Isokinetic Eccentric Quadriceps Muscle Performance Assessment in Patellofemoral Joint Primary and Secondary Injury Prevention: An Intra-Rater Reliability and Standard Error of Measurement Pilot Study.

Introduction: Quadriceps muscle weakness is implicated in the onset and persistence of patellofemoral joint (PFJ) pain, which commonly manifests during the early stance-phase of gait when eccentric quadriceps muscle performance (ecc- QMP) is required to decelerate momentum and shock-absorb forces away from articular tissues. Therefore, assessment of eccQMP is prudent in PFJ primary and secondary injury prevention, but reliable measurement procedures are scarce in the literature. Objective: To assess critical psychometric properties of a new isokinetic eccQMP assessment procedure linked closely to the biomechanics of gait during stair and hill descent, using a specific knee range-of-motion and velocity-of-motion (specificity of testing1). It was hypothesised that procedures would demonstrate good intra-rater reliability (intraclass correlation coefficient [ICC] ≥0.75). Study design: Between-day (D1/D2) repeated measures. Setting: biomechanics laboratory. Study population: eight athletes volunteered (male n=6, female n=2, age 23.0±3.6yr; height 157.0±35.8cm; mass 86.0±36.4kg). Assessment: athletes were seated on an isokinetic dynamometer set to eccentric mode. For specificity of testing, dynamometer configuration was knee flexion/extension range-of-motion 10-80° and velocity-of-motion 60°/s then 120°/s. Three maximal-effort knee flexion (eccQMP) trials were performed for both velocities. Peak torque (PT; Newton-metres [Nm]) and time-to-peak torque (TTPT; milliseconds [ms]) were measured. Limb order was ran- domised for D1 then repeated D2. Main outcome measurements: relative reliability (ICC 2,1) and absolute reliability (standard error of measurement (SEM)). Results: For 60°/s: PT ICC/SEM, right 0.95/13.5Nm, left 0.98/10.2Nm; TTPT ICC/SEM, right 0.12/1121.0ms, left 0.12/666.3ms. For 120°/s: PT ICC/SEM, right 0.85/23.8Nm, left 0.96/15.1Nm; TTPT ICC/SEM, right 0.76/174.4ms, left 0.05/694.7ms. Conclusion: For both 60°/s and 120°/s, eccentric PT consistently demonstrated good relative reliability (ICC>0.75) but TTPT did not (ICC<0.75). The SEM was consistently lowest when the highest ICCs were evident. The new isokinetic eccentric quadriceps PT assessment procedures demonstrate psychometric properties that qualify them for potential use in PFJ primary and secondary injury prevention. [ABSTRACT FROM AUTHOR]