We tried to reveal radiographic clues for the possibility of damages to the important structures, including the peroneal nerve and the anterior tibial artery, caused by a proximal interlocking screw with a medial to lateral oblique direction (ObML-PIS).

The length of the proximal tibiofiular joint (PTFJ) was measured from the tip of the fibular head to the end of PTFJ on the simple oblique radiographs of 22 cases of tibial intramedullary (IM) nailing. The center (O) of the IM nailing, from the tibial anterior cortex at the level of insertion of an ObML-PIS, was measured on the simple lateral radiographs. The angle POA (P: a point 10 mm anterior from the anterior fibular border, A: a point on the tangent line from the O point to the posteromedial cortex of the fibula) was measured on the MR axial view of 60 cases, and within this angle an ObML-PIS could injure the important anatomical structures. Transverse and 45-degree oblique diameters of the proximal tibia on the MR axial view were also measured.

The PTFJ length was 18.5±3.3 mm and the O point was located at 15.3±3.4 mm posterior from the tibial anterior cortex. The angle POA was 21.4±6.2-67.8±6.7 degrees with medial to lateral oblique directions. The transverse diameter of the proximal tibia was 58.0±5.8 mm and the 45-degree oblique diameter was 50.7±6.2 mm.

Special caution may be needed when we use an ObML-PIS because it is located at the level distal from the end of the PTFJ and within the POA angle, and the peroneal nerve and anterior tibial artery can possibly be severed.