Objectives:Biceps Popeye deformity is a common finding with rupture of the long head of the biceps tendon (LHBT), biceps tenodesis failure or length-tension mismatch during tenodesis. The Popeye muscle is a cosmetic deformity of the arm that may be accompanied by cramping and muscle fatigue and many patients are dissatisfied with the symptoms and appearance. Although prior studies have described physiologic landmarks to optimize the length-tension relationship during biceps tenodesis after LHBT rupture, no study has assessed the biceps muscle appearance after tenodesis “in-situ” prior to the release of the LHBT from the superior labrum for biceps tendon pathologies without complete rupture. Therefore, the purpose of this study is to assess clinical outcomes of an all-arthroscopic technique for biceps tenodesis which maintains the anatomic length-tension relationship of the LHBT prior to tenotomy from the superior labrum. We compared this group of patients to a control group of patients who underwent an interference screw tenodesis technique that required cutting the LHBT from the superior glenoid prior to tenodesis with an estimation of the anatomic length-tendon relationship potentially contributing to subtle biceps Popeye deformity. We hypothesize that an “in-situ” anatomic length-tension relationship tenodesis technique would reduce the risk of a Popeye deformity, reduce cramping and muscle fatigue, and have improved patient-reported outcome measures compared to an estimated length-tension relationship tenodesis with an interference screw.Methods:Consecutive patients who underwent arthroscopic biceps tenodesis with concomitant rotator cuff procedures were enrolled in this study from 2019-2021 and patients were grouped based on a change in senior author’s tenodesis technique, with the initial cohort having an arthroscopic interference screw subpectoral biceps tenodesis after tenotomy from the superior labrum in an “estimated” length-tension relationship technique (Group 1), and the later cohort having an arthroscopic suprapectoral biceps tenodesis “in-situ” with an anatomic length-tension relationship (Group 2) with the LHBT tied to the side of the humerus with all-suture unicortical anchors. Patients were assessed at a minimum of 3-month follow-up and asked about post-operative anterior arm pain and biceps muscle spasms, and if they notice any difference in appearance between their bicep muscles on a 4-point Likert scale (none, mild, moderate, severe). Patient-Reported Outcomes (PROs) of Veterans-Rand 12, American Shoulder and Elbow Score (ASES), EuroQol- 5 Dimension (EQ-5D), PROMIS 10, and Single Assessment Numeric Evaluation (SANE) were collected. Bilateral bicep images of participants were taken in three forearm positions with the elbow flexed 90 degrees: (1) maximal supination, (2) neutral, and (3) maximal pronation. Review of pronation, supination, and neutral forearm rotation bilateral biceps images were evaluated, after blinding and de-identification, by two shoulder and elbow fellowship-trained board-certified orthopedic surgeons for visual appearance and grade of Popeye deformity (none, mild, obvious Popeye). Non-parametric between-group comparison and analysis were performed with statistical significance set at p < 0.05.Results:Sixty-two patients (53% female, age 58.7 ± 9.0 years) were enrolled (33 in Group 1 and 29 in Group 2) with a mean follow-up of 9.8 ± 6.5 months. There were no significant differences between groups with respect to gender, age, and laterality of biceps tenodesis, as well as type and size of rotator cuff repair. There were no significant differences in ASES, EQ5D, and SANE scores between the two technique groups. However, PROMIS 10 Physical Health Scores were significantly improved in Group 2 (15.7 ± 2.3) compared to Group 1 (14.4 ± 2.9) (p=0.03). Patients in Group 2 experienced significantly less pain in their anterior arm than patients in Group 1 (19% vs. 33%, p=0.02) however there were no differences in biceps muscle spasm (3.4% vs. 5.2%, p=0.21). There also were no significant differences in patient-perceived biceps deformity between Group 1 (17.2%) and Group 2 (27%) (p=0.26). Similarly, there were no significant differences in surgeon-perceived biceps deformity between Group 1 and Group 2 (30.3% vs. 24.1%, p=0.47). Interrater reliability for surgeon assessment of a Popeye deformity was found to have a substantial agreement with a Kappa value of 0.77 (p <.0.001), 95% CI (0.645, 0.855).Conclusions:An arthroscopic suprapectoral biceps tenodesis performed “in-situ” with an anatomic length-tension relationship did not reduce the incidence of patient or surgeon perceived Popeye muscle deformity compared to an interference screw tenodesis performed after tenotomy in an “estimated” length-tension relationship technique. Interestingly, the “in-situ” length-tension technique reduced anterior arm pain and improved PROMIS 10 physical health scores post-operatively compared to the “estimated” interference screw technique.