OBJECTIVE:
To identify the risks to intraarticular structures of the knee during tibial portal creation and to identify the safe zone for tibial nail placement.

STUDY DESIGN:
Cadaveric anatomic.

LOCATION:
University trauma center.

METHODS:
Forty fresh frozen cadaveric knees were studied to elaborate the risks of tibial portal creation and nail placement to the intraarticular structures of the knee. Nails were placed through medial and lateral parapatellar approaches, and the distance from the nail portal to the intraarticular structures of the knee was measured. A safe zone for portal placement was determined.

RESULTS:
The tibial portal location averaged 4.4+/-3 millimeters lateral to the midline of the plateau. Actual intraarticular structural damage occurred in 20 percent of the specimens; however, an additional 30 percent demonstrated the nail to be subjacent to one of the menisci. A lateral paratendinous approach placed the lateral articular surface at most risk, and a medial paratendinous approach placed the medial meniscus at most risk. The safe zone for nail placement was identified and is located 9.1+/-5 millimeters lateral to the midline of the plateau and three millimeters lateral to the center of the tibial tubercle. The width of the safe zone averaged 22.9 millimeters and was as narrow as 12.6 millimeters.

CONCLUSION:
Damage to the intraarticular structures of the knee is possible during tibial nailing with a superior portal. The safe zone for nail placement is small and can be exceeded if a reamed nail is used. The safest starting point for tibial nailing should be slightly lateral to the center of the tibial tubercle.