Evaluation of Thoracic Kyphosis, Trunk Rotation, and Balance in Rotator Cuff Pathology

Plain-language summary

This study aims to investigate the relationship between thoracic kyphosis angle, trunk rotation mobility, and balance performance in individuals with rotator cuff pathology. The rotator cuff, consisting of the supraspinatus, infraspinatus, teres minor, and subscapularis muscles, plays a crucial role in providing both static and dynamic stability to the shoulder joint. Rotator cuff pathologies are among the most common causes of shoulder pain and functional limitation, with their prevalence increasing with age. Although shoulder pain has traditionally been considered a localized musculoskeletal problem, recent biomechanical evidence highlights the importance of the kinetic chain concept, which emphasizes the interconnected function of the upper extremity with the lower extremity, thoracic spine, and postural control mechanisms. Within this framework, thoracic spine mobility and postural stability are considered key factors in preventing pathological loading on the rotator cuff tendons. The thoracic spine serves as a fundamental biomechanical platform for scapulothoracic joint function. Increased thoracic kyphosis has been shown to negatively affect scapular upward rotation and posterior tilt during humeral elevation, contributing to narrowing of the subacromial space and increased mechanical stress on the rotator cuff tendons. In addition, trunk rotation mobility plays an essential role in efficient energy transfer along the kinetic chain, particularly during functional movements such as reaching or throwing. Limitations in trunk rotation may disrupt this energy transfer, resulting in compensatory loading of the shoulder complex and increased injury risk. Furthermore, kinesiophobia associated with chronic pain may alter movement strategies, reduce physical activity levels, contribute to muscle atrophy, and indirectly impair postural control mechanisms. Balance performance is maintained through the integration of visual, vestibular, and somatosensory systems. In individuals with rotator cuff pathology, impaired proprioceptive input from the shoulder girdle and increased pain-related postural sway may lead to decreased performance in dynamic balance tasks such as the Y-Balance Test. In contrast, in healthy individuals, postural control strategies have been shown to correlate with self-perception and body awareness levels. Based on this theoretical framework, the primary aim of the present study is to compare thoracic kyphosis angle, trunk rotation mobility, static balance, and dynamic balance performance between individuals with rotator cuff pathology and healthy controls, and to examine the relationships between these variables. It is hypothesized that individuals with rotator cuff pathology will demonstrate significant differences in these parameters compared to healthy individuals. The study will be conducted at the Physical Therapy Unit of Iğdır State Hospital and will include individuals aged 18-65 years. Sample size calculation was performed using G\*Power software based on a previously reported effect size (Cohen's d = 0.63) for thoracic kyphosis. With an alpha level of 0.05 and statistical power of 80%, at least 36 participants per group were required. To account for potential dropouts, a total of 80 participants will be included, consisting of at least 40 individuals with rotator cuff pathology and 40 healthy controls. All participants will provide written informed consent, and sociodemographic and clinical information will be collected through face-to-face interviews. Thoracic kyphosis angle will be measured using a smartphone-based digital inclinometer by calculating the angular difference between T1-T2 and T12-L1 vertebral levels. Trunk rotation range of motion will be assessed using a digital goniometer. Static balance performance will be evaluated using the Single Leg Stance Test under eyes-open and eyes-closed conditions. Dynamic balance performance will be assessed using the Y-Balance Test protocol, in which reach distances in three directions are normalized according to leg length. These measurement tools have been reported to demonstrate high validity and reliability in clinical research. In conclusion, this study seeks to demonstrate that rotator cuff pathology should not be considered solely a localized shoulder disorder but rather a condition associated with impairments in the kinetic chain, including thoracic spine mobility and postural control mechanisms. The findings are expected to highlight the importance of assessing thoracic mobility and balance performance in shoulder rehabilitation programs.

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