The test retest reliability of gait outcomes in subjects with anterior knee pain.

Introduction: Anterior knee pain (AKP) is a common condition frequently causing young, athletic patients to attend sports rehabilitation centres. Abnormal biomechanics are thought to contribute towards the development and chronicity of the condition. Gait analysis is commonly used to identify abnormal biomechanics in subjects with AKP, however the reliability of these measurements are unknown. Therefore, the aim of this study was to quantify the test retest reliability of hip, knee and ankle kinematics during gait in an AKP population so the true effects of an intervention can be established.

Methods: Thirty-one subjects with AKP attended the 3D Motion Analysis Laboratory at Tygerberg Medical Campus of Stellenbosch University in Cape Town, South Africa, for gait analysis. Participants returned seven days later at approximately the same time to repeat the gait analysis assessment from day one. The same assessor tested all subjects on both occasions. The intra-class correlation coefficients (ICC) and standard error of measurement (SEM) were calculated for hip, knee and ankle kinematic outcomes on the affected side and used for analysis.

Results: All outcomes obtained were acceptable to excellent test retest reliability scores for both measures of relative reliability (ICC = 0.78-0.9) and measures of absolute reliability (SEM = 0.94-4.2°). Hip frontal plane and ankle sagittal plane outcomes were the most reliable and had the lowest measurement error. Hip transverse plane outcomes were least reliable and demonstrated the highest measurement error.

Conclusion: Hip, knee and ankle kinematic factors that are commonly associated with AKP can be measured reliably using gait analysis. Daily and weekly variation in symptoms in an AKP population may influence the reliability of knee sagittal plane outcomes. Therefore, it is important to document factors that could influence the kinematics such as pain, activity levels and the use of pain medication.