Acromioclavicular joint (ACJ) cysts are an uncommon and unusual sequela associated with shoulder pathophysiology. The majority of literature on ACJ cysts consists of individual case reports with no definitive literature review currently available. In addition to a comprehensive literature review, four clinical cases are presented in this report. First described by Craig (1984), a total of 41 cases have been previously reported in the literature. Of these cases, five occurred with the rotator cuff musculature intact. The remaining 36 cases of ACJ cysts occurred in patients with a complete tear/avulsion of the rotator cuff. Previous attempts at compiling a complete record of all reported cases have combined several distinct conditions into a single category. This article presents two distinct etiologies for the pathogenesis of ACJ cyst formation. In the presence of an intact rotator cuff, a Type 1 cyst can form superficially and be limited to the ACJ. Following a massive or traumatic tear of the rotator cuff, mechanical instability of the humeral head can cause a deterioration of the inferior acromioclavicular capsule (cuff tear arthropathy) and an overproduction of synovial fluid. Overtime, a "geyser" of fluid can form between the glenohumeral and the ACJ, forming a Type 2 cyst. This differentiation and categorization is essential for appropriate classification and treatment.

To evaluate the selected biomechanical differences of a double-row trans-osseous equivalent rotator cuff repair with a knotless versus knot-tying medial row using suture tape in regard to repair displacement, stiffness, and ultimate load to failure. Methods: In 16 fresh-frozen human shoulders (8 matched pairs), double-row rotator cuff repairs were performed with medial-row mattress knots (MK) on one side, the other without (NK). Two DVRT (Differential Variable Reluctance Transducer) sensors were attached between the humerus and 3 mm above the repair site and were used to measure the displacement across the repair during cycling. The biomechanical parameters measured were repair displacement, stiffness, and ultimate load to failure. The supraspinatus was loaded in a similar fashion to previously described protocol using cyclic loading and load to failure testing. 1 Results: All data from paired specimens were compared using paired Student t tests. No statistically significant difference (SSD) in displacement across the repair over the 200 cycles of the test was noted between the two groups (MK ¼ 0.591 ± 0.501 mm; NK ¼ 0.439 ± 0.417 mm, p ¼ 0.618). No SSD in stiffness was noted between the two groups (MK ¼ 32.87 ± 6.31 N/mm; NK ¼ 27.98 ± 9.69 N/mm, p ¼ 0.120). No SSD in ultimate load to failure was noted between the two groups (MK ¼ 501.2 ± 126.1 N; NK ¼ 416.8 ± 120.0 N, p ¼ 0.116). Conclusion:There was no statistically significant different between knotless versus knotted medial row double row rotator cuff repair constructs using suture tape in regard to displacement across the repair site, stiffness and ultimate load to failure. Despite previous evidence suggesting inferiority of knotless medial row technique using suture constructs, this evidence may support the biomechanical equivalency of knotless medial row technique using suture tape.

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