Abstract
BackgroundAccurately measuring in-vivo motion of the knee's patellofemoral (PF) joint is challenging. Conventional measurement techniques have largely been unable to accurately measure three-dimensional, in-vivo motion of the patella during dynamic activities. The purpose of this study was to assess the accuracy of a new model-based technique for measuring PF joint motion.MethodsTo assess the accuracy of this technique, we implanted tantalum beads into the femur and patella of three cadaveric knee specimens and then recorded dynamic biplane radiographic images while manually flexing and extending the specimen. The position of the femur and patella were measured from the biplane images using both the model-based tracking system and a validated dynamic radiostereometric analysis (RSA) technique. Model-based tracking was compared to dynamic RSA by computing measures of bias, precision, and overall dynamic accuracy of four clinically-relevant kinematic parameters (patellar shift, flexion, tilt, and rotation).ResultsThe model-based tracking technique results were in excellent agreement with the RSA technique. Overall dynamic accuracy indicated errors of less than 0.395 mm for patellar shift, 0.875° for flexion, 0.863° for tilt, and 0.877° for rotation.ConclusionThis model-based tracking technique is a non-invasive method for accurately measuring dynamic PF joint motion under in-vivo conditions. The technique is sufficiently accurate in measuring clinically relevant changes in PF joint motion following conservative or surgical treatment.
Highlights
Measuring in-vivo motion of the knee's patellofemoral (PF) joint is challenging
While these studies have provided helpful information about patellar tracking, static analyses can not quantify PF joint function during dynamic activities, 2D analyses are incapable of capturing the complex 3D relationship of the patella relative to the femur, and bone pins [17,18] limit the number of willing volunteers and make serial studies over time impractical since bone pins can not be reliably reattached in the exact location
The purpose of the study was to assess the accuracy of this model-based tracking technique for in-vivo PF joint motion by comparing the model-based technique to an accurate radiostereometric analysis (RSA) technique that measures joint motion by tracking the position of implanted tantalum beads [36]
Summary
Measuring in-vivo motion of the knee's patellofemoral (PF) joint is challenging. In-vivo studies of PF joint motion have traditionally relied upon static twodimensional (2D) radiographs [11,12,13,14,15], 2D video digital fluoroscopy [16], intracortical bone pins [17,18], x-ray photogrammetry [19], electromagnetic sensors [20], static CT [21,22], and static MRI [23,24,25,26] While these studies have provided helpful information about patellar tracking, static analyses can not quantify PF joint function during dynamic activities, 2D analyses are incapable of capturing the complex 3D relationship of the patella relative to the femur, and bone pins [17,18] limit the number of willing volunteers and make serial studies over time impractical since bone pins can not be reliably reattached in the exact location
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