Radiographic Measures of Patellar Tracking After Total Knee Arthroplasty: Comparing the Native Patellar Midpoint...

Area of Science:

• Orthopedic Surgery
• Radiographic Imaging
• Biomechanical Analysis

Background:

• Accurate assessment of patellar tracking is crucial in total knee arthroplasty (TKA).
• The midpoint of the native patella (MPNP) method may inaccurately reflect patellar position due to asymmetric morphology and non-resurfaced patellae.
• Alternative landmarks like the patellar median ridge (MR) or center of the patellar prosthesis (CPP) may offer improved accuracy.

Purpose of the Study:

• To compare the accuracy of the MPNP method versus MR/CPP methods in assessing patellar translation post-TKA.
• To determine if landmark selection significantly alters the measured magnitude or direction of patellar translation.

Main Methods:

• Retrospective review of 413 primary TKAs (213 unresurfaced, 200 resurfaced).
• Measurement of patellar translation using pre- and postoperative Merchant view radiographs.
• Comparison of MPNP method with MR (unresurfaced) or CPP (resurfaced) methods.

Main Results:

• The MPNP method consistently overestimated lateral patellar translation compared to MR/CPP methods both pre- and postoperatively (P < 0.001).
• Differences were most significant in unresurfaced patellae, with mean differences of 4.74 mm preoperatively and 4.41 mm postoperatively.
• A high rate of reclassification from lateral to neutral or medial shift was observed when using MR/CPP methods.

Conclusions:

• Landmark selection critically impacts radiographic assessment of patellar tracking in TKA.
• The MPNP method overestimates lateral translation, particularly in cases with patellar morphological asymmetry or medialized prosthetic placement.
• MR and CPP methods provide more anatomically accurate and consistent patellar position assessments for TKA.