ACL Avulsion Fracture

Definition

 

Tibial spine avulsion at the bony insertion of the ACL on the tibia

- ACL intact

 

Anatomy

 

Bony fragment

- ACL tibial insertion attached

- anterior horn of lateral meniscus often attached

 

The intermeniscal ligament is a block to reduction

 

Aetiology

 

Children aged 8 - 14

Tibial eminence ossification is weaker than ACL at this age

Knee hyperextension +/- valgus

 

Clinical

 

Swollen knee with haemarthrosis

Lack of full extension due to a mechanical block

 

Meyers & McKeever classification

 

Tibial spineTibial spine 2

 

Type I:   Undisplaced

Type II:  Partially displaced with anterior portion hinged

Type III:  Completely Displaced

Zaricznyj Type IV: Comminuted

 

Xray

 

Bony ACL 1Bony ACL 2

Xray showing likely Type II with anterior hinging

 

ACL Avulsion Type 2

Type II / III

 

CT

 

Can help classify and thus guide treatment

 

Bony ACL 4Type 3 ACL Avulsion

Type II                                                          Type III

 

Avul 6Avul 7

Type IV

 

MRI

 

Rhodes et al J Paediatr Orthop 2018

- 77 patients with ACL tibial avulsion

- meniscal entrapment identified in 40%

- 30% meniscal tear, 70% osteochondral injury

- 32% other ligament injury

 

MRI ACL avulsion

Sagittal MRI demonstrating small bony fragment with ACL attached

 

Nonoperative treatment

 

Indication

 

Type I - 6 weeks cast / splint in extension

Type II - attempt closed reduction

 

Closed reduction and casting

 

Indication

 

Type II

 

Technique

 

Attempt closed reduction

- anaesthesia / image control

- long leg cast in full extension

- trap fragment under condyles

 

Block to reduction

- usually intermeniscal ligament

- can be medial or lateral meniscus

 

ACL avulsion reduced in extension

Xray demonstrating reduction of fragment with knee in hyperextension and in cast

 

Operative Management

 

Indications

 

Type II that doesn't reduce / blocked by intermeniscal ligament

Type III

Type IV

 

Options

 

Open / medial arthrotomy

Arthroscopic repair

 

Fixation Techniques

 

1. Physeal sparing screw

 

Image guided

- directed posterior and obliquely

 

Advantage

- strong fixation

- may be able to range knee earlier

 

Disadvantage

- not indicated in comminuted fractures / Type IV

- second surgery to remove screw

- iatrogenic risk to posterior NV structures

 

2.  Suture fixation

 

Advantage

- comminuted fractures

 

Disadvantage

- technically challenging

- may tether physis if transphyseal

 

Techniques

A.  All epiphyseal if > 4 years of growth

B.  Trans-physeal if < 4 years of growth

 

Tie over bony bridge or use cortical buttons

 

Open fixation

 

Technique

 

Medial parapatellar arthrotomy

- need to remove portion of fat pad for visualisation

- intermeniscal ligament may block reduction

- remove callus / hematoma

- replace fragment under intermeniscal ligament

- want to impact fragment to tension stretched ACL

 

Arthroscopic suture fixation

 

ACL 2ACL 3ACL 4

Fragment flipped and insertion debrided          Avulsion fragment reduction                          Passage of two loop sutures with scorpion

 

ACL 6ACL 7ACL 5

ACL tibial jib with beath pin                          Beath pin cannulated, loop wire passed           Retrieval of sutures

 

Technique

 

Clean haematoma, ensure can reduce fragment with probe

- can consider temporary fixation with K wire

- arthroscopic suture passer (i.e. arthrex knee scorpion)

- pass sutures x 2 through ACL above bony fragment

- cannulas can be useful for suture management

 

Reduce fragment and hold with ACL tibial guide

- medial tibial incision, pass beath pins x 2 (preferable cannulated)

- 1 cm between tunnels

- beath pins exit through bony fragment

- retrieve sutures

- reduced fragment, knee in full extension

- tie over bony bridge or over cortical button

 

Technical note

 

1. Passing sutures anterior to the bony fragment rather than through may help anatomical reduction

2.  Companies make cannulated beath pins, allowing suture loops to be passed up the pins

 

Post operative

- TWB for 4 - 6 weeks

- full extension for 4 - 6 weeks

- then begin ROM exercises

- no sport 6 - 12 months

 

Suture bridge surgical technique video

 

Vumedi video

 

Vumedi video

 

Arthroscopic cortical button physeal sparing

 

Bony ACL 5Bony ACL 6

 

Outcomes / Complications

 

Operative v Non operative

 

Likely that surgery limits ongoing instability

 

Gans et al Am J Sports Med 2014

- systematic review of 580 pediatric and adolescent patients

- no difference in outcomes between open and arthroscopic techniques

- no difference in outcomes between screw and suture fixation techniques

- reduced laxity and stiffness after surgical treatment of Type I and II fractures

 

Stability

 

Residual instability common despite surgery due to ACL stretching before injury

 

Kocher et al Arthroscopy 2003

- 6 patients average age 12 two years after arthroscopic fixation

- abnormal Lachmans in 5/6

- abnormal pivot shift in 2/6

- all had excellent functional outcomes

 

Quinlan et al Arthros Sports Med Rehab 2021

- 66 patients average age 11 with mean follow up 6 years

- surgical fixation of Type II and III

- 92% reported knee as normal

- 9% limited by instability and pain

- 7% subsequent ACL rupture

 

Stiffness

 

Stiffness can be a problem in the surgical group

- a combination of surgery and prolonged immobilization

 

Edmonds et al J Paediatr Orthop 2015

- 57 surgical patients, 19 treated with casting

- mean age of 12

- arthrofibrosis 12% in surgical group, 0% in casting

- casting group 17% incidence second surgery for instability / loose bodies / impingement

 

Nonunion

 

Rare

Typically in setting of nonoperative treatment of completely displaced fractures (Type III)

 

Malunion

 

Nonoperative treatment

- anterior fragment remains displaced

- may cause impingement and loss of extension

- may be associated with residual laxity

 

ACL Avulsion MalunionACL MRI avulsion

Xray and MRI demonstrating residual anterior elevation of fragment causing impingement

 

Growth plate disturbance

 

Associated with transphyseal drilling with > 4 years growth remaining