A tibial tubercle avulsion fracture is usually an injury to the knee occurring in adolescence, during the transitional phase of physeal closure just prior to completion of growth. This fracture most often is an isolated injury related to pushoff or landing while jumping as the quadriceps eccentrically contracts to support the individual's weight.
The fracture tracks through the proximal tibial epiphysis and may extend into the anterior portion of the knee joint. The proximal tibia physis closes from posterior to anterior, and the fracture pattern is dependent on the amount of physeal closure present at the time of injury. Some authors consider this injury to be a variant of a Salter-Harris III fracture pattern. Open reduction and internal fixation is recommended, as reduction is difficult to maintain against the pull of the quadriceps muscle.
An extended classification system was developed that includes types I, II, III, IV, and V. Types I, II, and III, may be further classified into A, B, and C types. Type A indicates displacement, type B indicates comminution, and type C, added by Frankl, indicates associated patellar ligament avulsions. Further classification of more extensive injury was added, including type IV introduced by Ryu and type V described by Mckoy. 
The difficulty with this fracture is in maintaining a satisfactory reduction against the proximal pull of the quadriceps muscle. The patient usually is very close to the end of growth, and fixation of the fragment should not affect remaining growth. In the rare instance in which this fracture occurs in a younger individual, suturing of the periosteum and retinaculum and temporary smooth Kirschner wire (K-wire) fixation may be performed.
Anatomy and Pathophysiology
The proximal tibia physis progressively closes from posterior to anterior. The tibial tubercle is vulnerable to injury during the transitional phase of closure.
The tibial tubercle physis is in continuity with the tibial plateau. The physis progressively fuses from posterior to anterior, making it most vulnerable to avulsion in adolescents aged 13-16 years.
The mechanism of injury usually is an indirect force caused by sudden contraction of the quadriceps muscle. During sudden acceleration and deceleration forces, the quadriceps mechanism forcefully contracts against the patellar tendon insertion. When the force is greater than the strength of the tibial tubercle physis, a fracture is created, leading to avulsion of the tibial tubercle. Additional predisposing factors include patella baja, tight hamstrings, preexisting Osgood-Schlatter disease, and disorders involving physeal abnormalities. 
Tibial tubercle avulsion fractures are commonly seen in athletic males (frequently basketball players) aged 14-16 years.  These fractures account for 1-3% of physeal injuries.
With appropriate surgical treatment and postoperative therapy, a complete recovery without residual symptoms is expected. A return to sports may be expected once the lower extremity strength is 90% that of the unaffected extremity, usually 4-6 months after injury.
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