Likely Diagnosis and Management of Post-Traumatic Left Shoulder and Rib Pain with Limited Range of Motion
This patient most likely has a soft tissue injury involving the rotator cuff, shoulder capsule, or lateral collateral ligament complex of the elbow, with possible associated rib contusion or costochondral injury; the next step is to obtain MRI of the left shoulder without IV contrast to evaluate for rotator cuff tear and capsular injury, given that all plain radiographs are normal.
Clinical Reasoning
Why Soft Tissue Injury is Most Likely
The mechanism of injury (fall on outstretched arm with elbow impact) typically produces axial loading forces that can cause both elbow ligamentous injuries and shoulder rotator cuff pathology 1.
The patient's inability to fully extend the elbow (only 110 degrees) is highly sensitive for underlying injury, but with normal elbow radiographs, this points toward ligamentous or tendinous pathology rather than fracture 1.
The severe limitation in shoulder abduction (<45 degrees), flexion (only 90 degrees), and rotation (only 45 degrees) with the characteristic pain relief position (arm across abdomen) strongly suggests rotator cuff injury or capsular tear 2.
The posterior lateral rib pain radiating to the posterior shoulder, aggravated by thoracic pressure and deep breathing, suggests either rib contusion or referred pain from shoulder pathology; however, the chest X-ray was normal, making rib fracture less likely 3.
Differential Diagnosis Priority List
Rotator cuff tear (partial or full-thickness) - Most consistent with the mechanism, pain pattern, and severe functional limitation 2.
Lateral collateral ligament complex injury of the elbow - Explains the elbow extension limitation and the protective positioning 1.
Shoulder capsular injury or adhesive capsulitis (acute) - Can develop rapidly after trauma and explains the global range of motion restriction 2.
Rib contusion or costochondral injury - Explains the rib pain, though less likely to cause the degree of shoulder dysfunction seen here 3.
Occult fracture (radial head, greater tuberosity of humerus) - Less likely given comprehensive normal radiographs, but cannot be completely excluded 1.
Immediate Next Steps
Primary Imaging Recommendation
- Order MRI of the left shoulder without IV contrast as the next imaging study 2.
- MRI is the gold standard for evaluating rotator cuff tears, capsular injuries, and labral pathology in the setting of acute trauma with normal radiographs 2.
- In acute shoulder trauma, post-traumatic joint effusion or hemarthrosis typically provides sufficient visualization of soft tissue structures without the need for intravenous contrast or arthrography 2.
- MRI will also demonstrate bone marrow edema from occult fractures that were not visible on plain films 2.
Secondary Imaging Consideration
If MRI is unavailable or contraindicated, obtain ultrasound of the shoulder, though this has lower sensitivity for partial-thickness rotator cuff tears and cannot evaluate intra-articular pathology as comprehensively 2.
For the elbow specifically, if clinical suspicion for occult fracture remains high (given the inability to fully extend), obtain CT of the left elbow without IV contrast 1.
Clinical Management Pending Imaging
Immobilize the left arm in a sling with the forearm across the abdomen (the patient's position of comfort) to minimize pain and prevent further injury 4.
Prescribe adequate analgesia (NSAIDs plus short-term opioids if needed) to control pain and facilitate early range-of-motion exercises once the diagnosis is confirmed 4.
Avoid aggressive range-of-motion testing or physical therapy until imaging excludes significant rotator cuff tear or ligamentous disruption, as premature mobilization can worsen outcomes 2, 1.
Schedule urgent orthopedic follow-up (within 3-5 days) to review imaging and determine whether surgical intervention is needed 4.
Critical Pitfalls to Avoid
Do not assume that normal radiographs exclude significant injury in a patient with this degree of functional impairment; soft tissue injuries (rotator cuff tears, ligament ruptures) are radiographically occult and require MRI for diagnosis 2, 1.
Do not delay advanced imaging (MRI or CT) in patients with persistent inability to extend the elbow or severe shoulder dysfunction; early diagnosis reduces the risk of chronic disability and improves surgical outcomes if needed 1.
Do not overlook the possibility of combined injuries (elbow ligamentous injury plus shoulder rotator cuff tear) in this mechanism of trauma; both sites require independent evaluation 1, 4.
Do not prescribe physical therapy or aggressive mobilization before obtaining MRI, as this can convert a partial rotator cuff tear into a complete tear or worsen ligamentous instability 2.
If the patient develops signs of neurovascular compromise (numbness, weakness, pallor, absent pulses), obtain urgent vascular surgery consultation, as axillary artery or brachial plexus injury can occur with this mechanism 4.
Expected Imaging Findings and Their Implications
If MRI Shows Rotator Cuff Tear
Full-thickness tears typically require surgical repair, especially in a young active patient, to restore function and prevent chronic disability 2.
Partial-thickness tears may be managed conservatively with physical therapy and NSAIDs, but surgical repair is indicated if conservative management fails after 3-6 months 2.
If MRI Shows Capsular Injury or Labral Tear
- Capsular tears and labral injuries often require arthroscopic repair to restore stability and prevent recurrent instability 2.