Shoulder Biomechanics and Rehabilitation

We are dedicated to improving the quality of life for individuals with shoulder pain and those who have undergone rotator cuff repair surgery.

Our research is centered on the premise that clinicians cannot effectively treat patients without understanding the unique factors contributing to each individual’s condition. Shoulder conditions often prove especially challenging to treat because the shoulder is a complex system consisting of three joints and approximately 20 muscles that must work together to produce the motion needed for functional, occupational, and recreational activities. In particular, the rotator cuff – a group of four key shoulder muscles – is essential to shoulder health because it contributes to joint stability in ways that are not yet fully understood. Unfortunately, rotator cuff pathology is common and often leads to considerable shoulder pain and disability, which can persist even after surgical repair of a torn rotator cuff. As rehabilitation researchers, we approach these clinical challenges by investigating the movement-related factors associated with shoulder pathology, symptom manifestation, and functional decline. Ultimately, our primary goals are to:

  1. Develop targeted prevention and treatment strategies for individuals with shoulder pain by understanding the modifiable biomechanical factors contributing to rotator cuff pathology.
  2. Develop patient-specific rehabilitation guidelines for individuals after rotator cuff repair by understanding the patient, tissue, and rehabilitation factors that affect repair integrity and functional outcomes.

Our approach is to conduct rigorous, clinically relevant research that integrates clinical assessment, diagnostic imaging, and state-of-the-art methods of assessing the human movement system with the passion and expertise of a multi-disciplinary research team.

Faculty Investigator

Rebekah Lawrence, PT, PhD

State-of-the-art biplane radiographic motion capture allows for precise quantification of human movement and is used to study joint movement and mechanics.

Current Research Studies

Investigating the Multi-factorial Etiology of Rotator Cuff Pathology in Human Subjects

A rotator cuff tear is a common shoulder condition affecting approximately 40% of individuals over the age of 60. This condition is often painful, debilitating, and impairs quality of life. Despite their prevalence, the cause of rotator cuff tears is not fully understood but is generally believed to involve extrinsic factors (i.e., tendon impingement during shoulder motion), intrinsic factors (i.e., tendon degeneration), and overuse. These factors have been studied extensively in animal models, which have provided support for each factor contributing to rotator cuff pathology and, perhaps more importantly, that a combination of factors may be more impactful than any individual factor. Therefore, the objectives of the proposed studies are to: 1) develop a preliminary multivariable model classifying the effects of extrinsic, intrinsic, and overuse factors on rotator cuff pathology in asymptomatic individuals (K99); 2) extend the model with additional asymptomatic participants (R00); and 3) expand the model to include symptomatic participants (R00).

Funding: NIH/NIAMS (K99-AR075876, R00-AR075876)

Check out: https://pubmed.ncbi.nlm.nih.gov/34636897/, https://pubmed.ncbi.nlm.nih.gov/32807327/, https://pubmed.ncbi.nlm.nih.gov/35880416/

Quantifying the minimum distance between the glenoid and rotator cuff footprint as a measure of rotator cuff internal impingement. Figure from: Lawrence RL, et al., J Orthop Res, 2022.

Determine the impact of simulated scapular movement impairments on mechanisms of rotator cuff tendon injury

Scapular movement impairments are often observed in individuals with shoulder pain and have been hypothesized as an underlying cause of rotator cuff pathology. For example, movement impairments (e.g., insufficient upward rotation) are believed to impact the frequency or magnitude of rotator cuff impingement, which can occur during shoulder motion when the rotator cuff tendon becomes abraded under the coracoacromial arch (subacromial impingement) or entrapped against the glenoid (internal impingement). However, the impact of scapular movement impairments on these potential mechanisms of tendon injury remain unclear. Therefore, this study aims to determine the extent to which simulated changes in scapular kinematics impact the acromion-to-footprint (subacromial) and glenoid-to-footprint (internal) distances.

Check out: https://pubmed.ncbi.nlm.nih.gov/30658048/, https://pubmed.ncbi.nlm.nih.gov/31377124/

A view from the back of the shoulder of a 53 year-old asymptomatic male when his arm was overhead (120° humerothoracic elevation). Movement impairments in scapulothoracic upward/downward rotation are simulated on his actual shoulder motion, with decreasing upward rotation bringing the rotator cuff tendon footprint closer to the glenoid resulting in an increased likelihood of internal impingement.

Development of a low-dose CT protocol for radiographic motion analysis and modeling

Biplanar x-ray imaging is the gold standard for non-invasively quantifying shoulder motion. However, it is not without risks as current data collection protocols use clinical CT scans, which expose a person to about the same radiation dose they would typically receive from natural sources over three years. Although this amount of radiation is not known to increase an individual’s risk for cancer, mitigating risks is a core tenant of the responsible conduct of research. Therefore, this study will determine the dose-accuracy trade-off between incrementally lower-dose CT scans and the kinematic and geometric accuracy.

Funding: NIH/NIAMS (R00-AR075876)