Quantifying Frontal Plane Knee Motion during Single Limb Squats: Reliability and Validity of 2-Dimensional Measures.    

Authors: Gwynne CR, Curran SA

Individuals with patellofemoral joint (PFJ) pain have been found to demonstrate abnormal lower extremity mechanics during functional tasks such as running, hop landing, step-down maneuvers, and single limb squats.  Altered frontal plane knee alignment during such activities is often described as “dynamic knee valgus”. Dynamic knee valgus is characterized by excessive knee abduction, combined with femoral adduction and internal rotation and relative external tibial rotation and is thought to result due to weakness or diminished or delayed neuromuscular activation of hip musculature.  Control of frontal plane knee motion is important, as dynamic knee valgus during functional activity may result in increased frontal plane loading of the PFJ and contribute to etiology or exacerbation of PFJ pain symptoms. Identification of individuals who demonstrate excessive knee valgus during functional tasks may allow for identification and modification of abnormal movement patterns.  Therefore, the purpose of this study was to describe a 2-D video capture procedure that quantifies frontal plane knee alignment as a single measure (frontal plane projection angle, FPPA) during single limb squats at 60° of knee flexion.  The validity of 2-D FPPA was determined by correlating 2-D results with those determined from established methods (3-D motion analysis). In addition, 2-D methods were assessed for reliability and associated measurement error.

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