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CAS-TKR may restore mechanical axis in cases of significant femoral bowing
Huang T.W. J Bone Joint Surg (Br). 2011;93-B:345-350.
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In cases of significant femoral bowing, computer-assisted total knee replacement restored the mechanical axes closer to normal compared with a conventional technique, according to the results of a retrospective study.
T. W. Huang, MD, W.H. Hsu, MD, and colleagues at Chang Gung University in Taiwan, studied how femoral bowing affected component placement in total knee replacement (TKR), specifically in regard to re-establishing the correct mechanical axis. They hypothesized that computer-assisted (CAS) TKR would produce more accurate alignment than conventional TKR in this Asian population study.
The study included 212 patients (306 knees) who underwent TKR between January 2006 and December 2009. The investigators used five radiological measurements to assess the accuracy of component placement and postoperative alignment. Results showed that with conventional TKR, there were significant differences in the mechanical axes between the bowed and non-bowed group (176.2° vs. 179.3°).
“For patients with significant femoral bowing, the reconstructed mechanical axes were significantly closer to normal in the CAS group than in the conventional group (179.2° vs. 176.2°, P<.001),” the authors wrote. “Femoral bowing resulted in inaccuracy when a conventional technique was used.”
While the debate about the benefits of computer-assisted surgery (CAS) navigation technology in its various guises continues, especially with regards to its universal application to all knee replacement surgeries, the goal of a well-balanced, well-aligned knee replacement is fully accepted.
Until now, no one has addressed the role of navigation in different racial physionomies. Hsu and co-authors raise the issue of femoral geometry differences in Asian patients — with more than 60% demonstrating significant femoral bowing — and the potential of this bowing to adversely affect postoperative long-leg mechanical alignment and component positioning in conventionally-implanted knee arthroplasties. This research clearly demonstrates the ability of CAS to avoid this, although the price was a significantly longer tourniquet time (67 mins vs. 87mins; P<0.001).
This paper is important for several reasons.
First, it raises the issue of racial differences in femoral anatomy and how CAS can yield better outcomes in terms of alignment and component positioning in patients with significant femoral bowing.
Second, it also confirms that in the hands of high-volume arthroplasty surgeons, good component positioning and long-leg alignment can be achieved in those knees without significant femoral deformity using conventional instrumentation.
Third, it suggests that all Asian patients being subjected to knee arthroplasty must be assessed preoperatively with long-leg alignment films to identify those with significant femoral bowing. This would allow selective CAS to optimize their outcome.
Next time you undertake a total knee arthroplasty in an Asian patient ask yourself, “Have I assessed this femoral anatomy?” If not, you better use CAS!
– Alberto Gregori, FRCS
Clinical Director Orthopaedics
NHS, Lanarkshire
Disclosure: He has received departmental research support from BBraun Aesculap, BrainLab and Biomet, and educational support from Boehringer Inglheim.