Biological Augmentation in ACL Reconstruction - Techniques, Types, and Procedure

Introduction

Anterior cruciate ligament (ACL) injuries are common and can cause significant knee damage. The goal of surgery is to restore knee movement and stability. However, there is still a risk of graft tearing again, both in initial and revision surgeries. Biologic augmentation aims to speed up scar tissue formation or improve graft integration to resemble the original ACL attachment. The goal is to allow for more intense rehabilitation and a quicker return to pre-injury activity levels.

What Is Biological Augmentation in ACL Reconstruction?

In ACL reconstruction, "biological augmentation" refers to applying methods or supplies that enhance the procedure's results and speed up the healing process. It entails adding biological elements to the graft used in ACL reconstruction surgery to aid in better integration and healing, such as growth factors, stem cells, or tissue scaffolds. The objective is to enhance the healing process and forge a stronger bond between the graft and the surrounding tissues, enhancing the stability and success of the repaired ACL over the long term.

What Are Different Techniques of Biological Augmentation Used in Anterior Cruciate Ligament?

Various biological augmentation (BA) techniques have been explored in ACL reconstruction (ACLR), which include:

• Remaining ACL tissue.

• Bone substitutes.

• Calcium phosphate-treated grafts.

• Shockwave therapy.

• Patient's adult stem cells.

What Are the Different Types of Materials Used in ACL With Biologic Augmentation?

Various biological substances enhance ACL reconstruction (ACLR). One commonly used substance is platelet-rich plasma (PRP), which contains growth factors that promote healing. PRP can be used in different ways during ACLR, such as:

1. For healing the donor site.

2. Helping the tendon graft mature.

3. Improving its integration with the surrounding bone.

In animal models, different biomaterials enhance the healing at the graft-tunnel interface. These include materials like:

1. Chitin.

2. Bioglass.

3. Gelatin.

4. Hyaluronic acid polystyrene sodium sulfonate.

5. Collagen matrix.

Other materials, including stem cells, gene therapy, alternative autologous tissues, and environmental modifications, have also been studied to improve ACLR outcomes.

How Healing Occurs in the ACL After an Injury?

The ACL heals differently from other thick tissues following an injury. There are three main differences:

• The ACL forms a thin layer of synovial tissue on the surface of the torn ends, which aids in the repair process because it lacks a temporary structure that helps in healing.

• The ACL does not have tissue bridging the gap between the torn ends, unlike other ligaments. As the blood clot dissipates in the joint fluid, it prevents the formation of a hematoma and a temporary scaffold for healing.

• The ACL undergoes a reparative phase lasting about 8 to 12 weeks, during which the body tries to repair the ligament. However, ACL fibroblasts (specialized cells in the ligament) have limited mobility, growth, and ability to produce the necessary components for healing. They also have higher levels of certain enzymes that break down tissues and weaker adhesive strength.

How Is ACLR Done Using Single-Anteromedial Bundle Biological Augmentation?

1. Setting up for Surgery: During surgery, the patient is positioned lying on their back with support around their knee. The patient's leg is positioned with a cushioned band around the thigh, and support is placed under the foot to keep the knee bent at a 90-degree angle.

2. Harvesting the Graft: The surgeon chooses the semitendinosus (ST) tendon to use as a graft which is obtained about 8 to 10 millimeters in diameter and 12 cm (4.7 inch) long. Typically, three layers of ST tendon have been used. The graft is harvested while preserving the bone by helping with its stability and blood supply. The size is evaluated by checking the desired dimensions by folding it over and measuring it. Then, the graft is prepared by looping it with a special device called TightRope RT (fixation device) after creating tunnels in the bone. This ensures that the graft is adjusted accurately.

3. Placement of the Graft: The surgeon moves the graft from the lower leg bone (tibia) to the upper leg bone (femur) after bending the knee at a 90-degree angle. A specialized camera called an arthroscope checks where the graft leaves on the outside of the femur. Through a tiny hole in the bone, the movement of a device is directed by the TightRope button. The TightRope tensioning device is then used to fix the graft to the femur. Screws hold the remaining portion of the graft in the tibia in place.

4. Preserving the Remnants: Preserving the remnants containing the ACL cells and blood vessels during surgery can have biological benefits that aid in ligament healing. To preserve the ACL remnants, surgeons use techniques that minimize damage to the surrounding tissues, avoid overstuffing the joint, and, if necessary, secure the remnant to the graft.

Overall, this technique of ACL reconstruction aims:

• To preserve the natural tissues.

• Utilize their biological properties for healing.

• Improve the outcome of the surgery.

When Is It Safe for an Individual to Return to Sports After ACLR Surgery?

• When making this choice, various things are considered, including psychological aspects, physical functionality, general fitness level, and more.

• Eighty percent of patients can return to any sport, and around sixty to seventy percent can return to their pre-injury level of performance or competitive sports.

• Factors such as symmetrical hop test performance, younger age, male gender, playing at an elite level, and positive psychological response can increase the likelihood of a triumphant return.

• Fear is a common factor influencing athletes' decisions about returning to sports. This fear is not related to the fear of reinjury but includes concerns about potential income loss, having to go through rehabilitation again, and feeling inadequate in their sport.

• Life priorities and personal characteristics also play a role. Some athletes may change sports or adjust their priorities due to life transitions or shifts in priorities.

• Motivation, fear, cognitive appraisal, and other individual perceptions can impact an athlete's readiness to return to their sport.

• The rehabilitation strategy must be customized for each patient, and reflection time must be provided.

• The athlete's attitude toward the place of sport in their lives may have altered because of the injury and its process.

• In some cases, it may be necessary to consider other activities to avoid a high risk of reinjury and potential progression to osteoarthritis, especially in restoration cases.

Conclusion

Bioaugmentation is a potential solution for common athletic injuries like ACL tears, but it is not a magical treatment. Surgeons need realistic expectations and consider other factors that can affect outcomes. Current studies on bioaugmentation for ACL repair provide insights into combining tissue engineering principles (cells, growth factors, scaffolds, and mechanical stimuli).