Multiligamentous injury/Dislocation of the knee

          Multiligamentous injury/Dislocation of the knee
                                                           

                                                  Dr KS Dhillon

Introduction

There are 4 main ligaments which stabilize the knee, namely the extra-articular collateral ligament and the intra articular cruciate ligaments. The structures in the posterolateral and posteromedial corner also contribute joint stability.

When two or more of these are disrupted, the term multiligament injury is used. With such disruptions a knee dislocation or a substantial subluxation will occur.

Multiligament knee injuries are potentially devastating. Fortunately these injuries are uncommon. The estimated prevalence of multiligamentous knee injuries is about 0.02% to 0.2% of all orthopaedic injuries. The most common type of dislocation is anterior and/or posterior dislocation.
Knee dislocations are often associated with vascular and nerve injuries besides soft tissue injuries and fractures.

There are no guidelines and consensus regarding the best way to treat these injuries. The outcome of treatment is getting better over the years and the number of devastating complications is getting less.
This article will review the anatomy of the knee stabilizer, classification of knee dislocation, diagnosis, treatment and complications associated with knee dislocation and multiligamentous injury to the knee.

Anatomy of knee ligaments

There are 4 main ligaments that stabilize the knee. Two of them are intra-articular and two are extra-articular. The extra-articular ligaments include the medial and lateral collateral ligaments and the intra-articular include the anterior and posterior cruciate ligaments.

The anterior cruciate ligament (ACL) is an intracapsular but extrasynovial structure that consists of 2 bundles, the posterolateral (PL) and the anterolateral (AL) bundle. It arises from the lateral femoral condyle in the intercondylar notch with the PL bundle originating posterior and distal to the AL bundle. The insertion on the tibia is broad and irregular, anterior to and between the intercondylar eminence. The AL fibres are tight in flexion and extension while th PL fibres are tight in extension and loose in flexion. The Pl fibres prevent pivot shift of the tibia. The blood supply is from the middle geniculate artery and the innervation is from the posterior articular branches of tibial nerve. Its function is to prevent anterior translation of the tibia on the the femur.

 The posterior cruciate ligament is also intra-articular and extrasynovial. It arise from the medial femoral condyle and inserts on the  tibial sulcus and consists of two bundles.  The shorter, thicker and stronger anterolateral and the longer, thinner and weaker posteromedial bundle. Its blood supply is  middle geniculate artery. It prevents posterior translation of the tibia on the femur. 

The medial collateral ligament (MCL) arises from the medial femoral condyle and inserts on the medial side of the tibia. It consists of two components, the superficial and deep components. The superficial component arises from the medial femoral epicondyle and lies deep to gracilis and semitendinosus and inserts into the periosteum of the medial proximal tibia deep to the Pes Anserinus. The deep portion (medial capsular ligament) attaches to the medial meniscus and divides into the meniscofemoral and meniscotibial portions. It is separated from the superficial ligament by a bursa. The posterior fibres blend with the posterior capsule.

The MCL resists valgus angulation and the superficial portion contributes 57% and 78% of medial stability at 5 degrees and 25 degrees of knee flexion, respectively.

The lateral collateral ligament (LCL) also known as the fibular collateral ligament originates at the lateral femoral condyle posterior and superior to insertion of popliteus, runs superficial to the popliteus and inserts on the fibula anterior to the popliteofibular ligament on the fibula.
It resists varus angulation and is tight in extension and lax in flexion.                           

Structures in the Posterolateral corner (PLC) and the Posteromedial corner (PMC) also contribute to stability of the knee. The components of PLC include the LCL, Popliteus muscle and tendon, popliteofibular ligament and the lateral capsule. There is variable contribution from the arcuate ligament, iliotibial band and the fabellofibular ligament. The PLC works synergistically with the PCL to control external rotation and posterior translation.

The Posteromedial corner structures lie deep to the MCL and include the
insertion of semimembranosus, posterior oblique ligament, oblique popliteal ligament and the posterior capsule. They provide important rotatory stability.
The MCL has the strongest tensile strength at 4000N, followed by PCL 2500 N, the ACL 2200 N, and the LCL at 750 N.

Multiligament knee injury

The main ligamentous structures that stabilize the knee are the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), lateral collateral ligament and posterolateral corner, and medial collateral ligament and posteromedial corner. When two or more of these are disrupted, the term multiligament injury is used. With such disruptions a knee dislocation or a substantial subluxation will occur.

Often the terms multiligamentous knee injury and knee dislocation are interchangeably used. In some knee dislocation spontaneous reduction occur and the injury gets labelled as multiligamentous injury. One of the most frequently used anatomical classification of knee dislocation is the one by Schenck [1] which was modified by Wascher [2].

Schenck classification of knee dislocation

         KD I          Injury to single cruciate + collaterals
         KD II         Injury to ACL and PCL with intact collaterals
         KD III M    Injury to ACL, PCL, MCL
         KD III L     Injury to ACL, PCL, FCL
         KD IV        Injury to ACL, PCL, MCL, FCL
         KD V         Dislocation + fracture

“C” and “N” caps are used for associated injuries. “C” = arterial injury.
“N”=  neural injury, either tibial or the peroneal nerve. ACL= anterior cruciate ligament; FCL= fibular collateral ligament; KD= Knee Dislocation, Classification I–V; MCL= medial collateral ligament.

Prevalence of multiligamentous injuries

Multiligament knee injuries are potentially devastating. Fortunately these injuries are uncommon. The estimated prevalence of multiligamentous knee injuries is about 0.02% to 0.2% of all orthopaedic injuries [3,4].

The most common type of dislocation is anterior and/or posterior dislocation. Green and Allen [5] reported a 31% incidence of anterior dislocation, 25% posterior, and 3% rotatory dislocation. Frassica et al [6] reported a 70% incidence of posterior dislocation, 25% anterior, and 5% rotatory dislocations. Rotatory dislocations are least common and of the rotatory dislocation, posterolateral dislocation is the most common. Frequently this type of dislocation is irreducible by close means because the medial femoral condyle button-holes through the anteromedial capsule.
Most of the knee dislocations are close dislocations. The incidence of open dislocation varies between 19% and 35% of all dislocations [7,8]. Open dislocations usually carry a worse prognosis.

Associated injuries

1.Vascular injury

The incidence of vascular injury with knee dislocations has been estimated to be around 32% [5]. The incidence is about 50% with anterior and posterior dislocation [9]. There are two mechanisms of injury to the popliteal artery. One is stretching leading to rupture due to hyperextension of the knee. Stretching leading to rupture occurs because the artery is relatively fixed, proximally at the adductor hiatus and distally at tendinous arch of the gastrocnemius-soleus complex. Such injury is usually seen in anterior dislocation of the knee.

The other mechanism of injury is a direct contusion of the artery by the posterior tibial plateau in patients with posterior dislocation of the knee. Direct contusion leads to intimal damage with thrombus formation hours or days after the dislocation. Hence the initially examination may be normal [10]. In patients with bicruciate ligament ruptures the dislocation can reduce spontaneously but the incidence of arterial injury can be high [11].

Prolonged obstruction of the popliteal artery, which is an “end-artery” to the leg, with minimal collateral circulation through the genicular arteries, can lead to ischemia and eventual amputation of the limb [12].

Injury to the popliteal vein is less common. Any obstruction to blood flow in the vein is treated by surgical repair of the vein. Lacerations can be be closed successfully by lateral suture. If a repair will cause stenosis, then autogenous venous tissue can be used as a patch graft in the lateral suture repair.  A transected vein where adequate length remains, an end-to-end venous anastomosis can be carried out [13].



2.Nerve injury

Knee dislocations can be associated with an injury to the peroneal nerve or the tibial nerve. The incidence of nerve injury is about 20% to 30% [14] which is lower than the incidence of vascular injury. This is probably because the nerves are not as tightly anchored around the knee as the blood vessels.The peroneal nerve is more often injured than the tibial nerve. Posterior dislocation is more commonly associated nerve injuries [15].

3.Associated fractures

Since dislocations of the knee are often due to high energy trauma, fractures around the knee are commonly seen with knee dislocation. The incidence of associated fracture is around 60% [16]. Fractures of the tibial plateau and ligament avulsion fractures of the proximal tibia and distal femur are commonly seen.

4. Soft tissue injury

Besides the ligament injury, a dislocation of the knee can cause injuries to the menisci. Forty-one to 44% of patients with knee dislocation have been found to have a medial meniscal tear [17,18].

Diagnosis of multiligamentous injury

The clinical presentation would include a history of knee trauma and knee pain with or without deformity. About 50% of the dislocations reduce spontaneously, hence there maybe no deformity on presentation.In the other 50% there will be an obvious deformity of the knee. When there is a deformity an immediate reduction is carried out except when there is a ‘dimple sign’ present. A ‘dimple sign’ indicates buttonholing of medial femoral condyle through medial capsule seen in posterolateral dislocations. Close reduction in such a situation will lead to skin necrosis and is a contraindication to closed reduction.

Clinical examination will show anteroposterior, mediolateral or rotatory instability. Neurovascular examination is important with vascular examination receiving the top priority. After reduction, if the pulses are absent or diminished an immediate exploration and vascular repair is indicated. Ischemia time of more than 8 hours is associated with amputation rates of about 86% [19].
If the pulses are present and normal than the Ankle-Brachial Index (ABI) should be measured. If the ABI is more than 0.9, then monitor with serial examination. If the ABI is less than 0.9, an arterial duplex ultrasound or CT angiography is done. If arterial injury is present vascular surgery would be indicated.

Imaging studies

Before close reduction of the knee dislocation, plain anterior posterior and lateral radiographs of the knee are taken which will show the direction of the dislocation and also show associated fracture. The radiographs will aid in close manipulation and reduction of the knee dislocation. If there is evidence of arterial injury, an angiogram would be indicated. Any obstruction to venous outflow would mean the need for venography. After stabilization of the patient and after initially treatment of the dislocation, a MRI of the knee has to be done for further management of the injuries to the knee. MRI is useful in detecting damage to the ligaments and to assess meniscal as well as cartilage injury.
It is however a static study which cannot demonstrate the functional status of the injured ligament. A stress radiograph is more useful to assess the functional status of the ligaments of the knee [20].

Treatment of knee dislocation

Close reduction

A dislocated knee is an orthopaedic emergency and close reduction should be carried out in the emergency department after x rays have been done. The manipulation of the knee is done under conscious sedation and analgesia, by slow gradual leg traction applied at the ankle, while appropriate manipulation of the proximal tibia is carried. Once the dislocation has been reduced, neurovascular examination has to carried out. The limb is than placed in either a long leg splint or knee immobilizer. Post-reduction x rays are than performed to ensure that the reduction has been achieved. The presences of a ‘dimple sign’ would be a contraindication for a close reduction, because close reduction may lead to skin necrosis.

Urgent operative intervention

Urgent surgical intervention with external fixation is indicated, in patients where vascular repair has been undertaken and in patients with open dislocation, open fracture dislocation, irreducible dislocation, compartment syndrome, in patients with multiple trauma and also in patients where the reduction cannot be maintained.
Four-compartment fasciotomy is usually carried out when the ischemia time is more than 2.5 hours and when there is a compartment syndrome [14].

Definitive treatment of knee dislocation

Historically, knee dislocations were treated conservatively with a plaster cast or a brace for varying periods of time [21]. Favourable results with non-operative treatment have been reported in the past [22-25]. The trend nowadays favours surgical stabilization of the dislocated knee [26-30]. There, however, are no high-quality studies to guide treatment. There are no prospective randomized trials comparing nonoperative with operative treatment of patients with dislocation of the knee.

Levy et al [28] did a systematic review of the literature to compare the outcome of nonoperative versus operative treatment of knee dislocations. Their review suggests that ‘early operative treatment of the multiligament-injured knee yields improved functional and clinical outcomes compared with nonoperative management or delayed surgery’. There were only 4 studies comparing operative versus nonoperative treatment. The review had limitation, which included a lack of uniform outcome measures which made comparisons difficult.

Almekinders and Logan [31] did a comparison between patients treated conservatively and those treated surgically and found that the outcome was comparable. Although the outcome was comparable, the conservatively treated knees had gross ligament instability compared to the surgically stabilize knees. This is the basis on which most surgeons recommend surgical stabilization of the knee in patients with knee dislocation.

Dedmond and Almekinders [32]  carried out a meta-analysis to determine whether operative or nonoperative treatment had better outcomes after knee dislocation. Their analysis evaluated 132 knee dislocations treated surgically and 74 treated nonsurgically. They found no significant difference in the patients ‘ability to return to preinjury employment or athletic activity or in the amount of instability between the two groups’. They also found that significant disability is still possible after successful surgical treatment.

There are several authors who have showed improved ability to return
to sporting activities among patients who had surgical repair or reconstruction [33,34].
Although the the outcomes of surgically treated knee dislocations have improved, persistent pain, postoperative stiffness and the inability to return to the preoperative activity level continue to be a serious concern [35].

Timing of surgical intervention

There are some controversies about when to do surgical intervention after a knee dislocation. When intervention is in the first 3 weeks it is usually referred to as acute intervention and delayed intervention when it is after 3 weeks [36]. The presences of open injuries, vascular injuries, life threatening injuries and knee instability after close reduction would demand acute intervention. Despite the concerns about joint stiffness and loss of motion after acute intervention, many authors have reported good subjective and objective outcomes after acute repair and reconstruction of ligaments [27,28,37,38,39].

Harner et al [27] reported better subjective outcome scores and improved stability in patients with acute surgical reconstruction as compared to patients who had delayed surgical intervention.
Mook et al [40] did a systematic review of the literature to determine whether early, late, or staged operative treatment produced better outcomes. They found that delayed surgical intervention could potentially lead to stability equivalent to acute surgical management. Acute surgery is often associated with range of motion deficits. Early mobility after acute surgery produces fewer range-of-motion deficits but did not reduce the rate of follow-up manipulation or arthrolysis. Staged procedures may produce better subjective outcome and less range of motion deficits but did not reduce the need for follow up surgery for joint stiffness. Patients who had delayed surgical intervention did not need further intervention for knee stiffness.

Spontaneous healing periarticular ligaments and other soft tissues is well known. The medial and lateral collateral ligaments can heal spontaneously. Spontaneous healing of the PCL [41] and the ACL [42] has been reported. There may be a case for initially conservative treatment of multi-ligamentous injuries and a delayed repair/reconstruction of ligaments if there remains persistent symptomatic ligament laxity.

There are no standard guidelines for treatment of ligament injury after knee dislocation. Treatment has to be tailored to the requirements for an individual patient.

Complications

Complications associated with knee dislocation includes:

• Arthrofibrosis (stiffness) is the most common complication (38%), often seen delayed with delayed mobilization
• Laxity and instability (37%)
• Peroneal nerve injury (25%) which is most often with posterolateral dislocations. The results are poor with acute, subacute, and even delayed (>3 months) nerve exploration. Neurolysis and tendon transfers are the usual mode of treatment.
• Vascular compromise. Beside damage to the vessel, claudication, skin changes, and muscle atrophy can also be seen. Limb amputation and death are less common now with prompt recognition and treatment of complication.
• Deep venous thrombosis has also been associated with knee dislocations [43] .
• Acute compartment syndrome, which often necessitates a fasciotomy [44].
• Posttraumatic osteoarthritis is reported in 29.6% to 53% of knees [45]
• Postoperative infections range from 0% to 17.4% [45].

Conclusions

Dislocations of the knee are rare injuries and an orthopaedic surgeon would see a very limited number of cases in his career. They represent a complex and challenging clinical problem. Failure to recognize and treat the injuries which occur with knee dislocation can have devastating outcome especially if vascular injury is missed or there is a delay in detecting it.

There is no consensus regarding the best way to treat the ligament injuries in patients with knee dislocations. This is due to the fact that there are no prospective randomized controlled trials comparing nonoperative with operative treatment of patients with dislocation of the knee. This may in part be due to the rarity of such injuries. Treatment has to be tailored to the needs of the individual patient. On a positive note the outcome of treatment appears to be improving over the years. The number of devastating complications such as death and amputations are also getting rarer.

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