2017 ISAKOS Biennial Congress ePoster #1285
Use Of The “Runway” As An Independent Guide To Rotational Alignment Of The Tibial Cutting Jig In Total Knee Arthroplasty (TKA)
Ciaran McGarvey, MA, MSc, FRCS(Tr&Orth), London UNITED KINGDOM
Bradley Rael Gelbart, FC Orth (SA) Mmed Ortho Surg(WITS), Johannesburg, Gauteng SOUTH AFRICA
Ponky Firer, Prof., Johannesburg SOUTH AFRICA
Department of Trauma and Orthopaedics, University of the Witwatersrand, Johannesburg, SOUTH AFRICA
FDA Status Cleared
Summary
This prospective anatomic study identified the runway as a anatomic landmark which can be used to position the tibial cutting jig at an average of 3.7 degrees from the anatomic axis of rotation of the tibia.
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Abstract
Introduction
Correct rotation of the tibial component is important in determining patella tracking in fixed bearing TKA. In mobile bearing TKA, incorrect tibial tray rotation will result in asymmetric coronal gaps if a cutting jig with a slope is used. The anatomic axis of tibial rotation was previously defined by Cobb as running perpendicular to the mid-point of a line joining the centres of the medial and lateral tibial plateaus. The runway was defined in this study as a virtual rectangle overlying the intercondylar eminence, running from posterior to anterior, with the longer sides aligned to the tibial spines
Method
This prospective anatomic study was undertaken between May and August 2016. Eighty-two consecutive primary TKAs were performed by two surgeons at a single institution. An extramedullary cutting guide with a 7degree posterior slope was aligned along the runway and the position of the jig marked on the tibial plateau. The resected tibial plateau was traced onto paper and the position of the jig marked. The centre of the medial and lateral plateaus were determined as the centre of a best fit circle, and the anatomic axis of rotation drawn. The angle between the anatomic axis of rotation and the cutting jig was then calculated.
Results
The runway was identified in 80/82 cases. Twenty-three tibial cuts were not resected whole and were excluded. Fifty-seven specimens were included in the study.The first twelve consecutive specimens were used to compare inter and intra-observer reliability between two observers. The mean intra-class coefficient was 0.89 for intra-observer reliability and 0.76 for inter-observer reliability, Fifty-seven specimens were analysed by a single observer. Mean deviation of the runway was 3.7degrees (range 0-12degrees, standard deviation 3.0degrees) compared to the anatomic tibial axis. Deviation from the anatomic axis was <5degrees in 42/57 specimens, 5-10degrees in 14/57 specimens and >10degrees in 1/57.
Conclusion
The runway is a novel, and near universal, anatomical landmark that can be used instead of the tibial tubercle to guide rotation of the tibial cutting jig in TKA.