Reasons for failure of ACL graft
- Surgical error (tunnel malpositioning, inadequate tensioning or fixation of the initial graft)
- Failure to recognise a secondary laxity (eg postero lateral corner)
- Biological failure, ie failure of graft incorporation or ‘ligamentisation’
- Rehab issues
Complications of ACL recon
Continuing instability may be due to :
- Immediate graft failure, ie poor fixation
- Suboptimal tunnel placement - either the graft being too vertical (with correction of AP laxity but not rotational stability) or the tunnels being too anterior (femoral and tibial tunnels) or posterior (tibial tunnel)
- Cyclical creep of the graft due to inappropriately advanced accerelated rehab
- Traumatic graft rupture due to too early a return to contact sport
Other complications include :
- Loss of motion
- Infection (superficial, deep)
- Long term anterior knee pain
- Saphenous nerve irritation or neuroma formation
- Cyclops lesion formation - scar tissue anterior to the graft usually associated with anterior tibial tunnel placement
- Hardware complications
- Neuro vascular complications
- Fracture of the tibia, femur or patella
- Development of a complex regional pain syndrome
Determinants of outcome in ACL reconstruction
- Graft strength
- Graft fixation
- Other factors than stability, which are important for long-term outcome (pain, ROM, OA changes)
Load to failure of native ACL
2000 N
Classic acute history of ACL tear
absent in up to 30% of ACL injuries
- Non-contact rotational injury
- Swelling normally present with one hour (due to haemarthrosis)
- ‘pop’ or ‘snap’
- Usually cannot continue in the sport im which the patient was participating
Examination in ACL injury
- Lachman test (ap laxity at 20° of knee flexion with a poor end point) - most specific
- Anterior drawer sign (knee flexion at 90°)
- pivot glide or pivot shift
Segond fracture
Avulsion injury of the lateral tibial plateau that is very suggestive of ACL injury with lateral ligament complex injury
Aims of rehab before ACL recon
- Regain full extension and flexion of the knee
- Rehabilitate the quadriceps and hamstring mechanisms
- Normal gait pattern
- Eliminate swelling
- Restore symmetry to the lower limbs
Features of acute ACL injury in MRI
normal MRI scan does not exclude an ACL injury
- Disruption of the ligament
- Laxity of the ligament
- Secondary changes to PCL alignment
- Bone bruising
- Sometimes interstitial damage to the ligament causing a ‘sausage effect’
Why should the knee be ‘quiet’ at the time of ACL reconstruction?
To minimise the risk of arthrofibrosis
Structure that is most effective in providing stability of knee rotation
Postero-lateral bundle of the ACL
Goals of ACL recon
- Stabilise the knee joint
- Restore normal kinematics
- Prevent early onset degenerative arthrosis
Anatomy ACL
- Intra-articular but extra-synovial structure
- Blood supply from the middle genicular artery, arising from the popliteal artery
- Provides proprioceptive feedback that is protective to the knee, provides stability (anterior translation and rotational stability)
- AM bundle is tighter in flexion, PM bundle is tighter in extension
- Mean length of 31-38mm and width of 11mm
Risk factors for ACL tear
- Hyperlaxity
- Genetic predisposition
- Raised BMI
- Hormones
- Female gender (relative risk ratio 2-6 times than males)
Goals of prevention programs (ACL injuries)
- Decrease peak vertical ground reaction force
- Increase knee flexion angle
- Decrease knee valgus
Consequences of tunnel malpositioning
- Impingement
- Deficits in ROM
- Recurrent instability
- Graft failure
Autografts (ACL)
- Hamstrings (semitendinosus and gracilis, doubled to create a 4-strand ACL graft)
- Bone-patella tendon bone
- Quadriceps with or without bone block
Weak link in any ACL recon
Graft fixation on the tibia
–> graft axis is parallel to the applied force whilst its bone mineral density is considerably less than the distal femur
Which ACL recon technique entirely spares the the femoral physis (where growth occurs)?
All-inside technique
Most common surgical error in arthroscopic ACL recon
Anterior femoral tunnel placement, often due to poor visualisation
May cause loss of knee flexion
May cause graft overstretching and failure
Empty lateral wall
= empty notch
Sign on coronal MRI
indicates avulsion of ACL from the femoral origin
Bone bruises
Trabecular microfractures
Occur in more than half of acute ACL injuries
What should be achieved prior to surgery?
Full ROM and good quadriceps strength
Why primary repair of ACL tears currently not recommended?
Myofibroblasts ‘coat’ the ends of the ACL stumps, making primary healing unlikely
