Axial and tangential views of the acromioclavicular joint: the introduction of new projections.

Background: Routine anteroposterior radiographs of the acromioclavicular (AC) joint with or without weight bearing have limitations in demonstrating the AC joint. Transarticular fixation with Kirschner wire is a treatment choice for AC dislocations. However, percutaneous fixation of the AC joint is technically demanding. The C-arm fluoroscopy can be used as routine intraoperative guidance to facilitate this procedure. The current study aims to introduce new projections, the axial and tangential views of AC joint, to help evaluate the severity of the injury and facilitate the percutaneous procedure.

Methods: Three shoulder specimens were used to find the projection directions of the axial and tangential views of the AC joint by using the digital radiography (DR) unit. The axial and tangential views were taken of 20 adult volunteers by referencing the projection directions determined in the shoulder specimens. The angles showed on the DR system and the angles between the coronal plane of the body and the vertical plane of the flat panel detector (FPD) during taking these radiographs were recorded. The C-arm fluoroscopy unit was used to take the axial and tangential views referencing the angles measured on the DR system. Routine anteroposterior radiographs of the AC joint were taken on the volunteers. The minimal distances from the distal clavicle to the acromion were measured on both tangential and anteroposterior radiographs. The data was statistically analyzed.

Results: The clear axial and tangential radiographs of AC joints of the volunteers were obtained using both DR and C-arm fluoroscopy units. The angles demonstrated on the DR window are (20.8 ± 2.4)° for male and (18.3 ± 2.3)° for female. During taking the axial views, the angles between the coronal plane of the body and vertical plane of FPD are (23.3 ± 3.2)° for male and (20.1 ± 2.4)° for female. During taking tangential views, the corresponding angles are (117.5 ± 3.7)° for male and (113.1 ± 3.3)° for female. On the tangential radiographs, the minimal distance from the distal clavicle to the acromion is (6.1 ± 1.2) mm, wider than the same measurement on the anteroposterior radiographs (P < 0.05). Statistical analyses showed no significant differences in the above-mentioned angles and the minimal distances between the left and right AC joints (P > 0.05). There were no significant differences in the above-mentioned angles between DR and C-arm fluoroscopy units (P > 0.05).

Conclusions: The axial and tangential radiographs of the AC joint can demonstrate the joint clearly and they can be easily obtained with both DR system and C-arm fluoroscopy unit in similar projection directions.