Muscle Thickness, Trunk Proprioception, and Postural Stability in Rotator Cuff Pathology

The rotator cuff consists of the supraspinatus, infraspinatus, teres minor, and subscapularis muscles and their tendons and surrounds the shoulder joint. Rotator cuff syndrome includes various conditions affecting the rotator cuff, such as subacromial impingement syndrome, bursitis, tendinitis, and partial- or full-thickness rotator cuff tears. Rotator cuff-related shoulder pain generally refers to a painful clinical condition that occurs during shoulder elevation and external rotation and is accompanied by limitations in shoulder movement and function. Its etiology is multifactorial. The combination of extrinsic mechanical compression, such as narrowing of the subacromial space, and tendon overuse, such as repetitive overhead activities, has been identified as one of the main mechanisms underlying rotator cuff pathology. Diagnosis is based on medical history, physical examination, and imaging when necessary.

Sequential physiological muscle activations in the upper and lower extremities create an integrated biomechanical task. This sequential organization is referred to as the kinetic chain. During activities predominantly involving the upper extremity, energy is generated and transferred from the proximal to the distal segments. A disruption within the kinetic chain may result in dysfunctional biomechanical outcomes and contribute to the development of pain and injury. Impairments in the proximal components of the kinetic chain may negatively affect shoulder function. Therefore, in patients with shoulder disorders, all components that may impair kinetic chain function should be evaluated.

Core stability is defined as the ability to control the position and movement of the trunk over the pelvis in order to enable optimal force generation and the transfer and control of force and movement to the distal segment during activity. Core muscle activity provides both stability and movement. This mechanism enables proximal stability for distal mobility, the sequential transfer of force from proximal to distal segments, and the generation of intersegmental moments that move and protect the distal joints. The core region is important for providing local strength and balance. It is also positioned at the center of almost all kinetic chains involved in sporting activities. Therefore, adequate core muscle strength facilitates effective control of balance and movement and supports the optimal functioning of kinetic chains associated with both upper- and lower-extremity activities.

The sensorimotor system includes all sensory and motor components involved in maintaining joint stability, together with their central integration and processing mechanisms. This system consists of several components, including proprioception, joint position sense, kinesthesia, force sense, and neuromuscular control. When a shoulder injury occurs, not only mechanical structures such as the joint capsule and glenoid labrum may be affected, but the sensorimotor system may also be impaired. Shoulder injuries may be accompanied by deficits in both proprioception and neuromuscular control, which may consequently result in balance impairments.

Some studies have suggested that pain may also contribute to balance impairment. A possible explanation is that pain-processing mechanisms, the neuronal networks responsible for balance control, and pain-related muscle inhibition partly involve shared pathways within the central nervous system. A recent study conducted in Türkiye that investigated balance in patients with shoulder pain reported a significant difference in balance between the patient and control groups. The study also found that balance impairment was positively associated with pain severity.

This study aims to investigate the relationships between latissimus dorsi and abdominal muscle thickness, trunk proprioception, and postural stability in individuals with rotator cuff pathology. The study will also examine whether these measurements differ between individuals with rotator cuff pathology and healthy participants.

Inclusion criteria

Rotator Cuff Pathology Group

• Willing to participate in the study and able to provide written informed consent
• Aged 18 years or older
• Unilateral shoulder pain lasting for at least 3 months
• Right-hand dominance
• Diagnosis of rotator cuff pathology

Healthy Control Group

• Willing to participate in the study and able to provide written informed consent
• Aged 18 years or older
• Right-hand dominance
• No current shoulder pain

Exclusion criteria

• Unwilling or unable to provide written informed consent
• Younger than 18 years
• History of a chronic orthopedic or neurological condition that may affect shoulder, abdominal, or periscapular muscle function
• History of injury or surgery involving the abdominal region
• Bilateral shoulder pain or bilateral shoulder pathology
• Chronic low back pain
• Recent history of lumbar spine injury or surgery
• Presence of a comorbid condition that may cause balance impairment
• History of neuromuscular disease
• History of malignancy
• Pregnancy
• Receipt of physical therapy or rehabilitation for the shoulder region within the previous 6 months