• Marvin Minkus, Carmen Hann, Markus Scheibel, and Natascha Kraus.
• Department of Shoulder and Elbow Surgery, Center for Musculoskeletal Surgery, Charité-Universitaetsmedizin Berlin, Campus Virchow-Klinikum, Augustenburger Platz 1, 13353, Berlin, Germany.
• Arch Orthop Trauma Surg. 2017 Jun 1; 137 (6): 845-852.

IntroductionClassification of AC-joint instability is based on radiologic evaluation of anteroposterior (a.p.) stress views of both shoulders, neglecting the horizontal component of instability. Recent studies have proposed an association of dynamic posterior translation (DPT) and inferior clinical results. The purpose of this study was to quantify DPT in modified Alexander views and correlate it with other radiological and clinical data.Materials And MethodsThirty-two patients (4 f, 28 m, mean age 34.1) with acute AC-joint dislocation (16 = RW III, 16 = RW V) underwent radiological examination including bilateral a.p. stress views with measurement of the coracoclavicular distance (CCD) and bilateral modified Alexander views with different approaches to quantify DPT (overlapping area OAAC, overlapping length OLAC). In addition, the Constant Score, Subjective Shoulder Value, Taft Score (TF), and the Acromioclavicular Joint Instability Score (ACJI) were obtained.ResultsIn Rockwood (RW) type III injuries, a mean CCD of 15.8 (9.8-22.8) mm, OAAC of 50.9 (0-216.6) mm2, and OLAC of 6.5 (-4.7-17.9) mm were found. RW V patients showed a CCD of 23.1 (13.7-32.0) mm; OAAC 7.0 (0-92.3) mm2; and OLAC -4.8 (-19.6-9.8) mm. Particularly in RW III the CCD, OAAC and OLAC revealed significant correlation with the ACJI (r = -0.64/r = 0.72/r = 0.68, p < 0.05) and TF (r = -0.56/r = 0.68/r = 0.51, p < 0.05). The proposed quantification tools for DPT were found to have a moderate-to-strong correlation with the score results, especially with AC-joint specific scores. RW type V injuries had a moderate correlation with clinical parameters (OAAC with ACJI: r = 0.44, p > 0.05 and OLAC with TF: r = -0.45, p > 0.05).ConclusionsMeasuring the OLAC is a convenient way for quantifying DPT in modified Alexander views. It showed significant correlation with clinical scores, indicating the relevance of DPT in patients with AC-joint injury.

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