Study Guide

Knee Dislocations - Traumatic

Key Points:

Rare in the pediatric population; distal femur or proximal tibia physeal injuries more common
Knee dislocations are orthopedic emergencies, requiring proper neurovascular exam and monitoring

Description:

Sir Astley Cooper in 1825 was the first to report on knee dislocation. Knee dislocations involve multiple ligament disruptions (>2 of 4), with associated possible neurovascular injury. They can result from high, low, or ultra-low energy trauma. Incidence is relatively low, less than 1 in 100,000 of all hospital admissions (adult and pediatric) and account for less than 0.02% of all orthopedic injuries. This leads to a paucity of high level research. But, the potential of morbidity is high from these injuries. The reported incidence of associated vascular injury ranges from 16-64% due to popliteal artery tethering between adductor hiatus and gastro-soleus arch.
The mean age of injury is reported at 32 years. Data is negligible on skeletally immature patients. One case report described a high-energy knee dislocation without an ACL disruption in a skeletally immature 12-year-old female. The young child with a severe knee injury may not have classic findings as seen in an adult with a true knee dislocation. Pediatric patients will have less ability to ‘cooperate’ with neurologic exams and a high index of suspicion for complications with these injuries must be present.

Clinical Findings:

Findings can vary from a grossly deformed knee to a swollen knee. Inspection may note ecchymosis, abrasions, swelling or a “dimple sign” where the femoral condyle gets entrapped in the joint capsule and soft tissue. Prompt reduction of a dislocated knee is warranted. A thorough neurovascular exam is important given the high risk of popliteal artery and peroneal nerve injuries. Ankle-brachial indices (ABI) for the bilateral lower extremities should be completed on every patient. Concern for abnormal perfusion based upon pulse examination or ABIs indicates the need for vascular surgery consultation and further evaluation. Late thrombosis is possible with an arterial stretch injury, so careful monitoring is important after correction of the deformity and immobilization of the injured extremity.

Imaging Studies:

Initial orthogonal radiographs may confirm dislocation. A dislocation is described based upon the position of the tibia in relationship to the femur. If a reduction is required, post-reduction imaging should be completed. Physical exam findings may lead to emergent arteriography, or MRI/CT angiogram for evaluation of the arterial structures. An MRI will also evaluate ligament, capsule, and intra-articular injuries.

Schenck Anatomic Classification:

Dislocation with ACL only disrupted
Dislocation with complete ACL/PCL disruption
ACL/PCL and one collateral disrupted
ACL/PCL and both collaterals disrupted
Dislocation with periarticular fracture.

Treatment:

Associated unstable fractures, open injuries, vascular injuries, or severe joint instability warrant immediate operative intervention; which may include external fixator placement, irrigation and debridement, or open reduction internal fixation.
Nonoperative treatment is reserved for very low functional demand patients, critically ill patients, grossly contaminated wounds or significant soft tissue injury surrounding the knee. Treatment can consist of long leg cast or brace locked in extension for several months.
Operative intervention, although found to have improved outcomes, is controversial in regards to timing and reconstructive options. Early arthroscopic intervention may be complicated by the presence of capsular defects. Extravasation of fluid may not only make functional arthroscopy difficult, but may lead to dangerous swelling. Gravity inflow without pump usage is recommended. Surgeons must monitor the patient closely for compartment syndrome due to the risk for fluid extravasation.
Cruciate and posterior lateral ligament reconstruction, as opposed to repair, may result in higher overall rate of return to activities, lower rate of flexion loss, and lower rate of posterior sag sign. Medial collateral ligament reconstruction may also be required in the setting of multiple ligament injuries. Patients receiving operative treatment within three weeks of injuries appear to have better functional outcomes, but the literature is inconsistent.

Complications:

Complications are frequent and serious. These include persistent joint instability, arthrofibrosis, neurovascular injury, infection, repair/reconstruction failure, and deep venous thrombosis/pulmonary embolism. Compartment syndrome can occur and in younger children a single test may not identify this limb threatening complication. Difficulty cooperating with neurologic exams and infrequent occurrence of these injuries place pediatric patients at greater risk for serious complications. Although compartment pressure monitoring, ankle-brachial indices, and imaging studies can be performed, the identification of compartment syndrome is a clinical diagnosis and requires urgent intervention with fasciotomies and stabilization of associated injuries.

References:

Cole,W. Arterial injuries associated with fractures of the lower limbs in childhood. Injury. May 1981: (12): 460-463
Fanelli GC et al. Multiple ligament knee injuries. DeLee & Drez’s Orthopaedic Sports Medicine, Third Edition. Page 1747-17565
Flowers A and Copley L. Case report: High energy knee dislocation without anterior crucial ligament disruption in a skeletally immature adolescent. Arthroscopy. Sept 2003; 19(7): 782-786
Levy BA, et al. Decision Making in the Multiligament-Injured Knee: An Evidence-Based Systematic Review. Arthroscopy. April 2009;25(4):430-43.

Top Contributors:

Jennifer Beck M.D.