Editor in Chief, Journal of Sport Biomechanics
Anterior cruciate ligament (ACL) injury is one of the most common knee injuries, often requiring reconstructive surgery. The choice of graft type significantly influences functional outcomes, complication rates, and return to activity. Commonly used grafts include autografts (from the patient), allografts (from a donor), and synthetic grafts (1). In this letter, we discuss the advantages and disadvantages of these graft types:
a) Autograft (Hamstring or Patellar Tendon): Advantages include a lower risk of disease transmission and better biological compatibility. However, disadvantages involve donor-site pain, hamstring muscle weakness, or knee issues associated with patellar tendon harvesting.
b) Allograft: This method shortens surgery time and eliminates the need for graft harvesting, making it suitable for patients with multiple injuries. However, drawbacks include the risk of disease transmission and potential graft failure due to thermal or chemical processing.
c) Synthetic Grafts: These innovative grafts eliminate the need for tissue harvesting and allow for faster recovery. However, their disadvantages include mechanical failure, inflammation, and limited suitability for high-intensity athletes.
The selection of a graft depends on patient-specific factors, including activity level and the surgeon’s preference, as each graft differs in stiffness and biological integration (2).
For instance, ACL reconstruction with a hamstring graft is widely used in orthopedic surgery due to its biomechanical and biological advantages. This technique minimizes donor-site complications and provides long-term satisfactory outcomes. However, recent advances in surgical techniques, graft fixation, and rehabilitation protocols warrant re-evaluation of this approach. Firstly, while hamstring grafts are preferred for their minimal impact on the extensor mechanism, concerns remain regarding post-surgical hamstring strength deficits and re-injury risk (3). Studies suggest that targeted rehabilitation programs focused on hamstring strengthening can mitigate these risks and improve functional outcomes and graft durability.
Secondly, innovations in graft fixation techniques, such as adjustable-loop devices, have enhanced graft stability and reduced tunnel widening. These advancements, combined with precise surgical techniques like anatomical ACL reconstruction, facilitate better replication of native ligament biomechanics and may improve clinical outcomes (3, 4). Moreover, patient-specific factors—including age, activity level, and pre-existing joint conditions—play a crucial role in graft selection. Comparative studies on hamstring, patellar tendon, and quadriceps tendon grafts emphasize the need for individualized treatment planning to optimize outcomes. While hamstring grafts remain a cornerstone of ACL reconstruction, ongoing research and surgical advancements continue to refine treatment strategies. We encourage further investigations into the biomechanical properties of different graft types, considering factors such as age, sex, anthropometric characteristics, activity level, and rehabilitation duration. Addressing these variables is essential, as one of the greatest challenges in ACL surgery remains achieving ligament reconstruction while preserving its natural function and minimizing the long-term risk of knee osteoarthritis. Finally, we highlight key challenges for researchers to explore in future studies.
Challenges
1.    Mechanical and biological compatibility of grafts with the natural ligament
The anterior cruciate ligament (ACL) is a complex structure with unique mechanical and biological properties. None of the graft types—autografts, allografts, or synthetic grafts—can fully replicate the structure and function of the native ACL. The native ligament contains proprioceptive receptors essential for knee stability and function, which current grafts fail to replicate.
2.    Secondary injuries and osteoarthritis
Even after successful surgery, many patients develop knee osteoarthritis over time. The underlying causes remain unclear, but potential factors include altered knee loading, compensatory movement patterns, and graft limitations.
3.    Risk of re-injury and graft durability
Some patients, particularly professional athletes, experience graft failure after returning to high-intensity physical activity. Selecting the optimal graft type and surgical technique for long-term durability remains a major challenge.
4.    Optimizing the healing and recovery process
Ligament reconstruction requires vascular and cellular integration within the graft. Research on biomaterials, growth factors, and tissue engineering is still in its early stages, with limited clinical applications.
Why these challenges remain unresolved
1.    The ACL is a highly specialized structure, and no graft fully replicates its mechanical and biological complexity.
2.    The development of osteoarthritis is influenced by multiple factors, necessitating long-term studies to identify its precise causes.
3.    Safe return to sports and re-injury prevention depend on multiple factors, including surgical technique, rehabilitation protocols, and patient-specific characteristics.
Solutions and suggestions
•    Advancements in tissue engineering and biomaterials to develop grafts that closely mimic the native ACL.
•    Strengthening grafts with growth factors and gene therapy to enhance healing.
•    Refining surgical techniques for more precise ligament reconstruction.
•    Utilizing artificial intelligence to predict osteoarthritis and re-injury risk factors.
Conclusion
These challenges highlight the complexity of ACL reconstruction and present significant opportunities for future research. Current evidence indicates that no existing graft type can fully restore the native ACL's structure and function. When selecting a graft, factors such as the patient’s activity level, biological compatibility, and long-term durability against re-injury play a crucial role. Addressing these challenges requires continued innovation in surgical techniques, rehabilitation protocols, and biomaterials research.
 
Ethical Considerations
Compliance with ethical guidelines
This article is a letter to the editor and does not directly use any human or animal samples.
Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.
Authors' contributions
All authors equally contributed to the preparation of this article.
Conflicts of interest
The authors declared no conflict of interest.