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Treatment of Tibial Eminence Fractures
Introduction
Tibial eminence fractures are bony avulsions of the anterior cruciate ligament (ACL) from its insertion on the intercondylar eminence of the tibia. The intercondylar eminence is a narrow, raised area between the medial and lateral tibial spines. Tibial eminence fractures, while an intra-articular injury, involve a nonarticular portion of the tibia. The ACL has a broad insertion along the anterolateral aspect of the medial tibial spine, with fibers attaching all the way to the anterior base. With a tibial eminence fracture, enough force is applied through the insertion of the ACL that the tibial spine is avulsed off the plateau along with the ligament. The anterior horn of the lateral meniscus is also frequently disrupted, as it remains attached to the avulsed fragment. The anterior horn of the medial meniscus attaches just anterior to the eminence and can become trapped within the fracture site, potentially blocking attempts at closed reduction. Interposition of the anterior horn has been reported to occur in 45% of displaced tibial eminence fractures.
Incidence
Tibial eminence fractures are relatively rare, with an estimated incidence of approximately 3 of 100,000 children. Classically, these fractures are categorized as pediatric injuries and occur most commonly in children between 8 and 14 years of age. The relative weakness of the incompletely ossified tibial eminence in this skeletally immature population is believed to result in the bony avulsion of the ACL, as opposed to the midsubstance tear seen in older patients. Despite the classic pediatric description, recent studies suggest that the incidence of tibial eminence fractures in skeletally mature adults may be similar to or even greater than that seen in the pediatric population.
Mechanism of Injury
Both adult and pediatric tibial eminence fractures are thought to occur through a similar mechanism. These fractures can result from a forceful twist/pivot, as occurs with tears of the ACL, forceful flexion of the knee with the tibia in an internally rotated position, or by forceful hyperextension of the knee. In Meyers and McKeever’s initial report on 35 tibial eminence fractures in children, a fall from a bicycle was the most common mechanism of injury. More recent studies suggest that skiing, soccer, and contact sports are now more frequent causes of eminence fractures. In adults, falls and motor vehicle collisions are the most common mechanisms of injury, responsible for over 50% of cases.
Physical Examination
The clinical presentation of a patient with a tibial eminence fracture is similar to that seen with an ACL rupture. Patients typically present with a large knee effusion and difficulty bearing weight due to pain and/or instability. As with assessment of all traumatic knee injuries, a through neurovascular examination should be performed and documented. ACL stability can be assessed with Lachman, anterior drawer, and pivot-shift testing. Patient guarding may limit the utility of these examination maneuvers in the early postinjury period. Range of motion should be assessed for any limitations. The inability to achieve full extension in the acute setting may indicate fragment displacement and/or meniscal entrapment. The joint line should be palpated for areas of tenderness; however, concomitant meniscal pathology is infrequently encountered.
Classification
Tibial eminence fractures are commonly described using the Meyers and McKeever classification system, in which fractures are categorized according to the degree of displacement seen on the lateral radiograph ( Fig. 138.1 ). A type I fracture describes a minimally or nondisplaced fracture in which there is complete bony opposition between the fragment and the fracture bed. A type II fracture describes partial displacement, with the anterior third to half of the eminence fragment being elevated while the posterior hinge remains intact. A type III fracture occurs when the eminence fragment is completely lifted off the tibial plateau, with no bony opposition. Type IV fractures describe a displaced and comminuted eminence fracture.
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