The Natural History of High-Grade Partial Thickness Rotator Cuff Tears: The Conversion Rate to Full Thickness Tears and Affecting Factors

Background: Information regarding the progression of high-grade partial thickness rotator cuff tears (PTRCTs) is scarce. We aimed to assess the clinical outcome and the conversion rate to full thickness tears in patients with high-grade PTRCTs who underwent nonoperative treatment and to determine the factors associated with tear progression. Methods: A total of 52 patients with high-grade PTRCTs, which were detected by magnetic resonance imaging or ultrasonography (USG), were treated conservatively between 2010 and 2017. They were followed up with USG at 6- to 12-month intervals for a mean of 34 months (range, 12-105 months). The average patient age was 57 years (range, 34-70 years), and 34 patients were women. Age, sex, body mass index, arm dominance, symptom duration, subscapularis tendon involvement, tear location, and trauma history were compared between patients with and without conversion to full thickness tears. Results: A substantial percentage of high-grade PTRCTs progressed to full thickness tears (16/52, 30.8%). According to Kaplan-Meier analysis, the full thickness conversion rate was 30.8% at 3 years and 64% at 4 years. The full thickness conversion rate was higher in patients with subscapularis tendon involvement (p = 0.012). Conclusions: A considerably large proportion of high-grade PTRCTs progressed to full thickness tears. Therefore, regular monitoring of tear progression should be considered after conservative treatment of high-grade PTRCTs, particularly in patients with subscapularis tendon involvement.