Anterior Cruciate Ligament Injury
- Anterior Cruciate Ligament (ACL) Injury is one of the most common sport injuries among young patient.
- 40% and 50% of all knee ligament injuries.
- Female athletes have a 2 to 8 times higher risk of ACL tear compared to male athletes because:
- Women have a greater total valgus knee loading in landing.
- Women land more erect.
- Women have increased quadriceps-to-hamstring strength, causing increased anterior sheer.
- Smaller notches, smaller ligaments (reduced area in cross section), increased generalized ligament laxity, and increased knee laxity are additional proposed factors.
Anatomy of the Anterior Cruciate Ligament:
- The anterior cruciate ligament is composed of longitudinally oriented bundles of collagen tissue (90% type I collagen and 10% type III collagen).
- The ligament is surrounded by synovium making it extrasynovial structure.
- The ligament is 31 to 35 mm in length, and 11 mm in diameter.
- The anterior cruciate ligament originates from a semicircular area on the posteromedial aspect of the lateral femoral condyle and inserts on the tibial plateau, on a broad, irregular, oval area anterior and between the spines of the tibia.
- The tibial attachment site is larger and more secure than the femoral site.
- Tension in the anterior cruciate ligament is least at 30 to 40 degrees of knee flexion.
See Also: Meniscus of the Knee Anatomy
The ACL has two bundles:
- Anteromedial bundle:
- It is tight in flexion.
- Primarily an anterior restraint.
- Evaluated by Lachman test and anterior drawer test.
- Posterolateral bundle:
- Tight in extension.
- Primarily a rotatory restraint.
- Evaluated by pivot shift test.
The anterior cruciate ligament secondary function is to resist tibial rotation and varus-valgus angulation at full extension.
The anterior cruciate ligament has proprioceptive function, as evidenced by the presence of mechanoreceptors in the ligament.
Blood Supply and Innervation:
- Anterior cruciate ligament receives its blood supply via branches of the middle genicular artery.
- Additional supply comes from the retro-patellar fat pad via the inferior medial and lateral geniculate arteries.
- The osseous attachments of the anterior cruciate ligament contribute little to its vascularity.
- The posterior articular nerve, a branch of the tibial nerve, innervates the anterior cruciate ligament.
Mechanism of injury
- Mechanism of ACL injury is typically a valgus load with internal tibial rotation and anterior tibial translation while the knee is in almost full extension.
- Acute lateral meniscus tears are more common than acute medial tears.
- Medial meniscus tears occur more often with chronic anterior cruciate ligament deficiency.
- Medial collateral ligament injuries occur in approximately 25% of cases.
- Posterolateral corner (PLC) injuries occur in approximately 10% of cases.
See Also: Knee Meniscus Tear
Symptoms & Signs:
- ACL injury is commonly associated with an audible felt “pop”.
- Hemarthrosis that begins within 12 hours of injury.
- Pain, Instability and inability to return to sport.
- The Lachman test is the most sensitive examination for acute anterior cruciate ligament injuries.
- The pivot shift test.
- The anterior drawer test of the knee.
- AP View: Segond fracture (an avulsion fracture of the lateral capsule) is pathognomonic for an ACL tear.
- Lateral View: look for the degree of posterior tibial slope. Values greater than 13 degrees have been associated with ACL failure.
- It is useful in confirming the diagnosis of ACL tear.
- Signs of an ACL tear include:
- Disruption of ACL fibers.
- Fibers no longer parallel to Blumensaat line.
- Inability to visualize fibers of ACL.
- “Empty lateral wall” or “empty notch” sign indicating avulsion of ACL from the femoral origin
- Bone bruises (trabecular microfractures) occur in more than half of acute ACL tears.
On sagittal imaging, fibers of an intact ACL should parallel the Blumensaat line.
Treatment Of ACL Tear
- Treatment choice of ACL tear should be selected based on:
- The age.
- Activity level.
- Associated injuries.
- Other medical factors.
- Primary repair of ACL tears is not currently recommended, because myofibroblasts cover the end of the ACL stumps, making primary healing impossible.
- Initial treatment of ACL tear consists of:
- Physical therapy for mobilization (Immobilization is avoided).
- Full ROM and good quadriceps control should be achieved prior to surgery.
- ACL reconstruction indications include:
- Younger age.
- Older but active patients.
- Active patients.
- Prior ACL reconstruction failure.
- Single-bundle graft reconstruction is the most commonly performed reconstruction.
- Graft selection depends on patient factors and surgeon’s preference.
- Graft types include:
- A bone-patella-tendon-bone (BPTB) autograft.
- A four-strand hamstring autograft.
- A quadriceps tendon autograft.
- An allograft.
- Graft types include:
1. Bone-Patella-Tendon-Bone (BPTB) Autograft:
- Demonstrates faster incorporation into the bone tunnels than does hamstring autograft.
- It’s often the graft of choice for patients who desire an early return to sports activity.
- There is a higher incidence of arthritis associated with the use of BPTB autograft than with hamstring autograft 5 to 7 years after ACL reconstruction.
- BPTB autograft harvest risks include:
- Anterior knee pain.
- Pain with kneeling.
- Loss of extension.
- Poorer recovery of quadriceps strength.
2. Hamstring Autograft:
- Its advantages include:
- Smaller incision.
- Less peri-operative pain.
- Less anterior knee pain.
- Fixation strength may be less than Bone-Patella-Tendon-Bone (BPTB).
- It carries the risk of weakness of knee flexion and internal rotation, along with injury to branches of the saphenous nerve.
- May be associated with a higher rate of rerupture in younger, more active patients.
- Chemical-processed or irradiated allografts have demonstrated increased rates of failure compared to fresh-frozen allografts.
- Allografts have been demonstrated to incorporate into bone tunnels more slowly.
- Allograft risk also includes infection risk.
Associated injuries treatment:
- MCL injury:
- Allow MCL to heal (varus/valgus stability) and then perform ACL reconstruction.
- Meniscus tear:
- Meniscal repair should be performed at same time as ACL reconstruction.
- Increased meniscal healing rate when repaired at the same time with ACL tear.
- Posterolateral corner injury:
- Reconstruct at the same time as ACL or as 1st stage of a 2 stage reconstruction.
- Exercises that do not endanger the ACL graft:
- Exercises dominated by the hamstrings (isometric hamstrings) .
- Exercises that result in quadriceps activity with the knee flexed beyond 60 degrees.
- Exercises involving active knee ROM between 35 and 90 degrees of flexion.
- Closed-chain rehabilitation (fixation of terminal segment of extremity [i.e., foot planted]) and compressive loading have been emphasized because they allow physiologic contraction of the muscles around the knee.
- Open-chain extension exercises place increased stress on the reconstructed ACL and should be avoided for the first 6 weeks.
- Early progressive eccentric exercise has yielded good initial results in terms of quadriceps and gluteus maximus muscle size and function after ACL reconstruction
Complications after treatment of ACL tear:
- Tunnel malposition: the most common technical error:
- Vertical graft placement results in decreased rotational stability.
- Anterior placement of the femoral tunnel results in limited flexion.
- Arthrofibrosis: often occurs with reconstruction for acute ACL tears.
- Aberrant hardware placement
- Infection: occurs in less than 1% of cases.
- Graft contamination:
- Graft contamination by dropping on the floor is rare.
- The majority of surgeon favored retention of the graft with disinfection rather than harvesting a new autograft or switching to allograft.
- A combination of chlorhexidine gluconate and triple antibiotic solution (gentamicin, clindamycin, polymyxin) in sterile saline appears to be the most effective disinfecting regime.
- Infrapatellar contracture syndrome.
- Patella Tendon Rupture.
- Patella fracture.
- Late arthritis.
- Tunnel osteolysis.
- Local nerve irritation : saphenous nerve.