# ACL Injury: Reconstruction Techniques and Graft Selection

## Introduction

The anterior cruciate ligament (ACL) is the primary restraint to anterior tibial translation and a critical stabilizer of the knee. ACL injuries are among the most common ligamentous injuries in orthopedic sports medicine, with an estimated 200,000 injuries occurring annually in the United States. Understanding the anatomy, biomechanics, reconstruction techniques, and graft options is essential for the orthopedic surgeon.

## Anatomy and Biomechanics

The ACL originates from the posteromedial aspect of the lateral femoral condyle and inserts on the anterior tibial spine. It is composed of two functional bundles: the anteromedial (AM) bundle, which is taut in flexion, and the posterolateral (PL) bundle, which is taut in extension. The ACL serves as the primary restraint to anterior tibial translation and as a secondary restraint to internal rotation and valgus stress. Its blood supply comes from the middle genicular artery, and its poor intrinsic healing capacity means that torn ACLs do not reliably heal on their own.

## Mechanism of Injury and Diagnosis

The classic mechanism is noncontact pivoting, deceleration, or landing with the knee near extension. Patients often report a "pop," immediate swelling from hemarthrosis within 2 to 4 hours, and episodes of giving way. The Lachman test is the most sensitive clinical examination maneuver with sensitivity exceeding 85%. The pivot shift test is the most specific test for ACL insufficiency and is best assessed under anesthesia. MRI confirms the diagnosis with greater than 95% sensitivity and specificity.

## Indications for Reconstruction

Reconstruction is indicated for active patients with functional instability who desire to return to cutting or pivoting sports, patients with associated repairable meniscal tears or multiligament injuries, and younger patients with high activity demands. Nonoperative management may be appropriate for low-demand patients or those willing to modify activities.

## Graft Selection

### Autograft Options

| Graft | Advantages | Disadvantages | Best For |
|-------|-----------|---------------|----------|
| Bone-Patellar Tendon-Bone (BPTB) | Bone-to-bone healing; rigid fixation; gold standard | Anterior knee pain; kneeling discomfort; patellar fracture risk | Young athletes in cutting/pivoting sports |
| Hamstring (gracilis + semitendinosus) | Less donor site morbidity; smaller incision | Tunnel widening; slower incorporation; hamstring weakness | Patients concerned about anterior knee pain |
| Quadriceps tendon | Large cross-section; versatile (with/without bone block); low anterior knee pain | Less long-term data than BPTB | Growing option for primary reconstruction |
| Allograft (various) | No donor site morbidity; shorter OR time | Higher re-rupture rate (up to 4x in patients < 25) | Revision cases; multiligament injury; low-demand patients |

Bone-patellar tendon-bone (BPTB) is considered the gold standard, offering bone-to-bone healing and rigid fixation, though it carries a higher rate of anterior knee pain and kneeling discomfort. Hamstring tendon (gracilis and semitendinosus) causes less donor site morbidity with a smaller incision but has potential for tunnel widening and slower soft tissue incorporation. Quadriceps tendon is increasingly popular due to its large cross-sectional area and versatility (with or without a bone block), and it produces lower anterior knee pain than BPTB.

### Allograft Options

Allograft options include BPTB, Achilles tendon, tibialis anterior or posterior, and hamstring allografts. They offer no donor site morbidity, shorter operative time, and smaller incisions. However, they carry higher re-rupture rates in young, active patients (up to a fourfold increased failure risk in patients under 25 years) and are best reserved for revision cases, multiligament reconstruction, or lower-demand patients.

## Surgical Technique

### Tunnel Placement

Anatomic reconstruction aims to replicate the native ACL footprint. The femoral tunnel is positioned at the center of the native AM bundle footprint on the lateral wall of the intercondylar notch. The tibial tunnel is placed at the center of the native ACL tibial footprint, angled 55 to 65 degrees in the coronal plane. Vertical graft placement is non-anatomic and fails to restore rotational stability.

### Fixation Methods

Femoral fixation options include suspensory devices (cortical buttons), interference screws, and cross-pin fixation. Tibial fixation options include interference screws (metallic or bioabsorbable), post-and-washer, and hybrid techniques. Suspensory fixation provides reliable initial strength, while interference screws offer aperture fixation closer to the joint line.

### Single-Bundle vs. Double-Bundle

Single-bundle reconstruction remains the standard of care with reliable outcomes. Double-bundle techniques aim to restore both the AM and PL bundles but have not shown consistent clinical superiority. Double-bundle reconstruction is technically demanding and carries a risk of tunnel convergence.

## Rehabilitation

Rehabilitation emphasizes early range of motion and weight-bearing as tolerated, with a progressive strengthening program over 6 to 9 months. Return-to-sport criteria include greater than 90% limb symmetry index on hop tests and quadriceps and hamstring strength within 10% of the contralateral side. The average return to sport is 9 to 12 months, and psychological readiness should also be considered.

## Complications

Graft failure or re-rupture occurs in 5 to 10% of cases overall, with higher rates in young athletes and with allograft in active patients. Loss of motion (arthrofibrosis), particularly loss of terminal extension, is another concern. Tunnel malposition remains the most common technical error. The contralateral ACL injury risk is 10 to 15% within 10 years. Other complications include infection (less than 1%), hardware-related symptoms, and donor site morbidity.

## Clinical Pearls

The Lachman test is the most sensitive clinical test, and the pivot shift is the most specific. Anatomic tunnel placement is the single most important factor in surgical outcomes. Autograft is preferred over allograft in young, active patients due to lower re-rupture rates. Return-to-sport decisions should incorporate objective functional testing and psychological readiness. Early ACL reconstruction with concomitant meniscal repair improves long-term joint preservation.

## References
1. Diermeier T, Rothrauff BB, Engebretsen L, et al. "Treatment After ACL Injury: Panther Symposium ACL Treatment Consensus Group." *Knee Surgery, Sports Traumatology, Arthroscopy*. 2020;28(8):2390-2402.
2. Musahl V, Karlsson J. "Anterior Cruciate Ligament Tear." *New England Journal of Medicine*. 2019;380(24):2341-2348.
3. Mouarbes D, Menetrey J, Marot V, et al. "Anterior Cruciate Ligament Reconstruction: A Systematic Review and Meta-analysis of Outcomes for Quadriceps Tendon Autograft Versus Bone-Patellar Tendon-Bone and Hamstring-Tendon Autografts." *American Journal of Sports Medicine*. 2019;47(14):3531-3540.
4. Webster KE, Feller JA. "Exploring the High Reinjury Rate in Younger Patients Undergoing Anterior Cruciate Ligament Reconstruction." *American Journal of Sports Medicine*. 2016;44(11):2827-2832.