Review Question - QID 4655

The clinical presentation is consistent with a young woman who has developed a symptomatic pseudotumor following hip resurfacing. Her hip discomfort is related to a mass that has developed around the left hip.

Pseudotumors, also referred to as Aseptic Lymphocyte-Dominated Vascular-Associated Lesions (ALVAL), are sterile inflammatory lesions that most commonly occur from metal-on-metal articulations. They occur at an incidence of 0-39% with metal-on-metal resurfacing hip components. The exact mechanishm of formation is unclear, however excessive wear is considered the initiating process, leading to the release of microscopic metal particles. These are cytotoxic to macrophages once phagozytised, leading to necrosis within the lesions and the development of semi-solid or fluid-filled masses around the implant. Lymphocytes are thought to be responsible for the tissue reaction. Patients often do not complain of pain, but present with a mass around the hip that causes discomfort.

Hart et al. performed a case-control study comparing patients with well-functioning metal-on-metal hip resurfacing to those who have painful prostheses. They found no significant difference between the painfree and painful groups with MRI diagnosed pseudtumors (61% vs. 57%). They concluded that the presence of a pseudotumor should not automatically necessitate revision surgery.

Daniel et al. reviewed the current concepts surrounding pseudotumor. Risk factors associated with pseudotumor formation and failure are female gender, age under 40, hip dysplasia, metal hypersensitivity, and small components. Larger components have been found to decrease the risk of failure.

Figure A is an AP pelvis radiograph of a patient following a left hip resurfacing surgery. Figures B and C are axial and coronal MR images demonstrating a large pseudotumor around the left hip resurfacing. Illustrations A and B identify the large pseudotumor as outlined in red.

Incorrect Answers:
Answer 1: While infection should always be ruled out with symptomatic prosthetic joints, the radiograph and MRI clearly represent a pseudotumor from a metal-on-metal hip resurfacing.
Answer 2: Hypersensitivity reaction would be a rare presentation 2.5 years following a hip resurfacing.
Answer 3: Femoral neck fracture is a risk in the initial post-operative period (<20 weeks).
Answer 4: The radiograph shows a hip resurfacing device in good position with no evidence of loosening.