Knee Dislocation Surgery

Knee dislocations are uncommon.[1] A knee dislocation is defined as complete displacement of the tibia with respect to the femur (see the image below), with disruption of three or more of the stabilizing ligaments.[2, 3]  Small avulsion fractures from the ligaments and capsular insertions may be present.

Knee anatomy relevant to dislocations is related to the four main ligament and neurovascular structures. The anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL), the medial collateral ligament (MCL), and the posterolateral corner (lateral collateral ligament [LCL], arcuate complex, popliteus, and biceps femoris), together with the joint capsule, are responsible for knee stability.[2]

Knee dislocation requires injury to at least three of the four main ligaments. The popliteal artery is relatively fixed proximally as it exits a fibrous tunnel at the level of the adductor hiatus, enters the popliteal space, and then is again tethered distally under the soleus. When the knee dislocates, the popliteal artery is stretched and vulnerable to injury. Popliteal artery injury occurs in up to 53% of patients with knee dislocations.

The peroneal nerve is tethered as it winds around the fibular neck. With knee dislocation, the peroneal nerve is at risk. Peroneal nerve injury may occur in up to 23% of patients with knee dislocations. Nearly one half of the patients with peroneal nerve injuries have a permanent deficit.[4]

Fractures about the knee are fairly common in knee dislocations. These can be severe periarticular fractures, commonly tibial plateau fractures or ligamentous and tendinous avulsion fractures.[5] Few data exist on the true incidence of these fractures, in that many reports do not mention them. One unpublished study noted a 35% (eight of 23 cases) incidence of fractures associated with high-velocity knee dislocations (Owens, unpublished data, 2003). The presence of the fracture may alter management and require supplemental bony fixation or may allow ligamentous repair versus reconstruction.

Multiple ligament injuries are required for knee dislocation. Generally, both cruciates and one or both collateral ligaments are injured. However, knee dislocations have been described with one of the cruciates intact. It is important to evaluate the competence of each ligament and to consider the possibility of a knee dislocation in knees with three or more ligaments torn. Vigilance is required because of the high incidence of neurovascular injuries associated with knee dislocation (vascular injuries 5-79%, nerve injuries 16-40%).

Classification

Knee dislocations are classified into five types on the basis of the direction of tibial displacement, as follows[6] :

• Anterior
• Posterior
• Medial
• Lateral
• Rotational

An anterior knee dislocation usually results from a hyperextension injury to the knee that initially tears the posterior structures and drives the distal femur posterior to the proximal tibia. A posterior knee dislocation usually results from a direct blow to the proximal tibia that displaces the tibia posterior to the distal femur. Valgus forces cause medial dislocations. Varus forces cause lateral dislocations of the knee.

Rotational or rotatory dislocations are the result of indirect rotational forces, usually caused by the body rotating in the opposite direction of a planted foot. Rotatory dislocations can be of four different types, named for the direction of the displaced tibial plateau. For example, posterolateral rotatory dislocation describes a posterior position of the lateral tibial plateau and is the most common rotatory dislocation reported.

Knee dislocations can also be classified as either open or closed and as either reducible or irreducible.

Most knee dislocations are the result of high-energy injuries, such as motor vehicle or industrial accidents. They also can occur with low-energy injuries, such as those that occur in sports. The reported mechanisms of injury are variable, but the most common are motor vehicle accidents (50-60%), followed by falls (30%), industrial-related accidents (3-30%), and sports-related injuries (7-20%).

The Mayo Clinic recorded 14 knee dislocations during an interval of 2 million admissions.[7] In a large series from Los Angeles County Hospital, 53 knee dislocations were reported over a 10-year period. A study from Finland reported 837 knee dislcoations over a period of 14 years and found the incidence to be highest in men aged 18 to 29 years (29 dislocations per 1 million person-years in 2011).[8]

The true incidence of knee dislocations is higher than reported because as many as 50% of knee dislocations spontaneously reduce before patients present to the emergency department.

Multiple outcome studies after surgical intervention for knee dislocation universally report that patients rarely claim that their knee function is normal.[9, 10]  Wascher reported results after ACL reconstruction, PCL reconstruction, or both in 13 patients with knee dislocations, and results after a mean of 38 months follow-up care.[11]  One patient claimed his knee felt normal, six returned to unrestricted sports activities, and four returned to modified sports.

Shapiro reported the outcome after allograft reconstruction of the ACL and PCL after traumatic knee dislocation.[12]  Seven patients had an average of 51 months follow-up care postoperatively. Only one patient had significant pain, three had occasional or rare sensations of knee instability, and all seven were able to return to work or school. Four patients required knee manipulation at an average of 16.8 weeks postoperatively for knee arthrofibrosis. The functional grading was excellent in three, good in three, and fair in one.

Yeh reported the outcome after arthroscopic reconstruction of the PCL with open repair of collateral ligaments and capsule in 23 patietns followed for a mean of 27 months.[13]  At the latest follow-up visit, the mean knee extension was 1° and knee flexion was 129.6°.

In isolated knee dislocations, patients are usually able to describe the mechanism of injury and the intense pain associated with dislocation. Since many of these injuries are high-energy motor vehicle collisions, evaluation for life-threatening injuries is the first priority.[14]

In the secondary survey, evaluation of the limb usually reveals an obvious deformity of the knee. The appearance of knee dislocations may be less dramatic in individuals who are obese. The limb should be examined thoroughly for pulses, capillary refill, sensation, and motor strength. Vascular compromise may present as a stocking-glove type distribution of hypesthesia or anesthesia, decreased capillary refill, cyanosis, and poikilothermia.[15]  Distal pulses may be absent, and an expanding hematoma, bruit, or thrill may be present in the popliteal fossa.

Standard anteroposterior (AP) and lateral radiographs can be obtained to detect a knee dislocation (see the image below).[16]  After reduction, repeat AP and lateral radiographs are obtained to confirm reduction. Oblique views after reduction may delineate small avulsion or rim fractures and osteochondral fractures.[17]

With technological advances in Doppler imaging, the need for arteriography in postreduction limbs that have normal vascular examination findings is controversial.[18]  Some argue that unremarkable findings on Doppler obviate the need for arteriography, which is more expensive and is associated with a low but real risk of complications.[19]  The authors had a patient who was discharged home 2 days after initial unremarkable findings on arterial Doppler study and returned the next day with an acute occlusion of the popliteal artery from an intimal flap. The authors continue to strongly recommend routine arteriography in these cases.

For ligament injuries of the knee, magnetic resonance imaging (MRI) can be used to assess the extent and location of ligament disruption, meniscal tears, and subtle injuries to the bone, as well as to determine which tears are repairable.[20, 21]

Emergency vascular surgery is indicated for limbs that are dysvascular after reduction. For indications for surgical repair of ligament avulsions, see Surgical Therapy.

Nonsurgical management is recommended in patients who have low functional demands or cannot cooperate with postoperative rehabilitation, such as those with significant closed head injuries (see Nonoperative Therapy).

Knee arthroscopy is contraindicated within 2 weeks of knee dislocations because capsular tears cause fluid extravasations into the leg that may result in compartment syndrome (see Surgical Therapy).

Reduction

After evaluation, closed reduction should be performed expeditiously. Reduction is performed by stabilizing the distal femur and applying longitudinal traction on the tibia and reversing the direction of the dislocation. The knee should reduce easily with a satisfactory clunk. Neither the physician nor the assistant should apply any pressure over the popliteal fossa during the reduction, to lessen the risk of additional injury to the popliteal artery.

A medial skin furrow is indicative of a posterior lateral dislocation, with the medial femoral condyle buttonholed through the capsule or extensor mechanism.[22] This is usually irreducible by closed means. Gentle longitudinal traction should be applied. If the furrow appears to deepen with traction, an open reduction should be performed promptly. After reduction, the knee should be immobilized in 15-20° of flexion in a knee immobilizer. A Jones dressing can be applied after arteriogram.

Postreduction assessment

After reduction, vascular and neurologic status should be recorded again. Repeat anteroposterior (AP) and lateral radiographs are obtained to confirm reduction. If the limb is dysvascular, an emergency vascular surgery consultation should be obtained. If the limb appears well perfused, then arteriography is recommended.[23, 24, 17, 25]

The role of noninvasive Doppler studies has been controversial.[18] Occult intimal injury to the popliteal artery with initially normal pulses has been reported.[24] The artery later underwent thrombosis with acute vascular insufficiency. The authors strongly recommend that arteriography be performed on all patients with knee dislocations, unless they have a dysvascular limb, in which case emergency vascular surgery is indicated.[26, 27, 28]

Best results are obtained if vascular repair is performed within 6-8 hours of the time of injury. Vascular repairs within 6 hours still have resulted in an 11% amputation rate. Vascular repair after 8 hours resulted in an 86% amputation rate.

AP and lateral radiographs should be repeated in the first week to confirm reduction. The authors generally obtain these radiographs approximately 3 days post injury, after the knee is placed in a hinged knee brace locked in extension. The films should be scrutinized for tibial subluxation, particularly in the posterior direction. If subluxation is present, external fixation should be considered.

Evaluation of knee ligamentous injury

Although many ligament injuries can be deduced from the mechanism of injury and direction of dislocation, stability is best determined with physical examination.[29] However, it is very difficult to perform a good examination acutely because of the swelling and pain of the injury.[30]

Given that many dislocations are associated with other injuries in motor vehicle accidents, opportunities are often available to examine the knee with the patient under anesthesia in the operating room for another procedure (see the image below). Immediate diagnosis is not necessary, because ligament surgery ideally is performed on an elective basis.

Magnetic resonance imaging (MRI) can be used to determine the extent and location of ligament disruption, meniscal tears, and subtle injuries to the bone[31] (see the image below). The authors perform MRI in all patients on an elective basis within the first week after injury.

It is important to stress to the patient and the family that a knee dislocation is a devastating injury and that the knee is unlikely to be normal again, regardless of treatment. Knees that have dislocated are at risk for significant knee stiffness, chronic pain, arthrosis, and instability.

Indications for nonsurgical management

Nonsurgical management is recommended in patients who have low functional demands or cannot cooperate with postoperative rehabilitation (eg, patients with significant closed head injuries). These patients can initially be treated with a knee immobilizer and Jones dressing and, when swelling diminishes, converted to a hinged knee brace locked in extension. The brace can be unlocked when good quadriceps control is achieved.

Rehabilitation continues to maintain range of motion (ROM), emphasizing extension.[14] If tolerated, gentle active and active-assisted flexion is performed in the prone position for 2 months to minimize posterior tibial sag. Strengthening begins with isometric hamstring and quadriceps cocontraction and progresses to isotonic exercises.

Knee arthroscopy is contraindicated within 2 weeks of knee dislocations because capsular tears cause fluid extravasations into the leg that may result in compartment syndrome. Knee arthroscopy can be performed safely after 2 weeks with low pressures (gravity) only and careful monitoring of the leg.

Surgical options

Acute repair can be performed within weeks of injury, and direct repair of ligament avulsions may lead to better results than reconstructive procedures. MRI helps determine where the tear is located and which tears are repairable.

Generally, posterolateral corner injuries are repaired acutely because reconstructions are less successful.[32] Midsubstance tears of the medial collateral ligament (MCL) are not repaired acutely, because a high percentage may heal with conservative treatment. Midsubstance tears of the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) are usually reconstructed later.

MCL and lateral colalteral ligament (LCL) avulsions can be repaired primarily with suture or screws with a soft-tissue washer if an avulsion from the origin or insertion is present. ACL and PCL avulsions from their femoral or tibial origins can be repaired primarily in a similar fashion, but midsubstance tears should not be repaired primarily. Meniscal tears can also be addressed with primary repair to the capsule, with or without partial meniscectomy.

Discussion continues on which type of graft is best. Because so few clinical series of knee dislocations have been published, and such small numbers of patients have been reported, scientific data are insufficient to recommend one graft type over another.

Because of the extent of trauma to a dislocated knee, the authors have been reluctant to harvest tissue from the same knee. The authors recommend patellar tendon allograft, which can be split to perform both ACL and PCL reconstruction with exposure to a single donor. In those patients who are uncomfortable with cadaver tissue, the authors recommend harvesting contralateral central third quadriceps and patellar tendon for PCL and ACL reconstruction, respectively.

Timing of surgery

Ideally, ligament repair should be performed within 3 weeks after injury because scar formation makes later operations more difficult. It is prudent to delay surgical intervention until the skin and soft tissues have recovered from the initial insult (usually 1-2 weeks later). Rehabilitation should begin as though patients were going to be treated nonoperatively.

Timing of ligament reconstruction is somewhat controversial, with some surgeons advocating early reconstruction. Delayed reconstruction is often preferred to allow rehabilitation of the knee and to increase the range of motion preoperatively; if the patient complains of knee instability, then reconstruction of the ACL, PCL, and MCL can be performed. Again, the reconstruction of the ligaments can be performed with autografts, allografts, or a combination of both.[12, 11, 13] Generally, all the ligament reconstructions are performed in one operation; staged operations have not demonstrated superior results.[33, 34] Delayed reconstruction is an option for patients who may not be candidates for acute repair.

The optimal repair sequence is controversial. Some advocate first reconstructing the PCL and repairing the posterolateral corner. Then, at a later time, the ACL can be reconstructed, if necessary. Some believe that posterolateral corner repairs should not be performed without simultaneous PCL reconstruction. Most surgeons favor early posterolateral corner repair since repairs have better results than late reconstructions.

The authors advocate delayed ligament surgery on those patients who do not have a posterolateral corner injury. In patients with posterolateral corner tears and significant posterior sag on lateral radiograph in a hinged knee brace locked in full extension, the authors reconstruct the PCL at the time of the posterolateral corner repair. Rehabilitation generally takes longer than that for a single- or double-ligament tear to the knee because of the severity of the injury. The authors have found that most patients are ready for cruciate ligament reconstruction by 3 months.

Preparation for surgery

Before any surgical intervention for ligament repair or reconstruction, ensure that the skin condition is optimized. Any abrasions or lacerations should receive local wound care. Consider a plastic surgery consultation in injuries with tissue loss. If necessary, delay surgery until the skin is healed. An operative strategy based on the surgeon's experience and preference is critical to optimize results and decrease complications.[35] Many different sequences and techniques have been advocated, but few data are available to allow objective comparison of their results.

Operative details

The authors prefer an acute repair of the posterolateral corner. The peroneal nerve is identified at the fibular neck and traced proximally, so that it can be protected throughout the surgery. After identifying the location of injury of each of the posterolateral structures, repair proceeds from deep to superficial.

Repairing or reconstructing the popliteus tendon is important. The popliteus tendon is usually torn from its femoral attachment or midsubstance and can be repaired with nonabsorbable suture, with or without a suture anchor. The lateral capsule is often peeled off the tibia and can be repaired with transosseous sutures or suture anchors approximately 1 cm below the joint line. The arcuate complex, LCL, and biceps femoris can be repaired as a unit if avulsed together off the fibular head. They can be repaired safely together or separately through drill holes in the fibular head if the peroneal nerve is protected. The most superficial structure, the iliotibial band (ITB), is repaired last.

The wound is closed over a small Hemovac drain, which is removed the following day.

An important aspect of knee dislocation surgery is postoperative rehabilitation.[36] After a posterolateral corner repair, the knee is placed in a Jones dressing and the knee brace is locked at 30° for 2 weeks to promote wound healing and to minimize stress on the peroneal nerve and popliteal artery. Active quadriceps exercises are begun immediately.

Early protected range of motion is important to prevent arthrofibrosis.[36] When both cruciates are torn, knee flexion is performed in the prone position to minimize the posterior tibial sag.

Complications of knee dislocation include the following[22, 23] :

• Popliteal artery injury
• Peroneal nerve injury
• Knee instability
• Knee arthrosis
• Knee stiffness
• Chronic pain

After surgical intervention, complications include graft failure, infection, incisional dehiscence, knee arthrofibrosis, and the need for future surgery or knee manipulations.[37] In a 2014 study, Whelan et al found posterior cruciate ligament reconstruction to be an independent risk factor for the development of heterotopic ossification after knee dislocation surgery.[38]