Background

IncidenceRevision ACL Ruptured Graft MRI BPTB Allograft

 

Up to 8% patients with ACL reconstruction will have recurrent instability and graft failure

- increased with surgical inexperience

 

Graft can

 

1.  Be inadequate from the start

- inadequate tension

- poor tunnel placement

 

2.  Stretch 

- poor tunnel placement

- impingement

- non isometric

 

3.  Rupture

- may be trauma

- may be surgical issues

 

Causes Rupture

 

A. Technical Failure

 

Non anatomic tunnel placement

Inadequate notchplasty

Improper tensioning

Graft impingement

Failure graft fixation

Insufficient graft material 

 

B.  Biological Failure

 

Failed ligamentisation

Infection

 

C.  Failures due to trauma

 

Early (before graft incorporation)

Late (after incorporation)

 

Graft rupture best seen on T1

 

ACL Graft Rupture Coronal MRIACL Graft Rupture MRI SagittalRuptured ACL Graft MRI T1

 

D.  Failures due to laxity of secondary restraints

 

Rotatory instability / Varus / Valgus instability

- posterolateral corner / PCL

Skeletal malalignment

 
Technical Issues

 

A.  Non anatomic Tunnel Placement

 

Most common

- 70 - 80% Technical Failures

 

Mal-positioned grafts incur excessive tension

- impinge and become lax

 

Femoral Tunnel

 

Most common error in ACL Reconstruction

- errors in femoral placement are less forgiving

- either get a loss of motion or graft failure

 

Optimal placement

- lateral radiograph 

- intersection of Blumensaat's line and

- line extended from the posterior femoral cortex

 

ACL Graft Rupture Anterior Femoral TunnelACL Graft Rupture Femoral Tunnel Anterior

 

A.  Anterior femoral placement 

- increases tension in flexion / loss of flexion

- stretching of the graft required to obtain flexion

 

B.  Posterior femoral placement

- increases tension in extension

- need to stretch to obtain extension

 

C.  Superior femoral placement

- 12 o'clock position

- AP stability

- rotationally unstable / continue to pivot shift

 

ACL Graft Failure Vertical TunnelsACL Graft Rupture Graft Too VerticalACL Failure Graft Too Vertical

 

Tibial Tunnel

 

More forgiving

 

Ideal Tibial tunnel placement 

- posterior and parallel to the tibial intersection of Blumensaat's line in full extension

- this will prevent it impinging on the notch

 

A.  Anterior placement 

- increases tension in flexion

- may result in notch impingement in extension

- stretching of graft

 

B.  Posterior placement 

- causes PCL impingement 

- reduces the graft's ability to control AP translation

 

ACL Tibial Tunnel PosteriorFailed ACL Posterior Tibial Tunnel

 

C.  Lateral placement 

- causes impingement on the medial wall of the lateral femoral condyle

 

B.  Inadequate notchplasty

 

Graft is often larger than native ACL

- especially with BPTB

- need to assess

- debride anterior lateral part of notch and roof

 

Impingement

- loss of extension

- formation Cyclops lesion

 

ACL Graft Cyclops Lesion

 

C.  Improper Tensioning

 

Under tensioning 

- non-functioning graft

 

Over tensioning

- constrain the knee

- affect graft incorporation

 

The ideal tension is unknown

- tension BPTB graft to 5-10 lb at 10-15 degrees flexion

- tension hamstring graft to 10-15 lb at 20-30 degrees of flexion

- cyclically preload & maintain tension until secured

 

D.  Graft Fixation Failure

 

Takes 6-12 weeks for graft incorporation to occur with hamstrings

 

Graft fixation needs to be strong for this period

 

E.  Tunnel Lysis

 

Revision ACL Tibial Tunnel LysisFailed ACL Tibial Tunnel Lysis

 

Very common, cause unknown

 

No evidence that contributes to instability

Important in revision setting

 

Cause

- more common tibial side than femur

- tends to stop after 3/12

- postulated to be from synovial fluid pistoning

- hence fluid finds it easier to come down tibial tunnel as screw placed outside in

- also seen more on femoral side with endobutton (windscreen wiper effect)