Posterior tibial slope angle is associated with flexion-type Salter-Harris II and Watson-Jones type IV fractures of the proximal tibia

Purpose Flexion-type Salter-Harris (SH) II fractures of the proximal tibia, also described as Watson-Jones (WJ) IV fractures, are rare injuries reported among adolescent athletes who are close to skeletal maturity and remain elusive. Due to this classification disagreement, the various treatments range from nonoperative to operative types, and no previous studies have explained the mechanisms of injury or the source of the fracture forces. This retrospective matched case-control study aimed to identify radiological factors that are associated with the fracture forces and to elucidate the mechanisms of these injuries. Methods Sixteen flexion-type SH II/WJ IV fractures of the proximal tibia in 12 adolescents (12 males, mean age of 14.6 years) were retrospectively reviewed, and knee alignment on plain radiographs was assessed to compare the radiological outcomes of the operated knees (n = 7), nonoperated knees (n = 9), and uninjured contralateral knees (n = 8). The results were compared to healthy age- and sex-matched control subjects (n = 24 knees). Results With regard to the radiological outcomes, the posterior tibial slope angle (PTSA) was significantly greater in the nonoperated knees (19.0 degrees +/- 1.6 degrees), operated knees (16.8 degrees +/- 1.3 degrees), and uninjured knees (13.6 degrees +/- 1.3 degrees) than in the healthy knees of the matched control subjects (9.6 degrees +/- 0.4 degrees). The anatomical tibiofemoral angle was significantly less in the nonoperated knees (0.7 degrees +/- 0.6 degrees) than in the healthy knees of the matched control subjects (3.7 degrees +/- 0.4 degrees). Conclusions These findings suggest a relationship between an increased PTSA and flexion-type SH II/WJ IV fractures of the proximal tibia, considering the deteriorating effects of an increased PTSA on knee kinematics. Adolescent active athletes with an increased PTSA and partially closed epiphysis of the proximal tibia are at risk for suffering from flexion-type SH II/WJ IV fractures of the proximal tibia until the closure of the proximal tibial epiphysis.