients, three of which had clinically important increases (13-148 cm 3 ; 28-74 cm 3 ; 47-104 cm 3 ). Three pseudotumors (one solid and two cystic) disappeared completely (the largest measured 31 cm 3 ). One solid pseudotumor decreased in size (24 to 18 cm 3 ). In five revised patients, pseudotumors completely disappeared in four patients. The fifth patient had two masses that decreased from 437 cm 3 to 262 cm 3 and 43 cm 3 to 25 cm 3 . All revision patients had a reduction of chromium (40.42 μ/L to 2.69 μ/L) and cobalt ions (54.19 μ/L to 0.64 μ/L). Of five isolated fluid collections, four completely disappeared (two metal-on-metal and two metal-on-polyethylene) and one (metal-on-metal) increased from 26 cm 3 to 136 cm 3 . Conclusions: Our observations suggest pseudotumors frequently increase in size in asymptomatic patients with occasional remission of small masses. Revision resulted in remission of pseudotumors. Level of Evidence: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence. © 2013 The Association of Bone and Joint Surgeons®.