Tag Archives: ACL

ACL Reconstruction: Which Option Is Best For You?

200,000 ACL injuries occur each year, and ACL reconstruction is the 6th most performed surgery in the United States, so to come back bigger, faster, and stronger, the right recovery path is critical.

The anterior cruciate ligament (ACL) is a critical part of the knee joint that connects the femur (‘thighbone’) to the tibia (‘shinbone’). Its main functions are to support the knee joint during side-to-side motion, such as cutting, shuffling, or pivoting, and to prevent the tibia from moving too far forward relative to the femur. When an ACL ruptures, it is very common to reconstruct it to bring someone back to performance level.

Location of the ACL inside the knee joint with other labeled bones and ligaments with another diagram showing a ruptured ACL.
Image from Wikimedia Commons “Anterior Cruciate Ligament”

The basis of ACL reconstruction is using living tissue, also known as grafts, to replace, and function as a substitute, for the torn ACL. There are four types of ACL reconstruction surgeries that use different types of grafts. Those four types of surgeries are classified as autograft reconstruction, allograft reconstruction, xenograft reconstruction, and synthetic reconstruction. Autograft surgeries require one’s own grafts to repair the ACL, allografts require a cadaver’s grafts to repair the ACL, xenografts require an animal’s grafts, and synthetics require manufactured materials. Additional articles on xenograft reconstruction and synthetic reconstruction can be accessed here and here.

Each surgery requires the removal of the damaged ACL, and then the incorporation of a new substitute by tunneling the newly selected graft through the femur and tibia. Within the autograft group, the two popular grafts for reconstruction are patellar tendon and hamstring tendon, with quadricep tendon being another, less popular, choice. The patellar tendon surgery takes the middle third of the patellar tendon, a tendon that connects the kneecap to the tibia, and makes sure to include the bony ends.

The hamstring tendon surgery takes two small slivers of each of the two hamstring tendons, connecting the hamstring muscle to the tibia, coils them up, and then finally bundling them to increase strength.

A knee joint with bones, ligaments, and tendons labeled.
Image from Wikipedia “Knee Joint”

For the allograft surgeries, a surgeon may select an Achilles, patellar, hamstring, or quadricep tendon from the donor.

It is very important to choose the right surgery. While the determination of which surgery and technique to perform falls heavily on the surgeon’s and patient’s preference, there are advantages and disadvantages of each technique which tend to persuade the choice of surgery. The main concepts surrounding the decision of which surgery to perform are the activeness of the patient, muscle strength, and previous knee injuries. Depending on the job, sport, or activity of the patient and the desired return time, one technique may be a better fit.

For a patient participating in low demand activities, allograft surgery may be the best fit due to less post-surgery pain and quicker surgery time, however it is very expensive and offers less tensile strength compared to autografts. As for autograft surgeries, patellar tendon reconstruction allows faster recovery time due to the bone-to-bone bonding and offers a strong substitute for a torn ACL, however future knee pain is very common. Hamstring tendon reconstruction requires more recovery time; however, the post-surgery pain is significantly less than the patellar tendon reconstruction and the tensile strength of the hamstring tendon is the strongest possible substitute.

Additional reading and comparisons between the popular autografts and allograft techniques can be accessed here and here.

Do you have an ACL?

Whenever there is a lower extremity injury in sports, the first thing people always ask is: “Was it the ACL?” I, like everyone else, assumed everyone had an ACL because I did not believe that you could walk without one, let alone play sports. To my surprise, I discovered that not everyone has an ACL. Some people are born without one, while others lose their ACL’s. Hines Ward, an NFL All-pro wide receiver, went his whole football career without an ACL. Ward lost his ACL during an accident when he was about 4 years old and the doctors were unaware. He did not find out that he did not have an ACL until he was making the transition from college to the NFL.

 

Being born without an ACL it is referred to as the congenital absence of the anterior cruciate ligament and is an extremely rare condition. Only about 2 in every 100,000 live births are subject to this congenital absence of the ACL. It is caused by an insufficient development of the knee joint when a baby is in the womb. Others do not have ACL joints due to a complete rupture of the ligament. There was a case of a 25 year old woman who had instability in her left knee joint and had no history of knee trauma. Physical investigations showed no swelling or tenderness, but after an MRI it was discovered that she had no ACL joint and the PCL was hypoplastic.

 

The knee is essentially a hinged joint that is held together by the medial collateral (MCL), lateral collateral (LCL), anterior cruciate (ACL) and posterior cruciate (PCL) ligaments.

labelled structure of the knee. Shows the quadricep muscles, quadricep tendons, patella, femur, tibia, fibula, Patellar tendon, meniscus, MCL, PCL, LCL, and ACL

Perry, Pig Knees And Rising Youth ACL Tears, 2018The ACL is a major ligament in the knee that connects the femur (thigh bone) to the tibia (shinbone). The ACL is similar to an actin filament. It has a rope-like structure and is best loaded under tensile loading. The ACL prevents forward movement of the tibia on the femur, as well as hyperextension, which is the straightening movement of the knee that goes beyond the normal range of motion in the joint. By preventing these motions, the ACL provides stability to the knee joint and allows for dynamic motions. Without this stability in the knee joint, humans would not be able to walk normally, let alone perform complex movements done in sports.

picture of actin filament with the plus and mins ends labelled
Mechanobiology Institute, What are actin filaments?, 2018.

 

People with knee joints that lack ACL’s tend to develop a knee joint where the femur bone fits into the tibia a bit like a shallow ball and socket joint. A knee joint without an ACL uses the meniscus to perform the same function. The meniscus is a tough rubbery cartilage that normally acts as a shock absorber between the tibia and fibula. In order for their meniscus to serve the same function as the ACL, the meniscus undergoes deformation to make it better suited for tensile loading. More information about ACL’s can be found here.

Exciting Advance in ACL Repair

Anterior Cruciate Ligament (ACL) injuries are among the most common in sports, with nearly 100,000 tears annually. Additionally, the rate of pediatric tears has been increasing at a rate of 2.3% each year for the past 20 years. The high incidence of this injury is in part due to the structure of the knee complex, where the ACL is located. The ACL helps connect the two longest bones in the body and is responsible for rotation and transferring body weight to the ankle. Specifically, the primary functions of the ACL are to prevent the tibia from sliding too far in front of the femur and to provide rotational stability to the joint. This rotational motion, combined with a lack of muscle support at the knee, is why so many athletes tear their ACL. A recent paper looked into how a team of doctors led by Dr. Martha Murray at Boston Children’s Hospital have come up with a promising new approach to repairing the injured ligament.

Two side views of the knee joint, one showing a healthy knee and one showing a complete ACL tear.
Photo by BruceBlaus on wikimedia.org

Due to its environment, ACLs do not repair on their own like other ligaments do. The synovial fluid, which resides in the knee complex to reduce friction in the joint, limits blood flow to the ACL and PCL (posterior cruciate ligament). When injuries occur to these ligaments, the lack of blood flow prevents clotting. In most other ligaments, clotting would occur and would function as a “bridge” for the two ends of the torn ligament to grow and heal across. Due to ACLs not being able to undergo this process, the current method for repair is to take a graft from the patient’s hamstring or patella and replace the torn ACL with the new graft. While this method is typically successful, Dr. Murray’s team estimates that the re-tear rate is about 20% and up to 80% of patients develop arthritis in their knee 15-20 years after the surgery. To combat this, Dr. Murray drew inspiration from how other ligaments heal and developed Bridge Enhanced ACL Repair (BEAR). The premise of this technology is to take a “sponge” that is composed of proteins that are naturally found in the ACL, and insert it between the torn ends of the ACL.  Using sutures, the sponge is moved into position and the two ends of the ACL are pulled into the sponge. Blood is then drawn from the patient and inserted into the sponge. This environment acts as a blood clot and stimulates the ACL to repair itself. Clinical trials have shown that the sponge resorbs completely after 8 weeks, at which point the two ends of the torn ACL have begun to join back together. While the BEAR treatment is still relatively new, early results are encouraging with patients seeing similar results to patients that undergo traditional ACL reconstruction. Though it is difficult to predict the rate at which patients who receive BEAR treatment will develop arthritis, animal testing has shown lower instances of osteoarthritis development, which is promising news for those who suffer from this common injury.

For more information about the BEAR technology check out Boston Children’s Hospital website or this recent article. A short video detailing the technology can also be seen below.

Female Athletes Compete Against Higher Risk of ACL Injuries Than Males

Female athletes face a greater rate of anterior cruciate ligament (ACL) rupture than males. According to Dr. Karen Sutton and Dr. James Bullock from the Department of Orthopaedics and Rehabilitation at Yale University, female athletes are 2 to 8 times more likely to tear their ACL than male athletes. The majority of these injuries (more than two-thirds) are from non-contact situations. A variety of anatomical, biomechanical, and hormonal factors attempt to explain this difference.

Female soccer player stretching her leg
Photo by rawpixel on Unsplash
Differences between female and male lower-body anatomy show the disparity in Q-Angle that results
Taken from Desrosiers, Soccer Nation 2018

Some anatomical factors that help stabilize the knee joint and may be linked to ACL injuries include: the quadriceps angle (Q angle), tibial slope, and intercondylar notch. The Q angle is the angle formed between the upper leg at the hip joint and the lower leg at the knee joint. This angle tends to be 3.4-4.9 degrees greater in females than males when measured in a standing position. The figure at right shows the Q angle difference between men and women that is caused by anatomical differences including a wider pelvis in females. A greater Q angle causes more strain on the quadriceps muscle away from the centerline of the body, which can affect the position of the ACL to be more prone to rupture.

Tibial slope is a quantity used to describe the position of the tibia relative to the femur. When the tibia is positioned more forward than the femur there is a greater posterior tibial slope and therefore increased ACL strain. On average, females have shown to have a greater tibial slope, which may contribute to the higher incidence of ACL injuries. The figure below illustrates the biomechanics of posterior tibial slope: the effect of the knee joint compressive load (down arrow) and the force of the quadriceps (up arrow) result in an anterior shear force, causing anterior translation of the tibia relative to the femur (right-directional arrow) .

Biomechanical force diagram describing posterior tibial slope
Modified from Sutton and Bullock, JAAOS 2013

In terms of biomechanical differences between men and women, women have greater natural muscle contractions for movement away from the centerline of the body. This translates to a difference in landing positions for women compared to men – females tend to land more straight, creating more force on the knee joint, while males absorb the impact better by naturally flexing their knees upon landing. The hamstring to quadriceps ratio (H:Q ratio) is the functional strength of the hamstring muscles (peak torque) relative to the strength of the quadriceps in motion. Poor muscle strength has been linked to higher risk of lower extremity injury. Males have the ability to increase their H:Q ratio during sport motion, but females fail to do so. Women have also shown greater internal rotation laxity – slackness or lack of tension in a ligament – than men. Generalized laxity was also significantly greater among individuals who suffered a noncontact ACL injury compared to an uninjured control group.

Hormonal factors are an additional consideration that researchers have explored, but the results have been inconclusive in making a direct link between hormone levels and the rate of ACL injury.

Additional reading on this topic can be found at VeryWellHealth and SoccerNation. The following video shows some advice for female ACL injury prevention.