Table 1.
Comparisons between the TRI and non-TRI groups.
Table 2.
Comparisons between the TRI and matched-control groups: laterality and diagnosis.
Table 3.
Comparisons between the TRI and matched-control groups: Diagnosis according to injured sites.
Table 4.
Comparisons between the TRI and matched-control groups: Severity.
Fig 1.
Common tibial fracture patterns in the trampoline-related injury (TRI) and matched-control groups.
For the TRI group, the most common tibial fracture pattern (42 of 184 lower-extremity injuries) was proximal tibial fracture with a transverse or short oblique fracture line (left), and most of them presented neutral or varus angulation. In contrast, for the matched-control group, cases with proximal tibial fracture were relatively rare (only 6 of 184 lower-extremity injuries) and half of the patients with a proximal tibial fracture presented valgus angulation. Therefore, compression with varus shearing force seems to be the main injury mechanism in TRI. On the other hand, tibial shaft fractures, which mostly occurred in the matched-control group, presented as long oblique or spiral fractures, which indicate a torsional injury mechanism (right).
Fig 2.
Varus shearing force in trampoline-related injury.
(A) It is known that when multiple children are using a trampoline at the same time, the smaller children receive excessive axial loading during landing due to the upward recoil on the mat caused by a heavier jumper [7, 13]. However, when considering the presence of cortical buckling and angulation, a somewhat additional varus shearing force seems to be combined with the compressive force (gray arrows). Although more studies are needed, we postulate that this varus force originates from the inclined mat. (B) Even when a smaller jumper lands on the trampoline simultaneously with a heavier jumper, the inclined mat can cause varus stress. (C) This assumption can also be supported by the incidence of elbow fractures. Lateral condylar humeral fractures, which are associated with hyperextension with varus stress in injuries involving falling on a stretched arm, were relatively more frequent in the group with trampoline-related injuries (Table 3).
Fig 3.
Suggested preventive measures for trampoline-related injuries (TRIs).
Under the assumption that the varus shearing force plays an important role in the occurrence of TRI, altering the design of trampolines or using specially designed footwear may contribute to preventing TRI or reducing TRI-related physeal injuries. (A) The trampoline consists of a taut and strong mat that is connected to a peripheral steel frame with many coiled springs. Because of this structure, when a child lands on the mat, the mat becomes inclined to the center, generating varus force. (B) Therefore, it can be postulated that the varus shearing force can be reduced by using additional coiled springs that are vertically positioned. (C) With respect to the varus shearing force caused by slippage of the foot and the inclined mat, wearing of anti-slippage footwear during trampoline use might also prevent injury.