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Metal on Metal Risk Factors for Pseudotumor in Metal-on-Metal Hip Replacements

Josephine

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Risk Factors for Pseudotumor in Metal-on-Metal Hip Replacements PAPER NO. 658
Shiraz Sabah, MD, London, United Kingdom
Karuniyan V. Vipulendran, Haverfordwest, United Kingdom
Johann Henckel, BM, London, United Kingdom
Keshthra Satchithananda, FRCR, London, United Kingdom
Adam Mitchell, MD, London, United Kingdom
Anastasia Papadaki, MSc, London, United Kingdom
Donald McRobbie, PhD, London, United Kingdom
John Skinner, FRCS, London, United Kingdom
Alister Hart, FRCS, London, United Kingdom


INTRODUCTION: Pseudotumors are sterile, inflammatory lesions associated with large-diameter metal-on-metal hip replacements (MOM-HR). They may be diagnosed using cross-sectional imaging during the investigation of an unexplained, painful MOM-HR. Pseudotumors are an important clinical problem due to their association with unexplained hip pain and rare reports of devastating periprosthetic tissue damage. We aimed to investigate risk factors for pseudotumor and to determine which were associated with poor prognosis.

METHODS: We conducted a case-control study in 149 consecutive patients that had metal artifact-reduction sequence MRI performed at our center. We identified 81 cases with pseudotumor (three solid, 78 fluid-filled) and 68 controls without pseudotumor. We analyzed demographic, prosthesis, positioning and serological data. We performed subset analyses in the pseudotumor group to compare well-functioning patients (n=21) with patients with unexplained pain (n=60).

RESULTS: Solid pseudotumors were all painful, but were uncommon when compared to fluid-filled pseudotumors. Distributions of risk factors for pseudotumor are presented in Table 1. No significant differences between groups were found for any risk factor. Risk factors that may be important in prognostication in pseudotumor patients are presented in Table 2. Female sex (p=0.001), raised blood metal ion levels (p=0.003) and small head size (p=0.027) were associated with painful pseudotumor.

DISCUSSION AND CONCLUSION: There are currently no obvious risk factors for pseudotumor in MOM-HR. All common implant types are affected, whether they are well-functioning or painful. Our data agrees with published studies in that female sex, raised blood metal ion levels and small head size were associated with poor clinical status. However, we found the presence of a fluid-filled pseudotumor was not and provide this new information. Patients with solid pseudotumors and extensive soft tissue destruction should be revised.

Table 1. Comparison of factors that may be linked to pseudotumor in 149 patients with MOM-HR that had MARS MRI performed at our centre.

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Table 2. Comparison of 81 patients with pseudotumor on MARS MRI to determine factors that may be associated with poor prognosis.

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