JOA - 2026-09-21 - Journal Article
Knee Society Radiographic Evaluation System Update: Standardizing Assessment of Patellar Translation in Resurfaced and Unresurfaced Patellae.
Lonner JH, Mont MA, Scuderi GR, Clarke HD, DellaValle CJ, Haas SB
Topics
Key Takeaway
The 2015 Knee Society Radiographic Evaluation System's use of the native patella midpoint as the reference landmark systematically overestimates lateral patellar translation in both unresurfaced patellae and medialized patellar prostheses.
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Summary
The 2015 Modern Knee Society Radiographic Evaluation System referenced the native patella midpoint to assess patellar translation in TKA, a method that fails to account for unresurfaced patellae (where the median ridge is the functional tracking landmark) and medialized patellar prostheses. This expert update proposes substituting the median ridge of the native patella or the midpoint of the patellar prosthesis as the reference point depending on resurfacing status. No comparative radiographic data or patient outcomes are reported; the recommendation is based on anatomic and technical rationale.
Key Limitation
The proposed landmark update is not validated against any radiographic dataset, leaving the actual reduction in measurement error and improvement in inter-observer reliability unquantified.
Original Abstract
The Modern Knee Society Radiographic Evaluation System was published in 2015, when routine patella resurfacing in total knee arthroplasty (TKA) was the norm and little attention was given in the United States to either selective patella resurfacing or leaving the patella unresurfaced as a matter of course in all cases. The method advocated for assessing patella translation at that time referenced the midpoint of the native patella relative to the trochlear sulcus. Recognizing the growing preference for leaving the patella unresurfaced in TKA when there is no major lateral patellar facet wear and the tendency to medialize the patella prosthesis when resurfacing it, referencing from the midpoint of the native patella may erroneously suggest that the patella is translated laterally, even when it is not. We offer an update to the methodology for assessing the translational position of the patella, referencing either the median ridge of the native patella when unresurfaced or the midpoint of the patellar prosthesis when resurfaced, rather than the midpoint of the native patella.