Anterior Cruciate Ligament (ACL) Injuries
Written and edited by Aruna Seneviratne, M.D.
Several ligaments stabilize the human knee. They are the Anterior Cruciate Ligament (ACL), the Posterior
Cruciate Ligament (PCL), the Medial Collateral Ligament (MCL), the Lateral Collateral Ligament (LCL), and
the Posterolateral Corner Complex (PLC). Injury to the ACL is can lead to instability of the knee. Injuries
to the ACL can occur in isolation or in combination with other injuries - usually ACL, LCL, and PLC
injuries. Meniscal tears can also occur concurrently. These injuries typically occur during participation in
sports that involve lateral movements such as soccer, skiing, football, etc. Women have a 5-7 fold increased
risk of ACL ruptures and it is hypothesized that its due to anatomic variations, neuromuscular control
mechanisms, and other factors. Hormonal differences have been largely disputed through rigorous scientific
study, including a study published by Dr. Seneviratne investigating the influence of estrogen on ACL
tenocyte function ( Seneviratne AM, Attia E, Williams RJ, Rodeo SA, Hannafin J."The
Effect of Estrogen on
Ovine Anterior Cruciate Ligament Fibroblasts: Cell Proliferation and Collagen Synthesis."
of Sports Medicine, November 2003).
ACL tears can lead to knee instability, and that may lead to microscopic damage to the articular cartilage
(the smooth articulating surface of joints), which in turn may lead to osteoarthritis in the future. There
are two categories of patients - copers (10% of patients) and non-copers. Copers are able to continue with
their activities of daily living and sports without having instability of the knee. These patients have very
strong hamstring muscles that compensate for the lack of an ACL. Non-copers have overt knee instability with
sports, and sometimes with simple walking. Knee pain usually resolves after about 3 weeks of the injury, and
patients can generally walk with without too many symptoms.
Biology: Why does it occur?
These injuries occur due to high-energy trauma - motor vehicle accidents or sporting injuries. They require
prompt medical attention. The LCL and PLC are outside the knee joint and have greater healing potential than
the PCL which is inside the knee joint. Therefore, early repair of the LCL and PLC have been advocated to
make use of this healing response that occurs within the first three weeks from injury. The PCL tends to
demonstrate less robust healing, and late reconstruction is advocated.
Common Diagnostic Techniques:
History: Diagnosing the problem begins with a detailed history that your surgeon will obtain from you.
Physical Exam: A thorough physical examination is then conducted by your surgeon.
X-Rays: Plain radiographs (X-Rays) are the most important diagnostic study that is performed initially. For
the knee your surgeon will obtain specialized views. Usually these are weight bearing x-rays - i.e.: you
will be standing for the x-rays.
MRI: Your surgeon may obtain additional studies such as an MRI to look more closely at all ligaments and
Depends on a variety of factors including patient age, activity level, degree of instability etc. Older
patients are usually treated non-operatively with physical therapy. Athletes who play high demand sports
such as basketball, soccer, football, and skiing, require surgical reconstruction of the ACL. Dr.
Seneviratne will carefully evaluate each patient and recommend the optimum course of treatment.
Surgery is performed arthroscopically, with a small incision on the front of the knee to harvest the graft.
The graft can be the central third of the patella tendon, or the hamstrings. The graft is placed through 2
precisely placed tunnels in the tibia and femur, and fixed with titanium screws, thereby reconstructing the
ligament in an anatomically accurate fashion. Surgery takes about 60-90 minutes, and is an outpatient
procedure where the patient goes home the same day. Dr. Seneviratne performs a footprint ACL reconstruction
using flexible reamers and the anteromedial portal technique.
You will be placed into a brace, and you are allowed to weight bear as tolerated. You will start range of
motion exercises of the knee immediately. Physical therapy is started usually on post op day one, but most
definitely within 1 week of surgery for edema control, muscle activation, and other modalities to aid
healing. Rehabilitation for this type of injury can last up to 6 months.
Where can I get more information on the surgery and its rehabilitation protocol after surgery?
Dr. Seneviratne has a detailed booklet on this topic.
What are the risks of ACL reconstructive surgery?
Infection, bleeding, damage to nerves and blood vessels, blood clots that form in your legs (DVT), blood
clots that can break off and travel to your lungs causing a pulmonary embolus (PE). Knee stiffness is an
Is quadriceps weakness a permanent problem?
Permanent quadriceps weakness may occur in about 20 percent of patients undergoing ACL reconstruction -
regardless of graft choice. A variety of factors are responsible for it including the use of a femoral nerve
block at the time of surgery, inadequate rehabilitation post operatively, and other factors.
What are the graft choices for ACL reconstruction?
ACLs can be reconstructed using your own tissue - the central third of the patellar tendon with two bone
plugs harvest from the patella and tibia or hamstring tendon. Allograft tissue (cadaveric tissue harvested
at time of death) can also be used. Dr. Seneviratne prefers to use the patient's own tissue as it heals
faster and eliminates the risk transmitting diseases such as HIV or Hepatitis B although those risks are
very remote. There is a role for allograft use, and Dr. Seneviratne will evaluate each patient and customize
treatment for the patient.
What is the re-rupture rate of a reconstructed ACL?
For bone patellar tendon bone autograft ACL reconstructions - 3%
For hamstring ACL reconstructions - 4-13%
For allograft (cadaver tissue) ACL reconstructions - about 20%
How long is the recovery period?
Early healing is 6 weeks. Full and mature healing can take upto 1 year. Most professional athletes are out
of sports participation for a whole year. However, most patients walk without a limp at about 6-8 weeks, and
can jog on a treadmill at 8 weeks post op.
Can I return to my pre-injury level of play?
Yes. Many professional athletes have returned to their previous level of play - Peekaboo Street - won gold
medal in skiing, Tom Brady - quarterback for New England Patriots won superbowl after ACL reconstruction.