This study investigates whether tightness of a small chest muscle called the pectoralis minor is associated with the development of partial rotator cuff tears in the shoulder. Using a propensity score matched case-control design, the study compares patients with rotator cuff tears (case group, n=45) to patients with intact rotator cuffs (control group, n=45).

Adults aged 18-55 with shoulder pain who are evaluated by MRI and/or shoulder arthroscopy at Gazi University Hospital may be invited. The case group includes patients found to have partial rotator cuff tears during arthroscopy. The control group includes patients whose rotator cuff was documented as intact by MRI. Groups are matched 1:1 on age, sex, BMI, and dominant side.

Before surgery, two trained clinician measures shoulder posture and pectoralis minor length using simple external tools (a digital caliper and ruler-like square). For arthroscopy patients, the surgeon records general arthroscopic findings. No extra procedures are added for research.

We expect to include 90 participants total. The primary hypothesis is that pectoralis minor tightness is more prevalent in patients with rotator cuff tears compared to controls. A secondary hypothesis is that tears in patients with pectoralis minor tightness more often partial-thickness bursal side rotator cuff tear. Results may help clinicians understand shoulder mechanics and improve prevention or rehabilitation strategies.

Rationale and Objectives Pectoralis minor (PM) tightness alters scapular position (anterior tilt, internal rotation) and may increase subacromial compression. This propensity score matched case-control study evaluates whether PM tightness is associated with the development of partial rotator cuff tears (RCTs).

Design and Setting Single-center, propensity score matched case-control study at a tertiary academic hospital (orthopaedic shoulder service, Gazi University Hospital). Care is not altered by participation. All surgical and imaging procedures are standard of care; research procedures are limited to noninvasive postural/PM length measurements and structured data collection.

Participants Inclusion criteria consisted of patients aged 18-55 years who were scheduled to undergo surgical treatment for a partial-thickness rotator cuff tear (case group) and individuals aged 18-55 years with no evidence of rotator cuff or other shoulder pathology on magnetic resonance imaging (control group). Patients were excluded if they had a history of trauma, thoracic outlet syndrome, systemic inflammatory disease, prior surgery on the affected shoulder, and declined participation in the examination. After application of the eligibility criteria, patients with partial-thickness rotator cuff tears will be matched in a 1:1 ratio with patients without rotator cuff or other shoulder pathology. Matching was performed based on age, sex, body mass index (BMI), and dominant extremity involvement. Covariate balance was assessed using absolute standardized differences, with a predefined threshold of 0.1.

Study Procedures

Preoperative assessments (same-day or pre-op clinic):

• Pectoralis minor length (mm): Pectoralis minor length was measured using a digital caliper, with the coracoid process and the fourth rib adjacent to the sternum serving as palpable anatomical landmarks; three trials recorded; mean used for analysis.
• Medial scapular border-thoracic distance (mm) using rulers.
• Forward shoulder posture using a 300 mm square.
• Imaging abstraction: Standard shoulder radiographs and MRI summarized.
• Anatomical and radiological measurements were assessed by two independent authors blinded to patient's group status.

Intraoperative assessment (for arthroscopy patients):

Surgeons document tear characteristics using a standardized form based on video visualization.

Sample Size and Power A priori power analysis was performed using effect sizes derived from PMI measurements in previous studies (Cohen's d = 0.91-1.83).Using the smallest effect size as a conservative estimate, a minimum sample size of 20 patients per group was required to achieve 80% power at a two-sided α level of 0.05.

Statistical Analysis Plan

• Software: IBM SPSS Statistics-26, R (MatchIt package)
• Normality: Shapiro-Wilk test
• Comparisons: Paired t-test / Wilcoxon / McNemar for matched pairs
• Primary outcome: Presence of rotator cuff tear (case vs control) as a function of PM tightness
• Secondary outcome: The tear is a partial bursal surface tear as a function of PM tightness in the case group
• Significance level: two-sided alpha=0.05

Inclusion criteria consisted of patients aged 18-55 years who were scheduled to undergo surgical treatment for a partial-thickness rotator cuff tear (case group) and individuals aged 18-55 years with no evidence of rotator cuff or other shoulder pathology on magnetic resonance imaging (control group). Patients were excluded if they had a history of trauma, thoracic outlet syndrome, systemic inflammatory disease, prior surgery on the affected shoulder, and declined participation in the examination.

Inclusion criteria consisted of patients aged 18-55 years who were scheduled to undergo surgical treatment for a partial-thickness rotator cuff tear (case group) and individuals aged 18-55 years with no evidence of rotator cuff or other shoulder pathology on magnetic resonance imaging (control group). Patients were excluded if they had a history of trauma, thoracic outlet syndrome, systemic inflammatory disease, prior surgery on the affected shoulder, and declined participation in the examination.