Definition
An acromioclavicular joint injury, also called a shoulder separation, is a traumatic injury to the AC joint.
It involves disruption of the:
· Acromioclavicular (AC) ligaments
· Coracoclavicular (CC) ligaments
Diagnosis
Diagnosis is made with bilateral focused shoulder radiographs.
Imaging is used to assess:
· AC interval widening
· CC interval widening
Treatment
Treatment depends on:
· Patient activity level
· Degree of separation
· Degree of ligament injury
Options include:
· Immobilization
· Surgical reconstruction
Epidemiology
Incidence
· Common injury
· Accounts for about 9% of shoulder girdle injuries
Demographics
More common in:
· Males
· Athletes
Etiology / Mechanism
· Usually caused by a direct blow to the shoulder
· Often occurs during a fall onto the shoulder
Anatomy
Joint Structure
The AC joint is a diarthrodial joint
It is formed by:
· The medial acromion of the scapula
· The lateral clavicle
· The joint surface has an oblique orientation
It contains a fibrocartilaginous intra-articular disc
· Similar to the meniscus of the knee
· Involutes with age
· Usually disintegrates by age 40
Motion
Main motion: gliding
Rotation is minimal
With shoulder elevation:
· The clavicle rotates 40–50° posteriorly
· Only about 8° of rotation occurs through the AC joint
Ligaments and Stability
Static Stability
Joint capsule
Acromioclavicular (AC) ligaments
· Control horizontal motion
· Provide anterior-posterior stability
Components:
· Superior
· Inferior
· Anterior
· Posterior
Posterior and superior AC ligaments are most important for stability
Coracoclavicular (CC) ligaments
· Control vertical motion
· Provide superior-inferior stability
Consist of:
· Conoid ligament
Most important for vertical stability
Attaches to the conoid tubercle
Inserts on clavicle about 4.5 cm medial to the lateral edge
· Trapezoid ligament
Attaches to the trapezoid tubercle
Inserts on clavicle about 3 cm medial to the lateral edge
Dynamic Stability
· Anterior deltoid
· Trapezius
Clinical Presentation
Symptoms
Pain, usually over the AC joint
Pain may radiate to the trapezius
Physical Exam
Tenderness over:
· Lateral clavicle
· AC joint
Abnormal shoulder contour compared with the opposite side
Stability assessment:
Horizontal stability
· Evaluates AC ligaments
· Cross-body adduction may show pain or instability
· Horizontal instability may suggest need for more aggressive treatment
Vertical stability
· Evaluates CC ligaments
AC Joint Provocative Tests
O’Brien’s test
· Superficial pain localized to the AC joint suggests AC pathology
· Deep pain suggests a SLAP lesion
Cross-body adduction test
· May reproduce AC joint pain
Imaging
Radiographs
Required views:
Bilateral AP view of the AC joints
· Compare with the opposite side
· Measure displacement from the top of the coracoid to the bottom of the clavicle
· Use about 1/3 penetration on AP view to visualize the joint
Axillary lateral view
· Required to diagnose Type IV injuries
Zanca view
· Beam angled 10–15° cephalad
· Uses about 50% of standard shoulder AP penetration
Additional Views
· Cross-body adduction view
· Scapular Y view with cross-body adduction stress
· Weighted stress views
Now used less often
· May help differentiate Type II from Type III
Important Mimics
Fractures can resemble AC separations:
· Base of coracoid fracture
· Distal clavicle fracture (Neer type 2A)
Rockwood Classification
Type I
· AC ligament: sprain
· CC ligament: normal
· Exam: AC tenderness
· X-ray: normal
· Treatment: sling
Type II
· AC ligament: torn
· CC ligament: sprain
· Exam: AC horizontal instability
· X-ray: AC joint disrupted, CC distance increased < 25% of opposite side
· Treatment: sling
Type III
· AC ligament: torn
· CC ligament: torn
· Exam: AC joint disrupted
· X-ray: CC distance increased 25–100% of opposite side
· Treatment: controversial
· Type IIIA
Vertical instability
No horizontal instability
· Type IIIB
Vertical instability
Horizontal instability
Type IV
· AC ligament: torn
· CC ligament: torn
· Exam:
Skin tenting
Posterior fullness
· X-ray:
Lateral clavicle displaced posteriorly through the trapezius on axillary lateral view
Reducibility: not reducible
· Treatment: surgery
Type V
· AC ligament: torn
· CC ligament: torn
· Exam:
Severe shoulder droop
Does not improve with shrug
· X-ray:
CC distance increased > 100% of contralateral side
Reducibility: not reducible
· Treatment: surgery
Type VI
· AC ligament: torn
· CC ligament: torn
Rare
May have associated injuries and paresthesias
· X-ray:
Inferior dislocation of the lateral clavicle
Lies in subacromial or subcoracoid position
Reducibility: not reducible
· Treatment: surgery
Differential Diagnosis
Coracoid fracture
· Base of coracoid fracture can mimic CC ligament disruption
· Superiorly displaced distal clavicle, but normal CC distance
Distal clavicle fracture (Neer 2A)
· Can mimic AC separation
· Ligaments remain attached to the distal fragment
Pediatric medial clavicle physeal injury
Pediatric distal clavicle physeal injury
Treatment
Nonoperative Treatment
· Brief immobilization with early motion
· Indications:
· Type I and II injuries
· Most Type III injuries
· Good results when clavicle displacement is < 2 cm
Methods:
· Sling immobilization
· Ice
· Activity modification
· Physical therapy
Rehabilitation:
Early shoulder range of motion
Functional motion by 6 weeks
Return to normal activity by 12 weeks
Corticosteroid injections may be considered
Outcomes:
Type III injuries treated nonoperatively may have worse early DASH scores
Similar function by 1 year
Lower rate of secondary surgery than operative treatment
Complications:
AC joint arthritis
Chronic subluxation and instability
Operative Treatment
Open reduction and internal fixation (ORIF)
Indications:
Acute Type IV, V, or VI injuries
Acute Type III injuries in:
▪ Laborers
▪ Elite athletes
▪ Patients with cosmetic concerns
Chronic Type III injuries that failed nonoperative treatment
Note:
Earlier belief: acute injuries = ORIF, chronic injuries = CC ligament reconstruction
New studies show no major outcome difference between delayed surgery and immediate surgery in Type III injuries
Contraindications:
Poor compliance with rehab
Skin problems over the surgical site
Surgical Techniques
General Goals
Reduce the AC and CC intervals
Restore stability using:
◦ Ligament reconstruction
◦ Soft tissue graft
◦ Implant fixation
◦
Modified Weaver-Dunn
Distal clavicle excision
Transfer of the coracoacromial ligament to the distal clavicle
Recreates CC ligament function
Can be reinforced with internal fixation
Options:
◦ Autograft
◦ Allograft
Implant Fixation Options
• Suture fixation
• Hook plate
• CC screw (Bosworth)
• Cortical flip button / Dog Bone
• K-wire
Specific Operative Techniques
CC Screw Fixation (Bosworth Screw)
• Has fallen out of favor
• Screw is placed from distal clavicle to coracoid, superior to inferior
• Pros:
◦ Rigid fixation
• Cons:
◦ Risk of screw being too long
◦ May damage structures below the coracoid
◦ Screw removal is often needed at 8–12 weeks
• Complications:
◦ Hardware irritation
◦ Hardware failure
◦ Screw breakage or pullout
CC Suture Fixation
• Suture is passed around or through the clavicle and around the coracoid base
• Can use suture anchors
• Pros:
◦ No risk of hardware migration
• Cons:
◦ Less strong than screw fixation
◦ Must be placed carefully due to nearby neurovascular structures
• Complications:
◦ Suture erosion causing distal clavicle fracture
◦ Hardware irritation
AC Pin Fixation (Phemister Technique)
• Can be performed percutaneously
• Uses smooth wire or pin across the AC joint
• Cons:
◦ High hardware irritation
• Complications:
◦ High risk of pin migration
• Generally not used now
AC Hook Plate Fixation
• Uses a hook plate over the superior distal clavicle
• Pros:
◦ Rigid fixation
• Cons:
◦ May require a second surgery for plate removal
Complications:
· Acromial erosion
· Hook pullout
CC Ligament Reconstruction with CA Ligament
· Also called the Modified Weaver-Dunn procedure
· Distal clavicle excision
· Transfer of the coracoacromial ligament to the distal clavicle
· Reinforced with internal fixation
Cons:
· CA ligament is only about 20% as strong as the native CC ligament
· Failure risk increases without internal fixation
CC Ligament Reconstruction with Free Tendon Graft
· Can be arthroscopically assisted
Graft options:
Autograft
· Palmaris longus
· Semitendinosus
Allograft
· Tibialis anterior
Technique:
· Figure-of-eight graft around the coracoid
· Fixation through clavicular tunnels
· Often reinforced with internal fixation
Pros:
· Better restoration of native CC ligament strength
Cons:
· Risks of graft harvest or allograft use
· Failure if not reinforced
Complications
Residual AC joint pain
· Seen in about 30–50%
AC arthritis
· More common after surgery than nonoperative treatment
Hardware failure
· CC screw breakage or pullout
Coracoid fracture
· Can occur with coracoid tunnel drilling