Courtesy Dr Elmar Herbst, Dr Ashok Shyam, Ortho TV

Anterolateral Rotatory Instability (ALRI) of the Knee

Introduction

Anterolateral rotatory instability (ALRI) is a complex instability pattern that commonly occurs following anterior cruciate ligament (ACL) injury. Although ACL reconstruction restores anterior stability in most patients, residual rotational instability may persist despite technically successful surgery. Understanding the biomechanics, anatomy, contributing factors, and treatment options for ALRI is essential for achieving optimal outcomes in ACL reconstruction.

Definition and Biomechanics

Normal Knee Kinematics

In the normal knee:

The center of rotation lies near the medial tibial spine
Rotational movement is well controlled by the ACL and surrounding soft tissues

Changes After ACL Injury

After ACL rupture:

The center of rotation shifts medially
The lateral compartment demonstrates:
- Increased anterior translation
- Increased internal rotation

These abnormal movements produce anterolateral rotatory instability.

Clinical Assessment

Pivot Shift Test

The pivot shift test is the primary clinical examination used to evaluate ALRI.

Grading

Grade I — Mild instability
Grade II — Moderate instability
Grade III — Severe instability

Not all pivot shifts are identical, and instability patterns vary between patients. Therefore, management should be individualized.

Clinical Significance

Persistent rotational instability following ACL reconstruction is clinically important because it is associated with:

Poor patient-reported outcomes
Functional instability
Increased risk of osteoarthritis

Even after well-performed ACL reconstruction, approximately 10–15% of patients may continue to experience residual instability.

Anatomy of the Anterolateral Complex (ALC)

Evolution of the Concept

Initial attention focused on the anterolateral ligament (ALL). However, current understanding suggests that the ALL is not a distinct and consistently identifiable ligament.

The concept has therefore evolved into the broader anterolateral complex (ALC).

Components of the Anterolateral Complex

The ALC includes:

Iliotibial Band (IT Band)

Superficial fibers
Deep fibers (Kaplan fibers)

Capsular Structures

ALL-like capsular thickening
Lateral capsule

Meniscocapsular Attachments

Attachments involving the lateral meniscus

Important Anatomical Insights

Kaplan Fibers

Kaplan fibers, originally described in 1958, are now recognized as important stabilizers of rotational knee stability.

ALL as a Capsular Thickening

The ALL is better understood as part of the capsular complex rather than a separate discrete ligament.

Role of Meniscocapsular Structures

Meniscocapsular attachments contribute significantly to rotational control and pivot shift stability.

Biomechanics of ALRI

Primary and Secondary Restraints

Primary Restraint

Secondary Restraints

Iliotibial band
Meniscus
Capsular structures

Among secondary stabilizers, the IT band is considered the most important restraint to rotational instability.

Pivot Shift Mechanics

The pivot shift phenomenon mainly occurs within the first 30–40 degrees of knee flexion.

Contribution of Different Structures

ALL Contribution

Approximately 10–15%

IT Band Contribution

Major restraint to rotational instability

Limitations of Cadaveric Studies

Many cadaveric studies remove the IT band during dissection. This may artificially exaggerate the role of the ALL.

In vivo studies demonstrate that the iliotibial band plays the dominant role in controlling rotational stability.

Why ACL Reconstruction May Fail to Restore Normal Kinematics

Non-Anatomic Reconstruction

Improper tunnel placement or non-anatomic reconstruction remains a major cause of persistent ALRI.

Consequences include:

Increased internal rotation
Abnormal knee biomechanics
Residual pivot shift

Causes of Residual Instability

Persistent instability following ACL reconstruction may result from several factors.

1. Missed Secondary Stabilizers

Failure to recognize injury to secondary stabilizers may contribute to ongoing instability.

2. Meniscal Pathology

Particularly important lesions include:

Posterior root tears
Lateral meniscal instability

These injuries can significantly increase pivot shift instability.

Clinical Recommendation

Meniscal injuries should always be carefully assessed and repaired whenever possible.

Posterior Tibial Slope

Biomechanical Effect

An increased posterior tibial slope leads to:

Increased anterior tibial translation
Greater rotational instability

Management Considerations

In revision ACL cases with excessive slope, slope-reducing osteotomy may be considered.

Bony Factors

Underlying bony deformities may contribute to persistent instability patterns.

These abnormalities cannot be adequately corrected with soft tissue reconstruction alone.

Generalized Ligamentous Laxity

Patients with generalized hyperlaxity have an increased risk of:

Persistent rotational instability
Graft failure
Residual pivot shift

Chronic ACL Deficiency

Long-standing ACL injuries often develop more complex instability patterns due to:

Secondary soft tissue stretching
Meniscal damage
Altered biomechanics

Chronic injuries may therefore require additional stabilization procedures.

Role of Anterolateral Procedures

Types of Procedures

Lateral Extra-Articular Tenodesis (LET)

ALL Reconstruction

Both procedures are designed to augment rotational stability.

Benefits of Anterolateral Augmentation

Studies have demonstrated that adding an anterolateral procedure may:

Reduce graft failure rates
Improve rotational stability
Reduce persistent pivot shift

Reported Failure Rates

ACL reconstruction alone: approximately 11%
ACL reconstruction with LET: approximately 4%

The estimated number needed to treat (NNT) is approximately 14 to prevent one graft re-tear.

Risks of Anterolateral Procedures

Potential complications include:

Over-constraint of the knee
Increased lateral compartment pressure
Possible early osteoarthritis

Because of these risks, anterolateral procedures should be used selectively.

Indications for Anterolateral Augmentation

Common indications include:

Revision ACL reconstruction
High-grade pivot shift
Generalized ligamentous laxity
Young athletes returning to pivoting sports
High-risk patients

Surgical Principles of LET

Preferred Graft

A strip of iliotibial band is commonly used rather than hamstring grafts.

Technique Overview

The graft is:

Passed beneath the lateral collateral ligament
Fixed near the lateral femoral epicondyle

Knee Position During Fixation

20–30° knee flexion
Neutral rotation

Critical Technical Points

Important principles include:

Avoid overtensioning the graft
Preserve lateral structures
Avoid injury to the lateral collateral ligament

Excessive tension may lead to stiffness and over-constraint.

Key Takeaways

All ACL injuries produce some degree of rotational instability
Even technically successful ACL reconstruction may not completely restore normal rotational kinematics
The ALL is not a distinct ligament but part of the broader anterolateral complex
The iliotibial band is the primary restraint to rotational instability
Evaluation should always include:
- Meniscal status
- Tibial slope
- Bony alignment
- Generalized laxity
Anterolateral procedures are valuable in selected patients but should be used carefully to avoid over-constraint

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