INTRODUCTION — Dislocations of the tibiofemoral joint of the knee are true surgical emergencies. Without rapid identification and repair, associated vascular injuries may jeopardize the leg [1,2]. Immediate reduction followed by careful neurovascular assessment is necessary.
This topic will review the mechanisms and management of acute tibiofemoral dislocations. Patellar dislocations and procedural sedation for the performance of joint reduction is discussed separately. (See "Recognition and initial management of patellar dislocations" and "Procedural sedation in adults in the emergency department: General considerations, preparation, monitoring, and mitigating complications" and "Procedural sedation in children: Approach".)
ANATOMY — The anatomy of the knee is discussed separately; elements of special relevance to tibiofemoral dislocation are reviewed here. (See "Physical examination of the knee", section on 'Anatomy'.)
The four major ligaments responsible for maintaining the stability of the knee are the anterior cruciate, posterior cruciate, medial collateral, and lateral collateral ligaments (picture 1 and figure 1 and picture 2). Tibiofemoral dislocations cause injuries to multiple ligaments. Usually both cruciate ligaments and one or both of the collateral ligaments are injured.
The popliteal artery is the continuation of the femoral artery. It originates at the tendinous hiatus of the adductor magnus muscle, which firmly anchors it to the femoral shaft (picture 3 and image 1). Within the popliteal space, the artery gives off five branches which arise above and below the knee joint creating a collateral system about the knee. Distally, the popliteal artery is held firmly against the bone by the tendinous arch of the soleus muscle. Thus, the popliteal artery is tethered across the popliteal space like a bowstring, making it susceptible to injury during knee dislocation . Up to 40 percent of patients with knee dislocations sustain an associated vascular injury .
The peroneal nerve winds around the fibular neck. It provides sensation to the dorsum of the foot and controls ankle dorsiflexion. The peroneal nerve is injured in up to 23 percent of patients with knee dislocations .
CLINICAL PRESENTATION AND MECHANISM OF INJURY — Tibiofemoral dislocations, although infrequent, are potentially limb-threatening injuries. They are often caused by high energy trauma (eg, motor vehicle collision) and involve injuries to multiple knee ligaments [6-11], but may also occur following falls to the ground . An algorithm for the management of tibiofemoral joint dislocation is provided (algorithm 1).
Many tibiofemoral dislocations are clinically obvious given the history of acute trauma and the abnormal position of the knee. Often a significant hemarthrosis and ecchymosis are present. Pain and swelling often limit the physical examination at the initial presentation, but a clinical assessment of the direction of dislocation can be made. The "dimple sign" is a transverse groove in the skin at the medial joint line caused by invagination of a portion of the medial capsule (picture 4) [13,14]. When present, the “dimple sign indicates a posterolateral knee dislocation that cannot be manually reduced.
It is important to note that a significant number of dislocations spontaneously reduce prior to medical evaluation, in which case the diagnosis can be difficult [1,11,15]. Limb-threatening vascular injuries following knee dislocation have been misdiagnosed as compartment syndrome or missed altogether for this reason [16,17].
Therefore, it is important to inquire about the mechanism and the position of the leg immediately following the injury, and whether it changed subsequently. Assess distal and popliteal pulses, motor function, and sensation of the lower extremity. To the degree possible given patient discomfort, evaluate the structural integrity of each knee ligament. The knee examination is described separately. (See "Physical examination of the knee", section on 'Anatomy'.)
The diagnosis of tibiofemoral dislocation should be assumed whenever gross instability of the knee is detected, regardless of the absence of obvious deformity, particularly following trauma of any kind . Hyperextension of the knee (>30 degrees) when the leg is lifted by the heel suggests gross instability .
Tibiofemoral dislocations are defined by displacement of the tibia with respect to the femoral condyles. There are five main types, of which posterior and anterior dislocations are the most common [2-4,19]:
●Posterior – Result from a direct blow to the proximal tibia that displaces it posterior to the distal femur.
●Anterior – Result from a hyperextension injury to the knee that tears the posterior structures and drives the distal femur posterior to the proximal tibia.
●Medial – Result from valgus forces to the proximal tibia.
●Lateral – Result from varus forces to the proximal tibia.
●Rotatory – Result from indirect rotational forces, usually caused by the body rotating in the opposite direction of a planted foot. Rotatory dislocations are subdivided into anteromedial, anterolateral, posteromedial, and posterolateral. Posterolateral dislocations are irreducible by closed reduction. (See 'Contraindications and precautions' below.)
Dislocations are also classified as open or closed, based upon the presence or absence of lacerations at the knee joint, and as reducible or irreducible. Irreducible injuries are rare, and opinions vary as to the best treatment.
Many knee dislocations are the result of high-energy injuries [6,8,20]. The most common reported mechanisms are motor vehicle accidents, falls, industrial accidents, and sports-related injuries. Both contact and high velocity (eg, downhill skiing) sports may result in such injuries. Knee dislocations may also occur from low-energy trauma . The risk for these injuries appears higher in obese individuals [21-23], and the possibility of associated neurovascular injury persists.
Contraindications and precautions — Posterolateral dislocations are irreducible by closed reduction. Reduction is prevented because the medial femoral condyle is buttonholed through the medial capsule and the medial collateral ligament is invaginated into the joint . The presence of an anteromedial skin furrow indicates a posterolateral dislocation. If the furrow deepens when gentle longitudinal traction is applied, an open reduction should be performed promptly .
Analgesia and sedation — Provide appropriate analgesia. Generally this means procedural sedation, which is discussed separately. There are no reports of intraarticular injection for analgesia. (See "Procedural sedation in adults in the emergency department: General considerations, preparation, monitoring, and mitigating complications" and "Procedural sedation in children: Approach".)
Method of reduction — Closed reduction of the dislocated knee should be performed immediately and must not be delayed if there is any sign of vascular impairment. Only patients with good peripheral pulses may undergo prereduction imaging .
Generally two clinicians are required to reduce the knee. The procedure is performed as follows:
●One clinician stabilizes the distal femur; the other grasps the tibia.
●Apply longitudinal traction to the tibia (often longitudinal traction is all that is required with severe ligamentous disruption).
●If traction alone is unsuccessful, reverse the direction of the dislocation. As examples, for an anterior dislocation, lift the distal femur anteriorly and push the tibia posteriorly; for a posterior dislocation, do the opposite. For medial rotatory dislocations, rotate the tibia laterally.
For isolated anterior or posterior dislocations, the knee should reduce easily with a satisfactory clunk. Special care should be taken to avoid applying any pressure at the popliteal fossa during reduction to avoid further injury to the popliteal artery . Emergency (ie, immediate) orthopedic consultation is necessary if the knee cannot be reduced.
Initial care and evaluation — Immediately after the tibiofemoral joint is reduced, look closely for signs of vascular injury. An algorithm for the management of tibiofemoral joint dislocation is provided (algorithm 1).
Meticulous evaluation of the extremity's circulatory status includes palpating the distal and popliteal pulses, measuring an ankle-brachial index (ABI), and performing a screening duplex ultrasound, if available. Obtain emergency (ie, immediate) bedside consultation by a vascular surgeon if the limb manifests ANY sign of vascular compromise . Such signs may include diminished or absent pulses, pale or dusky skin, paresthesias, and paralysis. (See "Clinical features and diagnosis of acute lower extremity ischemia".)
The ABI is a ratio of measurements of upper and lower extremity perfusion that is calculated using the systolic blood pressure in the brachial, posterior tibial, and dorsalis pedis arteries. In one prospective series of 38 patients with acute knee dislocation, no patient with an ABI of 0.9 or above sustained an arterial injury while every patient with an ABI below 0.9 did . The performance and interpretation of the ABI is discussed separately. (See "Noninvasive diagnosis of upper and lower extremity arterial disease", section on 'Ankle-brachial index'.)
Once the examination is complete, immobilize the knee in 15 to 20 degrees of flexion using a knee immobilizer.
The vascular examination following a tibiofemoral dislocation is of limited accuracy and fraught with potential pitfalls. For these reasons and because many emergency clinicians will not have experience with these uncommon but potentially limb-threatening injuries, it is best to follow a management protocol, such as the one provided (algorithm 1) [16,30].
The pulse examination has limited accuracy in the setting of traumatic knee dislocation. According to a metaanalysis of seven studies including 284 dislocations, the finding of abnormal pedal pulses has a sensitivity of 0.79 (95% CI 0.64-0.83), specificity of 0.91 (95% CI 0.78-0.96), positive predictive value of 0.75 (95% CI 0.61-0.83), and a negative predictive value of 0.93 (95% CI 0.85-0.96) .
Other elements of the physical examination are likewise limited. The degree of initial deformity cannot be used as an indication of the likelihood of injury to the popliteal vasculature . The presence of warm skin over the dorsum of the foot and toes has been reported in the presence of complete popliteal arterial occlusion and cannot be considered evidence of an intact blood supply. Perhaps most importantly, the presence of full dorsalis pedis and posterior tibial pulses following reduction does NOT invariably mean that the popliteal vessels are free of injury . Contusions of the popliteal artery or severe injury to the intimal and medial layers without loss of continuity is a common consequence of traction injury and can lead to thrombus formation within hours to several days.
Approaches to imaging of the lower extremity vasculature following knee dislocation vary. We suggest a selective approach based upon the clinical evaluation (algorithm 1). However, at some trauma centers, imaging of the lower extremity arteries is performed on all patients with tibiofemoral dislocation due to the limitations of the physical examination.
In either case, consult vascular surgery immediately should any arterial injury be identified. For patients without apparent vascular injury at the time of the initial evaluation, close surveillance, including daily vascular checks, must be performed for several days. Further study is needed to determine the appropriate role for noninvasive Doppler studies .
Patients with multiple trauma who are hemodynamically stable are generally evaluated with computed tomography (CT). Preliminary studies suggest CT with angiography provides accurate assessment of extremity vascular trauma [33-36]. Its role in the assessment of vascular injury following knee dislocation is likely to expand.
After a thorough vascular assessment, magnetic resonance imaging (MRI) may be obtained to determine the extent of injury following knee dislocation. MRI allows for the identification of ligamentous injury as well as injuries to the joint capsule, meniscus, and articular cartilage [11,20,37]. Bone marrow edema, occult fractures, and bruising may also be found. Identifying the full spectrum of injury assists surgical planning. If multiple ligamentous injuries were not anticipated but are identified on MRI, we recommend immediate imaging of the popliteal artery.
COMPLICATIONS — Popliteal artery injury is the most dangerous potential complication following tibiofemoral dislocation [12,28,38,39]. Delay in diagnosis and repair increases the period of warm ischemia and the corresponding risk for irreparable injury requiring above-knee amputation. After eight hours of ischemia, the great majority of injuries will require amputation . Of note, popliteal artery lesions or thrombosis may not become clinically apparent for up to several weeks following the acute knee injury .
Other potential short-term complications include peroneal nerve injury, compartment syndrome of the leg, and deep vein thrombosis [38,41,42]. Complications may also include pseudoaneurysm, instability, arthrosis, stiffness, and chronic pain. Associated fractures may occur, including injuries of the tibial plateau, tibial shaft, and the proximal fibula. (See "Overview of lower extremity peripheral nerve syndromes", section on 'Fibular (peroneal) nerve' and "Acute compartment syndrome of the extremities" and "Clinical presentation and diagnosis of the nonpregnant adult with suspected deep vein thrombosis of the lower extremity".)
FOLLOW-UP CARE — After postreduction radiographs are performed, the patient is admitted to the hospital overnight for close monitoring of the limb's vascular function. Serial reassessment of the neurovascular status is of the utmost importance, and exams should be performed every three to four hours for a minimum of 24 hours .
Following discharge, anteroposterior and lateral radiographs should be repeated within the first week to confirm reduction. Close orthopedic follow-up is necessary to assess ligamentous injury and determine the need for surgical reconstruction . The patient should be provided with clear written instructions to return immediately to the emergency department for any sign of vascular compromise, and these signs should be carefully explained.
SUMMARY AND RECOMMENDATIONS
●Mechanism, danger to limb, algorithm for management – Tibiofemoral dislocations, although infrequent, are potentially limb-threatening injuries. They are caused most often by high energy trauma and involve injuries to multiple knee ligaments. An algorithm for the management of tibiofemoral joint dislocation is provided (algorithm 1).
●Clinical presentation – Many tibiofemoral dislocations are clinically obvious given the history of acute trauma and the abnormal position of the knee. Often a significant hemarthrosis and ecchymosis are present. Pain and swelling often limit examination, but assessment of the direction of the dislocation can be made. Of note, a significant number of dislocations spontaneously reduce prior to medical evaluation, in which case the diagnosis can be difficult. (See 'Clinical presentation and mechanism of injury' above.)
●Reduction – The method for reduction of tibiofemoral dislocations is described in the text. Posterolateral dislocations are not reducible by closed reduction techniques because the medial femoral condyle is buttonholed through the medial capsule and the medial collateral ligament is invaginated into the joint. (See 'Procedure' above.)
●Complications including popliteal artery injury – Popliteal artery injury is the most dangerous potential complication of tibiofemoral dislocation. Delay in diagnosis and repair increases the risk for irreparable injury, possibly requiring above-knee amputation. A meticulous evaluation of the extremity's circulatory status is mandatory and should include: palpating the distal and popliteal pulses, measuring an ankle-brachial index (ABI), and performing a screening duplex ultrasound, if available. Obtain immediate bedside consultation by a vascular surgeon if the limb manifests any sign of vascular compromise. Such signs may include diminished or absent pulses, pale or dusky skin, paresthesias, and paralysis. (See 'Initial care and evaluation' above and 'Complications' above.)
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