Explaining and understanding the preservation of ACL remnants during surgery: a key advancement in ligament reconstruction.
This article is based on the study “Anatomical Inside-Out Remnant-Preserving Anterior Cruciate Ligament Reconstruction: A Surgical Technique for Biological ACL Reconstruction” by Prof. Cavaignac and his peers, published in Arthroscopy Techniques (March 2025).
The growing interest in ACL remnant preservation stems from its biological and functional benefits. The remnants of the anterior cruciate ligament (ACL), particularly the tibial stump, contain mechano receptors and vascular structures that are crucial for proprioception, graft revascularisation and overall healing.
Traditionally, surgeons removed the ACL remnant to improve visibility and simplify graft placement. However, several recent studies, including the work led by Professor Etienne Cavaignac, have demonstrated that retaining this tissue significantly enhances outcomes. By acting as a natural biological scaffold, the remnant promotes faster and more effective ligamentisation of the graft, essentially helping the body to recognise and integrate the new tissue.
This technique offers:
Rather than being an obstacle, the remnant is now viewed as an asset, provided it is properly managed during the procedure.
The technique described in the 2025 study is known as anatomical inside-out remnant-preserving ACL reconstruction, which specifically focuses on the precise conservation of viable remnant tissue.
The procedure begins with a thorough evaluation of the knee using a 30° arthroscope. The surgeon assesses the quality, length and vascularity of the ACL remnant through the anterolateral portal. If the tissue is well-vascularised and intact, the procedure continues with femoral notch debridement in a posterior-to-anterior fashion, a step essential to avoid damaging anterior remnant fibres.
The creation of the tibial tunnel is done with great care using the so-called "knock-on-the-door" technique. This involves a low-speed drill to ensure minimal trauma to the remnant. The reamer is introduced gradually, with special attention paid to maintaining the alignment of the tunnel within the remnant tissue to preserve its anatomical integrity.
Notably, the procedure avoids the use of remnant tensioning stitches, which can reduce vascularity. Instead, the remnant is preserved passively, maintaining its original attachment and biological functions.
Graft preparation uses a semitendinosus tendon, harvested and folded into a tripled or quadrupled graft. The tendon remains attached to its tibial insertion, a practice which enhances stability and healing.
Once the graft is passed through the tibial and femoral tunnels, fixation is achieved with an interference screw and the final arthroscopic check confirms optimal positioning within the remnant. The knee is then fully extended to ensure there is no soft-tissue interposition.
While the technique offers compelling advantages, remnant preserving in ACL reconstruction is not universally applicable.
Contraindications include:
Furthermore, the technique requires a learning curve. Accurate tunnel placement is more challenging when remnants obscure visual landmarks. The risk of complications such as cyclops lesions, nodular fibrosis that can impede extension, is slightly increased if the remnant is not managed properly. However, this can bemitigated by ensuring full knee extension intraoperatively and confirming there is no graft impingement.
Advantages must always be balanced against the specific conditions of the patient’s knee. In selected cases, the benefits outweigh the risks and offer a more physiological reconstruction.
Another point worth noting is the absence of a need for remnant tensioning. Studies have shown that trying to actively tension the remnant can lead to cellular damage, impairing the biological advantages we aim to preserve. Passive conservation, as outlined in the study, is currently the safest and most effective method.
The ACL is more than just a mechanical structure, it contains sensory nerve endings and vascular channels that contribute to knee proprioception and healing. ACL remnant preservation leverages these biological properties.
The preserved remnant acts as a bridge that promotes faster graft revascularisation (restoration of blood flow) and ligamentisation (conversion of the graft to a ligament-like structure). This translates into a more robust integration of the graft within the joint. Patients also retain a better sense of knee position and movement, a function mediated by mechano receptors in the ACL tissue.
Several studies cited in the article demonstrate that patients undergoing remnant preserving ACL reconstruction show better outcomes on proprioceptive tests and sport-specific performance evaluations. In addition, graft rupture rates tend to be lower in these patients, with the remnant acting as a protective cushion during the critical early stages of healing.
In short, the approach is not only technically effective but also biologically sound.
The anatomical inside-out remnant-preserving ACL reconstruction technique is a promising development in sports traumatology. By preserving the ACL remnant, surgeons can promote faster healing, maintain proprioception and reduce graft failure.
While the technique requires surgical precision and is not suitable for every patient, it offers a new standard of care for those with viable remnant tissue.
For patients seeking expert care in ACL reconstruction, Professor Etienne Cavaignac is an internationally recognised leader in the field, combining surgical precision with a patient-focused approach to rehabilitation and recovery.
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