Abstract
Category:
Trauma
Introduction/Purpose:
Surgical fixation of ankle fractures with syndesmotic instability using quadricortical fixation through the fibula and tibia is commonly performed to maintain mortise congruency. Quadricortical fixation can be achieved by screws or suture buttons however both involve unprotected drilling and placement of hardware through the medial distal tibia which places anatomic structures at iatrogenic risk. These structures may include the anterior tibialis tendon, the saphenous neurovascular bundle (SNVB) and posteriorly, the posterior tibialis tendon (PTT). This study aims to radiographically map the anatomic course of these structures at risk on a lateral radiograph as would be used intraoperatively during syndesmotic fixation.
Methods:
Eighteen fresh-frozen cadaveric feet were dissected with preservation of all soft tissue and neurovascular structures over the medial distal tibia. While preserving fascial and tendinous sheath attachments, the SNVB and the PTT were identified and marked with metal wiring. Standardized and calibrated lateral radiographs were obtained to determine the anatomic course of these structures. Lateral radiographs of the distal tibia and fibula were analyzed by a grid system comprised of 1 cm row-increments moving cranially from the ankle joint up to 5 cm and by 3 evenly distributed parallel columnar zones from anterior to posterior (see Figure). The anterior boundary of the columnar zone was placed at the anterior tibial shaft and the posterior boundary was placed at the posterior malleolus of the tibia. The position of respective metal wires placed within the SNVB and the anterior portion of the PTT were charted according to this grid system and results compiled.
Results:
The SNVB was located in zone 1 or 2 (or anterior to zone 1) in 97.3% of specimens (107/110). The SNVB traversed from proximal-posterior to distal-anterior. For the 16 specimens that crossed a columnar zone, the most common crossover was from zone 2 to zone 1 at 3-4 cm above the ankle joint which occurred in 43.8% (7 of 16) specimens.
The PPT was found in zone 3 in all specimens (n=18) with only one specimen demonstrating crossover of a columnar zone into zone 2 at its most distal extent (0-1 cm). The PTT was noted to pass behind (radiographically overlap) with the tibia in 83.3% (15 of 18) of specimens between 1 and 3 cm above the ankle joint.
Conclusion:
Inappropriate placement of quadricortical syndesmotic fixation may place structures on the medial ankle at risk given blind drilling and hardware placement. The SNVB is at considerable risk along the anterior course of the distal tibial while the PTT is only at risk in zone 3 at the distal extent of the tibia when a true lateral radiograph is obtained. This grid system allows a simple intra-operative check to guide safer placement of quadricortical syndesmotic fixation.