April 11, 2024

Anterior cruciate ligament is an important stabilizer of the knee which prevents anterior translation of the tibia as well provides rotational stability.

ACL anatmy
ACL ligament

31-35 mm length

31.3 mm2 cross-section

Primary blood supply: Middle genicular artery

Insert on the tibial plateau: Medial to insertion of the anterior horn of the lateral meniscus and anterolateral to the anterior tibial spine

Treatment Options for ACL Injury

  1. Non-operative treatment
  2. Operative Measures
    1. Repair of ACL (Isolated or with augmentation)
    2. Reconstruction with either allograft/ autograft/ synthetics
  3. Postoperative rehabilitation

Non-operative treatment

  • Excessive rehabilitation
  • Knee brace (+/-)
  • Counseling

For the patient who is willing to make lifestyle changes and avoid activities that cause recurrent instability, non-operative methods can help

Operative treatment

Indication for surgery is ideal in the following group of patients

  • Young age
  • Preinjury hour of sports participation

Primary Repair in an ACL tear is not currently recommended as myofibroblasts coats the ACL stump; Making healing impossible

Acute Repair:

Bony avulsion occurs with anterior cruciate ligament attached=> Fixed with sutures, screw placed through fragment

Augmentation of primary repair is done by tissue and approach for reconstruction with, augmenting tissue is passed through the posterior capsule in the intercondylar notch (HIGH) over the lateral femoral condyle

Preserve femoral attachment of ACL

Secured by screw/ staplers

The tibial tunnel should be placed anterior medial to the tibial footprint (to minimize disruption of the tibial attachment of ACL)

Reconstruction for ACL Insufficiency

Primary repairs routinely fail (So, need reconstruction)


Intraarticular Reconstruction:

Persistent postoperative stiffness + avulsion laxity => So, discouraging (Lack of IA blood supply)

Extraarticular Reconstruction:

Restraining band over the lateral side of the knee


  • In front of gerdy tubercle on the anterolateral aspect of the tibia
  • Proximal to the origin of LCL

Extraarticular process

  • Iliotibial band tenodesis
  • Bicepsplasty

But extraarticular processes do not recreate the normal anatomy of the function of the ACL

When used alone => FAILED (High failure rate)

So, currently, the extraarticular process is done in conjunction with the intraarticular process

Intraarticular Reconstruction

Improved by

  1. Graft placement
  2. Graft selection
  3. Graft tensioning
  4. Graft fixation
  5. Rehabilitation

Graft Selection

Autograft advantages: No chance of disease transmission, Very less chance of inflammatory reaction

Biological Graft: Undergoes revascularization and re-collagenization ( 50% loss of graft strength occurs after implantation)

Commonly used:

  • Bone patellar tendon-bone graft (BPTB)
  • Hamstring (Quadrupled) tendon graft

Normal ACL

Ultimate load:

1725 +/- 269 N

2160 +/- 157 N ( Young)


182+/- 33 to 242 +/- 28 N

Some differences between Bone patella tendon bone graft and hamstring tendon graft

Bone -Patella – tendon – Bone Graft (BPTB)Hamstring Tendon Graft
8-11 mm wideTriple or quadruple strand semitendinous or
Taken from central 1/3 rd of the patella with bone blockQuadruple strand (Semitendinous / Gracialis) taken
Fold growth (3-4) times
Ultimate tensile load: 2300 NUltimate tensile load: 4108 N
Stiffness: 620 N/ mm
Rigid fixation with bony ends with faster incorporation of bony tunnel
Anterior knee painLack of rigid bone fixation
Pain in kneeling is greaterThe problem in tendon healing in the osseous plane
Poor recovery of quadriceps strength
Slightly increase in laxity than BPTB graft
Intratendinious calcificationInjury to the Saphaneus nerve
Higher incidence of arthritis

The potential weakness of the knee: Flexion + Internal rotation
Difference between BPTB graft and Hamstring graft

In quadriceps: Ultimate tensile: 2352 N

Graft Placement

Femoral Tunnel malposition in ACL Injury
Femoral Tunnel malposition in ACL Injury

Femoral tunnel malposition

Too anterior (a): a will be tight in flexion and lax in extension

Too posterior (b): b will be tight in extension and lax in flexion

Tibial tunnel malposition

Too anterior: Root impingement with extension tight in flexion

Too posterior: Impinge with PCL

Rehabilitation protocol after multiple ligament reconstructions in the knee

ACL injury

Partial weight-bearing with brace locked: 0-4 weeks

Weight-bearing as tolerated with brace unlocked: 4-6/8 weeks

Low impact aerobics: 6/8 weeks to 12 months

Double bundle repair vs Single bundle repair

Double bundle repair should be reserved for high-demand patients such as sportsmen, and athletes, considering it provides better stability, less failure, and revision. However, for the general population single bundle repair is sufficient to get good to excellent functional outcomes in the majority of cases.

Closed Chain exercises:

  • Preferred in the patient with ACL reconstructed Knee
  • The foot is in contact with the couch ( making the chain closed), the knee joint is thus so loaded that during movements the graft is protected from shearing stress and the contour of the joint helps to stabilize the knee and protect the graft.

Open Chain exercises:

The limb is not weight-bearing: Restricted quadriceps exercises put a strain on the anterior cruciate ligament, particularly in terminal extension of the limb

“foot is in the air= Chain is open”

See also: Anterior Drawer test and door stopper effect