Why Does my Shoulder Hurt? Understanding the Presence of Pain in Individuals With Full-thickness Rotator Cuff Tears

Why Does my Shoulder Hurt? Identifying Factors Associated With the Presence of Pain in Individuals With Full-thickness Rotator Cuff Tears

Full-thickness rotator cuff tears (FTRCT), defined as "through-and-through" tears of one of the shoulder tendons, affect up to 32% of the population (mostly individuals older than 50 years) and are one of the most painful and debilitating shoulder diagnoses. One of the primary challenges for clinical decision-making is the poor association between the presence of FTRCT (detected by medical imaging) and pain, as studies have shown that 2/3 of people with FTRCT are asymptomatic. This challenges the notion that FTRCT causes pain, and highlights the fact that symptoms may be explained by other variables. A better understanding of the factors leading to the development of pain in people with FTRCT would optimize clinical care (including prevention).

The objective of this study is to identify variables associated with pain in people with FTRCT by 1) comparing people with FTRCT with (Symptomatic Group; n=40) and without pain (Asymptomatic Group; n=40); 2) comparing people who initially have pain-free FTRCT (Asymptomatic Group) who develop pain over a 2-year period to those who do not develop pain; and 3) comparing people who initially have painful FTRCT (Symptomatic Group) who become pain-free over a 2-year period to those who remain symptomatic. All participants will undergo an ultrasound examination to confirm the presence of FTRCT, and information on a number of variables (sociodemographic, anatomical, genetic, psychosocial, pain sensitivity, neuromuscular, biomechanical) will be collected. All participants will then be followed for 2 years before being revaluated for pain. Variables will be analysed to determine those associated with pain. As it is crucial to improve our understanding of the mechanisms leading to pain, this project has the potential to impact the musculoskeletal health of Canadians. By considering multiple variables associated with FTRCT, its results could lead to the development of tangible solutions to optimize prevention and recovery.

Background: Symptomatic full-thickness rotator cuff tears (FTRCT) affect up to 32% of the population and represent one of the more painful and debilitating shoulder diagnoses. The prevailing model for care pathway decisions is heavily influenced by medical imaging. Yet, the association between FTRCT observed on medical imaging and the presence of pain is poor, as two thirds of FTRCT are asymptomatic. This poses a great challenge to clinical decision-making and questions the belief that FTRCT causes pain. As other factors may explain the presence of pain, a better understanding of this phenomenon needs to be sought.

Objective/hypothesis: The primary objective is to identify variables associated with the presence of pain in individuals with FTRCT. The hypothesis is that given its complex aetiology, no single outcome will be highly associated with pain, rather it will be important to consider several outcomes and their interactions. Secondary objectives include: to explore if a) baseline variables or b) a change in these variables following baseline can predict the development of pain in individuals who initially have asymptomatic FTRCT, and to study if a) baseline variables or b) a change in these variables following baseline can predict the resolution of pain in individuals who initially have symptomatic FTRCT.

Methods: 40 adults with a FTRCT and shoulder pain (Symptomatic Group), and 40 adults with a FTRCT without shoulder pain (Asymptomatic Group) will be included. They will demonstrate a FTRCT on US examinations performed by a radiologist. Included participants will take part in a baseline evaluation during which sociodemographic, anatomical, genetic, psychosocial, pain sensitivity, neuromuscular and biomechanical variables will be assessed. The primary objective (cross-sectional design) will be achieved by determining if differences between groups are based on a sole or on several independent variables, and their relative impact on pain (recursive partitioning, principal component analysis, MANOVA).

The secondary objectives (prospective design) will be achieved by following all participants for 2 years. Every 3 months, the participants will complete a web-based questionnaire asking if they have had shoulder pain. Participants in the Asymptomatic Group who develop pain and participants in the Symptomatic Group who become pain-free will be asked to participate in a follow-up evaluation within a week. Participants who remain pain-free in the Asymptomatic Group and with pain in the Symptomatic Group during the follow-up period will also be asked to participate in a follow-up evaluation at the end of the 2 years (same follow-up evaluation for all participants, similar to baseline evaluations). Logistic regressions will be used to identify the variables associated with pain development and with pain resolution.

Relevance: Before implementing new intervention strategies, a better understanding of factors associated with the presence of pain is needed. By looking at different variables that could explain pain, this project will improve our understanding of FTRCT and fill important knowledge gaps.

Inclusion Criteria (all participants):

• Presence of a full-thickness rotator cuff tear (on ultrasound examination performed by a radiologist)
• 50 to 80 years of age
• Degenerative tear (no significant trauma)

Inclusion Criteria for the Symptomatic group:

• unilateral or bilateral shoulder pain (at least 2/10 on a visual analog scale [VAS] evaluating usual shoulder pain)
• positive response to: 'In the past 4 weeks, have you had pain in your shoulder' and 'If yes, was this pain bad enough to limit your usual activities or change your daily routine for more than 1 day?'

Inclusion Criteria for the Asymptomatic group:

• report no current shoulder pain (0/10 on a VAS evaluating usual shoulder pain)
• negative response to: 'In the past 4 weeks, have you had pain in your shoulder'
• do not report any past significant shoulder pain (any pain greater than or equal to 2/10 that lasted longer than 4 weeks, required the use of medications or prompted a physician visit)

Exclusion Criteria:

1. unable to understand French or English;
2. history of upper limb fracture;
3. previous shoulder surgery;
4. cervicobrachialgia or shoulder pain reproduced by neck movement;
5. shoulder capsulitis (restriction of at least 30% in 2 or more directions);
6. rheumatoid, inflammatory or neurological diseases;
7. corticosteroid injection in the previous 6 weeks;
8. cognitive problems interfering with evaluations (Mini-Mental State Examination ≥ 24)