Collateral Ligament Pathology

Updated: Feb 07, 2017
  • Author: Michael P Nogalski, MD; Chief Editor: Thomas M DeBerardino, MD  more...
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Overview

Practice Essentials

The medial and lateral collateral ligaments of the knee are 2 distinct entities, are injured by different mechanisms, and often generate different algorithms for treatment. Treatment of these structures, when the injury is isolated, often is conservative and involves brief protection and functional rehabilitation. In lateral-sided injuries, other structures, such as the entire posterolateral complex, the anterior cruciate ligament (ACL), and the posterior cruciate ligament (PCL), can be injured as well. [1, 2]

Management of these injuries depends on an understanding of the biology, anatomy, and mechanical function of these structures. Over the past 2 decades, research into the basic science of ligaments, mostly in animal models, has improved the understanding of the injury and repair mechanisms. Each injury is considered with respect to isolated injuries, combined injuries of the ACL and PCL, and combined injuries in knee dislocations.

Isolated lateral collateral ligament (LCL) injuries are rare. More commonly, this ligament is injured as a component of a posterolateral injury of the knee. In addition, an isolated injury to the LCL or posterolateral complex is unusual and often occurs with a PCL injury or with an ACL/PCL injury. An isolated LCL injury is treated in much the same way as a medial collateral ligament (MCL) injury (usually one of low grade). Attention should be focused on the entire posterolateral corner of the knee when a lateral injury to the knee is suspected.

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Problem

If untreated, injuries to the collateral ligaments can result in functional instability of the knee in daily activities, work, and sports. This is often noted in association with other ligament injuries of the knee.

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Etiology

Medial collateral ligament injuries of the knee

A valgus stress with or without a combined rotational stress to the knee most commonly causes this injury. The foot or lower leg usually is held in a fixed position, and the upper leg and body moves or twists in relation to the lower leg. MCL tears can also be noncontact injuries. The MCL may also be injured in conjunction with tears of the ACL, PCL, and/or lateral complex. [3, 4, 5]

Lateral collateral ligament injuries

A direct blow to the medial knee usually is the mechanism of injury that results in isolated LCL tears. Injury to the posterolateral structures of the knee come from medial blows to the knee with the knee in flexion and from rotational forces placed on the knee at the same time. Wrestling is thought to be a sport that can generate pure LCL injuries. [6]

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Pathophysiology

In animal studies, the medial collateral ligament has been found to heal with fibroblast proliferation in the hematoma/plasma exudate that occurs in the zone of injury. Similarities to tendon healing in the collateral ligament healing process have been cited by investigators, as opposed to the cruciate ligaments, which heal with fibrocartilaginous cells.

Functional treatment with protection from valgus stress has been found to improve healing and orientation of the collagen fibers in the healed ligament. Some animal studies have shown elongation of the ligament, but, as noted below, clinical studies have not found this to be a significant problem in isolated MCL injuries. [7, 8, 9, 10, 11] Clinical studies, which started with the work of Indelicato, have also documented slight laxity after healing, but minimal functional significance has been identified. [12, 13, 14, 15]

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Presentation

Medial collateral ligament injuries of the knee

As mentioned above, these may be either contact or noncontact injuries. Generally, pain is experienced at the time of injury and increases over the following few days. Patients often are able to bear weight on the leg after sustaining isolated injuries. A pop often is felt in complete or combined ligament injuries. The patient usually is unable to continue playing when the injury occurs during a game. Swelling over the medial side of the knee may occur gradually. An effusion may also be noted. If a large effusion develops quickly, especially if it is identified as a hemarthrosis, a tear of the ACL has quite possibly occurred. [16]

Often, the patient holds the knee in slight flexion. A mild or large effusion may be present. If a large effusion occurred shortly after the injury, other injuries, such as an ACL tear, are likely and should carefully be ruled in or out. Palpation of the knee reveals tenderness over the medial side of the knee, and it may be in the specific part of the MCL that is injured. In severe injuries, ecchymosis may be observed 1-2 days following the injury.

Isolated testing of the ligament should be performed with the knee in 20 degrees of flexion. Pain with valgus stress and no medial joint space other than a normal (equal to the other injured side) opening of 0-5 mm indicates a grade 1 sprain. Pain and opening of the joint space up to 10 mm with an endpoint indicates a grade 2 injury to the MCL. Complete joint space opening of more than 10 mm indicates a grade 3 injury. Marked medial laxity suggests possible concomitant knee ligament injuries or reduced knee dislocation.

Careful evaluation of the medial joint line and tests for meniscal injury should also be performed to confirm that the pain is due to stress of the ligament and not to mechanical pain from a torn medial meniscus. The Apley grind/distraction test can be helpful but not entirely diagnostic or specific for this. With the patient prone, the knee is flexed to 90 degrees and the foot and ankle are grasped. The tibia is then rotated on the femur with distraction and compression of the tibia on the femur. If pain is generated in the unloaded situation, in which the ligament is stretched, then the medial pain is likely due to ligamentous or capsular injury. If the pain is worsened by compression, then a meniscal or chondral origin of the pain is more likely.

The patellofemoral joint and the medial retinacular structures should be evaluated and palpated for signs of retinacular tears and signs of instability as well. A torn or strained medial retinaculum can be very painful and can generate similar pain and have a similar history of injury. Vastus medialis disruptions are observed in up to 21% of knee ligament injuries. [17]

Lateral collateral ligament injuries

Specific examination maneuvers can be performed to identify injury to the lateral or posterolateral structures and to distinguish between pure rotational instability due to a torn posterolateral complex and additional laxity due to PCL insufficiency. In any case, a routine examination should be performed to carefully evaluate all ligaments around the knee if a lateral or posterolateral injury is suspected.

Valgus testing at 30 degrees should demonstrate laxity of the LCL. The quality of the endpoint should be noted, and if this test finding is indeed positive, a search for other injuries with the other tests outlined below should be initiated. With the knee in a figure-of-4 position, the LCL can be palpated as a taut structure when intact. If a soft spot is present in this region, the LCL, at minimum, has been injured. In any suspected lateral injury, careful evaluation of the peroneal nerve for possible injury is prudent. See Other Tests for diagnostic tests for LCL injuries.

LCL injuries can be grouped into classes similar to those in MCL injuries. Grade 1 injuries show normal or up to 5 mm of joint space opening with a solid endpoint. A similar solid endpoint is observed with grade 2 injuries, but opening up to 10 mm is possible. Grade 3 injuries demonstrate greater than 10 mm of joint space opening and often are associated with other ligament injuries.

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Epidemiology

Despite the relatively common nature of medial collateral ligament injuries in particular, the frequency of collateral ligament injuries is not well defined in the literature.

In a longitudinal cohort study, Roach and colleagues examined the epidemiology of isolated MCL sprains that occurred at the United States Military Academy between 2005 and 2009. During 17,606 student person-years over the study period, 128 cadets sustained isolated MCL injuries, resulting in an incidence rate of approximately 7.3 per 1000 person-years. Males had a 44% higher incidence rate than females. Contact sports such as wrestling, hockey, judo, and rugby were associated with the highest injury rates. [18]

A survey of sports-related knee injuries in US high school students found that medial collateral ligament injury was the most common, being reported in 36.1% of cases; the lateral collateral ligament was involved in 7.9% of knee injuries. [19]

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Indications

Conservative management of isolated collateral ligament injuries is the general rule. Reattachment of displaced bony avulsions of the ligaments is a reasonable consideration, and this would allow for early motion of these injuries.

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Relevant Anatomy

Medial collateral ligament injuries of the knee

The MCL has been found in dissection and anatomy studies to have 2 primary components—a more superficial ligamentous structure, the superficial MCL, and a deeper capsular MCL complex. The deep layer is attached to the medial meniscus and transitions into the posterior oblique ligament (POL) just posterior to the posterior edge of the superficial MCL. [20, 21] The superficial MCL attaches to the medial epicondylar region and to an area well inferior to the joint line, posterior to the insertion point of the pes anserine bursa. The POL has 3 portions: the tibial, superficial, and capsular arms. Grood et al found the MCL to be the primary static restraint to valgus stability at 25 degrees of flexion. [22] The ACL was also identified as a significant contributor to valgus stability. [22]

Grade 1 or 2 injuries involve a portion of the ligament and are partial-thickness injuries. Grade 3 ligament injuries are complete tears of the superficial and deep layers of the MCL. Bony avulsions can occur but are unusual. If an avulsion is observed, pathologic bone at the avulsion site should be considered.

Lateral collateral ligament injuries

The LCL extends from the lateral epicondyle to the fibular head and is the primary restraint to varus stress of the knee. Below the LCL is the rest of the posterolateral complex, made up of the arcuate complex, the posterolateral capsule, and the popliteus tendon. The arcuate complex, which is associated with the posterior-lateral capsule, attaches as well to the fibular head. The lateral capsule is thick in its middle third and is analogous to the deep fibers of the MCL. Deep to the capsule, the popliteus tendon winds around to insert on the lateral condyle intra-articularly. The LCL limits lateral joint opening with varus stress on the knee. The posterolateral complex has been shown to be most effective in controlling external rotation of the tibia on the femur at 30 degrees of knee flexion. [22]

Injuries to the LCL complex probably involve a spectrum of injuries, from an isolated LCL injury, which would come from a pure varus stress, to an injury to the LCL and posterolateral ligament complex. This combined injury usually involves more energy and rotational forces.

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Contraindications

The main problem to be avoided in the treatment of collateral ligament injuries is loss of motion and strength. Operative treatment usually is contraindicated in isolated injuries because the results of nonoperative treatment have been shown to be equal to, if not better than, those for operated isolated MCL injuries. [12, 23]

In isolated collateral ligament injuries, conservative treatment usually is indicated, and few, if any, contraindications to conservative management exist. Even if skin conditions (eg, burns, degloving injuries) or other circumstances do not allow for bracing, relative protection usually suffices because these patients have other pressing issues that limit mobility. Interestingly, patients who have severe periarticular soft-tissue injuries usually have considerable stiffness with or without ligamentous injury. Delayed treatment is optimal in this situation because of the stability that may be afforded by exuberant soft-tissue reaction and possible heterotopic ossification. In these situations, early operation may further stimulate the scar response around the joint.

The usual other operative risks, when considered against the excellent outcome for conservative but aggressive functional mobilization and bracing, clearly argue strongly for nonoperative management.

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