Scapular dyskinesis (SD) is present in as many as 67–100% of athletes with shoulder injuries [1], but also in many asymptomatic individuals [2]. It is characterized by increased protraction with a prominent scapular medial border and an inferior angle, resulting in atypical and inefficient kinematics of the arm and shoulder [3, 4]. Disrupting scapulothoracic kinematics overloads the compensatory musculature, limits shoulder strength and range of motion, and causes pain [5,6,7,8,9,10]. SD may occur due to several shoulder pathologies, including injury of the acromioclavicular joint, rotator cuff tear, clavicular fracture, shoulder impingement, multidirectional instability, and labral injury [11,12,13,14,15,16,17,18]. Furthermore, scapular muscles are essential contributors to scapular positioning both at rest and during shoulder movement [11, 19]. The upper and lower trapezius muscles, as well as serratus anterior, have been shown to be key muscles for maintaining optimal scapular stability during shoulder motion [20, 21]. While trapezius and serratus anterior muscles initiate upward rotation and posterior tilt, the lower trapezius plays a key role in scapular stability in the overhead position of the arm, as well as in the descent from maximum elevation [22, 23]. The rhomboids, levator scapulae and pectoralis minor assist the trapezius and contribute to controlling medial and lateral scapular translation [23].

The latissimus dorsi originates on the thoracolumbar aponeurosis of T7 through the iliac crest and inserts on the crest of the lesser tuberosity of the humerus with direct and indirect attachments to the inferior border of the scapula in supposedly two-thirds of the cases [24, 25]. It affects scapular motion as the prime mover of the arm and its effect on SD plays a relatively small role in the literature. Recently, a significant relationship between increased latissimus stiffness and altered scapular kinematics due to the pull of the latissimus dorsi on the inferior border of the scapula was found [24]. Thus, regardless of the specific cause of the altered scapular kinematics, an apparent relationship seems to exist between the latissimus dorsi and SD. Furthermore, many anatomy books depict the inferior angle of the scapula as one of the origins of the latissimus dorsi muscle [26,27,28,29,30,31,32,33,34]. According to our clinical surgical observation, the position of the scapula can change significantly in relation to the muscle belly of the latissimus dorsi, which may create a dynamic track on which the inferior border of the scapula is overlapped by the muscle belly and glides under it during arm movement (Video 1 and 2). This dynamic restraint, dependent on the degree of the latissimus overlap, can theoretically play a significant role in preventing SD by stabilizing the inferior border of the scapula against the chest and optimizing the position of the scapula throughout the range of motion, for example, when performing pull ups. Therefore, the aim of this study was to evaluate the latissimus-scapula overlap (LSO) in patients without any pathologies of the upper extremities or thorax and its variance in arms up and down positions.