Remnant preserving ACL reconstruction in high grade ACL partial tear

ACL reconstruction with Remnant preserving technique: 
Treatment for High grade Anterior Cruciate Ligament (ACL) Partial Tears

Treatment selection is crucial for anterior cruciate ligament (ACL) partial tears, to achieve favorable long-term outcomes.

 

I had the opportunity to present on this topic at ACL Symposium in Korea, and the key considerations can be summarized in three points:

1) Patient factors (such as overall health, obesity, environment, and activity level) are the most critical considerations.

2) The amount of remaining ACL tissue  

3) Presence of concomitant injuries  

Among them, this article focuses on the second point—the significance of the remaining ACL tissue in treatment selection.

 

The ACL consists of two bundles:

1. Anteromedial (AM) bundle – responsible for anterior-posterior (AP) stability, particularly in knee flexion.

2. Posterolateral (PL) bundle – responsible for rotational stability, primarily in knee extension.

1) If less than 50% of the ACL is torn, conservative treatment should be considered as the primary option.

2) If more than 50% of the ACL is torn, the likelihood of progression to a complete rupture is approximately 50%. In such cases, both early surgical intervention and a trial of conservative treatment can be considered, depending on the patient’s condition.

For athletes or highly active individuals, remnant-preserving ACL reconstruction is a viable surgical option.

For the general population, conservative treatment may be attempted, but activity levels should be significantly reduced to prevent further injury.

Case: Remnant-Preserving ACL Reconstruction in a 23-Year-Old Male

Patient 

A 23-year-old male presented to our clinic with a history of a partial ACL tear sustained at age 21, which was treated conservatively at another university hospital. He had functioned well for two years, but ultimately experienced a feeling of knee instability, leading to a re-tear.

Notably, the patient was preparing to become an emergency medical technician (EMT)—a profession requiring a high level of physical activity.

Preoperative Evaluation

MRI images from the previous hospital showed ACL remnants, but the ligament appeared thin and the fiber orientation was irregular. This case was classified as a high-grade partial tear, nearly complete tear.

In this patient, a small portion of the AM bundle remained, but the PL bundle was completely absent.

Objective instability 

Lachman test: Grade 2+ anterior instability was observed.

Pivot shift test: Grade 2+ (clunk) was noted.

Stress radiographs: A 10.5 mm side-to-side difference in anterior tibial translation was measured.

Based on these findings, surgical intervention was deemed the most favorable long-term option. Since no additional malalignment or other conditions requiring correction were found, ACL reconstruction was planned and performed.

 

Graft Selection for ACL Reconstruction

Three graft options were considered:

1. Autograft (Hamstring Tendon)

2. Autograft (Quadriceps Tendon with Bone Block)

3. Allograft (Cadaveric Tendon)

Research has consistently shown that autografts yield better outcomes than allografts in ACL reconstruction.

Hamstring tendon autograft is the most commonly used.

Quadriceps tendon autograft (harvested with a bone block) promotes faster graft incorporation and is often preferred in athletes requiring rapid rehabilitation.

In remnant-preserving ACL reconstruction, the goal is to preserve the remaining ACL fibers while reinforcing the injured portion with a graft. Hamstring autografts are the preferred choice for this technique.

Since this patient had residual ACL fibers, a hamstring autograft was selected for reconstruction.

Intraoperative Findings 

Arthroscopy confirmed that the ACL remnant was present but had significantly lost its function.

Although removing the remaining ligament (take-down) and performing a standard reconstruction would be simpler, preserving the remnant results in superior outcomes, albeit with a more technically demanding procedure.

 

Remnant-Preserving ACL Reconstruction: Key Technical Considerations 

To preserve the ACL remnant while expanding the femoral tunnel, the trans-septal portal technique is essential. This approach enables direct visualization from behind, allowing for precise tunnel placement using an outside-in technique with a flip cutter. Standard tunnel expansion techniques (transtibial or transportal) cannot be used in remnant-preserving ACL reconstruction.

A recent ESSKA (European Society for Sports Traumatology, Knee Surgery, and Arthroscopy) survey of orthopedic surgeons under age 45 revealed that a majority routinely inspect the posterior compartment during knee arthroscopy, further highlighting the importance of this portal.

The images below show intraoperative findings through the trans-septal portal:

Medial meniscus posterior horn.

making the trans-septal portal.

Lateral meniscus posterior horn

 

  

 

Femoral tunnel placement is the most critical step in ACL reconstruction and must be performed with precision.

 

Fine-tuning the guide pin position is crucial—deviations of more than 3 mm from the ideal location can lead to poor outcomes.

Once the flip cutter guide was positioned ideally, a 20 mm tunnel was reamed using a retrograde flip cutter. Since the autograft thickness was 7.5 mm, an 8 mm tunnel diameter was selected. (graft diameter in Asian patients are usually around 8mm)

  

Tibial tunneling 

The guide pin was placed at the PL bundle’s insertion site, followed by antegrade reaming to create the tibial tunnel.

After clearing excess tissue around the tunnel using a shaver, the hamstring autograft was positioned and secured at the 20 mm mark, using a stay suture for controlled tightening.

Post-Fixation Arthroscopic Findings

After securing the graft, an arthroscopic view from the anterior perspective reveals that the reconstructed ligament is concealed behind the patient’s native ACL fibers.

Using a probe, we confirmed that the graft was firmly fixed.

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Anterolateral Ligament (ALL) Reconstruction

For anterolateral ligament (ALL) reconstruction, we performed the Lateral Extra-Articular Tenodesis (LET) using the Lemaire technique. 

Since the isometric point varies among individuals, it is crucial to identify the tunnel position before performing ACL reconstruction to prevent tunnel collision between the ACL and ALL tunnels.

However, this is beyond the scope of this article; detailed explanation would be followed in the future article. 

Postoperative CT Findings

Postoperative CT scans confirm that both the femoral and tibial tunnels are positioned optimally.

Additionally, even in full knee extension, the graft aligns parallel to Blumensaat’s line, indicating proper tunnel placement and graft trajectory.

Both ACL and ALL reconstructions were successfully completed without tunnel collisions.

Multiple pin insertion marks are visible on the lateral femoral condyle, reflecting the efforts to identify the optimal isometric point.

 

Conclusion

As with all medical treatments, treatment decisions for ACL injuries require careful consideration of multiple factors.

The treatment of partial ACL tears is even more complex, requiring greater precision in surgical techniques to achieve optimal outcomes.

By refining surgical strategies and individualizing treatment approaches, we can enhance long-term success for patients undergoing ACL reconstruction.

Hyo Yeol Lee, MD., PhD.

Department of Orthopaedic Surgery (Knee Surgery and Sports Medicine)

Chungbuk National University Hospital