Tibial tubercle fractures are uncommon injuries that most frequently occur during maximal proximal tibial physeal growth. These fractures account for less than 1% of all physeal injuries.¹ Most studies are limited to case reports or relatively small series of patients with this fracture pattern. Despite being uncommon, tibial tubercle fractures have been associated with severe complications, including compartment syndrome, intraarticular damage, limb length discrepancy, extensive soft tissue damage, and limited knee range of motion.²,³,⁴,⁵,⁶ This chapter provides an overview of this uncommon clinical entity, including presentation, diagnosis, and management. We also present an operative strategy for addressing these injuries.

The tibial tubercle is a bony elevation on the anterior proximal tibia and is the distal attachment site for the patellar ligament. The tibial tubercle serves as the terminal attachment for the knee’s extensor mechanism. The proximal part of the extensor system is the quadriceps muscle that consists of the rectus femoris, vastus medialis, vastus intermedius, and vastus lateralis. The quadriceps muscles attach distally to the superior pole of the patella through the quadriceps tendon. The patellar ligament extends from the inferior pole of the patella and attaches distally on the tibial tubercle. When the quadriceps muscles contract, the force is transmitted distally through the tibial tubercle and the knee extends.

The proximal tibia has two ossification centers. The primary ossification center is the proximal tibial physis. The secondary ossification center is the tibial tubercle apophysis. The tibial tubercle develops in four stages.⁷ The first stage involves a completely cartilaginous tubercle, prior to the development of the secondary center of ossification. The second stage occurs when the apophysis develops via the secondary ossification center but is not yet connected to the proximal tibial physis. This stage occurs at approximately age 8 to 12 years in females and 9 to 14 years in males. The third stage of development, referred to as the epiphyseal phase, is defined as when the tibial physis and the apophysis become contiguous. This typically occurs at age 10 to 15 years for females and 11 to 17 years for males. The fourth and final stage of tibial tubercle development arises when the physis is fused completely and is no longer cartilaginous.

During the apophyseal stage of development, the patellar tendon inserts in an area that corresponds to the fibrocartilage proximal and anterior to the secondary ossification center.⁸ The patellar tendon mainly attaches proximally at the level between the secondary ossification center and the proximal tibial epiphysis. As development of the tibial tubercle progresses to the epiphyseal phase, the patellar tendon inserts through fibrocartilage on to the downward-projecting tongue of the proximal tibial epiphysis. During the final stage of tibial tubercle development, the patellar tendon inserts directly into bone and fractures of the tibial tubercle rarely occur.

Tibial tubercle fractures are rare injuries that account for less than 1% of all physeal injuries.¹ The reported incidence is relatively low and ranges from 0.4% to 2.7%.⁹,¹⁰ However, given the disastrous sequelae of a missed fracture, accurate injury assessment and diagnosis is critical. These injuries occur mostly in boys while engaged in sports activities during a growth period when there is maximal epiphyseal growth.¹¹ The age range at the time of injury is typically between 13 and 16 years.¹² During this phase, the epiphysis is still open and the apophysis between the tibial tubercle and the rest of the tibia is a weak location for potential fracture. The predominance of males sustaining these fractures could relate to the delayed closure of their proximal tibial epiphysis and their increased participation in vigorous sporting activity.¹³

Tibial tubercle fractures can be confused with Osgood-Schlatter (OS) lesions by the inexperienced clinician. In fact, some studies have shown an association between OS lesions and subsequent tibial tubercle fractures.¹¹,¹⁴ Ogden et al.⁴ described an OS lesion as primarily involving the anterior portion of the epiphysis or ossification center of the tuberosity, but there is no involvement of the physis. Furthermore, tibial tubercle fractures are acute disruptions, whereas OS disease tends to be chronic and symptomatic.⁴

In 1903, Dr. Osgood⁵ described that the majority of tibial tubercle fractures result from violent quadriceps contraction during exercise or activity. He also acknowledged some documented cases where the injury occurred from a fall on a hard surface with a flexed knee. In 1955, Watson-Jones¹⁵ described the injury mechanism a result of violent knee flexion against a contracting quadriceps mechanism. Hand et al.⁶ reiterated Watson-Jones’ postulated mechanism. A now classic case series completed by Levi and Coleman¹¹ in 1976 added that tibial tubercle fractures can occur when the quadriceps contracts with a fixed foot. Each of these mechanisms can overlap with the other.

Biomechanically, avulsion of the tibial tubercle arises when the patellar tendon traction exceeds the strength of the underlying physis. This can take place during jumping or landing, times when there is sudden acceleration or deceleration of the knee extensor mechanism.⁸ The phases of development are associated with specific injury patterns recognized in tibial tubercle fractures. Bolesta and Fitch⁹ illustrate this in a patient who suffered an injury through the proximal tibial physis at 16 years of age, which healed with a closed reduction. Five months later, the same patient suffered a tibial tubercle avulsion through the epiphysis and diaphysis with a similar mechanism of injury as the proximal physis was closing from posterior to anterior.⁹

Some risk factors have been identified that predispose children to tibial tubercle fractures. Maffulli and Grewal¹⁷ hypothesized that patients with this fracture may have quadriceps strength that is greater than their peers. There are also reports of pathologic fractures of the tibial tubercle in patients with underlying myelomeningocele or skeletal dysplasia.⁴ Many individuals with tibial tubercle fractures have a history of OS lesions.⁴,¹⁸ The association with OS lesions could indicate an underlying vulnerability of the tibial tubercle in certain patient populations. This could be the result of stronger quadriceps, inflexible knee flexors, or impaired coordination of these opposing forces about the knee.⁸

Typically, tibial tubercle fractures occur during violent quadriceps contraction in an athletic youth.⁵ Most injuries happen during activity or vigorous play.¹¹ Examples include attempts to prevent oneself from falling,⁵,¹⁶,¹⁹ gymnastics,⁴,¹¹,¹⁹ soccer,¹³,¹⁹,²⁰ jumping,⁴,⁶,⁹,¹¹,¹⁹,²¹ climbing,¹¹ playing football or basketball,⁴,⁶,⁹,¹¹,¹⁹,²⁰,²¹ running,⁴,¹³ hurdling,¹³,¹⁹ skateboarding,⁴ or high jumping.⁶,¹³,¹⁹ Another possible history for injury involves falling on a flexed knee on a hard surface.⁵,¹¹,¹³,²⁰