Collateral Ligament Pathology 

Updated: Apr 10, 2021
Author: Michael P Nogalski, MD; Chief Editor: Thomas M DeBerardino, MD 


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]

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. 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. Instead, LCL or posterolateral complex injury 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.

Given the excellent results with conservative treatment of isolated collateral ligament injuries, controversy has waned in this area. Injuries of the ACL and MCL still generate some discussion, but most authors favor conservative management of MCL injuries in this setting, with ACL reconstruction for appropriate patients. Primary repair of the MCL in this setting has few proponents currently.

Lateral complex injuries are less well defined, and numerous approaches are possible. Timing of the repair of isolated lateral injuries is also still debated. Continued improvement in understanding of the lateral side of the knee and defining the role that the lateral side plays in PCL injuries is ongoing.

Relevant Anatomy

Medial collateral ligament injuries of the knee

Dissection and anatomy studies have shown that the MCL has 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.[3, 4] 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 that the MCL is the primary static restraint providing valgus stability at 25 degrees of flexion, and that the ACL also contributes significantly to valgus stability.[5]

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.[5]

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.


In animal studies, the medial collateral ligament heals 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.[6, 7, 8, 9, 10] Clinical studies, which started with the work of Indelicato, have also documented slight laxity after healing, but minimal functional significance has been identified.[11, 12, 13, 14]


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.[15, 16, 17]

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.[18]

In a study of athletes in the 2016 Olympic Games who underwent at least one knee MRI, ACL sprains had a significant association with medial and lateral meniscal tears and bone contusions.[19]


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.[20]

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.[21]

During the 2016 Olympic Games, 74.4% of athletes who underwent MRI for knee pain were diagnosed with anterior cruciate and medial collateral ligament (ACL/MCL) sprains.  Althletes participating in wrestling, hockey, track and field and judo competitions represented the majority of the diagnoses.[19]

A study of 2460 knee injuries among students playing football at American universities found MCL was the most common injury (1389; 56.4%) followed by ACL (522; 21.2%).[22]   


Outcome is related directly to the severity of the injury and the functional rehabilitation possible. Patients with isolated injuries typically do well if the injuries are managed safely but aggressively. Injuries to the ACL and MCL usually are associated with early return of full extension and patellar mobility and subsequent strength. Results of other multiple ligament injuries are best reviewed in the literature regarding knee dislocations.




Collateral ligament inuries may be either contact or noncontact injuries. Generally, pain is experienced at the time of injury and increases over the following few days. Patients with isolated injuries often are able to bear weight on the leg. Patients with complete or combined ligament injuries often report feeling a "pop" at the time of injury. 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.

Physical Examination

Often, the patient holds the knee in slight flexion. A mild or large effusion may be present. If the effusion is large and occurred shortly after the injury, especially if it is identified as a hemarthrosis, other injuries, such as an ACL tear, are likely and should carefully be ruled in or out.[23] Palpation of the knee reveals tenderness over the medial side of the knee, and it may be in the specific part of the medial collateral ligament (MCL) that is injured. In severe injuries, ecchymosis may be observed 1-2 days following the injury.

Medial collateral ligament injuries of the knee

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.[24]

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 posterior cruciate ligament (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 lateral collateral ligament (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.



Imaging Studies

Radiography and a physical examination usually suffice for grade 1 collateral ligament injuries in which the diagnosis appears straightforward. With more pain, larger effusions, or if the diagnosis is unclear, magnetic resonance imaging (MRI) may be of value. A repeat examination 2 weeks after the injury may provide more accurate findings.

According to American College of Radiology (ACR) Appropriateness Criteria for imaging acute knee trauma, plain radiographs are usually appropriate for the initial evaluation. MRI without intravenous contrast is recommended as the most approriate follow-up study if no fracture is found.[25]

MRI is very sensitive and specific for medial collateral ligament (MCL) injuries; however, only a physical examination can quantitate or grade the injury. Meniscal, other ligamentous, patellofemoral, and possibly chondral injuries can be identified.[26]  Grade 3 MCL injuries may be associated with other concomitant injuries, and if suspicion exists, MRI is helpful in evaluation. 

In lateral collateral ligament injuries, plain radiographic findings may be normal or, in bony avulsions of the lateral collateral ligament (LCL), show a fibular head avulsion fracture. MRI is the optimal test to demonstrate the lateral structures. MRI can also be used to evaluate the other structures in the knee, such as the posterior cruciate ligament (PCL), anterior cruciate ligament (ACL), MCL, and menisci.[27]

For a more in-depth discussion, see Collateral Ligament Injury MRI.

Diagnostic Procedures

Examination under anesthesia has some value, especially in combined ligament injuries when evaluation of the knee would be painful and less accurate. Arthroscopy has little value in the evaluation of these specific injuries but does aid in the evaluation of associated ligamentous, chondral, and meniscal injuries.

Posterolateral Tests

In the posterolateral drawer test, the examiner supports the patient's foot and, with the knee first at 30 degrees and then at 90 degrees of flexion, places a posterolateral spin on the tibia by pushing laterally on the medial anterior tibia. Findings should ideally be compared with a normal opposite knee. The angle of the foot with respect to the midsagittal plane can be used to gauge the amount of spin that the tibia has with respect to each femur. If the posterolateral spin of the tibia is greatest at 30 degrees and minimal at 90 degrees, then a posterolateral complex injury is likely. If the posterolateral spin is larger at 90 degrees, then PCL injury associated with a lateral complex injury is likely.

In the external recurvatum test, both legs are raised off the examination table with the examiner grasping the great toe while the patient is supine. If the tibial tubercle rotates outward and the knee goes into recurvatum, laxity of the posterolateral corner is present. Comparison with the opposite lower extremity can help identify normal versus abnormal rotation and recurvatum.

The posterolateral spin test at 30 and 90 degrees uses the same principle as the posterolateral spin test above but uses the thigh-foot angle, as measured with an external rotation on the tibia exerted on the feet with the knees at 30 and 90 degrees. Having an assistant hold the knees together and performing this test with the patient supine is helpful. The patient is asked to place his or her knees at positions of 30 and 90 degrees as set by the examiner. With an assistant holding the knees together, the thigh-foot angle is assessed after exerting an external rotation force on both feet simultaneously. Side-to-side differences of greater than 10 degrees are thought to be significant. Significantly increased external rotation at 30 degrees indicates a posterolateral complex injury. If the spin is also increased at 90 degrees, then likely both the PCL and posterolateral complex are injured.



Approach Considerations

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

The main complication 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 as good as, if not better than, those for surgically treated isolated MCL injuries.[11, 28]

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 with conservative but aggressive functional mobilization and bracing, clearly argue strongly for nonoperative management.

Medical Care

Medial collateral ligament injuries of the knee

In general, the treatment of isolated medial collateral ligament (MCL) injuries is conservative and based on functional results, with a period of protection and then aggressive strengthening and functional rehabilitation. Return to activity usually is allowed when the knee is at full (or at least 80%) strength, full range of motion, and causing no pain.[29]

In grade 1 injuries, a period of protection with a hinged knee brace or hinged neoprene sleeve and weight bearing as tolerated is recommended initially. Physical therapy, with modalities and strengthening, can optimize an early return to activities such as sports and work. Many patients probably can go to a home- or gym-based exercise program of quadriceps and hamstring strengthening. Proprioceptive training probably would also help minimize future problems and allow for the most efficient return of high levels of activity with confidence.

Grade 2 injuries usually require a 2- to 4-week period of protected weight bearing, and hinged knee brace protection for 6 weeks. Physical therapy is very helpful in regaining strength and function in this situation.

Grade 3 isolated injuries are not as common and usually involve consideration of other simultaneous injuries. If the injury appears to be truly isolated, conservative treatment has been very successful. A hinged knee brace with 4 weeks of non-weight bearing and subsequent aggressive rehabilitation is usually optimal.

A case report describes successful treatment of a grade 3 MCL injury with a series of three sequential leukocyte-rich, platelet-rich plasma (LR-PRP) Injections spaced evenly one week apart, in addition to an early physical therapy regimen. The total treatment time was 31 days, compared with the 35-49 days that would be expected in such cases.[30]

As discussed below, combined anterior cruciate ligament (ACL) and MCL injuries are prone to motion problems and arthrofibrosis. Initial management should focus on protection of the MCL with a hinged knee brace, achieving range of motion (especially terminal extension), and then treating the ACL with individualized treatment according to the functional demands of the patient. A grossly lax MCL demands careful search for other ligament injuries (including possible knee dislocation) and warrants consideration of repair of the MCL and posteromedial capsule.

Lateral collateral ligament injuries

Isolated lateral collateral ligament (LCL) injuries usually are treated easily, but associated injury to other structures of the knee often occur when the LCL is lax, and the knee should be evaluated thoroughly before treatment of an apparently isolated LCL injury is undertaken. LCL injuries that are low grade are well managed with protection in a hinged knee brace and protected weight bearing for 4 weeks, with subsequent rehabilitation. Displaced fractures of the fibular head with associated varus instability are best addressed by fixation of the fracture and early rehabilitation.

Conservative treatment should be strongly considered for isolated posterolateral complex injuries. Posterolateral complex injuries with associated high-grade (3 or 4) posterior cruciate ligament (PCL) injuries present a strong argument for addressing both the PCL and posterolateral injuries.[31, 32]  A paucity of data exists, and research to clearly define the efficacy of operative management of PCL/posterolateral complex injuries is minimal, but biomechanical studies clearly support fixation to minimize posterior and rotational translation of the tibia with respect to the femur.[33]

Grade 1 and 2 isolated posterolateral ligament complex injuries are treated reasonably with a hinged brace initially and immobilization initially at 45 degrees for 3 weeks. Progressive range of motion and weight bearing after 3 weeks as comfort allows enables progression in rehabilitation. Grade 3 posterolateral injuries warrant repair, especially because the results of reconstruction are not as good as those of acute repair.

High-grade (3 or 4) PCL injuries with associated posterolateral injuries often require consideration for repair of the posterolateral corner in association with PCL reconstruction. Reconstruction of the posterolateral corner is considered, especially when associated with chronic PCL injury.

Medial collateral ligament and anterior cruciate ligament injuries

Often, the MCL is injured at the same time as the ACL. This combination injury has been found to increase the potential for a stiff knee, especially if operative treatment is undertaken on an early basis. At times, even a nonoperative approach to this combination of injuries can result in an arthrofibrotic knee, which often includes a relatively immobile patella and stiff medial retinaculum.

The clinical observations of Jokl in 1984, Shelbourne in 1992,[14]  and Elsasser in 1974 have strongly suggested that the MCL does not need surgical repair in ACL/MCL injuries. In addition, of those patients who did undergo ACL reconstruction with and without MCL repair, the nonoperative group had quicker recovery of motion.[14, 34, 35]  However, true complete capsular tears of the MCL warrant consideration for repair.

Surgical Care

Medial collateral ligament injuries

As mentioned above, rarely is surgical treatment of the medial collateral ligament required. Surgery may be needed to stabilize the medial side of the knee, for example, in multiple ligament injuries such as knee dislocations.[36]  Attention to restoration of the anatomy and avoidance of shortening the superficial portion of the MCL (which may occur with anchoring of the ligament too close to the knee joint) are important. If a laceration of the MCL has occurred or an end-to-end repair is performed, Krackow suture technique affords good purchase on both ends. Tying the sutures in extension to avoid flexion contracture is optimal.

Lateral collateral ligament injuries

In the acute knee dislocation, repair of the posterolateral complex can be achieved by direct repair of the injured structures. Surgical approach is dictated by the group of ligaments injured. In any lateral approach, identification and protection of the peroneal nerve is paramount. To avoid capture of the knee in flexion, the knee should be in full extension when tying these sutures. Suture anchors may be needed to help supplement the repair. Postoperative treatment is usually that of a hinged knee brace and progression of range of motion as per the general plan for the combination of ligaments injured. Limited weight bearing is usually necessary to protect the soft-tissue repairs for a 6-week period.

Restoration of the symptomatic chronic posterolateral injuries usually requires stabilization of the posterolateral corner with autogenous tissue, such as the peroneal tenodesis, as described by Clancy; allograft patellar tendon, as described by Noyes; or split Achilles tendon.[37, 38, 39]  The author favors the Clancy procedure for its reproducibility, but often the hardware on the lateral side causes symptoms and requires eventual removal.

Medial collateral ligament and anterior cruciate ligament injuries

Timing of surgery to address ACL injury in the setting of MCL injuries is an important consideration. Clear differences in recovery of range of motion after ACL reconstruction have been demonstrated by Shelbourne and Harner in 1992, in cases involving concomitant MCL injuries. Optimal waiting time is probably about 3 weeks. This author has performed ACL reconstruction successfully in grade 1-2 MCL injuries in a 2-week period as long as the preoperative range of motion is at full extension and to 90 degrees of flexion.

Kitamura and colleagues, in a study of 37 patients with multiligamentous knee injuries, reported good clinical outcomes and postoperative medial stability at a minimum of 2 years of follow-up with combined MCL and cruciate ligament reconstruction using hamstring tendon autografts.[40]

Preoperative Details

A good physical examination and radiographic and MRI studies allow for the most accurate evaluation of the injuries involved and approach required.

Intraoperative Details

Using local tissues during surgery to repair the MCL and LCL may not be optimal. The surgeon should be prepared to use other tissues, such as hamstring tendon or allograft, if a problem is anticipated.

Postoperative Details

Immobilization and functional rehabilitation depend on the procedure performed and the surgeon's confidence in fixation of the tissue that was repaired or reconstructed. General protocol guidelines involve use of a hinged knee brace with varied range of motion allowed, depending on the structures addressed at the time of surgery and the surgeon's confidence in fixation of the repaired or reconstructed structures. Weight bearing usually is allowed progressively over a 6- to 8-week period, with emphasis placed more on motion than strength during this period.


In general, stiffness is more common than laxity in collateral ligament injuries. In those injuries that are treated with surgery, stiffness is the most common problem. Residual weakness due to noncompliance or heterotopic ossification can occur but is rarely debilitating or symptomatic enough to warrant removal. This is known radiographically as a Stieda-Pellegrini lesion, which is an ossification of the MCL.

As noted above, peroneal nerve injuries can be associated with lateral-sided injuries.

With operative management come the usual risks of infection, neurovascular injury, stiffness, deep venous thrombosis, and anesthetic-related complications.

Long-Term Monitoring

Periodic evaluations at 2- to 4-week intervals are required for both operative and nonoperative management of collateral ligament injuries. Early evaluation of range of motion and then later evaluation for strength are necessary to direct effective and optimal recovery.

For patient education information, see Knee Injury and Knee Pain.