25 August 2026

Using Ultrasound Muscle Ratios to Inform Shoulder Injury Diagnosis

Shoulder Injuries and Diagnostic Limitations

Shoulder injuries are among the most common musculoskeletal conditions affecting military personnel and can impact physical performance, operational readiness, and return-to-duty timelines. Because optimal rotator cuff function is essential for shoulder stability, strength, and movement, accurately evaluating these injuries is critical for Service members who duties often require high levels of physical performance. Yet diagnosing shoulder dysfunction can be challenging. Traditional physical examination techniques, strength testing, and movement assessments may have limitations in identifying subtle changes in rotator cuff health or detecting injury risk, particularly within active military populations.

The study, “Establishing Limits of Normal for Important Muscles and Tendons of the Rotator Cuff using Ultrasound” conducted through the Musculoskeletal Injury Rehabilitation Research for Operational Readiness (MIRROR) program within the Uniformed Services University’s Center for Advanced Research for Military Optimization, Readiness, and Rehabilitation (ARMORR), examined whether sonographic measurements and ratios could provide a more standardized way to evaluate rotator cuff health in military beneficiaries.

Rotator cuff muscle size can provide important insight into shoulder function and potential pathology following injury. Magnetic resonance imaging (MRI) has traditionally been used to assess and diagnose, but MRI studies can be expensive and patients may experience lengthy wait times for imaging. To address these barriers and support quicker return-to-duty timelines, musculoskeletal ultrasound offers a practical tool clinicians can use during the clinical exam, when trained providers and equipment are available.

The study evaluated whether ratios comparing adjacent rotator cuff and shoulder muscles may offer a more standardized method for interpreting ultrasound measurements across an active, healthy, military population. The study addressed a key limitation as absolute muscle measurements can vary based on sex, body composition, and fat-free mass, which can make a single measurement harder to interpret on its own. By comparing adjacent neighboring muscles, the researchers sought to determine whether relative muscle ratios could provide a more reliable reference point for identifying disproportionate muscle development, dysfunction, or pathology.

Establishing Normative Reference Values

Researchers measured the upper trapezius, supraspinatus, infraspinatus, and teres minor muscles, then calculated three ratios:

· upper trapezius to supraspinatus thickness ratio,
· supraspinatus to infraspinatus cross-sectional area ratio,
· infraspinatus to teres minor cross-sectional area ratio.

The methodology builds upon established imaging practices, including use of supraspinatus occupation ratios in the shoulder assessment and ultrasound-based cross-sectional area ratios used in lower extremity research.

The study enrolled 128 participants across three military treatment facilities and evaluated 231 shoulders. Most participants were active-duty Service members. Using a standardized ultrasound protocol, investigators established normative measurements and ratios within a healthy, physically active military beneficiary population.

What the Findings Revealed

While average rotator cuff muscle measurements differed between biological males and females, the corresponding ratios demonstrated negligible differences across sexes. This finding is particularly important because it suggests muscle ratios may provide a more universally applicable tool than absolute measurements. By reducing the influence of sex-related differences in muscle size, these ratios may offer clinicians a more practical and standardized reference for evaluating shoulder health across diverse military populations. The establishment of normative reference values may also improve clinicians’ ability to identify abnormal findings associated with rotator cuff dysfunction, injury, or disease.

According to Dr. Marin Smith, Senior Research Physical Therapist, “The accurate and timely diagnosis of rotator cuff pathology, which a systematic diagnostic ultrasound examination has the potential to yield, could guide appropriate treatment selections for active-duty Service Members to optimize rehabilitation and expedite return to duty.”

Early and accurate diagnosis is a critical component of musculoskeletal injury management. Delays in identifying rotator cuff pathology can prolong rehabilitation, limit physical performance, and delay return-to-duty outcomes for Service members. By establishing normative ultrasound-based reference values and muscle ratios, this study provides clinicians with additional tools to assess shoulder health more efficiently and consistently. The findings support the broader use of musculoskeletal ultrasound as an accessible, cost-effective diagnostic resource within military medicine.

For ARMORR and MIRROR, the research reflects an ongoing commitment to advancing evidence-based approaches for injury prevention, diagnosis, rehabilitation, and recovery. By developing practical tools that support clinical decision-making, researchers are helping improve musculoskeletal care while supporting the readiness and operational effectiveness of the force.

Interested in the full research? Read the study in Military Medicine: https://academic.oup.com/milmed/advance-article-abstract/doi/10.1093/milmed/usag162/8653565?redirectedFrom=fulltext

This work was funded in part by the Musculoskeletal Injury Rehabilitation Research for Operational Readiness (MIRROR), Department of Physical Medicine & Rehabilitation, Uniformed Services University, Bethesda, MD, (HU00011920011).