Payments directly related to the presentation topic, according to criteria adopted by Okike and colleagues, were also more likely to be reported than those indirectly related or unrelated.
The researchers noted that the AAOS policy required disclosure from participants who "received something of value from a commercial company or institution, which relates directly or indirectly to the subject of their presentation."
Payments were considered directly related in the study if the presentation topic focused specifically on knee or hip implants.
Presentations on other aspects of knee or hip arthroplasty, such as antibiotic prophylaxis during such procedures, were deemed indirectly related to payments from the five companies.
Presentation on other topics altogether were classified as unrelated.
Okike and colleagues identified 208 payments as directly related to the presentation topics, of which 165 were disclosed (79 percent).
Fifty-nine payments went to physicians presenting on unrelated topics, of which 29 were disclosed (49 percent). Half of the 32 payments to physicians whose presentations were indirectly related went undisclosed.
Okike and colleagues said the high rate of nondisclosure could have relatively innocent explanations.
"One possibility is that the physicians in question did not consider the undisclosed payments to have been related to the subject of their presentation," they said, noting that their survey found this to be at common explanation.
The disclosure requirement may also have been confusing, the researchers said. "The policies regarding conflict of interest and its disclosure are constantly in flux, and it is possible that additional education regarding disclosure requirements may be needed."
Okike and colleagues identified several limitations to their study. Their method of determining payment relatedness could have been faulty, and omissions in the printed meeting program may have led the researchers to undercount disclosures submitted by participants, they noted. Their survey also had a low response rate.
In addition, the study focused on disclosures at one meeting of a single specialty society, covering a specific set of payments.
In a prepared statement responding to questions about the study, AAOS President Dr. Joseph D. Zuckerman, said that "Since 2008, we have taken steps to make our process and emphasis on mandatory disclosure more robust."
Zuckerman, head of orthopedic surgery at the NYU Hospital for Joint Diseases in New York City, said those steps included:
Launching an electronic system for reporting disclosures, accessible all year long
Requiring that all payments and relationships be disclosed, whether or not they are related to presentation topics
Increasing education efforts for members on the importance of disclosure
He added that relationships with industry are good for physicians and patient care, as long as they are transparent.