What findings should be ruled out on knee and shoulder radiographs?

What to Rule Out on Knee and Shoulder X-rays

On knee radiographs, rule out fractures (particularly tibial plateau, patellar, and avulsion fractures), joint effusion/lipohemarthrosis, and alignment abnormalities; on shoulder radiographs, rule out fractures (proximal humerus, clavicle, scapula), dislocations, and acromioclavicular joint separations ≥Grade 3.

Knee Radiographs: Key Findings to Exclude

Fractures

• Tibial plateau fractures - most critical to identify as they often require CT for surgical planning 1
• Patellar fractures - best visualized on patellofemoral (sunrise) view 1
• Avulsion fractures - indicate ligamentous injury (ACL, PCL, collateral ligaments) 1
• Occult fractures - may only show subtle signs requiring advanced imaging 2

Joint Effusion and Lipohemarthrosis

• Joint effusion - visible on lateral view with knee at 25-30° flexion 1
• Lipohemarthrosis - seen on cross-table lateral with horizontal beam; indicates intra-articular fracture 1
• This finding has high specificity for occult intra-articular fracture even when bone appears normal

Alignment Abnormalities

• Patellar subluxation or dislocation - requires patellofemoral view 1
• Gross deformity - indicates significant fracture or dislocation 1

Subtle but Significant Signs

Critical pitfall: Radiographs may appear nearly normal but harbor serious soft-tissue injuries 2. Look for:

• Bone marrow edema patterns (subtle density changes)
• Small avulsion fragments suggesting ligament tears
• Abnormal fat pad displacement
• Subtle cortical disruptions

Shoulder Radiographs: Key Findings to Exclude

Fractures

• Proximal humerus fractures - most common in acute trauma 3
• Clavicle fractures - readily visible on standard views 3
• Scapular fractures - indicate high-energy trauma 3
• Glenoid rim fractures - associated with dislocation/instability 3

Dislocations and Instability

• Glenohumeral dislocation (anterior > posterior) - requires immediate reduction 3
• Acromioclavicular joint separation ≥Grade 3 - therapeutically significant finding requiring orthopedic consultation 4
• Hill-Sachs lesion - compression fracture of posterolateral humeral head from anterior dislocation 3
• Bankart lesion (bony) - anterior glenoid rim fracture from dislocation 3

Other Critical Findings

• Infection - rare but must not be missed 4
• Malignancy - lytic or blastic lesions 4
• Osteonecrosis - requires specific treatment 5

Clinical Decision-Making Algorithm

For Knee Radiographs

Obtain radiographs if ANY Ottawa Knee Rule criteria present 1:

1. Age >55 years
2. Isolated patellar tenderness
3. Fibular head tenderness
4. Inability to flex knee to 90°
5. Inability to bear weight (4 steps) immediately and in ED

Do NOT obtain if: No fall, no swelling, and patient can bear weight 4 - 99% of these are therapeutically uninformative

For Shoulder Radiographs

Obtain radiographs if ANY present 3, 4:

1. Fall or trauma
2. Swelling present
3. Pain at rest
4. Restricted range of motion
5. Deformity
6. Age considerations with trauma

Do NOT obtain if: No fall, no swelling, normal range of motion 4 - 100% therapeutically uninformative in this group

Standard Views Required

Knee

• Minimum: AP and lateral (lateral at 25-30° flexion) 1
• Add patellofemoral view if patellar fracture or dislocation suspected 1
• Cross-table lateral if lipohemarthrosis suspected 1

Shoulder

• Minimum: AP and lateral views 3
• Additional views based on clinical suspicion (axillary, scapular Y, Grashey) 6

When Initial Radiographs Are Negative

Knee

If clinical suspicion remains high despite negative radiographs 1:

• MRI without contrast - for suspected ligament/meniscal tears or occult fractures
• CT without contrast - for complex fracture characterization or when MRI contraindicated

Shoulder

If clinical suspicion remains high despite negative radiographs 3:

• CT without contrast - for occult fractures, especially in elderly or high-energy trauma
• MRI without contrast - for rotator cuff tears, labral pathology (acute trauma creates natural arthrogram from hemarthrosis)
• Ultrasound - equivalent to MRI for rotator cuff evaluation in experienced hands

Critical caveat: Radiographs have low sensitivity for soft-tissue injuries. A normal radiograph does NOT exclude significant ligamentous, meniscal, or rotator cuff pathology 1, 2. Clinical judgment supersedes imaging findings 1.