Lack of agreement between computer navigation and post-operative 2-dimensional computed tomography (CT) measurements for component and limb alignment in total knee arthroplasty (TKA)

•CT is often used to verify component alignment in navigated TKR•Alignment was compared between intraoperative navigation and post-operative CT in 50 cases•Average results did not differ, however individual differences > 2° were observed in up to 42% of cases.•The reliance of both measurement techniques on manual landmark registration may contribute to differences.•Surgeons should consider the potential mismatch between modalities when considering post-operative alignment.

BackgroundThe purpose of this study was to assess the degree of mismatch between intraoperative navigation data using imageless computer navigation and post-operative CT scan measurements with respect to bone cuts, component and limb alignment during TKA.MethodsIntraoperative navigation data including bone cut verification and overall limb alignment during TKA was compared to postoperative CT measurements of component and limb alignment according to the Perth protocol. The proportion of cases with mismatch between navigation and CT measurements at two and three degree thresholds was identified.ResultsIn a total sample of 50 primary TKAs, 20% of cases showed a mismatch of more than two degrees between navigation and CT obtained measurements for coronal femoral alignment, 42% for femoral rotation, 16% for tibial component coronal alignment and 32% for overall limb alignment.ConclusionMismatch between intraoperative navigation data and postoperative CT measurements suggests that postoperative CT scan alignment data should be interpreted with caution. A surgeon should consider a multitude of factors when analysing component and limb alignment postoperatively.