PurposeTo evaluate the correlation between suture contamination and rotator cuff tendon retear after arthroscopic rotator cuff repair. MethodsPatients undergoing primary arthroscopic rotator cuff repair from April 1st, 2020 to September 30th, 2022 were enrolled. Those younger than 18 years, with a history of prior shoulder surgeries or shoulder infection episodes, or who declined participation, were excluded. A 5 cm section of the first-cut suture, originating from the anchor eyelet ends, in each rotator cuff repair surgery was subjected to bacteria culture and polymerase chain reaction (PCR) analysis. Patients with positive culture findings were matched 1:1 to those with negative culture reports based on age, sex, tear size as well as involved tendons, preoperative fatty infiltration grade (Goutallier grade) and preoperative muscle atrophy grade (Warner score). Postoperative rotator cuff tendon retear assessments were conducted at the 6-month mark using the Sugaya classification via magnetic resonance imaging. The Wilcoxon signed-rank test was used for matched-pair comparisons between the groups. ResultsA total of 141 patients (60 males and 81 females) with a mean age of 61.0 ± 8 years were finally enrolled. Twenty-six patients (18 males and 8 females) had a positive culture, while 115 patients (42 males and 73 females) had a negative culture. After the propensity score matching process, 24 culture-negative patients (16 males and 8 females) were selected as the culture-negative group. Age, fatty infiltration grade, and muscle atrophy grade were not significantly different between matched groups. The retear grade in the culture-positive group was found to be significantly higher than that in the culture-negative group (P = 0.020) under the matched-pair comparison. C. acnes. was the most prevalent bacterial species responsible for suture contamination. ConclusionsThe matched-pair analysis revealed that the presence of bacterial contamination on sutures was associated with a higher risk of retear in MRI following arthroscopic rotator cuff repair.