Posttraumatic torsional injury as an indirect cause of fibular intraneural ganglion cysts: case illustrations and potential mechanisms.

Trauma has been loosely associated with the development of fibular intraneural ganglion cysts. Sporadic reports of direct trauma to the proximal lateral leg in the region of the superior tibiofibular joint (STFJ) capsule support the development of a capsular rent and the subsequent egress of joint fluid from the articular joint. This report provides evidence to suggest that indirect trauma from torsion can link concomitant ankle injury and fibular nerve palsy (foot drop) and fibular intraneural ganglion cysts. We present two cases to illustrate different potential mechanisms. One patient sustained an ankle ligamentous injury which was translated through the interosseous membrane (IOM) to the proximal leg region, affecting the STFJ and the fibular nerve (ascending pathway). The second patient had blunt injury to the popliteal fossa in combination with a twisting injury to the leg. In this latter case we offer two plausible explanations: (1) combined knee and ankle injury resulting in an ascending pathway mechanism; and (2) a knee injury which disrupted the STFJ, resulting in a translational force down the leg (descending pathway). We believe that fibular intraneural cysts from the STFJ result from direct and indirect trauma. Additional reports of similar cases and sophisticated biomechanical testing will allow us to delineate the exact mechanisms for these injury patterns.