OBJECTIVES:
To determine the safe zone for transfixation wires in the proximal tibia to avoid intracapsular penetration.

METHODS:
The material consisted of five fresh cadaver knees (two paired) and seven knees of volunteer subjects (three paired). High-resolution magnetic resonance imaging (MRI) was performed on each knee after distension with a gadolinium solution. The distance d from the subchondral bone to the insertion of the reflected joint capsule was measured. Selected cadaver knees were then anatomically sectioned to correlate the MRI findings with anatomic measurements.

RESULTS:
On the anteromedial side of the knee, the distance from the reflected joint capsule to the subchondral bone was less than eleven millimeters in all specimens except one. Posteromedially, d was smaller and ranged from two to four millimeters. On the lateral side of the knee anterior to the proximal tibiofibular joint, this distance ranged from six to nine millimeters. In all knees but two, d was greatest at the posterior aspect of the proximal tibiofibular joint, ranging from eight to thirteen millimeters. In one volunteer knee, the septum that separates the knee joint from the proximal tibiofibular joint was either torn or attenuated, resulting in complete communication between these two synovial cavities.

CONCLUSIONS:
Proximal tibial transfixation wires away from the tibiofibular joint are likely to be extraarticular if kept greater than fourteen millimeters from the subchondral bone. In the region of the proximal tibiofibular joint, a safe distance is unclear because it is difficult to know preoperatively which knee has a torn septum.





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