Background: For high-grade dislocation of the acromioclavicular (AC) joint, surgical treatment is widely recommended. This study aimed to evaluate the clinical and radiological outcomes after arthroscopic-assisted stabilization of acute high-grade AC joint dislocations using a low-profile suture button (LPSB) combined with percutaneous AC cerclage fixation. A secondary objective was to quantify clavicular tunnel widening (cTW) and explore its correlation with clinical and radiological outcomes. Methods: This retrospective study included 45 patients with acute Rockwood type V injuries treated with the LPSB technique and additional AC cerclage. Clinical outcomes were the Constant Score (CS), Subjective Shoulder Value (SSV), Taft Score (TF), AC Joint Instability Score (ACJI), and VAS for pain upon palpation. Radiological assessment included coracoclavicular (CC) distance and percentage deviations compared to the contralateral side, reclassified according to Rockwood, dynamic posterior translation (DPT), cTW measurements, and assessment of ossifications and AC joint osteoarthritis. Results: After 35.3 months, significant improvements were observed in CC distance and percentage deviation. A total of 27.3% were reclassified as Rockwood type III and 2.3% as type V. Initial overreduction persisted in 18.2%. DPT was observed in 34.1% of cases. The mean CS was 89.64, the SSV was 91.1, and the VAS was 0.8. cTW occurred only below the superior button and increased significantly over time, showing a negative correlation with the SSV but no correlation with any radiological outcome parameter. No implant-related revision surgery was reported. Conclusions: Arthroscopic-assisted stabilization of acute high-grade AC joint dislocations using the LPSB technique with AC cerclage fixation provides excellent clinical outcomes and high patient satisfaction, with minimal implant-related complications and no need for revision surgery due to implant issues. Although cTW occurs, its clinical impact appears limited within this procedure.