ANATOMY

The tibia is the primary weight-bearing bone of the knee joint. The most proximal aspect of the tibia is comprised of the medial and lateral tibial condyles. The articular surfaces of the condyles are the medial and lateral tibial plateaus, which articulate with the corresponding medial and lateral femoral condyles. The plateaus are separated by the intercondylar eminence, which serves as the site of attachment for the anterior and posterior cruciate ligaments and the fibrocartilaginous menisci.⁴ Specifically, the midpoint of the intercondylar eminence serves as the distal attachment of the ACL.

The mechanism of injury for tibial eminence fractures is similar to an ACL tear; however, it involves an avulsion fracture at the ACL insertion. The injury may be associated with valgus and external rotation. It is often seen in skiers and is related to a boot-induced injury after the skier lands on the tail of the ski or to the phenomenon referred to as a “phantom foot” injury, which involves forced internal rotation with knee flexion. Although seen frequently in skiers, it is also seen in other sports, bicycle accidents, motor vehicle accidents, and pedestrian versus motor vehicle injuries.

Tibial eminence fractures are seen in children usually between the ages of 8 and 15 years.^3,5,6 Although this fracture pattern is commonly associated with a childhood injury, it is also seen in adults.^2,7,8 It is theorized that this occurs more commonly in children because of the relative weakness of the incompletely ossified tibial eminence as compared with the fibers of the ACL. It has also been proposed that the injury occurs secondary to greater elasticity of the ligaments in younger people.⁹

PATIENT EVALUATION

Classification

Meyers and McKeever first described the classification scheme for tibial eminence fractures in 1959.² Their classification divides these fractures into three types based on displacement of the avulsed fracture fragment (Fig. 2-1). Type I represents a nondisplaced or minimally displaced fracture at the anterior margin. Type II fractures involve the anterior third or half of the avulsed bone displaced proximally, with an intact posterior hinge resembling a bird’s beak. Type III fractures have a completely displaced fracture. These have been further subdivided into IIIA and IIIB fracture classifications.¹⁰ Type IIIA fractures involve the ACL insertion only, whereas the IIIB type includes the entire intercondylar eminence. Some have labeled comminuted fractures as type IV.¹⁰

FIGURE 2-1 Meyers and McKeever classification of tibial intercondylar eminence fractures.

(Adapted from Lubowitz JH, Elson WS, Guttman D. Part II: Arthroscopic treatment of tibial plateau fractures: intercondylar eminence avulsion fractures. Arthroscopy. 2005;21:86-92.)

Associated injuries with fractures of the tibial eminence are common. Meniscus injuries are the most common injuries seen; however, these fractures may be associated with chondral and ligamentous injuries as well.^11,12 In an unpublished study, we found an interposed intermeniscal ligament in 80% of types II and III injuries. This has profound implications for treatment strategies. In addition, tibial eminence fractures are also seen with tibial plateau fractures, specifically Schatzker types V and VI fractures.¹³

TREATMENT

The goal for management of tibial eminence fractures should be no different than for any other intra-articular fracture. Anatomic reduction and rigid fixation that allow for early range of motion should be the treatment for these fractures. Debate has ensued over anatomic reduction versus overreduction. It has been proposed that overreduction may result in excessive tension of the ACL, which results in limited knee range of motion.¹⁴ Others have countered this by stating that plastic deformation of the ACL occurs prior to the avulsion fracture and thus overreduction would result in a better outcome.⁹ Numerous studies have documented residual laxity in well-reduced tibial eminence fractures, and most have concluded that the laxity is not symptomatic.^15–17 More studies are needed to answer the question of anatomic versus overreduction, but there is consensus that any displacement requires at least an anatomic reduction.

Management has been based on the Meyers and McKeever classification, with recommendations for immobilization in extension for type I fractures. Some controversy exists in regard to what degree the knee is to be extended for nonoperative management. Meyers and McKeever have recommended immobilization in 20 degrees of flexion.^2,8 Similarly, Beaty and Kumar have recommended immobilization in 10 to 15 degrees of flexion.¹⁸ Fyfe and Jackson based their recommendations of flexing the knee to 30 to 40 degrees because the ACL is taut in extension and, with some flexion, the tension on the avulsion fragment would be less.¹⁹ These authors favor immobilization in full extension to avoid a flexion contracture, which can occur if the knee is kept in a flexed position. We encourage straight leg raises and quadriceps isometrics and allow full weight bearing, as tolerated, in a brace locked in full extension. The knee should not be immobilized in hyperextension because extensive stretch on the popliteal artery may result in a compartment syndrome.¹³ Regardless of the position of immobilization, close follow-up with radiographs weekly for 4 weeks should help confirm maintenance of reduction.

Treatment of type II fractures has been controversial. Closed reduction may be attempted by aspiration of the hemarthrosis and knee extension performed to allow the femoral condyles to help reduce the fracture.²⁰