Disclosure Knee dislocations are uncommon. A knee dislocation is defined as complete displacement of the tibia with respect to the femur, with disruption of 3 or more of the stabilizing ligaments (Girgis, 1975). Small avulsion fractures from the ligaments and capsular insertions may be present. For excellent patient education resources, visit eMedicine's Breaks, Fractures, and Dislocations Center. Also, see eMedicine's patient education article Knee Dislocation. Frequency: The Mayo Clinic recorded 14 knee dislocations during an interval of 2 million admissions (Frassica, 1991). The largest reported series of knee dislocations is from Los Angeles County Hospital, where 53 knee dislocations were reported over a 10-year period. 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. Etiology: 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%). Pathophysiology: 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 3 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 The 5 types of knee dislocations, based on the direction of tibial displacement, are anterior, posterior, medial, lateral, and rotational (Kennedy, 1963). 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 4 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 dislocations reported. Knee dislocations can also be classified as open or closed and as reducible or irreducible. Clinical: 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 (Taylor, 1972). 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 (Zoys, 2001). Distal pulses may be absent, and an expanding hematoma, bruit, or thrill may be present in the popliteal fossa.
Emergent vascular surgery is indicated for dysvascular limbs (see Postreduction assessment). For indications for surgical repair of ligament avulsions, see Surgical options.
Relevant Anatomy: Knee anatomy relevant to dislocations is related to the 4 main ligament and neurovascular structures. The anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and posterolateral corner (lateral collateral ligament [LCL], arcuate complex, popliteus, and biceps femoris) together with the joint capsule are responsible for knee stability (Girgis, 1975). Knee dislocation requires injury to at least 3 of the 4 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 (Wood, 1991). Fractures about the knee are fairly common in knee dislocations. These can be severe periarticular fractures, commonly tibial plateau fractures (Moore, 1981) or ligamentous and tendonous avulsion fractures. Few data exist on the true incidence of these fractures, as many reports do not mention them. One unpublished study noted a 35% (8 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. Contraindications: 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 Nonsurgical management). 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). |
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Imaging Studies:
Medical 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 (Hill, 1981). 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 neurological status should be recorded again. Repeat anteroposterior and lateral radiographs are obtained to confirm reduction. If the limb is dysvascular, then emergent vascular surgery consultation should be undertaken. If the limb appears well perfused, then arteriography is recommended (McCutchan, 1989; Jones, 1979; Treiman, 1992; Kaufman, 1992).
The role of noninvasive Doppler studies has been controversial (Lynch, 1991). Cases of occult intimal injury to the popliteal artery with initial normal pulses are reported (McCutchan, 1989). The artery later underwent thrombosis with acute vascular insufficiency. The authors strongly recommend arteriograms be performed on all patients with knee dislocations, unless they have a dysvascular limb, in which case emergent vascular surgery is indicated (Kirby, 1999). 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.
Anteroposterior and lateral radiographs should be repeated in the first week to confirm reduction. We generally obtain these radiographs approximately 3 days postinjury, 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 (Thomsen, 1984). However, it is very difficult to perform a good examination acutely because of the swelling and pain of the injury (Hughston, 1985). Since many dislocations are associated with other injuries in motor vehicle accidents, opportunities are often present to examine the knee with the patient under anesthesia in the operating room for another procedure (see Image 3). Immediate diagnosis is not necessary since ligament surgery is ideally performed on an elective basis. MRI can be used to determine the extent and location of ligament disruption, meniscal tears, and subtle injuries to the bone (see Image 2). The authors obtain an MRI on 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 it is unlikely that the knee will be normal again, regardless of treatment. Knees that have dislocated are at risk for significant knee stiffness, chronic pain, arthrosis, and instability.
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, emphasizing extension (Taylor, 1972). 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. Surgical 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. Knee arthroscopy can be performed safely after 2 weeks with low pressures (gravity) only and careful monitoring of the leg.
Complications of knee dislocation include popliteal arterial injury, peroneal nerve injury, knee instability, knee arthrosis, knee stiffness, and chronic pain (Jones, 1979; Hill, 1981). After surgical intervention, complications include graft failure, infection, incisional dehiscence, knee arthrofibrosis, and the need for future surgery and/or knee manipulations.
Multiple outcome studies after surgical intervention for knee dislocation universally report that patients rarely claim that their knee function is normal. Wascher (1999) reported the 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. One patient claimed his knee felt normal, 6 patients returned to unrestricted sports activities, and 4 returned to modified sports. Shapiro (1995) reported the outcome after allograft reconstruction of the ACL and PCL after traumatic knee dislocation. Seven patients had an average of 51 months follow-up care postoperatively. Only one patient had significant pain, 3 patients had occasional or rare sensation of knee instability, and all 7 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 3, good in 3, and fair in 1 patient. Yeh (1999) reported the outcome after arthroscopic reconstruction of the PCL with open repair of collateral ligaments and capsule. Twenty-three patients had a mean follow-up care of 27 months. At latest follow-up visit, the mean knee extension was 1° and knee flexion was 129.6°.
With technology advances in Doppler imaging, controversy exists regarding the necessity of arteriograms in postreduction limbs that have normal vascular examination findings (Lynch, 1991). Some argue that unremarkable findings using Doppler obviate the need for arteriogram, which is more expensive and is associated with a low but real risk of complications (Applebaum, 1990). 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. Discussion exists regarding what type of graft is best. Since so few clinical series of knee dislocations and small numbers of patients are published, 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.
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