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.

Fig. 1

The study group was selected from a previous cohort of 75 patients reported by Williams et al. [42]. Twenty-two patients with positive ultrasound findings (SM, CM, FC) were eligible for this study. MOM = metal on metal; MOP = metal on polyethylene; US = ultrasound; SM = solid mass; CM = cystic mass; FC = fluid collection.

Fig. 2

Pseudotumor sizes (cm³) increased over time in four of six nonrevised large head metal-on-metal THAs. SM = solid mass; US = ultrasound; CM = cystic mass.

Fig. 3

Pseudotumor sizes (cm³) increased over time in two of three nonrevised hip resurfacing arthroplasties. CM = cystic mass; SM = solid mass; US = ultrasound.

Fig. 4

Pseudotumors disappeared (* or decreased in size [cm³]) after revision of four large head metal-on-metal THAs and one resurfacing hip arthroplasty. * One large head metal-on-metal patient had three different masses labeled a, b, and c.

Fig. 5

Chromium ion levels (in parts per billion [μg/L]) decreased in all revised patients (four large head metal-on-metal THAs and one resurfacing hip arthroplasty).

Fig. 6

Cobalt ion levels (in parts per billion [μg/L]) decreased in all revised patients (four large head metal-on-metal THAs and one resurfacing hip arthroplasty).

Fig. 7

Fluid collections disappeared over time in two metal-on-polyethylene and two metal-on-metal THAs and increased in size in one metal-on-metal THA. MOM = metal on metal; MOP = metal on polyethylene; PT = pseudotumor; US = ultrasound.