Most Appropriate Investigation for Shoulder Dislocation
X-ray (radiography) is the most appropriate initial investigation for a typical presentation of shoulder dislocation.
Initial Imaging Approach
Radiography is the preferred initial diagnostic modality because it can delineate shoulder malalignment and most shoulder fractures, which are the two primary concerns in acute shoulder trauma 1. The American College of Radiology explicitly states that radiography is preferred over all other modalities for initial evaluation 1.
Standard Radiographic Views Required
A complete shoulder trauma series must include at minimum three views 1:
- Anteroposterior (AP) views in internal and external rotation 1, 2
- Axillary lateral view OR scapular Y view 1, 2
The axillary or scapular Y view is absolutely vital because glenohumeral and acromioclavicular dislocations can be misclassified on AP views alone 1. This is a critical pitfall—posterior shoulder dislocations are missed in more than 60% of cases initially when only AP views are obtained 3, 4.
Technical Considerations
- Perform radiographs upright whenever possible, as shoulder malalignment can be underrepresented on supine imaging 1, 3
- The scapular Y view is preferred by 81% of patients over the axillary view due to less pain, and is equally accurate for diagnosis 5
- Additional specialized views (Stryker notch, Bernageau) can be added if specific lesions like Hill-Sachs deformities need evaluation 1
Why Not Other Modalities Initially?
CT (Option C)
CT is not appropriate for initial evaluation despite being superior for characterizing fracture patterns 1. The American College of Radiology explicitly states that "radiography is preferred over CT for initial evaluation because radiography is able to diagnose displaced fractures and shoulder malalignment, which are the primary concerns in the initial assessment of shoulder trauma" 1. CT should be reserved for cases where radiographs are indeterminate or when complex fracture characterization is needed 1, 3.
MRI (Option B)
MRI is not indicated as the initial study for acute shoulder dislocation 1. While MR arthrography is considered the gold standard for imaging traumatic shoulder pain overall, it is suboptimal as an initial study due to its invasive nature and the fact that immediate management decisions (reduction, fracture identification) depend on bony alignment, not soft tissue detail 1. MRI becomes appropriate when radiographs are noncontributory and soft tissue injury needs evaluation, typically after 2-3 weeks of persistent pain 3.
Post-Reduction Management
Post-reduction radiographs are essential to confirm successful reduction and rule out iatrogenic fractures 2, 6. While the majority (62.5%) of fractures are visible on pre-reduction films, more than one-third (37.5%) may only be visible on post-reduction radiographs 6. The same views should be obtained post-reduction to ensure proper alignment 2.
Critical Pitfall to Avoid
Never attempt shoulder manipulation or reduction without radiographic confirmation of the injury pattern, as this could convert a stable fracture into a displaced one or worsen neurovascular compromise 3, 7. The two orthogonal views are mandatory to avoid missing posterior dislocations, which appear deceptively normal on AP views alone 3, 4.
Answer: A) X-ray