Plane Talk About Shoulder Radiographs
Warren G. Harding III, MD; Kevin D. Nowicki, MD
THE PHYSICIAN AND SPORTSMEDICINE - VOL 26 - NO. 2 - FEBRUARY 2021
The evaluation of patients who have pain, loss of motion, instability, or weakness in the shoulder is often enhanced by x-ray assessment. A common approach to radiographic examination of the shoulder is to take two anteroposterior (AP) views, one with the humerus in external rotation and one with the humerus in internal rotation.
However, if both of these views are taken in the true AP plane, some information may be missed and problems may be misdiagnosed. A better method is to use the scapular AP plane rather than the true AP plane for the external rotation view. In general, the combination of a scapular AP view with external rotation and a true AP with internal rotation will rule out most significant disease (1).
A Reciprocal RelationshipWe have observed a consistent reciprocal relationship between the anatomic plane and radiographic appearance of the glenohumeral (GH) and acromioclavicular (AC) joints in the scapular AP view of the shoulder and in the true AP view. This relationship can be used to improve reliability in radiographic assessment of the shoulder joints.
In the scapular AP view (figure 1), in which the x-ray beam diverges 35° from the sagittal plane, the normal GH joint shows clearly and without overlap, whereas the AC joint is poorly defined and difficult to assess. Conversely, a true AP of the shoulder (figure 2) allows for clear assessment of the AC joint, while the GH articulation demonstrates normal overlap and is not as well delineated. If the patient's AC joint is superimposed on the scapula, additional AP views with the x-ray beam angled upward 12° to 35° may improve visualization (2).
The rotational position of the humerus influences the usefulness of the radiographs. The greater tuberosity and contiguous soft tissues are profiled in external rotation, while an internal rotation view can reveal the Hill-Sachs lesion, which indicates anterior instability of the GH joint (3). For patient comfort, convenience, and consistency, the best clinical results are obtained when the humerus is in external rotation for the scapular AP view and in internal rotation for the true AP view. This allows for complete assessment of the proximal humerus and maximizes the benefit from each view.
An additional benefit of using the scapular AP view with external rotation of the humerus is visualization of the scapulohumeral line. This line—created by the axillary border of the scapula, inferior surface of the head and neck of the humerus, and proximal medial shaft of the humerus—normally forms a continuous smooth arch (figure 1b). The scapulohumeral line is interrupted in posterior dislocation of the shoulder, as described by Dorgan (4), and in other abnormalities as well. (The scapulohumeral line is similar to, but not the same as, Moloney's line, which is seen in the lateral transthoracic view of the shoulder as an uninterrupted line formed by the axillary border of the scapula, the inferior portion of the humeral neck, and the humeral shaft.)
The use of the scapular AP view along with the true AP view permits increased confidence in evaluation of the AC and GH joints, as each can easily be examined for alignment, narrowing, and spurring without possible misinterpretation due to limited visibility. This decreases the need for additional radiographic views, reduces the patient's exposure to x-ray radiation, reduces the demand on the patient's and x-ray technician's time, and decreases use of film. This can lower the cost of the evaluation and improve patient satisfaction. In short, simply using a scapular AP view in place of the usual true AP view with external rotation provides important enhancements of the study.
Additional ViewsFor completeness, it is often wise to obtain an axillary view in addition to the AP views. This permits assessment of the anterior-posterior configuration of the GH and AC joints and will reveal anterior or posterior subluxation or dislocation if present. The more consistent the position of the arm, the more reliable the resulting x-ray.
A "Y" view should be obtained if the patient's pain, loss of motion, or suspected trauma prevents adequate abduction of the arm to obtain the axillary view. A "Y" view should also be obtained if the scapulothoracic articulation or the body of the scapula is suspected of being the source of the problem.
Dr Harding is a clinical instructor of orthopedic surgery at the University of Cincinnati College of Medicine and practices at Wellington Orthopaedic and Sports Medicine in Cincinnati; Dr Nowicki is an orthopedic surgeon at Central Florida Orthopaedics and Sports Medicine in Orlando. Dr Harding is a member of the American Orthopaedic Society for Sports Medicine.
Copyright (C) 192021. The McGraw-Hill Companies. All Rights Reserved