ACL Repair: Graft Materials, Fixation Devices, and Augmentation

What materials are used in ACL repair?

ACL repair primarily involves the use of various graft materials—either from the patient's own body (autografts), donor tissue (allografts), or, less commonly, synthetic options—alongside specialized fixation devices to secure the new ligament.

Understanding the Need for ACL Repair

The Anterior Cruciate Ligament (ACL) is a critical stabilizer of the knee joint. A tear of the ACL, often sustained during sports activities, significantly compromises knee stability, leading to "giving way" sensations and increased risk of further joint damage. Since the ACL has limited capacity to heal itself, surgical reconstruction is often recommended, particularly for active individuals. The essence of ACL reconstruction is replacing the damaged ligament with a new tissue graft that can replicate its function.

The Primary Material: Graft Choices

The most crucial material in ACL repair is the graft itself, which serves as the scaffold for a new ligament to grow. The choice of graft significantly impacts surgical outcomes, rehabilitation, and potential complications.

Autografts (Patient's Own Tissue)

Autografts are harvested from the patient's own body. They are the most common choice due to excellent biocompatibility, no risk of disease transmission, and superior long-term integration. However, harvesting an autograft creates a "donor site morbidity," meaning pain or weakness at the site where the tissue was taken.

• Patellar Tendon Autograft (BTB) This graft involves taking the central one-third of the patellar tendon along with a small bone block from the patella (kneecap) and another from the tibia (shin bone). This is often referred to as a "Bone-Tendon-Bone" (BTB) graft.

  • Advantages: Strong initial fixation due to bone-to-bone healing, excellent tensile strength, and a long track record of success.
  • Disadvantages: Potential for anterior knee pain (pain at the front of the knee), patellar fracture, and kneeling discomfort at the donor site.

• Hamstring Tendon Autograft This graft typically uses two of the hamstring tendons: the semitendinosus and the gracilis. These tendons are harvested through a small incision on the inner side of the knee and then folded to create a four-strand or even six-strand graft for increased strength.

  • Advantages: Less anterior knee pain and kneeling discomfort compared to BTB, smaller incision, and less donor site morbidity overall.
  • Disadvantages: Slower initial bone-to-tendon healing (compared to bone-to-bone), and a theoretical, though often clinically insignificant, loss of hamstring strength.

• Quadriceps Tendon Autograft An increasingly popular option, this graft involves harvesting a portion of the quadriceps tendon, often with a small bone block from the patella. It can be taken with or without the bone block (bone-quadriceps tendon or soft-tissue quadriceps tendon graft).

  • Advantages: Large, strong graft with a good length, potentially less anterior knee pain than BTB, and a lower incidence of kneeling pain.
  • Disadvantages: Can be a more technically demanding harvest, and some patients may experience temporary quadriceps weakness.

Allografts (Donor Tissue)

Allografts are tissues harvested from a deceased human donor. These grafts undergo rigorous processing and sterilization to minimize the risk of disease transmission.

• Common Allograft Sources: Patellar tendon, Achilles tendon, tibialis anterior, and hamstring tendons are frequently used.
• Advantages: Eliminates donor site morbidity, potentially shorter surgical time, and multiple grafts can be taken if needed (e.g., for multi-ligament injuries).
• Disadvantages: Higher cost, slower incorporation into the host bone (biological integration), and a slightly higher reported re-rupture rate in younger, highly active individuals compared to autografts. Despite rigorous screening, there is a theoretical, albeit extremely low, risk of disease transmission.

Synthetic Grafts

Historically, various synthetic materials (e.g., Gore-Tex, Kennedy LAD) were attempted for ACL reconstruction. However, most failed due to issues like poor integration, wear, inflammatory reactions, and high failure rates. While largely abandoned in the U.S. for primary ACL reconstruction, some synthetic grafts (e.g., LARS) are still used in specific scenarios or in other countries, often for chronic ruptures or as augmentation rather than primary replacement.

Fixation Devices

Once the graft is placed into tunnels drilled in the femur and tibia, it must be securely fixed until biological healing occurs. A variety of fixation devices are used:

• Interference Screws These are bioabsorbable (made from materials that dissolve over time, like PLLA or PEEK) or metallic screws that are inserted alongside the graft within the bone tunnels. They "interfere" with the graft, compressing it against the tunnel wall to provide immediate stability.

• Buttons (Cortical Fixation) These are small, flat plates (often metallic, titanium, or bioabsorbable) that are deployed on the outer surface (cortex) of the bone. A high-strength suture or tape loop connects the button to the graft, pulling the graft into the bone tunnel. This provides strong, suspensory fixation.

• Staples and Posts Less commonly used as primary fixation today, staples or posts can be used to secure the graft to the bone, particularly in older techniques or for additional reinforcement.

Augmentation and Biologics

Newer technologies and biological agents are sometimes used to augment the repair or enhance healing:

• InternalBrace™ / Augmentation Devices These are synthetic tapes or sutures that run parallel to the graft, providing additional mechanical support and protecting the healing graft during the early rehabilitation phase. They are not meant to replace the graft but to augment its strength.

• Platelet-Rich Plasma (PRP) / Stem Cells While still largely considered experimental for routine ACL reconstruction, some surgeons may use PRP or concentrated bone marrow aspirate (containing stem cells) injected around the graft site to theoretically promote faster healing and better graft incorporation.

Choosing the Right Material

The decision of which graft material and fixation method to use is highly individualized and depends on several factors: the patient's age, activity level, sport demands, presence of other knee injuries, surgeon's preference and experience, and patient's willingness to accept potential donor site morbidity or allograft risks. A thorough discussion with your orthopedic surgeon is essential to determine the most appropriate approach for your specific situation.

Conclusion

ACL repair is a complex orthopedic procedure relying on a carefully selected tissue graft and robust fixation methods. While autografts remain the gold standard due to their biological advantages, allografts offer a viable alternative, especially for certain patient profiles. Ongoing research continues to explore new graft materials, fixation devices, and biological adjuncts to further improve outcomes and accelerate recovery for individuals undergoing ACL reconstruction.