Risk of vascular injury when screw drilling for tibial tuberosity transfer.

Purpose: During tibial tubercle transfer, popliteal vessels are at risk from drills and screws. The risk is around 0.11%, as described in the literature. We reviewed knee injected CT scan for analysis of the location of arteries, identified landmarks allowing minimizing risks, and defined a safe zone.

Material And Method: Distances between the posterior cortex and arteries were measured on CT scans from 30 adults (60 knees) at three levels (proximal part of the tibial tuberosity, 20 mm and 40 mm distally). Data were used to create a "risk map" with different angular sectors where the frequency of the presence of arteries was analyzed in each area. We also analyzed the position of 68 screws of 47 patients who underwent a medial tibial tuberosity transfer.

Results: The nearest distance between artery and the posterior tibial cortex was found at the level corresponding to the top of the tuberosity with less than 1 mm, while the largest distance was found at the distal level. We were able to define a safe zone for drilling through the posterior tibial cortex which allows a safe fixation for the screws. This zone corresponds to the medial third of the posterior cortex. When the safe zone is not respected, screws that overtake the posterior cortex may be close to arteries as observed for 37 of the 68 screws analyzed.

Conclusion: We described new landmarks and recommendations to avoid this complication during tibial tuberosity transfer.