PurposeTo report clinical and activity specific outcomes after arthroscopic RCR(ARCR) for full-thickness supraspinatus tears in active individuals younger than or equal to 45 years of age. The pre hoc hypothesis was that patients in this age group would demonstrate significant improvements in clinical outcomes following ARCR along with a significant improvement of athletic abilities. MethodsPatients were included in this study if they were (1)active individuals between 18 and 45 years of age at the time of surgery, (2)had a full-thickness rotator cuff tear(RCT) of the supraspinatus tendon with or without anterior or posterior extension and (3)underwent ARCR. Pre- and postoperative patient-reported outcomes scores including the American Shoulder and Elbow Surgeons(ASES) score, Disabilities of Arm, Shoulder and Hand(Quick-DASH), Single Assessment Numeric Evaluation(SANE), Short Form-12 Physical Component Summary(SF-12PCS) were prospectively collected and postoperative patient satisfaction(scale of 1-10) was recorded at a minimum of 2 years postoperatively. Attainment of the minimal clinically important difference(MCID) and patient acceptable symptom state(PASS) for the ASES was calculated. Athletic activity specific outcomes and return to activity(RTA) were investigated prospectively via a custom-made comprehensive questionnaire. ResultsBetween 11/2005 and 6/2020, of 1149 RCRs performed by the senior author, 54 patients (mean age 40.9 years,13 female; follow-up 69.7 ± 35.2 months in a range of 24.6 – 179.6 months) were included into the outcomes analysis. Of those, 4 patients(7.4%) had progressed to revision rotator cuff repair. At a follow-up of 5.8 years, outcome scores had significantly improved compared to preoperative baselines (ASES55.6±13.8to90.1+15.8;p<.001;QuickDASH38.9±18.4to 11.9±17.1;p<.001, SANE60.7±22.7to79.3±27.6;p=.001, SF-12PCS41.6±8.3to51.9±9.0;p<=.001). 93.6% of the patients reached the MCID and 72.6% reached the PASS. Median satisfaction was 9.5/10. 86% of the patients returned to sports, while 67% of the patients returned to a similar level compared to preoperatively. All sport specific metrics such as shoulder strength and endurance(p<.001), intensity(p<.001), and impairments from pain affecting speed(p=0.002), endurance(p=.002) and competition(p<.001) significantly improved postoperatively. ConclusionARCR of full-thickness RCT in active individuals aged 45 or younger results in a clinically relevant improvement of outcomes, function and quality of life at a minimum of 2 years and mean 5.8-year follow-up with a low rate of revision. While 86% of patients were able to RTA and sport specific outcome metrics significantly and substantially improved compared to preoperatively, a return to preinjury levels was not reliably achieved in all patients, with particular limitations observed in overhead active individuals. The data support the hypothesis that patients in this age group demonstrate significant improvements in clinical outcomes following ARCR along with significant improvements in athletic abilities.