eMedicine Specialties > Orthopedic Surgery > Knee

Anterior Cruciate Ligament Pathology

Author: John Maguire, MBBS, FRACS(Ortho), MSpMed, Fellow, Department of Orthopedic Surgery, North Sydney Orthopedic and Sports Medicine Center
Coauthor(s): Mervyn J Cross, MBBS, FRACS, Director of the Australian Institute of Musculoskeletal Research, Department of Orthopedic Surgery, North Sydney Orthopedic/Sports Medicine Center, Crows Nest, Australia
Contributor Information and Disclosures

Updated: Apr 13, 2009

Introduction

The anterior cruciate ligament (ACL) is one of the most commonly injured ligaments of the knee. Injuries occur predominantly in a young and sports-active population. Many patients are left with significant disability following injury to the ACL. Understanding and preventing associated meniscal pathology is the key to management of this condition. This article endeavors to explain the complex nature of the ligament and its injuries and aid the reader in making informed management decisions.

History of the Procedure

Bonnet first discussed ACL injury in the medical literature in 1845. Further discussion was made by Segond in 1879. Stark made the first reports in the English literature in 1850. In 1900, Battle described surgical intervention when he attempted repair of the ACL. Subsequent operative descriptions include those by Groves and Jones in 1913.

In 1917, Groves described a reconstructive procedure. He used the iliotibial band (ITB) as the graft. In 1918, Smith detailed combined intra-articular and extra-articular procedures. Zur Verth first used the patellar tendon graft in 1933. Campbell used this same donor tissue in 1936. In 1966, Bruckner reported using the patellar tendon as a free graft. Since that time, numerous entries have been made in the literature describing natural history, operative reports, and surgical series.

Problem

Anterior cruciate ligament injury often occurs in the young and sports-active population.

Frequency

Incidence of anterior cruciate ligament injury in the United States is estimated to approach 1 case per 3000 individuals. Over 100,000 injuries occur per year from snow skiing in the United States alone. Estimated cost of management is in the order of 2 billion dollars annually, which is a significant problem. The authors' series has demonstrated an incidence of 1.5% of the population of New South Wales, Australia, with males affected twice as often as females.

Females are at higher risk of ACL injury when considering sports participation numbers. This is believed to be related to both intrinsic factors (increased Q angle, decreased notch width, increased joint laxity, hormonal influences) and extrinsic factors (less muscle strength, different muscle activation patterns, altered cutting and landing patterns). Further investigation is required to fully identify which of these factors are the most important and if any alterations to ACL injury patterns can be made as a result of intervention.

Etiology

Approximately 70% of anterior cruciate ligament injuries occur through noncontact mechanisms. Patients experience giving way of the knee when attempting to rapidly change direction. This involves deceleration, coupled with a cutting, pivoting, or sidestepping maneuver. The remainder of cases tend to occur through direct contact and often are associated with other ligament injury.

Pathophysiology

The anterior cruciate ligament acts as the primary restraint to anterior tibial translation and guides the screw-home mechanism associated with knee extension. The ACL acts secondarily to prevent varus and valgus, particularly in the extended knee. Injury leads to abnormal kinematics of the knee. Subluxation episodes occur, creating abnormal shear forces on the meniscus and articular cartilage. Subsequent meniscal injury therefore is increased significantly. The authors have found a significant increase in this meniscal pathology with delay of ACL reconstruction. Associated with this meniscal pathology is an increased incidence of osteoarthritis. A series conducted by the authors demonstrates a 15% incidence of ACL tears in patients undergoing total knee replacement (TKR). This incidence is at least 3 times the incidence of ACL tears found in the general population.

Presentation

Clinical presentation of anterior cruciate ligament injury occurs either as an acute injury or as a more chronic problem of recurrent instability.

Acute injury

Patients with acute injury present following an instability episode as previously described. More than 50% of these patients state that they felt a pop as the injury occurred. Up to 80% of these patients develop a rapid hemarthrosis (see Image 1) over the subsequent 4 hours. Some studies demonstrate that occurrence of ACL injury may be as high as 70% in all hemarthroses and must be excluded in such injuries.

Clinical signs in the acute phase include a large hemarthrosis, limited range of motion (ROM), and joint-line tenderness.

Chronic ACL instability

Chronic presentations tend to involve repeated instability episodes, particularly when attempting the cutting maneuver.

Presentation also may be associated with mechanical pain related to meniscal tears or early osteoarthrosis.

Recurrent effusions and a history of locking also are important points in assessing associated injury.

In chronic presentations, a similar assessment is made. Meniscal pathology should be sought with joint-line palpation and the McMurray maneuver. Pivot-shift and jerk tests are performed more easily and can provide a better indication of the degree of rotatory instability. The Lachman test can be negative in chronic cases. The ACL can scar to the posterior cruciate ligament (PCL), thus limiting anterior translation of the tibia. As the scarring is nonanatomic, the pivot-shift phenomena persists, as does symptomatic instability. This should be kept in mind in chronic cases.

Indications

The aim in treating patients with anterior cruciate ligament injuries is to prevent recurrent instability and associated meniscal injury. Once meniscal pathology occurs, there is a much higher incidence of osteoarthritis.

Following acute injury, the major indications for surgical reconstruction are related to the degree of instability and level of activity. Activity levels can include sporting or work-related activities. Reviewing the patient profile in the history from the patient is very important in the decision-making process.

Daniel defines patients at highest risk as those who participated in more than 50 hours of high-level activity per year prior to injury and have marked instability.^1,2 Instability was defined as having a KT-1000, manual max test of greater than 5 mm of anterior translation. In those with translation of greater than 7 mm, this was defined as marked instability. Surgical intervention can be justified in these cases, as these patients were found to be at greatest risk of requiring further surgery.

In the less active group, the decision for surgery becomes more controversial. A nonoperative management plan with extensive physical therapy and activity avoidance can be undertaken. If patients experience ongoing instability or are unwilling to modify activity levels, surgery should be considered.

In chronic cases, the major indication for surgical reconstruction is recurrent instability. Other types of surgical intervention may be required to deal with associated pathology, such as arthroscopy, partial meniscectomy, or meniscal repair. High tibial osteotomy also may be required to correct varus alignment, especially in degenerative cases and complex instabilities.

Relevant Anatomy

Anatomy of the anterior cruciate ligament is very complex. The ligament is intra-articular but extrasynovial. The ACL is described as being composed of 3 main bundles. These bundles include the anteromedial, posterolateral, and intermediate. The ACL really functions as a continuum, with a portion being tight through all ranges of knee flexion.

The ligament courses obliquely, running from the tibia anteriorly and medially to the femur posteriorly, superiorly, and laterally. The broad tibial footprint lies at a point one third to one half the distance between the medial and lateral tibial spines, 5–7 mm anterior to the posterior cruciate ligament (PCL). On the femoral side, the attachment lies on the medial aspect of the lateral femoral condyle, just anterior to the posterior aspect of the intercondylar notch. An intercruciate ligament joins the ACL to the PCL. This intercruciate ligament may have some role in proprioception and coupling of the 2 ligaments.

The microstructure of the ligament is composed of collagen fiber bundles, grouped into fascicles. Type I collagen is the predominant collagen type, comprising over 90%. Types III and VI also are found. Elastin is found in significant amounts and provides some of the elastic properties of the ligament.

The major blood supply for the ACL comes from the synovium and fat pads. The middle geniculate and terminal branches of the inferior medial and lateral geniculate vessels are the vessels involved.

Sensory receptors and nerve fibers have been identified in the ligament and associated feeding blood vessels. This suggests some sensory role and possible proprioceptive function.

Contraindications

Surgical contraindications are limited and include the following:

• Active infection
• Soft-tissue abrasion
• Patient reluctance to participate in the complex rehabilitation required

However, relative contraindications are common and include the following:

• Patient is less than 2 weeks from injury
• Low activity levels
• Preexisting osteoarthrosis
• Skeletal immaturity
• Inflammatory arthropathy

• Search for CME/CE on This Topic »

• Intercondylar Eminence Fractures (Orthopedic Surgery)

• Foot, Ankle, Knee, and Hip Center
• Knee Injury Causes
• Knee Injury Overview
• Knee Injury Symptoms
• Knee Injury Treatment
• Knee Pain Introduction