Introduction
Visual assessment of movement is commonly used in sports medicine and aims to recognise quality of movement for identifying athletes predisposed to future injury.1–4 For the lower extremity, a series of postural malalignments during single-limb weight bearing or landing have been characterised by excessive pelvic drop, femoral internal rotation, knee valgus, tibia internal rotation and foot pronation.5–7 These malalignments are reportedly associated with overuse syndromes such as patellofemoral pain syndrome,8 iliotibial pain syndrome,9 femuro-acetabular impingement,10 tibial stress fractures11 and injuries such as anterior cruciate ligament injuries.12 The single leg squat (SLS) is used to assess movement quality in the lower limb performed by squatting from a single-leg stance while the quality of the movement is observed and assessed. The SLS is described in the literature in various ways, including single-limb mini squat,13 unilateral squat,14 one legged squat,15 single legged squat,16 single leg mini squat17 and single leg small knee bend.18 Thus, a variety of protocols for assessing and performing the SLS are presented,13 14 19–22 making it difficult to define a uniform test as ‘the SLS test’. Some authors propose a simple segmental approach as they assess only the relation between the foot and the knee,13 while others propose a multisegmental approach, assessing the whole kinetic chain from the foot to the trunk.19 In addition, assessment criteria vary,14 22 as does performance in terms of squatting depth, arm position, support and position of the non-weight-bearing leg (ie, front, middle and back).13 22–27 Similar to the SLS are the forward step-down (FSD) and lateral step-down (LSD) tests. These tests differ from the SLS by being performed standing on a 15–25 cm high box. Even if studies have shown kinematic and kinetic differences between various SLS28 and in addition between SLS and FSD,29 the movement patterns during the descendent phase are the same; flexion at the knee, hip and trunk, pelvic tilt, hip adduction and knee internal rotation and abduction.28 29 The common denominators for these test are that they visually assess balance, stability, knee control, overall motor control, coordinated movement quality and dynamic alignment throughout the body. That is to say, the same construct with regard of lower extremity coordination patterns of the foot, knee, hip and pelvic. Based on this similarity in construct, the FSD and LSD will be included and analysed in this meta-analysis together with the SLS.
Previous literature reviews on the measurement properties of clinical tests to assess movement quality have focused on weight-bearing activities in general (eg, drop jump, tuck jump, lunge and SLS)30 31 and showed poor to very good inter-rater and intrarater reliability. For clinical and research purposes, it is important that a test is reliable. Reliability in general is affected by factors such as the complexity of the rating scale (dichotomised or multiple-rating, number of segments assessed), the definitions of the rating criteria, the velocity of the tests and the examiner’s training and clinical experience.31 32 Besides the large between-subject variation due to biomechanical differences between individuals, an important aspect of reliability measures of these tests is the within-subject variation. Although 3D33–37 and 2D studies27 38–40 report joint kinematics with fair to good agreement over time, the SLS, FSD and LSD joint kinematics have not yet been adequately assessed for within-subject reliability using visual assessment.31 To our knowledge, no review and meta-analysis have previously summarised the reliability of the SLS and included the FSD and LSD. Thus, the aim of this study was to perform a review and meta-analysis on the inter-rater and intrarater reliability of visual assessment of the SLS, including the FSD and LSD.