Follow-up, revision parameters for metal-on-metal hip implants outlined
In a recent presentation, one surgeon outlined his indications for follow-up and revision of metal-on-metal total hip replacements.
Thomas P. Schmalzried, MD, presented his experience at the International Congress for Joint Reconstruction San Diego 2012 meeting, which was held in collaboration with Orthopedics Today.
Although there has been no standard of review established in the United States, Schmalzried noted routine follow-up should be considered good practice.
“Routine follow-up has been recommended,” he said. “The goals of follow-up are to identify the problems, but also to reassure when everything is satisfactory.”
Schmalzried mentioned the special risks inherent in metal-on-metal hip replacements, including higher monoblock loosening rates and adverse local tissue reactions (ALTRs). An issue with the taper of an implant, he said, may lead to ALTR despite good implant positioning. Variables to be considered during follow-up include the patient, component position and implant.
“Head size seems to matter when we talk about total hip replacement in metal-on-metal bearings,” Schmalzried said. “Loosening is the issue you get when you start looking at large diameter bearings. The majority are greater than 36 mm.”
In terms of radiographic assessment, Schmalzried recommended a low anteroposterior pelvis shot with the beam centered on the pubic bone, a true lateral shot and a table-down lateral shot. These radiographs should be used, he said, to analyze fixation, position and the presence of osteolysis.
The risk factors for revision, Schmalzried said, include a lateral opening angle of 55° or greater, increased combined anteversion and monoblock sockets with large heads. Variables related to this, he added, include female patients, due to their smaller size, and dysplastic anatomy — which could lead to increased combined anteversion.
According to Schmalzried, revision should be considered in patients who display poor clinical results, such as pain or mechanical symptoms. Pseudotumor or other soft tissue involvement, such as edema and necrosis, are also a sign that revision should be performed within 3 months. Osteolysis and high metal ion levels should also bring revision into consideration.
Schmalzried stressed he still observes asymptomatic patients with “clean” MRIs, regardless of their metal ion levels.
- Schmalzried TP. Metal-metal hip bearings. Presented at the International Congress for Joint Reconstruction San Diego 2012 in collaboration with Orthopedics Today. April 27-29. San Diego.
- Thomas P. Schmalzried, MD, can be reached at the Joint Replacement Institute at St Vincent Medical Center, 2200 W Third St., Ste. 400, Los Angeles, CA 90057; email: email@example.com.
- Disclosure: Schmalzried receives royalties and research funds from DePuy, as well as research funds from Wright Medical, Corin, the Piedmont Foundation, and St. Vincent Medical Center.