MRI diagnosis in multiligamentous injuries of knee with associated dislocations and neurovasacular sequelae: a retrospective analysis of injury patterns

Background Simultaneous injury of two or more knee ligaments with concurrent tears involving the anterior cruciate and medial collateral ligaments is considered to be associated with femorotibial knee dislocations (KD). The purpose of this study is to characterize multiligamentous knee injury patterns associated with dislocations on MRI and to describe the incidence of their sequelae such as tibial plateau fractures, peroneal nerve injuries, and posterolateral corner (PLC) injuries. Participants and methods After obtaining institutional ethical committee approval, we retrospectively identified 108 multiligamentous knee injuries in 100 patients who met with trauma and were treated at our tertiary care center between April 2014 and December 2018. Descriptive statistics were reported using numbers and percentages for categorical variables in cases of multiligamentous injuries, ipsilateral tibial plateau fractures, ipsilateral femoral fractures, peroneal nerve injury, arterial injury, compartment syndrome, and PLC injuries. Results The most common (39.8%) injury pattern was a combined disruption of the anterior cruciate ligament, posterior cruciate ligament, and PLC. Schenck KD III-M was the most common injury type in KD, constituting 16.7%. Medial-sided injuries were the most common injury patterns seen with KD. There was a significant risk of peroneal nerve injury with lateral-sided injuries. Conclusion KD, though rare, may have devastating clinical sequelae such as compartment syndrome if not recognized and treated. Therefore, it is necessary to recognize imaging findings of femorotibial joint dislocations and associated injuries to the adjacent neurovascular bundles.


Introduction
Multiligamentous knee injuries are sometimes isolated but more often are the result of high-energy trauma and as such have various comorbidities (Fig. 1). Recent reports have suggested that similar injury patterns are associated with vascular injury and peroneal nerve palsy in 19 and 20% of patients, respectively, and were done in small numbers of participants, which reported wide variations in the rates of associated injuries [1]. Fractures in association with knee dislocations (KD) have been reported to be as high as 60% in patients with high-energy injuries, with 41% noted to have multiple fractures of the extremities [2]. According to previous studies, the incidence of multiligamentous knee injuries ranges from 0.001 to 0.013% in all patients evaluated for orthopedic injuries [3]. There is a surge in numbers from recent years, likely because of the improved survival of the critically injured trauma patient and the increased awareness of ligamentous injuries [4]. Bicruciate ligament injuries have been reported to be equivalent to KD regarding frequency of major arterial injuries, the mechanism of injury, and severity of ligamentous injury. A missed diagnosis of KD can result in increased morbidity and risk of limb loss [5].

Anterior cruciate ligament
Approximately 70% of anterior cruciate ligament (ACL) injuries have a noncontact mechanism [6]. The classic history of the noncontact injury involves a sudden deceleration, hyperextension, or twist, accompanied by a 'pop', significant pain, and subsequent swelling of the knee. The mechanism This is an open access journal, and articles are distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as appropriate credit is given and the new creations are licensed under the identical terms. most commonly involves a valgus stress. This cascade of movements occurs when an athlete performs a straight-leg landing or a one-step stop with the knee hyperextended. ACL and posterior cruciate ligament (PCL) injuries rarely occur in isolation and are often associated with injuries to the secondary/supporting ligamentous structures that provide both static and dynamic stability against rotational forces.

Posterior cruciate ligament
The two most common mechanisms of PCL tear injury are forced hyperflexion and sustaining a posterior blow to the proximal tibia. Forced hyperflexion is the most common mechanism for an isolated PCL injury. During hyperflexion, the anterolateral component comes under increasing tension with knee flexion. The posteromedial component usually remains intact. A posterior blow to the proximal tibia of a flexed knee occurs with dashboard injuries to the knee during motor vehicle accidents causing to fall on a flexed knee. Hyperextension, most often is associated with a varus or valgus force, can also cause PCL injury.

Posterolateral corner injury
Posterolateral corner (PLC) injuries result in posterolateral rotational instability; they rarely occur in isolation [7]. PLC injuries often occur in combination with cruciate ligament disruption, and they are most commonly associated with PCL injury (Table 1). Posterolateral instability is characterized by posterior subluxation and external rotation of the tibial plateau in relation to the femur. Therefore, a PCL injury necessitates careful scrutiny of the PLC structures on MRI. In the setting of trauma, PLC injury is most commonly caused by a direct blow at the anteromedial proximal tibia with a posterolateral force vector and knee in near full extension ( Table 2). PLC injury is also seen with highvelocity trauma such as a complete KD. Bone marrow edema at the styloid process of the fibular head without fracture on MRI also warrants close investigation of the PLC structures for associated injury.

Posteromedial corner injury
The posteromedial corner (PMC) consists of ligamentous, meniscal, and myotendinous components that provide both static and dynamic constraint of anteromedial tibial rotation, in addition to secondary restraint of anterior tibial translation. The tendinous and ligamentous anatomy of the PMC, though complex, can be consistently identified on routine MRI. The PMC consists of the following structures: the oblique popliteal ligament, semimembranosus tendon, posteromedial capsule, posterior oblique ligament, deep components of the medial collateral ligament (MCL) complex, and the posterior horn of the medial meniscus (Table 3). PMC injuries occur most often during sports-related activities and are frequently overlooked, both clinically and at initial imaging, because they are often overshadowed by the more obvious cruciate and collateral ligamentous injuries. PMC injuries occur in combination with PCL injury, combined PCL and ACL injuries, ACL injury, MCL injury, and O'Donoghue's triad of ACL, MCL, and medial meniscal injury.     [10] described a pathophysiologic approach to the classification, which covers the full range of complex ligamentous lesions occurring in KDs. As per this classification, there are two types of mechanism of injury, which can be evaluated through dynamic and static imaging. The first mechanism of injury, gaping, is a low-energy mechanism without weight bearing in the knee that results in ligament tear. The second mechanism of injury, translation, is a low-energy mechanism with weight bearing in the knee that results in ligamentous detachment. When only a single mechanism is involved, the lesion is classified as simple [11]. Simple translation results in pure anterior or posterior dislocation, whereas simple gaping results in both cruciate ligament lesions [12]. These mechanisms can also occur in combination during high-energy injuries and result in dislocation with peripheral tearing of ligaments.

Purpose of study
The purpose of this study is to characterize multiligamentous knee injury patterns associated with dislocations on MRI and to describe the incidence of their sequelae such as tibial plateau fractures, peroneal nerve injuries, and PLC injuries.
We have described the mechanism of injury, ligamentous disruptions, and imaging findings of various types of KDs including injuries of the femorotibial, proximal tibiofibular, and patellofemoral joints. A step-by-step approach has been performed to evaluate the following: fractures and bone contusions − effusion and capsular disruption − cruciates − collaterals − menisci − extensor mechanism − posterior, lateral, and medial corner − cartilage − soft tissue. The MRI sequences the authors have used in such assessments were coronal and sagittal proton density, along with fat-suppressed sagittal and axial proton density/T2-weighted images.

Participants and methods Participants
After obtaining institutional ethical committee approval, we retrospectively identified 108 multiligamentous knee injuries in 100 patients who were treated at our tertiary care center between April 2014 and December 2018.

Inclusion criteria
In this study, the inclusion criteria were multiligamentous injuries to the ACL, PCL, or collateral ligaments and associated KDs on MRI, according to the classification of Schenck [9] (KD II, KD III, and KD IV; Table 4).

Exclusion criteria
The exclusion criteria were severe intra-articular fractures of the ipsilateral knee and skeletal immaturity.

Evaluation
We verified multiligamentous injuries by MRI with clinical and surgical findings by fellowship-trained orthopedic specialists. All MRI studies were reviewed and confirmed by a senior radiologist. If discrepancies were noted, we took both MRI and surgical findings into consideration, acknowledging the fact that MRI does not necessarily differentiate between severe ligamentous sprain and discontinuity. MRI included T1-weighted and T2-weighted axial, coronal, and sagittal views and were evaluated for  ligamentous injuries, fracture patterns, and associated KD when assessing ligamentous injury patterns. MRI studies were obtained and evaluated when examination findings suggested KDs or multiligamentous knee injury.

Data collection
Data were obtained from the medical records of all 108 knees by using a predefined protocol that included orthopedic examinations, MRI findings, operative notes, and progress notes throughout the hospital course. Demographic information, arterial injuries, nerve injuries, associated fracture patterns, and KDs were recorded from initial evaluation.

Statistical analysis
Descriptive statistics were reported using numbers and percentages for categorical variables in cases of multiligamentous injuries, ipsilateral tibial plateau fractures, ipsilateral femoral fractures, peroneal nerve injury, arterial injury, compartment syndrome, and PLC injuries.

Results
A total of 108 multiligamentous knee injuries in 100 patients who met with trauma during the 4.5 years period were evaluated in our tertiary care center. The right knee was affected in 44 of the 100 study patients, the left knee was affected in 56, and bilateral knee injuries occurred in eight. Moreover, 70 patients were male and 30 were female. The average age of the patients was 32 years (range: 18-86 years). The most common (39.8%) injury pattern was a combined disruption of the ACL, PCL, and PLC (Figs 2 and  3). Overall, 30% of knees had associated ipsilateral tibial plateau fractures, and 20% had associated ipsilateral femoral fractures (Figs 4 and 5). Peroneal nerve injury occurred in 30% of knees, arterial injury in 20%, and compartment syndrome in 18%. The incidences of ligamentous injury based on MRI findings were as follows: ACL, 89.8% (97 of 108 extremities); PCL, 79.6% (86 of 108 extremities); PLC, 75.9% (82 extremities); and MCL, 26.8% (29 extremities). The noted injury patterns in multiligamentous knee injuries are shown in Table 5. The injury patterns associated with peroneal nerve injury are noted in Table 6. Peroneal nerve injuries were associated with PLC injuries in 87.5% of cases (28 of 32 knees). Further analysis of the specific injured structures showed that the lateral collateral ligament was involved 93.2% of the time     Table 7. Overall, 48% of patients presented with dislocated knees, which is consistent with previously reported rates of ∼50%.
Injuries to the affected extremity are shown in Table 8.

Discussion
Multiligamentous knee injuries are complex injuries that often require emergent treatment. Multiligamentous injuries have been defined as a complete cruciate tear (grade III) with a partial/ Coronal T1-weighted MRI of knee joint in a 71-year-old woman with trauma demonstrating intra-articular distal femoral fracture involving the medial condyle (arrow) with fracture line extending into the lateral condyle suggesting Hoffa fracture.      Coronal T1-weighted MRI of knee joint demonstrating a Schatzker IV tibial plateau fracture with a depressed component (arrow). complete tear of medial/lateral collateral (grade II/III) or a partial or complete tear of the other cruciate ligament (grade II or III). KDs remain the most common cause of multiligamentous injuries with various life-threatening and limb-threatening complications occurring with dislocation of the knee. Our findings suggest that multiligamentous knee injuries might be more prevalent than the 0.001-0.013%, as suggested in the literature [3].
The most important finding in this study was injuries with ACL, PCL, and PLC injuries being the commonest, constituting 39.8%, and Schenck KD III-M was the most common injury type in KDs, constituting 16.7%. The mean age at the time of injury was higher (38.5 years) than in previous studies. In our study, injuries with both cruciate ligaments torn and intact collaterals (KD II) were the least common (7.4%). Common peroneal nerve injuries were present in 29.6%, tibial plateau fractures in 29.6%, and vascular injuries in 20.3% of patients in this study. There were significantly greater odds for both common peroneal nerve injuries and popliteal artery injuries with lateralsided injuries (KD III-L). Additionally, peroneal nerve injury was significantly associated with vascular injury. Medial-sided injuries were the most common injury patterns seen with KDs. There was a significant risk of peroneal nerve injury with lateral-sided injuries. PLC injuries commonly involved popliteus-lateral collateral ligament combination in 49.4% followed by popliteuslateral collateral ligament-biceps femoris in 31.4%.
Johnson et al. [13] conducted a literature review of multiligamentous knee injuries in 2008 and found that up to 86% of KDs occur in male patients with a mean age between 30 and 32 years and that only 5% of patients present with bilateral injuries. These numbers are similar to our findings, with 70% male patients, ages averaging 32 years, and bilateral injuries present in only 8% of patients.
Robertson et al. [14], meta-analysis of previous KD studies, found that 41% of patients had ACL, PCL, and MCL injuries. Mechanisms of injury in our study were similar to those of the studies reviewed, and we found that the combined ACL-PCL-PLC injury pattern was the most prevalent (39.8%), with the ACL-PCL-MCL injury pattern accounting for only 16.7% of cases. PLC injuries might have an increased likelihood of being missed and might therefore have been underreported. PLC injuries had a high prevalence in our study and were noted in 75.9% of injured knees (82 of 108 knees) which is much higher than previously reported in the literature.
The peroneal nerve is susceptible to injury because of its relatively fixed position around the neck of the fibula. The incidence of peroneal nerve injuries occurring in association with KDs has been reported to be ∼20% [15]. Our results found a higher incidence of peroneal nerve dysfunction at 30%. Similar to our findings, Niall et al. [16], in their review of 55 patients, found associated peroneal nerve injuries in 25% of patients with KDs. In this study, peroneal nerve injuries were associated with PLC injuries in 87.5% of cases (28 of 32 knees). Bottomley et al. [17] reported that 44% of KDs with avulsion fracture of the fibular head or soft-tissue avulsion from the fibular head had associated peroneal nerve damage. Our findings show that multiligamentous knee injuries are associated with fibular head fractures and bony avulsions 22% of the time (24 of 108 extremities).
Fractures are common in association with multiligamentous knee injuries. Lustig et al. [18], in a prospective study of KDs and bicruciate knee injuries, found that 34% of patients had multiple fractures and 17% of the dislocations were associated with ipsilateral limb fracture. Overall, 25% (27/108) of the patients in our study sustained ipsilateral extremity fractures. Moreover, 29.6% of affected knees had ipsilateral tibial plateau fractures, and 20.3% had ipsilateral femoral fractures.
Initial trauma evaluation revealed that 48% of our patients presented with dislocated knees. This rate is consistent with previously reported rates of ∼50% [19]. These injuries do not always present with gross deformity, which makes understanding their mechanism and injury patterns more important.

Conclusion
Multiligamentous knee injuries should be closely evaluated at presentation and during the hospital course as they serve as a marker of concomitant trauma to allow for early intervention for limbthreatening emergencies. KDs, though rare, may have devastating clinical sequelae such as compartment syndrome if not recognized and treated. Therefore it is necessary to recognize imaging findings of femorotibial joint dislocations and associated injuries to the adjacent neurovascular bundles.

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Conflicts of interest
There are no conflicts of interest.