Blowout fracture of the orbital floor with entrapment caused by isolated trauma to the orbital rim.

There are two main theories on the cause of blowout fractures of the orbit: the "hydraulic" theory and the "buckling force" theory. Although both mechanisms have been shown responsible for experimental blowout fractures, the role of isolated rim trauma in producing clinical blowout fractures with entrapment of orbital soft tissues continues to be questioned. I examined a 69-year-old patient who developed a blowout fracture with clinical evidence of entrapment after isolated trauma to the orbital rim. Five days previously the patient had had a cataract extraction and implantation of an intraocular lens in the ipsilateral eye, which remained undisturbed by the trauma. This case supports the role of a buckling force to the rim in producing orbital blowout fractures. Review of the circumstances of injury in large series of blowout fractures suggests that this mechanism may be operative in the majority of cases.