What is a grade 1 separation of the acromioclavicular (AC) joint?

Grade 1 AC Joint Separation

A grade 1 acromioclavicular (AC) joint separation is a mild sprain involving only partial tearing of a few fibers of the AC joint capsule, with intact coracoclavicular ligaments and no joint displacement. 1

Anatomic Definition and Injury Severity

• Grade 1 represents the mildest form of AC joint injury, resulting from a mild force applied to the shoulder that causes microscopic tearing of only a few fibers of the acromioclavicular joint capsule 1
• The AC ligaments are stretched but not completely torn, and the coracoclavicular ligaments remain completely intact 1
• There is no displacement or subluxation of the clavicle relative to the acromion on radiographic imaging 1
• The joint remains stable with no widening of the AC joint space on stress radiographs 1

Clinical Presentation

• Patients typically present with localized pain and tenderness directly over the AC joint 2
• Minimal swelling may be present at the AC joint, but no visible deformity or "step-off" is apparent 2
• Pain is exacerbated by shoulder movement, particularly horizontal adduction (cross-body adduction) and overhead activities 2
• The shoulder maintains full range of motion, though movement may be limited by pain 2

Diagnostic Imaging

• Standard radiography with anteroposterior views in internal and external rotation plus axillary or scapular-Y view should be obtained to rule out fracture and confirm no joint displacement 3
• Radiographs in grade 1 injuries show normal alignment of the AC joint with no increase in the coracoclavicular distance 1
• The clavicle remains at the same level as the acromion with no superior displacement 1

Management Approach

Grade 1 AC joint separations respond favorably to conservative management and do not require surgical intervention. 2, 4

Initial Treatment Phase (First 7-14 Days)

• Implement relative rest with activity modification to avoid aggravating movements, particularly overhead activities and heavy lifting 2, 4
• Apply ice for 15-20 minutes every 2-3 hours during the acute phase to reduce pain and inflammation 4
• Use a simple sling for comfort during the first few days only if needed, but avoid prolonged immobilization beyond 3-5 days to prevent shoulder stiffness 2, 4
• Initiate pain control with acetaminophen or NSAIDs as first-line pharmacologic management 4

Rehabilitation Protocol

• Begin gentle pendulum exercises and passive range of motion within the first week as pain allows 2, 4
• Progress to active-assisted range of motion exercises once acute pain subsides, typically within 7-10 days 2, 4
• Advance to strengthening exercises of the rotator cuff and scapular stabilizers once full pain-free range of motion is achieved 2, 4
• Gradually return to sport-specific activities and full function, typically within 2-4 weeks for grade 1 injuries 2, 4

Prognosis and Expected Outcomes

• Grade 1 AC joint separations have excellent prognosis with conservative treatment, with most patients achieving full recovery and return to previous activity levels 2, 4
• Surgical intervention is never indicated for grade 1 injuries 2, 1
• Patients can typically return to work within days and return to sports within 2-4 weeks depending on activity demands 4

Critical Pitfalls to Avoid

• Do not immobilize the shoulder for prolonged periods, as this leads to unnecessary stiffness and delayed recovery 2, 4
• Ensure adequate radiographic evaluation to confirm the diagnosis and rule out higher-grade injuries or associated fractures 3
• Do not rush return to overhead activities or contact sports before achieving full pain-free range of motion and adequate strength 2, 4