The Natural History of Inflammatory Pseudotumors in Asymptomatic Patients After Metal-on-metal Hip Arthroplasty

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 cm³; 28-74 cm³; 47-104 cm³). Three pseudotumors (one solid and two cystic) disappeared completely (the largest measured 31 cm³). One solid pseudotumor decreased in size (24 to 18 cm³). In five revised patients, pseudotumors completely disappeared in four patients. The fifth patient had two masses that decreased from 437 cm³ to 262 cm³ and 43 cm³ to 25 cm³. 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 cm³ to 136 cm³.

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.