Os Acromiale

Definition 

 

Failure of fusion of adjacent ossification centers

 

Epidemiology

 

Incidence 3%

 

Bilateral in 60%

 

Anatomy

 

4 ossification centers present in acromion

- pre-acromion

- mesoacromion

- metaacromion

- basiacromion

 

The basiacromion fuse to spine of scapula by 12

 

Pre / Meso / Meta appear by 18

- Unite by age 22 - 25

- If un-united = Os Acromiale 

 

Types

 

1.  Meso-Acromion

-  most common

- level with posterior aspect clavicle

 

 Os Acominale XrayOs Acromionale MRI AxialOs Acromionale MRI Sagittal

 

2.  Pre-acromial

- less common

- level with anterior border acromion

 

 Os Acrominale MRI T2

 

3.  Meta-Acomial

- rare

 

X-ray

 

Best seen on axillary lateral

 

Factors favoring diagnosis of os acromiale over fracture 

- bilateral occurrence (Xray other side)

- rounded borders with uniform space

 

MRI

 

Useful investigation

- may show oedema if problematic

 

Os Acromionale MRI 1Os Acromionale MRI 2

 

Bone scan

 

Can be very important

- unlikely to be symptomatic if cold

- may be symptomatic / need addressing if hot

 

Symptomatic Os Acromionale

 

1.  Non union

- painful

- MRI / bone scan shows inflammation

 

2.  Dynamic impingement

- fragment moves with deltoid contraction

- decreases size of SS outlet

- impingement symptoms

 

Os AcromionaleOs Acromionale 3

 

Surgery

 

Indications

- failure of non operative treatment

 

Options

 

1.  Excision

- small fragment / pre-acromion

- risk defunctioning deltoid

- can perform arthroscopically and leave deltoid attachment intact

- open excision with careful reattachment

 

Pagnani JSES 2006

- arthroscopic excision in 11 shoulders of athletes

- all returned to sport at 14 weeks

- no loss of strength detected

 

Os Acromiale Arthroscopic

 

2.  ORIF

- large fragment / mesoacromion

- take down non union

- bone graft / 2 x AP 3.5 mm screws / TBW

- especial care with deltoid reattachment

 

Os Acromionale ORIF 1 Os Acromionale ORIF 2Os Acromionale ORIF 3

 

Risk of nonunion

 

Os Acromionale Nonunion 1Os Acromionale Nonunion 2Os Acromionale Nonunion 3Os Acromionale Nonunion 4

 

Peckettet al JSES 2004

- ORIF in 26 patients

- Union 25/26, 2 fractures

- 30% required removal metalwork

 

3.  Arthroscopic SAD