The Impact of Tendon Structure and Pain-Related Fear on Pain Outcomes in Rotator Cuff Tendinopathy Following Resistance Exercise

Rotator cuff (RC) tendinopathy is a leading cause of shoulder pain which is defined by damage to tendon structure. Resistance exercise is a known effective intervention for RC tendinopathy intended to restore deficits in tendon structure. However, outcomes are highly variable and are often related to fear of moving and/or hurting their shoulder, known as pain-related fear. No study has defined the relative contributions of tendon structure and pain-related fear to pain outcomes following resistance exercise. PURPOSE: Define the relative contributions of pain-related fear and tendon structure to patient-reported pain outcomes following 8-weeks of resistance exercise. METHODS: Participants (n=49) with RC tendinopathy were enrolled. Measures of tendon structure, pain-related fear, and pain were collected at 0-, 4-, and 8-weeks over a standardized 8-week resistance exercise program. Ultrasound images of the supraspinatus tendon were collected, and the average thickness at 5-,10, and 15mm from the insertion was calculated. On ultrasound images, peak spatial frequency radius (PSFR) was also calculated using spatial frequency analysis to define collagen disorganization; PSFR is the distance between the two most predominant frequencies in the image. Pain-related fear was measured using the Fear-Avoidance Beliefs Questionnaire Physical Activity (FABQ-PA) and Work (FABQ-W) subscales, Pain Catastrophizing Scale (PCS), and Tampa Scale of Kinesiophobia (TSK) at each visit. Pain was measured via an average of 3 ratings on the Penn Shoulder Score Pain Subscale. Separate linear mixed models with a random intercept for each participant were fit for each pain-related fear scale. Each model predicting pain over time included fixed effects for a pain-related fear scale, tendon thickness, PSFR, weeks, and the interaction between the fixed effects and weeks. RESULTS: FABQ-PA (estimate: -1.1, SEM: 0.5, p = 0.004), FABQ-W (estimate: -1.0, SEM: 0.4, p = 0.01), PCS (estimate: -1.2, SE:0.4, p = 0.001), and TSK (estimate: -0.9, SE:0.4, p = 0.03) significantly predicted shoulder pain over time independent of tendon structure. CONCLUSION:Increased pain-related fear is more strongly related to increased shoulder pain following 8-weeks of resistance exercise than tendon structural deficits.