Session IX - Tibia

The Safe Zone for Tibial Nailing

Paul Tornetta, III, MD; Joseph Riina, MD; Jeffrey Geller, MD; Boston Medical Center, Boston, MA; SUNY University Health Science Center at Brooklyn, Brooklyn, NY

Introduction: Recent reports have emphasized the high incidence of knee pain after reamed tibial nailing. The purpose of this study was to evaluate the intraarticular risks of tibial nailing and to describe the ideal location for portal placement.

Methods: Forty fresh cadaveric knees were used for the study (20 pairs). A tibial nail was placed by an experienced trauma surgeon via a paratendonous approach (one lateral and one medial for each pair). Both were performed through a midline incision from the distal pole of the patella to the joint line. The portal was placed using a straight 10 mm awl without reaming. A separate team of surgeons subsequently dissected the knee by releasing the patellar tendon proximally and reflecting it distally. Measurements were made with calipers and included the distance to the medial and lateral menisci and articular surface, the tibial width, the distance of the portal from the midline, and the distance from the ACL footprint. Any intraarticular structure that was damaged or impinged upon was recorded. The trauma surgeon was blinded to the findings of the dissections until the end of the study. The safe zone for portal placement was identified.

Results: The portal averaged 4.4 ± 3.1 mm lateral to the midline and varied only 6%. Using a medial approach the portal was closest to the medial meniscus (2.5 ± 3.8 mm) while the lateral articular surface was most at risk via a lateral approach (3.3 ± 3 mm). Actual structural damage occurred in 20% of the specimens; however, an additional 30% demonstrated the nail to be subjacent to one of the menisci. The "sweet spot" or safe zone for nail placement was only 23 ± 9 mm in width and located 9 ± 5 mm lateral to the midline and 3 mm lateral to the center of the tubercle. Data is summarized in two tables:

Discussion: The location of the portal was not significantly different using a lateral or medial approach and was fairly consistent between specimens. Although the nails were placed slightly lateral of midline, the actual safe zone was even more lateral, averaging 9 mm from the midline. This is due to the larger size of the medial meniscus and articular surface. Even using a 10mm awl, the incidence of intraarticular injury was 20%. These findings, along with the small size of the safe zone, may help to explain the incidence of knee pain after tibial nailing, particularly if reaming is performed. In 15% of knees, the safe zone is 18 mm wide, so perfect portal placement would be necessary to avoid intraarticular injury.

Conclusion: Tibial nailing places the medial meniscus and lateral articular surface at risk. In some knees the safe zone is smaller than commonly used reamers. The ideal location for portal placement is 9 mm lateral to the midline and 3 mm lateral to the center of the tibial tubercle. The width of the sweet spot is only 23 mm. These anatomic relationships should be understood in order to decrease the risks of nailing.