Background:​ Shoulder pain is a common problem treated by physicians and physical therapists. A large number of these patients have injury to the rotator cuff. There is a range of severity in rotator cuff disease, which likely includes a high proportion of partial thickness tears (PTT). This condition is difficult to diagnose since current methods to identify PTT (imaging and physical assessment special tests) are inadequate. Other items from physical assessment may help with the patho‐anatomical diagnosis of PTT, but there is also growing support for diagnostic approaches which emphasize movement as the basis for classification of shoulder conditions. The objective of this study was to determine if clinical presentation factors that focus on demographics, injury history, physical assessment and patient reported outcomes were associated with a surgical diagnosis of PTT in a group of patients all previously diagnosed with full thickness tear (FTT) using imaging.

Methods:​ A secondary analysis was performed using pre‐operative baseline data from two randomized controlled trials of 452 adult patients awaiting rotator cuff repair surgery. All subjects were previously diagnosed with imaging as having a FTT. Nineteen factors were assessed for association with an outcome of PTT or FTT (which was diagnosed at the time of surgery.) Factors were selected for analysis based on previous identification in the literature as having association with PTT or FTT, and were limited to those items collected in both primary studies. Logistic regression was used to test independent associations of each factor with the outcome. Items with univariate association of p<0.20 were entered into multivariate logistic regression analyses. Several multivariate models were purposefully built, ensuring no collinearity between the variables. Confounding was controlled for by noting change in the regression output as variables were maintained or removed from the models. Several purposeful steps were performed in various combinations to arrive at a final reduced model that identified the key factors associated with PTT (significance level p<0.05).

Results:​ Comparison of the data in the two primary studies showed a small number of statistical differences in the variables, but none with clinical significance. This allowed for combining the two data sets for secondary analysis. Of the 452 subjects, 32 (7.1%) had PTT. In the total group, 294 (65%) subjects were male and of the PTT subjects, 23 (71.9%) were male. A majority of participants (n=303;​ 67%) reported an atraumatic onset to shoulder symptoms. In multivariate analyses, the Constant Power score, which assesses abduction strength, was the sole factor statistically associated with PTT (Odds Ratio 1.067, 95% CI 1.017, 1.120, p= 0.008). A traumatic mechanism of injury showed a trend toward significance in analysis, but was not statistically significant in the final multivariate model (p= 0.067). Other factors from the assessment:​ age, pain at rest, pain with activity, active range of motion (flexion, abduction, scaption, eternal rotation at 0° abduction, external rotation at 90°abduction, internal rotation at 90°abduction), Western Ontario Rotator Cuff Index scores (total and dimensions), and SF‐36 Physical Component Summary and Mental Component Summary scores, did not show association with PTT (p>0.520).

Conclusion:​ The findings of this study indicate that a higher Constant Power score is associated with having a PTT in a group of patients previously diagnosed with imaging as having a FTT. Mechanism of injury (traumatic onset) showed a trend toward association with PTT. Other findings from patient assessment which were evaluated did not help distinguish this diagnosis. Clinicians could consider adding a structured evaluation of abduction strength, like the Constant Power score to a physical examination of suspected rotator cuff patients.

A major limitation in this study was related to the sample of PTT subjects:​ all were high‐degree PTT so the sample was not representative of all PTT patients. To improve the body of information provided by this study, similar research should be undertaken with a broader spectrum of PTT subjects.

Perhaps our findings are not solely affected by the selection of subjects. There is a growing collection of studies that show an inconsistent relationship between tissue pathology and impairments. The identification of only a small number of clinical assessment factors associated with PTT in this study may suggest using a different assessment approach that is less focused on patho‐anatomy in future research studies.