Accuracy of needle placement in ACJ injections

Localization of the Acromioclavicular joint (ACJ) even at arthroscopic surgery may be difficult because of its small size, osteophytes, variable anatomy of the joint and capsule. Therefore injection of the ACJ in the clinic may well be inaccurate. The aim of this study was to review the clinical accuracy of needle placement in ACJ injections, if performed without the aid of image intensification. Sixty patients with 66 shoulders were injected in the Day Unit in our department. The joint was palpated clinically, and the needle was placed in the site thought to be in the AC Joint. An image intensifier was then used to check the position of the needle in the AP and axillary views. The needle was considered correctly placed if between the bony boundaries of the acromion and clavicle. This was found in only 26 injections (39.4%). The remaining 40 injections (60.6%) were misplaced, either laterally in 21 injections (31.8%), medially in 13 (19.8%), anteriorly in 3 (4.5%) and inferiorly in 3 injections (4.5%). Theses were then reinserted under image intensifier guidance. The misplaced injections would have lead to inaccurate clinical outcomes, and decision making. This study is similar to other studies in that X-ray guidance improves the accuracy of injections and surgery. However the potential error rate for the small, anatomically variable AC joint is high. There is a 60% potential for ACJ injections to be out of the joint if performed by palpation alone, and we recommend the routine use of image intensification guidance.