MIS TKA associated with increased early revision, surgeon reports

SAN FRANCISCO — Despite the promise of smaller incisions, minimally invasive total knee arthroplasty procedures may result in a higher number of revisions compared to traditional open procedures.

Robert L. Barrack

Furthermore, total knee arthroplasty (TKA) procedures performed by "community" surgeons may contribute significantly to the number of revision TKA procedures being performed on patients overall, according to a study presented here at the American Academy of Orthopaedic Surgeons 75th Annual Meeting.

"There is unlimited support in the literature for MIS (minimally invasive surgery), at least in the short term. A number of problems with these studies are [that they] are by ... very experienced, high-volume surgeons. And it may not be representative of what's happening with lower-volume surgeons with less experience," said Robert L. Barrack, MD.

"There is little [evidence] available in the literature at this point on MIS total knees performed by community surgeons," he added. "Are these MIS procedures contributing to the revision burden? Are the revisions of MIS different from revisions of total knee performed through standard incisions?"

To investigate this issue, Barrack and colleagues reviewed a consecutive series of revision TKAs performed by community surgeons over 3 years. They excluded infection-related revisions and re-revisions. They also completed a detailed clinical and radiographic review at the time of revision to determine the revision diagnosis, he said.

"We compared MIS total knees to the revisions of knees performed through the standard incision," Barrack said.

Overall, the investigators reviewed 236 first-time revisions out of more than 400 revision procedures performed at three centers. Of these, 193 were performed using standard TKA approaches and 43 were done using MIS approaches — about 18% overall, he said.

Barrack noted that MIS patients were significantly younger, and there was a trend toward more women undergoing MIS procedures.

"Most striking was [the] time to revision, which was drastically shorter at less then 15 months compared to 80 months for the standard incision group," Barrack said.

The investigators also found that MIS knees were much more likely to fail within 12 months to 24 months, and were also much more likely to have malrotation or instability as the cause of failure.

"But, on a positive note, they were much less [prone] to lysis or wear as a cause of failure," he said, laughing.

Barrack acknowledged that there were some study limitations, including the fact that the researchers don't know what percentage of TKAs are performed using MIS approaches. "But it is highly unlikely that enough MIS is being done to justify this many early failures," he said.

MIS now constitutes a substantial percentage of revision total knees, at least at the three centers participating in the study, Barrack said.

"There were a number of early failures at only 15 months on average, [which is] a concern. Malrotation and stability and loosening are the failure modes," he said.

"The good news is that these were fairly straightforward revisions. The bad news is that early revisions for instability [and] malposition are not historically associated with good results" Barrack added.

For more information:
Barrack RL, Barnes Cl, Miller DW, et al. Minimal incision surgery as a risk factor for early failure of total knee arthroplasty. #103. Presented at the American Academy of Orthopaedic Surgeons 75th Annual Meeting. March 5-9, 2008. San Francisco.