Tibial tubercle apophyseal fractures are more frequently the result of jumping activities, especially at the initiation of the jump during eccentric loading at maximal quadriceps force, but may also be seen during eccentric loading while landing (Fig. 29-2).4,7,8,19,29,30,34 Moreover, tibial tuberosity fractures are reported almost exclusively in boys who tend to have greater quadriceps strength and may overcome the stability of the apophysis with a violent contraction of the muscle.4,5,7,8,19,26,29,30,34
Associated Injuries with Proximal Tibial Physeal Fractures
Although the proximal tibial physis and the tibial tubercle apophysis are intimately associated with each other, fractures of the two locations have a unique set of associated injuries. The proximal physis fracture is at risk for ligamentous, vascular, and neurologic injury; whereas, the tubercle apophyseal fractures are also at risk for compartment syndrome.
Ligamentous injuries and internal derangement of the knee joint may occur during Salter–Harris III and IV proximal tibial physeal injuries in 40% of patients.41 In contrast, the tibial tubercle fractures may rupture the patellar ligament, quadriceps tendon, collateral, and cruciate ligaments in a far greater frequency.4,28,29,35 Even an avulsion of the anterior tibialis muscle has also been reported.25,53
Vascular compromise in proximal tibial physeal fractures can be devastating, but they are uncommon in isolated tubercle injuries.6,46,55 The popliteal artery is tethered by its major branches near the posterior surface of the proximal tibial epiphysis. The posterior tibial branch passes under the arching fibers of the soleus. The anterior tibial artery travels anteriorly over an aperture above the proximal border of the interosseous membrane. A hyperextension injury that results in posterior displacement of the proximal tibial metaphysis may stretch and tear the tethered popliteal artery (Fig. 29-3). Even a minimally displaced fracture at presentation may have had significant displacement at the time of injury, and should therefore be monitored for vascular injury.50 Diagnostic workup of these fractures does not mandate routine angiography as long as motor function, pulses, warmth, and color are monitored closely after reduction during the initial 48 to 72 hours.
Regarding vascular injuries, the tibial tubercle avulsion fractures are at risk for bleeding of the anterior tibial recurrent artery (which traverses the base of the tubercle) into the anterior compartment. Rather than resulting in direct ischemia, this vascular compromise is associated with indirect ischemia through the development of compartment syndrome.37
A peroneal neuropathy may also be associated with a fracture of the proximal tibial physis, but it will often undergo spontaneous resolution of symptoms.
Signs and Symptoms of Proximal Tibial Physeal Fractures
Physical examination of children with either a proximal physis or tubercle apophysis fracture may not be dissimilar. Pain, knee effusion, and a hemarthrosis will often be present in both. Limb deformity may or may not be present in either fracture type, and hamstring spasm may limit knee extension on examination.
The physeal injuries will have pain over the tibial physis distal to the joint line, in contrast to the tubercle injuries that will hurt directly anteriorly. Sometimes, the tubercle fractures will have a freely movable osseous fragment palpated subcutaneously between the proximal tibia and the femoral condyles, and may result in skin tenting; whereas, in the physeal fractures, the proximal metaphysis of the tibia is displaced posteriorly creating a concavity that can be palpated anteriorly at the level of the tibial tubercle. A valgus deformity suggests medial displacement of the metaphysis.
The associated injuries need to be identified at this time, as well. Ischemia caused by disruption of the popliteal artery or secondary to compartment syndrome should not be delayed. Poor perfusion, pallor, and distal pain should be recognized for potential signs of vascular compromise. Pulses should be ascertained and compartments should be assessed by palpation and assessment of sensation plus passive and active toe motion.
When the proximal end of the metaphysis protrudes under the subcutaneous tissues on the medial aspect of the knee, a tear of the distal end of the medial collateral ligament should be suspected in association with a physeal fracture. The presence of patella alta may represent either severity of tubercle displacement or rupture of the patella tendon. With a small avulsion, the child may be able to extend the knee actively through intact retinacular tissue, but active extension is impaired with larger injuries.
Imaging and Other Diagnostic Studies for Proximal Tibial Physeal Fractures
Plain radiographs are the mainstay of evaluation for fractures, but nondisplaced physeal fractures may not be visible. Associated hemarthrosis can sometimes be the only indication of fracture and is primarily recognized by identifying an increased separation of the patella from the distal femur on lateral views (Fig. 29-4). Occasionally, relatively nondisplaced physeal fractures may have small Thurston–Holland fragments that extending either into the epiphysis or into the metaphysis. Often, fracture lines may only be visible on oblique view radiographs. At other times the metaphyseal fragments can be quite large (Fig. 29-5). Stress views can often differentiate a proximal tibial physeal fracture from a ligament injury, but there is potential risk for physeal injury and increased pain in a clinical setting when performing these x-rays. Often MRI can be done if indicated, to distinguish these two injury patterns, and it is safe, accurate, and a more comfortable method for diagnosis of obscure fractures or ligamentous injuries than stress radiographs (Fig. 29-6).48 Moreover, CT scans can define the bony injury better than MRI or plain film and is often helpful to determine treatment for Salter–Harris III and IV injuries (Fig. 29-7).
The standard method of identifying tibial tubercle fractures is via the lateral plain radiograph; however, more severe injuries should warrant advanced diagnostic imaging to help identify articular disruption and internal derangement that is often seen in these fracture patterns. Although, most patients with tibial tubercle fractures are adolescents (with developed secondary ossification of the tibial tubercle), fractures may occur in the more immature child and be seen merely has a small fleck of bone on plain film (Fig. 29-8). In order to improve the utility of diagnostic plain film, the lateral projection view should be done with the tibia rotated slightly internal to bring the tubercle perpendicular to the x-ray cassette.
With regard to the tibial tubercle, it is important to remember that normal ossification may progress from more than one secondary center of ossification. Opposite leg films may be helpful to distinguish normal ossification versus minimally displaced fragments, but patella alta may be more reliable in that comparison.
Classification of Proximal Tibial Physeal Fractures
Proximal tibial physeal fractures are most commonly described using the Salter–Harris classification scheme that denotes the direction of fracture propagation relative to the growth plate. A recent study in 2009, proposed the first specific classification for these pediatric proximal tibia fractures that was based on the direction of force and fracture pattern.30 This classification scheme utilized the following mechanism of injury: Valgus, varus, extension and flexion–avulsion (Fig. 29-9). The youngest children (aged 3 to 9 years) sustain valgus and varus mechanism injuries with resultant metaphyseal fractures from activities such as a trampoline. The slightly older age group of 10 to 12 was more prone to extension mechanism injuries that resulted in tibial spine fractures and the greater than 13-year-old group sustained predominately flexion–avulsion mechanism injuries that resulted in tibial tubercle fractures. Within this mechanism of injury classification, there was also evidence that fracture location was age dependent. The mean age for metaphyseal fractures (including the Cozen fracture) was just under 4 years. The mean age for tibial spine fractures was 10 years old, the mean age for Salter–Harris I and II was 12 years old and Salter–Harris III and IV injuries mean age was about 14 years old (Fig. 29-10).
Most separations of the proximal tibial epiphysis are Salter–Harris I and II injuries. The frequency of Salter–Harris III injuries in the past literature may be skewed by the inclusion or exclusion of displaced tibial tubercle fractures, but the incidence of Salter–Harris IV injuries depends on whether certain open injuries to the knee are included (i.e., lawnmower injuries).6,46 If the Salter–Harris classification is utilized, then some predictable findings can be expected.
In Salter–Harris I injuries, 50% are nondisplaced and this may be secondary to the overhanging tubercle preventing anterior displacement and the fibula preventing lateral displacement of the metaphysis. In contrast, about two-thirds of Salter–Harris II fractures are displaced with medial gapping and lateral Thurston–Holland fragment resulting in a valgus deformity and often a proximal fibula fracture. Salter–Harris III fractures are predominately tibial tubercle fractures in children and have their own classification scheme.
Shelton and Canale46 and Burkhart and Peterson6 included tubercle avulsions in their reviews of proximal tibial physeal fractures, but these injuries are often considered separately.34,46,51 Watson-Jones51 described three types of avulsion fractures of the tibial tubercle, with subsequent modifications by Ogden and associates34 who noted that the degree of displacement depends on the severity of injury to adjacent soft tissue attachments (Fig. 29-11). Ryu42 and Inoue24 proposed a type IV fracture in which the physeal separation occurs through the tibial tuberosity and extends posteriorly into the horizontal tibial physis. A study from San Diego was recently presented by the authors delineating a three-dimensional classification of tibial tubercle fractures, in order to highlight the risk for associated pathology.36 It is based on skeletal maturity and ossification of the secondary ossification center as it relates to increasing need for surgery and risk for compartment syndrome (Fig. 29-12). San Diego type A tibial tubercle fractures occur in the youngest population (mean age 12.7 years) with most of the physis and apophysis open resulting in a largely cartilaginous fracture that is seen as a fleck of bone at the distal tibial tubercle. These are at low risk for compartment syndrome, but potentially greatest risk for premature physeal closure because of age. They require only sagittal plain radiographs for appropriate diagnostics. The San Diego type B fracture is found in a slightly older population wherein the physeal and apophyseal cartilage is primarily open (Fig. 29-13A and B). These are basically the same has the Ryu variant wherein the apophysis and proximal physis fracture as a single unit, and they are at the greatest risk for compartment syndrome, vascular injury, and growth arrest. The San Diego type C fracture is found in even older patients with closing growth plates that are partially open following a predictable pattern of closure. These fractures always involve the articular surface and require either pre-operative three-dimensional imaging or intra-operative intra-articular evaluation (Fig. 29-14A and B). These fractures almost always require surgical intervention. Finally, the San Diego type D fractures are found in the oldest population and most of the proximal tibial physis and apophysis have closed leaving only the most distal aspect of the tubercle unfused and at risk for fracturing. They look similar to the type A injuries, but occur in more skeletally mature individuals. These have the lowest risk of complications of all the groups and can be treated with either casting or screw fixation (Fig. 29-15A and B).
Outcome Measures for Proximal Tibial Physeal Fractures
There are no specific outcome scores or tools validated for proximal tibial physeal fractures; however, most studies have utilized plain radiographs to determine healing and a few have utilized return to sports for functional outcomes.
PATHOANATOMY AND APPLIED ANATOMY RELATING TO PROXIMAL TIBIAL PHYSEAL FRACTURES
Present at birth, the ossific nucleus of the proximal tibial epiphysis lies central in the cartilaginous anlage. Usually singular, it can occasionally have two ossification centers, not including the universal secondary center of ossification of the tubercle that appears between 9 and 14 years of age. Closure of the proximal tibial physis and union between the epiphysis and tubercle centers occurs commonly in girls between 10 and 15 years and in boys between 11 and 17 years of age.
The development of the tibial tubercle has been further defined by Ehrenborg.15 After birth is the cartilaginous stage that exists prior to development of the secondary ossification center and persists until the age of 9 years in girls and age of 10 years in boys. This is followed by the apophyseal stage, in which the ossification center appears in the tongue of cartilage that drapes over the anterior tibial metaphysis. The epiphyseal stage is marked by the tubercle and epiphyseal bony union, and this is followed by the final bony stage, wherein the proximal tibia becomes fully ossified. There is evidence that closure of the physis follows a predictable pattern.3,13,18,33,36,45,47 In the sagittal plane, the proximal tibial physis has been shown to close in a posterior to anterior direction, with subsequent progression of closure toward the tubercle apophysis which is closing in a proximal to distal direction, simultaneously. In the coronal planes, the proximal tibial physis is closing in a medial to lateral direction; whereas, in the axial plane, the tibia is closing in a posteromedial to anterolateral direction.
As previously discussed, the anatomy of the collateral ligaments provides some protection from epiphyseal disruption. The superficial portion of the medial collateral ligament extends distal to the physis inserting into the medial metaphysis, therefore acting as a medial buttress. The lateral collateral ligament inserts on the proximal pole of the fibula, and this entire lateral construct acts like a lateral buttress. Anteriorly, the patellar ligament attaches to the secondary ossification center of the tibial tuberosity that is draped over the metaphysis serving as a constraint to posterior displacement. Yet, this design of terminal insertion of the powerful quadriceps at the boundary between the secondary ossification centers of the tubercle and the proximal tibial epiphysis does place the tubercle at risk for isolated or combined avulsion fractures. This risk is minimal until adolescence when the quadriceps mechanism is matured because some fibers of the patella tendon extend distal to the apophysis into the anterior aspect of the upper tibial diaphysis. Therefore, it is important to recognize that these adolescent avulsions often have extensive soft tissue damage that extends down the anterior diaphysis.
The distal portion of the popliteal artery lies close to the posterior aspect of the proximal tibia. Firm connective tissue septa hold the vessel against the knee capsule placing it at risk for injury during proximal tibia physeal fractures (Fig. 29-16). The lateral inferior geniculate artery crosses the surface of the popliteus muscle, anterior to the lateral head of the gastrocnemius, and turns forward underneath the lateral collateral ligament. The medial inferior geniculate artery passes along the proximal border of the popliteus muscle, anterior to the medial head of the gastrocnemius, and extends anterior along the medial aspect of the proximal tibia. The popliteal artery divides into the anterior tibial and posterior tibial branches beneath the arch of the soleus muscle. Much of the blood supply to the proximal tibial epiphysis is derived from an anastomosis between these geniculate arteries.10,20 The tibial tubercle receives its main blood supply from a plexus of arteries behind the patellar ligament at the level of the attachment to the tibial tubercle.10 This vascular anastomosis arises from the anterior tibial recurrent artery and may be torn with this fracture.37,53 Several small branches extend down into the secondary ossification center. A smaller part of the blood supply enters the superficial surface of the tubercle from adjacent periosteal vessels.