Os Acromiale

Definition 

 

Failure of fusion of secondary ossification centers

 

Epidemiology

 

Incidence 3 - 8%

 

Bilateral in 60%

 

Anatomy

 

Os illustration

 

4 ossification centers present in acromion

- pre-acromion

- meso-acromion

- meta-acromion

- basia-cromion

 

The basiacromion fuses to spine of scapula by 12

 

Pre / Meso / Meta appear by 18

- unite by age 22 - 25

- if un-united by age 25 = Os Acromiale 

 

Types

 

1.  Meso-Acromion

- most common (94%)

- level with posterior aspect clavicle

 

 Os Acominale XrayOs acromiale

Axillary lateral

 

Os Acromionale MRI AxialOs Acromionale MRI Sagittal

Axial MRI                                                 Sagittal MRI

 

2.  Pre-acromion

 

Uncommon

- level with anterior border acromion

 

 Os Acrominale MRI T2Os Acromiale MRI T2

 

3.  Meta-Acromion

 

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

 

Os 1 axillary lateralOs 1_0

 

MRI

 

Useful investigation

- may show edema if problematic

 

Os Acromionale MRI 1Os Acromionale MRI 2

Axial MRI with meso-acromiale

 

Bone scan

 

Can be useful

- unlikely to be symptomatic if cold

- may be symptomatic if hot

 

Symptoms

 

Pain

- inflammation at nonunion site (inflammation on MRI)

- fragment moves with deltoid contraction and causes impingement symptoms

 

Os AcromionaleOs Acromionale 3Os Acromiale 3

Axillary lateral showing meso-acromion              Scapula lateral xray showing os acromiale

 

Management

 

Indications

 

Failure of non operative treatment

Symptomatic os acromiale

 

Options

 

1.  Excision

2.  ORIF

 

Purnell et al. J Orthop Surg Res 2019

- systematic review of prospective and retrospective cases

- excision: 92% good or excellent results

- ORIF: 82% good or excellent results, 67% complication rate (non union, infection, seroma, removal hardware)

- acromioplasty: 67% good or excellent results

 

1.  Excision

 

Indications

 

Pre-acromion or meso-acromion

 

Options

 

Open - risk compromising deltoid insertion

Arthroscopic - leaves deltoid attach intact

 

Results

 

Pagnani et al JSES 2006

- arthroscopic excision in 11 shoulders of athletes

- all returned to sport at 14 weeks

- no loss of strength detected

 

Os Acromiale ArthroscopicOs acromiale arthroscopic

 

Vumedi video arthroscopic excision of os acromiale

 

2.  ORIF

 

Indications

 

Large fragment / mesoacromion

- take down non union

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

- especial care with deltoid reattachment

 

Vumedi video os acromiale fixation

 

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

 

Outcomes

 

Atinga et al J Should Elbow 2018

- 32 cases treated with screw fixation and bone graft

- 100% union at 3 months

- 1 infection, 1 seroma, 4 removal of metal work

 

Risks

 

Nonunion

- remove screws

- arthroscopic resection

 

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

Non union with evidence of lysis around screws